US3007863A - Method of treating a petroleum fraction using molecular sieve aluminosilicate selective adsorbents - Google Patents

Description

Nov. 7, 1961 H. METHOD OF TREATING A P V. HESS ET ETROLEUM FRACTION USING MOLECULAR SIEVE ALUMINO-SILICATE SELECTIVE ADSORBENTS Filed April 24. 1959 2 Sheets-Sheet 1 dam/feria V ,PEF-armar:- Fiom/cr Nov. 7, 1961 H. v. Hr-:ss ETAL 3,007,863 gISJECULAR METHOD OF TREATING A PETROLEUM FRACTION USING M SIEVE ALUMINO-SILICATE SELECTIVE ADSORBEN Filed April 24, 1959 2 Sheets-Sheet 2 .gni QQ mm. wwwa@ bb NM Wh hw mwb United States Patent O METHGD OF TREATING A PETROLEUM FRAC- TION USING MGLECULAR SIEVE ALUMINO- SILICATE SELECTIVE ADSGRBENTS Howard V. Hess, Glenham, and Edward R. Christensen,

Wappingers Falls, N.Y., assignors to Texaco Inc., a

corporation of Delaware Filed Apr. 24, 1959, Ser. No. 808,700 3 Claims. (Cl. 20S- 92) This invention relates to a method of treating petroleum fractions. More particularly, this invention relates to an improved hydrocarbon conversion process. In accordance with one embodiment this invention relates to the treatment of naphtha or petroleum fractions in the gasoline boiling range to improve their quality as motor fuels. Still more particularly, this invention is directed to the treatment of naphtha stocks containing straight chain hydrocarbons and non-straight chain hydrocarbons, especially naphtha stocks wherein the amount of straight chain hydrocarbons is substantial, i.e., in the range 530% by vol. and higher.

Various converting processes have been proposed for the treatment of naphtha stocks to produce a high quality, high octane motor fuel. These p-rocesses call for the vapor phase treatment of selected petroleum fractions in the gasoline boiling range by contact with an active converting catalyst such as a platinum-containing catalyst, a chromia-alurnina catalyst, a molybdena-alumina catalyst or the like. During treatment of these selected petroleum fractions a number of reactions take place substantially simultaneously. For example, in a treating operation employing -a platinum-containing catalyst in contact with a naphtha stock containing aromatics, naphthenes, isoparaffins and n-parafhns, dehydrogenation ofthe naphthenes to aromatics occurs. Substantially at the same time, especially when operating under more severe treating conditions, isomerization and dehydrogenation of the paraiinic components take place. Additionally under these conditions aromatization or dehydrocyclization of the parailinic components also takes place. Concurrently with these reactions, particularly under the more severe treating conditions, a certain amount of cracking takes place with the resulting deposition of carbon upon the catalyst and the formation of lighter molecular weight hydrocarbons, such as C4 hydrocarbons.

The platinum-containing treating catalysts employed in the present day commercial operations are expensive. Some of these platinum-containing catalysts are regenerable and some are non-regenerable- An important factor in the determination of the useful life of a treating catalyst, particularly a platinum catalyst, is the amount of carbon deposited or laid down upon the catalyst. The replacement of a spent treating catalyst, particularly a platinumcontaining catalyst, is also expensive. Moreover, the regeneration of a spent regenerable catalyst is an expensive operation and time consuming, all the more so in a renery operation when for purposes of regeneration it is necessary to take a catalyst case or unit offstream.

Accordingly it is an object of this invention to provide an improved process for treating petroleum fractions containing straight chain hydrocarbons.

It is another object of this invention to provide a flexible petroleum converting and/or treating process which is capable of handling a wide variety of petroleum fractions containing straight chain hydrocarbons and non-straight chain hydrocarbons, especially petroleum fractions in the gasoline boiling range, either a wide boiling or a narrow boiling cut.

