Synthesis of biodiesel with heterogeneous NaOH/alumina catalysts: Comparison with homogeneous NaOH

The activity and selectivity of a series of NaOH catalysts supported on alumina for the transesterification with methanol of refined sunflower oil have been investigated. The performance of the supported catalysts has been compared with that of homogeneous NaOH. The influence of the molar methanol/oil and catalyst/methanol ratios and of the NaOH loading of the supported catalysts has been considered. The results have shown that the transesterification rate largely depends on the catalyst/methanol ratio, whereas the reaction selectivity seems to be governed by the methanol/oil molar ratio. Calcination of the NaOH/γ-Al2O3 catalysts had a negative effect on their activity. On the other hand, the performance of the NaOH/alumina catalysts just dried at 393 K was not far of that of homogeneous NaOH. Measurements of sodium leached during the progress of the transesterification reactions have evidenced some lack of chemical stability of the supported NaOH catalysts under reaction conditions. Therefore, progress should be made to prepare more stable catalysts based on supported NaOH for this application.