US2935543A - Alkylation process - Google Patents

Description

May 3, 1960 R. SMITH ALKYLATION PRocEss ilnited States ALKYLATION PROCESS Randlow Smith, New Rochelle, N.Y., assigner to Texaco Inc., a corporation of Delaware This invention relates to a petroleum treating process for the production of high octane motor fuel components. More particularly, this invention relates to an improved alkylation process. Still more particularly, this invention relates to an improved alkylation process vinvolving in combination a number of treating steps coordinated with respect to each other for the production of a high octane motor fuel component.

In accordance with one embodiment the practice of this Iinvention is directed to the manufacture of a lhigh octane motor fuel component, alkylate, from a feed comprising substantially only straight chain hydrocarbons, such as n-butane and another feed containing an olenic hydrocarbon, such as propylene.

Itis an object of this invention to provide an improved alkylation process for the manufacture of a high :octane motor fuel component.

llt is another object of this invention to prov-ide an improved process for the manufacture of la high octane alkylate from `rela-tively highly volatile starting materials.

Still another object of this invention is to provide van 'alkylation `process `which is adaptable to a variety of charge stocks.

Yet 'another object vof this invention vis to provide an improved alkylation process wherein normal 'butane is a feed component and wherein the normal butane feed is ksuitably treated in accordance with 4the practice of this Ainvention toyield a high octane alkylate particularly useful as a motor fuel component.

How these `and other objects of this invention are accomplished will become vappa-rent in the light of the accompanying disclosure and drawing which schematically 'illustrates a process flow 'in -accordance 'with one embodiment of `the Jpractice of this invention.

' in `accordance with this invention `a feed comprising a saturated ysti-ight chain hydrocarbon is ysubjected to 'isomerization wherein 'the straight chain hydrocarbon is isomerized 'into van isomeric mixture comprising the aforesaid straight `chain hydrocarbon and the corresponding 'isomeric branched chain hydrocarbon. Following the 'isomerization reaction the isomate is subjected to contact with a selective adsorbent which preferentially adsorbs straight chain hydrocarbons to the substantial exclusionr `of non-straight chain hydrocarbons to adsorb straight chain hydrocarbons from said 'isomate The remaining unadsorbed isomeric branched chain 'hydrocarbons `are 'then ,introduced into an alkylation reaction Vzone in 'admixture 'with a suitable olenic hydrocarbon `wherein said olefnic hydrocarbon reacts with and alkylates said isomeric vbranched .chain hydrocarbon to yield an `alleyla- .tion .reaction effluent .comprising `unreacted .said isomeric branched chain hydrocarbons and alkylate. v Tllhe Vresulting `allor-lation reaction efliuent is then subjected to frac- -tionation lto ,separate therefrom Vsaid nnreacted isomer-ic branched chain hydrocarbon which is recycled to '.-the aforesaid -alkylation `reaction zone. Alkylate las product is separately-recovered from the alkylation 4reaction 4mixatent G ice ture. The adsorbed straight chain hydrocarbons, selectively adsorbed from the isomate by contact with said selective adsorbent, are desorbed therefrom and the resulting ydesorption eiuent comprising the desorbed straight chain hydrocarbons is returned to the aforesaid isomerization reaction zone. By operating in the manner indicated hereinabove a feed stream comprising substantially only straight chain hydrocarbon and a suitable oleinic feed are reacted to yield as product substantially only high octane alkylate.

In the aforesaid combination of operations involving isomerization, selective adsorption and desorption and alkylation, any suitable isomerization process effective for isomerizing straight chain saturated hydrocarbons, such as butane, into the corresponding isomeric branched chain saturated hydrocarbons, such as isobutane, might be employed. Similarly, any suitable alkylation reaction wherein a branched chain saturated hydrocarbon, such as isobutane, is reacted with or alkylated with an olenic hydrocarbon, such as propylene, might be employed therein.

With respect to the adsorption step wherein straight `chainhydrocarbons are selectively adsorbed from ad mixture with non-straight chain hydrocarbons it is preferred in 'the practice of this invention to employ as the selective adsorbent a solid, alumino-silicate molecular sieve type adsorbent, ie., adsorbent which selectively adsorbs straight chain hydrocarbons to the substantial `exclusion of non-straight chain hydrocarbons.

