Volume 90 Issue 36 | p. 9 | News of The Week
Issue Date: September 3, 2012 | Web Date: August 31, 2012

Membrane Separates Oil And Water With Ease

Materials: Hydrophilic-oleophobic combo could clean up oil spills
Department: Science & Technology
News Channels: Environmental SCENE, Materials SCENE, Nano SCENE
Keywords: hydrophobic, hydrophilic, membrane, POSS, oil spill, emulsion, separations
Even though oil and water don't mix, when they do come together, as in oil spills, they're difficult to separate. Researchers at the University of Michigan and the Air Force Lab have now developed a membrane that separates the substances with ease, via gravity filtration. In this clip, watch the membrane in action and learn about the materials it's made from.
Credit: University of Michigan/C&EN/YouTube

Oil and water usually don’t mix, but when the two end up together, say in an oil spill or in an emulsion, they can be nearly impossible to completely separate. But by combining a water-loving polymer with an oil-repelling silicon-based material, researchers have created a new breed of membrane that can separate bulk amounts of any type of oil-water mixture by simple gravity filtration.

The scientific team that created the hygro-responsive membrane, as it is called, believes it will become an energy-efficient, cost-effective means of cleaning up oil spills.

Traditional membrane-based filtration systems are energy-intensive because the targeted mixture typically must be pumped through the membrane for efficient separation. These membranes are subject to fouling by viscous materials such as oil, lose their effectiveness over time, and typically aren’t versatile enough to separate all types of oil-water mixtures, which range from oil and water layers to surfactant-laden emulsions.

A team led by materials scientist Anish Tuteja of the University of Michigan has devised membranes that for the first time sidestep such limitations (Nat. Commun., DOI: 10.1038/ncomms2027). Arun K. Kota in Tuteja’s group prepared the membranes by dipping polyester fabric or stainless steel mesh into a mixture of cross-linked polyethylene glycol diacrylate, which is hydrophilic, and fluorodecyl polyhedral oligomeric silsesquioxane, which is oleophobic.

Water (blue) readily wets the surface, and rapeseed oil (red) beads up on stainless steel (top) and polyester (bottom) hydrophilic-oleophobic membranes.
Credit: Nat. Commun.
This is a photo of water (blue) and rapeseed oil (red) on stainless steel (top) and polyester (bottom) superhydrophilic-superoleophobic membranes.
Water (blue) readily wets the surface, and rapeseed oil (red) beads up on stainless steel (top) and polyester (bottom) hydrophilic-oleophobic membranes.
Credit: Nat. Commun.

The fluorinated silsesquioxane, developed by team member Joseph M. Mabry and coworkers at the Air Force Research Laboratory at Edwards Air Force Base in California, is a Si8O12 cage molecule with a fluorodecyl group attached to each silicon atom. The combination of fluorinated groups and the microcrystallinity of the material make it one of the lowest surface energy materials known, imparting hydrophobic and oleophobic properties, Mabry says.

When an oil-water mixture or emulsion is poured onto one of the membranes, nothing appears to happen at first, Kota explains. After a few moments, rough micro­crystalline silsesquioxane regions on the membrane surface reconfigure to form a smooth, noncrystalline surface that allows the polymer to hydrogen bond with water. This reversible change in surface morphology allows water to completely wet the surface and permeate the membrane, which holds back the oil.

These AFM images of a hydrophilic-oleophobic membrane show that the dry surface is covered with crystalline regions of fluorinated silsesquioxane (left), but when wet with water the surface reconfigures and becomes smooth, allowing the water to pass through.
Credit: Nat. Commun.
These AFM images are of a superhydrophilic-superoleophobic membrane.
These AFM images of a hydrophilic-oleophobic membrane show that the dry surface is covered with crystalline regions of fluorinated silsesquioxane (left), but when wet with water the surface reconfigures and becomes smooth, allowing the water to pass through.
Credit: Nat. Commun.

The team has separated batches of oil-water mixtures and emulsions and shown that a continuous-flow system can operate for more than 100 hours without fouling the membrane or slowing down. Gibum Kwon in Tuteja’s group further led the development of a system that uses an electric field as a trigger to control membrane wetting for on-demand separations (Adv. Mater., DOI: 10.1002/adma.201201364).

