Sustainable valorization of waste cooking oil via low-temperature transesterification using BaO/ZnO nanocatalyst: Process optimization and mechanistic studies

Abstract

Biodiesel is widely regarded as a promising renewable energy source with minimal environmental impact. In our study, a novel catalyst, BaO/ZnO (BZO), was synthesized using wet-impregnation method and implemented in biodiesel production from waste cooking oil. The synthesized catalysts were physico-chemically characterized using different analytical techniques, including TGA, XRD, FTIR, BET, XPS, HR-SEM, and HR-TEM. NMR analysis was employed to quantify the synthesized biodiesel. Box-Behnken Design (BBD) model in the Response Surface Methodology (RSM) approach was implemented to optimize various reaction parameters involved in biodiesel production. The maximum biodiesel conversion of 97.3 % and yield of 97.1 % were obtained under optimized transesterification reaction conditions of 2.6 wt% catalyst loading at 39.9 ºC reaction temperature with a MeOH to oil molar ratio of 10.9:1 for the reaction time of 29.8 min. In addition, the synthesized BZO catalyst was recyclable up to five times, suggesting higher catalytic efficacy and stability throughout the reaction. The turnover frequency of the proposed catalyst was obtained to be 15.52 h-1. Kinetic and thermodynamic studies revealed that the obtained values of activation energy (Ea), enthalpy of activation (∆H#), and entropy of activation (∆S#) were 37.64 kJ mol-1, 35.76 kJ mol-1, and -150.73 J mol-1 K-1, respectively. Moreover, various fuel properties like kinematic viscosity, calorific value, flash point, pour point, and cloud point were consistent with ASTM D-6751 international standards. Green metrics study demonstrates that the overall biodiesel production process is sustainable and environmentally friendly.