Study on Mechanism of Action of Catalysts on Liquefaction of Bagasse Alkali Lignin

Abstract

Bagasse alkali lignin is the primary constituent of pulping black liquor. The phenolic products such as phenol, 2,6-dimethoxy-phenol and 2-methoxy-phenol were obtained by catalytic liquefaction from bagasse alkali lignin, with the aim of enhancing its use value. In the investigation, under optimal conditions, using SiO2-Al2O3 or FeS as catalyst, the phenols yield reached 54.10% and 55.18%, respectively. HPLC spectrum showed that the phenolic products of them were different. FT-IR and H-NMR spectrums showed that, using SiO2-Al2O3 as the catalyst, the α-O-4 and β-O-4 ether bonds and C-Cα bonds of lignin units were prone to break, forming 2,6-dimethoxy-phenol, 2-methoxy-phenol and phenol. While FeS action was more difficult, the α-O-4 and β-O-4 ether bonds and Cα-Cβ bonds of lignin units broke down. Then, the introduction of additional hydroxyl groups from glycols consequently increased the final product solubility. At the same time, Cα–C bond of the phenylpropane linkage was broken to produce phenolic chemicals. Third, part of the phenylpropane linkage was prone to break Cα–Cβ bond and structural rearrangement occurred. So the content of 2-methoxy-4-methyl-phenol and the total yield of phenols were high.