H2SO4 Alkylation Unit - Shutdown Procedure

[EmmanuelTop]

Why is it necessary to empty complete Alkylation Unit when unit is in circulation/shutdown regime more than 72 hours? Why is it necessary to perform neutralization and empty the complete unit instead of having time-unlimited isobutane circulation when following conditions are

1. Olefin feed is stopped
2. H2SO4 addition is stopped and acid is evacuated from the reactor to acid settler. Practically, there is no acid anywhere inside the equipment - of course, some amounts of H2SO4 remain inside reactor vessel, but there are no components that can make significant acid dillution over time.
3. Alkylate/refrigerant caustic and water wash are functioning as long as it is necessary to provide adequate pH value of effluent streams.

Why do we must neutralize and empty complete equipment after 72 hours of shutdown time, instead of having time-unlimited circulation/shutdown with equipment being filled with hydrocarbons?
The unit is licensed by Texaco, with Stratco reactor design and effluent refrigeration system.

Regards,


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[Milutin]

Dear Mr. Emmanuel,

Is it procedure for 72h circulation from plant manuel or from experience? What happens if you are in circulation regime more than 72h?
Perhaps you should ask process licensor for detailed procedure.

Regards,

Milutin