Preparation of sulfated carbon derived from rapeseed meal for highly active and stable biodiesel production

Biodiesel, an important renewable fuel, has greatly relieved the environmental pollution and the energy crisis. Herein, a sulfated biochar solid acid (RM@PAC-SO3CF3) derived from waste rapeseed meal in oil processing was obtained via KOH assisted carbonization, followed by sulfonation through a mild and clean quaternization of 1,3-propanesultone with self-doped nitrogen in carbon. The sulfonated carbon was subsequently served as an effective catalyst to promote the conversion of oleic acid to biodiesel. The catalyst had plentiful strongly acidic sulfonic groups of 0.64 mmol/g and super-high specific surface area of 1852 m2/g with porous structure. Accordingly, it showed a satisfactory catalytic efficiency of 95.6 % conversion under relatively mild conditions of 70 °C for 4 h, which was superior to sulfonated carbon prepared by conventional concentrated sulfuric acid sulfonation. Especially, the activation energy (Ea) in esterification reaction over RM@PAC-SO3CF3 was 30.17 kJ/mol, which was lower than that of most other sulfonated carbons. More importantly, the leaching and recyclability experiments proved its favorable stability and reusability owing to the stable bonding of sulfonic groups onto carbon framework, with only a mild decline in oleic acid conversion rate from 95 % to 90 % after five consecutive runs, revealing its great potential in biodiesel production.