Kinetics of chemical pretreatment and pre-hydrolysis of lignocellulosic biomass for sugar release, Part I: pseudo-homogeneous modeling

Pretreatment or pre-hydrolysis to increase the enzymatic digestibility of cellulose is a prerequisite step for bioconversion of lignocellulosic biomass (LCB) to biofuels and biochemicals. Kinetic modeling is important to optimizing the reaction conditions and understanding the reaction mechanisms. However, due to the complexity of the LCB structure and heterogeneity of the reaction system, rigorous kinetic modeling is not possible for biomass pretreatment system. Therefore, pseudo-homogeneous assumption is usually used for studying the kinetics of biomass component hydrolysis or solubilization. In this review article, we focus on the recent research progress on the pseudo-homogeneous modeling of biomass pretreatment for subsequent sugar release, covering major chemical approaches including acidic, alkaline, organosolv, and oxidative processes. Phenomenological modeling and kinetic modeling with Saeman's model, two-fraction model and potential degree of reaction (PDR) model are comprehensively discussed. Phenomenological models integrate operational variables, providing a convenient means for describing and predicting the pretreatment process. Pseudo-homogeneous kinetic models offer theoretical foundation for process optimization by simplifying the reaction system. However, these models are still facing limitations due to their pseudo-homogeneous assumptions, oversimplified reaction mechanisms, and difficulties in determining parameters. It is recommended that future works should be focused on developing new models with consideration of the heterogeneous structure of LCB and heterogeneity of pretreatment reaction system, and employing advanced detection technologies and data processing approaches to improve the modeling accuracy.