Researchers at the U.S. Department of Energy’s Joint BioEnergy Institute (JBEI) have developed a “high-gravity” one-pot process for producing ethanol from cellulosic biomass. The process is claimed to generate unprecedented yields while minimizing water use and waste disposal. The development could help make biofuels more economically competitive with fossil fuels as a source of transportation energy.

JBEI researchers led by Seema Singh and Blake Simmons developed a process that uses a combination of ionic liquid pretreatment, enzymatic saccharification and yeast fermentation for the production of concentrated fermentable sugars that result in high-titer cellulosic ethanol. “High gravity” means high biomass loading; the higher the biomass loading, the lower the costs of converting it to fuels.

“Our new one-pot process for making cellulosic ethanol was enabled by the discovery and use of a renewable ionic liquid derived from amino acids that commercially available enzyme mixtures and organisms can tolerate,” says Simmons, a chemical engineer and JBEI’s chief science and technology officer. “This eliminates the need for separations, recoveries and other operational steps, generating significant cost savings.”

Using "bionic" liquids resulted in yields that exceed the production distillation required for industrial ethanol production. Ionic liquids are powerful solvents that can be used to dissolve cellulosic biomass into sugars for the production of fuels. The renewable ionic liquid to which Simmons refers is one made from lignin and hemicellulose, two by-products of biofuel production from biorefineries. “Using 'bionic' liquids in our new one-pot high-gravity process, we were able to increase biomass digestibility and obtain ethanol titer yields of 41.1 grams/liter, which exceeds the production distillation required for industrial ethanol production,” says Singh, who directs JBEI’s biomass pretreatment program. “The reduction in water consumption combined with the improved overall process economics moves us closer to more affordable and sustainable second-generation biofuels.”

Simmons and Singh say that the one-pot process for producing cellulosic ethanol could also be applied to next generation or “advanced” biofuels, those that can be directly “dropped” into today’s gasoline engines and infrastructure. They are currently working with researchers in JBEI’s Fuels Synthesis Division to develop a microbial host capable of producing these advanced biofuels.