Any suitable isomerization process, vapor phase or liquid phase, vmay be employed in the practice of this Vinvention and such isomerization processes are well known in the art. For the most part these isomerization processes are ldistinguished as to Whether lor ynot 4the hydrocarbons to Vbe isomerized are isomerized in the liquid phase or fin the vapor phase. In liquid phase isomerization a catalyst consisting of aluminum chloride dissolved in molten antimony trichloride is sometimes employed. Generally `the hydrocarbon mixture undergoing liquid phase isomerization is admixed with hydrogen chloride gas vwhich acts as a catalyst promoterl during the isomerization reaction. Sometimes it is also desirable to admix hydrogen with the isomerization reaction mixture to improve the yield of the resulting isomerized hydrocarbons.

In vapor phase isomerization a catalyst comprising aluminum Vchloride promoted with hydrogen chloride is employed. Other catalysts suitable for use in vapor' phase isomerization are known and include precious metal-containing vcatalyst as well as platinum-containing catalysts.

Alkylation processes which are suitably employed in combination treating operations in accordance with `this invention are well known .in the art. Suitable alkylation processes, identified by the type of alkylation catalyst employed, include sulfuric acid alkylation processes as well as 'HF alkylation and aluminum chloride alkylation processes. In sulfuric acid, H'F and aluminum chloride alkylation processes a saturated branched chain hydrocarbon, such as isobutane, is `contacted in the liquid phase at a Asuitable low temperature with an oletinic hydrocarbon, such Yas propylene. In the alkylation reactor the oletinic hydrocarbon reacts with the branched Chain Visomeric hydrocarbon -to yield the corresponding alkylate. in the a-lkylation .reaction itis desirable to maintain ya great excess of isomeric saturated hydrocarbon therein, at least about 5:1, preferably at least 10:1, on la ,molar basis, to drive the reaction toward completion inthe direction of consumption :of the oleuiic hydrocarbon- There is recovered from .the alkylation :reactor tangahylation reaction keffluent comprising zunreacted isomeric.- sat;

' tion euent is fractionated into the above mentioned fractions, the alkylate being recovered as product and the `unreacted branched chain saturated hydrocarbon is returned to the alkylation reaction zone to contact addi- -tional olefinic hydrocarbon.

The various isomerization processes and alkylation processes which are suitably employed in the practice of this invention are described in the Oil and Gas Journal, March 25, 1957, pages 153-165. The disclosures of this reference with respect to isomerization processes and alkylation processes are herein incorporated and made part of this disclosure.

Any suitable selective adsorption process effective for the removal of straight chain saturated hydrocarbons vfrom branched chain hydrocarbons is satisfactorily employed in the practice of this invention. The invention, however, is particularly applicable to a selective adsorbent comprising certain natural or synthetic zeolites or alumino-silicates, such as a calcium alumino-silicate, which exhibits the property of a molecular sieve, that is, matter made up of porous crystals wherein the pores of the crystals are of molecular dimension and are of substantially uniform size. In general, zeolites may be described as water-containing alumino-silicates having a general formula (R,R2)O.Al2O3.nSiO2.mH2O wherein R may be an alkaline earth metal such as calcium, stron- -tium or barium or even magnesium and wherein R is an alkali metal such as sodium or potassium or lithium.

These materials, when dehydrated for the removal of substantially all of the water therefrom, retain their crystalline structure and are particularly suitable as selective adsorbents.

A particularly suitable solid adsorbent for straight `chain hydrocarbons is a calcium alumino-silicate, apparently actually a sodium calcium alumino-silicate, ymanufactured by Linde Air Products Company and designated Linde Type 5A Molecular Sieve. The crystals of this particular calcium alumino-silicate have a pore size or opening of about 5 Angstrom units, a pore size suiciently large to admit straight chain hydrocarbons, such as the normal paraflins, to the substantial exclusion of the non-straight chain hydrocarbons, i.e., naphthenic, aromatic, isoparainic and isoolefinic hydrocarbons. This particular selective adsorbent is available in various sizes, such as in the form of 174g or JAG" diameter pellets, or as a finely divided powder having a particle size in the range of 0.5-5.0 microns. In general, a selective adsorbent employed in the practice of this invention may be in any suitable form or shape, granular, spheroidal Vor microspheroidal.

