|Nghiem, Nhuan - John|
Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2011
Publication Date: 9/22/2011
Citation: Yoo, C., Nghiem, N.P., Hicks, K.B., Kim, T. 2011. Pretreatment of corn stover using low-moisture anhydrous ammonia (LMAA) process. Bioresource Technology. 102:10028-10034. Interpretive Summary: Production of fuel ethanol from cellulosic biomass feedstocks like switchgrass and corn stover by the biochemical option requires a pretreatment step. Most pretreatment processes have three serious problems which prevent commercial applications, namely destruction of valuable carbohydrates, high chemical costs in biomass, and use of very large volumes of water. Previously we developed the use of aqueous ammonia (SAA) and (SAA + ethanol)processes which preserve the original feedstock. In the carbohydrate content of this new work, we developed a further improved pretreatment process using anhydrous ammonia to minimize water and ammonia inputs for cellulosic ethanol production, designated the low moisture anhydrous ammonia (LMAA) pretreatment. We found following the pretreatment step the biomass could be hydrolyzed with commercial enzymes and fermented to ethanol without the need of an additional washing step, thus resulting in tremendous savings of water. This pretreatment method also achieved very high preservation of both cellulose and hemicellulose in the biomass feedstock. Ammonia recycle allowed significant savings on chemical costs. Ammoniation of the biomass using anhydrous ammonia, i.e. adsorption of ammonia onto the biomass in the flow-through reactor, also could work as a sterilization step, which would allow long-term storage of the feedstock. It is anticipated that this new pretreatment process would help improve the overall economics of cellulosic ethanol production and allow it to move closer to commercial feasibility.
Technical Abstract: A simple pretreatment method using anhydrous ammonia was developed to minimize water and ammonia inputs for cellulosic ethanol production, termed the low moisture anhydrous ammonia (LMAA) pretreatment. In this method, corn stover with 30 - 70 percent moisture was contacted with anhydrous ammonia in a reactor under nearly ambient conditions. After the ammoniation step, biomass was subjected to a simple pretreatment step at moderate temperatures (40 - 120 degree C) for 48 - 144 h. Pretreated biomass was saccharified and fermented without an additional washing step. With 3 percent glucan loading of LMAA-treated corn stover under best treatment conditions (0.1 g-ammonia + 1.0 g-water per g biomass, 80 degree C, and 96 h), simultaneous saccharification and cofermentation using recombinant E. coli KO11 and enzymes (15 FPU cellulase + 30 CBU beta-glucosidase + 1,000 GXU xylanase per g-glucan) resulted in 24.2 g/l (89 percent of theoretical ethanol yield based on glucan + xylan in corn stover).