Synthesis and characteristics of lignin-derived solid acid catalysts for microcrystalline cellulose hydrolysis

Three kinds of solid acid catalysts were prepared from alkali lignin in the waste liquor of pulping using carbonation- sulfonation method with different pretreatment. The lignin-derived solid acids (LDSAs) were characterized by FESEM, XRD, FTIR, TGA, BET and acid-base titration, respectively. A comparison study on the catalytic performance of LDSA prepared by different pretreatment method before carbonation in the hydrolysis of microcrystalline cellulose (MCC) was carried out. Results showed that the LDSA prepared by chemical activation with phosphoric acid (LPC-SO 3 H) exhibited superior catalytic activity due to its higher densities of -COOH group (1.68 mmol/g) as binding site and -SO 3 H group (0.88 mmol/g) as catalytic site as well as its larger specific surface area (488.4 m 2 /g) than those of the other two LDSAs. A total reducing sugar yield of 50.8% in MCC hydrolysis was obtained under the reaction conditions of temperature of 180 °C, time of 3 h, MCC concentration of 6 mg/mL and mass ratio of catalyst to MCC of 3.3 (w/w). Additionally, the value activation energy for hydrolysis of MCC to reducing sugars using LPC-SO 3 H was 83.31 kJ/mol, which was smaller than that using sulfuric acid.