oil water separation experiment

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Science Projects on Separating Oil and Water

How to Separate Oil & Water Layers

While oil and water do not mix and so will naturally separate, it can be difficult to actually remove the oil from the water. Large oil spills, such as the Exxon Valdez tanker spill in 1989 and the BP Deepwater Horizon incident in 2010, highlight the importance of this issue. There are several interesting science projects, ranging from simple to advanced, that illustrate different approaches to oil separation.

Natural Separation

One project you can do with oil and water is to show the natural separation of the two liquids. Put some water in a clear container and add food coloring to make the separation more obvious. Pour in some oil; it can be cooking oil, motor oil or some other kind. The oil may initially drop to the bottom due to the force of falling, but it will quickly rise to lie on top of the water. If you cap the container and turn it upside down, the oil will still make its way to the top. This experiment shows two scientific principles. First of all, the water and oil do not mix because they are very different chemically. The water is polar, which means each molecule has parts with small positive and negative electric charges. Oil is very nonpolar, which is why it doesn't mix well with polar liquids. As well, the density of oil is lower than water, so it naturally rises up, just like a helium balloon rises in air.

Separating an Emulsion

Take the container holding water and oil and shake it vigorously. The mixture will turn cloudy and you won't see two obvious layers anymore. You have made what is called an emulsion. An emulsion is a mixture of oil and water in the form of tiny droplets of the two liquids. Some common foods we eat are emulsions of oil and water, like salad dressing. An oil spill in a wavy ocean could form an emulsion, making the oil difficult to separate. You can experiment with ways to break the emulsion. Let your emulsion sit undisturbed for awhile and the oil may again form a separate layer. Adding salt to the mixture is one way to speed up the process; the salt dissolves in the water and makes it even more polar and less likely to mix with the oil.

Another way to separate oil from water is to soak up the oil. Most absorbent materials we use, like paper towels, are better at soaking up water, but pads made from polypropylene work the opposite way. This is because polypropylene is nonpolar like the oil and so prefers to absorb the oil layer. Polypropylene pads can be bought at auto supply stores and other outlets. Possible experiments could include testing which brand of pads works best and how long it takes to absorb a set quantity of oil.

Temperature

Water will become less dense when frozen into ice and this gives us another technique to separate oil and water. Although this would not be practical on a large scale, you can use it on a small scale to illustrate how densities change with temperature. Place some water and oil into a concave container, like a plastic bowl. The oil will rise to the top. Put the container in the freezer for a few hours and then take it out. The container will now have the oil on the bottom, underneath a slab of frozen water that you should be able to remove, thus separating the two.

Bioremediation

Strangely, there are bacteria that will eat oil spills. One such bacteria that scientists have experimented with is Pseudomonas. A challenging but fascinating experiment can be carried out by mixing colonies of Pseudomonas with different types of oils and nutrients and seeing which conditions give the best bacterial growth rates. This type of experiment should always be done with caution though since some strains of Pseudomonas can cause disease in humans.

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• Kids Science Experiments; "Freeze Oil and Water"

About the Author

Michael Judge has been writing for over a decade and has been published in "The Globe and Mail" (Canada's national newspaper) and the U.K. magazine "New Scientist." He holds a Master of Science from the University of Waterloo. Michael has worked for an aerospace firm where he was in charge of rocket propellant formulation and is now a college instructor.

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Ryan McVay/Lifesize/Getty Images

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Oil and Water Experiment

This classic oil and water experiment is sometimes referred to as “fireworks in a jar” because it looks like fireworks falling down from the oil. Kids will love learning about density and how oil and water do not mix in this fun and easy science experiment!

RELATED: Rain Cloud in a Jar

Oil and Water Science Experiment

This simple science experiment explores density using oil and water. Expand this further by mixing or trying other oils – does it act the same way? You can even use a pipette to add drops of colored water to oil in a jar or cup and observe what happens.

What is Density?

Density is the amount of mass per unit of volume. Let’s say you have two objects and they are the same size. If one object is heavier, then it is denser and if the other object is lighter, then it is less dense.

What you will see in this experiment is that oil is less dense than water, so it will float on top of the water.

The Science Behind It

Oil and water do not mix. Oil is less dense than water and floats on top of the water. Food coloring is water-based so it mixes with the water. When you add the food coloring to the oil it will not mix. Once you add the oil to the water, the food colored droplets start to drop down since they are heavier than the oil. Once they drop into the water they start to dissolve and look like tiny explosions (or fireworks).

Supplies Needed

Vegetable Oil – we used canola oil

Food Coloring

A Clear Jar or Vase

Watch the Video Tutorial Here

Steps to do an oil and water experiment.

1. Fill your jar or vase 3/4 full with water.

2. Add oil into a bowl. You do not need a lot like we used – you can even just use about 4 tablespoons of oil for a thin layer. A little more oil will show the difference in density slightly better for kids.

3. Add 4 -5 drops of food coloring for each color you want to add. We used green, blue and purple food coloring. You can use any colors you’d like but we would recommend no more than 3 as the colors will mix quickly and will make it harder to see them dropping down.

4. Whisk the food coloring into the oil. You can point out at this stage that you can already tell the oil and water will not mix.  It’s best to whisk and add the oil straight into the jar or vase before the food coloring settles on the bottom of the bowl or or it may not form droplets when you add it to the water.

5. Add the oil into the water.

Now wait and see all of the little drops start to come down from the oil (making “fireworks”).

We love how easy this simple science experiment is – and kids will love to observe or make their own fireworks in a jar too!

More Science Experiments for Kids

Try this fun and easy Grow a Rainbow Experiment . You only need washable markers and paper towel!

For another fun experiment, make some oobleck! 

Try a rainbow rain cloud in the jar experiment!

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Clean It Up – Oil Spill Experiment

February 20, 2020 By Emma Vanstone Leave a Comment

An oil spill is when sea water is contaminated with oil. This can be an accident or human error. Oil spills can be massively damaging to marine wildlife and also humans if the oil gets into the food chain . This hand-on oil spill science experiment is not only great for helping children visualise the effects of an oil spill, but also demonstrates how water and oil don’t mix and why oil floats on water .

Oil Spill Experiment for Kids

You’ll need

Clear plastic container

Vegetable oil

Spoon or pipette

Cotton wool

Cotton buds

Paper towel

Oil Spill Investigation Instructions

Step 1 – add oil to water.

Half fill the clear container with water. Drop a small amount of oil onto the water.

The oil will float on top of the water. Even if you shake the container ( cover it first ) the oil and water will separate again.

Use a cotton bud to move the oil around surface of the water.

Step 2 – Oil Clean Up

Pour enough water into the tray so the surface is completely covered and the tray is about half full.

Carefully drop two tablespoons of oil onto the surface of the water.

Experiment with the absorbent materials to discover which cleans up the oil spill the best.

Oil Spill Challenge s

Try to build something to contain oil to one area of the tray.

Try the experiment again, but this time use the same amount of each absorbing material and collect the oil for the same amount of time. Which material absorbs the oil the most effectively?

Another idea is to dip a feather in the oily water and watch as it starts to feel heavier. Imagine being a bird with oil covered feathers.  This activity can be further extended by exploring different methods of cleaning oil covered feathers. Water and water with washing up liquid are great things to try first.

Read about the biggest oil spills in history .

If you found our oil spill science experiment useful you might also enjoy our edible greenhouse gas models .

Last Updated on November 3, 2021 by Emma Vanstone

Safety Notice

Science Sparks ( Wild Sparks Enterprises Ltd ) are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.

These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.

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May 24, 2018

Mix It Up with Oil and Water

A science shake-up activity from Science Buddies

By Science Buddies & Megan Arnett

A little mixup: Use kitchen chemistry to make oil and water blend. 

George Retseck

Key concepts Chemistry Surfactants Density Polarity

Introduction You may have heard people say, “Those two mix like oil and water,” when they’re describing two people who don’t get along. Maybe you’ve also noticed shiny oil floating on the surface of water puddles after it rains. In both cases you understand that water and oil don’t go well together—but have you ever wondered why? So many other things can dissolve in water—why not oil? In this activity we’ll explore what makes oil so special, and we’ll try making the impossible happen: mixing oil and water!

Background Unlike many other substances such as fruit juice, food dyes or even sugar and salt, oils do not mix with water. The reason is related to the properties of oil and water. Water molecules are made up of one oxygen atom and two hydrogen atoms. In addition to having this very simple structure, water molecules are polar, which means there is an uneven distribution of charge across the water molecule. Water has a partial negative charge from its oxygen atom and partial positive charges on its hydrogen atoms. This polarity allows water molecules to form strong hydrogen bonds with each other, between the negatively charged oxygen atom on one water molecule and the positively charged hydrogen atoms of another. Other molecules such as salts and sugars are able to dissolve in water because of its polarity as well. The charges at either end of the water molecule help break up the chemical structures of other molecules.

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Oils, by contrast, are nonpolar, and as a result they’re not attracted to the polarity of water molecules. In fact, oils are hydrophobic, or “water fearing.” Instead of being attracted to water molecules, oil molecules are repelled by them. As a result, when you add oil to a cup of water the two don’t mix with each other. Because oil is less dense than water, it will always float on top of water, creating a surface layer of oil. You might have seen this on streets after a heavy rain—some water puddles will have a coating of oil floating on them.

In this activity we will test the power of surfactants to help us mix oil and water. The surfactant we will use is dish detergent, which helps break up the surface tension between oil and water because it is amphiphilic: partly polar and partly nonpolar. As a result, detergents can bind to both water and oil molecules. We’ll see the results of this property in this activity!

2 clear plastic water bottles with lids

2 cups of water

One-half cup of oil (olive, cooking or vegetable oils will all work)

Liquid dishwashing soap

Clock or timer

Permanent marker

Measuring cup

Measuring spoon

Food coloring (optional)

Preparation

Remove any labels from your water bottles.

Use your marker to label the bottles: Label the first “Oil+Water” and the second “Oil+Water+Soap.” Write the labels as close to the tops of the bottles as possible.

Pour one cup of water into each bottle.  

Carefully measure and pour one-quarter cup of oil into the bottle labeled Oil+Water. Allow the bottle to sit on a countertop or flat surface while you observe the water and oil. Does the oil sink to the bottom of the bottle, sit on top of the water or mix with it?

Repeat this step, adding one-quarter cup oil to the bottle labeled Oil+Water+Soap. Does the oil sink to the bottom, sit on top of the water or mix with it?

Carefully add three tablespoons of dish soap to the bottle labeled Oil+Water+Soap. Try not to shake the bottle as you add the dish soap.

Make sure the bottle caps are screwed on tightly to each bottle.

Holding a bottle in each hand, vigorously shake the bottles for 20 seconds.

Set the bottles down on a flat surface with plenty of light.

Note the time on your clock or set a timer for 10 minutes.

Observe the contents of each bottle. Hold them up to a light one at time so you can clearly see what is happening inside the bottle. Did anything change when you shook the bottles? Do the mixtures look the same in the both? If not, what is different between them? How would you explain the differences that you observe?

After 10 minutes have passed look at the contents of the bottles and note the changes. What does the oil and water look like in each bottle? Has the oil mixed with the water, sink to the bottom or rise to the top?

Extra:  Add food coloring to the water to get a lava lamp effect

Extra:  Test other types of soap, such as toothpaste, hand soap and shampoo by mixing them with oil and water. 

Observations and results In this activity you combined oil and water then observed how adding dish detergent changed the properties of this mixture. First you should have noticed that when you added the oil to the water they did not mix together. Instead the oil created a layer on the surface of the water. This is because oil is less dense than water and therefore it floats to the surface. When you shook the Oil+Water bottle you might have noticed the oil broke up into tiny beads. These beads, however, did not mix with the water. After you let the Oil+Water bottle sit for 10 minutes you should have observed the oil and water starting separating again almost immediately, and after another 10 minutes there was once again two distinct layers in your bottle.

In contrast you should have found shaking the Oil+Water+Soap bottle resulted in a lot of foam, but instead of immediately starting to separate, the mixture was a cloudy, yellow color. Eventually the oil and water should have separated into two layers again, but these layers should have appeared less distinct and cloudier than the layers in your Oil+Water bottle.

The difference between the two bottles results from adding dish detergent to the Oil+Water+Soap bottle. The detergent molecules can form bonds with both water and oil molecules. Therefore, although the oil and water aren’t technically mixing with each other, the dish detergent molecules are acting as a bridge between oil and water molecules. As a result, the oil and water molecules aren’t clearly separated in the bottle. Instead, you see a cloudy mixture, resulting from the oil, soap and water chains you’ve created by adding dish detergent.

More to explore Goo-Be-Gone: Cleaning Up Oil Spills , from Science Buddies Make Your Own Lava Lamp , from Scientific American The Chemistry of Clean: Make Your Own Soap to Study Soap Synthesis , from Science Buddies Science Activities for All Ages! , from Science Buddies

This activity brought to you in partnership with Science Buddies

Suggestions or feedback?

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Separating finely mixed oil and water

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Whenever there is a major spill of oil into water, the two tend to mix into a suspension of tiny droplets, called an emulsion, that is extremely hard to separate — and that can cause severe damage to ecosystems. But MIT researchers have discovered a new, inexpensive way of getting the two fluids apart again.

Their newly developed membrane could be manufactured at industrial scale, and could process large quantities of the finely mixed materials back into pure oil and water. The process is described in the journal Scientific Reports by MIT professor Kripa Varanasi, graduate student Brian Solomon, and postdoc M. Nasim Hyder.

In addition to its possible role in cleaning up spills, the new method could also be used for routine drilling, such as in the deep ocean as well as on land, where water is injected into wells to help force oil out of deep rock formations. Typically, Varanasi explains, the mixed oil and water that’s extracted is put in large tanks to allow separation by gravity; the oil gradually floats to the top, where it can be skimmed off.

That works well when the oil and water are “already large globs of stuff, already partly separated,” Varanasi says. “The difficulty comes when you have what is called an emulsion, with very tiny droplets of oil stabilized in a water background, or water in an oil background. The difficulty significantly increases for nanoemulsions, where the drop sizes are below a micron.”

To break down those emulsions, crews use de-emulsifiers, which can themselves be environmentally damaging. In the 2010 Deepwater Horizon oil spill in the Gulf of Mexico, for example, large amounts of dispersants and de-emulsifiers were dumped into the sea.

“After a while, [the oil] just disappeared,” Varanasi says, “but people know it’s hidden in the water, in these fine emulsions.” In the case of land-based drilling, where so-called “produced water” from wells contains fine emulsions of oil, companies sometimes simply dilute the water until it meets regulatory standards for being discharged into waterways.

“It’s a problem that’s very challenging to the industry,” Varanasi says, “both in terms of recovering the oil, and more importantly, not discharging the produced water into the environment.”

The new approach developed by Varanasi’s group uses membranes with hierarchical pore structures. The membranes combine a very thin layer of nanopores with a thicker layer of micropores to limit the passage of unwanted material while providing strength sufficient to withstand high pressure and throughput. The membranes can be made with contrasting wetting properties so their pores either attract oil and repel water, or vice versa.

“This allows one material to pass while blocking the other with little flow resistance,” Varanasi says. The choice of membrane, or a combination of both, could be based on which material predominates in a particular situation, he explains.

The pores have to be smaller than the droplets in order to block them, Varanasi says — which, in the case of nanoemulsions, leads to very small pores and significant flow resistance, limiting the throughput. Throughput can be improved by increasing the pressure gradient or making the separation layer very thin, but past attempts to make such thin, small-pore membranes have yielded materials that tear even under nominal pressure. The team’s solution: an ingenious process that makes large holes on one side that penetrate most of the way through the material, providing little resistance to flow, as well as nanoscale holes on the other surface, in contact with the emulsion to be separated. The thin layer with nanoscale pores allows for separation, and the thick layer with large pores provides mechanical support.

The approach can be adapted to industrial processes used today for making large membranes in a high-volume, roll-to-roll manufacturing system, so it should be relatively easy to achieve large-scale production, Varanasi says.

A polymer solution is poured onto a glass plate, Hyder explains; this casting plate is then immersed in a nonsolvent bath to induce precipitation to form a film. The technique creates a bilayered polymer phase: One layer is polymer-rich, and one is not. As they precipitate out, the polymer-rich phase develops the smaller pores; the polymer-lean phase makes the larger ones. Since the solutions form a single sheet of film, there is no need for bonding layers together, which can result in a weaker filter.

“There is no separate layer, it’s completely integrated, so the mechanical support is integral,” Hyder says. As a final stage, a different polymer is added to give the material — including the lining of the pores — surfaces that attract or repel oil and water. The skin layer thickness can be further optimized using polymeric pore formers to enhance throughput.

Solomon performed experiments showing the effectiveness of the membranes in separating nanoemulsions while maintaining integrity at high pressure. The team used various techniques — including differential scanning calorimetry, dynamic light scattering, and microscopy — to test the separation efficiency, showing more than 99.9 percent separation.

Microscopy images show the membrane in operation, with dye added to the water to make the droplets more obvious. Within seconds, an oil-water mixture that is heavily clouded becomes perfectly clear, as the water passes through the membrane, leaving pure oil behind. As shown in the microscope images, Solomon says, “We’re not only getting rid of the droplets you can see, but also smaller ones,” which contribute to the cloudy appearance.

