Activity of microporous lignin-derived carbon-based solid catalysts used in biodiesel production

Lignin is utilized as a carbon precursor to produce microporous lignin-derived carbon-based solid acid (MLC-S) ZnCl₂ activation and sulfonation with concentrated sulfuric acid. The effects of reaction conditions, namely the ratio of methanol to oleic acid, carbonization temperature, and catalyst dosage, on the efficiency of the esterification of oleic acid with methanol are investigated. As a carbon-based solid acid, the MLC-S offers high catalytic activity in the esterification, which is a crucial reaction in the synthesis of biodiesel. Compared with nonactivated lignin-derived carbon-based solid acid (LC-S), the highly porous structure of the MLC-S makes its active sites more accessible and ensures its excellent catalytic performance. Under the optimal conditions, the esterification of oleic acid with methanol reaches a conversion of 92.3%. Moreover, after recycling the MLC-S for five times, the extent of the esterification reaction is still as high as 72.9%. Obviously, the synthesized MLC-S has considerable potential for the esterification of oleic acid with methanol and thus for biodiesel production.