Preparation and Characterization of Biomass Carbon–Based Solid Acid Catalysts for the Esterification of Marine Algae for Biodiesel Production

Biomass carbon derived from rice husk (RH), Moringa oleifera seeds (MOR), and biomass of lipid extracted marine algae (BM) bearing sulfuric acid groups, were investigated for the potential application to environmental benign biodiesel production. The physiochemical characteristics of the biomass-derived catalysts were determined with Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and X-ray diffraction techniques. These studies confirmed the presence of sulfur-incorporated functional groups on the carbonaceous materials. The SO₃H-RH demonstrates the amorphous structure and higher surface area that enhances the possibility to attach –SO₃H group. The acid site density of the catalysts was measured by utilizing ion exchange titration. It was found that SO₃H-RH-based catalyst carries the most prominent acid site density (4.24 mmol/g by NaOH titration) when compared to other prepared solid acid catalysts. However, by employing SO₃H-RH and SO₃H-BM, almost full quantitative yield of ester was achieved with a 5 wt% mixture of catalyst/lipid for a reaction time of 20 min at a 5:1 M ratio of methyl alcohol/lipid extract. Whereas, they outperform the conventionally used sulfuric acid catalyst that gave 70% yield after 2 h under the same reaction condition. The results proved that the SO₃H-RH has highly porous carbon structure and greater surface area that prominently enhances the acid site density. Therefore, SO₃H-RH displays relatively better catalytic activity and stability when used compared to other solid acid and a sulfuric acid catalyst. The solid acid catalysts prepared from low-cost raw materials show enhance catalytic performance at room temperature and suitable for biodiesel production applications.