US2943037A - Naphtha treating process - Google Patents

Description

June 28, 1960 R. A. WOODLE ETAL 2,943,037

NAPHTHA TREATING PROCESS 2 Sheets-Sheet 1 Filed Jan. 7, 1957 #ETAP June 28, 1960 R. A. wooDLE ETAL 2,943,037

NAPHTHA TREATING PRocEss Filed Jan. 7, 1957 2 sheets-sheet 2 United States Patent O NAPHTHA TREATING PROCESS Robert A. Woodle, Nederland, Tex., John K. McKinley, Poughkeepsie, N.Y., and Roland F. Huhndorlf, Port Arthur, and Claude H. McIntosh, Groves, Tex., as-

l signors Vto Texaco Inc., a corporation of Delaware Filed Jan. 7, 1957, Ser. No. 632,739

3 Claims. (Cl. 20879)v tively low octane number. This is due to-the relatively high proportion of low octane normal paratlins, such as n-pentane,.nhexane, n-heptane,vnoctane and the like in Y jected to catalytic reforming to produce a reformerellluent having a relatively high octane number. This reformerV efiuent made up of hydrogen, butanes, pentanes and higher molecular weight' hydrocarbons is fractionated and there are separately recovered therefrom a hydrogen stream, va C, or butane hydrocarbon stream, a C5-or pentane hydrocarbon stream and a remaining reformate stream. These streams are then suitably treated and blended in accordance with the practice of thisinvensuch Vnaphthas. Because of their relatively lowoctane y numbers light naphthas are not particularly wellsuited for blending in present day high octane motor fuels wherein an octane number of 100 or greater isdesired. However,v i

since the light naphtha fraction usually comprises ajsubstantial portion of the crude `oil and in order to obtain a.satisfaotory yield of highy octane motor fuel from Ya given amount of crude oil, upgrading of the light naphtha fraction therefrom must be accomplished. .Y

A principal object of this invention is to provide an improved light naphtha conversion process.

Another object of this invention is to provide a process for the conversion of light petroleum fractions, particularly light petroleum naphthas Vcontaining vsubstantial amounts of straight chain hydrocarbons, in a plurality of relatively high octane streams suitable for blending in a high octane motor fuel.

Still another object of this invention is to providea process for upgrading light naphthas havinga boiling range in the range of 40-250 F. and containing a substantial amount of straight chain hydrocarbons, at least l about 5% by volume, to yield a plurality of relatively Y high octane hydrocarbon streams.

How these and other objects of this invention mayabe accomplished will become apparentfrom the accompanying detailed descriptionl and drawings which schematically illustrate an embodiment of the practice of this invention and wherein Fig. l is a ilow diagram of a naphtha treating process in accordance with one embodiment of the practice of this invention and wherein Fig. 2 graphical- Vly illustrates the advantages obtainable in the practice of this invention.

In accordance with our invention a light naphtha fraction, such as a light straight run naphtha, a light catalytic reformed naphtha, a light iluid catalytic cracked naphtha, a lightthermal cracked naphtha, natural gasoline, or mixtures thereof, is fractionated to separate therefrom a relatively high octane hydrocarbon stream, such as a streaml comprised essentially or predominantly of isopentane. The remaining naphtha fraction, substantially free ofvpentanes, particularly isopentane, is then subtion to -yield a plurality of hydrocarbon streams having a relatively improved octane number. For example, the remaining reformate stream is fractionated by selective adsorption to separate the straight chain hydrocarbons therefrom, thereby yielding a finished reformate having a higher octane number. The separated straight chain hydrocarbons may then be recovered and suitably con-l verted, as by isomerization, into a relatively higher octane number stream.

A petroleum naphtha fraction suitable for use in the.

practice of this invention might have an initial boiling point-in the range 40-85 F. and an end point in the range 175-250 F. Further, such a light petroleum fraction must contain both straight chain hydrocarbons and nonstraight chain hydrocarbons and might have the following compositions.

