Fabrication of hollow cage-like CaO catalyst for the enhanced biodiesel production via transesterification of soybean oil and methanol

Abstract Designing a cost-effective and environmentally-friendly heterogeneous catalyst for biodiesel production is an essential yet a challenging aspect for renewable energy applications. To achieve this, a newly fabricated hollow cage-like CaO catalyst (CaO-700N) was prepared by the pyrolysis of hollow CaCO3 under precisely controlled calcination temperature (700 °C) and N2 atmosphere. The prepared catalyst was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, temperature programmed desorption of CO2 and N2-adsorption/desorption. The newly fabricated CaO catalyst exhibited porous hollow cage-like structure, high basic strength and density, leading to high catalytic activity for the production of biodiesel via the transesterification of soybean oil with methanol. A biodiesel yield of 97.80 % was attained under the optimal reaction conditions of 3 wt% catalyst concentration, 15:1 methanol/oil molar ratio, 65 °C reaction temperature and reaction time of 2 h. The catalyst remained highly stable and maintained biodiesel yield of above 90.30 % after the fifth reuse. Based on the characterization and activity results, a suitable reaction mechanism for the catalytic conversion of soybean oil to biodiesel using hollow cage-like CaO catalyst was proposed. Moreover, the scaling up of transesterification with the synthetic biodiesel production of over 95.69 % for 4 h was reported. The physiochemical properties of synthetic biodiesel were in accord with the biodiesel standards. Attributed to the intriguing properties like cost-effectiveness, ease of synthesis and environmental greenness, the hollow cage-like CaO catalyst could be considered as a potential candidate for the production of biodiesel on industrial level application.