Tailored magnetic nano-alumina as an efficient catalyst for transesterification of waste cooking oil: Optimization of biodiesel production using response surface methodology

Abstract

In this study, an optimized method was presented for the preparation of Fe3O4@Al2O3 as an efficient nanocatalyst for waste cooking oil transesterification to biodiesel. The highest oil conversion was achieved using the catalyst with the Al2O3/Fe3O4 mass ratio of 0.5. It was characterized by XRD, SEM, TEM, DLS, FTIR, TPD, and VSM analysis. The XRD pattern was in agreement with the standard XRD pattern of cubic Fe3O4. The DLS analysis showed that the mean particle size of catalyst was around 193 nm. Temperature programmed desorption (TPD) of NH3 showed a broad peak at the temperature range of 400–450 °C, confirming the acidic sites on the surface of the catalyst. The VSM analysis confirmed that the catalyst saturation magnetization was high enough to be separated easily with a magnet. Response surface methodology was used to study the effects of time, temperature, and methanol/oil molar (M/O) ratio and their interactions on the oil conversion. According to the analysis of variance (ANOVA), the effect of time and temperature was much more significant than that of M/O ratio. In addition, the interaction between time and temperature was more significant than the other interactions. The transesterification kinetics was investigated, and the results showed the rate constants ranging from 0.001 to 0.157 min−1 and the activation energy of 55.48 kJ mol−1. Thermodynamic studies demonstrated that the nature of the reaction was nonspontaneous (ΔG = 93.80 kJ mol−1 at 373 K) and endergonic (ΔH = 54.08 kJ mol−1). The recovery of the catalyst was successfully performed at 400 °C, and the performance of the catalyst was acceptable after four cycles of recovery.