Still `another object of this invention is to provide a treating process wherein the useful onstream life of a treating catalyst, especially a platinum-containing catalyst,

is substantially increased, particularly when compared with the same catalyst employed in a catalytic conversion or treating operation in the conventional manner at the same degree of severity.

Still another object of this invention is to provide a combination treating operation wherein the amount of improved high quality, high octane motor fuels is increased.

Yet another object of this invention is to provide a method employed in combination with a petroleum converting or treating operation for increasing throughput when operated at a given degree of severity or conversion.

Still another object of this invention is to provide a combination catalytic treating operation for the production of high octane motor fuel not otherwise otbainable save at the expense of prohibitively shortened catalyst life.

In at least one embodiment of this invention at least one of the foregoing objects will be achieved.

How these and other objects of this invention are achieved will become apparent with reference to the accompanying disclosure and drawings wherein:

FIG. l is a block ilow diagram broadly outlining the process of this invention, and wherein FIG. 2 is a schematic flow diagram illustrating various embodiments of the practice of this invention.

AIn accordance with our invention We have provided an improved operation for treating or converting a petroleum fraction containing straight chain hydrocarbons and nonstraicht chain hydrocarbons which comprises contacting said fraction with a solid adsorbent which selectively adsorbs straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons to adsorb straight chain hydrocarbons from said fraction. The resulting petroleum fraction now having a reduced proportion of straight chain hydrocarbons is then desirably subjected to a treating or converting operation, such as catalytic reforming or isomerization to produce a petroleum fraction of improved quality.

The practice of this invention is particularly applicable to any petroleum fraction suitable for use in a catalytic reforming operation -for the production of aromatics or improved naphthas or motor fuels in the gasoline boiling' range, said petroleum fraction -containing straight chain hydrocarbons and non-straight chain hydrocarbons. By straight chain hydrocarbons is meant any aliphatic, acyclic or open chain hydrocarbon which does not possess side chain branching. Representative straight chain hydrocarbons are, of course, the normal parains and the normal oleiins, monoor polyolens, including the straight chain acetylenic hydrocarbons. The non-straight chain hydrocarbons comprise the aromatic and naphthenic hydrocarbons as Well as the isoolenic and isoparaiiinic hydrocarbons and the like. A petroleum fraction suitable for use in the practice of this invention might have an initial boiling point in the range 50-300 F. and an end point in the range 200-475 F., more or less. Furthermore, a petroleum fraction suitable for use in the practice of this invention contains both straight chain and nonstraight chain hydrocarbons, and might have a composition in the range:

Hydrocarbon type: Percent by volume The straight chain hydrocarbon or n-paralhn content of petroleum fractions suitable for use in the practice of this invention is frequently in the range of 5-50% by vol., more or less. Typical renery stocks or fractions such as a wide boiling straight run naphtha, a light Patented Nov. 7, 1961 straight run naphtha, a heavy straight run naphtha, a catalytic cracked naphtha, a thermally cracked or a thermally reformed naphtha may be employed in the practice of this invention.

Any solid adsorbent which selectively adsorbs straight chain hydrocarbons to the substantial exclusion of nonstraight chain hydrocarbons can be employed in the practice of this invention. It is preferred, however, to employ as the adsorbent certain natural or synthetic Zeolites or alumino-silicates such as a calcium alumino-silicate which exhibit the property of a molecular sieve, that is, inorganic materials made up of porous crystals wherein the pores of the crystal are of molecular dimension and are of uniform size. A suitable, commercially available molecular sieve adsorbent, apparently actually a sodium calcium aluminosilicate, has a pore size or diameter of about Angstrom units, a pore size suflicient to admit straight chain hydrocarbons to the substantial exclusion of the naphthenic and aromatic hydrocarbons, `and the isoparaiins, isobutane and higher. This particular selective adsorbent is available in various sizes such as 1/16" or ls" diameter pellets as well as finely divided powder form.