Hydrocarbon typ-e;A Y Percent by volume One treating'step, as indicated above, .employed in a combination treating `process of `ourinventionincludes- Y a selective adsorption operation wherein a relatively lhigh boiling portion of a catalytic reformate derived from the treatment of 'a light, naphtha fraction in accordance with the practice of this .invention is treated or contacted withl a solid selective adsorbent which selectively atlso'rbsv straight .chainI hydrocarbonrs'to the substantialexclusion carbons. Non-straight chain hydrocarbons whi'charesu'bl-VV stantiallyunaifected'or'unadsorbed bythe special selective` adsorbent employed'in the practice of this'inventionjin-A clude the isparains andthe lisoolelins such Vasisohexane,

Iisoheptanre, 'isoo'ctane isohexene, risoheptene;.isooctene andV the like as wellas the naphthenes and aromatic hy-f drocarbons.

Any solid adsorbentA which selectively adsorbsV straigliti chain hydrocarbn's'to the substantial exclusion of non- -straight chain'hy'drocarbons can be employed in the practice of this ir'uient'ion.^ Itis preferred, however, to employ asL the adsorbent `,certain natural or synthetic zeolitesjor.' alumino-silicates,A such as a calcium alumino-silicate,

ucts Company fand designatedtype Y5A molecular svtp-,

The crystals Aof this*particular calcium amiamo-silicate,pI Y Y apparently actuallyV a sodium calcium aluinino-silic'ate,`

have a pore sizeior.' diameter of abotSAn'gstronr f 2,9t3,o1. e 1

vPatented Jnnelzagissp,

apore size suic'ient to admit straight chain hydrocarbons, such as the n-paraflins, to the substantial exclusion of the non-straight chain hydrocarbons, such as the napthenic, aromatic, isoolefinic and isoparanic hydrocarbons, e.g., isobutane and higher. This particular selective adsorbent is available in various sizes, such as lAG and ls diameter pellets as well as in a finely divided powder form, suitable for employment in a fixed bed, a moving bed or a huidized bed adsorption process.

Other selective adsorbents may be employed in the practice of this invention. For example, it is contemplated that 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 amphoteric metal oxides.

Other suitable selective adsorbents are known and include the synthetic and natural zeolites which, when dehydrated, may be described as crystalline zeolites having a rigid three dimensional anionic network and having7 interstitial dimensions sufficiently large to adsorb straight chain hydrocarbons but sufiiciently small to exclude the non-straight chain hydrocarbons. The naturally occurring zeolite, chabazite, exhibits such desirable properties. Another suitable naturally occurring zeolite is analcite which, when dehydrated and when all or part of the sodium is replaced by an alkaline earth metal, such as calcium, yields a material which may be represented by the lformula (Ca, Na)Al2Si4O12.2H2O and which, after suitable conditioning, will adsorb straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons. Naturallyoccurring, or syntheticallyprepared pha'colite, grnelinite, hannotome and the like or suitableY modiiications of these products by ybase.` exchange are also applicable-in the practice of this invention.

-Y Other'solid adsorbents` which.. adsorb `straight chain hydrocarbons such as n-paraflins and Yn-olefins to the p substantial exclusion of non-straight chain hydrocarbons, including the aromatic and naphthenic'hydrocarbon's, are known. j

`Referring now to the drawing and in greater detail to Fig. 1 thereof there is schematically illustrated a flow diagram of one embodiment ofthe practice of this invention. A light straight run naphtha boiling in the range 604225 F. is introduced via line 10 into debutanizer 11 wherein the butanes or C4 hydrocarbons are removed overhead via line 12. The remaining bottoms portion is `recovered via line 14 and introduced into depentanizer 1 5A wherein the pentane .or C5 fraction comprised predominantly of n-pentane and isopentane 'is recovered overhead va Vline 16. The bottomsfrom depentanizer 15 comprising the relatively high molecular weight hydrocarbons, parafinic and non-paranic, aswell as straight chain and non-straight chain hydrocarbons, initially present in the light straight run naphtha isV recovered via line 1,8 and introduced into catalytic reformer 19 where they are subjected to catalytic reforming in contact with a suitable catalyst such as a platinum-containing catalyst, eg., platforming catalyst. Catalytic reformer 19 is operated under such conditions of temperature so as to effect the isomerizaon and/or dehydrocyclization of the straight chain parafinic hydrocarbons and the nonstraight chain parafiinic hydrocarbons introduced thereinto'via line 1d, as well as aromatization ofthe naphthenes. Y

