Unraveling alkyl-substituted sulfur-containing compound reactivity in hydrodesulfurization via multidimensional mass spectrometry and computational modeling

Abstract

Understanding the structural determinants of sulfur compound reactivity during hydrodesulfurization (HDS) is critical for optimizing catalyst design and deep desulfurization processes. This study integrates ultra-high resolution mass spectrometry (UHRMS), ion mobility spectrometry (IMS), and theoretical calculations to unravel the molecular transformations of alkyl-substituted benzothiophenes (BTs) and dibenzothiophenes (DBTs) in petroleum. UHRMS provided precise molecular formulas, while IMS resolved isomeric diversity, quantified via full width at half maximum (FWHM) analysis. Collision-induced dissociation (CID) differentiated long- and short-chain alkyl substitution patterns, and experimental collision cross-section (CCS) measurements were validated against theoretical calculations to confirm structural identities. Post-HDS analysis revealed reduced molecular diversity in DBTs (DBE = 9), indicating preferential reactivity of dominant isomers, whereas BTs (DBE = 6) exhibited increased isomer diversity and decreased average CCS, suggesting selective retention of compact, multi-short-alkyl-substituted isomers. Theoretical modeling further demonstrated that sulfur compounds with multiple short alkyl chains exhibit lower HDS reactivity, likely due to steric hindrance or thermodynamic stability. These findings highlight the critical role of alkyl substitution patterns in governing sulfur compound reactivity, providing molecular-level insights into structure-activity relationships. The methodology and results advance the rational design of HDS catalysts and process parameters, targeting recalcitrant sulfur species for efficient deep desulfurization in petroleum refining.