A comparative study on the catalytic performances of alkali metals-loaded KAlSiO4 for biodiesel production from sesame oil

Abstract

Orthorhombic phase KAlSiO4 and the alkali metals-impregnated samples were examined as the heterogeneous catalysts for transesterification of sesame oil to biodiesel. According to the structural and compositional characterization using XRD, FT-IR and EDX techniques, the products had the aluminosilicate frameworks containing a random network of tetrahedral Al and Si units charge-balanced with alkali metal ions that could act as the strongly basic active sites. The BET, SEM, and TEM analyses, and surface basicity determination indicated that the as-made microstructures were of type II, typical of mesoporous materials which supply many sites for fully contacting of triglyceride and methanol to develop their catalytic activity. The performances of catalysts for the transesterification of sesame oil were investigated and compared under optimum conditions: carbonate loading of 50 wt%; methanol to sesame oil molar ratio, 6:1; catalyst amount of 5 wt% (relative to the weight of sesame oil); reaction temperature, 75 ◦C and reaction time, 3 h. The composition of FAMEs was also successfully determined using gas chromatography–mass spectrometry (GC–MS) where peaks corresponded to fatty acid methyl esters of sesame oil. The results demonstrated that the catalytic activity of KAlSiO4 was remarkably increased, 21.6%–97.6%, with alkali metal impregnation method in the order of Li > K > Rb > Na > Cs. It seems that the small size of lithium ion causes its excellent interaction with KAlSiO4, more easily insertion in the framework and good dispersion on the support surface resulted in reasonably high activity in transesterification reaction.