Production of Diethyl Maleate via Oxidative Depolymerization of Organosolv Lignin from Wheat Stalk over the Cooperative Acidic Ionic Liquid Pair

Abstract

Lignin, the second largest component of biomass, is considered as an important alternative source of fossil reserves for the production of fuels and chemicals. Here, we developed a novel method to oxidatively degrade organosolv lignin into value-added four-carbon esters, particularly diethyl maleate (DEM), with the cooperative catalyst consisting of 1-(3-sulfobutyl) triethylammonium hydrogen sulfate ([BSTEA]HSO4) and 1-butyl-3-methylimidazolium ferric chloride ([BMIM]Fe2Cl7). Under optimized conditions (1.00 MPa initial O2 pressure, 160 °C, 5 h), the lignin aromatic ring was effectively cleaved by oxidation to form DEM with a yield of 15.85% and a selectivity of 44.25% in the presence of the synergistic catalyst of [BMIM]Fe2Cl7-[BSMIM]HSO4 (1/3, mol/mol). The structure and composition analysis of lignin residues and liquid products confirmed that the aromatic units in lignin were effectively and selectively oxidized. Furthermore, the catalytic oxidation of lignin model compounds was explored for obtaining a possible reaction pathway of oxidative cleavage of lignin aromatic units to DEM. This study provides a promising alternative method for the production of traditional petroleum-based chemicals.

Highly Efficient Conversion of Lignin into Diethyl Maleate Catalyzed by Molybdenum-Based Hybrid Catalysts

“…37 Recently, Zhao et al used the cooperative acidic ionic liquid pair of [BMIM]Fe 2 Cl 7 -[BSMIM]HSO 4 for cleaving the lignin aromatic ring to obtain DEM under 160 °C for 5 h, with a yield of 158.5 mg g −1 and 44.25% selectivity. 46 Compared with the above-mentioned results, the MoS 2 −MoC@NC 800 catalyst shows the highest yield of DEM (Table 1, entries 5−8). Both MoS 2 and α-MoC active sites in the MoS 2 −MoC@NC 800 catalyst can promote the cleavage of both C−O and C−C bonds in lignin, which contributes to such superior catalytic performance.…”

“…Meanwhile, the performances of other catalysts for depolymerization of lignin to DEM are listed in Table . ,, For example, Li and co-workers reported the polyoxometalate ionic liquid [BSmim]­CuPW 12 O 40 catalyst for oxidating lignin in air under 160 °C for 5 h, producing the yield of DEM with 404.8 mg g –1 . Later, they further synthesized hierarchical Ce–Cu/MFI nanosheets for lignin oxidation under 150 °C for 24 h, yielding 180.9 mg g –1 DEM with 61.5% selectivity .…”

“…Later, they further synthesized hierarchical Ce–Cu/MFI nanosheets for lignin oxidation under 150 °C for 24 h, yielding 180.9 mg g –1 DEM with 61.5% selectivity . Recently, Zhao et al used the cooperative acidic ionic liquid pair of [BMIM]­Fe 2 Cl 7 -[BSMIM]­HSO 4 for cleaving the lignin aromatic ring to obtain DEM under 160 °C for 5 h, with a yield of 158.5 mg g –1 and 44.25% selectivity . Compared with the above-mentioned results, the MoS 2 –MoC@NC 800 catalyst shows the highest yield of DEM (Table , entries 5–8).…”

Fabrication of S-Scheme g-C3N4/Zn4In2S7 Heterojunction Photocatalyst for Enhancing Selective Cleavage of β-O-4 Bond in Lignin Model Compounds and Lignin

“…Lignin is regarded as the most abundant sustainable aromatic biopolymer in nature and is promising in the production of aromatic oxygen-containing chemicals to replace traditional fossil resources. , In particular, lignin depolymerization to valuable chemicals has been plentifully studied in recent years. − Nevertheless, due to the complicated structure and recalcitrant characteristic of lignin, the valorization of lignin remains a challenge . One of the approaches in lignin valorization is C–O linkage breakage, especially the most abundant β-O-4 linkages constituting 43%–65% in native lignin .…”