Understanding the role of porous particle characteristics and water state distribution at multi-scale variation on cellulase hydrolysis of lignocellulosic biomass

Abstract

Porous particle characteristics of lignocellulosic biomass and the water state distribution surrounding particles determine enzyme/solute transfer, while inherently affecting the liquefaction and hydrolysis reactions. For submillimeter biomass particles (<500 μm), deep eutectic solvent pretreatment tended to create additional macropores (∼4%, pore volume of 4.3 mL/g) and micropores (∼3%, pore area of 2.26 m2/g) at the extragranular and cell wall scales, simultaneously with reducing particle size by 15%. The pretreated biomass exhibited preferential rapid liquefaction over sugar production, leading to a ∼70% reduction in particle size only after 3 h hydrolysis. This further increased particle porosity (∼85% after 12 h hydrolysis) with the transition from large surface-pores to interior micropores. The increases in the tissue/cell-scale pore size and intraparticle area had greater significance for improving hydrolysis performance than particle size reduction. Additionally, particle liquefaction released constrained water in capillary pores and enhanced slurry fluidity; capillary water and free water became main transfer carriers during the hydrolysis. Free water activity was positively related to sugar production (r = 0.80–0.85), and integrating it with particle component and porosity allowed for accurate prediction of hydrolysis yields (R2 = 0.98–0.99). Inspired by particle liquefaction, a short-time feeding strategy was proposed to reconstruct high-solid hydrolysis.