Modeling and simulation of coupled flow and reaction kinetics of the enzymatic hydrolysis of cellulose in realistic reaction vessels

The use of mathematical modeling and computer simulation has become prevalent throughout the petrochemical process industries. Validated models that capture relevant physical and chemical phenomena of a particular unit operation can be used to design and optimize that unit operation in silico with only limited supporting experimentation. Owing to the complicated chemistry and material properties of biomass, modeling and simulation of enzymatic hydrolysis, as well as other unit operations of biochemical conversion, have had limited success. A comprehensive mechanistic model for enzymatic hydrolysis that is suitable for reactor design must account for the fluid mechanics of the heterogeneous, multiphase slurries and the complex reaction network that arises from the many substrate, product, and catalyst species.

Here we present progress on the development of computational fluid dynamics (CFD) and reaction kinetics models for the enzymatic hydrolysis of cellulose particles. The CFD model is a generalized-Newtonian model that includes settling of cellulose particles and a concentration dependent viscosity. The reaction kinetics model is a population balance model (PBM) that accounts for the distribution of cellulose polymer lengths and multiple enzyme species. To enable tractable simulations, the PBM kinetics model was simplified by using the method of moments. Coupled CFD-kinetics simulations were implemented by alternating simulation steps of CFD followed by reaction kinetics in order to accommodated the vastly different time scales of fluid flow (seconds) and enzymatic hydrolysis reaction (hours). The results from model simulations were validated against experimental results. Model simulations are subsequently used to indicate potential improvements to reactor designs.