Research progress of hydrodesulfurization catalyst

Hydrodesulfurization (HDS) is one of the important processing methods in oil refining industry. In recent years, with the deterioration of crude oil in the world , the increase in the processing capacity of sulfur-containing and high-sulfur crude oil in refineries, the importance of HDS keeps growing. Typical sulfur compounds in petroleum, reaction networks and the research progress of HDS catalysts in domestic and overseas are reviewed below.

Sulfur compounds and reaction networks in diesel oil

Sulfur is one of the main impurity elements commonly found in pertroleum. Sulfur content in crude oil varies by origin. Typical sulfur compounds in petroleum distillates can be divided into non-heterocyclic and heterocyclic types. Non-heterocyclics mainly include thiols, disulfides and thioethers. Heterocycles mainly include thiophene and its alkyl or phenyl substituents.

HDS is a kind of process that with a catalyst and hydrogen,the sulfur compounds of petroleum fractions are produced into

hydrocarbons and hydrogen sulfide through desulfurization reaction. Non-heterocyclic sulfur compounds are easier to desulfurize, the reaction is simple,which it breaks into C-S or S-S breaks, then hydrogenates for molecular fragments, finally generates hydrocarbons and hydrogen sulfide. There are two main reaction paths for the removal of sulfur in heterocyclic sulfur compounds: Path one is to directly remove sulfur in molecules, which is called hydrodesulfurization (DDS) reaction path; path two is to first hydrogenate and then remove sulfur in molecules, which is called prehydrodesulfurization (HYD) reaction path.

Dibenzothiophene in diesel and sulfur in alkyldibenzothiophene are the most difficult to remove, such as dibenzothiophene (DBT), 4,6-dimethyldibenzothiophene (4.6-DMDBT), especially 4 ,6-dimethyldibenzothiophene. Due to its large steric hindrance, it is difficult for sulfur atoms to contact the active center, even under harsh hydrogenation conditions, a considerable part still exists in hydrogenated diesel. It is considered to be one of the most difficult sulfur-containing compounds to desulfurize.