Pretreatment of Corn Stover for Bioethanol Production Using Low-Moisture Anhydrous Ammonia (LMAA); Ammoniation and Pretreatment

In the past several decades, various pretreatment methods have been suggested to enhance the enzymatic digestibility and fermentability of lignocellulosic biomass. Although a few of them may be effective, several cost barriers which prohibit scale-up exist including high chemical input and excessive water use. In order to solve these problems, a simpler pretreatment method using anhydrous ammonia was developed. In this method, corn stover with 30~70% moisture was used, which was contacted with anhydrous ammonia in a packed bed reactor. After the ammoniation step, biomass was treated at different reaction temperatures (40-120°C) and reaction times (24-96 h). Pretreated biomass was directly saccharified and fermented “with no additional washing step.” Therefore, it is anticipated that this method can reduce energy cost substantially due to the extremely low liquid loading and moderate conditions applied. With the treated solids, we have obtained significantly improved ethanol fermentability (>85%) using E.coli KO11 strain. 

In this investigation, it is speculated that ammonia swells cellulose structure effectively and ammoniation prevents methoxyl groups on lignin from absorbing cellulase enzymes, thus it enhances the enzyme hydrolysis rate and ethanol fermentation yield of lignocellulosic biomass. Ammoniation pretreatment can also supply assimilable nitrogen (up to 1.25 wt.% of the weight of dry biomass) for microorganism growth in the fermentor.  

In this paper, various pretreatment conditions such as moisture levels, residual ammonia concentrations, reaction time, and reaction temperature were explored to reduce the pretreatment cost and its pertinent costs. Enzyme digestibility and ethanol fermentation test results will also be presented.