Effect of excessive hydrogen during pre-sulfiding of CO sulfur-tolerant shift catalyst
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During pre-vulcanization, if the heater fails and the system has to be shut down for an extended period, hydrogen supply should be stopped as well as sulfur injection. The system should be kept insulated and at pressure; if necessary, nitrogen should be introduced to displace hydrogen and reduce its concentration in the system. Why is it necessary to reduce the hydrogen concentration? What are the effects of too much hydrogen?
The main role of H2 is to produce H2S, which is used in the sulfidation reactions of MoO3 and CoO, while part of the H2 participates in the reduction reactions of MoO2 and CoO. Therefore, a low concentration of H2 is not conducive to the sulfidation of the catalyst, while a high concentration can easily reduce the catalyst directly to metallic Mo and Co, resulting in no sulfidation effect and potentially triggering side reactions.
Could these elemental forms of Mo and Co be reduced back to their sulfide forms at a later stage?
It will not be restored; only the catalyst becomes inactive
Could you explain in more detail why it can’t be reduced?
One is that the loss of low-temperature activity is irreversible; another is that impurities in the gas can partially block the pores and are difficult to remove completely; furthermore, high temperatures cause cobalt to sublimate. It is only possible to add some new reagent to the upper part of the bed layer; ideally, a pre-conversion furnace or detoxification tank should be installed before the main converter