Interreactor particle transfer process and arrangement

A process for transferring catalyst particles between reactors in a multi-stage catalytic reactor system wherein a hydrocarbon reactant stream flows serially through a plurality of reaction zones and catalyst particles flow from the bottom of a reaction zone discharging catalyst upwardly to the top of a reaction zone receiving catalyst, said process comprising:

• a) passing a purge gas at a substantially constant rate into a purge chamber located at the bottom of a first reaction zone upwardly into said first reaction zone;
• b) intermittently withdrawing catalyst from the bottom of said first reaction zone downwardly through a discharge conduit, passing a portion of said purge gas downwardly through catalyst in said discharge conduit into a lift vessel, passing purge gas from said lift vessel upwardly through a lift conduit to a second reaction zone and discharging catalyst particles from said discharge conduit into said lift vessel at least until catalyst particles contact the bottom of said discharge conduit;
• c) intermittently increasing the flow of a lift gas into said lift vessel, from a first rate to a second, passing a portion of said lift gas up said lift conduit into said second reaction zone, entraining catalyst particles with said flow of lift gas up said lift conduit to transfer catalyst particles from said lift vessel to said second reaction zone under dilute phase conditions, passing a portion of said lift gas up said discharge conduit to retard catalyst flow downwardly through said discharge conduit and to interrupt any flow of purge gas down said discharge conduit;
• and,
• d) decreasing the flow of said lift gas to said lift vessel to said first rate to initiate the withdrawal of catalyst from said first reaction zone under step b.