Topochemistry of delignification behaviors of various lignocelluloseics by thermochemical treatment

Lignin in lignocellulosic biomass exhibits pronounced heterogeneity in spatial distribution, chemical structure, and concentration within the cell wall.This heterogeneity plays a key role in governing delignification behavior during thermochemical treatments and should be understood from a topochemical perspective.Hydrothermal treatment generally results in preferential delignification from the secondary wall, while lignin in the compound middle lamella remains resistant due to its condensed structure.In contrast, subcritical phenolic and supercritical alcoholic solvent systems promote solvolytic reactions, enabling delignification to proceed even in more recalcitrant regions.Other treatments, including steam explosion, ionic liquids, and deep eutectic solvents, further demonstrate that solvent properties strongly influence lignin redistribution and the formation of secondary products.Overall, delignification is governed by the interplay of structural heterogeneity, linkage-dependent reactivity, solvent characteristics, and mass transport processes, providing key insights for the rational design of lignin valorization strategies.