Transesterification of waste cooking oil to biodiesel using Ca and Zr mixed oxides as heterogeneous base catalysts

Heterogeneous solid catalysts comprising CaO and ZrO2 mixed oxides with various Ca-to-Zr molar ratios were synthesized by means of coprecipitation method. These synthesized mixed oxide catalysts were used for the transesterification of waste cooking oil (WCO) as feedstock with methanol to produce biodiesel fuel (BDF) at 65 °C and 1 atm. The influences of Ca-to-Zr molar ratio, catalyst loading, methanol-to-oil molar ratio, and the reaction time on the BDF yield were carefully investigated. In addition, the stability of prepared solid catalysts was studied. These catalysts were characterized by using techniques of X-ray diffraction, X-ray florescence, X-ray photoelectron spectroscopy, surface area measurement (BET method), and temperature-programmed desorption. Moreover, the obtained experimental results clearly indicate that the activity of synthesized catalysts increases with increasing the Ca-to-Zr molar ratio but the stability of the catalysts decreases as well. Under the appropriate transesterification conditions at 65 °C (i.e., catalyst loading = 10 wt.%, methanol-to-oil molar ratio = 30:1, and reaction time = 2 h), a BDF yield of 92.1% could be achieved over CaO-ZrO2 catalyst with a Ca-to-Zr molar ratio of 0.5. Furthermore, the obtained experimental results clearly indicate that synthesized catalysts can be used as recyclable, stable, and active catalysts for the production of BDF from WCO.

► We synthesized Ca and Zr mixed oxides for the production of biodiesel from WCO.
► We examine the effects of various parameters on the biodiesel yield.
► Appropriate amount of catalyst loading is 10 wt%.
► Solid catalyst with a Ca-to-Zr molar ratio of 0.5 is appropriate.