What are the requirements for isothermal dehydrogenation when shutting down the reactors in various hydrogenation units?
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We don’t have any specific requirements here; using hot hydrogen with oil instead of constant-temperature dehydrogenation doesn’t seem appropriate. I’m not sure what other practitioners do in this regard
After the temperature of the hot hydrogen with oil is reduced by 20–50 degrees, nitrogen is introduced to carry out isothermal dehydrogenation. It usually takes about 12 hours. At this point, a test is required; if the CO level is below 30 ppm, the process can be terminated early. Otherwise, more time will be required.
After the hot hydrogen treatment with oil is completed, we replace it with nitrogen; the temperature is maintained at 275 degrees for 24 hours of hydrogenolysis. Once the concentration of hydrogen plus hydrocarbons in the circulating gas is below 0.5%, the temperature is reduced to 250 degrees and kept constant, again ensuring that the concentration of hydrogen plus hydrocarbons in the circulating gas remains below 0.5%. Finally, the temperature is set at 225 degrees, with the same requirement that the concentration of hydrogen plus hydrocarbons in the circulating gas stay below 0.5%. Constant-temperature hydrogenolysis completed
Is it necessary to do this every time the hydrogenation unit is shut down? How strict are you about it there?
Exxon data: Nitrogen environment at 290 degrees for 24 hours; the pressure varies depending on the unit, such as 4.2 MPA for residue hydrogenation
Hot hydrogen purging is carried out at 300°C for 72 hours; after nitrogen displacement, the temperature is reduced to 250°C for 16 hours of isothermal dehydrogenation.
Actual isothermal dehydrogenation is difficult to carry out in a nitrogen environment; it is time-consuming and labor-intensive. It is hard to remove the residual hydrogen from the equipment under our operating conditions. As long as the rate of cooling and pressure reduction is controlled during shutdown, there will be no problems
It’s hydrogen; 60%-70% of the operating pressure is sufficient
What is the basis for testing for CO?
During the shutdown process, CO analysis is primarily used as a key indicator when removing the catalyst, in order to prevent the formation of nickel carbonyl.