Soaking in aqueous ammonia (SAA) pretreatment of whole corn kernels for cellulosic ethanol production from the fiber fractions

Authors: Norvell, Katherine; Nghiem, Nhuan

Submitted to: Fermentation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2018
Publication Date: 10/16/2018
Citation: Norvell, K.L., Nghiem, N.P. 2018. Soaking in aqueous ammonia (SAA) pretreatment of whole corn kernels for cellulosic ethanol production from the fiber fractions. Fermentation. 4(87):1-10. https://doi.org/10.3390/fermentation4040087.
DOI: https://doi.org/10.3390/fermentation4040087

Interpretive Summary: A simple process was developed for production of additional ethanol from corn fiber in a dry-grind ethanol plant. In this process, whole corn kernels were soaked in aqueous ammonia solutions at 105 degrees C for 24 h. The pretreated corn then was subjected to a conventional mashing procedure and subsequently ethanol fermentation using a commercial strain of natural Saccharomyces cerevisiae with addition of a commercial cellulase. Pretreatment of the corn with 7.5 wt % ammonia solution plus cellulase addition gave highest ethanol production, which improved the yield in fermentation using 25 wt% solid by 14% compared to the baseline (untreated corn without cellulase addition). This increased yield is because in conventional corn fermentation only the sugars from starch are fermented but with our process modications sugars from both starch and cellulose are fermented. The process developed can potentially be implemented in existing dry-grind ethanol facilities as a “bolt-on” process for additional ethanol production from corn fiber.

Technical Abstract: Corn fiber is a co-product of commercial ethanol dry-grind plants, which is processed into distillers dried grains with solubles (DDGS) and used as animal feed, yet it holds high potential to be used as feedstock for additional ethanol production. Due to the tight structural make-up of corn fiber, a pretreatment step is necessary to make the cellulose and hemicellulose polymers in the solid fibrous matrix more accessible to the hydrolytic enzymes. A pretreatment process was developed in which whole corn kernels were soaked in aqueous solutions of 2.5, 5.0, 7.5 and 10.0 wt% ammonia at 105 degrees C for 24 h. The pretreated corn then was subjected to a conventional mashing procedure and subsequently ethanol fermentation using a commercial strain of natural Saccharomyces cerevisiae with addition of a commercial cellulase. Pretreatment of the corn with 7.5 wt% ammonia solution plus cellulase addition gave highest ethanol production, which improved the yield in fermentation using 25 wt% solid from 334 g ethanol/kg corn obtained in the control (no pretreatment and no cellulase addition) to 379 g ethanol/kg corn (a 14% increase). The process developed can potentially be implemented in existing dry-grind ethanol facilities as a “bolt-on” process for additional ethanol production from corn fiber, and this additional ethanol can then qualify as “cellulosic ethanol” by the EPA’s Renewable Fuels Standard and thereby receive RINS (Renewable Identification Numbers).