Abstract:
A system for alkylating hydrocarbons which includes an improved method of safely handling alkylation catalyst is disclosed. The process includes passing the alkylation catalyst from a settler vessel to a catalyst receiving vessel, via a catalyst cooler, for containment therein in the presence of a condensible gas. Also disclosed is a method for controlling the pressure in the catalyst receiving vessel by controlling the rate of removal of vapors.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Division of application Ser. No. 11/095,835 filed Mar. 31, 2005, now U.S. Pat. No. 7,678,957, the contents of which are hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a system for the alkylation of an olefin with an isoparaffin utilizing an acidic catalyst mixture. In another aspect, this invention relates to a system useful for handling fluids in an alkylation process. 
     The use of catalytic alkylation processes to produce branched hydrocarbons having properties that are suitable for use as gasoline blending components is well known in the art. Generally, the alkylation of olefins by saturated hydrocarbons, such as isoparaffins, is accomplished by contacting the reactants with an acid catalyst to form a reaction mixture, settling the reaction mixture to separate the catalyst from the hydrocarbons, thereby forming a catalyst phase and a hydrocarbon phase. The hydrocarbon phase is further separated, for example, by fractionation, to recover the separate product streams. Normally, the hydrocarbon phase of the alkylation process contains hydrocarbons having three to ten carbon atoms per molecule. In order to have the highest quality gasoline blending stock, it is preferred for the alkylate hydrocarbons formed in the alkylation process to be highly branched and contain seven to nine carbon atoms per molecule. 
     The safe handling and storage of alkylation catalyst has long been a concern to those operating alkylation units. Refiners have typically employed catalyst receiving vessel(s) located below a settler vessel which is/are suitable for receiving the alkylation catalyst volume contained in the alkylation unit and/or suitable for holding make-up catalyst needed to periodically recharge the alkylation process as catalyst is consumed during operation. These catalyst receiving vessels have typically been operated under a blanket of non-condensible gas such as nitrogen, and non-condensible gases can otherwise enter the catalyst receiving vessel during transfer operations. These catalyst receiving vessels are usually vented to a flare, via a treating system wherein acid is neutralized, during a catalyst transfer from the process unit or during a fresh catalyst receiving operation. Such venting is preferably minimized due to environmental and economical considerations. One problem with the current catalyst receiving vessel system is that as the pressure in the catalyst receiving vessel increases due to the addition of catalyst to the vessel containing non-condensible gas, the motive force for transferring catalyst diminishes. While this is not necessarily detrimental to a fresh catalyst loading operation, it is a significant safety concern for the transfer of catalyst from the process (usually reserved for emergency situations) wherein faster transfer times are preferred. 
     Therefore, development of an improved system for transferring alkylation catalyst to a catalyst receiving vessel would be a significant contribution to the art. 
     BRIEF SUMMARY OF THE INVENTION 
     It is, thus, an object of the present invention to provide an improved system for transferring alkylation catalyst to a catalyst receiving vessel. 
     A further object of this invention is to provide an improved system for transferring alkylation catalyst to a catalyst receiving vessel using gravitational force and/or pressure differential while minimizing the extent to which vapors in the catalyst receiving vessel are vented. 
     Another object of this invention is to provide a system for transferring alkylation catalyst to a catalyst receiving vessel while minimizing the size of the catalyst receiving vessel. 
     A yet further object of this invention is to provide a system for the quick transfer of catalyst from an alkylation process. 
     Other broad objects of this invention are to improve the environmental safety of the alkylation process and to improve the economics of operating an alkylation unit. 
     In accordance with a first embodiment of the present invention, a system is provided including the following: a settler vessel comprising a settler vessel top, a settler vessel bottom, an upper zone containing a hydrocarbon phase and a lower zone containing a catalyst phase, wherein the settler vessel bottom is positioned at a first elevation; a catalyst cooler comprising a catalyst cooler top and a catalyst cooler bottom, wherein the catalyst cooler top is positioned at a second elevation below the first elevation; a riser reactor connected in fluid flow communication with the catalyst cooler and the upper zone of the settler vessel; a first conduit connected in fluid flow communication with the riser reactor for introducing a hydrocarbon mixture to the riser reactor for contact with at least a portion of the catalyst phase; a second conduit connected in fluid flow communication with the lower zone of the settler vessel and the catalyst cooler for transferring the at least a portion of the catalyst phase from the lower zone of the settler vessel to the catalyst cooler; a third conduit connected in fluid flow communication with the upper zone of the settler vessel for removing at least a portion of the hydrocarbon phase for further processing, wherein the improvement comprises: providing a catalyst receiving vessel comprising a catalyst receiving vessel top, a catalyst receiving vessel bottom, a pressure, an upper zone and a lower zone, wherein the catalyst receiving vessel top is positioned at a third elevation below the first elevation, and wherein the catalyst receiving vessel is suitable for receiving the catalyst phase and/or the hydrocarbon phase from the settler vessel; providing a fourth conduit connected in fluid flow communication with the catalyst cooler and the catalyst receiving vessel suitable for transferring fluid from the catalyst cooler to the catalyst receiving vessel with the fourth conduit having interposed therein a valve for blocking passage of fluid through the fourth conduit and, alternately, for allowing passage of fluid through the fourth conduit; providing a fifth conduit connected in fluid flow communication with the upper zone of the catalyst receiving vessel for adjusting the pressure of the catalyst receiving vessel by removing vapors from the catalyst receiving vessel; and providing a sixth conduit connected in fluid flow communication with the upper zone of the catalyst receiving vessel for introducing a condensible gas into the catalyst receiving vessel to inhibit air from entering the catalyst receiving vessel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The FIGURE is a simplified schematic flow diagram presenting an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The system of the present invention will be described with reference to the FIGURE. 
