Boosted biodiesel production from castor oil via zinc-doped lime catalyst using a Taguchi design approach

Abstract

This study aims to optimize biodiesel production from non-edible castor oil using a zinc-doped lime-based calcium oxide (Zn-CaO) catalyst, synthesized via wet impregnation. The properties of the synthesized Zn-CaO nanocatalyst, including morphology, crystal size, and vibrational energies, were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier-transform infrared (FT-IR) spectroscopy, yielding favorable results. Various transesterification parameters were optimized using a Taguchi-based approach: temperature (55–65 °C), methanol-to-oil ratio (7.53–15.07), and catalyst loading (1–5% w/w). XRD and SEM analysis confirmed that calcining limestone at 900 °C produced nanocrystalline Zn-CaO. Adding 5% Zn (w/w) reduced the crystallite size from 16.84 nm to 9.75 nm, increased surface area and catalytic activity, and thereby improved biodiesel production efficiency. The study demonstrated that the 5% (w/w) Zn-doped CaO nano-catalyst achieved the highest fatty acid methyl ester (FAME) conversion of 95.21% under optimized conditions, which included a methanol-to-oil molar ratio of 15:1, a reaction temperature of 55 °C, a catalyst loading of 5% by weight, and a reaction time of 120 min. The method was tested at a pilot scale and showed repeatability. The produced biodiesel meets ASTM D6571 standards. This study demonstrates the potential of lime-based nanocatalysts as a cost-effective material for converting castor oil into biodiesel, thereby contributing to sustainable energy solutions.