Dynamic Interfacial Catalysis: Calcium Hydroxide Drives Lignocellulose Depolymerization and Structural Reconfiguration toward High-Efficiency Fermentable Sugar Production

Abstract

Mild pretreatment conditions and high solids loading are essential for the cost-effective conversion of lignocellulosic biomass into biofuels and bioproducts. However, the mechanisms underlying efficient cell wall deconstruction under such conditions remain poorly understood. Here, we investigated densifying lignocellulosic biomass with calcium hydroxide chemicals (DLC(ch), a room-temperature, high-solids pretreatment) and elucidated a dynamic interfacial catalytic mechanism governing lignocellulose depolymerization and structural reconfiguration. During DLC(ch) pretreatment, mechanical densification created abundant solid-liquid interfaces within the cell-wall microenvironment, where solid Ca(OH)2 continuously dissociated to release OH– and Ca2+. The OH– selectively cleaved glycosidic bonds, lignin-carbohydrate ester linkages, and some lignin ether bonds, whereas the resulting soluble derivatives rapidly interacted with Ca2+ to form insoluble calcium-organic deposits via chelation. This coupled process sustained cell wall deconstruction during room temperature storage and generated characteristic cotton-like deposits. Upon subsequent treatment, these deposits became intercalated between the cellulose microfibrils, forming a sandwich-like “cellulose-deposit-cellulose” architecture that enhanced cellulase accessibility. DLC(ch) pretreated corn stover achieved 94.7% glucan conversion after 70 days of room temperature storage, supporting high yield fermentable sugar production (548 kg per tonne of corn stover). These findings provide a mechanistic basis for developing low-cost, energy-efficient, and water-saving lignocellulosic biorefinery processes.