Elucidation of sulfur behavior in ultra deep hydrodesulfurization using 35S radioisotope tracer methods: Part I. Hydrodesulfurization of dibenzothiophene with lower concentration over a sulfided Ni-Co-Mo/Al2O3 catalyst Original Research Article

In order to investigate the behavior of sulfur on sulfided Ni-Co-Mo/Al2O3 catalyst in the ultra deep hydrodesulfurization (HDS), a novel radioactive 35S tracer method was developed. Both radioactive 35S-labeled elemental sulfur and dibenzothiophene (DBT) were used to label the catalyst under the practical HDS, and then HDS reactions of DBT of 0.001–1.0 wt.% (content of sulfur: ca. 2–200 ppm) were carried out over the 35S-labeled catalyst at 260 °C and under 5.00 MPa. By tracing the changes in the radioactivity of formed [35S]H2S, the behavior of sulfur on the catalyst was determined. Either [35S]S or [35S]DBT can be used to label the catalyst well and the behavior of sulfur on the catalyst did not change with the type of 35S agent. The release rate of [35S]H2S from 35S-labeled catalyst in the HDS of DBT became remarkably slow when the concentration of DBT decreased to less than 0.01 wt.%. The amount of labile sulfur participating in the HDS of DBT also decreased with decreasing the concentration of DBT. This indicates that the labile sulfur on the catalyst is not uniform and only some part but not all of labile sulfur participates in the ultra deep HDS.