There is recoveredfrom catalytic reformer 19 via line 20 a total reformer effluent comprising hydrogen, together with al small amount of normally gaseous hydrocarbons such as methane and ethane, as well asa C4 hydrocarbon fraction: comprising. butane and isobutane, a C5 hydrocarbon. fractionl comprising n-pentane and isopentane together with relatively-high molecular weight reformed hydrocarbons such as 'non-straight chain C6, C7 and C8 and higherhydrocarbons, such as isohexane, isoheptane,

isopentane, benzene, toluene, xylenes and the like. The reformer eflluent from catalytic reformer 19 is carried via line 20 into gas separator 21 wherein the normally gaseous portion thereof comprised substantially entirely of hydrogen is removed overhead via line 22. The remaining liquid reformer effluent passes from separator Z1 via line 24 into debutanizer 25 wherein there is recovered overhead via line 26 the C4 hydrocarbon fraction comprising butane and isobutane which is blended or otherwise admixed with the C4 hydrocarbon fraction obtained initially from the light straight run naphtha via debutanizer 11 and line 12; The resulting admixture of the butanes may be separately recovered for blending purposes via line 28.

The bottoms from debutanizer 25 is removed via line 29 and introduced into depentanizer 30 wherein the pentane or C5 hydrocarbon fraction thereof is recovered and then preferably admixed with the C5 fraction recovered overhead from depentanizer 15 via line 16 and introduced via line 32 into deisopentanizer 34 from which isopentane or a portion thereof is recovered overhead via line 35. The remaining bottoms reformer eflluent recovered from depentanizer 3G via line 36 is introduced into adsorber unit or adsorption zone 38. The remaining reformer effluent introduced into adsorption zone 38 comprises reformed relatively high molecular weight hydrocarbons, including non-straight chain parainic hydrocarbons such as isohexane, isoheptane, isooctane and the like as well as the cyclic aromatic hydrocarbons such as benzene, toluene, xylenes together with some unreacted or unconverted straight chain hydrocarbons such as n-hexane, n-heptane, n-octa'ne and the like. l `There is provided within adsorption zone 33 a selective`ads'orbenty such as Linde type 5A molecular sieve which'lselectively adsorbs straight chain hydrocarbons to th'e'substantial exclusion of non-straight chain hydrocarbons. The selective adsoiption unit or adsorption zone may comprise a fixed bed, a fluidized bed or a nioving bed of selective adsorbent maintained at a suitable temperature, such as a temperature in the range 20G-750 F., to effect selective adsorption of the straight chain hydrocarbons from the remaining reformer effluent introduced thereinto. The adsorption operation is carried out at any convenient pressure, such as a pressure in the range 0-500 p.s.i.g. Desirably the temperature and pressure within adsorption zone 38 is adjusted so that the reformer efiluent undergoing fractionation therein is maintained in' the vapor or gaseous phase. Liquid phase adsorption, although operable, is less preferred.

Following the selective adsorption operation carried out within selective adsorption unit 38 Athere is recovered therefrom via line 39 a finished reformate or reformed naphtha comprised substantially only of non-straight chain hydrocarbons and having an increased octane number as compared with the light straight run naphtha introduced intothe process via line 10. The finished reformed naphtha recovered from the process via line 39 may be used directly as a motor fuel or as a high octane blending component of a high octane motor fuel. Advantageously, this finished reformed naphtha may also be blended with the butanes recovered from debutanizer 11 and de'- butanizer 25 via lines 12 and' 26, respectively.

