Kinetic modeling for enzymatic hydrolysis of pretreated Creeping Wild Ryegrass

Abstract

A semimechanistic multi-reaction kinetic model was developed to describe the enzymatic hydrolysis of a lignocellulosic biomass, Creeping Wild Ryegrass (Leymus triticoides) (CWR). This model incorporated one homogeneous reaction of cellobiose to glucose and two heterogeneous reactions of cellulose to cellobiose and cellulose to glucose. Adsorption of cellulase onto pretreated CWR during enzymatic hydrolysis was modeled via a Langmuir adsorption isotherm. This is the first kinetic model which incorporated the negative role of lignin (nonproductive adsorption) using a Langmuir-type isotherm adsorption of cellulase onto lignin. The model also reflected the competitive inhibitions of cellulase by glucose and cellobiose. The Matlab optimization function of "Isqnonlin" was used to fit the model and estimate kinetic parameters based on experimental data generated under typical conditions (8% solid loading and 15 FPU/g-cellulose enzyme concentration without the addition of background sugars). The model showed high fidelity for predicting cellulose hydrolysis behavior over a broad range of solid loading (4-12%, w/w, dry basis), enzyme concentration (15-150 FPU/g-cellulose), sugar inhibition (glucose of 30 and 60 mg/mL and cellobiose of 10 mg/mL). In addition, sensitivity analysis showed that the incorporation of the nonproductive adsorption of cellulase onto lignin significantly improved the predictability of the kinetic model. Our model can serve as a robust tool for developing kinetic models for system optimization of enzymatic hydrolysis, hydrolysis reactor design, and/or other hydrolysis systems with different type of enzymes and substrates.