The factors influencing stability of Ca-Al mixed oxides as a possible catalyst for biodiesel production

The Ca-Al mixed oxides with a constant molar ratio of Ca/Al and different calcination conditions (temperature from 250 to 950 degrees C and flow - air or nitrogen) were synthetized from hydrocalumite as a precursor. The synthetized mixed oxides were tested in the transesterification of rapeseed oil including the determination of calcium leaching to the liquid products. The leaching was compared with the amount of calcium oxides in the catalyst. The minimum leaching was found for calcination in a flow of nitrogen and 650 degrees C. Moreover, it was found, that the leaching started when the conversion was high and when glycerol was formed. The stability of the catalyst in the reaction components such as oil, methanol, ester and glycerol was determined by diffractograms of the catalyst and by calcium in these components. The highest leaching of calcium was in glycerol and the amount was approximately the same as in transesterification, while in other components it was insignificant. According to the diffractograms (before and after leaching), the phase of mixed oxides was stable during transesterification and leaching was caused by the CaO contained in the catalyst. It was also found, that the significant factor influencing the leaching was water contained in the reaction components. (C) 2015 Elsevier B.V. All rights reserved.