Ways to Prevent Pump-Around Heat Exchanger Fouling and Extend Run Lengths on a Benzene Hydrogenation Unit

Abstract

A process for hydrogenation of an aromatic hydrocarbon including introducing a hydrocarbon feed comprising the aromatic hydrocarbon, a hydrogen feed comprising hydrogen, and a hydrogenation catalyst into a hydrogenation reactor operable with a liquid phase and a gas phase to produce a hydrogenation product; removing a gas phase product stream comprising the hydrogenation product; withdrawing a portion of the liquid phase; subjecting the withdrawn portion to heat exchange to provide a reduced-temperature withdrawn portion; introducing the reduced-temperature withdrawn portion back into the hydrogenation reactor; and at least one of: (a) providing at least two heat exchangers to effect the subjecting of the withdrawn portion of the liquid phase to heat exchange; (b) separating a decomposition product of the hydrogenation catalyst, the hydrogenation catalyst, or both, from the withdrawn portion of the liquid phase prior to the heat exchange; and (c) reducing exposure of the hydrogenation catalyst to an oxygen-containing species.

1 . A process for liquid phase hydrogenation of an aromatic hydrocarbon, the process comprising:
 introducing a hydrocarbon feed comprising the aromatic hydrocarbon, a hydrogen feed comprising hydrogen, and a hydrogenation catalyst into a hydrogenation reactor operable with a liquid phase and a gas phase, whereby at least a portion of the aromatic hydrocarbon is hydrogenated to produce a hydrogenation product;   removing, from the hydrogenation reactor, a gas phase product stream comprising the hydrogenation product;   withdrawing, from the hydrogenation reactor, a portion of the liquid phase;   subjecting at least a portion of the withdrawn portion of the liquid phase to heat exchange, thus providing a reduced-temperature withdrawn portion;   introducing the reduced-temperature withdrawn portion back into the hydrogenation reactor;   providing at least two heat exchangers to effect the subjecting of the withdrawn portion of the liquid phase to heat exchange, such that a first heat exchanger of the at least two heat exchangers can be online while a second heat exchanger of the at least two heat exchangers is offline; and   (a) separating a decomposition product of the hydrogenation catalyst, the hydrogenation catalyst, or both, from the withdrawn portion of the liquid phase prior to subjecting the at least a portion of the withdrawn portion of the liquid phase to heat exchange; (b) reducing exposure of the hydrogenation catalyst to an oxygen-containing species; or (c) both (a) and (b).   
     
     
         2 . The process of  claim 1 , wherein the aromatic hydrocarbon comprises benzene and the hydrogenation product comprises cyclohexane; wherein the hydrogenation catalyst comprises nickel and at least one aluminum alkyl; or both. 
     
     
         3 . The process of  claim 1 , wherein the hydrogenation catalyst is introduced as a liquid phase catalyst, as a slurry comprising a solid catalyst, or both. 
     
     
         4 . The process of  claim 3 , comprising (a), and wherein separating the decomposition product of the hydrogenation catalyst, the hydrogenation catalyst, or both, from the withdrawn portion of the liquid phase comprises passing the withdrawn portion of the liquid phase through a cyclone. 
     
     
         5 . The process of  claim 4 , wherein the at least a portion of the withdrawn portion of the liquid phase is pumped into the at least one heat exchanger via a pump, and wherein the cyclone is downstream of the pump and upstream of the heat exchange or upstream of the pump. 
     
     
         6 . The process of  claim 3 , wherein the hydrogenation catalyst is introduced as a Slurry catalyst. 
     
     
         7 . (canceled) 
     
     
         8 . The process of  claim 4  further comprising reintroducing at least a portion of the separated hydrogenation catalyst into the hydrogenation reactor. 
     
     
         9 . The process of  claim 1 , comprising and wherein reducing exposure of the hydrogenation catalyst to the oxygen-containing species comprises drying the hydrocarbon feed, the hydrogen feed, both the hydrocarbon feed and the hydrogen feed, or a mixture of the hydrocarbon feed and the hydrogen feed prior to introducing same into the hydrogenation reactor. 
     
