(270d) A Comprehensive Kinetic Investigation of Enzymatic Hydrolysis of Cellulose

Enzymatic hydrolysis of Lignocellulosic biomass depends on many factors; physical properties of substrate (composition, crystallinity, degree of polymerization etc.), enzyme synergy (origin, composition etc.), mass transfer (substrate adsorption, bulk and pore diffusion etc.) and intrinsic kinetics. Most of these effects occur concurrently, therefore cannot be distinguished from each other. A three-step approach was taken to investigate these effects independently for the purpose of building a comprehensive kinetic model.

In the first stage, assessment of intrinsic kinetics of enzymatic hydrolysis was performed using data obtained from non-crystalline cellulose (a product of Biofuels Laboratory, Auburn University). The NCC reaction is unhindered by mass transfer resistances, or physical properties of substrate. Four reactions were identified as important steps in the mechanism of enzymatic hydrolysis. The reactions are: (1) Cellulose?Cellobiose, (2) Cellobiose?Glucose, (3) Cellulose?cello-oligosaccharides (COS), (4) COS ? Glucose. From batch experiments using NCC, the time-course data on cellulose, COS, Cellobiose, and Glucose was taken. This data were used to estimate the parameters in the kinetic model that accounts for inhibitory effects of reaction intermediates and products (cello-oligosaccharides, cellobiose and glucose). The model predictions of cellulose, COS, Cellobiose, and Glucose profiles, has shown a good agreement with experimental data generated from hydrolysis of different initial compositions of substrate (NCC supplemented with COS, G and G2). Enzymatic hydrolysis experiments were then performed on Alpha Cellulose to study the effects of crystallinity and bulk mass transfer on the hydrolysis. These effects were incorporated into the previously developed intrinsic kinetic model. Finally, hydrolysis experiments were performed on corn stover to investigate the effects of lignin and hemicellulose in the biomass on enzymatic hydrolysis. From the cumulative insights obtained from these three sequential studies, a comprehensive mechanism of enzymatic hydrolysis of lignocellulosic biomass was constructed. This model incorporates the intrinsic kinetics, effects of enzymatic adsorption onto the substrate surface, crystallinity and composition of the substrate, bulk mass transfer on the enzymatic hydrolysis.