Natural Gas Warning

A glass beaker in a Guelph chemistry lab holds a novel ceramic product that may also contain the secret for cleaning up a toxic waste byproduct of natural gas wells in Western Canada and other parts of the world. So say emeritus professor Nigel Bunce and lab colleagues who are studying “green” electrochemistry to treat sour brines created in oil and gas extraction.

Sour brine consists of water contaminated with sulfide and chloride. Besides corroding metal pipes, hydrogen sulfide is released in air as a smelly and toxic substance. Bunce hopes to develop a cheap, reliable way to treat these wastes using a trademarked ceramic material called Ebonex.

He says his work might ultimately give industry a better alternative to current treatments, notably reinjecting sour brines into underground wells. Currently, companies moving that material to those wells need to transport it under pressure to prevent release of hydrogen sulfide C an expensive process.

Bunce studies the use of electrochemistry, or conversion of electrical energy into chemical energy, to treat water-borne wastes. His MacNaughton Building lab belongs to the Electrochemical Technology Centre in the Department of Chemistry.

He’s seeking suitable anode materials for oxidation reactions to convert the contaminant sulfide into “greener” sulfate. But where to find something that is cheap, long-lasting and effective?

“The problem is in finding a suitable anode material to meet those requirements,” says Bunce.

Earlier, he tried boron-doped diamond, coke used in steelmaking and an iridium oxide-based material. Those showed promise for treating hydrogen sulfide but would be expensive, too short-lived or too complicated for companies to use, he says.

Now he’s studying Ebonex, a ceramic that conducts electricity and that is electrochemically stable in water whether used as an anode or as a cathode. As a ceramic, Ebonex can be readily formed into an electrode in an electrochemical cell, an important point for companies looking to fashion a material for specific needs, he says.

Electrodes are either anodes (where an electrical current leaves the cell) or cathodes (where the current enters the cell). With sour brines, oxidation occurring at the anode changes the sulfide to sulfate.

Although the process worked with Ebonex, the reaction tended to run down quickly. Working with research associate Dorin Bejan and master=s student Shaimaa Elsherif, Bunce tried a “flip-flop” trick. Switching polarity periodically to change the anode into a cathode and back again rejuvenated the electrochemical cell to keep the process going.

Bejan says the result was surprising. “One day we said: ‘Let=s take this anode and make it a cathode for a while.’ The anode-like activity came back.”

Bunce believes this process is more promising than other researchers’ attempts to use microorganisms for biological oxidation of sour brine. “It’s faster and there are no concerns about toxicity toward micro-organisms.”

Other scientists have also tried adding extra chemicals, but he says chemical agents add costs and yield poisonous sludge that still needs proper disposal. Salts naturally present in these brine solutions make it easy to pass an electrical current through them without adding more chemicals.

This work has been funded by the Natural Sciences and Engineering Research Council and Imperial Oil Ltd.