Enhanced pyrolysis and oxidation of asphaltenes adsorbed onto transition metal oxides nanoparticles towards advanced in-situ combustion EOR processes by nanotechnology

• Transition metal oxides catalyze the oxidation of the adsorbed asphaltenes.
• The higher the redox activity of metal oxides, the lower is the activation energy.
• Spreading role of silica surface slightly decreases the activation energy.
• Metal oxides nanoparticles enhance both pyrolysis and oxidation of asphaltenes.
• The nanoparticles could improve the efficiency of in-situ combustion EOR processes.

The effects of redox activity of transition metal oxides nanoparticles on the kinetics of pyrolysis and oxidation of asphaltenes adsorbed onto the metal oxides surfaces were studied. Co3O4, NiO, CuO, Mn2O3, Fe2O3, and WO3 nanoparticles were synthesized and characterized by BET, XRD, FESEM, HRTEM, H2-TPR, and O2-TPD techniques. Asphaltenes were extracted from a heavy oil sample and adsorbed onto the metal oxides and fumed silica. The asphaltenes adsorption capacity (in mg/m2) of the nanoparticles decreases in the order of NiO > Fe2O3 > WO3 > Mn2O3 > CuO > Co3O4 > silica. The off gases of temperature programmed pyrolysis and oxidation (TPP and TPO, respectively) of the adsorbed asphaltenes were analyzed by an on-line FTIR equipped with a gas cell. TPP of the adsorbed asphaltenes on NiO with the highest adsorption capacity indicates that the coke formation increases by 11%, as compared to virgin asphaltenes, improving in-situ combustion process. TPO profiles of the asphaltenes, either virgin or adsorbed onto the surfaces, exhibit a low- and a high-temperature peak. The spreading role of the silica surface lowers the TPO low-temperature peak by about 100 °C, compared to that of the virgin asphaltenes. While catalytic oxidation of the asphaltenes by the metal oxides shifts both low- and high-temperature TPO peaks by about 100–150 °C to lower temperatures. Furthermore, kinetics of carbon oxides evolution during TPO of the asphaltenes was formulated by power-law grain model. The calculated activation energy for the asphaltenes oxidation over the nanoparticles increases in the order of Co3O4 < NiO < CuO ≈ Mn2O3 < Fe2O3

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