Transesterification of Low-Quality Triglycerides over a Zn/CaO Heterogeneous Catalyst: Kinetics and Reusability Studies

Abstract

Zinc-doped (0.25–7 wt %) calcium oxide (Zn/CaO) has been prepared in nanocrystalline form by a simple wet chemical method followed by calcination up to 950 °C. The structural analysis has been investigated by powder X-ray diffraction (XRD), whereas the surface morphology and average particle size of Zn/CaO were determined by scanning electron and transmission electron microscopic studies, respectively. The catalytic activity of the prepared Zn/CaO toward the transesterification of cotton seed oil with methanol was found to be a function of its calcination temperature, crystallite size, and basic strength. A pseudo-first-order kinetic model was applied to evaluate the kinetic parameters for the transesterification of waste cotton seed oil with methanol, and a first-order rate constant (<i>k</i>) and activation energy (<i>E</i>_a) were found to be 0.10 min^–1 and 43 kJ mol^–1, respectively. The catalyst, Zn/CaO, was amenable to recovery and recycling for at least five consecutive reaction cycles. The Koros–Nowak criterion test has been employed to demonstrate that measured catalytic activity was independent of the influence of transport phenomenon. Further, Zn/CaO was also found as an efficient catalyst for the complete transesterification of a variety of triglycerides (having up to 8.4 wt % free fatty acids), such as virgin cotton seed oil, soybean oil, waste cotton seed oil, castor oil, karanja oil, jatropha oil, and mutton fat. Thus, the present work demonstrates the application of high free fatty acid containing waste or non-edible oils as feedstock, without any pre-treatment, for biodiesel production