(372e) Examining Cell-Wall Transport Effects on Enzymatic Hydrolysis By Mechanistic Modeling

Enzymatic hydrolysis of ligno-cellulosic biomass is a complicated process involving a multitude of physicochemical transformations. Many models have been proposed to describe this process, usually emphasizing the reaction kinetics of component species, the mechanics of depolymerization of cellulose by enzymes, and the evolving accessibility of cellulose through the digestion of surface cellulose. Recent microscopy results suggest that, in addition to solubilizing and removing chemical components from the cell wall, pretreatment can change the enzyme accessibility of biomass by mechanical disruption of cell wall structure. This distruption of the cell-wall structure has a significant impact on enzymatic hydrolysis rate and overall conversion yield. Accordingly, we propose a hindered-diffusion-reaction system for modeling the enzymatic hydrolysis of pretreated biomass. In our model, enzyme from the bulk diffuses into the cell-wall remnants, adsorbs onto cellulose microfibrils, and hydrolyzes cellulose into soluble sugars, which then diffuse independently. Diffusion is hindered by the local solids content of the cell wall, which is solubilized over the course of the reaction. The local surface accessibility of cellulose is related non-linearly to the local solid-volume fraction of cellulose, representing micro-scale inaccessibility due to microfibrils. Simulation results are presented with a speculative parameter set, and the important features of the model are discussed.