Exoskeleton of a Mollusk (<i>Pila globosa</i>) As a Heterogeneous Catalyst for Synthesis of Biodiesel Using Used Frying Oil

Abstract

A heterogeneous catalyst has been derived from a waste material (i.e., exoskeleton of mollusk) for transesterification of a waste feedstock (i.e., used frying oil (UFO)) for synthesis of biodiesel. The exoskeleton of mollusk shell was crushed, ground, and calcined at 900 °C to derive CaO as a heterogeneous catalyst. The catalyst was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray fluorescence spectroscopy (XRF), and differential thermal analysis/thermogravimetric (DT/TG) analysis. The XRD peaks observed at 2θ = 31.80, 36.93, and 53.37° were characteristic of CaO and showed high crystallinity. The FTIR absorption bands of the calcined shell were observed at 1474, 870, and 502 cm–1, which are attributed to the vibration of CO32– molecules, and a sharp peak at 3640 cm–1 indicated the presence of OH– stretching due to Ca(OH)2. The XRF analysis demonstrated the Pila globosa shell to comprise 79.86% of calcium along with few minor elements (viz. Pd, I, Te, Sb, Sn, W, Al, Si, Sr, Cr, S). The (DT/TG) analysis showed the decomposition of calcium carbonate present in Pila globosa at 860 °C. The waste-driven substances (exoskeleton of mollusk as catalyst and UFO as feedstock) resulted in a high yield (92%) and conversion (97.8%) of biodiesel that was obtained at a 10:1 (methanol to oil) molar ratio, 4.0 wt % catalyst, at 60 ± 0.5 °C in 5 h reaction. The conversion of UFO to biodiesel was determined by 1H FT-NMR.