Reduction of the catalyst in the hydrogenation reactor
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I am new to hydrogenation units, and I would like to ask that hydrogenation catalysts generally exist in a sulfided state; due to the presence of hydrogen gas during the reaction, this may lead to the reduction of the catalyst. What I don’t understand is under what circumstances only a hydrogenation reaction takes place without the catalyst being reduced. Could someone please explain to me when hydrogen actually reduces the catalyst, and when it does not participate in the reduction process but only carries out the hydrogenation reaction?
The presence of sufficient hydrogen sulfide will prevent reduction! This is also why a certain level of hydrogen sulfide content must be maintained in normal production
If I remember correctly, it should revert at 230 degrees, so we started adding sulfur at 170 degrees
I didn’t quite understand the question; the passivation of hydrogenation catalysts occurs as a reaction with oxygen, while sulfidation is, conversely, a reduction reaction. What the original poster meant by “restore” seems to be “passivate”?
Generally, 180 degrees is used as the threshold; above this temperature, hydrogen sulfide in the cyclic hydrogen can be reduced when its concentration is below 500 PPm, whereas it will not be reduced at temperatures below this value or when the hydrogen sulfide concentration is above 500 PPm.
Newly installed catalysts are in an oxidized state; only by pre-sulfurizing them to convert them into a sulfided state can the catalysts become active. Generally, in the presence of hydrogen (without hydrogen sulfide), the temperature of the catalyst should not exceed 230 degrees. The safe temperature is generally below 180 degrees.
Circulating hydrogen contains hydrogen sulfide; by controlling the level of hydrogen sulfide, the catalyst will not be reduced. The catalyst is most active in its sulfided state~~~
New catalysts are in an oxidized state, so it is necessary to sulfide the catalyst in order to convert it from an oxidized state to a catalytically active sulfided state. During pre-vulcanization, pay attention to the sulfur injection temperature, which is generally 175 degrees Celsius; the specific value should be referred to in the information provided by the catalyst supplier. Normal production hydrogen contains a certain concentration of hydrogen sulfide, generally above 50 ppm; under such conditions the catalyst does not get reduced. However, high concentrations of hydrogen sulfide can inhibit the desulfurization reaction in the reactor. However, catalyst reduction can also occur under conditions of a higher hydrogen-to-oil ratio and higher temperature.
Under normal production conditions, the hydrogen sulfide concentration should be maintained at no less than 0.05%; in an environment free of hydrogen sulfide, the temperature should not exceed 230°C, and reduction generally does not occur.