Synthesis of biodiesel from sunflower oil with silica-supported NaOH catalysts

BACKGROUND: A series of NaOH catalysts supported on commercial silica have been prepared by conventional incipient wetness impregnation and their activity tested in the reaction of transesterification of refined sunflower oil with methanol at 323 K and atmospheric pressure. The effects of the molar methanol/oil ratio, catalyst concentration, NaOH loading and calcination of the supported catalysts have been investigated. RESULTS: It has been found that the transesterification rate largely depends on the catalyst/methanol ratio and that calcination of the NaOH catalysts supported on silica, even at moderate temperatures, had a very negative effect on their activity. Selectivity, on the other hand, is more affected by the methanol/oil ratio. Selectivity for methyl esters (biodiesel) improved with the methanol/oil ratio due to an increased transesterification rate of diglycerides, whereas the selectivity for monoglycerides was not affected. CONCLUSION: The NaOH/silica catalysts suffered from a significant lack of chemical stability under reaction conditions as evidenced by measurements of sodium extracted during the reaction progress; therefore, their performance was affected by the presence of Na dissolved in the methanol phase. (c) 2008 Society of Chemical Industry.