Assessing the molecular structure basis for biomass recalcitrance during dilute acid and hydrothermal pretreatments

TLDR

Cellulosic ethanol is a promising alternative to fossil fuels, but lignocellulosic biomass is intrinsically recalcitrant due to complex plant cell walls, so pretreatments such as dilute acid and hydrothermal are needed to increase sugar release. This review examines how structural changes in cellulose, hemicellulose, and lignin during dilute acid and hydrothermal pretreatments reduce biomass recalcitrance. The authors discuss how these pretreatments alter biomass porosity, thereby facilitating enzymatic hydrolysis and lowering recalcitrance.

Abstract

Abstract The production of cellulosic ethanol from biomass is considered a promising alternative to reliance on diminishing supplies of fossil fuels, providing a sustainable option for fuels production in an environmentally compatible manner. The conversion of lignocellulosic biomass to biofuels through a biological route usually suffers from the intrinsic recalcitrance of biomass owing to the complicated structure of plant cell walls. Currently, a pretreatment step that can effectively reduce biomass recalcitrance is generally required to make the polysaccharide fractions locked in the intricacy of plant cell walls to become more accessible and amenable to enzymatic hydrolysis. Dilute acid and hydrothermal pretreatments are attractive and among the most promising pretreatment technologies that enhance sugar release performance. This review highlights our recent understanding on molecular structure basis for recalcitrance, with emphasis on structural transformation of major biomass biopolymers (i.e., cellulose, hemicellulose, and lignin) related to the reduction of recalcitrance during dilute acid and hydrothermal pretreatments. The effects of these two pretreatments on biomass porosity as well as its contribution on reduced recalcitrance are also discussed.