Adding carbon-capture technology to a conventional coal plant can nearly double the price of the electricity it produces. This fact represents one of the big obstacles to passing legislation to regulate carbon-dioxide emissions. Now researchers at Codexis, based in Redwood City, CA, are using genetically engineered enzymes to make carbon-dioxide capture less expensive–their method could increase electricity costs by less than a third.
The new enzymes increase the efficiency, by a factor of 100, of a solvent used to capture carbon dioxide. This promises to decrease the energy needed to capture and store the greenhouse gas. The researchers developed new ways to engineer enzymes that can operate at the high temperatures inside a coal plant’s smokestack.
The standard way to capture CO2 is to use a solvent called monoethanolamine (MEA). Carbon dioxide is absorbed by the solvent, which separates it from the other flue gases. To store the carbon dioxide it has to be freed by applying heat–this produces a pure stream of carbon dioxide that can be compressed and permanently sequestered. The energy required to do this decreases the power output of a coal plant by about 30 percent. Combined with the extra equipment and materials needed to capture the CO2, this increases the cost of the electricity produced by roughly 80 percent. Codexis’s approach could limit this cost increase to 35 percent or less, says James Lalonde, the company’s vice president of biochemistry and engineering R&D.
Researchers at Codexis genetically modified an enzyme, called carbonic anhydrase, involved with respiration in many organisms, including humans. Carbonic anhydrase helps a solvent called methyl diethanolamine (MDEA) bind with carbon dioxide. The most challenging problem was altering the enzymes so they could survive at the high temperatures found in smokestacks. The enzymes can survive at temperatures around 25 °C, but quickly stop working at temperatures higher than 55 °C to 65 °C.