Transesterification of palm oil to biodiesel using rice husk ash-based catalysts

•Novel heterogeneous rice rusk ash-based catalysts were developed.•The optimum catalyst is 30% RHA800-800.•Maximum biodiesel yield of 91.5% is achieved using the novel catalyst.•The novel catalyst can achieve a desirable recyclability.

In the present study, rice husk ash (RHA, a solid waste from agriculture) was served as the support for loading calcined eggshell (another material derived from waste source) to prepare solid base catalyst. This catalyst was then applied for catalytically converting palm oil into biodiesel. The effects of catalyst preparation conditions (such as rice husk treatment temperature, the loading of calcined eggshell on the RHA, and the calcination temperature of eggshell-loaded RHA), reaction conditions (such as reaction time, methanol-to-oil molar ratio and catalyst loading) and the catalyst reusability were carefully studied. The experimental results revealed that 30% RHA800-800 exhibited the highest catalytic activity. More specifically, when the reaction was carried out with a reaction time of 4 h, methanol-to-oil molar ratio of 9:1, and catalyst loading of 7 wt.%, the biodiesel yield could reach 91.5%. Besides, after reused for more than 8 cycles, the catalyst could still possess a rather high biodiesel yield (above 80%).