Acid-catalyzed hydrolysis of conifer lignosulfonate in black liquor for the production of value-added chemicals

Commercial sodium lignosulfonate from conifer black liquor (RSL) was used in our study to investigate acid-catalyzed hydrolysis of lignosulfonate (LS) by inorganic acids in aqueous solution. Before the hydrolysis process, RSL was purified by alcohol-water solution. Combustion method and gel permeation chromatography (GPC) of the high performance liquid chromatography system (HPLC) were used to detect the purification efficiency. The results showed that methanol-water solution had better purification effect. In addition, for the purified RSL (PSL-M), 0.5 mol/L NaOH solution was chosen as the best dissolving medium through the comparison of aggregation behaviors of PSL-M in deionized water and various concentrations of NaOH solutions. In the following acid-catalyzed hydrolysis process, the experimental results proved that the three kinds of inorganic acids (HCl, H2SO4 and H3PO4) could catalytically hydrolyze PSL-M to lower molecular weight fractions and other organic chemicals, but HCl had the best efficiency. Moreover, in 0.5 mol/L NaOH solution, PSL-M (solid-liquid ratio, 50 g/L) catalytically hydrolyzed by 0.68 mol/L HCl at 50 °C for 10 min could produce 1.729 g/kg isovanillic acid, 0.088 g/kg vanillin, 0.007 g/kg syringaldehyde, 0.056 g/kg acetosyringone and 0.024 g/kg acetovanillone respectively.