Geopolymer catalysts derived from palm oil mill ash for biodiesel production from Calophyllum inophyllum oil

Chemical Engineering has a decisive role in a circular economy based on abundantly available waste materials. Renewable catalysts synthesized from abundant palm oil mill bottom ash (POBA) were applied in the biodiesel (methyl ester) production from Calophyllum inophyllum (CI) oil. Two different geopolymer materials, NaSil-geo and KSil-geo, were synthesized, characterized, and tested in converting CI into biodiesel. It was found that KSil-geo is highly effective in the transesterification process of CI with methanol to produce biodiesel. The fatty acid methyl ester (FAME) yield was obtained at 97% under the conditions reaction of 2% catalyst loading, methanol to oil molar ratio of 12:1, reaction temperature of 65 °C, and the transesterification reaction time of 120 min and stirring rate of 400 rpm. The properties of biodiesel produced in the form of cetane number, flash point, kinematic viscosity, density, and the fatty acid methyl ester content were obtained at 54.2, of 134 °C, 4.4 mm2/s, 878 kg/m3, 99.65%, respectively. The reusability tested of the catalyst verified that the synthesized catalyst could be reused up to 5 times. The physical and chemical properties of the biodiesel produced to meet the standard of biodiesel specifications ASTM D6751 and SNI 7182:2015.