Other solid 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 over nonstraight 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 solid selective adsorbents are known and include the synthetic and natural zeolites which, when dehydrated, may be descrbed as crystalline zeolites having a rigid three dimensional anionic network and having interstitial dimensions sufficiently large to adsorb or to permit the entry of straight chain hydrocarbons but sufiiciently small to exclude non-straight chain hydrocarbons. The naturally occurring zeolite chabazite exhibits such desirable properties. Another suitable naturally occurring zeolite is analcite NaAlSi2O6H2O which when dehydrated and when all or part of the sodium is replaced by calcium yields a material which may be represented by the formula (Ca,Na2)Al2Si4O12.2H2O and which, after suitable conditioning, Will adsorb straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons. Naturally occurring or synthetically prepared phacolite, gmelinite, harmotome and the like, or suitable modifications of these produced by base exchange are also suitable. Other solid adsorbents which selectively adsorb straight chain hydrocarbons such as the nparaflins and n-olefins to the substantial exclusion of the non-straight chain hydrocarbons, including the aromatic and naphthenic hydrocarbons, are also known.

Referring now to FlG. l of the drawing which sets forth in a block flow diagram various embodiments of the practice of this invention, a fresh feed petroleum fraction which may have a wide or narrow boiling range, containing straight chain hydrocarbons (n-paraflins and/ or n-olefms) in admixture with non-straight chain hydrocarbons (aromatic and/ or naphthenic and/ or isoparafiinic hydrocarbons) is optionally supplied to a suitable feed preparation and/ or fractionation unit. Should the fresh feed contain substantial amounts of undersirable polar or polarizable compounds such as sulfur-containing compounds, oxygenated hydrocarbons, nitrogen-containing compounds and the like, it is sometimes desirable, although not necessary, to remove these materials from the fresh feed prior to the special subsequent feed treatment in accordance with this invention. The removal of these polar or polarizable materials may be accomplished by solvent extraction, extractive distillation, hydrogenation, dehydration, acid or caustic washing and the like or by any suitable combination. Processes for removing or effectively neutralizing the above-indicated polar and polarizable materials in a petroleum fraction are well known in the art.

The above-mentioned feed preparation operation may be carried out in a vapor or liquid phase and might involve Vapor-liquid, liquid-liquid, vapor-solid and liquidsolid contacting operations depending upon the operating conditions necessary to effect the desired feed preparation or purification. Following the above-indicated feed preparation or concomitantly therewith, if desired, the feed may be fractionated to remove relatively low boiling and/ or relatively high boiling components to produce the desired feed containing straight chain hydrocarbons and non-straight chain hydrocarbons to be treated in accordance with this invention. The fractionation operation may be operated to produce a narrow boiling or wide boiling fraction depending upon the qualities of the finished treated product desired.

Following the feed preparation and/or fractionation operations the feed is contacted with a solid selective adsorbent material, in powder, beaded, microspheroidal, granular or pelleted form, for the selective adsorption of the straight chain hydrocarbons. Although it is preferred to remove substantially all of the straight chain hydrocarbons, it is realized that it is not necessary in the practice of this invention to adsorb or separate substantially all of the straight chain hydrocarbons. The extent or degree of straight chain hydrocarbon removal is governed by various factors including capacity of the equipment involved, the quality desired in the finished treated product, yield considerations, the particular subsequent hydrocarbon treating or converting operation, and the like.

The feed petroleum fraction undergoing treatment may be present during the selective adsorption operation either in the liquid phase or in the gas or vapor phase. The capacity of the solid adsorbent material as a selective adsorbent for straight chain hydrocarbons is substantially unaffected by the phase condition of the feed petroleum fraction in contact therewith provided, of course, suicient time is allowed to substantially saturate the adsorbent.

