Sudden spike in temperature of the hydrogenation catalyst bed
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There is a trickle-bed hydrogenation reactor; after loading the hydrogenation catalyst (a copper-based catalyst in an oxidized state, with the catalyst in a loose form), the reactor’s head is reset in order to ensure airtightness of the reactor. After the reactor has been properly purged with nitrogen, the pressure is maintained at 0.5 MPa. Then hydrogen was introduced to raise the reactor pressure to 5 MPa; the inlet and outlet valves of the reactor were closed to maintain this pressure. After about 2 hours, the reactor pressure dropped suddenly, and the temperature of the catalyst bed rose rapidly from 4°C to over 350°C (in a very short time). During the airtightness testing period, no heating medium was circulated in the reactor jacket. Could someone please explain why this is the case? Thank you very much!
I don’t know why the company in question does this. Before pre-sulfiding a hydrogenation catalyst, it needs to be dried and dehydrated using nitrogen. If the hydrogen pressure is to be maintained at 5 MPa, then the nitrogen pressure also needs to be 5 MPa at that stage; only after drying and dehydration can the hydrogen pressure be increased. This is my interpretation of what you mentioned: a catalyst that hasn’t been dried contains moisture, and when compressed to 5 MPa, the temperature of the water molecules rises, turning them into water vapor. As this water vapor moves downward, it is absorbed by the surface of the catalyst, releasing a large amount of heat as a result, which causes the temperature in certain sections of the catalyst bed to rise sharply. This situation has a significant impact on the catalyst. In the presence of hydrogen, the metal components in the catalyst can be easily reduced by hydrogen, leading to catalyst deactivation. Moreover, without proper drying, the catalyst is prone to breaking and losing its mechanical strength. I hope those with more expertise can criticize and correct me if there are any mistakes in my explanation.
May I ask, what is the purity of your hydrogen?
After compression (to 5 MPa), the temperature of the water molecules rises and they turn into water vapor. When this descending water vapor is absorbed by the surface of the catalyst, a large amount of heat is released, causing the temperature in a certain section of the bed to rise sharply. My question is: can the temperature change by such a large amount after water is vaporized under pressure? ? ?
It’s not that the temperature of the water vapor is so high; rather, when moisture is absorbed on the surface of the catalyst, a large amount of heat is released.
I generally agree with the views of the Yilin members. Its main exothermic reaction is likely to occur when the catalyst is reintroduced; it is in an oxidized state, and upon contact with hydrogen a reduction reaction takes place, causing the catalyst to transform into elemental metal. I don’t know yet whether the poster’s reactor has been put into use; I want to see if there are any differences in performance after the catalyst is used!
I have not used hydrogenation catalysts based on copper peroxide; I believe it is a phenomenon caused by the reduction of copper oxide under hydrogen, which consumes hydrogen and releases heat.
In my opinion, the hydrogen pressure you have is too high. Moreover, it’s important that the system be airtight when using hydrogen; if the nitrogen used for filling the hydrogen reactor contains oxygen, the temperature of the bed layer will increase
Can the startup of the device omit the nitrogen purging and airtightness testing steps?
It is likely that copper oxide reacts with hydrogen, releasing a large amount of heat; since this heat cannot be removed in time, the temperature rises and the pressure drops.