Fragmentation of Woody Lignocellulose into Primary Monolignols and Their Derivatives

Abstract

Lignin, which is biosynthesized through oxidative radical polymerization from primary monolignols during plant growth, represents the most abundant source of renewable aromatic resources. The search for efficient and selective catalysts for the production of monolignols and their corresponding unsaturated derivatives from the direct depolymerization of lignin is of great interest and importance, as such products are important platform chemicals for the synthesis of natural products, pharmaceuticals, and functional materials. We report herein the first case of a supported molybdenum catalyst that functions as an efficient and selective catalyst for the fragmentation of woody lignocelluloses, leading to monolignols and ethers in high yields with high selectivity. Hydrogenation of the side chain and recondensation were not observed, suggesting that etherification acts as a new stabilization mechanism in the current Mo catalytic system. The (hemi)­cellulose components were well preserved and amenable to valorization via enzymatic hydrolysis and chemocatalytic conversion. This method constitutes an economically responsible pathway for lignin valorization as well as fractionation and sequential utilization of all of the biomass components.

Unlocking Structure–Reactivity Relationships for Catalytic Hydrogenolysis of Lignin into Phenolic Monomers

“…Prolonging the reaction to 6 h led to decreased monomer yields (38.8 wt %). The results were in line with our previous reports …”

Total utilization of lignin and carbohydrates in Eucalyptus grandis: an integrated biorefinery strategy towards phenolics, levulinic acid, and furfural

“…Recently, the direct reductive catalytic fractionation (RCF) of lignocellulosic biomass was emerged as a new protocol for biomass fractionation and lignin depolymerization [15,19]. Such processes usually employed a heterogeneous catalyst based on ruthenium [20,21], palladium [22][23][24][25][26][27][28], nickel [29][30][31], copper [32], and molybdenum metals [33][34][35]. During RCF, protolignin in lignocellulose matrix was firstly depolymerized into phenolic monomers through the cleavage of C-O bonds in β-O-4 linkages [8,35].…”

“…Such processes usually employed a heterogeneous catalyst based on ruthenium [20,21], palladium [22][23][24][25][26][27][28], nickel [29][30][31], copper [32], and molybdenum metals [33][34][35]. During RCF, protolignin in lignocellulose matrix was firstly depolymerized into phenolic monomers through the cleavage of C-O bonds in β-O-4 linkages [8,35]. The selectivity-control of monophenols bearing different endchains at para position, such as propyl [22,36], propenyl [37], propanol [38], ethyl and allyl ether [34,35], has been realized by the choice of catalysts and/or additives [39].…”

“…During RCF, protolignin in lignocellulose matrix was firstly depolymerized into phenolic monomers through the cleavage of C-O bonds in β-O-4 linkages [8,35]. The selectivity-control of monophenols bearing different endchains at para position, such as propyl [22,36], propenyl [37], propanol [38], ethyl and allyl ether [34,35], has been realized by the choice of catalysts and/or additives [39]. The RCF process also left a solid fraction as a pulp containing cellulose and hemicellulose components with high retentions, which could be readily retrieved by filtration process.…”

“…Eucalyptus is considered as one of the fastest-growing sources of fiber, which is widely applied to artificial board, pulping, and paper-making industries owing to its wide adaptability and high photosynthesis. We recent reported the RCF of hardwood, softwood and herbaceous plants with Mo [33][34][35], Ni [30,31] and Pd [23] catalysts. These results encourage us to continually explore the transformation of all three biopolymers into monomeric chemicals based on RCF process.…”