The contact of the feed with the selective solid adsorbent may be effected by various means. For example, operating with the feed petroleum fraction in the liquid phase a simple and direct method of effecting contact with the solid particle-form selective adsorbent is to employ the adsorbent in the form of a fixed bed or to form a slurry of the petroleum fraction and the solid adsorbent material. After sufficient time the slurry may be settled and the liquid phase decanted by suitable means. Advantageously the resulting solid adsorbent material is recovered and washed witha straight chain or a nonstraight chainV hydrocarbon or a mixture thereof, such as a petroleum fraction, having a boiling point such that the separation of this wash liquid from the surface occluded feed or the adsorbed straight chain hydrocarbons is readily accomplished by distillation. A suitable liow boiling wash liquid is a hydrocarbon in the molecular weight range C3-C5, such as n-butane or isobutane or mixtures thereof. After washing to remove the surface-adsorbed material from the solid adsorbent the adsorbent is desirably dried, such as by flash vaporization. Following this washing operation the adsorbent is stripped of its straight chain hydrocarbon content. Heat to desorb the adsorbed straight chain hydrocarbons may be applied to the adsorbent by any suitable means such as by forcing or by passing a desorbing liquid, gas or vapor therethrough, such as the above-identified wash liquid, e.g. n-propane, n-butane, isobutane, n-pentane, isopentane, flue gas, hydrogen, nitrogen, methane or natu-ral gas and the like. The resulting stripped solid adsorbent material is thenrecycled to the aforementioned contacting or adsorption operation.

Besides the above-indicated method of effecting contact between the feed petroleum fraction `and the solid adsorbent material, the following other methods may be employed. A suitable amount of the solid adsorbent may be introduced directly into a liquid or vapor stream of the feed, such as into a refinery transfer line, to effect contact. The resulting admixture may be separated by any suitable means such as by settling, filtration vand by means of cyclone or gas-solids or liquid-solids separators and the like. in accordance with yet another method of contacting, the feed petroleum fraction may be treated with the solid selective adsorbent by circulation pumping wherein a slurry of the liquid feed and solid adsorbent is continuously recycled within a suitable treatment vessel until the desired extent of straight chain hydrocarbon removal has been effected.

In still another method of effecting contact between the solid adsorbent and feed petroleum fraction, in the liquid or vapor phase, the feed is countercurrently contacted with a downwardly moving stream or bed of particle-form selective adsorbent. The adsorbent upon issuing from the bottom of the contacting or adsorbing vessel is stripped of surface adsorbed material, especially when the feed is in the liquid phase, and passed to a regenerator or desorber wherein the adsorbent flows downwardly in countercurrent contact with a desorbing medium. The resulting desorbed `or regenerated solid adsorbent is then recycled to the top of the aforementioned contacting or adsorbing vessel for further contact with the fe-ed. In a modification of this particular operation, when the feed petroleum fraction being treated is in the vapor phase, the solid adsorbent issuing from the bottom of the contacting vessel may be subjected to a relative high temperature gas lift operation which would serve not only to desorb or regenerate the solid adsorbent material but also to lift and recycle the adsorbent back into the top of the contacting vessel.

In yet another method Ifor effecting contact between the solid adsorbent material and the feed petroleum fraction for the removal of straight chain hydrocarbons therefrom, a fluidized bed of a solid adsorbent material may be maintained by passing upwardly therethrough the vaporized fresh feed to be treated. A stream of the adsorbent material is continuously removed from the fluid adsorber and passed through a fluid regenerator wherein the adsorbent material maintained in the fluidized condition is desorbed by passing upwardly therethrough at high temperature a suitable desorbing medium, such as iiue gas, hydrogen, nitrogen, natural gas, etc. The desorbed and regenerated adsorbent is continuously removed from the fluid regenerator and recycled to the duid adsorber to contact additional fresh feed.

In still another method for effecting the removal of straight chain hydrocarbons from a fresh feed petroleum fraction, liquid fresh feed is contacted with the solid particle selective adsorbent preferably in the form of la fixed bed. After the removal of straight chain hydrocarbons from the fresh feed has been carried out to the extent desired,l a liquid desorbing medium readily separable by distillation from the adsorbed straight chain hydrocarbons, such as n-butane, preferably at a temperature substantially the same as that employed during the adsorption operation, or at an elevated temperature, preferably at temperature of 400 F. or higher, is passed into contact and through the fixed bed of adsorbent. The desorbing medium after sucient time displaces the adsorbed straight chain hydrocarbons within the pores of the solid adsorbent material and the resulting desorbed hydrocarbons are separately recovered.

