An insight to pretreatment, enzyme adsorption and enzymatic hydrolysis of lignocellulosic biomass: Experimental and modeling studies

Enzymatic hydrolysis of lignocellulosic biomass is an attractive method for sustainable cellulosic ethanol production. Considering the complex lignin-cellulose-hemicellulose network of lignocellulosic biomass, enzymatic hydrolysis is a complicated heterogeneous catalytic process and is affected by numerous factors. To reveal the mechanism and obtain the main influencing factors of enzymatic hydrolysis is of great significance to optimize the hydrolysis condition and guide the hydrolysis design. This work comprehensively reviewed the research progress of enzymatic hydrolysis using both experimental and theoretical model evidence. Experimental study of the pretreatment indicated that physicochemical or acid pretreatment is preferable for herbaceous feedstocks, while alkaline pretreatment is proved to be more suitable for lignin-rich woody feedstocks. Preceded by hydrothermal or chemical pretreatment can decrease the energy consumption of mechanical refining. The recalcitrance of different parameters including the enzyme and substrate properties to enzyme adsorption and hydrolysis was comparatively analyzed to optimize the reaction. Theoretical models were comprehensively studied to elucidated the mass transfer mechanism at the molecular level so as to further reveal the reaction mechanism and the key rate-limiting step. Experimental and modeling studies both indicated that the accessible cellulose surface area and pore volume are the main parameters limiting the hydrolysis. Enzyme diffusion is a key rate-limiting step in the beginning of the reaction but affects little for particles with a radii smaller than 5 × 10−3 cm. This paper also deeply analyze the linking between experimental and modeling studies which provide some meaningful reference for the optimization of the conversion process.