Towards a deep understanding of the evolution and molecular structures of refractory sulfur compounds during deep residue hydrotreating process

A deep insight into the molecular structure of the refractory sulfur compounds during residue hydrotreating process was realized by controlling the hydrodesulfurization (HDS) rate from 91.7% to 99.2%. The reactivity and the molecular-level evolution of the sulfur compounds were characterized by APPI FT-ICR MS and CID FT-ICR MS combined with HDS kinetic analysis. It was found that during deep RHT process, the increased reactivity order of sulfur families is mainly determined by the increased order of aromaticity and the decreased order of alkyl-substituted carbon number. Furthermore, the most refractory sulfur compounds have dominate double bond equivalent (DBE) of 10–12, followed by 9, and carbon number range of 36–38, and their skeleton typically include 2–3 aromatic rings and 0–1 naphthenic/cyclohexene ring, whose substitution positions near the sulfur atom may possibly be occupied by alkyl side chains with carbon number 4–9. This work reveals the reactivity order of individual sulfur compounds and its key influencing factors, and especially the molecular structure of the most refractory sulfur compounds, which may provide a deep understanding about the sulfur evolution. The molecular structures of the most refractory sulfur compounds during residue hydrotreating process were studied via controlling the HDS rate at ultra-high level, e.g. 99.2%, and DBT-like sulfurs are identified as the most refractory compounds with typical structures of dominate DBE = 10–12 and carbon number = 36–38, containing 2–3 aromatic rings and 0–1 naphthenic/cyclohexene ring, whose substitution positions near the sulfur atom are possibly occupied by alkyl side chains with carbon number of 4–9. [Display omitted] •Reactivity order under deep RHT process: T > BT > 5R-p > 5R > NBT > DBT.•Aromaticity and alkyl-substituted carbon number determine reactivity of sulfurs.•Most refractory sulfur compounds with DBE of 10–12 and carbon number of 36–38.•Skeletons and alkyl side trains of most refractory sulfurs were characterized.