Unraveling the molecular-level structures and distribution of refractory sulfur compounds during residue hydrotreating process

Molecular-level structures and distribution of refractory polycyclic aromatic sulfur heterocycles (PASHs) during residue hydrotreating process (RHT) are investigated. A prior atmospheric pressure photoionization (APPI) FT-ICR MS was used to obtain the distribution of refractory PASHs. Then the key refractory PASHs were further dissociated by collision-induced dissociation (CID) to identify the isomers and gain their fragment ions. During deep hydrodesulfurization (HDS), S1 class compounds detected in the RHT products was identified as the major refractory sulfur compounds. Moreover, an increase in the aromatic structure of S1 class species is present during RHT. The key refractory PASHs are these with DBE = 9–12, which also determine HDS depth during RHT process. From the CID experiments, as indicated by an increase of abundance of fragmentation of alkyl(C1-C4)-substituted DBT, alkyl(C2)-substituted DBT in particular, these key refractory PASHs have a structure of alkyl(C2)-substituted DBT, such as 4,6-DMDBT. In addition, the molecular chemical formula and molecular structure for these key refractory PASHs were proposed, shedding a light on the development of industrial HDS catalysts and optimization of RHT process