Microwave-Assisted Upgrading of Heavy Crude Oil Using Oil-Soluble Transition Metal Precursors: Structural Insights into Asphaltene Transformation

Oil-soluble catalyst precursors (OSCPs), which are usually defined as metal–ligand complexes, enhance the efficiency of in situ thermal processes for heavy oil upgrading by preventing the precipitation and agglomeration of metal particles. This study was designed to investigate the effect of OSCPs containing transition metals (Fe, Ni, and Co) on the efficiency of microwave heating with the aim of improving heavy oil quality. It should be noted that to date, these compounds have not been thoroughly investigated in the context of microwave heating. The experiments were carried out using 2 wt % OSCPs and industrial magnetrons operating at 1 kW and 2.45 GHz. According to the SARA analysis results, the presence of Fe had the greatest effect on increasing the content of saturated compounds and reducing the content of heavy compounds. Moreover, the rheological property (viscosity) of heavy oil in the presence of Ni, Co, and Fe, decreased by 54.26%, 48.79%, and 63.99%, respectively. Asphaltenes are polar compounds that exhibit a strong ability to absorb microwaves; therefore, structural changes in these molecules are expected. X-ray diffraction (XRD) was performed on the crystalline parameters of the asphaltene stack. In the presence of the catalytic system, the average aromatic stack height (Lc) was reduced compared to AHCO and control samples. Also, through 13C NMR data analysis, the aliphatic part of the asphaltenes was reduced and the Car content and aromaticity factor (FCA) were also increased. Remarkably, the findings introduce OSCPs as a promising strategy for improving the efficiency of microwave-assisted in situ upgrading of heavy oil.