Surfactant-enhanced ZnOx/CaO catalytic activity for ultrasound-assisted biodiesel production from waste cooking oil

Abstract

The production of biodiesel from waste cooking oil (WCO) is very important for improvement of the environment and reduction of fossil fuel-based energy consumption. In this work, ZnO_x/CaO non-homogeneous catalysts were synthesized through a urea-precipitation calcination method for the transesterification of WCO as feedstock. The optimal Zn : Ca mass ratio was 0.2. The effect of the morphological structure of the catalyst to the biodiesel yield was investigated using different levels of surfactants. The crystalline shape, microstructure and elemental state of catalysts were investigated using XRD analysis, SEM and XPS. Ultrasonication was used to accelerate transesterification reactions. The highest biodiesel yield (97.6%) was achieved under an alcohol : oil molar ratio of 12 : 1, 2 wt% of catalyst loading, temperature of 65 °C, reaction duration of 40 min, 130 W of ultrasonic power and ultrasonic pulse mode of 5 s on and 1 s off. The synthesized biodiesel was analyzed further using spectroscopy (FT-IR and ¹H-NMR). Cycling experiments of catalysts and XRD analysis of used catalysts demonstrated the excellent stability of the polyvinylpyrrolidone-critic acid-treated ZnO_0.2/CaO catalysts. This study can provide guidance for the construction of high-performance non-homogeneous catalysts for biodiesel production. This strategy could have a beneficial impact on the environmentally friendly production of biodiesels and control of environmental pollution.