The production of ethanol from lignocellulosic biomass is now becoming a reality and conversion processes are improving. Process economic studies for production of lignocellulosic ethanol indicate that a minimum ethanol concentration of at least 4% (w/w) prior to distillation is required. Taking this fact into consideration, the total non-soluble lignocellulosic solids loaded for enzymatic hydrolysis must be above 15% (w/w) for most biomass materials. Enzymatic hydrolysis at higher solid loadings is significantly inhibited by: (1) higher concentration of inhibitors (e.g. organic acids, furans and phenolic compounds) (2) free monomeric sugars and (3) mass transfer limitations.

Ammonia Fiber Expansion (AFEX) is a novel alkaline pre-treatment technology used to pretreat lignocellulosic biomass that may produce reduced inhibitor levels compared to other pretreatments. It is the aim of this study to understand how high non-soluble solid loadings can affect the enzymatic hydrolysis of AFEX treated corn stover. In this study, corn stover was pretreated using optimal AFEX conditions. The pretreated samples were hydrolyzed using commercial enzymes with and without water washing under high solid loadings. In addition, protein rich substrates were also used as additives to improve enzymatic hydrolysis. Sugar conversions after enzymatic hydrolysis and ethanol fermentation profiles using Pichia stipitis were determined for a range of glucan loadings (1-12%). Details of these findings will be discussed.