The straight chain hydrocarbons' adsorbed within the selective adsorbent employed Within adsorber unit 38 are' desorbed therefrom. In accordance with one embodiment of the practice of this invention the desorption of the adsorbed straight chain hydrocarbons is effected by contacting the selective adsorbent with the gaseous fraction recovered from gas separator 21 via line 22. As' indicated hereinbefore, this gaseous fraction is composed predominantly of hydrogen. The desorption operation is carried out at arelatively elevated temperature, usuallyr in the range 400 F.-800 F., preferably at a tempera'-4 4J-smania the desorption operation is carried out at' a :suitable .temperatureV and pressure'so that the resulting 'desorbed straight chain hydrocarbons are desorbed or recovered in the gaseous phase. A suitable desorption temperature is in the range 30G-800` F. and a pressure in the range 0-500 p.s.i.g. If desired, isothermal and/or isobaric adsorption and desorption operationsmay be employed.

compatible wthor otherwiseV chemically inert with respect to the straight chain hydrocarbons to be desorbed and chemically inert with respect to the adsorbent employed may be utilized. It is preferred, however, as previously indicated to employ the reformer hydrogen efuent recovered` from gasA separator 21 via line 22 or another material such as" av C4 hydrocarbon (butane and/or isobutane) readily separable by distillation from the resulting straight chain hydrocarbon desorbate.

The desorbed straight chain hydrocarbons are recovered from adsorber unit 38 via line 40. If desired, thetotal desorption eluent comprising the desorbed straight chain hydrocarbons and gaseous desorbing medium (hydrogen) is returned via lines 41, 42 and 18 to catalytic reformer 19. When the practice of this invention is carried out in accordance with this embodiment the straight chain hydrocarbons originally present in the light straight run naphtha introduced into the process via line 10 are substantially completely converted to non'straight chain hydrocarbons, either the corresponding non-straight chain isoparainic hydrocarbons and/or the related cyclic aromatic hydrocarbons. f

If desired, the desorption efuent recovered from adsorber unit 38 via line 40 may beY introduced via line 44 together with the bottoms from deisopentanizer 34 comprised predominantly of n-pentane into isomerizer 45. As indicated in Fig. l, isomerizer 45, if desired, may

. AEXAMPLE "y i i lighty straight run gasoline was debutanized and depentanizved to yield a reformer charge stock having an initial boiling pointof 150 F. and an end point of`206 F.Y The APIKgravity of the charge stock was 71.8 and a hydrocarbon-,type analysis of the charge stock showed that'it contained 3.4% by weight aromatics, 1% by weight olens, 72.3% by Weight paraflins and 23.3% by weight naphthenes. The charge 'stock had an ASTM research octaneNo., clear, of 65.6, +3 cc. TEL of 82.0.

The charge stock was subjected to catalytic reforming (platforming) by contact under reforming conditions of temperature and pressure with a platinum-containing catalyst (UOPR-S platforming catalyst). The resulting reformate was depentanized toyield areformate having an ASTM research octane No., clear, of 75.4, +3 cc.

' TEL of92.2 i

be supplied with gaseous hydrogen recovered from gas,v

separate'` isomerizers' (notillustrated). are provided to v eifectseparate isomerization ofthe n-pentanes Vand sepa? rate isomerization of the desorbedstraight chain hydrocarbons emanating from adsorberV unit 38. The isomate or isomerizer effluent issuing from isomerizer 45 via line 48 maybe I,reintrodlglced into adsorbervunit'v38pvia line 49 to effect separation ofthe non-straight chain and the straight chainhydrocarbons therein. Further, ifV desired, the resulting isomerizer eiiluent may be'admixed Yor otherfrom deisopentanizer-34 viaV line 35. t

' Blending 'of the isomerizerefluent with the `isopentarie infline 35 is `particularly desirable or suitable when the isomerizer euent is comprised substantially only of `C54 hydrocarbons such as would be the case when a separate isomerization facility is provided for the n-pentane recovered from deisopentanizer 34.

