Maximizing biodiesel production from waste cooking oil with lime-based zinc-doped CaO using response surface methodology

Biodiesel is one of the alternative fuels, commonly produced chemically from oil and methanol using a catalyst. This study aims to maximize biodiesel production from cheap and readily available sources of waste cooking oil (WCO) and lime-based Zinc-doped calcium oxide (Zn-CaO) catalyst prepared with a wet impregnation process. The Zn-CaO nanocatalyst was produced by adding 5% Zn into the calcinated limestone. The morphology, crystal size, and vibrational energies of CaO and Zn-CaO nanocatalysts were determined using SEM, XRD, and FT-IR spectroscopy techniques, respectively. The response surface methodology (RSM), which is based on the box-Behnken design, was used to optimize the key variables of the transesterification reaction. Results showed that when Zn was doped to lime-based CaO, the average crystalline size reduced from 21.14 to 12.51 nm, consequently, structural irregularity and surface area increased. The experimental parameters of methanol to oil molar ratio (14:1), catalyst loading (5% wt.), temperature (57.5 °C), and reaction time (120 min) led to the highest biodiesel conversion of 96.5%. The fuel characteristics of the generated biodiesel fulfilled the American (ASTM D6571) fuel standards. The study suggests the potential use of WCO and lime-based catalyst as efficient and low-cost raw materials for large-scale biodiesel production intended for versatile applications.