Biodiesel production by transesterification of low-cost feedstock (waste cooking oil) using mesoporous cubic-MgO nanocatalyst: Optimization using response surface methodology

Abstract

Non-toxic nanoscale metal oxide structures are emerging as potential material in energy and environmental applications because of their enhanced and controllable properties. In this research work, MgO nanoparticles were synthesized by sol–gel method. The calcination temperature and time was optimized at 600°C, 2 hours. The obtained mesoporous MgO nanoparticles (size 15 nm) had a band gap of approximately 3.3 eV. MgO nanoparticles shows a zeta potential value of 17.3 mV, which is considered to be incipiently stable. Biodiesel production was carried out using cubic MgO nanoparticles. Response surface methodology (RSM) and one factor method was employed for the optimization of operating variables. RSM predicts 90% of biodiesel yield at optimal 1% (w/w) of catalyst, 16:1 methanol to oil molar ratio, 65°C of reaction temperature in 42 minutes which is also verified experimentally (89.5%). Biodiesel yield of approximately 92% is obtained using one factor method at higher reaction time of 2 hours, reaction temperature of 60°C with 12:1 methanol to oil molar ratio and 2% (w/w) of catalyst. The hexadecanoic acid, stearic acid, linoleic acid and oleic acid in the waste cooking oil gets transformed into hexadecanoic acid methyl ester, methyl stearate, 9,12-octadecadienoic acid methyl ester and 9-octadecenoic acid methyl ester during transesterification which is inferred from GC–MS spectrum. Transesterification reaction follows pseudo-first-order kinetics. MgO nanocatalyst when reused in the transesterification shows a yield of approximately 90% up to four cycles.