Catalytic Esterification of Palm Fatty Acid Distillate into Biodiesel Over Sulfonated Iron Oxide Catalyst

Abstract

The palm fatty acid distillate (PFAD), as a low-cost feedstock, was catalytically esterified into biodiesel (also known as fatty acid methyl ester, FAME) using sulfonated iron oxide (HSO₃ˉ/Fe₂O₃) catalyst. In this work, the catalyst was synthesised via self-propagating combustion (SPC) method, towards a greener synthesis technique, followed by sulfonation with chlorosulfonic acid (HSO₃Cl) to enhance the catalyst’s acid properties. The catalysts were characterised and the success of sulfonation process was determined. From this study, Fe₂O₃ catalysts were proven to be pure and single-phase. The success of the sulfonation then was verified by the presence of sulfur, functional groups of S-O asymmetric vibration and S=O symmetric vibration, and increasing total acidity. Then, the sulfonated Fe₂O₃ catalyst was used to esterify the PFAD feedstock in methanol in which the esterification parameters were also optimized to obtain maximum free fatty acid (FFA) conversion. It was found that 15:1 of methanol-to-PFAD molar ratio, 4 wt.% of catalyst loading, 80 °C of reaction temperature and 5 h of reaction time produced 95.5% of FFA conversion. Interestingly, the sulfonated Fe₂O₃ catalyst can be considered as a superacid solid catalyst that enables boosting the esterification of the PFAD feedstock into biodiesel.