For the purpose of studying manufacture of CaO catalyst for biodiesel production, a calcined limestone of commercial availability was ground in the presence of biodiesel and the resultant CaO-biodiesel mixture was employed for transesterification of vegetable oil with methanol. Biodiesel, which used as the grinding solvent, allowed surface oxide phase of CaO catalyst to be guarded against atmospheric CO2 and H2O, because the wet-grinding was much more effective in activating CaO catalyst than the atmospheric dry-grinding. Then, the wet-grinding was carried out with the industrial machines of media-agitating type for preparation of CaO catalyst consisting of fine particles. The prepared CaO catalyst was so fine that its average particle diameter reached 0.5 μm. The activity measuring tests provided data indicating that the transesterifying activity of CaO catalyst was enhanced by reducing its average particle diameter. Moreover, a small amount of water contained in biodiesel, which was used as the grinding solvent, seemed to enhances the transesterifying activity of CaO catalyst. Finally, we discussed a way to recycle CaO catalyst collected after the transesterification, for verifying that CaO catalyst consisting of fine particles is feasible for biodiesel production process.
