Abstract
In this study, a highly active and reusable La3+/ZnO-TiO2 photocatalyst was prepared by sol–gel method. The production of biodiesel from waste cooking oil by a two-step method. In the first step, under the UV irradiation, La3+/ZnO-TiO2 photocatalytic esterification of ethanol with free fatty acids (FFA) in waste cooking oil (WCO) was studied. In the second step, NaOH catalyzed the transesterification of triglycerides with ethanol. La3+/ZnO-TiO2 photocatalysts were characterized by TG, XRD, SEM-EDS, HRTEM, BET, UV–vis spectroscopy and Raman spectra. The optimum conditions were obtained by orthogonal design. At 35 °C, the ethanol/oil molar ratio is 12:1, the catalyst dosage is 4 wt%, the UV irradiation time is 3 h, the reaction time is 3 h, and the conversion of FFA reaches 96.14%. After 5 cycles of experiments, the conversion rate of FFA is more than 87%, which indicates that the catalyst has stable activity and simple recovery. The reaction mechanism of photocatalytic esterification was proposed and the kinetics of esterification was studied. Through the analysis of the characteristics of biodiesel, it is proved that the biodiesel by the method mentioned in this study conforms to GB 25199-2017 and EN 14214 standards. Therefore, La3+/ZnO-TiO2 as a new photocatalyst opens up a new way for biodiesel production.
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