Activity of a Sulfonated Carbon-Based Catalyst Derived from Organosolv Lignin toward Esterification of Stearic Acid under Near-Critical Alcohol Conditions

[Image: see text] In this study, an environmentally benign carbon-based catalyst derived from extracted bagasse lignin (EL) was successfully synthesized by solvothermal carbonization and sulfonation with methane sulfonic acid (MSA). Interestingly, the results indicated that the use of MSA as a sulfonation agent made a catalyst with higher thermal stability than conventional sulfuric acid. Thus, in comparison to the catalyst prepared by using sulfuric acid, the catalyst prepared by using MSA (EL–MSA) exhibited higher catalytic activity in the esterification of stearic acid under near-critical methanol conditions. Under optimum conditions (260 °C for 5 min, a 9:1 methanol-to-stearic-acid molar ratio, 5 wt % catalyst loading, and 10% v/v toluene), the esterification over the EL–MSA catalyst promoted a 91.1% methyl stearate yield. Moreover, the results also revealed that the high thermal stability of the EL–MSA catalyst not only affects its great catalytic activity, but it also prevents damage to the porous structure and decomposition of acidic surface oxygen-containing functional groups. It contributes to the excellent reusability of the catalyst. After the fifth run, a high yield of 82.8% was obtained. The effect of alcohol type on the catalyst performance was also studied. It was found that the EL–MSA catalyst also presented good performance toward esterification with ethanol and propanol, from which ethyl stearate and propyl stearate with a more than 80% ester yield can be achieved.