Accumulation Trends of Thiophene Derivatives in the Cracking Products of Ozonated Sour Vacuum Gas Oils

Abstract

This study proposes a promising method for processing sour vacuum gas oils by combining ozone-assisted oxidation with subsequent heat treatment. Ozone, used as an oxidant at varying molar ratios relative to the feedstock’s sulfur content, promotes the formation of thermally unstable oxygenated intermediates, such as sulfones and sulfoxides. The formation trends of thiophene, benzothiophene, and dibenzothiophene homologues—typical sulfur compounds present in straight-run distillate fractions—are investigated in detail during the thermal cracking of oxidized vacuum gas oils. Under optimal conditions (oxidation at 2.5 mol O₃ per mol S, cracking at 450°C for 150 min), the combined process increases the desulfurization degree of the liquid product by 52% relative to the initial feedstock and by 43% compared to thermal cracking without prior oxidation. For the first time, it is demonstrated that pre-oxidation with ozone reduces the content of thiophenes (by a factor of ~3.6) and benzothiophenes (approximately fourfold) in the thermal cracking products.