Particularly suitable solid selective adsorbents which may be employed in the practice of this invention include the synthetic and natural zeolites which, when dehydrated, may be described as crystalline zeolites having a Irigid three dimensional anionic network and having intterstitial dimensions suiciently large to `adsorb srtaight chain hydrocarbons but sufliciently small to exclude the non-straight chain hydrocarbons possessing larger molecular dimensions. The naturally occurring zeolite, chabazite, exhibits such desirable properties. Another suitable naturally occurring zeolite is analcite NaAlSi2O6.H2O

base exchange modifications of these zeolites, may also 'bei employed in the practice of this invention.

i assegna' sorbed hydrocarbons in the gaseous phase.

Other solid inorganic or mineral selective adsorbents are known. It is contemplated that selective adsorbents having the property of selectively adsorbing straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons in the manner of a molecular sieve may be obtained by suitable treatment of various oxide gels, especially metal oxide gels of the polyvalent am photeric metal oxides.

The adsorptive separation of the straight chain hydrocarbons from the hydrocarbon fraction undergoing treatment may be carried out in the liquid or gaseous phase and at any suitable temperature and pressure effective in the adsorptive separation operation. It is desirable, however, to coordinate .the adsorption separation conditions, e.g., temperature and pressure, with the desorption separation conditions, more fully described hereinafter, so as to effect the most economical use of the ma- .terials employed and for ease of control.

The adsorptive separation or adsorption of the straight chain hydrocarbons by the solid selective adsorbent may be carried out at any suitable temperature, such as a temperature in the range Sil-500 F., sufficient to effect the adsorptive separation of the desired straight chain hydrocarbons, and at any suitable pressure, such as a pressure in the range 0-10,000 p.s.i.g. and higher, the temperature and pressure being adjusted with respect to the hydrocarbon mixture undergoing treatment depending upon whether or not it is desired to maintain the hydrocarbon mixture undergoing separation in liquid phase or in the vapor or gaseous phase.

Liquid phase adsorption may be carried out by simply slurrying the solid selective adsorbent with the liquid hydrocarbon mixture being treated, followed by separation or decantation of the resulting treated hydrocarbon euent, now substantially free of or having a substantially reduced straight chain hydrocarbon content. Liquid phase adsorption may also be carried out by percolating the liquid hydrocarbon mixture to be treated `through a bed of solid adsorbent material. It is usually preferred, however, to carry out the adsorptive separation operation in the gaseous phase, that is, to maintain the hydrocarbon mixture undergoing treatment in the vapor phase during the adsorption operation. In such an operation any suitable method for effecting gas-solid contact vmay be employed, for example, a fixed bed, a moving bed or a iluidized bed or a gas-entrained mass of selective adsorbent may be employed during the gas phase adsorptive separation operation. After sufficient time, the solid adsorbent is separated from the resulting treated hydrocarbon mixture, now having a reduced proportion of straight chain hydrocarbons, and the separated rsolid adsorbent is then subsequently treated to desorb the adsorbed straight chain hydrocarbons therefrom. y

The desorption of the adsorbed hydrocarbons (straight chain hydrocarbons) from the solid adsorbent material may be made at any suitable temperature and pressure. For example, the desorption operation may be carried out at a pressure in the range 0-10,000 p.s.i.g. It is preferred, however, that the desorption operation be carried out in the gaseous phase, that is, the gaseous desorption or desorbing iuid and the resulting desorbed hydrocarbons yare both present in the resulting desorption efuent in the gaseous or vaporous phase. Accordingly, the desorption temperature and the desorption pressure are adjusted to maintain the desorption uid and the de- Gene'rally a desorption pressure in the range 102,`000 p.s.i.g. is suitable. It is sometimes desirable to carry out the desorption operation at a pressure substantially lower than the adsorption pressure. Isobaric adsorption-desorption operations are advantageous in some instances; however the pressure employed during the adsorptive separation operation is not determinative of the desorption pressure.

Any suitable desorption temperature suilciently high to effect desorption of the adsorbed straight chain hydrocarbone may. be employedrin the practice'of this' invention. Usually -atemperature in the range 40.04.100- AF. is employed during the desorption operation.. It is ge`n erally preferred, however, to carry out the desorption operation at an elevated temperature in the range 300- 1100 F. The desorption temperature employed, however, shouldv not be'excessively high, for example not greater than about ll-l300 F., particularly inthe instance wherein a material such as Linde Type A Molecular Sieve, that is, a calcium alumino-silicate, is employed as ther selective radsorbent since these temperatures are excessive and lead to the destruction of the adsorbent,

presumably by collapse ofthe crystal structure, with resultant. loss of the selective adsorption properties of this particular adsorbent. l

