Transesterification of vegetable oil into biodiesel catalyzed by CaO: A review

Vegetable oil is one of the biomass resources generated from carbon dioxide and water with the aid of photosynthesis, and is converted into an alternative to fossil diesel fuel by transesterifying with methanol. The eco-friendly fuel, termed as “Biodiesel”, is manufactured with the help of alkali hydroxide, but its homogeneous catalysis gives rise to some technological problems: a massive amount of wastewater, soap formation and so on. Therefore, much interest has been taken in utilizing the heterogeneous catalysis of solid base for biodiesel production. Calcium oxide (CaO) is a candidate for the solid base catalyst from an economical point of view. In the present work, we reviewed CaO catalyst for the vegetable oil transesterification on the basis of a variety of the concerning research papers. After catalytic properties of the basic sites generated on CaO were described preliminarily, a mechanism on the vegetable oil transesterification catalyzed by CaO was explained. Then, procedure to prepare the active CaO catalyst, its deactivation occurring under the reacting condition and modification of CaO catalyst were discussed. Finally, the practical use of CaO catalyst for industrial biodiesel production was studied with pointing out the required future works.