Anish Tuteja, an assistant professor of materials science and engineering at the University of Michigan who was not involved in this research, calls it "a very interesting and innovative approach to fabricating membranes that can separate out nanoemulsions." He adds that the method this team used "is quite innovative. People have previously attempted to fabricate hierarchical membranes, but this is probably one of the simplest and most scalable techniques for fabricating such membranes."

Assuming the membranes perform well under real-world conditions, Tuteja says, "they could have a very big impact. Oil-water nanoemulsions are ubiquitous in a number of industries, and these membranes could enable rapid separation of those emulsions with high purity and efficiency."

The team is working with Shell, which supported the research through the MIT Energy Initiative, to further test the material.

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Related links.

• Paper: "Separating Oil-Water Nanoemulsions using Flux-Enhanced Hierarchical Membranes"
• Kripa Varanasi
• Lab for Manufacturing and Productivity
• Department of Mechanical Engineering

Related Topics

• Hydrophobic materials
• Fossil fuels
• Mechanical engineering
• Nanoscience and nanotechnology

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FREE K-12 standards-aligned STEM

curriculum for educators everywhere!

Find more at TeachEngineering.org .

• TeachEngineering
• A Slippery Situation: Oil Spill Cleanup and Polarity

Hands-on Activity A Slippery Situation: Oil Spill Cleanup and Polarity

Grade Level: 7 (6-8)

(two 50-minute class periods: one period to introduce concepts and get familiar with setup, and one period to design a solution and test it.)

Expendable Cost/Group: US $0.00

Group Size: 3

Activity Dependency: None

Subject Areas: Chemistry, Earth and Space, Measurement, Physical Science, Problem Solving

NGSS Performance Expectations:

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Engineering connection, learning objectives, materials list, worksheets and attachments, more curriculum like this, pre-req knowledge, introduction/motivation, vocabulary/definitions, investigating questions, troubleshooting tips, activity extensions, activity scaling, additional multimedia support, user comments & tips.

Oil spills are a common environmental problem for which solutions are still being engineered today. Chemical dispersion (demonstrated by soap in this activity) is a legitimate technique used to clean up oil spills. Oil spills have negative environmental impacts, as oil sinks to the bottom of the ocean and is not removed. Skimming, absorption, and manual removal are techniques used to clean up oil spills on a large scale. Students are able to get a glimpse of the actual design process that goes into solving this environmental issue.

After this activity, students should be able to:

• Understand the concept of polarity and polar molecules.
• Explain whether polar and nonpolar molecules mix.
• Discuss the effects of oil spills on the environment.
• Brainstorm solutions to simple environmental issues.

Educational Standards Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards. All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN) , a project of D2L (www.achievementstandards.org). In the ASN, standards are hierarchically structured: first by source; e.g. , by state; within source by type; e.g. , science or mathematics; within type by subtype, then by grade, etc .

Ngss: next generation science standards - science.

Each group needs:

• 1 plastic tub (18.9 L or similar)
• cup or beaker (see through)
• Oil Spill Cleanup Worksheet
• 1/4 cup cooking oil
• 1 tbsp oil-based dye or cocoa powder

For the entire class to share:

• food scale or similar (optional)
• remediation materials
• kitchen salt
• plastic spoons
• twine / string (6.35 m ball or similar)
• cotton balls
• craft sticks

Familiarity with the nature of molecules and atoms.

A basic understanding of states of matter.

A familiarity with electric charge and/or magnets and how they repel or attract.

Today we’re going to start by looking at some photos of oil spills in the ocean. Do you know how they can impact sea life, and how long they can last in the environment? (Optional: Show Slide 5 of the Oil Spill Cleanup Presentation .) Do you see how the oil separates from the water to form a film on top of the sea? We’re going to be observing and analyzing the fact that oil separates from water, and our engineering/design challenge is to clean up oil spills from the ocean. (If possible, try to demonstrate oil’s hydrophobic properties by getting a clear beaker or test tube and pouring water, then oil, to see how it floats and mixes.)

(After demonstrating the environmental impacts and the phenomenon of interest, have the students discuss as a class how the hydrophobic properties of oil could potentially impact the environment through oil spills. (Optional: Show Slide 7 of the Oil Spill Cleanup Presentation .) Some guiding questions that can be asked include:

• What might happen if oil came into contact with an animal, such as a bird or fish? Would it stick? Would it be easy to remove? 
• The oil would stick to the animal’s skin or could be dangerous if consumed. The oil on the skin would stick and would be difficult to remove. 
• Does the fact that the oil floats on water make it easier to clean up?  
• As the oil floats on the surface, it is easier to see and make strategies to remove it. 
• What are other places in nature where things repel each other? Why or how does this happen?
• Other occurrences of repulsion in nature can be found in magnetic fields. For instance, magnets with opposite poles attract each other, while like poles repel when their fields interact. This is similar to the concept of polarity, where molecules with opposite charges attract. 
• Do molecules have any properties that would make them repel each other?  
• Magnetic forces repel one another. 
• Can you (students) think of any ways to clean up an oil spill? (Hypothesizing solutions in a guided manner will help students come up with solutions when they begin to design and experiment.) 
• Much like the methods simulated in the project, skimming and using adsorbents are effective methods for oil removal. 
• How can engineers use the design process to formulate solutions for these problems? 
• The engineering design process is a vital tool used to implement a methodical approach for solutions. Defining, researching, and developing a scope of solutions to the problem provides a foundation for engineers to develop an optimized strategy.) 

Oil comes from accumulated organic matter below the ocean floor that developed into hydrocarbon material from heat and pressure over a long period of time. Oil (and natural gas) is predominantly used as an energy source for transportation, manufacturing, etc. It is shipped across the ocean because of the large global demand for oil. 

Oil spills can occur from extraction and transportation accidents, equipment failure, natural disasters, or other contributing errors. Oil spills have detrimental effects on aquatic ecosystems by contaminating the water and food sources with harmful chemicals, which have long-term ecological impacts. Additionally, oil coats the water surface, compromising essential processes such as oxygen uptake and photosynthesis. 

Oil spill duration is dependent on factors such as how much is spilled, as well as cleanup and mitigation measures employed. Some can be short term, while others take years to clear. 

Real-world applications would include skimming oil from the water surface or applying chemical dispersants to break down oil in the case of a spill. Other removal methods entail controlled oil burning or natural biodegradation. 

Machines such as skimmers and booms create a barrier to contain the oil and collect it from the surface through adsorption and suction. The increased focus on environmental stability and sustainability has brought about new technology to reduce the need for oil production and use. Satisfactory alternatives include renewable energy sources, electric power, natural gas, and biofuels. 

Polarity: Hydrophobic means it has water-repelling properties and is more common with nonpolar molecules. This is important for many biological occurrences that hydrophilic molecules protect from water molecules. Polarity happens when molecules have charges that either attract or repel specifically in environments where the need for opposing forces acting as a total net force are required. Polarity is relevant to many real-world concepts, such as when understanding how molecules obtain their composition. 

The Engineering Design Process (EDP) is a vital tool for engineers to strategize an alternative and creative approach when formulating solutions. This process includes the following components:

• Ask: Identify the needs and constraints.
• Research: Research the problem.
• Imagine: Develop possible solutions.
• Plan: Select a promising solution.
• Create: Build a prototype.
• Test: Test and evaluate the prototype.
• Improve: Redesign as needed.

Before the Activity

• Gather materials and make copies of the Oil Spill Cleanup Worksheet for students.
• Find images of oil spills to show students for the activity Introduction.
• Optional: Review the activity learning goals, molecules and charges, and polarity using Slides 1-4 of the Oil Spill Cleanup Presentation .
• Review the Engineering Design Process  and Design Thinking  (also see Slide 6 of the Oil Spill Cleanup Presentation for a visual).

With the Students

• Divide the class into groups of three or four students each.
• Consider having groups nominate a notetaker to fill out the Oil Spill Cleanup Worksheet and split into roles.
• Optional: Show Slides 8-10 of the Oil Spill Cleanup Presentation to introduce the activity.
• Instruct groups to prepare their solution as described in Part 1 of the Oil Spill Cleanup Worksheet .

If a scale is available, have groups measure the weight of their “uncontaminated” water. (Students should weigh the initial contaminated water in the container as a comparison to the final to see how much of the oil was extracted. The ruler measurement may not be exact, so the weight is used as an indicator that material was removed.)

• Instruct students on how to simulate their oil spill, drifting between groups to supervise. Groups should add 1/4 cup of dyed oil to their water and attempt to mix. As students complete the activity, they should be recording observations on the Oil Spill Cleanup Worksheet .
• If a scale is available, have groups measure the weight of their “contaminated” water.
• Instruct students to attempt to remove the oil from the water, using the materials provided. Give students about 20 minutes to try different strategies.
• Students should be recording qualitative data (observations) and quantitative data (based on scale or ruler).

• Following the prompts in the Oil Spill Cleanup Worksheet , groups should discuss the results of their oil cleanup. Drift between groups to help students brainstorm and answer questions.
• Full-class discussion (20 minutes): Ask students to share the strategies they used to clean up their water. Optional: Show discussion questions on Slides 11-12 of the Oil Spill Cleanup Presentation .
• Which materials did they use? What worked? What didn’t?
• Ask students to write on the board or share why they think a particular strategy did or did not work.
• Ask groups to share their designed oil cleanup machines and the motivation behind the designs.
• Discuss with students the real-world applications of oil cleanup in fresh and saltwater environments and discuss real-world oil cleanup machines. Students should be able to identify which real-world machine most closely resembles their own and state clearly on their worksheet what cleanup technique they are employing.
• Discuss how polarity concepts relate to other real-world concepts.
• Collect worksheets from groups.
• Clean up by disposing of liquids down a drain and disposing of solids in the trash.

absorption: Technique to remove oil by using absorbents (i.e., filter).

covalent bonds: Bonds formed by sharing electrons.

hydrophobic: Repellent toward water; does not mix with water.

non-polar: A molecule where electrons are equally shared between atoms, creating zero dipole moment.

polar molecules: A molecule where distribution of electrons between atoms is uneven, creating a dipole moment (i.e., one end of the molecule is slightly positive while the other end is slightly negative).

polarity: The degree to which a molecule has properties of molecular attraction.

skimming: Technique used to physically separate oil from water (via adsorption) and place it in collection tanks (i.e., floating booms).

Pre-Activity Assessment

Brainstorming: As a class, discuss what students already know about oil spills, how they can harm the environment, and how they are cleaned up. Do students know where oil comes from, what it is used for, or why it is shipped across the ocean? Ask students if they know of anything in their lives that uses oil (gasoline-powered cars and asphalt are good examples if students cannot think of any).

Pre-Assessment Question: Have students write what they know about oil and water mixing and polar molecules to get a sense of their understanding. Have them share in small groups if there is time.

Activity Embedded (Formative) Assessment

Group Discussion: Once the concepts of polarity have been explained, have students hypothesize ways to clean up an oil spill. Does the fact that the oil does not mix with the water help make this process easier? What will happen if a dispersant (such as dish soap) is added to the mixture?

Design: Have students design their own oil spill cleanup method and sketch it out in groups. This is a chance for them to use what they learned from testing, but also to be creative. It is okay if their solutions are not totally realistic; it is more important for them to think outside the box.

Instructor Checkpoint: Have students check in with the instructor before attempting to remove contaminants to ensure they gathered the correct readings. This is also an opportunity for the instructor to ask questions and confirm students are on the right track.

Post-Activity (Summative) Assessment

Worksheet Group Check: Have students compare the answers they put on the Oil Spill Cleanup Worksheet for their groups.

Class Discussion: To wrap up, discuss with the class how oil spills affect the environment. What impacts do oil spills have on wildlife and humans? Are there alternatives to using oil for modern technology?

Making Sense Assessment: Have students reflect on the science concepts they explored and/or the science and engineering skills they used by completing the Making Sense Assessment .

• What happens when you mix soap with oil and water? Do the two begin to mix?  (Answer: When water and oil are mixed together, they are separated due to their molecular and polarity differences. When continuously mixed, the oil will form a layer on top of the water but, if left untouched, the two substances will separate completely.)
• What kind of molecule do you think soap is, polar or nonpolar? Could it be both?  (Answer: Soap is partly polar and partly nonpolar, so you could say that it is partly both.)
• What was the most effective way to clean up the oil from the water? Why do you think this was?  (Answer: Based on the methods used for this project, the cotton balls had the best outcome because they eliminated the most cocoa (oil) from the water. Another close solution would be the rubber bands, because they were used to skim the oil from the rest of the water. It closely simulates the real-world technique of skimming, which uses a boom and a skimmer.)
• Chemicals like soap are sometimes used to clean up oil spills in the ocean. Do these chemicals make the oil go away? What effect do you think mixing oil with water has on the environment?  (Answer: The interaction between oil and soap is immiscible, meaning that it won’t dissolve when mixed. Therefore, using chemicals like soap is beneficial for managing oil dispersion, but it won’t eliminate or degrade it completely. It can have an adverse effect on aquatic environments in terms of contamination or limiting essential sunlight and oxygen exposure.)

Safety Issues

Safety precautions before starting the activity:

• Some liquids are safe to dispose of down the sink drain, and solids can be disposed of in the trash.
• Dispose of extra oil and any oil-filled water by adding the oil to kitty litter or coffee grounds in a nonrecyclable container. Dispose of the container and oil-solid mix in the trash.
• Although the bacteria that occur naturally during the experiment are generally harmless, students should nevertheless wash their hands after handling oils and powders.
• Materials should not be consumed.
• Make sure that the oil and cocoa are thoroughly mixed before the mixture is added to the water. If it is not well mixed, the cocoa will separate in the water and make the experiment difficult to observe.
• Try to avoid adding dish soap immediately before trying other methods during the cleanup design section of the experiment. Adding dish soap immediately makes it difficult to see how the other methods will work. It might be useful to remove the dish soap as an option until a few minutes have passed, and then provide it.
• If necessary, some groups might need to dump their oil spill and remake it if it gets particularly messy.
• Providing paper towels to set dirtied tools down on and clean the table surface can help minimize mess.
• To demonstrate polarity in water, teachers can do a demonstration where a stream of water is bent using a charged object. Allow students time to predict the outcome and explain why they think the water will or will not bend.
• For a more hands-on polarity demonstration with younger children, have them experiment with magnets, ferric metals, and non-magnetic materials such as wood or plastic.
• For older students, have them add salt to the water to simulate the ocean, and discuss ionic bonds and how they interact with polar molecules. Why does salt dissolve in water? What property of water would help the salt dissolve?

To enhance the activity to fit your teaching curriculum, here are some other ways to adjust the lesson:

• For lower grades, have more emphasis on environmental impact, as this real-world application will likely be easier for students to grasp.
• For upper grades, incorporate a curriculum about electronegativity, dipole moments, and molecular geometry. In this way, students will connect chemistry concepts with a real-world issue.

To reinforce deeper understanding of curriculum and polarity concepts, encourage students to explore the given simulation before class activity.

• Molecule Polarity simulation
• Molecule Polarity - Polarity | Electronegativity | Bonds - PhET Interactive Simulations (colorado.edu)

Students explore an important role of environmental engineers—cleaning the environment. They learn details about the Exxon Valdez oil spill, which was one of the most publicized and studied human-caused environmental tragedies in history.

Students learn about the basics of molecules and how they interact with each other. They learn about the idea of polar and non-polar molecules and how they act with other fluids and surfaces. Students acquire a conceptual understanding of surfactant molecules and how they work on a molecular level. ...

Environmental engineers play a big role in the cleanup of oil spills. But how do you clean up a huge amount of oil that has been mixed in a body of water like the ocean? In this activity, students simulate a spill and cleanup and learn the effectiveness of different methods.

Students learn about oil spills and their environmental and economic impact. They experience the steps of the engineering design process, starting by brainstorming ways to clean up oil spills, and then designing, building and re-designing oil booms to prevent the spread of oil on water. During a con...

Bezonik, Patrick and Arnold, William. Water Chemistry: An Introduction to the Chemistry of Natural and  Engineered Aquatic Systems. New York, New York: Oxford University Press, 2011.

“How Do We Clean Up Oil Spills?” YouTube, 21 April 2015, https://www.youtube.com/watch?v=3DbSlAg3F3A. Accessed 17 November 2022.

“ Offshore Drilling: Pros and Cons. ” BOP Products, 28 January 2022, https://www.bop-products.com/blog/drilling/offshore-drilling-pros-and-cons/. Accessed 17 November 2022.

“Oil Spills: Impact on the Ocean - sea, effects, temperature, percentage, important, largest, types, source, marine.” Water Encyclopedia, http://www.waterencyclopedia.com/Oc-Po/Oil-Spills-Impact-on-the-Ocean.html. Accessed 17 November 2022.

Upholt, Boyce. “ Ten Years after Deepwater Horizon, Worries Remain.” Hakai Magazine, 20 April 2020, https://hakaimagazine.com/news/10-years-after-deepwater-horizon-worries-remain/. Accessed 17 November 2022.

Contributors

Supporting program, acknowledgements.

This curriculum was developed under National Science Foundation grant number 2205067. Any opinions, findings, and conclusions, or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

Last modified: March 13, 2024

Oil and Water Science Experiment: A Simple and Engaging Activity for Kids

Discover the captivating world of science exploration for kids with the oil and water science experiment. This easy and fun experiment explores why oil and water don’t mix, providing an opportunity for parents and children to bond over a hands-on learning experience. Read on to learn how to conduct this simple science experiment for kids and unleash their curiosity.

