Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel Full Length Article Transesterification of waste cooking oil for biodiesel production catalyzed by Zn substituted waste egg shell derived CaO nanocatalyst Manash Jyoti Borah a, ⁎ , Ankur Das a , Velentina Das a , Nilutpal Bhuyan b , Dhanapati Deka a a Biomass Conversion Laboratory, Department of Energy, Tezpur University, 784028, India b Biofuel Laboratory, Department of Energy, Tezpur University, India GRAPHICAL ABSTRACT ARTICLE INFO Keywords: Biodiesel Transesterification Nanocatalyst FAME Characterization ABSTRACT 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% Zn 2+ concentration in CaO) nano- catalysts 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 ( 1 H NMR) and Carbon Nuclear Magnetic Resonance ( 13 C NMR) techniques. These results suggest that Zn doped CaO nanocatalyst is a promising catalyst for biodiesel production. https://doi.org/10.1016/j.fuel.2019.01.060 Received 10 May 2018; Received in revised form 4 January 2019; Accepted 8 January 2019 ⁎ Corresponding author. E-mail address: manashjyoti90@gmail.com (M.J. Borah). Fuel 242 (2019) 345–354 0016-2361/ © 2019 Published by Elsevier Ltd. T