High selectivity transalkylation

#1. Field of the Invention

#This invention involves a process for high selectivity, short contact time, catalytic transalkylation of alkylaromatic hydrocarbon compounds of from 7 to 10 carbon atoms, e.g. toluene, wherein the transalkylation is performed in a fluidized catalyst system absent added hydrogen. The catalyst for use in the present process is a porous acid-active zeolite having a fluid activity index of at least about 18. High selectivity to desired product, e.g. greater than equilibrium amounts of paraxylene from a feedstock of toluene, is achieved by way of the present process when reaction conditions are maintained within the following approximate ranges:

#______________________________________ Reactor inlet temperature 300 .degree. F - 1200.degree. F Reactor pressure 0 psig - 200 psig Catalyst/alkylaromatic hydrocarbon compound feedstock (wt/wt) 1 - 60 Catalyst residence time 0.01 second - 300 seconds Feedstock residence time 0.01 second - 300 seconds Slip ratio, defined as the ratio of catalyst residence time to feedstock residence time 1 - 2 ______________________________________

#The drawing depicts a typical fluidized catalyst system, e.g. a riser/transport system, for use in the present process whereby an alkylaromatic hydrocarbon feedstock may advantageously be transalkylated at short contact time to provide a product exhibiting highly selective conversion.

#As shown in the drawing, an alkylaromatic hydrocarbon feedstock and transalkylating agent, as described herein, are fed via line 2 through feed preheater 3 into the inlet of riser 4 for admixture with hot catalyst introduced via standpipe 6 provided with flow control valve 8. The catalyst may be hot, regenerated catalyst from a regeneration or catalyst cascaded from a previous chemical or hydrocarbon conversion reaction, such as, for example, from a fluid catalytic cracking process. The mixture of catalyst, hydrocarbon feedstock and transalkylating agent travels up the riser 4, within which reaction takes place under reaction conditions described herein. Residence time within the herein described limits is controlled by retaining the suspension initially formed in the riser 4 during flow therethrough. Additional hydrocarbon feedstock and/or transalkylating agent may be introduced to riser 4 at one or more spaced apart downstream feed injection points 10 and 12 for residence times less then that employed for the feed introduced by line 2 but within the residence time limits herein described.

#The hydrocarbon vapor-catalyst suspension passed upwardly through riser 4 is discharged into one or more cyclonic separation zones about the riser discharge and represented by cyclone separators 14 and 15. There may be a plurality of cyclone separator combinations comprising first and second cyclonic separation means attached to the riser discharge for separating catalyst particles from hydrocarbon vapors. Separated hydrocarbon vapors are passed from separators 14 and 15 to a plenum chamber 16 for withdrawal therefrom by conduit 18. Hydrocarbon vapors and gasiform material separated by stripping gas as defined below are passed by conduit 18 to separation equipment 19. From separation equipment 19 passes liquid product through line 20. Through line 21 passes gaseous product which may be useful for alkylation plant feed or as a chemical feedstock.

#Catalyst separated from hydrocarbon vapors in the cyclonic separation means is passed by diplegs represented by dipleg 22 to a dense fluid bed of separated catalyst 23 retained about an upper portion of riser 4. Catalyst bed 23 maintained in a dense fluid bed condition by rising gasiform material passes downwardly through a stripping zone 24 immediately therebelow and counter-current to rising stripping gas introduced to a lower portion thereof by conduit 26. Baffles 28 are provided in the stripping zone to improve the stripping operation.