Submitted to: Bioresource Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/14/2010
Publication Date: 2/11/2010
Citation: Taylor, F., Marquez, M., Johnston, D., Goldberg, N.M., Hicks, K.B. 2010. Continuous High-solids corn liquefaction and fermentation with stripping of ethanol. Bioresource Technology. 101:4403-4408. Interpretive Summary: To improve the security of liquid fuel supplies, while creating jobs and businesses in rural areas, the government has mandated the use of renewable fuels in gasoline. Currently, the lowest-cost renewable fuel is ethanol produced from corn in fermentors, where yeast cells consume the glucose sugar that comes from the starch in the corn. However, ethanol produced this way may be too expensive to compete directly with straight gasoline. To reduce the cost of producing ethanol, continuous fermentation and stripping were proposed. In stripping, the volatile component of a liquid mixture evaporates into a gas. In continuous fermentation and stripping, ethanol is continuously removed from the fermentor, thereby greatly increasing the fermentation rate. Previously, it was shown how the conventional fermentation process can be modified to save approximately $0.03 per gallon on the production of fuel ethanol. These savings are primarily due to the increased concentration of corn in the mixture entering the fermentor, as compared with current industrial practice. Now the same process has been demonstrated at even greater levels of corn solids. Application of this technology will benefit ethanol producers, corn growers, and transportation fuel consumers.
Technical Abstract: Removal of ethanol from the fermentor during fermentation can increase productivity and reduce the costs for dewatering the product and coproduct. One approach is to recycle the fermentor contents through a stripping column, where a non-condensable gas removes ethanol to a condenser. Previous research showed that this approach is feasible. Savings of $0.03 per gallon were predicted at 34% corn dry solids. Greater savings were predicted at higher concentration. Now the feasibility has been demonstrated at over 40% corn dry solids, using a continuous corn liquefaction system. A pilot plant, continuously fed corn meal at more than one bushel (25 kg) per day was operated for 60 consecutive days, continuously converting 95% of starch and producing 88% of the maximum theoretical yield of ethanol. A computer simulation was used to analyze the results. The fermentation and stripping systems were not significantly affected when the CO2 stripping gas was partially replaced by nitrogen or air. It was concluded that previous estimates of potential cost savings are still valid.