This blog post may contain affiliate links. When you make a purchase through these links, I may earn a small commission, at no additional cost to you. I only recommend products that I genuinely believe can benefit you and your family! Your support helps maintain and improve all things A Pop of You.   Thanks so much !

Oil and Water Science Experiment

Welcome to our toddler activities blog, where we strive to provide parents with easy and achievable activities to engage and educate their children. In this article, we will delve into the exciting world of science exploration for kids with a focus on the oil and water science experiment. This simple experiment not only stimulates curiosity but also offers a hands-on learning experience for your little ones. Let’s dive in and explore why oil and water don’t mix and how you can conduct this engaging experiment with your children.

Understanding the Concept

Before we jump into the experiment, let’s briefly understand why oil and water don’t mix. As we know, oil and water are two different substances with distinct properties. Oil is a type of fat that doesn’t dissolve in water because its molecules are not attracted to water molecules. Instead, oil molecules are attracted to each other, creating a separate layer when mixed with water. This phenomenon is due to differences in polarity between oil and water molecules. These charges are like little magnets that make water molecules stick together. Since oil doesn’t have these charges, it doesn’t mix with water. It’s kind of like how some toys don’t fit together because they are made differently. Isn’t it interesting?

To conduct the oil and water science experiment, you will need the following materials:

• A clear glass or glass baking dish
• Vegetable oil or any other cooking oil
• Condiment dishes
• Eye droppers
• Spoon or stirrer

Step-by-Step instructions :

Follow these simple steps to conduct the oil and water science experiment:

• Fill the bottom of the glass or dish with oil
• Lay out four condiment dishes filled with water. Add a few drops of food coloring to each. This step can add an extra visual element to the experiment.
• Using a different eyedropper for each separate color, squeeze colored water into the tube and release it in the glass of oil. Repeat this process with the different colors of water.
• Observe how the oil and water interact. What do you notice?
• Use the spoon or stirrer to gently mix the oil and water together. What happens? Why?

Exploring the Science

Now that you’ve conducted the experiment, it’s time to learn more about the science behind why oil and water don’t mix. As mentioned earlier, the difference in polarity between oil and water molecules is the key factor. Water molecules are polar, meaning they have a positive and negative end. On the other hand, oil molecules are nonpolar, lacking charged ends. Since opposites attract, water molecules stick together, creating a cohesive force called surface tension.

When you mix oil and water, the water molecules bond with each other, causing the oil to form separate droplets or a layer. The oil molecules repel the water molecules due to their nonpolar nature. This separation occurs because oil and water are immiscible, meaning they cannot form a homogeneous mixture.

Discussing the Results

After mixing the oil and water together, you likely observed the oil separating from the water and floating on the surface. The two substances did not blend or create a uniform solution. This is a great opportunity to engage your child in a discussion. Ask them questions like, “Why do you think the oil and water didn’t mix?” or “What did you observe when we stirred them together?”

Encourage your child to think critically and come up with their own explanations. This kind of open-ended discussion fosters their scientific thinking and problem-solving skills.

Further Exploration

To extend the learning experience, consider trying these variations of the oil and water science experiment:

• Use different types of oils, such as olive oil or coconut oil, and compare the results.
• Test the effects of temperature by conducting the experiment with cold and hot water.
• Explore the interaction of oil and water with other substances, such as vinegar or dish soap.

These variations will spark curiosity and allow your child to witness firsthand how different factors can influence the outcome of an experiment.

The perfect introduction to STEM

The oil and water science experiment is a fantastic way to introduce your child to the wonders of science. By engaging in hands-on activities like this, children develop a deeper understanding of the world around them and nurture their natural curiosity. As parents, we can encourage their scientific exploration by providing them with simple science experiments like the one we discussed today. So, gather your materials, create a bonding experience, and watch your child’s face light up as they discover the fascinating reason why oil and water don’t mix. Remember, science is all about exploration, questioning, and discovery. Have fun experimenting with your little scientists!

Hey, I’m Katelyn, the “Achievably Extra” Mom! Join me for creative family fun and practical tips! Let’s inspire each other!

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Science Experiments

Mixing Oil & Water Science Experiment

Have you ever heard the saying, “Oil and water don’t mix”? For this easy science experiment, we observe exactly what does happens when we mix oil and water, then we’ll add another item to the mix to see how it changes!

With only a few common kitchen items, kids can explore density and the reaction of adding an emulsifier (dish soap) to the experiment. A printable instruction sheet with a materials list, demonstration video, and a simple scientific explanation are included.

JUMP TO SECTION: Instructions | Video Tutorial | How it Works

Supplies Needed

• Glass Jar with a lid (a pint canning jar works great)
• 1 cup Water
• Food Coloring
• 1 cup Oil (we used vegetable oil)
• 2 teaspoons Dish Soap

Mixing Oil & Water Science Lab Kit – Only $5

Use our easy Mixing Oil & Water Science Lab Kit to grab your students’ attention without the stress of planning!

It’s everything you need to  make science easy for teachers and fun for students  — using inexpensive materials you probably already have in your storage closet!

Mixing Oil & Water Science Experiment Instructions

Step 1 – Start by filling the jar with 1 cup of water.

Step 2 – Add a few drops of food coloring to the water and stir until combined. Make some observations about the water. What happened when the food coloring was added? Was it easy to mix the food coloring into the water? Does the food coloring stay mixed with the water? What do you think will happen when we pour the oil into the jar? Write down your hypothesis (prediction) and then follow the steps below.

Step 3 – Next pour 1 cup of oil into the jar. Make a few observations. Does the oil behave the same was as the food coloring did when you added it to the water?

Step 4 – Securely tighten the lid on the jar and shake it for 15-20 seconds.

Step 5 – Set the jar down and watch the jar for a couple of minutes. Observe what happens to the oil and the water and write down your findings. Did the oil and water stay mixed together? Was your hypothesis correct? Do you think there is anything else that can be added to the jar to prevent the oil and water from separating?

Step 6 – Next, take the lid off the jar and squirt in 1-2 teaspoons of dish soap.

Step 7 – Tighten the lid back on the jar and shake again for another 15-20 seconds.

Step 8 – Set the jar down and watch the liquid for a minute or two. Observe what happens to the oil and the water now that the dish soap has been added to the mix. Write down your findings. Did the oil and water stay mixed together this time? Do you know why adding the dish soap preventing the oil and water from separating? Find out the answer in the how does this experiment work section below.

Video Tutorial

How Does the Science Experiment Work

The first thing you will observe is that oil and water will not stay mixed together, no matter how hard you shake the jar. Instead, the oil slowly rises to the top of the water. This is because of the density of the two liquids. Density is a measure of the mass per unit volume of a substance. Water has a density of 1 g/mL (g/cm3). Objects will float in water if their density is less than 1 g/mL. Objects will sink in water if their density is greater than 1 g/mL. The oil is LESS dense than the water. This is because the molecules of oil are larger than the molecules of water, so oil particles take up more space per unit area. As a result, the oil will rise to the top of the water.

The second thing you will observe is that adding dish soap to the mixture changed the results of the experiment. When oil, water and dish soap are mixed together, the oil and water don’t separate like they did when they were the only two items in the jar. This is because of the chemistry of the oil, water and soap molecules.

Oil (and other fats) are made of nonpolar molecules, meaning they cannot dissolve in water. Water is made of polar molecules that can dissolve other polar molecules. Soap is made of molecules that have a hydrophilic (“water-loving”) end and a hydrophobic (“water-fearing”) end. Without soap, water and oil cannot interact because they are unlike molecules. When you add soap to the mixture, the hydrophobic end of the soap molecule breaks up the nonpolar oil molecules, and the hydrophilic end of the soap molecule links up with the polar water molecules. Now that the soap is connecting the fat and water, the non-polar fat molecules can be carried by the polar water molecules. Now the oil and water can be mixed together and stay mixed together!

I hope you enjoyed the experiment. Here are some printable instructions:

Mixing Oil & Water Science Experiment

• Glass Jar with a lid (a pint canning jar works great)

Instructions

• Start by filling the jar with 1 cup of water.
• Add a few drops of food coloring to the water and stir until combined.
• Pour 1 cup of Oil into the jar.
• Securely tighten the lid on the jar and shake it for 15-20 seconds.
• Set the jar down and watch the liquid for a minute or two. Observe what happens to the Oil and the Water.
• Next, take the lid off the jar and squirt in 1-2 teaspoons of dish soap.
• Tighten the lid back on the jar and shake again for another 15-20 seconds.
• Set the jar down and watch the liquid for a minute or two. Observe what happens to the Oil and the Water now that the dish soap has been added to the mix.

Reader Interactions

October 4, 2017 at 11:43 am

Super ….. !

October 6, 2017 at 12:12 pm

Hi ! This gives us really good experiment

November 6, 2017 at 3:40 pm

This was the best science fair project ever

November 14, 2017 at 5:10 pm

December 10, 2017 at 10:38 am

This experiment is fun

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• Published: 16 April 2019

One-step synthesis of a steel-polymer wool for oil-water separation and absorption

• Ali T. Abdulhussein 1 ,
• Ganesh K. Kannarpady 1 &
• Alexandru S. Biris 1  

npj Clean Water volume  2 , Article number:  10 ( 2019 ) Cite this article

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• Environmental sciences
• Materials science

Methods for the efficient and affordable remediation of oil spills and chemical leaks are crucially needed in today’s environment. In this study, we have developed a simple, magnetic, porous material based on polydimethylsiloxane (PDMS) and steel wool (SW) that can fulfill these needs. The PDMS-SW presented here is superhydrophobic, superoleophilic, and capable of absorbing and separating oils and organic solvents from water. The material is mechanically and chemically stable, even in salty environments, and can be magnetically guided. It exhibits good selectivity, recyclability, and sorption capacity, and can quickly and continuously absorb and remove large amounts of oils and organic solutions from stationary and turbulent water. In addition, PDMS-SW’s inherently high porosity enables direct, gravity-driven oil-water separation with permeate flux as high as ~32,000 L/m 2 ·h and separation efficiency over 99%. The solution immersion process used to prepare the material is easily scalable and requires only a single step. Thus, with its demonstrated combination of affordability, efficiency, and ease of use, PDMS-SW has the potential to meet the demands of large-area oil and chemical clean-ups.

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Introduction.

The global, rapidly increasing use of oil as a main source of energy has led to frequent marine oil exploitation and transportation. Unfortunately, this increased marine–oil interaction has resulted in catastrophes such as oil spills and chemical leaks. 1 Spilled oils and organic solvents harm both the environment and the economy. 2 , 3 , 4 For example, in 2010, around 5 million barrels of crude oil spilled into the Gulf of Mexico, killing many marine animals and organisms and costing $600 million. 5 , 6 Therefore, efficient, effective methods for cleaning up oil and chemical spills in salt and fresh water are desperately needed.

Methods such as in situ burning, dispersing factors, solidifiers, enhanced bioremediation, skimmers, and booms have been utilized to clean up oil spills, but they generally have low separation efficiency, limited sorption capacity and recyclability, and high operation costs, and they can even introduce secondary pollution during the clean-up process. 7 , 8 , 9 , 10 Solutions that use superwetting materials have also been explored, mainly based on absorbency treatment and direct oil–water separation (filtration treatment), and encouraging outcomes have been achieved. 11 , 12 A wide range of superwetting materials that are superhydrophobic, superoleophilic, and superoleophobic under water have shown significant promise for oil–water separation, 13 , 14 including carbonaceous hydrogels/aerogels, 15 sponges, 16 and films 17 and manganese nanowires. 18 However, the costly, toxic reagents/equipment and complex, lengthy fabrication methods and technologies required to create these materials limit their practical use.

Inorganic mineral products, 19 natural sorbent materials, 20 artificial organic polymer absorbents, 21 surface-treated polyurethane, 22 inorganic or metallic-based meshes, 23 and membranes 24 , 25 have also been developed to separate oil and water. Unfortunately, most of these materials suffer from poor separation efficiency, lack of selectivity, low absorption capacity, inconvenient recycling, low stability, low flux, or degradation and polymer swelling, severely hampering their practicality. 9 , 26 Thus, a solution for oil spills and chemical leaks is still needed. Ideally, this solution would be a versatile material with low fabrication costs and stable performance in both fresh and salt water environments, able to be used as both a highly efficient absorbent (high capacity, selectivity, recyclability, and reusability) and a separator with high separation efficiency, high permeate flux, and low power.

In the oil–water separation field, “smart sorbents” are gaining popularity; these materials’ absorption properties can be controlled by electrical, phonetic, thermal, or magnetic input. 27 Of these inputs, magnetically controllable absorbents have recently received great interest, as they can be easily driven to the contaminated area simply by exploiting the magnetic field. Researchers have integrated and tested various water-repellent tools with magnetic materials. 5 , 14 , 28 , 29 , 30 , 31 , 32 To date, three main strategies have been used to synthesize magnetic absorbents. 27 The first method involves depositing a magnetic layer on the porous absorbent’s surface. This method has two major potential disadvantages: (1) it can decrease the pore volume, which impacts absorption capacity, particularly if the magnetic particles are larger than microns, 33 and (2) the magnetic coatings might not be stable, meaning that, in order to recycle the absorbent, repeating the deposition and synthesis procedures will generally be necessary. 28 The second strategy involves polymerizing superhydrophobic absorbents with magnetic nanoparticles, but production costs are high, and most of the products collapse or fracture under compression or stretching. The final method entails integrating polymeric materials with magnetic nanotubes, 27 but it requires expensive nanomaterials and multiple, lengthy preparation steps, prohibiting large-scale fabrication.

In summary, creating magnetic separators tends to be costly and complex, requiring magnetic nanoparticles/materials, and most have exhibited poor oil–water separation properties, such as low selectivity, poor recyclability/reusability, and low absorption capacity and stability. Ideal magnetic absorbent materials would be produced in one step without the need for magnetic nanomaterials. In this study, we report for the first time a one-step, simple, and affordable solution immersion method to fabricate superhydrophobic, superoleophilic, and magnetic polydimethylsiloxane (PDMS)-modified steel wool (SW) for oil–water separation and absorption. This novel product does not require extra nanomaterials or complicated techniques. The PDMS-coated SW (PDMS-SW) absorbs various oils and organic solvents with high selectivity and sorption/separation capacities, outstanding recyclability, and excellent chemical, mechanical, and environmental stability. Because of its inherent magnetization, the modified SW can be guided by a magnet to selectively absorb oils floating on the water’s surface. In addition, the PDMS-SW can be utilized in conjunction with a vacuum apparatus to continuously absorb and remove oil pollutants from water in both calm and turbulent conditions, suggesting its usability for large-scale removal of oil pollutants in both pure and salty environments. In gravity-driven oil–water separation experiments, the material exhibited high separation efficiency and high flux, as well as effective oil separation in salty water.

Results and Discussion

Fabrication and characterization of the pdms-modified sw material.

Steel wool was chosen as the base material because it is porous, affordable, inherently magnetic, and commercially available; it also features high flexibility and mechanical stability that can be mass produced. PDMS was chosen as the coating because it is a commercially available silicone rubber that has high flexibility and mechanical stability. 34 PDMS can be irreversibly bound to many materials and itself without adhesives. 34 In addition, it can be used with SW without altering the wool’s inherent magnetization.

To create the oil-absorbent material, we dipped commercially available SW samples in a toluene solution containing PDMS, then followed this with a heat treatment. A schematic of this simple, fast preparation process is shown in Fig. 1 ; to the best of our knowledge, no one else has reported modifying commercial SW to enable its use for oil/water separation. The overarching rationale behind this preparation method and materials is as follows. First, it is easier and more practical to use a material that is commercially available than to find or create new materials. Second, the process is one step, simple, and cost effective and does not require extra (costly) nanoparticles, special chemicals, or complex treatments.

Schematic diagram of the fabrication process used to create the polydimethylsiloxane-modified steel wool

We utilized scanning electron microscopy (SEM) to study the microstructural morphology of the SW before and after PDMS modification. Figure 2a, d shows that the SW has an open porous network with uniform steel microfibers that are 25 μm in diameter, and the pores are different sizes, approximately 70 ± 20 μm on average. The wool’s open porous network helps it to rapidly uptake and transport oils, chemical solvents, outer gases, and other liquids. Importantly, SEM analysis indicated that this porous structure is nearly the same before and after PDMS coating, demonstrating that the modification did not damage the pristine structure of SW or block its pores. SEM micrographs at higher magnifications revealed that a pristine single SW fiber has a rough surface consisting of hierarchical structures (Fig. 2b, c ). SEM images also showed that, while the dip-coating process covered the fiber’s rough surface with a thin waxy PDMS film (Fig. 2e, f ), the modified SW had retained most of its original roughness. From these results, we can conclude that the wool’s hierarchical structures, together with its micro-porous architecture, formed a composite interface in which air can be trapped beneath water within the surface’s asperities, leading to superhydrophobicity (the Cassie–Baxter model). 35

Scanning electron microscopic images of a the original steel wool (SW), b a single SW fiber, c the single fiber at high magnification, d the modified SW, e polydimethylsiloxane (PDMS)-coated single fiber, and f PDMS-coated single fiber at high magnification

To further confirm that the SW was successfully modified by PDMS, we analyzed the surface chemistry of both the pristine and modified SW with X-ray photoelectron spectroscopy (XPS) (Fig. 3 ). XPS identified the SW’s main elemental peaks to be C 1s, O 1s, Si 2p, and Si 2s, with binding energies around 285, 532, 102, and 154 eV, respectively. New silicon peaks (Si 2p and Si 2s) appeared in the wide-scan spectrum for the modified SW, demonstrating that the Si-containing PDMS layer was incorporated successfully onto the SW’s fibers. In comparison with the pristine SW’s wide-scan spectrum, the modified SW did not have an N 1s or Fe 1s peak, indicating that the SW was well coated with PDMS. Furthermore, elemental mapping analysis on the surface of a PDMS-coated single fiber demonstrated clearly that Si was uniformly distributed throughout the whole fiber (Fig. 4 ), confirming successful coating by PDMS.

