Sodium hydroxide pretreatment of corn stover and subsequent enzymatic hydrolysis: An investigation of yields, kinetic modeling and glucose recovery

Many aspects associated with conversion of lignocellulose to biofuels and other valuable products have been investigated to develop the most effective processes for biorefineries. The goal of this research was to improve the efficiency and effectiveness of the lignocellulose conversion process by achieving a more basic understanding of pretreatment and enzymatic hydrolysis at high solids, including kinetic modeling and separation and recovery of glucose. Effects of NaOH pretreatment conditions on saccharide yields from enzymatic hydrolysis were characterized in low- and high-solids systems. Factors associated with pretreatment and hydrolysis were investigated, including duration of pretreatment at different temperatures and NaOH loadings, as well as different solids and enzyme loadings. Under relatively mild pretreatment conditions, corn stover composition was essentially equivalent for all time and temperature combinations; however, components were likely affected by pretreatment, as differences in subsequent cellulose conversions were observed. Flushing the hydrolyzate and reusing the substrate was also studied as a method for inhibitor mitigation while increasing overall glucose yields. Flushing the PCS throughout the hydrolysis reaction eliminated the need to wash the pretreated biomass prior to enzymatic hydrolysis when supplementing with low doses of enzyme, thus reducing the amount of process water required. The robustness of an established kinetic model was examined for heterogeneous hydrolysis reactions in high-solids systems. Michaelis-Menten kinetics is the traditional approach to modeling enzymatic hydrolysis; however, high-solids reactions violate the main underlying assumption of the equation: that the reaction is homogeneous in nature. The ability to accurately predict product yields from enzymatic hydrolysis in high-solids systems will aid in optimizing the conversion process. Molecularly-imprinted materials were studied for use in both bulk adsorption and in column chromatography separations. Glucose-imprinted materials selectively adsorbed glucose compared xylose by nearly 4:1. Non-imprinted materials were neither selective in the type of sugar adsorbed, nor were they capable of adsorbing sugar at as high a capacity as the glucose-imprinted materials. Liquid chromatography with imprinted materials was not a suitable means for separating glucose from solution under the conditions investigated; however, many factors impact the effectiveness of such a separation process and warrant further investigation