     
         10 . The process of  claim 1 , comprising (b), and wherein reducing exposure of the hydrogenation catalyst to oxygen-containing species comprises contacting the hydrocarbon feed, the hydrogen feed, both the hydrocarbon feed and the hydrogen feed, or a mixture of the hydrocarbon feed and the hydrogen feed, with a component, wherein the component is a compound that will react with the oxygen-containing species. 
     
     
         11 .- 15 . (canceled) 
     
     
         16 . A process for hydrogenation of benzene to cyclohexane, the process comprising:
 introducing a benzene feed comprising benzene, a hydrogen feed comprising hydrogen, and a hydrogenation catalyst comprising nickel into a hydrogenation reactor operable with a liquid phase and a gas phase, whereby at least a portion of the benzene is hydrogenated to produce cyclohexane;   removing from the hydrogenation reactor a gas phase product stream comprising cyclohexane;   withdrawing from the liquid phase a pump-around stream from the reactor;   passing at least a portion of the pump-around stream to a heat exchanger bank comprising at least a first heat exchanger in parallel with a second heat exchanger such that the first heat exchanger can be online while the second heat exchanger is offline, and vice versa;   cooling the at least a portion of the pump-around stream in the heat exchanger hank to provide a reduced-temperature pump-around stream;   introducing the reduced-temperature pump-around stream back into the hydrogenation reactor; and   (a) separating a decomposition product of the hydrogenation catalyst, the hydrogenation catalyst, or both, from the pump around steam prior to passing the at least a portion of the pump around stream to the heat exchange bank; (b) reducing exposure of the hydrogenation catalyst to an oxygen-containing species; or (c) both (a) and (b).   
     
     
         17 . The process of  claim 16 :
 wherein the first heat exchanger and the second heat exchanger are about the same size, and wherein the first heat exchanger and the second heat exchanger produce low pressure steam when cooling the at least a portion of the pump-around stream; or   wherein the first heat exchanger and the second heat exchanger are not about the same size, wherein the first heat exchanger is larger and produces low pressure steam when cooling the at least a portion of the pump-around stream, and wherein the second heat exchanger is smaller and is cooled with cooling water or a refrigerated liquid.   
     
     
         18 .- 19 . (canceled) 
     
     
         20 . The process of  claim 16 , comprising (b) reducing exposure of the hydrogenation catalyst to an oxygen-containing species, and wherein (b) comprises drying, adding at least one aluminum alkyl, or a combination thereof. 
     
     
         21 . The process of  claim 1 , wherein the first heat exchanger and the second heat exchanger are substantially identical, and wherein subjecting the at least a portion of the withdrawn portion of the liquid phase to heat exchange produces a low pressure steam product. 
     
     
         22 . The process of  claim 1  further comprising operating with one of the at least two heat exchangers offline in order to remove a catalyst decomposition product therefrom. 
     
     
         23 . The process of  claim 1 , wherein the first heat exchanger is larger than the second heat exchanger. 
     
     
         24 . The process of  claim 1 , wherein the first heat exchanger operates with a first cooling medium and the second heat exchanger operates with a second cooling medium, wherein the first cooling medium and the second cooling medium have different compositions, the first heat exchanger and the second heat exchanger have different inlet temperatures, or both. 
     
     
         25 . The process of  claim 24  further comprising operating with the first heat exchanger offline in order to remove a catalyst decomposition product therefrom. 
     
     
         26 . The process of  claim 25 , wherein the first cooling medium of the first heat exchanger is a boiler feed water stream and a low pressure steam is produced therein, and wherein the second cooling medium is selected from the group consisting of cooling water and refrigerants. 
     
     
         27 . The process of  claim 16 , wherein the second heat exchanger is online and the first heat exchanger is offline, and further comprising servicing the first heat exchanger to remove a catalyst decomposition product therefrom. 
     
     
         28 . The process of  claim 16 :
 wherein the first heat exchanger and the second heat exchanger are about the same size, and wherein the first heat exchanger and the second heat exchanger produce low pressure steam when cooling the at least a portion of the pump-around stream; or   wherein the first heat exchanger and the second heat exchanger are not about the same size, wherein the first heat exchanger is larger and produces low pressure steam when cooling the at least a portion of the pump-around stream, and wherein the second heat exchanger is smaller and is cooled with cooling water or a refrigerated liquid.