Leaching and reusing analysis of calcium–zinc mixed oxides as heterogeneous catalysts in the biodiesel production from refined palm oil

Abstract

The scarcity of fossil oils in medium and long term has led to propose different alternatives to replace it, and this is the reason why biodiesel has been proposed as a suitable replacement of conventional diesel oil. One of the most widely inquired heterogeneous catalysts in biodiesel production is calcium oxide (CaO) due to some advantages such as low price and high activity. Unfortunately, this compound is leached by methanol, and in this case, compounds such as CaO and ZnO have been suggested as an alternative to avoid this unwanted phenomenon. According to this, in the current work mixed oxides of calcium–zinc catalysts were synthesized using the co-precipitation method, and later, they were characterized and their behaviors were studied identifying transesterification yields and catalysts life cycle varying some of its operational conditions. Methanol/oil ratio over catalyst amount and Zn/Ca atomic ratio were identified as the main factors that affect the transesterification reaction yield. The maximum yield was 86.99%, obtained with 7.5 wt% catalyst, Zn/Ca atomic ratio of 3.0, methanol/oil molar ratio of 30:1 and a reaction time of 2 h at 56.9 °C. To test its reactivation capacity, a reactivated catalyst with the best behavior was used again obtaining a yield of 83.87% which indicates an insignificant decrease in its catalytic activity. However, the leaching process was detected which does not allow a decrease in purification costs due to residual calcium oxide.