The following example is illustrative of the practice of this invention.

wise blended-via line 50-with the visopentanes recovered Y The depentauized reformate was then subjected to a selective adsorptive-separation operation employing a sodium calcium alumino-silicate molecular sieve typeadsorbent (Lindetype'SA molecular sieve) to yield 'a fmished reformate having an ASTM researchv octane No., clear, of 88.2, +3 cc. TEL of 99.8.

The straightvchain hydrocarbons separated from the reformate by selective adsorption are advantageously separately treatedY as by isomerization'to improve the octane number thereof. For` example, a mixture vof straight chain hydrocarbons lcomparable to the straight chain hydrocarbons separated from the reformate during the aforesaid selectiveadsorption operation having a com? positionof about 23% vby volume n-pentane, 56% by volume'n-hexane and 21% by volume .i1-'heptane and hav- -ing an ASTM researchoctane No., clear,.of 39 was contacted with" afplatinum.isomerization` catalyst at aV temperature of-aboutf850v Fi', at. a pressure of 550 p.s'.i.g. and aspace velocity of .1.v./hr./v. employing a hydrogen recycleratefof; about 4,000 s.c.f. per barrel' ofchargel The resulting isornate consisted `of a mixture of straight chain andfnonestraight'chain hydrocarbons `andhad an ASTM research octane No., clear, of about 74.

The V resulting isomate, in `accordancewith one embodiment of the practiceV of this invention, was then vapor'izedf` and contacted with asolid Vselective adsorbent for the removal ofi-fthe s'traightchain hydrocarbons therefrom under .conditions similar `to those employed in the treating of the depentanized catalytic reformate. The thusnished isomate exhibited an ASTM researchoctane f No.2; c1ear,;of"about 82:0; Blending of thenished catalytic reformate and thernished 'isomateV could then be carried out to yield a naphtha particularly suitable as a motorfuel. j f

Another mixturelof straight chain hydrocarbons comyparable to thehydrocarbonsdesorbed from thel s olid ,ad-

9i charger-.Contactinsttemperatures and the results'ubtained are `g1 enin Table-,I below:

' Table 1" Temperature, 1115....1,1... 920 943 Wt.- PercentRec very (Liquid). ,793.8 81.3 Bromine NoY v f v*20 22 Vol.; Percent Aromatics-.'-. 15 `13 ASTM Research OctaneNo k e0. 6 Y57.16 +3 ce. TEL/gal so. 4 so, 2

Other mixtures of straight chain hydrocarbons comparable to the straight chain hydrocarbons recovered during the desorption operation having a composition of about 23% by volume n-pentane, 56% by volume 7 n-hexane and 21% byvolumenlheptane and exhibiting an ASTM research octane number, clear, of 39 were contacted with various catalysts -uncierY isomeri'zingeonditions of temperature and at a pressure of about -500 p.`s.i'.g., a space velocity of 1.0 v./hr./v. and a hydrogen recycle rate of 4000 s.c.f./bbl. The catalysts, reaction .temperatures and ASTM researchoctaneY No., clear, of the convertedV products and of the finished converted products, Le., converted products after having been con- S -250 VF. and containing pentanes and higher molecular weight parainic-hydrocarbons to separate said pentanes from said high molecular weight parainic hydrocarbons, fractionating said pentanes -to separate isopen- Vtane from n-pentane, recovering the resulting separated isopentane, subjecting the separated n-pentane to isomerization to yield an isomerized effluent comprising isopentane, catalytically reforming the higher molecular weight paraflinic hydrocarbons to yield a reformer efliutacted with adsorbent for the removal of straightchain lo ent comprising hydrogen, C4 hydrocarbons, pentanes and hydrocarbons, are set out in Table II below:

l Table l1 higher molecular weight reformed hydrocarbons, sepa- Temp., F son 85o 90o Catalyst. Plat Baker Ultra Plat. Baker Ultra Plat. Baker Ultra Liq. Rec., Wt. Percent 95. 9 99. 3 90. 1 95.0 99. 0 88. 2 67.6 70. 1 72. 7 Converted Product, Octane No 60. 0 51. 0 54.0 75.4 74.0 77. l 89. 6 70.0 78. 9 Product Finished by Selective Adsorption, Octane Y No 78.0 61.0 72 0 S4 0 82.0 82.6 80.3

