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

Yunqiao Pu,Arthur J Ragauskas,Fan Hu,Brian H Davison,Fang Huang

doi:10.1186/1754-6834-6-15

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.

Highlights

With the increasing concerns on diminishing fossil fuel resources, climate change and energy security, the utilization of renewable and sustainable resources for the production of fuels, chemicals and materials has become a global research theme and in the future will play an important role in our energy portfolio
Poplar species with higher S/G ratios generally had a higher sugar release yield from enzymatic hydrolysis after dilute acid pretreatment; for substrates without pretreatment, sugar release was observed to increase when lignin content was below 20%, irrespective of the S/G ratio
Summary and conclusions In summary, dilute acid and hydrothermal pretreatments lead to substantial structural changes of lignin, hemicellulose and cellulose in lignocellulosic biomass

Summary

Introduction

With the increasing concerns on diminishing fossil fuel resources, climate change and energy security, the utilization of renewable and sustainable resources for the production of fuels, chemicals and materials has become a global research theme and in the future will play an important role in our energy portfolio. DA and hydrothermal pretreatments cause structural changes of lignin and cellulose as well as solubilization of hemicellulose, which in turn contribute to the reduction of biomass recalcitrance.

Results

Conclusion