Hydrogenation catalyst reduction conditions
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I have searched through many sources, which indicate that hydrogenation refining catalysts tend to be reduced in their oxidized state, while the reduction of catalysts in their sulfided state requires very stringent conditions; however, no specific details such as temperature, pressure, hydrogen purity, or hydrogen sulfide concentration were found. Professor Li Dading only suggested that sulfided catalysts do not undergo reduction at 230°C and 3000 ppm of H2S. Personally, I believe that as long as hydrogen sulfide is present, reduction will occur. I hope that experts and professionals will participate in the discussion!
The key to preventing the catalyst from being reduced is to maintain the hydrogen sulfide concentration in the recycled hydrogen; in my opinion, it does not need to be very high, but it should also not be lower than 300 ppm.
300 ppm seems a bit high; the hydrogen sulfide concentration is too high, as it will reduce the partial pressure of hydrogen over time and also inhibit the desulfurization reaction. We keep the hydrogen sulfide concentration in the recycled hydrogen after desulfurization at 100 ppm
Do you have desulfurization equipment? Control below 100 or above? How should the oil level be controlled during shutdown and startup in an oil-free state?
During normal production, the cyclic hydrogen level is above 2500 ppm. Does the 300 you mentioned refer to cyclic hydrogen or fresh hydrogen?
The catalyst can be reduced in the presence of hydrogen at 230 degrees Celsius, and only without hydrogen sulfide
The key is to keep the catalyst at a constant hydrogen sulfide concentration; the temperatures permissible for different catalysts should vary. Generally, hydrogenation refining catalysts do not undergo reduction at temperatures below 250°C and in the presence of 1000 PPM hydrogen sulfide.
What are the lowest temperature and highest hydrogen sulfide concentration at which a reduction reaction occurs?
What is the safe temperature in a state free of hydrogen sulfide with only hydrogen present?
Some sources state that it should not exceed 180 degrees, while others mention 220 degrees, in a sulfur-free state. I think it’s better to go with the lower value as a safety measure. At high temperatures, the level should be no less than 1000 PPM.
The unit underwent a full cycle: the reactor inlet temperature was 230 degrees, and the hydrogen sulfide level in the recycled hydrogen was 300 ppm. The operation continued for 3 days before returning to normal production, with no issues occurring with the catalyst.
230°C is the decomposition temperature of the vulcanizing agent (dimethyldiether) during the pre-vulcanization of hydrogenation catalysts. The condition for reducing the vulcanized catalyst with hydrogen is generally 290°C in an environment of hydrogen (free of hydrogen sulfide). Therefore, during normal production, the hydrogen sulfide concentration in the recycled hydrogen must be maintained at a certain level, and the purity of hydrogen must remain above 90%, in order to prevent the catalyst from being reduced.
A hydrogen sulfide concentration of around 500PPM in the circulating hydrogen is sufficient
In the absence of H2S, the safe operating temperature for sulfided catalysts during hydrogenation is below 175°C, as it is at 175°C that H2S begins to be generated, and at that point the catalyst has not yet been reduced. There are no special requirements regarding pressure.
It seems everyone has got the unit wrong; H2S should be kept at 0.1% = 1000 ppm so that the catalyst does not get reduced.
Thank you! Has it been confirmed that no reduction occurs below 290°C in a hydrogen environment (free of hydrogen sulfide)?
Our hydrofining catalyst does not undergo reduction at temperatures below 230°C and in the presence of 1000 PPM hydrogen sulfide.
Hydrogenation catalysts in an oxidized state can be easily reduced when exposed to hydrogen at high temperatures in the absence of hydrogen sulfide; this process converts the active metal in the catalyst from its oxidized state to elemental metal, with water being produced as a byproduct. This leads to the permanent deactivation of the catalyst. Therefore, after the catalyst has been dried in nitrogen at 250 degrees, the reactor inlet temperature must be slowly reduced to 150 degrees before hydrogen can be used to displace the gas in the reaction system in order to prepare for presulfiding. During presulfiding, whatever accident may occur, the reactor temperature must be kept below 150 degrees to prevent the catalyst from being reduced by hydrogen. During the pre-sulfurization of the catalyst, the reaction that is not desired is the reduction reaction. This reaction occurs in the absence of hydrogen sulfide in hydrogen; the higher the temperature, the easier it is for this reduction reaction to take place. When the temperature exceeds 230 degrees, the rate of this reaction **increases**.
Upstairs, could we discuss the reduction of sulfide states further?
Let me tell you something interesting: we use hydrogen to dry the catalysts at a temperature of 175°C, but due to poor control, the temperature in the catalyst bed rose to 195°C. In other words, even in a pure hydrogen environment, a temperature of 195°C is not sufficient for reduction. I discussed the temperature issue with the catalyst manufacturer, who replied that 195°C is a bit high, but the catalyst should be fine.
It’s possible that the situation you mentioned does exist, but for safety reasons, it is still advisable to use nitrogen for drying. I’m not sure which manufacturer’s catalysts you are using; in China, the catalysts are generally produced by the Fuyan Research Institute and the China Petroleum Research Institute. In recent years, since foreign catalysts are relatively cheaper, many people have started using Chevron’s catalysts as well.