18015: Mechanistic modeling of enzymatic saccharification of cellulose using continuous distribution kinetics

The enzymatic saccharification of biomass for the purpose of producing fuels and chemicals continues to exhibit poor process economics and hence remains the subject of intense research and development.  Mathematical models describing the kinetics of the enzymatically catalyzed hydrolysis reactions have ranged from simple, empirically based substrate-product models to highly detailed, mechanistically based molecular models.  While the former are often limited in their predictive ability to a narrow parameter space, the later are too computationally expensive to use for process design and optimization.

We have developed a kinetics model that incorporates the essential mechanisms of the enzymatic depolymerization of cellulose but retains the computational speed necessary for process design and optimization.  The model incorporates the distinct modes of action an endoglucanase (EGI) and an exoglucanase (cellobiohydrolase, CBHI) for depolymerization of insoluble cellulose polymer chains, and beta-glucosidase acting on soluble oligosaccharides. The processive action of CBHI is modeled using a population-balance approach to describe the depolymerization of cellulose chains, which incorporates distinct steps for adsorption, complexation, processive hydrolysis, and desorption. Random-chain scission of insoluble cellulose by EGI is also handled using population-balance equations, which allows for a kinetic description of the transformation of a polydisperse distribution of cellulose polymer lengths. Utilizing population balance models, which track the evolution of the distribution of polymer lengths, does not require solving equations for all chemical species present in the reacting mixture and affords computationally efficient simulations.