Synthesis of sulfonated carbon-based catalysts from organosolv lignin and methanesulfonic acid: Its activity toward esterification of stearic acid

This work aims to offer a new acid type, methanesulfonic acid, to produce environmentally benign sulfonated carbon-based catalysts for esterification. The sulfonated catalysts were synthesized using two types of lignin sources, commercial lignin (CL) and lignin extracted from sugarcane bagasse (EL) through solvothermal carbonization and followed by sulfonation step. Overall, lignin sources and types of sulfonic acids were the factors affecting the catalyst performance. The results indicated that the high oxygenated functional groups on surface of chars prepared from EL gave the materials with better catalytic performance than prepared from CL. Moreover, the catalysts functionalized with methanesulfonic acid presented the higher catalytic activity than with sulfuric acid due to their higher surface area and better thermal stability. The highest methyl stearate yield (89.2%) from esterification of stearic acid with methanol were achieved at 240 °C with the reaction time of 10 min using the molar ratio of stearic acid to methanol of 1:9 and catalyst loading of 5 wt% in case of using EL char as a carbon source and methanesulfonic acid as a sulfonating agent. The catalyst could also be reused up to seven cycles with a yield higher than 80%.