Composition of sulfur species in deasphalted oils and their molecular-level transformation during the hydrotreating process

•DAOs are separated into subfractions combining methylation and solvent extraction.•HDS chemistry of DAOs is unraveled by combining conversion and composition analysis.•Sulfides and thiophenes have similar reactivity but different evolution chemistry.•Polar fractions are refractory due to the unreactivity and inhibitors existing in them.