New research at the Integrated Bioprocessing Research Laboratory (IBRL) at the University of Illinois, Urbana-Champaign could lower ethanol production costs by simplifying the dry grind process.

“There are currently more than 200 dry grind plants that are processing corn to produce ethanol,” says Vijay Singh, director of IBRL and a professor of agricultural and biological engineering. “The dry grind process requires two different enzymes to convert corn starch to glucose, which is further fermented to ethanol by yeast.”

The dry grind process requires two different enzymes to convert corn starch to glucose, which is further fermented to ethanol by yeast. Image credit: Pixabay. Singh says that process has been simplified by combined use and optimization of three new technologies. A new corn developed by transgenic technology, known as amylase corn, produces one of these enzymes in the grain itself, and a newly engineered "superior yeast" provides the second enzyme, as well as fermenting the glucose.

“There is a high expression level of the first enzyme, α-amylase, in the new corn, so only a small amount of this corn is required to be mixed with conventional dent corn,” Singh notes. “The superior yeast provides the second enzyme, glucoamylase, and also provides an alternate metabolic pathway to reduce by-product formation during fermentation. Combined use of this corn and superior yeast can reduce the total enzyme addition by more than 80%.”

Another approach to improve the dry grind process is to use high solids in the plant. However, according to Singh, high solid concentrations lead to high ethanol build-up in the tank.

As high ethanol affects the yeast viability and inhibits its fermentation performance, Singh's team has added a third technology to the process: removing the ethanol as it is being produced using a vacuum flashing process. Only a couple of vacuum cycles of 1 to 1.5 hours can bring the ethanol concentration below the inhibitory levels without affecting yeast health and allow complete fermentation of corn solids up to 40%, Singh says.

Deepak Kumar, a postdoctoral research associate in agricultural and biological engineering, says that because the dry grind process uses a significant amount of water, adding more solid material to the slurry—40% as opposed to 30%-35%—results in reducing the amount of water used in the process, improving production process efficiencies and economics.

“When ethanol is produced, it is in a very dilute solution. You have a small amount of ethanol and a large amount of water,” says Kumar. “We cut down the water use by pushing high solids. When we reduce the amount of water, we also reduce the amount of energy required to remove the water.”