Thermal Conversion of High-Sulfur Crude Oil: Optimizing Fe-Based Catalyst Concentration for Viscosity Reduction and Upgrading Efficiency

Abstract

The influence of the concentration of the water-soluble Fe(NO₃)₃ catalyst precursor (from 0.2 to 0.6 wt % by metal) on the properties of heavy oil during the process of aquathermolysis at 300 °C for 24 h was studied. An increase in catalyst active sites leads to a reduction in viscosity by 58.3–85.3% relative to crude oil due to the growth of the light hydrocarbons by 9.9–19.5 wt % according to SARA analysis results. Additionally, there is an active release of gases, with CO₂ being released most intensively due to the water–gas shift reaction and hydrocarbon oxidation. One of the most significant upgrading processes is hydrodesulfurization, which occurs during the thermal decomposition of resins and asphaltenes of heavy oil. Secondary processes involving the transformation of light hydrocarbons also occur, including C–C bond breaking, as evidenced by the decrease in the amount of C₁₀–C₁₅ n-alkanes. The maximum positive effect of the catalyst is observed at 0.4 wt % by the metal concentration of Fe(NO₃)₃ because the presence of 0.6 wt % catalyst under aquathermolysis conditions intensifies oxidation and carbon formation processes.