Poisonous carbon monoxide gas emitted by steel mills and other industrial sources can be turned into useful things. Soon a New Zealand company with an unusual approach to this idea plans to use the gas to make ethanol and chemical precursors for a wide variety of plastics and solvents.
The company, LanzaTech, is using genetically engineered microorganisms that eat the gas. While it’s common for companies to use microorganisms such as yeast and bacteria to make ethanol and other products, the microorganisms generally feed on some form of sugar, such as glucose derived from corn starch. Rather than using food sources, LanzaTech feeds its microorganisms carbon monoxide. “It’s basically eating a gas stream,” says the company’s CEO, Jennifer Holmgren.
LanzaTech recently announced agreements to build commercial plants at a steel mill and a coal-fueled power plant in China. Emissions from steel plants worldwide would be enough to make about 30 billion gallons of fuel every year, Holmgren says. That’s equivalent to about 15 percent of the gasoline consumed in the United States.
The organisms can also survive on a mixture of carbon monoxide and hydrogen gas called syngas, which can be made by heating–under certain conditions–just about anything made largely of hydrogen and carbon, including plastics, wood chips, and coal. Usually syngas is converted into useful products through thermochemical processes that use inorganic catalysts. But these catalytic approaches also make waste products that have to be disposed of.
That explains another advantage of engineered microorganisms: they can be made to produce much higher yields of a desired product, says Andy Aden, a researcher at the National Renewable Energy Laboratory in Golden, Colorado. He also says that the cost of microorganisms and nutrients can be less than the cost of precious-metal catalysts typically used in thermochemical processes. And organisms can often tolerate impurities that would deactivate catalysts, Aden adds.
The LanzaTech process has the further advantage of not requiring hydrogen. As a result, it can work directly on the flue streams from steel plants, which often don’t include hydrogen. If hydrogen is present in a flue gas stream, it can either be fed to the organisms or separated and sold–it’s a valuable commodity.