     Referring to the FIGURE, therein is illustrated the inventive process, system or apparatus  10  including a settler vessel  100  comprising a settler vessel top  102 , a settler vessel bottom  104 , and an inside wall  106  which defines a settling zone comprising an upper zone  108 , and a lower zone  110 . Settler vessel bottom  104  is positioned at a first elevation. A riser reactor  112  is connected in fluid flow communication with upper zone  108  of settler vessel  100  and a catalyst cooler  114  comprising a catalyst cooler top  116  and a catalyst cooler bottom  118 . Catalyst cooler top  116  is positioned at a second elevation below the first elevation. A hydrocarbon mixture comprising at least one olefin and at least one isoparaffin is introduced into riser reactor  112  via a first conduit  120  connected in fluid flow communication with riser reactor  112  for contact with an alkylation catalyst within riser reactor  112  to thereby produce a reactor effluent. The reactor effluent is passed from riser reactor  112  to upper zone  108  of settler vessel  100  wherein the reactor effluent is separated into a hydrocarbon phase and a catalyst phase. 
     Upper zone  108  contains the hydrocarbon phase comprising, consisting of, or consisting essentially of unreacted isoparaffins, alkylate product and a component selected from the group consisting of hydrofluoric acid, water, a volatility reducing additive, and combinations of any two or more thereof. Lower zone  110  contains the catalyst phase comprising, consisting of, or consisting essentially of an alkylation catalyst. The alkylation catalyst comprises an acid which can comprise, consist of, or consist essentially of hydrofluoric acid. Optionally, the alkylation catalyst can comprise, consist of, or consist essentially of hydrofluoric acid and a component selected from the group consisting of acid soluble oil, other hydrocarbons, a volatility reducing additive, water and combinations thereof. 
     The volatility reducing additive can be any compound effective in reducing the volatility of a mixture resulting from the addition of the volatility reducing additive to hydrofluoric acid. More particularly, the volatility reducing additive can be a compound selected from the group consisting of sulfone, ammonia, methylamines, ethylamines, propylamines, butylamines, pentylamines, pyridine, alkylpyridines, picoline, melamine, hexamethylenetetramine and the like. 
     The sulfones suitable for use in this invention are the sulfones of the general formula:
 
R—SO 2 —R 1  
 
wherein R and R 1  are monovalent hydrocarbon alkyl or aryl substituents, each containing from 1 to 8 carbon atoms, and wherein R and R 1  can be the same or different. Examples of suitable sulfones include, but are not limited to, dimethylsulfone, di-n-propylsulfone, diphenylsulfone, ethylmethylsulfone and alicyclic sulfones wherein the SO 2  group is bonded to a hydrocarbon ring. In such a case, R and R 1  are forming together a branched or unbranched hydrocarbon divalent moiety preferably containing from 3 to 12 carbon atoms. Among the latter, tetramethylenesulfone or sulfolane, 3-methylsulfolane and 2,4-dimethylsulfolane are more particularly suitable since they offer the advantage of being liquid at process operating conditions of concern herein. These sulfones may also have substituents, particularly one or more halogen atoms, such as for example, chloromethylethylsulfone. These sulfones may advantageously be used in the form of mixtures of any two or more thereof. The most preferred volatility reducing additive is sulfolane.
 
     At least a portion of the catalyst phase can be passed, via a second conduit  122  connected in fluid flow communication with lower zone  110  of settler vessel  100  and catalyst cooler  114 , from lower zone  110  of settler vessel  100  to catalyst cooler  114  for cooling, thereby forming a cooled catalyst. At least a portion of the hydrocarbon phase is removed as a settler effluent stream, for further processing, from upper zone  108  of settler vessel  100  via a third conduit  124  connected in fluid flow communication with upper zone  108  of settler vessel  100 . At least a portion of the cooled catalyst is passed from catalyst cooler  114  to riser reactor  112  for use as at least a portion of the alkylation catalyst present in riser reactor  112 . 
