Theoretical Substantiation Based on DFT Calculations and Experimental Confirmation of Soft Conditions for Catalytic Aquathermolysis of Heavy Crude Oil

Catalytic aquathermolysis of carbon–heteroatom bonds in maltene fractions of heavy crude oil is theoretically studied by using DFT calculation techniques with the use of model compounds that mimic carbon–heteroatom bonds. The calculations show that the hydrolysis of carbon–heteroatom bonds cannot be thermodynamically achieved in the temperature range of up to 700 K. The heterolytic cleavage of bonds with the formation of ionic intermediates is the most preferable route. The noticeably lower kinetic barriers of the ionic mechanism compared with the homolytic cleavage reactions with the formation of free radicals make it possible to use soft aquathermolysis conditions in the presence of catalysts, thereby limiting polymerization and oligomerization reactions. The theoretical calculation results agree with experimental data on the catalytic aquathermolysis of dibenzyl sulfide at 200, 300, and 350 °C. The gas chromatography–mass spectrometry analysis shows that minimum coke formation can be achieved at 300 °C. An increase in the temperature to 350 °C leads to efficient sulfur removal in the form of gaseous H2S (7.139 wt %), although coke formation substantially increases (to 17.09 wt %). The combination of DFT calculations and experimental validation suggests that optimizing the catalyst composition and reaction temperature (≤300 °C) can maximize the desulfurization rate while minimizing undesired side reactions.