Acidolysis mechanism of lignin from bagasse during p-toluenesulfonic acid treatment

Lignin was efficiently separated from lignocellulosic biomass using p-toluenesulfonic acid (p-TsOH) treatment. However, lignin depolymerization and acidolysis have not been studied to date. In this study, the mechanism of lignin acidolysis was investigated. The structure of lignin in bagasse before and after the p-TsOH treatment was analyzed. The efficiency and selectivity of lignin depolymerization were evaluated. The lignin removal rate reached 88.81%. Hemicellulose was completely removed from lignin, and cellulose destruction was inhibited. The structure of lignin in bagasse was analyzed using nuclear magnetic resonance (NMR). The results revealed that alpha-methoxylated beta-O-4 intermediates were formed during lignin depolymerization. This indicated that the benzyl ether bonds were effectively catalyzed and broke, thereby promoting lignin dissolution. The lignin-carbohydrate complex structure was destroyed. The insoluble and soluble lignin in the hydrolysate were analyzed using NMR and gas chromatography-mass spectrometry. The results indicated that the catalyst promoted breaking of the C beta-O bonds in the beta-O-4 structures. Phenols and Hibbert ketones were formed. In addition, lignin sulfonation was confirmed by the presence of di-o-tolusulfone and di-p-tolusulfone. The low contents of beta-beta and beta-5 bonds in the reaction products indicated that lignin condensation was inhibited. The results demonstrated that lignin acidolysis was synergistically catalyzed by H+ and p-TsOH. It provides important theoretical support for efficient and clean separation of lignin using the p-TsOH treatment.