Abstract
Lignin was isolated from wheat straw via organosolv process and further transferred to monophenolic compounds via oxidative conversion. Wheat straw lignin (WSL) with purity at 91.4 wt% was acquired in the presence of heterogeneous and recyclable catalyst of Amberlyst‐45. WSL was characterized by infrared spectrometer (IR), nuclear magnetic resonance spectroscopy (NMR) including 1H NMR and 13C NMR spectra. The results showed that WSL possesses typical syringyl (S), guaiacyl (G), and p‐hydroxyphenyl (H) units, and it is mainly composed of S and G units. The product distribution was dependent on the composition of WSL. Derivatives from S and G units were found to be the main products. The oxidative conversion of WSL was performed by varying oxidant and catalyst. Both the formation of monophenolic compounds and aromatic aldehydes were enhanced by combining oxidants and catalysts. The composite catalyst composed of NaOH/NaAlO2 was effective for the oxidation of WSL in the presence of nitrobenzene and atmospheric pressure air. The total yield of monophenolic compounds reached up 18.1%, and yields at 6.3 and 5.7% for syringaldehyde and vanillin were achieved, respectively.
Highlights
Fossil fuels are being quickly consumed because of overexploitation resulted from a large increase in human population and industrial development
Methoxyl protons (–OCH3) produce a strong signal at 3.67 ppm. These results reveal that Wheat straw lignin (WSL) possesses typical G/S/H units with β–O–4 linkage
These results indicated that lignin obtained by organosolv fractionation is suitable to directly convert due to little difference in the yields of aromatic compounds derived from WSL and purified lignin
Summary
Fossil fuels are being quickly consumed because of overexploitation resulted from a large increase in human population and industrial development. The worldwide energy crisis and environmental impact have caused extensive research and development programs on the conversion of lignocellulose to produce chemicals and biofuels (Besson, Gallezot, & Pinel, 2014;Cheng et al, 2020;Nanda, Reddy, Vo, Sahoo, & Kozinski, 2018;Peng, Yao, Zhao, & Lercher&, 2012;Tsegaye, Balomajumder, & Roy, 2020). Lignin is the most important component in the support tissues of lignocellulose (Martone et al, 2009). It is the second most abundant natural plant material of biomass, accounting for nearly 30% of the organic carbon on Earth (Hage et al, 2009). The monolignols produce p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) units when they are
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