Keeping the FCC unit on hot standby, holding the catalyst inventory in the regenerator and keeping it “hot” with torch oil is usually done for short outages when a quick unit repair can be conducted. Catalyst circulation to keep the converter section hot can be maintained only for a brief period of time. Normally these warm/hot standbys are only done for a couple of days as a maximum.
Catalyst damage as you mention from loss of activity, loss of surface area will occur. Over longer periods of using torch oil the catalyst will tend to sinter resulting in higher density from loss of pore volume and surface area. This may lead to circulation issues.
Usually if a unit needs to be down for several days, unfortunately, a complete shutdown of the converter, emptying the unit inventory to the ecat hopper, etc. is required.
I would also suggest that you contact your catalyst supplier for their guidance and assistance in your current unit situation.
I hope my comments help.
Christopher Dean Refining Community – High Olefins FCC Technology Services