Transesterification of waste cooking oil for biodiesel production catalyzed by Zn substituted waste egg shell derived CaO nanocatalyst

[Display omitted] •Zn doped CaO nanocatalyst was employed in the transesterification of waste cooking oil to biodiesel.•Various reaction parameters were optimized following Response Surface Methodology (RSM) based on Box-Behnken design (BBD).•Maximum biodiesel conversion of 96.74% was recorded under the optimized reaction condition.•The synthesized catalyst not only exhibits a favorable catalytic performance but also has perfect reusability.•The fuel properties of the produced biodiesel were in agreement with the ASTM standards. This research paper deals with the synthesis of efficient and low cost heterogeneous catalyst from waste egg shells by wet impregnation method. A series of Zn doped CaO (0.5–2 wt% Zn2+ concentration in CaO) nanocatalysts were prepared and employed in the transesterification of waste cooking oil. Synthesized catalysts were characterized by powder X-ray Diffraction (XRD), Fourier Transform-Infrared (FTIR), Scanning Electron Microscopy (SEM), Energy dispersive X-ray (EDX), and Transmission Electron Microscopy (TEM) analysis. Various reaction parameters such as Zn doping, catalyst loading, methanol: oil molar ratio and reaction time were optimized following Response Surface Methodology (RSM) based on Box-Behnken design (BBD). Maximum biodiesel conversion of 96.74% was recorded under the reaction conditions of 20:1 methanol to oil molar ratio, 5 wt% catalyst loading, 65 °C reaction temperature and 4 h of reaction time. The confirmation for biodiesel synthesis was performed using Proton Nuclear Magnetic Resonance (1H NMR) and Carbon Nuclear Magnetic Resonance (13C NMR) techniques. These results suggest that Zn doped CaO nanocatalyst is a promising catalyst for biodiesel production.