Transesterification of edible, non-edible and used cooking oils for biodiesel production using calcined layered double hydroxides as reusable base catalysts

Fatty acid methyl esters (FAME) were produced from edible, non-edible and used cooking oils with different fatty acid contents by transesterification with methanol using calcined layered double hydroxides (LDHs) as solid base catalysts. Among the catalysts, calcined CaAl2-LDH (hydrocalumite) showed the highest activity with >90% yield of FAME using low methanol:oil molar ratio (<6:1) at 65 °C in 5 h. The activity of the catalyst was attributed to its high basicity as supported by Hammett studies and CO2-TPD measurements. The catalyst was successfully reused in up to four cycles. Some of the properties such as density, viscosity, neutralization number and glycerol content of the obtained biodiesel matched well with the standard DIN values. It is concluded that a scalable heterogeneously catalyzed process for production of biodiesel in high yields from a wide variety of triglyceride oils including used oils is possible using optimized conditions.

► Ninety percent yield of fatty acid methyl esters with <6:1 methanol:oil molar ratio for various triglyceride oils.
► Calcination and reaction carried out in ambient atmosphere.
► Hammett and TPD studies indicated necessity of appropriate strength of basic sites.
► Successful scale up at 1 kg with good yield of FAME and glycerol with high purity.
► Catalyst is reusable and some properties of FAME matched with standard values.