Pre-sulfurization of hydrofining catalysts
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The documents state that \"to prevent the catalyst from being reduced, the temperature at the highest point of the bed should be below 150°C when hydrogen is introduced into the system.\" Before hydrogen sulfide penetrates the catalyst bed, the temperature at the highest point of the bed should not exceed 230°C. Avoid the reduction of the catalyst’s metal components by high-temperature hydrogen.” From what I know, when DMDS is used as a vulcanizing agent, the system pressure is generally between 3.0 and 5.0 MPa, and DMDS is added once the reactor inlet temperature reaches 150°C. The decomposition temperature of DMDS is 200°C. So here comes the question: during the temperature increase from 150°C to 200°C, hydrogen has already been introduced into the system, but DMDS has not yet started reacting with hydrogen to produce hydrogen sulfide. During this period, won’t the catalyst be reduced by the hydrogen? Which expert can offer some guidance? Thank you.
It is generally believed that the temperature at which the catalyst is reduced by hydrogen is above 230°C. Hydrogen is introduced generally to increase the pressure in the reaction system. It is standard practice to limit the pressure in the reaction section to 25% of the design pressure when the temperature at any point within the vessel falls below the minimum pressure rating MPT specified by the manufacturer. At the same time, the adsorption heat of the material (usually the feed oil) in contact with the catalyst must also be considered. (Ranging from 10°C to 50°C)
Our unit is for diesel hydrogenation, and the presulfurized oil is also straight-run diesel that needs to be processed.
The catalyst will not be reduced at temperatures below 230°C. During operation, the temperature is maintained at 220°C, and samples are taken to analyze the hydrogen sulfide content. All of our hydrogenation units allow the temperature to be increased further as long as the system’s hydrogen sulfide level remains above 0.3%. DMDS continues to be injected during this period of constant temperature; if the measured hydrogen sulfide level is below 0.3%, sulfur injection continues at that constant temperature, with the hydrogen sulfide content analyzed every 30 minutes.
The reduction temperature for the oxidized-state catalyst is 230°C; for the sulfided state, it is believed to be 290°C, and this reduction takes place in the absence of sulfur
First, DMDS is injected at 150°C; at this point hydrogen has already been introduced into the system, satisfying the requirement that the temperature at the highest point of the bed layer should be below 150°C when hydrogen is introduced into the device. Second, during the heating from 150°C to 200°C, DMDS gradually decomposes, fulfilling the requirement that the temperature at the highest point of the bed layer should not exceed 230°C before hydrogen sulfide penetrates the catalyst bed layer℃”
The temperature range of 150–230 degrees corresponds to the process in which hydrogen sulfide is fully adsorbed after the decomposition of DMDS, until it penetrates through the catalyst bed; at this point, the reduction temperature is not yet reached
I’ve learned it, thank you for sharing!
Are these the specifications provided by the catalyst manufacturer? As the processes and technologies for producing catalysts continue to improve, are similar requirements and standards also constantly being raised for new types of catalysts?
It is based specifically on the data provided by the catalyst manufacturers, combined with empirical values; as all the experts mentioned above have explained； However, during this process, close attention must be paid to the temperature rise of the bed layer, as well as to the handling of any abnormalities that may occur. Do not raise the temperature blindly.
Thank you to all the experts; I’ve learned quite a bit about catalyst presulfidization procedures.