A Hydrotreater, or hydro-desulfurization (HDS) unit, is the process equipment used in petroleum refining to remove sulfur and nitrogen compounds from natural gas and other refined petroleum products like deisel, gasoline, and jet fuel. In petroleum refining, it is important to remove sulfur from the process stream in order to:
- Prevent sulfur from poisoning the noble metal catalysts in the subsequent catalytic reforming of the naphtha; and
- Reduce sulfur dioxide (SO2) emissions to meet more-stringent clean fuels specifications.
In the HDS process, the oil feedstock is first heated and combined with high-purity hydrogen gas. This mixture then enters a reactor filled with a catalyst, typically consisting of an alumina base impregnated with a metal (usually molybdenum or tungsten) and a co-catalyst (typically cobalt or nickel). These catalysts are chosen for their ability to facilitate the HDS process.
The hydrotreating reactor operates under high temperature and pressure conditions, typically between 572 - 752 ºF (300 - 400 ºC) and 440 - 1910 psi (30 - 130 bar). Under these conditions, the sulfur compounds in the oil react with hydrogen, forming hydrogen sulfide and yielding desulfurized hydrocarbons. In essence, sulfur is replaced by hydrogen in the hydrocarbon molecule through a process known as hydrogenolysis.
The mixture then exits the reactor and proceeds to a high-pressure gas separator, where the released hydrogen sulfide is removed from the hydrocarbon liquid. The liquid product is then typically directed to a stripping tower to remove any residual light hydrocarbons and hydrogen sulfide.
References
- https://www.aiche.org/resources/publications/cep/2021/october/overview-hydrotreating.
- https://en.wikipedia.org/wiki/Hydrodesulfurization.
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