' Although desorption of the adsorbed straight chain hydrocarbon from the yadsorbent containing the same may be accomplished Iby the mere application of heat it is preferred vin the practice of this invention to employ a hot gaseous or vaporized desorbing fluid. Particularly useful as a desorbing fluid inthe practice of this invention is a gaseous or vaporized straight chain hydrocarbon, such as. ethane, propane or butane and the like. When a straight chain hydrocarbon is employed to eifect de sorption of the adsorbed straight chain hydrocarbon. the desorption operation should be carried out at a. temperature above the criticaltemperatures of not only the'adsorbed straight chain hydrocarbons to be desorbed but alsoabove the critical temperature of the straight chain hydrocarbon employed -as the desorbing uid or agent.` For example, when propane or normal butane` is 'emf ployed to desorb adsorbed n-butane-from the adsorbent material, the desorptionoperation. is carried out at a temperature above the critical temperature of n-butane, i. e., above 307 F. "t

Although it is preferred in the practice of this. invention to employ a straight chain hydrocarbon, such. as ethane, propane or nbutane, Aas` the desorbing agent to effect desorption of the adsorbed straight chain hydro-v carbons from the adsorbent, other desorbing agents, such as hydrogen, methane, branched chain hydrocarbons and the like or mixtures of desorbing agents, are also suitably employed; When, however, a straight chain hydrocarbon such as n-butane is employed as the desorbing agent there results from the desorption operation a desorption. efluent which is comprised substantially only of straight ch-ain hydrocarbons such as n-butane. A feed comprising substantially only straight chain hydrocarbon butane, with a C3 oleiinicv hydrocarbon, propylene, a feed stream of normal butane supplied from' a suitable source,

such as from the bottoms of a C4 fractionator tower, is supplied via line 11 as feed to isomerizer 12 wherein the n-butane is isomerized employing aluminum chloride as the isomerization catalyst together with HC1 as the catalyst promoter. There is recovered fromisomerizer 12 via line 14 an isomate mixture containing n-butane and isobutane. The resulting isomate mixture is fractionated in fractionator 15 from which there is recovered overhead viagline 16 any light ends, such as HC1, which might have issued overhead via line 14 Vfrom isomerizer 12.. There is also withdrawn from the upper portion of fractionator 15 via line 18 a side stream comprising a Casaturated hydrocarbon, propane. The bottoms from fractionator 15 comprising substantially only n-butane and isobutane is recovered via line 19 and introduced into neutralizer 20 wherein any catalytic material, such as aluminum chloride, carried over from isomerizer 12 with the isomate mixture in line 14 is neutralizedrand effectively removed. The resulting neutralizedisomate mixture is then passed via line 21 into adsorber 22 where it is contacted with a suitable selective adsorbent for straight chain hydrocarbons to etfect the: selective adsorp tion and removal of. thev n`butane from. the isobutane.- There is recovered from adsorber 22 via line 24 a treated effluent comprising substantially only isobutane.

As illustrated in the drawing a companion adsorber. 25 having therein adsorbent material containingadsorbed n-butane is undergoing desorption by contact with gaseous propane introduced into the upper portion of, adsorber 25 via line 26. The resulting desorption eiiiueut cornprising n-butane and propane is recovered fromrthe adsorber 25 via line 2S and returned via lines 29 and 11 to isomerizer 12 wherein the thus` recycled n-butaneV undergoes isomerization in the presence ofthe propane employed to eifect desorption of the adsorbed. n-butane from the adsorbent within adsorber 25.

The isobutane-recovered from adsorber 22 via line` 24 u i is introduced in admixture with a suitableC. olefin-con taining feed,l propylene, supplied from a suitable source via line 30 into alkylationreactor 31. The-Cgfeed supplied via line 30 to alkylation reactor 31 comprises. propylene and propane. The C3 olefin feed may be derived from any suitable source, such as a C3 fraction separated from a catalytic cracker off-gas or from the pyrolysisr of propane. If desired, additional or supplemental isobutane in a C., feed stream containing substantially only isobutane or isobutane and n-butane, may be introduced from, a suitable source via lines 32 and 2.4 intonalkylation reactor 31.

