Transesterification of Waste Frying Oils Using ZnAl2O4 as Heterogeneous Catalyst

Abstract

In this paper, biodiesel production from waste frying oils was investigated with zinc aluminate (ZnAl 2 O 4 ) as a heterogeneous catalyst, synthesised by the combustion of urea with aluminium nitrate and zinc nitrate. The transesterification was studied at temperatures between 60 and 200 °C, in an alcohol:oil molar ratio of 40:1, 2 h reaction time, stirring at 700 rpm and different catalyst amounts (from 1% to 10% based on oil weight). The biodiesel yield was analyzed in a gas chromatographer. Synthesised and recovered catalyst were characterized for their physical and textural properties. Thermogravimetric analysis (TGA) and Differential scanning calorimetry (DSC) have been used to study the thermal behavior of the zinc aluminate spinel. Powder X-ray diffraction (XRD) was used to determine the spinel-type structure, which was confirmed by Raman and Fourier Transform Infrared (FTIR) Spectroscopy. The particle and pore sizes were measured by transmission electron microscopy (TEM) and He pycnometry respectively. The specific surface area was determined by BET surface area analysis to be 17.3084 ± 0.0804 m 2 .g -1 , and the density 4,61 g.cm -3 . Residual glycerin and biodiesel were also observed in the recovered catalysts. Optimal yields above 95% were measured for both methylic and ethylic routes. Moreover, the same catalyst was utilized for three reaction cycles without significant loss of biodiesel yield at the best reaction conditions, which indicates the feasibility of the proposed method.