Successive co-operation of supercritical water and silica-supported iron oxide nanoparticles in upgrading of heavy petroleum residue: Suppression of coke deposition over catalyst

• Supercritical water impregnation of α-Fe2O3 over/in silica support.
• Catalytic cracking of vacuum residue in SC-H2O.
• SC-H2O as hydrogen-donor solvent.
• No coke deposition over/in catalyst in SC-H2O.

The chemical effect of supercritical water (SC-H2O) on catalytic cracking of heavy petroleum residue was investigated over silica-supported hematite iron oxide nanoparticles, and the stability of catalyst against coke formation was approved by numerous analyses after sequence of reactions. First, the catalysts of process, with different active phase (α-Fe2O3) to support (SiO2) weight ratio, were prepared successfully via supercritical water impregnation approach. The performance of the α-Fe2O3–SiO2 was then considered on transformation of vacuum residue (VR) to lighter fuels in supercritical water medium. Comparing the results with non-catalytic degradation, i.e., SC-H2O pyrolysis, improvement of heavy oil conversion towards lighter fragments (maltene) was attained. The higher amount of asphaltene transformation as well as suppression in coke formation over/in catalyst could be attributed to larger portion of cracking occurred mainly in catalyst surface and pore volume (PV), whereas the cracking based on pyrolysis was accomplished free-radically in bulk volume (BV). In catalytic reaction, a consecutive cyclic reaction is taking place as; oxidative cracking of asphaltene over catalyst (with converting Fe3+ → Fe2+) followed by in-situ hydrogenation of cracked fragments via in-situ hydrogen resulted from dissociation of water (with converting Fe2+ → Fe3+). Moreover, SC-H2O reforming of hydrocarbons (CmHn) and conversion of those containing oxygen-containing groups, e.g., ethers, esters, carboxyls, carbonyls, to CO as well as related water–gas shift reaction (CO + H2O → H2 + CO2) would facilitate over catalyst by which higher amount of asphaltene conversion and maltene yield were attained.

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