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

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.

Digestibility of Betung Bamboo Fiber Following Fungal Pretreatment

“…More secondary degradation products might form during hydrolysis under severe acid hydrolysis conditions. Lignin removal due to acid treatment of cellulose has been reported to increase the crystallinity of cellulose, thus decreasing the penetration of hydrolyzing agents and the production of reducing sugar [25]. Hermiati [26] reported similar results using starch pulp and microwave irradiation for 12-15 min.…”

Bioethanol production from coconut husk fiber

“…The main constituents of lignocellulosic biomass are cellulose (C 6 H 10 O 5 ) x , hemicellulose (C 5 H 8 O 4 ) m and lignin (C 9 H 10 O 3 (OCH 3 ) 0.9-1.7 ) n , which represent 90% of the biomass dry mass, while ashes and extractives correspond to 10% (BALAT, 2011). The structural complexity of lignocellulosic biomass, generally defined as recalcitrance, hampers microbial and enzymatic treatments (PU et al, 2013), thereby becoming a critical factor for the use of lignocellulosic residues in the production of biofuels. Pretreatment of biomass for conversion to 2G ethanol (second generation ethanol) has shown to be challenging because it must eliminate lignin, reduce crystallinity of cellulose, and dissolve hemicellulose, turning the biomass into a feedstock more susceptible to biological and chemical hydrolysis (SARKAR et al, 2012).…”

Reductive Cleavage of C—O Bond in Model Compounds of Lignin

“…The reduction of dibenzofuran was chosen as a model reaction to optimize the reaction conditions, and the results are listed in Table 1. Dibenzofuran could not be reduced by NaH in the absence of any base ( 3 ] or that of Et 3 SiH/ KO t Bu as the reaction system. More importantly, no byproduct was detected, indicating obvious advantages over the combination of triethylsilane with bases.…”

“…[1,2] Lignin is the second most abundant biomass in nature, and is an important natural resource of aromatics. [3][4][5] The 4-O-5 linkage (e.g., diaryl and aryl alkyl ethers) is a representative C-O linkage in lignin, and its catalytic cleavage is considered as an efficient way to depolymerize lignin for production of aromatics. [3,4,[6][7][8][9][10][11] Various metal catalysts such as Ni, [12][13][14][15] Ru, [16,17] Cu, [18][19][20][21] Pd/Zn, [22] V [23][24][25][26] and Fe, [27] have been reported for catalysing the cleavage of aryl C-O in lignin model compounds including diaryl ethers and aryl alkyl ethers via oxidation or hydrogenlysis.…”