Esterification efficiency improvement of carbon-based solid acid catalysts induced by biomass pretreatments: Intrinsic mechanism

Effect of various reagents (i.e. H 2 O 2 , H 2 SO 4 , H 3 PO 4 and their mixtures) pretreatments on esterification activities of carbon-based solid acid catalysts synthesised by one-step sulphonation (150 °C for 4 h) was investigated. The results demonstrated that sulphonic acid density of catalyst positively correlated with the esterification efficiency and the high lignin content of the biomass stimulated the loading of sulphonic acid groups. The bamboo powder pretreated with 1% H 2 SO 4 yielded the highest lignin content (from 26.4% to 33.0%). The corresponding catalyst yielded the highest esterification efficiency (97.3%), which decreased to 82.9% after four cycles. On the other hand, the bamboo powder pretreated by H 2 O 2 and 30% H 3 PO 4 brought little effect on the increment of lignin content and esterification efficiency of the catalysts. Therefore, biomass pretreatment could be a solution of disposal acidic wastewater (like catalyst sulphonation wastewater) by reusing it as pretreatment reagents and improving the esterification efficiency of the catalysts.