Transesterification of waste frying oil using a zinc aluminate catalyst

The transesterification of waste frying oil (WFO) with methanol and ethanol was studied in a batch reactor using a zinc aluminate catalyst prepared by the combustion reaction method. The reaction runs were carried out for 2 hours, using alcohol:oil molar ratio of 40:1, temperature range of 60–200 °C, catalyst ratio of 1–10% wt., under 700 rpm stirring. The catalyst was characterized by XRD, EDX, TG, FTIR, N2 physisorption, NH3- and CO2-TPD. The catalyst showed a normal spinel structure and acid character (Lewis acid), in spite of the presence of both strong acid and base sites. Methyl and ethyl esters yields higher than 95% were obtained at 150 and 200 °C and the catalyst was recovered and reused in 3 reaction cycles, without significant loss of activity.