Q & A > Question Details
In our Hydrotreating & Hydrocracking Units, we do Catalyst Sulfiding in 2 stages: Low Temperature Sulfiding and High Temperature Sulfiding. What are the advantages of doing Sulfiding in 2 stages?
If we are treating heavier Feeds is 3 Stage Sulfiding used?
15/01/2020 A: Ganesh Maturu, Self, maturu.ganesh@gmail.com
Sulfiding is not depending on the Heavier feed or lighter feed and it depends on catalyst. Typically for all kind of CoMo (Cobolt + Molybdinum) and NiMo (Nickel + Molybdinum) Hydrotreating catalysts and zeolite based hydrocracking catalysts, we go with 2 stage sulfiding. There is a chemistry behind it.
1. Catalyst generally comes in Oxide form i.e CoO + MoO3.
2. First stage sulfiding happens at near to 220-250 deg C. For example CoMo catalyst is used and in first stage sulfiding, all the CoO converts to Co9S8 and MoO3 converts to MoO2S (Molybdinum Oxy Sulfide). During first stage sulfiding 60-80% of the sulfur update happens in Catalyst.
3. During second stage sulfiding at higher H2S partial pressures and temperatures at 310-330 deg C, MoO2S converts to MoS2 (molybdinum sulfide).
4. You may ask, why not we directly go to high temperature sulfiding i.e at 330 deg C. We always wanted to maintain controlled sulfiding and ensure exotherm does not cross the required levels. It may possible that Metal oxide becomes Metals (reduction takes place) if no H2S present in system at high temperatures initial phase itself.
5. Hence 2 stage sulfiding gives better control and ensures complete sulfiding.
08/01/2020 A: Jon Isley, Fluor, jon.isley@fluor.com
This question relates to the sulfiding procedures that originate from the hydroprocessing catalyst vendor. Suggest you pose this question to your catalyst supplier. In general, the procedures should be designed to best activate and maintain the catalyst integrity for an optimum run length. They may involve steps such as to de-water which a typical reason for sulfiding in stages.
08/01/2020 A: Robert Stults, Eurecat US, bstults@eurecat.com
In-situ catalyst sulfiding procedures are generally dependent on the type of catalyst being sulfided. Each supplier will have a variant procedure based on what their catalyst requires. Using the proper sulfiding technique for the specific catalyst is very important to maximize catalyst activity. A better option is to use Eurecat's Totsucat process. This is an ex-situ sulfiding that will maximize activity of the catalyst. The catalyst is delivered to the refinery totally activated and ready for a "Load and go" start-up. Totsucat will save the refiner a significant amount of time when compared to in-situ sulfiding, reduce manpower requirements, eliminate flare compliance issues and with Totsucat CFP allow the unit to start up with cracked feed. With Totsucat HC-AP, start up time of hydrocracking units can be cut in half.
08/01/2020 A: Steve Mayo, Eurecat, smayo@eurecat.com
In-situ sulfiding of hydroprocessing catalysts consists of low and high temperature stages to assure proper formation of metal sulfide morphology. In particular the stepwise conversion of MoO3 to MoS2 and incorporation of promoter metal (Ni/Co) into the active phase is optimized by sulfiding reactions at low and then high temperature. Sulfiding is complete after the high temperature stage, however, particularly for heavier feedstocks, a break-in period after the high temperature stage is beneficial. During the break-in period, the catalyst is slowly exposed to the heavy feedstock and higher operating temperatures over a period of days to weeks. During break-in, initially very high catalyst activity is tempered by slow deposition of carbon. Break-in stabilizes the active phase such that catalyst deactivation rate is moderated over the entire cycle.
08/01/2020 A: Jake Gotham, InSite Technical Services, jake.gotham@insitetechnical.com
Two stage sulphiding minimises the time taken to activate the catalyst without compromising catalyst activity or operational control.
The low temperature sulphiding step starts the sulphiding process while remaining below temperatures that might accelerate reduction of the catalyst. Once H2S breakthrough has been confirmed, the catalyst is heated up steadily during high temperature sulphiding stage. The presence of H2S minimises the risk of reduction, while the increasing temperature improves the speed of the sulphiding reactions.
On one sulphiding activity I supervised, unrelated operational issues forced the unit to wait at low-temperature sulphiding conditions for a week. When it was finally possible to increase temperature for high temperature sulphiding, there were no signs of further sulphiding reactions taking place. In other words, sulphiding can be completed in a single low-temperature step, but it will take longer due to the slower kinetics, and this is not recommended.
With units which process heavier feeds (e.g. VGO or resid), sulphiding usually starts with diesel feedstock. At some point there will be a transition to the normal boiling range feedstock. Depending on the circumstances of the individual unit, this might be before the end of sulphiding, or on completion of sulphiding. I don’t know if your question about 3 stage sulphiding refers to this. Depending on the circumstances of the specific unit and catalyst, there may be other activities that might be described as the third stage of sulphiding, though I’ve never heard this terminology being used. Examples might include high temperature soak on completion of sulphiding, titration of 2nd stage hydrocracker catalyst, introduction of liquid feed into a unit which was sulphided in the gas phase.
I hope this helps.