Within alkylation reactor `31 the isobutane an-d propylene undergo reaction with a resulting formation of the corresponding alkylate. There is recovered from alkylation reactor 31 via line 34 an alkylation reaction, effluent comprising unreacted isobutane, alkylate andfany propane originally contained in the C, olen feed and. any normal butane contained in the supplemental iso butane rsupplied to alkylation reactor 31.' The resulting alkylation reaction 'effluent is passed via line 34 into fractionator 35 where it undergoes fractionation with theV rc sultant recovery overhead via line 36x01" propane.- bottoms fraction recovered from fractionator' 35 via line 38 is introduced into deisobutanizer 39 wherein there recovered overhead via line 40 the unreactedy isobutane which is recycled via lines 46 and 24- tof'alky'lation rcactor 31. The bottoms 'is-suing from deisobutanizer. 39 via line 41 are introduced into debutanizer 42'whcrein there is recovered overhead via line 44 any vnormal butane which vmight have been introduced into. the. alkylation reactor with the supplemental isobutaine feed which is added via lines 32 and 24 to alkylationreactor 31. There is recovered as bottoms from debutanizer 42 via line: 24 the alkylate product, i.e.,. the resultingn reaction product of propylene and isobutane. Y

As illustrated in the drawing` the propane recovered overhead from fractionator 35 vvia line 36 is employed to effect desorption of the adsorbed normal butane fromthe adsorbent in adsorber 25. The propane is introduced into adsorber 2S from fractionator 35 via lines 36 and 26. If desired, the normal butane recovered overhead from debutanizer 42 via line 44, alone or in admixturc with the propane, may be employed to effect desorption of the adsorbed n-butane within adsorber 25 by introducing the n-butane recovered from debutanizer 42 into adsorber 25 via lines 44, 46 and 48. Further, as indicated in the drawing Vsupplemental propane as may be needed to effect complete .desorption of the n-butane from the adsorbent in adsorber 25 may be supplied from a suitable source via iinc 49 into line 36.

The propane employed to effect desorption of the adsorbed n-butane from the adsorbent within adsorber 25, and which is returned in the resultant desorption effluent via lines 28 and 11 to isomerizer 12, is recovered via lines 18 and 48 from the isomate mixture in line 14 after undergoing fractionation in fractionator 15. In the aboveindicated manner the propane employed to effect desorption ofthe adsorbed n-butane is retained within the ism.

eiiatiQri-adsorption-desorption system and does not cnti' the alkylation-fractionation and -recovery system.

" illustrated in the drawing, two adsorbers 22 and 25 are employed. When one adsorber, such as adsorber 22, is employed in the adsorption cycle the other adsorber, such las adsorber 25, is employed in the desorption cycle. Accordingly, when the adsorbent material within adsorber 22` is saturated with n-butane and when the adsorbent material vwithin adsorber 25 has been substantially completely depleted of any adsorbed n-butane, the isomate mixture issuing from neutralizer via line 21 is then introduced into adsorber via line 50 and the propane employed as desorbent uid is introduced into adsorber 22 via lines 36-and 51. When the adsorbers 22 and 25 are so employed there now issues from adsorber 22 via line 54 a desorption effluent comprising n-butane and propane. This desorption eluent in line 54 is recycled via lines 29 and 11 to isomerizer 12. At thesame time the adsorption eiliu'ent which issues from adsorber 25 via line 55 and comprising substantially only isobutane is intro duced via line 24 into alkylation reactor 31 to undergo alkylation reaction therein with propylene. Accordingly, by "employing in combination two adsorbers 22 and 25, one undergoing adsorption while the other undergoes desorption, the above-indicated combination of treating steps can be carried out substantially continuously.

As indicated in the accompanying drawing, the propane which is recovered overhead from fractionator 35 via line 36 was originally introduced into the alkylation reaction system together' with the C3 propylene-contaiuing feed. Further, the n-butane recovered overhead from debutanizer 42 via line 44 was originally introduced into the alkylation reaction system when supplemental isobutane feed is supplied to the alkylation reaction system via line 32'.' In the 'event no supplemental isobutane feed is supplied to the alkylation reaction system via line 32 debutanizer 42 would not be required, the alkylate product fraction being recovered as bottoms from deisobutanizer 39 via lines 41 and 47.

Although emphasis in this disclosure has been placed upon the applicabilityof the practice of this invention to the .alkylation of isobutane with propylene, it is mentioned that any suitable alkylation feed stocks, isomeric saturated hydrocarbon and olelinic hydrocarbon, are suitably ernployed in the practice of this invention. Suitable isomeric saturated hydrocarbons in addition to isobutane include the'isomeric pentanes and hexanes and the like and suitable olenic hydrocarbons include ethylene, the butenes including isobutylene, the .pentenes, the hexenes and the like.