P1at.-UOP platformng catalyst. Y Bakcr-Sinclair-Baker RD 150 catalyst. Ultra-Standard of Indiana ultraformlng catalyst.

The foregoing examples illustrate how a light naphtha fraction advantageously is treated to produce a plurality of upgraded stocks particularly suitable for blending to produce a high octane motor fuel.

Referring now to Fig. 2 of the invention which graphically illustrates the advantages of the practice of this invention there is illustrated the yield-octane relationships of naphtha fractions treated in accordance with the practicevof this invention. As illustrated in Fig; 2V the leaded octane (+3 ccs. TEL) of the finished gasolinerange from 99.8 to 104.4. A line correlating' the nshed. gasoline leaded octane yield data intersected 100 octane (+3 ccs. TEL) at about 55 volume percent'depentanized gasoline yield basis fresh feed to the catalytic reformer (platformer).

From the data presented hereinabveit isapparent that a depentanized light straight run gasoline canV be upgraded to above 100 octane (the research +3 cc.. TEL) by catalytic reforming (platforming) and subsequent iinishing or removal of the straight chain hydrocarbons from the depentanized reformate.

It has been shown that from 100 barrels of depentanized light straight run gasoline the following quantities of liquid materials would be produced Finished gasoline, ASTM Research Octane N o. -l- 100 4 3 ccs. TEL i Finished gasoline, bbls 55` N-pcntane, bbls. (which can be upgraded to isop'en-` tan Desorbate, bbls. (which can be upgradedY by isonicrization or aromatization to high octanehydrocarbons). Bntane, bbls rately separating said hydrogen, said C4 hydrocarbons and said pentane from said reformer eiiluent, separately recovering the resulting separated C4 hydrocarbons, subjecting the resulting separated pentanes to fractionation to separate isopentane from n-pentane, blending the thusseparated isopentane with the aforesaid previously separated isopentane and blending the thus-separated npentane with the aforesaid separated n-pentane prior to isomerization, subjecting the remaining reformer effluent ,to contact with a solid molecular sieve alumina-silicate selective adsorbent which selectively adsorbs straight chain hydrocarbons to the substantial exclusionof nonstraight chain hydrocarbons, said contacting operation being carried out at a temperature in the range ZOO-750 F. and at a pressure in the range of 0-500 p.s'.i.g. and under conditions Such that said reformer effluent is in the gaseous phase, recovering from the aforesaid selective adsorption operation a first hydrocarbon stream substantially free of straight chain hydrocarbons and desorbing the adsorbed straight chain hydrocarbons from said selective adsorbent by contacting said absorbent with gaseous aforesaid separated C4 hydrocarbons at a temperature in the range 40G-800 F. and at a pressure `in the range 0-500 p.s.i.g., said desorption temperature being 50-250 degrees Fahrenheit greater than the aforesaid ad# `sorptiontemperature and such that the resulting desorbed straight chain hydrocarbons are in the gaseous'phase.

2. A process in accordance with claim 1 wherein said straight chain hydrocarbons desorbed from saidselec'- tive adsorbent by contact with said C4 hydrocarbon are recycled to the aforesaid catalytic reforming operation.

3. A process in accordance With claim 1 wherein said straight chain hydrocarbons desorbed lfrom said`selective adsorbent are isomerized in the aforesaid isomerizaton operation.

