Preparation of biodiesel from soybean oil catalyzed by Al-Ca hydrotalcite loaded with K2CO3 as heterogeneous solid base catalyst

•Al-Ca hydrotalcite/K2CO3 was prepared as a solid base catalyst.•The catalyst can be applied to the transesterification under mild conditions.•The catalyst shows high activity and can be easily recovered and regenerated.

A novel heterogeneous solid base catalyst was prepared with the support of Al-Ca hydrotalcite, the load of K2CO3 and successfully applied to the transesterification of soybean oil with methanol to biodiesel (fatty acid methyl esters). The prepared catalysts were characterized using Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometer, transmission electron microscopy, thermogravimetry analysis, differential scanning calorimetry and the Hammett indicator methods. The results indicated that K2CO3 loaded to Al-Ca hydrotalcite was decomposed into catalytic active compositions of K2O and Al–O–K. The effect of various parameters such as reaction temperature, amount of catalyst, reaction time and the amount of methanol on the catalytic active was investigated. The optimal reaction conditions were obtained by this experiment: a methanol/oil mole ratio of 13:1, a reaction temperature of 65 °C, a catalyst amount of 2.0 wt.% and a reaction time of 2.0 h. The catalyst has longer lifetime and biodiesel yield could be still over 87.4% after being used for four cycles.