The study addresses the recurring problem of separating oil and water mixtures, and targets diverse applications including cleaning up oil spills, and extracting oil deposits from tar sands and reservoirs. Other potential beneficiaries are plastics manufacturers, chemical and pharmaceutical companies, mining companies and makers of cleaning products.

The new process can be used whenever industry requires an emulsion (the mixture of two liquids in which droplets of one are suspended evenly throughout the other), explains lead researcher and Queen's Chemistry Professor Philip Jessop. This might occur when cleaning spills, extracting oil from the ground, de-greasing metal equipment or metal surfaces, and manufacturing chemical products such as plastics.

Since oil and water don't normally mix, it's necessary to add a "surfactant" (surface active agent) in the layer between them before you can create an emulsion. "The problem is that in many situations, you later want the water and oil to separate again," he continues. But of the 'switchable' surfactants known so far, one is very expensive and contains metals, another is extremely toxic, and the third type is activated by light - which doesn't work well with opaque emulsions.

Old-fashioned soap can be made to "switch" but that requires large amounts of acid to be added, which is not desirable, says Dr. Jessop, Canada Research Chair in Green Chemistry. The surfactant developed by the Queen's team is also completely reversible and does not require metals, acid, or light.

Exposure to carbon dioxide (CO2) activates it, while bubbling air through the liquid turns it off again. CO2 and air were chosen because they are cheap, non-toxic and environmentally benign: the CO2 can be recycled material from power plants.

"You can do this over and over, timing it for exactly when you want the switch to occur," Dr. Jessop notes. And when the surfactant is turned off, causing oil and water to separate, the now-clean water may be returned to its source or recycled.

The new surfactant builds on Dr. Jessop's discovery last year of "switchable solvents" that change their properties when alternately exposed to carbon dioxide and nitrogen, making it possible to re-use the same solvent for multiple steps in a chemical process.

"Right now there are big separation problems causing enormous headaches in the oil industry," says Dr. Jessop. "If 'green chemistry' can solve these problems, then the environment benefits and companies profit financially as well. It's very much a win-win situation."

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