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Hello everyone!!

It is possible that the hydrodesulphurization catalyst (NiMo, CoMo) of a gasoline unit is reduced from its sulphidated state to its inactive (metallic) state, by supplying make-up hydrogen (without sulfur) and performing continuous gas purging of the gas system reaction (without supplying the unit with feed) and with a temperature of 30 ° C in the reactor?

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Answers
13/09/2019 A: Ganesh Maturu, Self, maturu.ganesh@gmail.com
I dont think any problem in continuously supplying H2 without sulfur to HDS catalyst at its operating pressure or lower pressures as the temperature is only 30 deg C. I have seen units with spare HDS reactor kept in H2 pressure continuously for 6-7 months and no activity loss after taking this reactor back to service. If any time, we see Reactor temperatures more than 250-300 deg C without H2S, there is possibility of metal reduction from sulfided form.
12/09/2019 A: Ed Ouwerkerk, OptiTreat Hydrotreating consultancy, ced.ouwerkerk@outlook.com
All, thermodynamic equilibrium between the metal and its sulfides depend on ppH2S/ppH2-ratio and this ratio depends on Temperature via the equilibrium constant. So, in principle the metallic state can prevail if the ppH2S is low enough. Above 200C one needs ppH2S/ppH2 < 10^-6 or so, but at ambient one needs < 1*10^-11... Note, that then still the kinetics will determine how FAST the metallic state will appear. In other words, stripping a sulfided cat into its metallic state at ambient T's is not going to happen...
11/09/2019 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
My guess is that it is possible. This is not quite the same situation but in one design I was involved with on a very low sulfur feed to a naphtha hydrotreater, the licensor include an injection pump to continuously inject some mercaptan to ensure that enough sulfur was present to keep the catalyst sulfided. On that basis, it appears that desulfiding of catalyst is certainly possible.
11/09/2019 A: Xavier Ruiz, Haldor Topsoe, xerm@topsoe.com
No, the HT catalyst will not be reduced under such conditions.
11/09/2019 A: Steve Mayo, Eurecat, smayo@eurecat.com
It is generally not recommended for flowing oil or hydrogen, in the absences of sulfur, to have continuous contact with a sulfided hydroprocessing catalyst. However, as long as temperatures are relatively low (<200 C) and contact time is not too long (<24 hours) no permanent catalyst damage is expected. Sulfur may be stripped from the catalyst during the period without sulfur present, with the amount stripped increasing with both temperature and time. In most cases the metals that lost sulfur can be re-sulfided when sulfur is again introduced to the system. Although unlikely, it must be noted that excessive conditions in the reactor without sulfur (T, P, time) have the possibility to cause metal reduction and permanent activity loss.