Transformation of waste cooking oil into biodiesel in a microwave reactor using nickel-loaded graphitic biochar catalyst

Abstract

This study focuses on the catalytic efficiency of synthesized metal-loaded graphitic biochar catalyst for one-step production of biodiesel from waste cooking oil (WCO). Biomass waste was a precursor for synthesizing nickel-loaded graphitic biochar (Ni-Ca-GBC). The artificial neural networks (ANN) modeling and response surface methodology (RSM) were applied to assess the reaction parameters and biodiesel conversion. The Box-Behnken Design (BBD) method was utilized to optimize reaction parameters for the transesterification reaction. The maximum fatty acid methyl esters (FAMEs) conversion was ca. 94.6 % at a catalyst loading of 6 wt.%, a reaction temperature of 80 °C, a methanol-oil molar ratio of 12:1, and a reaction time of 35 min. The maximum product yield was roughly 89.3 % using the same reaction parameters. Using optimized parameters of RSM, the maximum conversion (approximately 97.3 %) was achieved. Furthermore, Ni-Ca-GBC was compared with Ni-BC, Ni-Al-Fe-BC, and pristine biochar and showed maximum biodiesel conversion. The catalyst reusability was studied six times, and it was observed that the biodiesel conversion started to reduce after three times catalyst reuse. A comparative analysis of microwave (ca. 94.3 % conversion at 80 °C) and conventional heating (ca. 80.3 % at 80 °C) found that microwave heating was more efficient. ANN predictions appeared to be slightly more aligned with experimental results than RSM. Moreover, all the physicochemical properties of the biodiesel produced in this study were compatible with European norms (EN–14214) and American Society for Testing and Materials (ASTM D–6751) standards. This paper demonstrated the perspective of catalysts obtained from biomass to generate green fuels, which can help promote sustainable energy production.