References Cited in the iile of this patent UNITED STATES PATENTS 2,425,535. YI-Iibshman Aug. 12, '1947 '2,442,19l Black May 25 1948 2,443,607 Evering June 22, l1948 :2,818,449 Christensen et al. Dec. 3l, 1.957 2,818,455 Ballard et a1. '-..,Dec. 3.1, 1957

Claims (1)

1. A PROCESS FOR UPGRADING A LIGHT NAPHTHA FRACTION INTO A PLURALITY OF RELATIVELY HIGH OCTANE HYDROCARBON STREAMS WHICH COMPRISES FRACTIONATING A LIGHT NAPHTHA PETROLEUM FRACTION HAVING A BOILING RANGE IN THE RANGE 40-250*F. AND CONTAINING PENTANES AND HIGHER MOLECULAR WEIGHT PARAFFINIC HYDROCARBONS TO SEPARATE SAID PENTANES FROM SAID HIGH MOLECULAR WEIGHT PARAFFINIC HYDROCARBONS, FRACTIONATING SAID PENTANES TO SEPARATE ISOPENTANE FROM N-PENTANE, RECOVERING THE RESULTING SEPARATED ISOPENTANE, SUBJECTING THE SEPARATED N-PENTANE TO ISOMERIZATION TO YIELD AN ISOMERIZED EFFLUENT COMPRISING ISOPENTANE, CATALYTICALLY REFORMING THE HIGHER MOLECULAR WEIGHT PARAFFINIC HYDROCARBONS TO YIELD A REFORMER EFFLUENT COMPRISING HYDROGEN, C4 HYDROCARBONS, PENTANES AND HIGHER MOLECULAR WEIGHT REFORMED HYDROCARBONS, SEPARATELY SEPARATING SAID HYDROGEN, SAID C4 HYDROCARBONS AND SAID PENTANE FROM SAID REFORMER EFFLUENT, SEPARATELY RECOVERING THE RESULTING SEPARATED C4 HYDROCARBONS, SUBJECTING THE RESULTING SEPARATED PENTANES TO FRACTIONATION TO SEPARATE ISOPENTANE FROM N-PENTANE, BLENDING THE THUSSEPARATED ISOPENTANE WITH THE AFORESAID PREVIOUSLY SEPARATED ISOPENTANE AND BLENDING THE THUS-SEPARATED NPENTANE WITH THE AFORESAID SEPARATED N-PENTANE PRIOR TO ISOMERIZATION, SUBJECTING THE REMAINING REFORMER EFFLUENT TO CONTACT WITH A SOLID MOLECULAR SIEVE ALUMINA-SILICATE SELECTIVE ADSORBENT WHICH SELECTIVELY ADSORBS STRAIGHT CHAIN HYDROCARBONS TO THE SUBSTANTIAL EXCLUSION OF NONSTRAIGHT CHAIN HYDROCARBONS, SAID CONTACTING OPERATION BEING CARRIED OUT AT A TEMPERATURE IN THE RANGE 200-750* F. AND AT A PRESSURE IN THE RANGE OF 0-500 P.S.I.G. AND UNDER CONDITIONS SUCH THAT SAID REFORMER EFFLUENT IS IN THE GASEOUS PHASE, RECOVERING FROM THE AFORESAID SELECTIVE ADSORPTION OPERATION A FIRST HYDROCARBON STREAM SUBSTANTIALLY FREE OF STRAIGHT CHAIN HYDROCARBONS AND DESORBING THE ADSORBED STRAIGHT CHAIN HYDROCARBONS FROM SAID SELECTIVE ADSORBENT BY CONTACTING SAID ABSORBENT WITH GASEOUS AFORESAID SEPARATED C4 HYDROCARBONS AT A TEMPERATURE IN THE RANGE 400-800*F. AND AT A PRESSURE IN THE RANGE 0-500 P.S.I.G., SAID DESORPTION TEMPERATURE BEING 50-250 DEGREES FAHRENHEIT GREATER THAN THE AFORESAID ADSORPTION TEMPERATURE AND SUCH THAT THE RESULTING DESORBED STRAIGHT CHAIN HYDROCARBONS ARE IN THE GASEOUS PHASE.

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