The X-ray photoelectron spectroscopic spectra of a the original and b the modified steel wool

a Scanning electron microscopic image of polydimethylsiloxane-coated single fiber; b – d energy-dispersive X-ray spectroscopic element mapping of Si, C, and O, respectively

The pristine SW displayed superhydrophilic and superoleophilic properties (see Supplementary Fig. S1 ). However, after being coated with PDMS, the SW floated on the water’s surface without taking in water (Fig. 5a ); in contrast, the unmodified SW dropped to the bottom of the beaker. Figure 5a inset shows that the surface of the PDMS-SW looked like a silver mirror when held underwater by external pressure, a phenomenon that indicates that air was trapped between the solid interface and the water, thus confirming that the PDMS-SW aligned with the non-wetting Cassie–Baxter model. The superhydrophobicity of the modified wool also caused deposited water droplets to form a nearly spherical shape (Fig. 5b ). In addition to its superhydrophobicity, the modified SW showed excellent superoleophilicity—when motor oil was dropped onto its surface, the oil was absorbed immediately (Fig. 5b ).

a Photograph of the original and modified steel wools (SWs) after being placed in water. Inset: photograph of the modified SW after immersion in water by force; b photograph of water droplets (blue) as semi-spheres and motor oil (red) on the surface of the modified SW

Clearly, the hierarchical structures and PDMS coating on the SW, combined with the wool’s micro-porosity, made it superhydrophobic and superoleophilic. However, as is the case for a number of porous materials, it was difficult to precisely measure the superhydrophobicity of the modified SW using the water contact angle method. 36 This is because the water droplets were supported by the fibers of the SW, making the contact line between surface and droplet unobtainable, which is necessary for defining the contact angle (see Supplementary Fig. S2 ). Thus water droplet bouncing was used instead. 37 An 8-μl water droplet was dropped onto the PDMS-SW surface from a height of 20 mm, with a high-speed camera recording the bouncing process. The water droplet bounced off the modified SW easily, impinging the surface then bouncing off instantly, thus indicating high superhydrophobicity and low adhesion (see Supplementary Video S1 ). The potential energy of the droplet was converted to vibrational energy, causing it to rebound before undergoing damp oscillations and ultimately resting on the modified wool surface in a near-spherical shape. 38 , 39 In contrast, the oil droplet was absorbed by the modified SW instantly (see Supplementary Video S2 ). These results confirmed the simultaneous superhydrophobicity and superoleophilicity of the modified SW, suggesting its potential for real-world, selective oil separation and absorption from water.

Selective absorption by the modified SW

We performed two types of tests to evaluate the modified SW’s ability to selectively absorb oils/organic solvents in water. The first test was performed on floating oil (see Supplementary Fig. S3 , Fig. 6a , and Supplementary Video S3 ). An external magnet was used to control the PDMS-SW’s direction on the surface of the oil–water mixture, guiding it to the contaminated area. The magnetically guided material quickly absorbed the floating oil (colored with Sudan red) in the contaminated area, leaving only water underneath. The wool was then taken out of the solution. From start to finish, the procedure took only a few seconds. In the second test, we investigated the wool’s ability to selectively absorb oil under water, using dichloromethane (colored by Sudan red) as the oil because it sinks in water due to its high density. When we immersed the modified wool in the dichloromethane-contaminated water by an external force, all the oil was rapidly—within a few seconds—sucked up into the wool upon contact, leaving clean, clear water with no sign of colored oil when the wool was taken out (Fig. 6b and Supplementary Video S4 ). These rapid absorption kinetics result from the modified wool’s oleophilicity, capillaries, and high porosity.

Photographs of the modified steel wool a being guided by a magnet to remove floating oil and b absorbing dichloromethane at the bottom of a beaker

The PDMS-SW showed high absorption capacities—up to 12–27 times its own weight—for common oils and organic solvents, depending on the organic liquid’s density, viscosity, and surface tension (Fig. 7a ). This absorption capacity is higher than that of several absorbents reported recently for similar organic liquids, including a PDMS sponge (5–11 g/g), 40 aerogel composite (2–16 g/g), 41 nitrogen-rich carbon aerogel (5–16 g/g), 42 magnetic composite foam (13 g/g), 28 magnetic silicone sponge (7–17 g/g), 30 nanowire membrane (<20 g/g), 18 and polypropylene sponges (5–20 g/g). 43 In addition, although the capacity of the modified SW is lower than that of other absorbents, such as new carbon sponges, 29 , 44 , 45 films, 26 and aerogels, 4 these sorbents require costly fabrication materials, special chemicals, and complicated, lengthy processes, limiting their mass production. In contrast, the preparation method for the PDMS-SW is one step, simple, easily scaled up, and cost effective, and no expensive raw materials, special chemicals or nanoparticles, or complex equipment are required. Therefore, from methodology to cost to versatility, our modified SW offers major advantages over current options for cleaning organic leaks and oil spills.

a Absorption capacity of the modified steel wool (SW) for different oils and organic solvents; b collection of motor oil from the modified SW by simple mechanical squeezing; c , d the absorption capacity of the modified SW for hexane and motor oil, respectively, over 100 cycles

Recyclability of the modified SW

Recyclability and absorbate retrievability are key considerations when designing materials to remove oils and organic solvents, due to the need for environmental and economic sustainability. Our modified SW satisfies both considerations, as demonstrated by mechanical squeezing tests (Fig. 7b ). Hexane and motor oil were selected as the model absorbates for investigating the PDMS-SW’s cyclic absorption/squeezing behavior. Figure 7c, d shows the recyclability of the modified SW for hexane and motor oil, respectively, through 100 cycles. The results demonstrate that, because of the PDMS-SW’s elasticity, absorbates stored in its macrospores were able to be retrieved by mechanical squeezing. In addition, the porous structure of the modified SW stayed the same after multiple cycles of absorption/squeezing. The simplest process for releasing an organic liquid, mechanical squeezing is faster and more eco-safe and cost-effective than other reported recycling processes, such as heat treatment 4 and burning. 7 For hexane, the modified SW showed high recyclability, even after 100 absorption/retrieval cycles, with the absorbance capacity largely remaining the same. However, for the viscous oil (motor oil), a slight reduction in oil absorbance capacity was observed over the 100 cycles. This deterioration is due to residual oil remaining inside the pores of the modified SW because it could not be totally removed after squeezing the wool through that many cycles.

Rinsing with strong organic solvents such as dichloromethane, trichloroethane, or dimethylformamide could be a good option for removing residual oil that cannot be recovered sufficiently by ethanol or acetone. For example, many materials, such as surface-treated polyurethane, 46 organic fibrous sorbents, 47 and silicone-treated textiles, 48 have shown high absorption capacity, but their recyclability was not satisfactory because certain oils stayed in their pores and could not be adequately retrieved by alcohol or acetone due to low solubility in these solvents. However, rinsing with the powerful organic liquids listed above would dissolve these absorbents easily, rendering them useless. 26 In contrast, the modified SW had high stability with these organic solvents (see Supplementary Fig. S4 ); after rinsing with dichloromethane and drying at 80 °C for several hours, the PDMS-SW showed roughly the same absorption capacity as it did when fresh. Together, these results affirm the high recyclability and reusability of the PDMS-SW.

Continuous absorption of various contaminants in multiple conditions

In addition to being highly absorbent and recyclable, the ideal clean-up material would be able to continuously absorb and remove large amounts of oil and organic solvents from water. As illustrated in Fig. 8a , we investigated our modified wool’s ability to perform such continuous absorption. A small piece of the modified wool was folded and crammed into the end of a narrow tube, then that end was fixed in a beaker containing oil (toluene) and water; the water was colored blue to distinguish it from the clear toluene. The tube’s other end was connected to a vacuum pump by the filter flask. The modified wool absorbed the toluene quickly and repelled water completely. In addition, the toluene was absorbed and removed simultaneously by the wool piece when the vacuum system was turned on. A toluene stream formed in the tube, and the oil was gradually sucked out of the water. Eventually, all the toluene was completely removed from the water’s surface, leaving only blue water in the beaker. The retrieved toluene was collected into the filter flask, and no water droplets were seen in it.

Photographs show the continuous absorption and removal of toluene from a a nonturbulent oil–water mixture and b an oil–water mixture made turbulent by a magnetic stirring plate. The water was colored by methylene blue to enhance the visual impact

This experiment was also carried out with other contaminants in water: sesame oil, mineral oil, gasoline, and n-hexadecane. The modified SW completely separated the oils/organic solvent pollutants from the water surface (see Supplementary Figs S5 – S8 ), without absorbing any water. The PDMS-SW’s separation efficiency for sesame oil, mineral oil, gasoline, and n-hexadecane was 99.5, 99.3, 99.7, and 99.6, respectively. Furthermore, at least 25 L of gasoline were able to be continuously collected by the modified wool with a separation efficiency of 99.7%, as well as high working stability. Therefore, the PDMS-SW has excellent selective oil–water separation efficiency.

In real environments, such as the sea or a river, water is usually in motion rather than stationary, as it generally is in laboratory testing. Therefore, to mimic actual oil-polluted water conditions, we repeated the previous experiments under highly turbulent conditions. To create a turbulent effect, about 400 mL of toluene were added to a similar amount of water, and the mixture was strongly stirred via a magnetic bar at ~1080 rpm to cause oil droplets to form in the water. We then began the vacuum-aided process with an applied vacuum pressure of 5 kPa, as described above. The oil droplets were continuously separated from water once the vacuum was turned on, while the water was not impacted at all (Fig. 8b ).

While some continuous absorbents have been developed, 6 , 7 , 49 very few can continuously remove oil from seawater selectively and in both static and dynamic conditions, even though these are common environments for oil spills. Therefore, an inexpensive, salt-tolerant, superhydrophobic absorbent for efficient oil/seawater separation is urgently needed. To test our modified SW’s potential to fill this need, we repeated the previous experiment but with a complex oil (toluene)/saltwater mixture. To mimic seawater, we added 3.5 wt% NaCl to the water and mixed it well 50 before turning on the vacuum. The PDMS-SW removed all the transparent oil from the surface while leaving all the colored water in the beaker (see Supplementary Video S5 )—no water was visible with the naked eye in the retrieved oil. Furthermore, in around 7.25 s, the PDMS-SW removed the same amount of oil as a PDMS–graphene sponge did in 30 s. 6

We also tested the modified wool’s performance with the oil–saltwater mixture under highly turbulent conditions. The PDMS-SW continuously removed around 400 mL of toluene from the water, and no blue water was visible in the collected oil in the filtrate flask. The water level in the beaker was stable despite the lengthy continuous pumping, indicating that the water was unaffected by the modified SW. In addition, the separation efficiency was maintained at 99.9% (detailed procedure given in Supplementary Video S6 ).

The continuous, quick absorption performed by our inexpensive, simply prepared modified SW in fresh and saltwater offers a major advantage over other current absorbents, which require expensive, complicated fabrication and can rarely perform in saltwater. The results of all our tests show that the novel PDMS-SW has strong practical potential for continuously absorbing and removing large amounts of oil and organic solutions from water in fresh and marine environments.

Oil–water separation

In addition to selective absorption, direct separation of oil from water is one of the main treatment techniques for addressing water pollution. Various materials have been used to fabricate superwetting surfaces, including metallic-based meshes, 51 , 52 , 53 membranes, 24 , 54 films, 55 and filter papers 56 . While these materials displayed high oil–water separation efficiency and selectivity, they also had a number of drawbacks, including complex fabrication, costly raw materials, and weak mechanical and chemical stability, limiting their large-scale production. Therefore, an efficient, scalable oil–water separator for oil spills that is cost effective and has low power consumption remains a serious need.

Given its superhydrophobic and superoleophilic nature and high flexibility, we believed our modified SW could fill this need. To test this potential, we conducted a practical oil/water separation experiment (Fig. 9a ). First, a small piece of wool was cut (60 × 60 × 7 mm 3 ), placed on stainless-steel mesh, and fixed between two glass beakers. A mixture of cyclohexane (colored with Sudan red) and water (colored with methylene blue) was prepared and poured onto the PDMS-SW. The cyclohexane was able to rapidly penetrate the separator and pass to the bottom of the beaker underneath it, driven solely by gravity (Fig. 9b ). In contrast, the water was repelled by the modified SW and stayed in the upper beaker (Fig. 9c ). The entire oil/water separation procedure was performed within a few seconds (see Supplementary Video S7 ) with no additional force, demonstrating the easiness and low energy consumption of the process. Therefore, the PDMS-SW clearly allowed oils to rapidly pass through it but prevented water from doing so, thus separating the two.

Oil–water separation carried out by the modified steel wool (SW; oil dyed with Sudan red, water dyed with methylene blue): a before separation, b during separation, and c after separation (the separation process was driven by gravity). d Separation efficiency of the modified SW for various oil–water mixtures. e Flux for permeating different types of oils through the modified SW. The error bars indicate the standard deviations from triplicate measurements

Furthermore, mixtures of toluene, gasoline, and sesame oil with water were effectively separated by the modified SW, with separation efficiency values reaching over 99% (Fig. 9d ). Owing to its robust coating adhesion, the modified SW retained its superhydrophobicity after 40 separations, as demonstrated by XPS analysis (see Supplementary Fig. S9 ) and a water droplet bouncing off the surface (see Supplementary Video S8 ). In addition, we repeated these oil/water separation experiments with saltwater (3.5% salt). In a cyclohexane/saltwater mixture, the modified SW successfully separated the cyclohexane from the saltwater, with the separation efficiency staying >99% (see Supplementary Fig. S10 ).

Permeate flux is an important factor for evaluating oil–water separation, as higher permeate flux results in faster separation. 57 , 58 The modified SW displayed ultrafast separation of oil from water via gravity alone. Different oil fluxes that permeated through the PDMS-SW were evaluated and averaged after repeating 3 times; a 7-mm-thick wool sample was used. The average permeate flux values for the oils—toluene, gasoline, and cyclohexane—were 32,026.4 ± 141.2, 30,793.6 ± 432.7, and 27,029.1 ± 315.2 L/m 2 ·h, respectively (Fig. 9e ). These flux values are much higher than those of many advanced separators reported in the literature, including PFOTS-modified SiO 2 /carbon stainless-steel mesh (<1000), 59 a carbon-silica nanofibrous membrane (1500–3000 L/m 2 ·h), 58 a superhydrophobic and superoleophilic polyvinylidene fluoride membrane (700–3500 L/m 2 ·h), 60 and a polyethylene mesh (<7500 L/m 2 ·h). 57 The superoleophilic nature and open-pore network of the modified SW promoted this rapid mass transport. In summary, the PDMS-SW’s high separation efficiency, ultrafast permeate flux (25,000–33,000 L/m 2 ·h), reusability, low-cost raw materials, simple preparation, scalability, and usability in salty environments make it a promising tool for real-world oil–water separation.

The PDMS-SW’s water intrusion pressure ( P ) was also investigated by determining the maximum water column height ( h max ) that it could bear, via the following Eq. ( 1 ):

where ρ is the density of water, g is the acceleration of gravity, and h max represents the maximum height of water that the modified SW can support. The PDMS-SW was able to completely support a ~14.6-cm-tall column of water (Fig. 10 ) without allowing any water to pass through it. Thus the water intrusion pressure for the modified SW is 1.43 kPa.

Water intrusion pressure of the modified steel wool (water is dyed with methylene blue)

For the first time, to our knowledge, we have fabricated a superhydrophobic and superoleophilic PDMS-SW and demonstrated its efficient oil absorption and oil–water separation. The solution immersion method we used requires only a single, simple step, affordable materials, and no special chemicals or complicated equipment and, as a result, is easy to scale up. The highly porous PDMS-SW is also magnetic without the addition of expensive nanoparticles, which were previously considered required to make a material magnetic for this application. The modified SW’s magnetic properties allow it to be guided without contact to oil-polluted areas. Moreover, after collecting contaminants and undergoing mechanical squeezing, the PDMS-SW can simply be driven back to the contaminated area to recover more spilled liquid. In addition, the PDMS-SW’s raw materials can be commercially and affordably manufactured on a large scale. These factors make the PDMS-SW well suited for large-scale manufacturing and thus for large-scale removal of oil spills and clean-up of organic solvents from water. The modified SW not only shows high absorption performance, including high selectivity, high recyclability, and good capacity, but it can also continuously, quickly absorb and remove large amount of various oils/organic solvents from both calm and turbulent water. Furthermore, the PDMS-SW can separate oils from water with great efficiency. In addition, the oil–water separation process is ultrafast and solely gravity-driven. Finally, the modified SW performs highly stable absorption, even in salty environments. Based on the results of this study, we believe that the PDMS-modified SW is a promising material for water remediation, cleaning up large-scale oil spills, and oil recovery.

