Ultrasound-assisted transesterification of tropical goat fat – Palm oil blend for biodiesel synthesis

[Display omitted] •Goat fat and palm oil mixture is proven as a promising raw material for biodiesel.•Ultrasound considerably speeds up transesterification of oil in biodiesel synthesis.•Catalyst loading, temperature, and methanol-to-oil molar ratio affect biodiesel yield.•Ultrasound-assisted transesterification obeys the pseudo-first order reaction.•A maximum biodiesel yield of 78.50 % with 98.69 % purity was obtained from goat fat. The increasing trend of global energy demand has encouraged the development of renewable energies, especially those derived from biomass and agricultural residues. This work aimed to study the effect of catalyst loading, temperature, and methanol-to-oil molar ratio on the yield and the reaction kinetics of ultrasound-assisted transesterification of tropical goat fats for biodiesel synthesis. Prior to trans-esterification, the oil extracted from the tropical goat fat was mixed with an equal volume of tropical palm oil to prevent its solidification tendency. To reduce the free fatty acids content of the mixed oil, it was esterified using a methanol-to-oil molar ratio of 9 employing 1 wt% sulfuric acid as the catalyst at 65 °C and 400 rpm agitation speed for 60 min. Then, the esterified oil was further subjected to an ultrasound-assisted transesterification system with sodium hydroxide catalyst for the reaction kinetics and biodiesel synthesis studies. The biodiesel properties were evaluated by both laboratory tests and BiodieselAnalyzer® software, which employs the fatty acid methyl ester composition obtained from GC–MS analysis. The highest conversion (78.50%) was achieved at 65 °C, 2.5 wt% of NaOH, and 8:1 methanol/oil blend molar ratio for 60 min. The pseudo-first order reaction fitted all the experimental data very well by giving the R2 values higher than 0.98 and an apparent reaction rate constant of 2.15×10−2 min−1 at the optimum condition. Furthermore, all the examined biodiesel physicochemical properties fulfilled the ASTM D6751 standard suggesting the promising potential of goat fats as the raw material for biodiesel manufacture.