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.
