Cacao shell-derived solid acid catalyst for esterification of oleic acid with methanol

Cacao shell-derived solid acid catalyst (CS-SAC) was successfully prepared by partial carbonization followed by sulfonation at various temperature (80, 100, 120 °C) and time (4, 6, 8 h) settings. The catalysts were analyzed for their acid densities and tested for their activity in the esterification of oleic acid with methanol at 45 °C for 4 h, with methanol to oleic acid molar ratio of 7:1 and a catalyst loading of 5 %w/w. It was found that increasing the sulfonation temperature at sulfonation times of 4 and 6 h increased the solid’s total acid density and sulfonic acid density thereby increasing its specific catalytic activity. Prolonging sulfonation time at any temperature, however, had no significant effect. The highest specific catalytic activity of 14.0 mmol FAME·g−1 CS-SAC·h−1, which corresponds to 79% conversion of oleic acid was observed for SAC sulfonated at 120 °C for 4–6 h. Prolonged esterification up to 24 h resulted in high conversion of ∼94% even at a low temperature of 45 °C. Although the catalyst was later found to decrease in its activity during reuse, its catalytic activity remained stable after the 3rd cycle at a conversion of 48% of the oleic acid.