SW (super fine with #0000 grade code) was purchased from a local store in Arkansas, USA. PDMS (Sylgard 184) was purchased from Dow Corning, USA. Toluene, hexane, dichloromethane, cyclohexane, acetone, ethanol, n-hexadecane, mineral oil, sesame oil, methylene blue, and Sudan red 7B were provided from Fisher Scientific Inc., USA. Motor oil, silicone oil, and diesel oil were obtained from a local store. Gasoline was purchased from a local Shell gas station. All chemicals were utilized as received without any purification.

Fabrication

PDMS (Sylgard 184) is a silicon elastomer that consists of two parts: an elastomer base and a curing agent to promote cross-linking and hardening in order to produce a heat-resistant polymer. Briefly, in this study, the polymer and cross-linking agent were added in a 10:1 weight ratio to 50 mL of toluene. The mixture underwent constant magnetic stirring for 30 min or until it was a clear solution. A piece of commercial SW was cut and cleaned ultrasonically in acetone for 15 min. The SW piece was then put in the oven to dry at 80 °C for several hours. After drying, the SW was immersed into the PDMS–toluene solution for 30 s, removed and dried under atmospheric conditions for 1 h, and then cured in the oven at 80 °C for 24 h to obtain the final PDMS-modified SW.

Characterization

SEM was used to analyze the PDMS-modified SW’s surface morphology (JEOL SEM7000FE). In addition, the modified SW’s surface chemistry was analyzed using a Thermos Scientific K-Alpha X-ray photoelectron spectrometer. Elemental mapping was conducted using energy-dispersive X-ray spectroscopy (Genesis spectrum). Water bouncing videos were taken by a high-speed digital camera (HiSpec 1) at a rate of 1000 frames per second. All measurements were performed at ambient temperature.

Selective oil absorption and recyclability tests

Various oils/organic solvents were used in the absorption experiments. For each type of oil/solvent, a piece of modified SW was immersed in the oil/organic solvent until it was totally saturated, then removed and immediately weighed. The weight measurement should be carried out quickly to avoid any absorbate evaporation. The absorption capacity ( k ) of the modified SW was determined in weight-gain ratio, as given in Eq. 2 :

where Wa is the weight of the modified SW in the oil/organic solvent-saturated state and Wb is the weight of the modified SW in the initial state. Each test was repeated three times.

The recyclability of the modified SW was evaluated by performing cyclic absorption–simple squeezing tests with two organic solutions, hexane and motor oil, separately. The absorption capacity was then calculated.

A piece of the PDMS-SW was placed on stainless-steel mesh and secured between two glass containers. Oil–water mixtures were then poured onto the modified SW, with gravity being the only driving separation force. Each separation experiment was performed three times, and the separation efficiency was determined by the following Eq. ( 3 ):

where Va is the volume of water that remains on the surface of the modified SW after the oil–water mixture is poured and Vb is the volume of water in the oil–water mixture before pouring.

The flux ( F ) of the modified SW was calculated by the following Eq. ( 4 ):

where V is the volume of the permeating liquid through the modified SW, S is the effective contact area of the modified SW, and t is the permeating time.

Acknowledgements

Funding for this research was provided by the Center for Advanced Surface Engineering, under the National Science Foundation Grant No. IIA-1457888 and the Arkansas EPSCoR Program, ASSET III. We thank Dr. Shawn Bourdo and Dr. Anindya Ghosh for their valuable feedback and discussion. We thank Bijay Chhetri for his help with preparing Fig. 1 . The editorial assistance of Emily Davis is also acknowledged.

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The authors originated the idea for the experiments collaboratively. A.T.A. synthesized samples, carried out most of the characterization, and prepared the first draft of the manuscript. G.K.K. carried out XPS analysis and helped revise the manuscript. A.S.B. also helped revise the manuscript.

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Abdulhussein, A.T., Kannarpady, G.K. & Biris, A.S. One-step synthesis of a steel-polymer wool for oil-water separation and absorption. npj Clean Water 2 , 10 (2019). https://doi.org/10.1038/s41545-019-0034-1

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Share and Cite

Beek, L.; Barthlott, W.; Mail, M.; Klopp, K.; Gries, T. Self-Driven Sustainable Oil Separation from Water Surfaces by Biomimetic Adsorbing and Transporting Materials. Separations 2023 , 10 , 592. https://doi.org/10.3390/separations10120592

Beek L, Barthlott W, Mail M, Klopp K, Gries T. Self-Driven Sustainable Oil Separation from Water Surfaces by Biomimetic Adsorbing and Transporting Materials. Separations . 2023; 10(12):592. https://doi.org/10.3390/separations10120592

Beek, Leonie, Wilhelm Barthlott, Matthias Mail, Kai Klopp, and Thomas Gries. 2023. "Self-Driven Sustainable Oil Separation from Water Surfaces by Biomimetic Adsorbing and Transporting Materials" Separations 10, no. 12: 592. https://doi.org/10.3390/separations10120592

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6 Ways to Separate an Oil and Water Emulsion

An oil and water e mulsion refers specifically to the  fluid  that comes directly from an oil and gas well.  

When a well is produced, what comes to the surface is a mixture of crude oil, water, gas, and solids. After  the  gas has been separated from the liquid,  the oil and water  that remain  must also be separated .    

Emulsions in the oil industry are  either classified as  "water in oil "  or "oil in water" depending on the ratio of the volume of liquids.   

Gas brought to the surface is usually  " wet gas "  compos ed  of dry natural gas like methane mixed with liquid natural gases like ethane and butane.   

All  these components are separated using multiple principles of separation to achieve the desired end products that are considered valuable.    

In this video, we explain 6 principles used to separate an oil and water emulsion in the oil and gas industry.    

1. How Heat Separates an Oil and Water Emulsion

When separating liquids from each other,  heating to certain temperatures enhances  separation.  W hen the temperature  of an oil and water  emulsion  is increased, the  viscosity  of oil is   d ecreased .  This lower  viscosity  allows  the gas and water molecules  to be  more easily released.   Heating oil emulsions also increases density between oil and water.

A heater treater is a n  example of a vessel which uses th e  principle of temperature change to aid in separation.   For more on how a Heater Treater works, check out our training level 1 series.

2. Gravity Separation

Gravity separation is the most widely used method for oil  emulsion  separation.  The elements  in  the well stream  such as oil and water  have different gravities. 

The density differences  allow  water to se parate  by gravity.  With  enough time in a non-turbulent state, the differing specific gravities will naturally separate into distinct layers. 

To picture this, think of the emulsion as Italian dressing.  If you le t   the dressing  s et , the ingredients will separate according to their different specific gravities .  The olive oil will float on top because it is lighter than the vinegar, and the solids and other ingredients  will  fall to the bottom because they are the heaviest.

3. Retention Time

Separation occurs over time.  When you reduce the velocity of a  fluid,  you allow the fluid a certain amount of time for it to be separated by gravity. 

Retention time is the amount of time the fluid mixture stays in a steady or non-agitated state inside a separator. Longer  retention time  means more  separation.

A larger- diameter  or taller  vessel  will increase the retention time and allow more water to settle out by gravity.

In the video we show  a sample of a mixture from a free water knockout , and you can see three layers : o il, water and solid,  which separated over time.  

4. How Agitation Separates  an Oil and Water Emulsion

A  production fluid  is   agitated  when it hits the diverter plate at the inlet of  a vessel.   The sudden impact  on the plate  causes a  rapid  change in direction  and velocity   which  helps break the surface tension of the liquids and start the separation process. 

There are many  types  of  inlet  diverter s  in separators, and the  which is used depends on the attributes and volume of the well stream.  

A gitation   increases the  probability  that the liquid will coalesce and settle from the emulsion.  

5. Coalescing 

During coalescence, water droplets come together to form larger drops.

Picture  yourself  driving on a foggy morning. The fog tells us there is  is a lot of moisture in the air, but it doesn't actually condense into liquid until it hits your windshield.   

The same is true when gas hits  a hard surface. This may be a  diverter plate when it first enters the vessel, or a mist e liminator  as it exits.   

In vane-type mist eliminators, tiny droplets are removed from the vapor stream through inertial impaction.  The   wet   gas is   forced to change   directions,   causing mist   droplets to strike the vanes  a nd coalesce with other droplets, eventually falling.   

This inertial impaction also occurs in mesh-type mist eliminators.

Gas must flow around each strand of mesh, and when mist droplet strikes the filaments, they adhere and coalesce to form droplets large enough to fall.

Submicron droplets zig-zag through the close-packed fibers with "Brownian motion" and will eventually strike, adhere, coalesce, and drain.    

6. How C hemical  D emulsif iers  Separate   an Oil and Water Emulsion

Treating fluids with  demulsifiers  aids the separation process. The chemicals m ov e to the oil  and  water interface, weaken ing the surface tension  and  enhanc ing  coalescence .  Knowing which chemicals to use and the correct dosage can be complex, but the desired effect will  minimize  the amount of heat or  retention  time  required for separation.  

To speak with an expert about this separation process, c ontact an expert at your local Kimray store or authorized distributor .  

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ORIGINAL RESEARCH article

Numerical simulation study of oil–water separation based on a super-hydrophilic copper net.

• School of Advanced Manufacturing Engineering, Hefei University, Hefei, China

Green and environmentally friendly oil–water separation is an important technique for reducing environmental pollution. In this study, the oil–water separation effect of the super-hydrophilic copper net was optimized through numerical simulation and orthogonal experiments. To be specific, a super-hydrophilic copper net was prepared using the solution etching method to perform oil–water separation experiments, and a favorable oil–water separation effect was achieved. First, the influences of oil–water flow velocity, copper net mesh size, and surface wettability on the oil–water separation effect of the super-hydrophilic copper net were explored via single-factor experiments. The results showed that the oil resistance of the super-hydrophilic copper net degraded, and its oil–water separation effect became poor due to the increasing oil–water flow velocity, enlarged copper net mesh size, and reduced oil contact angle on the surface of the super-hydrophilic copper net. On this basis, the optimized oil–water separation parameters were obtained through orthogonal experiments. The optimized process parameters were as follows: velocity = 0.1 m/s, copper net mesh size = 30 μm, oil contact angle = 150°, and oil removal rate = 95.7%. Furthermore, the copper net was etched using sodium hydroxide and sodium persulfate mixed solution to prepare a 500-mesh super-hydrophilic copper net for the oil–water separation experiment and then the oil removal rate reached 96.4%. The study results provide a theoretical basis, method, and means for the practical application of super-hydrophilic copper nets.

1 Introduction

With economic development, oily wastewater discharge and treatment difficulties are continuously aggravated. The economical and efficient treatment of oily wastewater can not only save resources and promote resource recycling but also be conducive to environmental protection ( Zhang and Zhang, 2018 ; Chen, 2019 ; Lu et al., 2020 ).

Oily wastewater mainly comes from the petroleum industry and food processing industry ( Song and Wang, 2011 ; Yu, 2015 ; Hu et al., 2021 ; Xu, 2021 ; Liu et al., 2022 ). Oil–water separation technology mainly includes gravity separation, centrifugal separation, membrane separation, electrolysis separation, and air flotation separation ( Hu et al., 2015 ; Shao and Zhong, 2015 ; Zhang et al., 2017 ; Zhang et al., 2021 ). The membrane separation technology is more effective and less costly to operate, but it is prone to blockage when treating oily wastewater with a high oil content, resulting in membrane contamination. Superwetting materials are capable of rapid efficient oil–water separation by virtue of oil–water wettability difference, without secondary pollution, which has been deeply investigated by scholars. Zhang et al. (2018a) experimentally prepared a stainless steel net with super-hydrophobic and super-oleophilic characteristics to explore its oil–water separation ability and self-cleaning ability; Jung and Bhushan (2009 ) established a model and used to predict the oil drop contact angle in water by studying the wetting behaviors of water drops and soil in a three-phase interface; Zhang et al. (2018b ) ablated the Al, Fe, Cu, Mo, and stainless steel surfaces using lasers and prepared rough micro-nanocomposite surfaces. With the inherently high surface energy, Al, Fe, Cu, Mo, and stainless steel surfaces all showed super-hydrophilic and underwear super-oleophobic properties. The previously mentioned scholars used the prepared super-wettable materials to separate oil and water and achieved excellent results. However, the actual oil–water separation environment is often harsh and superwetting materials do not give good oil–water separation results in practice. With further research, more and more results showed that when the superwetting material is impacted, the oil–water separation effect will be affected ( Pi et al., 2017 ; Zhao et al., 2018 ). In recent years, computer simulation theories of fluid and material properties have been gradually developing. Liu and Yu, (2010) constructed a super-hydrophobic microchannel flow model and studied its flow characteristics via the numerical simulation technique; Qin (2013 ) explored the oil–water separation effect of a super-hydrophobic membrane-based spiral oil–water separator through the numerical simulation technique.

In this study, the flow field conditions on the water drop–oil drop contact surface of a super-hydrophilic copper net were simulated via FLUENT software. The influences of three factors—oil–water flow velocity, copper net mesh size, and oil contact angle—on oil–water separation were mainly studied. On this basis, the aforementioned influencing factors were subjected to an orthogonal experiment, and optimized process parameters were obtained. The super-hydrophilic copper net was prepared according to the process parameters, and oil–water separation experiments were conducted to verify the reasonableness of the simulation results.

2 Materials and methods

2.1 procedure of the simulation study, 2.1.1 modeling.

The wettability of materials is greatly influenced by their surface microstructure. Periodic rough surfaces, aperiodic rough surfaces, and composite rough surfaces can be prepared through laser ablation and chemical etching ( Pan et al., 2010 ; Cui et al., 2017 ). In this study, the surface microstructure of the super-hydrophilic copper net was simplified into a periodically distributed groove to simplify the calculation, and a 2D structure of its cross section was taken to establish a 2D model through Gambit software, as shown in Figure 1 .

FIGURE 1 . Schematic diagram of the groove structure for the super-hydrophilic copper net.

When simulating the oil–water separation of the super-hydrophilic copper net, the influences of three factors—velocity, net mesh size, and oil contact angle on the copper net surface—on the oil–water separation effect were mainly explored. The volume of fluent model (VOF model) ( Feng and Yao, 2012 ; Zhang and Yan, 2013 ) can be used to acquire clear interfaces between different phases by setting their surface tension and wall surface contact angle. Hence, the VOF model was chosen to simulate the oil–water separation of this super-hydrophilic copper net by abiding by the conservation law of mass, momentum, and energy, with the basic governing equation as follows:

The continuity equation of the VOF model is:

The continuity equation of the volume fraction is:

The momentum conservation equation is:

where ρ is the density, kg/m 3 ; ν denotes the velocity vector, m/s; t represents time, s; ∇ is a mathematical operator notation; α i is the volume fraction of phase i ; is the dynamic viscosity of fluid; g is the gravitational acceleration, m/s 2 ; P is the pressure intensity, Pa; and F represents the equivalent body force form of surface tension, N.

2.1.2 Numerical calculation method and boundary conditions

In this study, the flow field condition on the oil drop–water drop contact surface of a super-hydrophilic copper net was simulated. To simplify the calculation, a laminar flow model was selected. Given that a transient problem was the simulation object, pressure-implicit with the splitting of operators (PISO) algorithm was selected to accelerate the convergence rate of single iterative steps during transient calculation, harvesting a good convergence effect. As for the selection of the discretization method, the body force weighted scheme was chosen for pressure, second-order upwind discretization format for momentum, and geometric reconstruction format for the volume fraction. The initialization value of the sub-relaxation factor was set to default.

In this simulation, gravitational acceleration was set at 9.8 m/s 2 , initial operating pressure at 101,325 Pa, and water contact angle at 0°. Three-phase (oil, water, and air) fluids were involved in the simulation of oil–water separation for a super-hydrophilic copper net. To clearly observe the flow field conditions on the oil drop–water drop contact surface of this super-hydrophilic copper net, the three-phase computational domains were divided through patch function, where air was set as the primary phase, and the volume fractions of all the three phases in their respective computational domains were set at 1. The tensions on oil and water surfaces were set at 0.029 and 0.072 N/m, respectively.

2.1.3 Range analysis

Range analysis was performed according to the orthogonal experimental results. The experimental results corresponding to the m level of factors in column j as well as K jm and its mean value jm were calculated. Moreover, the range R j of factors in column j was calculated based on the jm value:

Here, R reflects the variation range of experimental results in case of changes in the factors in column j . A greater R -value manifested a greater influence of this factor on experimental indexes, so the sequence of influencing factors could be judged according to R .

2.2 Procedure of Cu net mesh and oil–water separation

The reagents required for the preparation of the super-hydrophilic copper net and super-hydrophobic copper net experiments are shown in Table 1 .

TABLE 1 . Experimental reagents and substrates.

A 500-mesh red copper net with a mesh size of 30 µm was selected as the substrate, and an etching solution was prepared by mixing 25 ml of 1 mol/L sodium hydroxide solution and 25 ml of 0.15 mol/L Na 2 S 2 O 8 solution. The dried red copper net was placed in the etching solution for reaction at room temperature for 60 min and then taken out and washed using deionized water. Subsequently, it was dried up in a blast air oven to prepare a super-hydrophilic copper net. The hydrophilicity of the super-hydrophilic copper net was examined using the OCA15EC optical contact angle meter and SU8010 scanning electron microscope, and the testing process was as follows: when measuring the contact angle of the prepared copper net surface, the SNS syringe needle was selected, and the dosing volume was set to 3 μL. The water was dropped at a dosing rate of 1 μL/s, and a thin film was formed on the surface of the copper net. The indirect contact angle was measured to be 0°, indicating that the copper net is super-hydrophilic, as shown in Figure 2 .