     The improvement comprising the following. Providing a fourth conduit  126  connected in fluid flow communication with catalyst cooler  114  and a catalyst receiving vessel  128  comprising a catalyst receiving vessel top  130 , a catalyst receiving vessel bottom  132 , a pressure, an upper zone  134  and a lower zone  136 . Catalyst receiving vessel top  130  is positioned at a third elevation below the first elevation and is suitable for receiving the catalyst phase from settler vessel  100 . Preferably, the third elevation is below catalyst cooler bottom  118  and catalyst receiving vessel  128  is also preferably suitable for receiving the hydrocarbon phase from settler vessel  100 . Fourth conduit  126  is suitable for transferring the catalyst phase to catalyst receiving vessel  128  and fourth conduit  126  has interposed therein a valve  138  for blocking passage of fluid through fourth conduit  126  and, alternately, for allowing passage of fluid through fourth conduit  126 . Valve  138  is positioned at a fourth elevation below the second elevation. In addition, the fourth elevation can be at or above the third elevation, or, alternately, below the third elevation. 
     A fifth conduit  140  is connected in fluid flow communication with upper zone  134  of catalyst receiving vessel  128  for adjusting the pressure of catalyst receiving vessel  128  by removing vapors from catalyst receiving vessel  128 , preferably for venting to a flare via a treating system wherein acid is neutralized. 
     Fifth conduit  140  preferably has interposed therein a vent valve  142  for blocking passage of fluid through fifth conduit  140  and, alternately, for allowing passage of fluid through fifth conduit  140 . 
     A sixth conduit  144  is connected in fluid flow communication with upper zone  134  of catalyst receiving vessel  128 , either directly or via fifth conduit  140 , for introducing a condensible gas into catalyst receiving vessel  128  to inhibit air from entering catalyst receiving vessel  128 . The use of a condensible gas allows for the use of a catalyst receiving vessel  128  which is smaller than a catalyst receiving vessel which would be necessary without use of a condensible gas. 
     From time to time as needed, a condensible gas is introduced into catalyst receiving vessel  128 , through sixth conduit  144 , to inhibit air from entering catalyst receiving vessel  128 . The condensible gas is preferably a hydrocarbon gas, is more preferably selected from the group consisting of propane, butane, isobutane, pentane, isopentane, liquefied petroleum gas, and combinations of any two or more thereof, and most preferably comprises isobutane. 
     At those times when it is desired to remove the catalyst phase from the alkylation system, valve  138  is opened to thereby allow transfer of the catalyst phase from settler vessel  100 , through catalyst cooler  114  and fourth conduit  126 , to catalyst receiving vessel  128  by gravitational force and/or pressure differential means. 
     The pressure of catalyst receiving vessel  128  is adjusted by allowing the removal of vapors from catalyst receiving vessel  128  through fifth conduit  140 . 
     As a further embodiment, a pressure transducer  146  is operably related to catalyst receiving vessel  128  which produces a pressure signal  148  representative of the pressure in catalyst receiving vessel  128 . 
     A pressure controller  150  is operably related to pressure transducer  146  and receives pressure signal  148  and an operator entered pressure signal  152 , which is representative of the desired value for the pressure in catalyst receiving vessel  128 , wherein pressure controller  150  establishes a pressure control signal  154 , responsive to pressure signal  148  and the operator entered pressure signal  152 , representative of the flow rate required to maintain the pressure in the catalyst receiving vessel  128 , represented by pressure signal  148 , substantially equal to the desired value for the pressure of the catalyst receiving vessel  128 , represented by operator entered pressure signal  152 . 
     The vent valve  142  is operably related to pressure controller  150  and vent valve  142  is preferably a control valve suitable for adjusting the flow rate of the material carried in fifth conduit  140  in response to pressure control signal  154 . 
     The pressure adjustment of catalyst receiving vessel  128  is preferably performed in the following manner. The pressure in catalyst receiving vessel  128  is measured via pressure transducer  146  producing pressure signal  148 . 
     Pressure signal  148  and operator entered signal  152  are introduced to pressure controller  150 . 
     Pressure control signal  154  is established via the pressure controller  150  and pressure control signal  154  is introduced to vent valve  142 . 
     The flow rate of the material carried in fifth conduit  140  is adjusted via vent valve  142  in response to pressure control signal  154 . 
     Whereas this invention has been described in terms of the preferred embodiments, reasonable variations and modifications are possible by those skilled in the art. Such modifications are within the scope of the described invention and appended claims.