The Roles of H2O/Tetrahydrofuran System in Lignocellulose Valorization

Abstract

Lignocellulosic biomass as a potential alternative to fossil resource for the production of valuable chemicals and fuels has attracted substantial attention, while reducing the recalcitrance of lignocellulosic biomass is still challenging due to the complex and cross-linking structure of biomass. Solvent system plays important roles in the pretreatment of lignocellulose, enabling the transformation of solid biomass to liquid fluid with better mass and heat transfer, as well as in the selective formation of target products. In particular, H 2 O/tetrahydrofuran (H 2 O/THF) system has recently been widely applied in lignocellulose valorization, which has been proved to exhibit outstanding efficiency for the conversion of lignocellulose, solubilization of the intermediates and products, and shifting reaction equilibrium, thereby significantly improving the yield and selectivity of target products, as well as the full utilization of lignocellulose. In addition, THF shows low toxicity, and is known as a renewable solvent which can be produced from bio-derived chemicals. Herein, this review concentrates on the advances of H 2 O/THF system in lignocellulose valorization in recent years. Several aspects relative to the roles of H 2 O/THF system are discussed as follows: the pretreatment of lignin, conversion of hemicellulose and cellulose components in lignocelluloses, and the promoting formation of valuable chemicals like furfural, 5-hydroxymethyl furfural (HMF), levulinic acid, and so on, as well as the inhibiting role in humins formation. This review might provide useful information for the design of effective solvent system in full utilization of lignocellulosic biomass.

Recent advances in the valorization of plant biomass

“…In CELF, a high temperature (>150 °C) is still needed to remain outside the known miscibility gap (71.8 °C to 137.1 °C) [ 89 ] of the THF(tetrahydrofuran)/H 2 O mixture. Generally, approximately 85–90% lignin from plant biomass can be solubilized and fractionated, because the molecular weight of lignin is dramatically reduced and the cross-condensation reaction is also minimized under THF/H 2 O mixture treatment [ 90 ]. The nearly pure lignin product without sugar and ash can be precipitated after THF solvent evaporation, which is a potential feedstock for promoting the hydrolysis of cellulose [ 91 ].…”

Efficient pretreatment using dimethyl isosorbide as a biobased solvent for potential complete biomass valorization

“…In addition, H2O was revealed to be a nucleophile agent to break the linkages between lignin and hemicellulose (e.g., hydrogen bonds, ether and ester bonds) owing to its higher hydrogen bond acceptor ability compared to THF. 37 For pretreatment using DMI/H2O at lower ratio e.g., 4:1, decreased lignin removal efficiency was observed which was echoed by findings for THF/H2O 37 and GVL/H2O 38 co-solvent systems. This is probably due to the reduced cleavage activity of sulfuric acid and the decreased dissolving ability of solvent due to the presence of water at a higher percentage.…”

“…Similar phenomena were reported for deep eutectic solvent (DES) and THF. 36,37 H2O in these cosolvents (e.g., THF/H2O) is considered as an efficient plasticizer favoring organic solvent diffusion into the compact lignin complexes, leading to the solubilization of lignin in solvent-water mixture.…”

“…For example, MeTHF, EAC and GVL dissolved S-and G-type lignin, while THF solvent showed high selectivity to fractionate and solubilize lignin with G and H units. 37 Table 1. Semi-quantitative information for subunits and interunit linkage in lignin before and after DMI/H2O co-solvent pretreatment.…”

Conversion of Cellulose Into 5-Hydroxymethylfurfural (HMF) In a H2O/Tetrahydrofuran/Cyclohexane Biphasic System With Al2(SO4)3 As Catalyst

“…Especially, the H 2 O-THF consisted biphasic system is frequently employed as reaction media for conversion of cellulose with impressive HMF yields (Cao et al, 2019;Jing et al, 2018;Shen et al, 2020;Shi et al, 2013;Yang et al, 2012). Compared with other O-contained organic solvents, the boiling point of THF was only 66 ℃, so THF could be easily separated with products for recycling (Li et al, 2020). Besides, THF can be synthesized from biomass-based derivatives, such as furfural and 1,4-butanediol (Lange & Wadman, 2020), thus is a promising renewable and green solvent.…”