Abstract
During liquid hot water (LHW) pretreatment, lignin is mostly retained in the pretreated biomass, and the changes in the chemical and structural characteristics of lignin should probably refer to re-/depolymerization, solubilization, or glass transition. The residual lignin could influence the effective enzymatic hydrolysis of cellulose. The pure lignin was used to evaluate the effect of LHW process on its structural and chemical features. The surface morphology of LHW-treated lignin observed with the scanning electron microscopy (SEM) was more porous and irregular than that of untreated lignin. Compared to the untreated lignin, the surface area, total pore volume, and average pore size of LHW-treated lignin tested with the Brunner-Emmet-Teller (BET) measurement were increased. FTIR analysis showed that the chemical structure of lignin was broken down in the LHW process. Additionally, the impact of untreated and treated lignin on the enzymatic hydrolysis of cellulose was also explored. The LHW-treated lignin had little impact on the cellulase adsorption and enzyme activities and somehow could improve the enzymatic hydrolysis of cellulose.
Highlights
Bioethanol production from lignocellulosic biomass has gained focus for easy availability of feedstock, no competition with the food supply, and reduction in net carbon emission [1, 2]
The residual lignin in the pretreated lignocellulose can negatively influence the enzymatic hydrolysis of cellulose via physical barrier and enzyme adsorption [4,5,6], and its chemical and structural characteristics are changed due to depolymerization and condensation reactions during Liquid hot water (LHW) pretreatment [7]
LHW pretreatment caused the redistribution of lignin which could influence the enzymatic hydrolysis [19]
Summary
Bioethanol production from lignocellulosic biomass has gained focus for easy availability of feedstock, no competition with the food supply, and reduction in net carbon emission [1, 2]. The residual lignin in the pretreated lignocellulose can negatively influence the enzymatic hydrolysis of cellulose via physical barrier and enzyme adsorption [4,5,6], and its chemical and structural characteristics are changed due to depolymerization and condensation reactions during LHW pretreatment [7]. The ball-milling process for isolating MWL could result in β-ether cleavage [9], and the isolation procedure for CEL could increase phenolic β-O-4 content [10] and BioMed Research International reduce molecular weight [11] She et al [12] reported that alkali could not change the main structural feature of lignin preparations isolated with 50% dioxane. This study was a preliminary try to explore the structural and chemical changes of lignin in the LHW process and would provide useful information for the future research
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