FIGURE 2 . Surface contact angle of the super-hydrophilic copper net.

The copper net was cut into 10 mm × 10 mm specimens, and the surface morphology of the prepared copper net was characterized using a cold field emission scanning electron microscope electron gun at an acceleration voltage of 15 KV. The surface morphologies of this super-hydrophobic copper net were characterized as shown in Figure 3 . After etching through the mixed solution, many tiny clusters attached on the copper net matrix and presented ordered growth around. It could be observed that micrometer needle-like structures were generated on the surface of the copper net substrate, which was mutually crossed and grew around in an unordered way. These clusters and micrometer needle-like structures formed composite micro-nanostructures on the copper net surface, thus greatly increasing the roughness of the copper net surface and endowing it with super-hydrophilicity.

FIGURE 3 . Surface morphologies of the super-hydrophilic copper net.

To test the oil–water separation effect of this 500-mesh super-hydrophilic copper net, an oil–water separation device was designed as shown in Figures 4 , 5 . Using restaurant oily wastewater as the separation object, it was first treated by air flotation and the measured animal and vegetable oil content was 54.5 mg/L, and the oil content was still high. Then, the secondary treatment of this oily wastewater was carried out by using a super-hydrophilic copper net. Before the oil–water separation experiment, the super-hydrophilic copper net was fully wetted using water. Next, 500 ml of oily restaurant wastewater pretreated through air flotation was taken and made to flow into the vessel slowly along the inner wall to prevent the oil–water separation effect from being impacted by too high oil–water flow velocity.

FIGURE 4 . Schematic diagram of the oil–water separation device.

FIGURE 5 . Experimental separation device.

3 Results and discussion

3.1 calculated results and analysis of the simulation study, 3.1.1 oil–water flow velocity.

The flow field conditions when oil and water drops contacted the super-hydrophilic copper net were simulated at simulation velocities of 0.1, 0.5, and 1 m/s under the net mesh size of 10 µm and oil contact angle of 150°. At the left was the aqueous phase and at the right was the oil phase, as shown in the following Figure 6 .

FIGURE 6 . Cloud picture of the oil–water volume fraction at a velocity of 0.1, 0.5, and 1 m/s.

It could be known from Figure 6 that water drops could completely wet and penetrate through this super-hydrophilic copper net. At a velocity of 0.1 m/s, oil drops failed to wet the super-hydrophilic copper net and were intercepted above it, thus realizing the goal of efficient oil–water separation. As the velocity was elevated to 0.5 m/s, the dynamic pressure was elevated, and oil drops were forcibly extruded into the groove structure on the partial copper net surface, but they did not completely wet the copper net, which was still oleophobic to some extent. When the velocity was increased to 1 m/s, oil drops were forcibly extruded into the groove structure on the copper net surface and passed through the net via meshes, and this super-hydrophilic copper net could not realize efficient oil–water separation under this circumstance.

3.1.2 Copper net mesh size

The flow field conditions when oil and water drops contacted the super-hydrophilic copper net were simulated at the velocity of 0.5 m/s under the oil contact angle of 150° and the copper net mesh size of 10, 40, and 70 μm, respectively, as shown in the following Figure 7 .

FIGURE 7 . Cloud picture of the oil–water volume fraction under the copper net mesh size of 10, 40, and 70 µm.

It could be known from Figure 7 that the copper net mesh size had a bearing on its oleophobic properties. When the copper net mesh size was continuously enlarged, oil drops would finally pass through this super-hydrophilic copper net. As the copper net mesh size gradually increases, the area of the super-hydrophilic copper mesh also increases, and its impact resistance will be weakened, so the effect of oil–water separation will become worse. Hence, it is important to select an appropriate copper net mesh size in order to enhance the oil–water separation effect.

3.1.3 Contact angle

The flow field conditions when oil and water drops contacted the super-hydrophilic copper net were simulated at the velocity of 0.1 m/s under a copper net mesh size of 70 µm and oil contact angles of 90°, 120°, and 150°, respectively, as shown in the following Figure 8 .

FIGURE 8 . Cloud picture of the oil–water volume fraction under the oil contact angle of 90°, 120°, and 150°.

As shown in Figure 8 , at the velocity of 0.1 m/s and copper net mesh size of 70 μm, water drops could freely pass through the super-hydrophilic copper net at contact angles of 90°, 120°, and 150°. As the oil contact angle was gradually enlarged, the contact area between oil drops and super-hydrophilic copper net was smaller. At the oil contact angle of 90°, partial oil drops penetrated through this super-hydrophilic copper net. When the oil contact angle increased to 150°, oil drops were nearly completely obstructed above the super-hydrophilic copper net, with its oleophobic properties gradually enhanced, which was better for improving the oil–water separation effect.

3.1.4 Three-factor three-level orthogonal experimental analysis

The aforementioned simulation results revealed that velocity, net mesh size, and oil contact angle exerted important influences on the oil–water separation effect of this super-hydrophilic copper net. Based on the simplified 2D super-hydrophilic copper net surface structure, a 2D numerical simulation model of this super-hydrophilic copper net was constructed ( Figure 9 ). Then, a three-factor three-level orthogonal experiment was carried out to further explore the influencing degrees of velocity, copper net mesh size, and contact angle on the oil–water separation effect of the super-hydrophilic copper net. The factor levels in the orthogonal experiment are listed in Table 2 , and the orthogonal experiment and its results are presented in Table 3 .

FIGURE 9 . 2D model drawing of the super-hydrophilic copper mesh.

TABLE 2 . Factor levels in the orthogonal experiment.

TABLE 3 . Orthogonal experiment and results.

During numerical simulation, outlet flow monitoring was set in FLUENT software. A stable outlet flow indicated that the oil–water separating flow field of this super-hydrophilic copper net was stable. In this case, the mass flow data of inlet and outlet oil were, respectively, recorded, and the oil removal rate was calculated accordingly through the following formula:

where η oil removal rate;

C1 mass flow of inlet oil, kg/s; and

C2 mass flow of outlet oil, kg/s.

The range analysis of orthogonal experimental results is presented in Table 4 . It could be known from the range analysis that the sequence of factors influencing the oil removal effect of this super-hydrophilic copper net was as follows: oil–water flow velocity > oil contact angle > copper net mesh size. The orthogonal experimental results reflected that the oil removal rate reached the highest value (95.7%) at the velocity of 0.1 m/s, oil contact angle of 150°, and copper net mesh size of 30 µm. Figure 10 is drawn under the aforementioned process parameters. As shown in Figure 10 , oil was basically intercepted above the super-hydrophilic copper net, while only a small quantity of oil passed through this net, which showed good oil resistance and water drainage functions under this circumstance.

TABLE 4 . Range analysis of orthogonal experimental results.

FIGURE 10 . Cloud picture of the oil-phase volume fraction.

3.2 Results of the oil–water separation experiment using the newly synthesized Cu net mesh

The animal and vegetable oil concentrations in water before and after the experiment were measured using an infrared oil meter ( Table 5 ). Through the treatment using a 500-mesh super-hydrophilic copper net, a good oil removal effect was achieved at a reasonable oil–water flow velocity, and the content of animal and vegetable oils was reduced to 1.98 mg/L, with the oil removal rate reaching 96.4%, which was approximate to the numerical simulation result. The water qualities before and after the treatment were compared as shown in Figure 11 .

TABLE 5 . Results of the oil–water separation experiment.

FIGURE 11 . Comparison diagram of water qualities before and after treatment.

The oil removal rates mentioned in Sun et al. (2018 ) were 98.8, 98.75, 99, 99.5, and 99.95%. Further experiments were conducted with three such oil–water separation devices connected in series, and it was measured that the content of animal and vegetable oils was reduced to 0.34 mg/L, and the oil removal rate could reach 99.4%, which is better or close to several membrane separation techniques mentioned in the reference ( Sun et al., 2018 ).

4 Conclusion

In this study, the surface structure of the super-hydrophilic copper net was simplified and three single-factor simulation experiments of oil–water flow rate, copper mesh pore size, and oil contact angle were conducted separately using FLUENT software. The simulation results show that all three factors have an important effect on the oil–water separation effect of the super-hydrophilic copper net. On this basis, the process parameters of oil–water separation using the super-hydrophilic copper net were optimized by orthogonal tests. The super hydrophilic copper net was prepared by etching the copper mesh with a mixture of sodium hydroxide and sodium persulfate, and the oil–water separation experiment was conducted, and then a better oil–water separation effect was obtained. The main conclusions are as follows:

1) With the increase in the oil–water flow velocity and copper net mesh size and the reduction of the oil contact angle on the surface of this super-hydrophilic copper net, its oil resistance performance is degraded, thus failing to achieve efficient oil–water separation.

2) The range analysis of orthogonal experimental results reveals that the oil–water flow velocity has the greatest influence on the oil–water separation effect, followed by the oil contact angle and the copper net mesh size. The optimized process parameters were as follows: velocity was 0.1 m/s, copper net mesh size was 30 μm, oil contact angle was 150°, and oil removal rate reached 95.7%.

3) Through the oil–water separation experiment through 500-mesh super-hydrophilic and super-hydrophobic copper nets, the oil removal rate reached 96.4%, being approximate to the numerical simulation result. Therefore, the reasonability and feasibility of the simulation experiment were further proved.

4) The oil removal rate can reach 99.4% by connecting three super-hydrophilic copper net oil–water separation devices in series. This technology has a high oil removal rate and a simpler method of membrane material preparation.

Data availability statement

The original contributions presented in the study are included in the article/Supplementary Material; further inquiries can be directed to the corresponding author.

Author contributions

Conceptualization, KB and WL; methodology, KB, WL, and MZ; software, KB and WL; validation, WL and KL; formal analysis, KB and WL; investigation, KB, MZ, and KL; resources, KB and WL; writing—original draft preparation, KB; writing—review and editing, WL and YT; supervision, KB, WL, and MZ; and project administration, KB. All authors have read and agreed to the published version of the manuscript.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors, and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

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Keywords: super-hydrophilic, copper net, oil–water separation, numerical simulation, contact angle

Citation: Bai K, Liu W, Zhao M, Li K and Tian Y (2022) Numerical simulation study of oil–water separation based on a super-hydrophilic copper net. Front. Environ. Sci. 10:945192. doi: 10.3389/fenvs.2022.945192

Received: 16 May 2022; Accepted: 05 August 2022; Published: 03 October 2022.

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Copyright © 2022 Bai, Liu, Zhao, Li and Tian. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Kun Bai, [email protected]

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

Numerical and experimental study on enhanced oil–water separation performance using hydrocyclone coupled with particles

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Shuang Zhang , Lixin Zhao , Longda Zhou , Lin Liu , Minghu Jiang; Numerical and experimental study on enhanced oil–water separation performance using hydrocyclone coupled with particles. Physics of Fluids 1 November 2023; 35 (11): 113331. https://doi.org/10.1063/5.0177823

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Oil is one of the world's most crucial energy sources. In recent years, the separation of hydrocyclones coupled with multiphase or multifield has emerged as a leading trend in oilfield-produced fluid pre-separation technology. The study of complex dynamics among particles is crucial in multiphase-coupled separation systems. In this paper, we explore a novel separation approach: hydrocyclone separation coupled with particles to enhance oil–water separation, based on the composite force field. The computational fluid dynamics-discrete element method is utilized to analyze the dynamic behavior of particles and oil droplets within the coupling field, as well as the interactions among particles, oil droplets, and the flow field. Furthermore, the effects of operating parameters on the hydrocyclone coupled with particles (HCCP) and the conventional hydrocyclone (CHC) are compared through separation performance experiments. Results show that within a swirling flow field, the introduction of particles significantly exerts a pronounced influence on both the flow characteristics of the continuous-phase and the motion behavior of oil droplets. The coupling effect between particle movement and hydrocyclone separation is most pronounced when the density ratio of particles to oil ranges from 0.94 to 1. The separation performance experiments show that compared to CHC, HCCP can improve by 2.12–8.22 percentage points, and HCCP not only enhances separation efficiency but also exhibits wider applicability than CHC at lower inlet flow rates and split ratios. The numerical simulation results closely matched the experimental findings. This study may provide a reference for developing and applying hydrocyclones coupled with multiphase.

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OIL-WATER SEPARATION IN LIQUID-LIQUID HYDROCYCLONES (LLHC) - EXPERIMENT AND MODELING

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Effect of adsorption of different types of surfactants on conglomerate reservoir minerals on chemical oil recovery efficiency

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• Published: 03 September 2024
• Volume 10 , article number  150 , ( 2024 )

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• Xiaolong Yan 1 ,
• Yu Tian 1 ,
• Yongmin Shi 1 , 2 ,
• Xiaoguang Wang 3 ,
• Runxi Leng 3 ,
• Haoxuan Zheng 1 &
• Shuai Zhao 1  

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Using surfactants to extract oil, the anionic surfactant Karamay petroleum sulfonate (KPS), the zwitterionic surfactant octadecyl betaine (BS-18) and the nonionic surfactant coconut oil fatty acid diethanolamide (6501) were selected for adsorption experiments with minerals contained in the conglomerate reservoir with different mineral compositions to study the adsorption law of different types of surfactants. Zeolite and montmorillonite, which have the highest specific surface area and zeta potential among the minerals in the conglomerate reservoir, have the most obvious adsorption effect on surfactants, resulting in a large amount of adsorption of KPS and BS-18. The three types of surfactants were then used to conduct physical simulation oil recovery experiments with conglomerate core samples, and the results showed that 6501 had better overall performance, the best adsorption resistance, and a higher degree of recovery in oil recovery experiments, which provided a basis for the selection of surfactants in the process of chemical drive in conglomerate reservoirs.

Article Highlights

The complex mineral composition and physicochemical properties of conglomerate reservoirs in the Junggar Basin are analyzed.

The adsorption degree of different types of surfactants on rock minerals in conglomerate reservoirs was studied.

The formula for chemical oil recovery in conglomerate reservoirs can be optimized through analysis and research.

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1 Introduction

With the increasing demand for energy and the continuous development of oil and gas prediction and development technology, the study of special reservoirs such as conglomerates has received more and more attention. Conglomerate reservoirs are reservoirs dominated by coarse clastic rocks such as conglomerate, conglomerate sandstone, etc. China is dominated by terrestrial oil-producing reservoirs, and conglomerate reservoirs do not account for a high percentage in general, but they account for a higher percentage in some areas, such as in the Junggar Basin of Xinjiang, where the percentage of conglomerate reservoirs reaches nearly 50% (Zhu et al. 2015 ). The conglomerate reservoirs in the Junggar Basin have a wide variety of minerals, especially the authigenic clay minerals are widely distributed, which have an important influence on the storage performance of conglomerate reservoirs (Yu et al. 2023 ). The content and types of clay minerals reflect the mineral evolution process during reservoir deposition, which can reflect the physical characteristics of the reservoir to a certain extent (Li et al. 2023 ). In addition, Guo Hui and others found that zeolite cements are also widely developed in glutenite reservoirs in the Junggar Basin (Guo et al. 2022 ). The presence of large amounts of clay minerals with zeolite-like minerals is not conducive to reservoir development.

At present, in the process of extracting conglomerate reservoirs, most of the primary and secondary oil recovery can only collect one-third of the oil, and there is still a large amount of crude oil that is difficult to recover. With the continuous development of oil recovery technology, there are three oil recovery technologies such as chemical drive (Hammond et al. 2011 ; Murison et al. 2014 ; Zhao et al. 2014 ), but there are not many studies related to chemical drive in conglomerate reservoirs.

Chemical drive is a method of oil recovery in which chemical agents are added to the injected water to change the physical and chemical properties of the replacement fluid and the interface between the replacement fluid and the crude oil and rock minerals, thus facilitating the production of crude oil (Herawati et al. 2022 ; Wang 2001 ). Depending on the chemicals used, conventional chemical drives generally include alkali drives, polymer drives, surfactant/polymer binary composite drives and alkali/surfactant/polymer ternary composite drives. With the development of oil drive theory and the research and development of new oil drive agents, new types of chemical drives such as foam drive and nano-composite drive have also appeared (Muggeridge et al. 2013 ; Liao et al. 2017 ; Hosny et al. 2023 ; Wang et al. 2012 ). Among them, surfactants play an important role in tertiary oil recovery. Generally speaking, commonly used surfactants include cationic, anionic, zwitterionic and nonionic types.The adsorption of cationic surfactants on sandstone reservoirs is significant, while the adsorption of anionic surfactants on carbonate reservoirs is significant (Lee et al. 2012 ). Losses due to adsorption of anionic and cationic surfactants also increase at higher salinities, resulting in unsuitability of the surfactant (Belhaj et al. 2020 ). Researchers have been able to show that the main driving forces behind surfactant adsorption are the surfactant type, physical (lithology) and chemical properties of reservoir rocks (Bera et al. 2013 ). So different minerals will affect surfactants differently, and their adsorption on rock minerals have different patterns and characteristics.

Most surfactants are stable and suitable under general conditions, and their adsorption has both positive and negative aspects (Kumar and Mandal 2019 ). Appropriate adsorption of surfactants on mineral surfaces can alter important interfacial properties and thus improve recovery, while excessive adsorption can be costly and of limited effectiveness (Zhong et al. 2019 ). Surfactant oil recovery can weaken the tension between the oil–water interface, change the wettability of the rock, so that the water and oil phases in the rock pores can be driven out, so that the oil-driving efficiency and recovery rate can be further improved (Hirasaki et al. 2011 ; Baek et al. 2022 ). The main factor that makes surfactants susceptible to depletion in porous media such as conglomerate reservoirs is adsorption, which ultimately leads to reduced recovery. The adsorption of surfactants is mainly physical and chemical adsorption such as electrical adsorption, ion exchange adsorption, intermolecular gravitational adsorption, and formation of hydrogen bond adsorption. The most common form of surfactant consists of a hydrocarbon tail chain and a polar head, and its main mechanism of adsorption is the electrostatic attraction between the charged solid surface and the charged polar head group of the surfactant molecule (Zhang et al. 2015 ).