Further, as mentioned hereinabove it is desirable in the practice of this invention to carry out the desorption of n-'butane from the adsorbent by employing a straight chain hydrocarbon under conditions such that the desorption temperature is greater than the critical temperature of the straight chain hydrocarbon employed' as -tlie' desorbing agent as'well as the adsorbed straight chain' hydrocarbon (nbutane) itself. The advantages of carry-vv ing out a desorption operation above the critical temperature of the desorbing agent as well as the critical temperatureof the hydrocarbon undergoing desorption are set forth in U.S. 2,818,455 issued December 31, 1957.v The disclosures of the above-identified patent with respect to carrying out a desorption operation above the crtical temperature of the hydrocarbon to be desorbed as well as'the desorbing agent itself are herein incorporatedand made part of this disclosure.

It is mentioned that in the accompanying disclosure and particularly in the drawing no reference has been made to conventional operating equipment, such as heatv exchangers, pumps, flow regulating devices, liquid level regulating devices and the like for reasons of clarity and not to clutter-up the specification and drawing. The employment of such devices in operations in accordance with the practice of this invention is readily apparent to those skilled in the art. Further, it is evident from the foregoing disclosure many modifications, substitutions and alterations are possible in the practice of this invention without departing from the spirit or scope thereof.

I claim: y

A petroleum treating process which comprises subjecting n-butane to isomerization to yield an isomate mixture comprising n-butane and isobutane, contacting said isomate mixture with a selective adsorbent which selectively adsorbs straight chain hydrocarbons to the sub-v stantial exclusion of non-straight chain hydrocarbons to adsorbk n-butane from said isomate mixture, passing the remaining visobutane to an alkylation reaction zone into admixture with an olenic hydrocarbon stream containing propylene and n-butane wherein said propyleue reacts with said isobutane to yield a corresponding alkylate, recovering from the alkylation reaction zone an alkylation reaction effluent comprising unreacted isobutane, nbutane and said alkylate, returning at least a portion of said unreacted isobutane to the aforesaid alkylation reaction zone, separating the aforesaid n-butane from the alkylation reaction efliuent, employing the separated nbutane to desorb thel adsorbed n-butane from said ad? sorbent, passing the resulting desorption effluent comprising only n-butane to the aforesaid isomerization reaction and recovering said alkylate as product from the aforesaid alkylation reaction eliuent.

References Cited in the tile of this patent` v UNITED STATES PATENTS '2,820,074 Pinesl Jan. 14, 195s

Claims (1)

1. A PETROLEUM TREATING PROCESS WHICH COMPRISES SUBJECTING N-BUTANE TO ISOMERIZATION TO YIELD AN ISOMTE MIXTURE COMPRISING N-BUTANE AND ISOBUTANE, CONTACTING SAID ISOMATE MIXTURE WITH A SELECTIVE ADSORBENT WHICH SELECTIVELY ADSORBS STRAIGHT CHAIN HYDROCARBONS TO THE SUBSTANTIAL EXCLUSION OF NON-STRAIGHT CHAIN HYDROCARBONS TO ADSORB N-BUTANE FROM SAID ISOMATE MIXTURE, PASSING THE REMAINING ISOBUTANE TO AN ALKYLATION REACTION ZONE INTO ADMIXTURE WITH AN OLEFINIC HYDROCARBON STREAM CONTAINING PROPYLENE AND N-BUTANE WHEREIN SAID PROPYLENE REACTS WITH SAID ISOBUTANE TO YIELD A CORRESPONDING ALKYLATE RECOVERING FROM THE ALKYLATION REACTION ZONE AN ALKYLATION REACTION EFFLUENT COMPRISING UNREACTED ISOBUTANE, NBUTANE AND SAID ALKYLATE,A RETURNING AT LEAST A PORTION OF SAID UNREACTED ISOBUTANE TO THE ARORESAID ALKYLATION REACTION ZONE, SEPARATING THE AFORESAID N-BUTANE FROM THE ALKYLATION REACTION EFFLUENT, EMPLOYING THE SEPARATED NBUTANE TO DESORB THE ADSORBED N-BUTANE FROM SAID ADSORBENT, PASSING THE RESULTING DESORPTION EFFLUENT COMPRISING ONLY N-BUTANE TO THE AFORESAID ISOMERIZATION REACTION AND RECOVERING SAID ALKYLATE AS PRODUCT FROM THE AFORESAID ALKYLATION REACTION EFFLUENT.

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