These membranes represent “a big step forward in energy-free approaches for removal of oil contaminants from water,” says Francesco Stellacci, a nanomaterials scientist at the Swiss Federal Institute of Technology, Lausanne. “It’s noteworthy that the method works for all oil-water mixtures with such high efficiency.”

The membrane design is patented, and discussions are under way with multiple business partners regarding commercialization, Tuteja tells C&EN. Kota adds that the simple dip-coating preparation method should allow the team to make membranes of any size or shape. The researchers envision the membranes being used to not only clean up oil spills but also to treat wastewater, purify fuels, and separate emulsions used in manufacturing processes.

“This is a simple yet very creative idea that may lead to great improvement in membrane separations,” says chemical engineering professor Abraham Marmur of Technion—Israel Institute of Technology, who studies surface-wetting phenomena. “It has the potential of saving energy in a wide range of applications. It is too early to tell whether it can be efficiently scaled up, but intuitively it does appear to be very promising, mainly because of its elegant simplicity.”

Chemical & Engineering News
ISSN 0009-2347
Copyright © American Chemical Society
Matthew Kramer (Tue Sep 04 21:28:31 EDT 2012)
I would love to use it in my lab for seperateion of "crushed diatoms" and the resulting oil and kerosene mix. You would have seawater and jet fuel!!

I would love a sample!! it looksto good to be true.
Wendell N. Harkey (Thu Sep 06 14:50:23 EDT 2012)
Have you thought of using this with surface separating vessels on oil production leases where the emulsion consists of raw crude oil, produced water, various formation solids, and natural gas? We currently use liquid de-emulsifiers by injecting them into the system with different types of pumps.
liujingxia (Thu Jun 20 05:24:26 EDT 2013)
I have the same thought.How about to use this membrane in seperatin raw curde oil and water.
teresa west (Wed Jan 30 17:49:18 EST 2013)
I have been looking long and hard for a way to separate the oil emulsion that
results from washing cutting oil off pipe with high pressure water.
This emulsion really bonds together. Even weeks of repose does not separate
this goo. This sounds too good to be true. When would this be commercially
James Judd (Tue Jun 04 01:27:07 EDT 2013)
This is what I've been looking for. How do I get a sample?
Steve Ritter (Wed Jun 05 17:13:01 EDT 2013)
Please contact Prof. Tuteja for inquiries about obtaining samples.
Bhaumik Sheth (Sun Jul 21 11:42:31 EDT 2013)
well, I am working on a project for oil spill problem. from where I can get a research paper & related literature of the project as a reference ? help if anybody know. thanks.
Ryan Li (Wed Jun 04 16:20:21 EDT 2014)
May I know the separation rate for it? like how much m³/m²? thank you
Harry Collins (Wed Apr 22 10:42:02 EDT 2015)
Has it gone on to be produced commercially yet ?
Akinade Akindeji (Thu Jun 25 14:34:20 EDT 2015)
Please I want to know how to make this membrane to separate oil and water.
Craig Barnfield (Wed Oct 28 02:17:06 EDT 2015)
I have been looking for a membrane to separate ethylene glycol and water, for one part of my recycling of test fluids for sub-sea use. Any way to get info on this.
Steve Ritter (Sun Nov 01 20:14:50 EST 2015)
Thanks for your comment, Craig. You might learn what you need by contacting the lead researcher, Anish Tuteja (http://www-personal.umich.edu/~atuteja/Group.html).
Thomas Wong (Fri Nov 20 11:04:38 EST 2015)
I have an idea how the membrane could be efficiently used, but can it be made Sturdy enough to withstand continuous rubbing?
Steve Ritter (Tue Mar 01 09:50:56 EST 2016)
Membrane Update: The Tuteja group is commercializing the coating for different membranes through a startup called HygraTek (www.hygratek.com). The cost of the coating, which can be applied on top of virtually any existing membrane, is now only about $1 per square foot of the membrane area. The total cost of the coated membrane depends on the material being coated, which can be inexpensive for filter paper or quite expensive for ceramic membranes.
Arris Tan (Mon May 23 13:27:52 EDT 2016)
Could this membrane works too for Lacquer Thinner mix in water to be separated? We need a fast separation method to handle it properly as its too dangerous when evaporate. Please advise me thanks.
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