In this paper, the minerals contained in the conglomerate reservoir were first analyzed, and the physicochemical properties of the minerals in the conglomerate reservoir were investigated through the determination of specific surface and zeta potential. Then different types of surfactants were selected for adsorption experiments with conglomerate reservoir minerals to determine the degree of interaction between different types of surfactants and conglomerate reservoir minerals. Finally, oil recovery experiments were conducted on natural conglomerate cores saturated with oil using chemical formulations of different types of surfactants to relate recovery rates to dynamic adsorption experiments. The selection and use of surfactants determine the oil recovery efficiency of chemical drive, and the study of the adsorption law between surfactants and rock minerals in conglomerate oil reservoirs has theoretical significance and practical guidance for the development of conglomerate oil reservoirs.

2 Experimental section

2.1 materials and instruments, 2.1.1 materials.

Surfactants: ① Anionic surfactant: karamay petroleum sulfonate, this is also the surfactant currently used in chemical oil recovery of conglomerate reservoirs in Xinjiang, abbreviated as KPS; ② Nonionic surfactant: coconut oil fatty acid diethanolamide, abbreviated as 6501; ③ Zwitterionic surfactant: octadecyl betaine, abbreviated as BS-18;

Polymer: Salt-resistant polymer, polyacrylamide (HPAM) as the main component, relative molecular weight 15 million, abbreviated as HPAM;

Chemical reagents: NaHCO 3 : analytically pure; NaCl: analytically pure;

Mineral and rock materials: ① Minerals: zeolite, montmorillonite, kaolinite, illite, chlorite, sodium feldspar, calcite; ② Cores: conglomerate core from Junggar Basin in XinJiang; ③ Chemically driven extractives from conglomerate reservoirs: Oil bearing mud and sand, it was extracted with petroleum ether, dried, pulverized, and sieved to a particle size of about 800 mesh before the experiment;

Experimental water: conglomerate reservoir formation water, NaHCO 3 type, mineralization 10000mg/L, its parameters are shown in Table 1 .

2.1.2 Experimental instruments

High Resolution Field Emission Scanning Electron Microscope, FEIVerios460, FEI, USA; Ultraviolet–Visible Spectrophotometer, UV-2200, Shunyu Hengping, Shanghai; Interfacial Tension Meter, TX-500C, Zhongchen, Shanghai; Specific Surface Pore Sizing Analyzer, V-Sorb2800P, Beijing Guoyi Precision Measurement Technology Co. Zeta Potential Analyzer, ZetasizerNanoZS, Malvern, UK; X-ray Diffraction Analyzer, D8Quest, Bruker, Germany; Magnetic Stirring Kettle with Water Bath, Keheng, Shanghai; Multi-functional Experimental Device for Oil Recovery in Core, Haian Petroleum Research Instrument Co.

2.2 Methods

2.2.1 analysis of mineral composition and content of conglomerate reservoirs.

Both conglomerate reservoir blocks and extracts were ground into fine powdery samples, and the mineral compositions were quantitatively analyzed by X-ray diffraction analysis, according to the standard of the oil and gas industry of the People’s Republic of China, SY/T 5162-2018, “Analysis method for clay minerals and ordinary non-clay minerals in sedimentary rocks by the X-ray diffraction”.

2.2.2 Mineral specific surface determination in conglomerate reservoirs

The specific surface and pore size of the conglomerate samples and the minerals contained in the reservoir were determined by a nitrogen adsorption specific surface pore size analyzer using the BET method and the Langmuir model as the basic working principle. Block samples were used for the conglomerates instead of powder samples, which preserves the fixed structure of the samples as much as possible and is closer to the real specific surface of the conglomerate reservoirs.

2.2.3 Zeta potential measurement

The nature of the surface charge of rock minerals and surfactants was determined by means of a zeta potential meter using Doppler electrophoresis as the basic operating principle.

2.2.4 Surfactant interfacial tension determination

By adopting the rotating drop method and taking into account the actual situation at the production site, a concentration of 3000 ppm was selected as the measurement concentration of surfactant, and the surfactant solution prepared from the formation water of the conglomerate reservoir was loaded into a sample tube, to which a drop of crude oil extracted from the conglomerate reservoir was then added. According to the oil and gas industry standard of the People’s Republic of China, SYT5370-2018, “Test method for surface tension and interfacial tention”, under the action of centrifugal force, gravity and interfacial tension, the crude oil of the low-density phase forms an ellipsoidal or cylindrical droplet in the surfactant solution of the high-density phase, and the shape of which is determined by the rotational speed and interfacial tension. Using an interfacial tensiometer, the equilibrium interfacial tension was determined after the interfacial tension was stabilized by setting the temperature at 30 °C (to simulate the formation temperature) and rotating at an angular speed of 5000 r/s. The equilibrium interfacial tension was determined by using a tensiometer.

2.2.5 Wettability test

Natural core sand with particle size less than 0.25 mm and dehydrated crude oil shall be mixed evenly at a mass ratio of 7:1, and placed in an oven at 30 °C (target formation temperature) for thermal aging for more than 48 h. The aged oil-bearing core sand shall be adhered to quartz with Double-sided tape to form an oil-bearing natural core sand mold, and different types of surfactant solutions shall be prepared with injected water as the aqueous phase, measure the contact angle of surfactant solution on the surface of oil bearing natural core sand model using a fully automatic contact angle tester.

2.2.6 Adsorption experiments

Standard curve drawing

Surfactant solutions were prepared with stratum water, and each surfactant was configured with five different concentrations of 10 ppm, 30 ppm, 50 ppm, 100 ppm and 200 ppm. The wavelength profiles of the five different concentration solutions were measured by ultraviolet spectrophotometer, and the absorbance at the same peak (wavelength) was determined, and the standard curve was plotted by connecting the five points.

Static adsorption experiment

Dilute the surfactant solution prepared with formation water to a series of concentrations as the initial concentration, noted as C 0 ; the conglomerate reservoir rock minerals and surfactant solution were added to a stoppered, mill-necked conical flask at a solid–liquid ratio of 1:9, shake it well, then cover the stopper and seal it well; place the conical flask in a constant-temperature water bath at 30 °C with a rotational speed of 60 r/min, and leave it there for 24 h (at this time, the adsorption has reached equilibrium) Remove; the adsorbed solution after shaking well poured into the centrifuge tube, centrifugal separation at 4000 r/min speed for 30 min; the upper clear liquid in the centrifuge tube was taken, shaken well and the concentration of surfactant in the clear liquid was determined. This concentration is the equilibrium concentration when the adsorption reaches equilibrium and is denoted as C t (Ni et al. 2018 ); The static adsorption capacity was calculated according to the following formula ( 1 ):

In the equation, Γ-static adsorption capacity, denotes the number of milligrams of surfactant adsorbed per gram of mineral, mg/g; V-volume of surfactant solution, L;C 0 -initial concentration of surfactant in solution, mg/L; C t -final concentration of surfactant solution after solution adsorption equilibrium, mg/L; G-mass of conglomerate cores, minerals, g.

Dynamic adsorption experiments

Using the multifunctional core oil recovery experimental device (Fig.  1 ), the conglomerate core was loaded into the gripper, and each surfactant was loaded into the intermediate container, the thermostat system was turned on, and the constant temperature was simulated for about one hour at the simulated stratigraphic temperature (30 °C). The injection pump was turned on, and the amount of the injection was adjusted, and the water was injected firstly, until the injection pressure was stabilized; the surfactant is then injected and samples are continuously taken at the outflow end to detect changes in surfactant concentration until the surfactant concentration is equal to or close to the initial concentration injected; finally, water was injected again to drive out the surfactant until the concentration of surfactant in the effluent was equal to or close to 0. Based on the measured concentration of surfactant in the effluent sample and the volume of the sample, the dynamic adsorption amount of surfactant was calculated by using the principle of material balance (Chen et al. 2016 ).

Multi-functional core oil recovery experimental device

2.2.7 Oil recovery experiments through physical simulation

The experiment simulated the actual conglomerate reservoir chemical drive production site, firstly, the polymer/surfactant binary composite drive mode was selected, and the natural conglomerate core was evacuated by vacuum pump for 4 h, and then the natural conglomerate core was saturated with crude oil under the condition of 30 °C for 20 h, and the oil-bearing saturation (S O ) and pore volume (PV) were calculated.

Prepare the multifunctional core drive oil recovery device, simulate the actual formation pressure of 12 MPa, the actual formation temperature of 30  C, and prepare the simulated injection water with the same mineralization as the formation. Start the advection pump, set the flow rate to 0.3 ml/min, and start injecting water to drive the oil, injecting two core pore volumes (i.e., 2PV) of water, at which time the water content at the extraction end can basically reach over 90%; then change the polymer/surfactant binary drive, open the corresponding valve, turn off the valve corresponding to the water drive, and after injecting a predetermined volume (2PV), turn off the valve corresponding to the chemical drive, and finally carry out the subsequent water drive for 2PV. Record the amount of oil recovered at each stage with the injection pressure to calculate the degree of oil recovery.

3 Results and discussion

3.1 influence of mineral components, 3.1.1 composition and content of minerals.

Conglomerate reservoirs are different from sandstone reservoirs in that they are very non-homogeneous, not only in physical characteristics such as pore structure, but also in the extreme complexity of the mineral rocks of which they are basically composed. Natural conglomerate cores were used to analyze the mineral composition and ingredients.

Firstly, the surface of the conglomerate core sample was scanned by energy dispersive spectroscopy (EDS) to obtain the mineral element composition (Fig.  2 ). From the surface energy spectrum scanning elements of the conglomerate sample in Fig.  2 , it can be inferred that the surface of the conglomerate reservoir contains a large amount of Si and Al elements in addition to conventional elements such as C, N, O, and S. The Al element content reaches 13%, and the Si element content reaches 25%. Therefore, it is inferred that the surface of the reservoir particles contains a large amount of water aluminum silicate products.

Scan of surface energy spectrum of conglomerate core samples (image resolution 500 um)

The surface minerals of the conglomerate reservoir were then characterized by scanning electron microscopy (SEM). It was observed that the surface composition of the conglomerate reservoir skeleton particles was complex, with the presence of a large number of clay minerals as well as zeolite minerals. The characteristic of kaolinite is most prominent in the sample, with page shaped kaolinite monomers and aggregates visible everywhere, as shown in Fig.  3 a; Simultaneously, illite with bridging pseudo hexagonal crystals was observed, as shown in Fig.  3 b; There are also coniferous and Flat noodles shaped chlorite secondary growth on the mineral surface, Fig.  3 c, honeycomb and flame like illite and montmorillonite mixed layer filling the interior of the pores, Fig.  3 d, and single crystal structure turbidite zeolites and spherical particle square zeolites, Fig.  3 e, f.

Characterization of surface mineral morphology in conglomerate reservoir. a Kaolinite observed on the surface of the conglomerate reservoir (image resolution 10 um), b Illite observed on the surface of the conglomerate reservoir (image resolution 2 um), c Chlorite observed on the surface of the conglomerate reservoir (image resolution 5 um), d Illite Montmorillonite mixed layer observed on the surface of the conglomerate reservoir (image resolution 30 um), e Turbidite zeolite observed on the surface of the conglomerate reservoir (image resolution 5 um), f Square zeolite observed on the surface of the conglomerate reservoir (image resolution 5 um)

Finally, the mineral content was analyzed by X-ray diffraction (XRD), and the results of the mineral content analysis of the natural core samples from the conglomerate reservoir were considered to be before the conglomerate reservoir was exploited, and the results of the mineral content analysis of the chemically driven extracts from the conglomerate reservoir were considered to be after the conglomerate reservoir was exploited, and the results are shown in Fig.  4 .

Mineral content of conglomerate reservoirs before and after development

The natural conglomerate reservoir is dominated by feldspar and quartz, with 34.1% feldspar and 37.5% quartz; The cementing material is dominated by sulfate minerals and clay minerals, with contents of 10.8% and 10.5%, the content of carbonate minerals is relatively low at 2.6%, and the content of zeolite minerals is about 3.7%, mainly turbidite and square zeolite, with a very small amount of corundum present. The complexity and variability of mineral types in conglomerate reservoirs have many hidden effects on the recovery efficiency of late-stage surfactants, which include the fact that surfactants can adsorb different grades of minerals on each mineral, and losses can occur, thus affecting the recovery rate.

The mineral composition of the conglomerate reservoirs has not changed essentially after chemical recovery. Feldspar and quartz, as the backbone minerals of the reservoir, are still most present. The proportion of carbonate minerals and clay minerals has become slightly smaller, the proportion of sulfate minerals and corundum has slightly increased, and the obvious change is the zeolite minerals, whose content has increased from 3.7 to 8.1%.

Clay minerals, a group of minerals that are relatively active in nature in conglomerate reservoirs, were analyzed for their relative content (Fig.  5 ). Kaolinite has the highest relative content of 36.9%, followed by a mixture of illite and montmorillonite at 30.5%, illite at 29.2%, and chlorite at the lowest relative content of 3.4%. It can be seen that there are large amounts of illite and montmorillonite in the clay minerals of conglomerate reservoirs, and both of them are transformed into mixed-layer minerals in large quantities during the diagenetic evolution, it is referred to as I-M mixed layer.

Relative content of clay minerals before and after conglomerate reservoir development

The clay mineral content in the total content after chemical drive did not change much, but the relative content changed significantly, the content of ilmenite mixed layer in the extracted material turned out to be the largest, increasing from 30.5 to 44%, illite content was the second largest, kaolinite content became significantly smaller, and the content of chlorite remained the smallest. In terms of mineral sensitivity, montmorillonite is a water-sensitive mineral, kaolinite is a quick-sensitive mineral, and illite and chlorite are in the middle.

The high percentage of zeolite and I-M mixed layer after chemical oil recovery indicates that these two minerals are very easy to hydrate, strong adsorption, a large number of adsorption of formation water and chemical agents, along with the injection of the formation of chemical together with the agent migration and be taken out of the formation. Therefore, in the face of conglomerate reservoirs with high content of clay minerals and zeolite minerals, it is especially important to choose suitable surfactants.

3.1.2 Physico-chemical properties of minerals

Specific surface measurements were performed on conglomerate reservoir core samples and contained minerals (Table  2 ). It can be seen that the specific surface of clay minerals is significantly larger than that of skeletal and carbonate minerals. As for the clay minerals, kaolinite has the smallest specific surface, 15.7 m 2 /g, illite has 20.62 m 2 /g, chlorite has 23.76 m 2 /g, montmorillonite has the largest specific surface area, 40.21 m 2 /g, and zeolite has a large specific surface, 31.58 m 2 /g. The specific surface of the actual core of the conglomerate is larger than that of the skeletal minerals quartz and feldspar, which also indicates that the constituent minerals of the conglomerate reservoir are more complex, with a large number of minerals with large specific surfaces present.

A larger specific surface means a stronger adsorption, and the strong specific surface free energy readily interacts physicochemically with chemical agents. Previous research also found that the clay minerals, montmorillonite adsorption is the strongest, it is a 2:1 type clay minerals, up and down the adjacent levels are O surface, the gravitational force between the crystal layer to intermolecular force is dominated by the interlayer gravitational force is weak, water molecules are easy to enter the crystal layer, montmorillonite exists lattice substitution, the number of cations that can be exchanged is many (Derjaguin and Landau et al. 1993 ), due to the lattice substitution produces more negative charge, around it, will inevitably be adsorbed equal amount of cations, hydrated cations to the clay to bring a thicker hydration film, which results in the expansion of montmorillonite. Montmorillonite and zeolite have strong adsorption, ion exchange, however, the two are not “one mother and one sibling”, zeolite is silica-aluminate minerals, montmorillonite is clay minerals, zeolite molecular sieve structure has a stronger adsorption, while montmorillonite will be swollen in contact with water. It has been analyzed by XRD that conglomerate reservoirs contain large amounts of I-M mixed layer minerals, which, in general, are more susceptible to swelling and dispersion in contact with water than single clay minerals.

Different types of conglomerate reservoir samples with different types of surfactants were selected to determine the nature of the surface charge of rock minerals and chemicals, and the results are shown in Table  3 . The zeta potential distribution of conglomerate reservoirs and minerals ranges from 0 to − 20 mV, with a wide span of potentials, mostly belonging to unstable systems. The larger the specific surface area of the clay minerals, the more charged they are, such as montmorillonite and zeolite. Skeleton mineral feldspar and carbonate mineral calcite, the electrification is very small.KPS surfactant belongs to anionic surfactant, Zeta potential is around − 40 mV, the higher the concentration, the better the stability, the comprehensive cost considerations, the general oilfield production using concentration of 3000 ppm.Nonionic surfactant 6501 is less electrically charged, and zwitterionic surfactant BS-18 is charged with Minimum.

