PHOTOCHEMICAL AND PHOTOCATALYTIC ESTERIFICATION OF WASTE COOKING OIL UNDER VISIBLE LIGHT IRRADIATION USING MECHANOCHEMICALLY SYNTHESIZED ZnO/SILICA

Abstract

Production of biodiesel from waste cooking oils via alkali catalyzed transesterification reaction is hampered by the unacceptably high amount of free fatty acids present in waste cooking oils. Therefore, catalytic esterification of waste cooking oil with small alcohols is performed before the transesterification reaction. Herein, ZnO/silica composite was synthesized via mechanochemical route and characterized using x-ray diffraction, x-ray fluorescence spectroscopy and scanning electron microscopy. Photochemical and photocatalytic esterification of free fatty acids in a sample of waste cooking oil with methanol was performed under visible light irradiation. The efficiency of photochemical esterification was found to be strongly dependent on the intensity of the light used. Significant increase in the efficiency of the photochemical esterification was observed when synthesized ZnO/silica composite was used as photocatalyst. The photocatalytic activity of the ZnO/silica composite visible light irradiation is attributed to the impurities present in silica support. Photocatalytic esterification using ZnO/silica composite is a promising method to reduce the FFA content of waste cooking oil under ambient conditions.