Biodiesel production from crude palm oil using sulfonic acid-modified mesostructured catalysts

Biodiesel production from crude palm oil containing high percentage of free fatty acids over sulfonic acid-functionalized SBA-15 materials (propyl-SO3H, arene-SO3H, perfluoro-SO3H) has been studied. The catalytic results showed that sulfonic acid-modified mesostructured materials were more active than conventional ion-exchange sulfonic resins (Amberlyst-36 and SAC-13) in the simultaneous esterification of free fatty acids and transesterification of triglycerides with methanol. The reusability of the catalysts was also investigated showing high stability for propyl-SO3H and arene-SO3H-modified mesostructured materials. In contrast, ionic-exchange sulfonic acid resins displayed low-conversion rates, being stronger this decay of activity in the second consecutive catalytic run. Interestingly, perfluorosulfonic acid-functionalized SBA-15 sample yielded a dramatic loss of activity indicating that Si–O–C bonding is not stable under the reaction conditions as compared with Si–C bond present in propyl-SO3H and arene-SO3H catalysts. Further functionalization of arene-SO3H SBA-15 catalyst with hydrophobic trimethylsilyl groups enhanced its catalytic performance. This material was able to produce a yield to FAME of ca. 95% as determined by 1H NMR in 4 h of reaction with a moderate methanol to oil molar ratio (20:1), 140 °C and a catalyst concentration of 6 wt.% referred to starting oil.