Molecular Structures of Refractory Sulfur Compounds in Heavy Oil Hydrodesulfurization Characterized by Collision-Induced Dissociation Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Hydrodesulfurization (HDS) is a widely used technology to reduce the sulfur content of heavy oils, and the HDS reactivities of sulfur compounds are closely related to their structures. In this work, the tandem mass spectra of sulfur-containing model compounds were measured by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with collision-induced dissociation. The influences of naphthenic rings, size of aromatic rings, number of heteroatoms, and number of alkyl side chains to the fragmentation behaviors of sulfur-containing model compounds were studied. Finally, the structure differences of sulfur compounds in heavy oils before and after hydrogenation were compared by tandem mass spectra of FT-ICR MS. The most refractory sulfur compounds in the heavy oil were those with fully conjugated aromatic rings attached with fewer and longer side chains. These results would be helpful for the development of a HDS catalyst/process for heavy oils. For example, developing a new HDS catalyst with high alkyl side-chain cracking activity may be conducive to HDS of heavy oils.