Abstract:
In this work, several transition metal-based acetylacetonates (Ni, Cu, and Fe) were prepared as oil-dispersed catalysts for heavy oil oxidation. X-ray diffraction (XRD), scanning electron microscopy (SEM), and Mössbauer spectroscopy were used for the characterization of catalysts. The effectivity of catalysts in the oxidation of heavy oil was investigated by a thermogravimetry method coupled with infrared spectroscopy (TG-FTIR) at four different heating rates (4, 6, 8, and 10 °C/min) and self-designed porous medium thermo-effect cell (PMTEC) techniques. The activation energy calculations using three isoconversional methods, Ozawa–Flynn–Wall (OFW), Kissinger–Akahira–Sunose (KAS), and Friedman, were performed based on thermal analysis data. The results showed that the bidentate ligand acetylacetonate (acac) provided good enough distribution of catalysts in heavy oil because in the presence of Cu(acac)2, Fe(acac)3, and Ni(acac)2, the oxidation temperature decreased in both fuel deposition (FD) and high-temperature oxidation (HTO). The activation energy of FD and HTO districts showed that Cu(acac)2 more efficiently catalyzed the oxidation of heavy oil than Fe(acac)3 and Ni(acac)2. The usage of Cu(acac)2 helped decrease the average activation energy of the in situ combustion process from 177 to 117 kJ/mol, from 187 to 127 kJ/mol, and from 198 to 128 kJ/mol based on OFW, KAS, and Friedman methods, respectively. The in situ transformation of the catalysts in the presence of heavy oil was studied under different isothermal conditions. Based on XRD and SEM data at 400 °C, Cu(acac)2 and Ni(acac)2 were transformed to CuO and NiO nanoparticles as the active form of catalysts. For Fe(acac)3, it was found that at 400 °C, it transformed to magnetite (Fe3O4) species; however, at 500 °C, hematite (α-Fe2O3) and maghemite (γ-Fe2O3) were the most predominant species. The heavy oil oxidation using these low-cost and easy to prepare catalysts could be the best route for improving the efficiency of in situ combustion in field applications.