DLVO theory (the theory that describes colloidal stability) suggests that the stability of a colloidal system is the net structure of the double electric layer mutual repulsion and van der Waals mutual attraction between particles as they approach each other. It is in the form of a colloidal solution that clay minerals exist in subsurface reservoirs. The energy barrier between the particles as they approach each other comes from the mutual repulsion force, and when the particles have enough energy to overcome this barrier, the mutual suction force will cause the particles to approach further and stick together irreversibly (Elimelech and O’Melia 1990a , b ; Zhao 2010 ). The presence of these physicochemically active minerals in conglomerate reservoirs has a great impact on surfactant injection, where zeolites and I-M mixtures have a huge specific surface with very strong chargeability, they adsorb a lot of formation water and surfactant, causing the formulation system of chemical oil recovery to be altered in the reservoir and reducing the energy efficiency of the surfactant.

3.2 Effect of interfacial tension

Surfactant solutions injected into oil formations can reduce the interfacial tension between oil and water, oil and rock, and change the wettability of the rock to improve recovery. Reducing the oil–water interface to ultra-low interfacial tension (10 −3 mN/m) is one of the main criteria for surfactant systems used in tertiary oil recovery. It is widely recognized that only by reducing the oil–water interfacial tension to the ultra-low interfacial tension region, the residual crude oil in the reservoir void can be deformed and flowed (Wang et al. 1995 ). The three surfactants were formulated into an aqueous solution using simulated formation water, and the concentration of surfactants was consistent with that used at the production site, which was 3000 ppm, and the results of interfacial tension are shown in Fig.  6 .

Interfacial tension diagram of three surfactants

BS-18 has the lowest interfacial tension of 10 −3  mN/m. Although its interfacial tension is the lowest, its solubility deteriorates due to the increase of hydrophobic groups as a result of the long carbon chain. In the solubilization of ionic micelles, the solubilization is mainly governed by the hydrocarbon chain length of the solubilizer molecules because the polar substances do not enter the interior of the micelles, but only solubilize on the surface of the micelles (Gong et al. 2019 ). On the other hand, the water solubility of 6501 was good, and the interfacial tension of 6501 was also ultra-low, with the interfacial tension in the range of 10 −2  mN/m and 10 −3  mN/m. The interfacial tension of KPS was the highest among the three surfactants, with the interfacial tension of 10 −2  mN/m.

3.3 Surface wettability reversal

The experiment simulated the actual oil reservoir surface sample making, the surface is oily, the contact angle of conglomerate reservoir formation water is more than 100°, 0.3% concentration KPS can change the wettability of the rock surface, the contact angle is about 60°, the contact angle of 0.3% concentration betaine is about 31°, and the 0.3% concentration 6501 changes the wettability of the rock surface with a better effect, and the contact angle is about 30% (Fig.  7 ). And choosing a point on the sample thin section, dropping 6501 first, and then dropping simulated formation water at the same point, it was found that the contact angle was reduced to a very low level (Fig.  8 ), so that the surface was changed from oleophilic to hydrophilic. The contact angle on the surface of the oil-bearing natural core sand model was reduced, and the wettability was obviously reversed, so that the oil film on the surface of the oil-bearing natural core sand model could be stripped off and the residual oil could be initiated, which is very important for improving the crude oil recovery (Sun et al. 2015 ).

Contact angle between formation water and surfactant on oily model surface. a Formation water contacts the surface of oil rock, b KPS contacts the surface of oil rock, c BS-18 contacts the surface of oil rock, d 6501 contacts the surface of oil rock

Contact angle before and after dropping 6501 on the oily model surface

KPS was compounded with 6501 in a 1:1 ratio and the contact angle decreased to 46.8° (Fig.  9 ). The combination of anionic surfactants and nonionic surfactants can also have positive effects, and many complex oil reservoirs can improve their performance through the combination of surfactants.

Contact angle of KPS compounded with 6501

In addition to alkanes, most crude oils contain small amounts of surface-active polar components, and divalent cations combined with acidic components in the oil can control the wettability of the oil–water-rock system. Mugele et al. ( 2015 ) removed divalent ions from the water, and observed that the contact angle between the water and the rock surface was reduced by about 10°, which could improve crude oil recovery by several percentage points (Herminghaus 2012 ). In this paper, the ionic surfactant was replaced with a nonionic surfactant, which again reduces the number of ions in the water that can be exchanged with the rock system, and controls the wettability by controlling the adsorption of ions to the solid–liquid interface, which from the results does change the wettability of the surface.

3.4 Adsorption results

3.4.1 establishment of standard curve.

Standard curves were fitted with UV spectrophotometry for the three surfactants and the fit was good as shown in Table  4 .

3.4.2 Static adsorption

The experimental results showed that the order of magnitude of adsorption of the anionic surfactant KPS on the rock minerals of the conglomerate reservoir was as follows: montmorillonite/zeolite > illite > chlorite > kaolinite > conglomerate core > calcite > feldspar (Fig.  10 ). KPS adsorption on montmorillonite and zeolite reached more than 40 mg/g, and the adsorption equilibrium concentration was also the highest, and the adsorption equilibrium was reached at 5000 ppm. Adsorption was lowest on the reservoir backbone mineral feldspar at about 6 mg/g, adsorption on calcite ~ 7 mg/g, with an adsorption equilibrium of 2000 ppm concentration on both. The amount of KPS adsorbed on the conglomerate core was about 9 mg/g, and the equilibrium concentration of adsorption was about 3500–4000 ppm. Combining the results of specific surface and zeta potential analysis, montmorillonite and zeolite have the largest specific surface area and both of them have high zeta potentials, which can be seen that they are active in physicochemical properties, so they cause a large amount of surfactant adsorption, while feldspars and calcite are on the contrary, so their adsorption amount is lower.

Adsorption of KPS on single minerals and cores

According to the same method, BS-18 and 6501 were used to do static adsorption experiments, and the results showed that the adsorption amount of BS-18 on rock minerals was comparable to that of KPS (Fig.  11 ), and the adsorption amount on zeolite and montmorillonite was up to 40 mg/g. The adsorption on clay minerals was still larger than that on conglomerate cores, and the adsorption amount on conglomerate cores was 5 mg/g.

Adsorption of BS-18 on single minerals and cores

The adsorption amount of 6501 was much lower than that of KPS and BS-18 (Fig.  12 ). 6501 adsorbed only 11–13 mg/g on zeolite and montmorillonite, and the concentration of the adsorption equilibrium was relatively low, with adsorption saturated at 3,000 ppm, and the adsorption amount was less than 3 mg/g on the conglomerate core.

Adsorption of 6501 on single minerals and cores

It can be seen that adsorption of anionic surfactants is also inevitable in the face of conglomerate reservoirs with complex mineral compositions, and even though electrical adsorption with negatively charged mineral rocks is reduced, multilayer adsorption still occurs. Del Hoyo et al. ( 2008 ) found that the adsorption of anionic surfactants in the interlayer space of montmorillonite, kaolinite, illite, etc. did not change the X-ray maps, suggesting adsorption on the surfaces or in the structural channels of these minerals. While all clay minerals adsorbed nonionic surfactants increased in stability. Surfactants interact with hydroalumino-silicates through functional groups of organic compounds, variable cations of clay minerals formed by ion–dipole or hydrogen bonding, and on the other hand, rearrangement of adsorbed surfactant molecules has been observed. So the interaction of the surfactant with the mineral produces adsorption while altering both.

3.4.3 Dynamic adsorption

The experiments were conducted according to the dynamic adsorption experimental conditions in Sect. 1.2.5 with a surfactant concentration of 3000 ppm. Injecting surfactant into a conglomerate core and driving it out with water, and the following results were obtained (Figs.  13 , 14 and 15 ).

Variation curve of dynamic adsorption concentration of KPS on conglomerate core with the number of driven out PVs

KPS surfactant dynamic adsorption capacity: 0.255 mg/g.

Variation curve of dynamic adsorption concentration of BS-18 on conglomerate core with the number of driven out PVs

BS-18 surfactant dynamic adsorption capacity: 0.261 mg/g.

Variation curve of dynamic adsorption concentration of 6501 on conglomerate core with the number of driven out PVs

6501 surfactant dynamic adsorption capacity: 0.046 mg/g.

It can be seen that the amount of dynamic adsorption is smaller than the amount of static adsorption, this is because the dynamic adsorption is simulated the oil recovery process for the experiment, the surfactant passes through the core and does not reach the adsorption saturation on the rock minerals, but the dynamic adsorption is more in line with the real state of the surfactant in the oil recovery process. From the results of the dynamic adsorption amount, the dynamic adsorption amount of 6501 was smaller than that of KPS and BS-18, with BS-18 having the largest adsorption amount.

3.5 Effect on recovery rate

3.5.1 relationship between adsorption and recovery rate.

The current chemical drive formulation used in oil recovery sites in conglomerate reservoirs is a binary blend solution of 3000 ppm concentration of KPS and 1800 ppm concentration of HPAM. So according to this formulation, dynamic adsorption experiments were carried out on conglomerate natural cores first, and then oil recovery experiments were carried out by physical simulation, and the experimental data were recorded to obtain Table  5 , in which a relationship can be established between the amount of adsorption of the chemical agent and the total degree of recovery.

Based on the specific surfaces of the four conglomerate natural cores, it can be seen that the minerals contained in the four cores are different, and rock minerals with larger specific surfaces will have stronger adsorption capacity. The experimentally obtained adsorption amount was used to establish a relationship with the degree of oil recovery (Fig.  16 ).

Polymer/surfactant adsorption correlation with recovery rate

Finally, the correlation between the adsorption amount of poly and surface agent and the oil recovery efficiency was obtained to be very good, with a negative correlation, indicating that the smaller the adsorption amount is, the higher the degree of oil recovery is.

Relationship equation between oil recovery efficiency and surfactant adsorption:

Relationship equation between oil recovery efficiency and polymer adsorption:

3.5.2 Recovery of different types of surfactants

Simulating the actual production situation of oil fields, chemical drive adopts a polymer/surface binary drive mode. In order to better compare the effects in parallel, HPAM is uniformly used for polymers, and different types of surfactants are used. Three chemical drive formulas are formulated, which are: (1) 3000 ppm KPS + 1800 ppm HPAM; (2) 3000 ppm 6501 + 1800 ppm HPAM; and (3) 3000 ppm BS-18 + 1800 ppm HPAM. Natural cores of conglomerate with the same physical properties were selected, and the injection pressure simulated the formation pressure of 12 MPa, and three sets of oil recovery experiments were done through physical simulation, and then compared in parallel.

In this case, the final degree of recovery after oil recovery with the formulation with KPS surfactant was 86.89%, and the chemical recovery partially increased the recovery by 17% points (Fig.  17 ). Subsequent water drives after the KPS drive improved recovery by 14% points.

KPS surfactant formulation drive oil recovery and injection pressure curves

The final degree of recovery after drive oil recovery with the formulation of BS-18 surfactant was 90.85%, and the chemical drive oil recovery improved the recovery by 23% points (Fig.  18 ). Subsequent water drives after BS-18 drives improved recovery by 15% points.

BS-18 surfactant formulation drive oil recovery and injection pressure curves

The final degree of recovery after drive oil recovery with the formulation of BS-18 surfactant was 91.45%, and the chemical drive oil recovery improved the recovery by 26% points (Fig.  19 ). Subsequent water drives after BS-18 drives improved recovery by 12% points.

6501 surfactant formulation drive oil recovery and injection pressure curves

According to the experimental results, the total oil recovery degree of 6501 is slightly higher than that of BS-18, and both of them reach more than 90%. KPS has the lowest level of oil recovery. However, comparing the results of chemical recovery (when injecting the second to fourth PV numbers), the 6501 binary system was the most effective in improving recovery. 6501 has the smallest adsorption on conglomerate reservoirs and minerals, and the small adsorption will make the surfactant more efficient in driving oil. The BS-18 binary system is also more effective in improving recovery, which will be slightly inferior to the effect of 6501 and superior to the KPS binary system, but the oil on the mineral surface of the rock driven by BS-18 becomes easier to be stripped off, so the effect of its subsequent water drive in improving recovery is the best.

The –SO 3− group and hydrocarbon group of the anionic surfactant KPS have strong adsorption with the surface of clay minerals, which is mainly due to the electrical attraction of metal active centers (Al 3+ , Fe 3+ , Fe 2+ , Ca 2+ , Mg 2+ , etc.) on the surface of clay to the surfactant ions, the electrical attraction between the Stern layer of the loaded negatively charged clay surface and the –SO 3− of surfactant, the dispersive and induced forces and hydrogen bonding between the surface of the clay minerals and the surfactant ions, as well as multilayered adsorption resulting from the colloidization of surfactants that have already adsorbed on the clay minerals. BS-18 also belongs to ionic surfactants, but because the structure of zwitterionic surfactants contains both anionic hydrophilic groups and cationic hydrophilic groups, so zwitterionic surfactants to change the wettability of the surface of the rock and mineral is better, and has a super-low interfacial tension, which makes up for the shortcomings of the larger adsorption amount (Hou 2016 ). The nonionic surfactant 6501 does not exist in solution in an ionic state, so it has high stability, is not easily affected by the presence of strong electrolytes, and is not easily affected by acids and bases, can be used in combination with ionic surfactants, has good compatibility, has good solubility in various solvents, and does not adsorb strongly on solid surfaces, thus increasing the degree of recovery to a high degree, and can be used as a preferred surfactant in conglomerate reservoirs with complex mineral compositions.

4 Conclusions

The mineral composition of conglomerate reservoir is diversified, containing a large number of minerals with active physicochemical properties, which are easy to interact with surfactants. In the conglomerate reservoir, there are I-M mixed layer minerals formed by montmorillonite and illite transforming and mixing with each other, as well as zeolite minerals with molecular sieve structure, which have the largest specific surface and the strongest electrically charged properties, which cause a large number of adsorption of surfactants, resulting in the loss and change of the chemical oil recovery formula system in the subsurface, which has a certain impact on the oil recovery efficiency;

The three surfactants we selected, KPS, BS-18, and 6501, all have good compatibility with the oil–water system of conglomerate reservoirs. However, in terms of reducing oil–water interfacial tension and changing surface wettability, BS-18 and 6501 are superior to KPS currently used in chemical oil recovery of conglomerate reservoirs in Xinjiang.

Although KPS is an anionic surfactant, it still adsorbs a lot with the negatively charged conglomerate reservoir because of multilayer adsorption. BS-18 is also an ionic surfactant, and its degree of adsorption is basically comparable to that of KPS. Whereas nonionic surfactant 6501 does not ionize in water and it does not contain ion-exchangeable anions and cations. When it encounters clay minerals, it forms hydrogen bonds with the polar group on the surface of the mineral crystal layer, and then adsorbs on the surface of the clay particles. Hydrogen bonding is not a chemical bond, but a special kind of intermolecular force. So facing conglomerate reservoir minerals, the adsorption of nonionic surfactants will be less than that of ionic surfactants;

The larger the adsorption amount of the surfactant, i.e., the lower the degree of its action in the oil recovery process in conglomerate reservoirs, so it will cause a decrease in oil recovery efficiency. The adsorption amount of KPS is large, so its oil recovery efficiency is the lowest, the adsorption amount of BS-18 is about the same as that of KPS, but the oil recovery efficiency will be higher than that of KPS, because BS-18 has hydrophilic and oleophilic amphiphilic properties, and it can change the wettability of the rock surface and reduce the interfacial tension between oil and water, which can make up for some of the loss generated by the adsorption. 6501 has the lowest adsorption amount and has been verified to have the highest oil recovery efficiency, so the nonionic surfactant 6501 can be used as the main surfactant for chemical oil recovery in conglomerate reservoirs.

Data availability

No datasets were generated or analysed during the current study.

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Acknowledgements

Firstly, the author would like to express gratitude to Shaanxi Key Laboratory of Chemical Additives for Industry for providing us with the experimental instruments and site, which enabled our research to be completed smoothly. Secondly, we would like to thank the Petroleum and Natural Gas Research Center of the School of Earth and Space at Peking University for their assistance in our experiment. Lastly, we would like to express our special thanks to the editors and reviewers for their valuable comments.

This work was supported by the National Natural Science Foundation of China [No.51904180] and the Xinjiang Conglomerate Reservoir Laboratory Development Project [2020D04045].

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Shaanxi Key Laboratory of Chemical Additives for Industry, College of Chemistry and Chemical Engineering, Shaanxi University of Science & Technology, Xi’an, 710021, China

Xiaolong Yan, Yu Tian, Yongmin Shi, Haoxuan Zheng & Shuai Zhao

School of Earth and Space Sciences, Peking University, Beijing, 100091, China

Yongmin Shi

PetroChina Xinjiang Oilfield Branch Exploration and Development Research Institute, Xinjiang, 834000, China

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X. Y.: Conceptualization, Methodology, Writing-Original Draft, Investigation, Data Curation. Y. T. and Y. S.: Conceptualization, Supervision, Writing-Review and Editing. X. W. and R. L.: Resources, Data Curation. H. Z. and S.Z.: Investigation, Data analysis, image mapping and revision. B. L.: Resources, Methodology. All authors reviewed the manuscript.

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Yan, X., Tian, Y., Shi, Y. et al. Effect of adsorption of different types of surfactants on conglomerate reservoir minerals on chemical oil recovery efficiency. Geomech. Geophys. Geo-energ. Geo-resour. 10 , 150 (2024). https://doi.org/10.1007/s40948-024-00868-5

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Received : 16 December 2023

Accepted : 12 August 2024

Published : 03 September 2024

DOI : https://doi.org/10.1007/s40948-024-00868-5

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