Kinetic dynamics in heterogeneous enzymatic hydrolysis of cellulose: an overview, an experimental study and mathematical modelling

Abstract

This paper presents an experimental study and mathematical analysis of how reaction kinetics of enzymatic cellulose hydrolysis are influenced by the changing dynamics and nature of interactions between enzymes, cellulose substrate, products (reducing sugars), and non-hydrolytic materials in a heterogeneous solid–liquid reaction system. An overview is presented to outline the historical development of theories in cellulose hydrolysis kinetics and to layout the key factors and mechanisms via which the heterogeneous enzymatic hydrolysis takes place. The limitation of current understanding and the degree of uncertainty surrounding the dynamic kinetics of the hydrolytic reaction and its mathematical modelling are discussed, and taken into consideration in proposing our own model. In synthesising a mechanistic kinetic model and in ensuing analysis, the focus is on examining the ongoing reaction dynamics of the hydrolytic reaction mediated by changing solid substrate structure, changing substrate surface composition, accumulative enzyme loss through non-productive binding, shear deactivation of enzyme, and product inhibition in continuous batch reactions. The proposed mathematical model is numerically analysed without resorting to the traditional approach of quasi-steady-state assumption, which itself is subjected to a close examination in this work. As a result of revisiting this classic heterogeneous enzymatic catalysis with new analysis and experiments, some new findings and understanding are presented of the complex reaction kinetics, especially time-dependent reaction dynamics associated with, e.g., continuous change of substrate structure and continuing loss of enzyme activity caused by various factors are presented. New parameters such as surface-active cellulose concentration coefficient ( β) and relative shear field residence time (Γ/Γ max) are incorporated into our model to enable some new and additional analysis. Computational simulation based on the proposed dynamic kinetic model shows that it predicts the hydrolysis reaction well. New understanding and suggestions are sought where discrepancy arises.