Catalytic properties of spinel-type mixed oxides in transesterification of vegetable oils

• Spinel-type mixed oxides are active in transesterification of vegetable oil.
• “Zn” containing spinels are more active compared to other spinel-type compounds.
• ZnFe2O4 is active in transesterification for non-edible oils also.
• ZnFe2O4 is reusable and suitable for use in fixed-bed reactor.

Crystalline mixed oxides of AB2O4 composition, where A = Co, Ni, Cu and Zn and B = Al, Fe and Co, were prepared by co-precipitation of hydroxides and calcination at 873 K. The catalytic activity of these materials in the transesterification of sunflower oil with methanol to produce fatty acid mono esters (FAME; biodiesel) was investigated. The transesterification activity was found to depend on element A, the order of activity being: Zn > Cu > Ni > Co. The Zn containing spinels were more active than the others and their activity was found to go through a maximum with Sanderson's intermediate electronegativity. Detailed investigations carried out on ZnFe2O4 revealed it to be a suitable solid catalyst for the transesterification of used cooking oil and Jatropha oil. The catalyst was reusable many times. The performance of this spinel was also investigated in a bench-scale (30 g catalyst loading) fixed-bed reactor.

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