It is mentioned that after each o-f the foregoing desorption or stripping operations it may be desirable to outgas the resulting desorbed or regenerated adsorbent material by subjecting the adsorbent to a reduced (as compared with the pressure employed during adsorption) or sub-atmospheric pressure so as to substantially completely empty the pores of the adsorbent material preferably immediately prior to contact with the fresh feed petroleum fraction being treated.

Following the adsorption operation for removal of the straight chain hydrocarbons from the fresh feed petroleum fraction, the resulting petroleum fraction, now containing substantially only or exclusively non-straight chain hydrocarbons, is passed to the desired subsequent treating `or catalytic conversion operation.

The practice of this invention is particularly applicable to an operation employing in combination with the abovedescribed straight chain hydrocarbon adsorption operation, Ia catalytic reforming step, such as a catalytic reforming operation wherein a mixture of non-straight chain hydrocarbons in vapor form contacts an active reforming catalyst. In this operation in combination with the prior feed treatment for the removal of straight chain hydrocarbons throughput and catalyst life are increased because of the removal of the straight chain hydrocarbons. 'I'he high molecular weight C, and C8 and higher straight chain hydrocarbons tend to crack and lay down carbon at an elevated temperature, such as a temperature in the range 70D-1000" F., whereas the lower molecular weight C6 and lower straight chain hydrocarbons are more refractory and less susceptible to reforming and tend to pass through the reforming operation relatively unchanged. Carbon deposition on a reforming catalyst, such as 'a platinum-containing catalyst, tends to diminish its activity and shorten its useful catalyst life. The lower molecular weight straight chain hydrocarbons, since they are more refractory and less susceptible to reforming, pass through the reforming operation relatively unchanged and act somewhat as an inert diluent therein.

V'arious catalytic conversion and reforming operations -and processes well known to those skilled in the art may be employed in combination with the practice of this invention. The reforming processes may be sufficiently identified and described to those skilled in the art by merely mentioning their descriptive name, and include such reforming processes as` Platforming, Ultraforming, Houdriforming, Catalytic Reforming, Catforming, Cycloversion, lixed bed Hydroforming, Fluid Hydroforming, Hyperforming, Thermofor Catalytic Reforming or Sovaforming and the like. Generally these reforming processes may be described as processes for upgrading relatively low octane naphthas or petroleum fractions in the gasoline boiling range to high octane motor gasolinas, or for producing high octane motor fuel components from naphthas or selected petroleum fractions, or for producing high yields of aromatics or high quality motor fuel components. These reforming operations may be cam'ed out by employing a iixed bed of catalyst, a moving bed of catalyst or a uidized catalyst or any combination thereof, and are operated at a temperature in the range 8251000 F., more or less, and a pressure in the range 150-900 p.s.i.g., more or less, depending upon the severity or extent of reforming desired or the quality or composition of the petroleum fraction undergoing reforming and/or reformed product desired. Various catalysts suitable for converting or reforming hydrocarbons may be employed, c g., platinumcontaining catalysts, molybdena-alumina catalysts, chromia-alumina catalysts and cobalt-molybdate catalysts, the reforming operation sometimes being defined merely by the particular catalyst employed therein.

As a result of the reforming operation there is recovered a reformate product of improved quality, in the case of motor fuel manufacture a reformed product comprising a high quality motor fuel having a research octane number clear of at least about and higher. If desired, particularly when the fresh feed petroleum fraction comprises a heavy straight run naphtha, eg. C7 and higher, there may be blended with this reformate, if desired or in order to meet motor fuel Volatility requirements or the like, a whole untreated light naphtha fraction, such as a 7 light straight run naphtha, which after suitable treatment in accordance with this invention, might be substantially free of straight chain hydrocarbons or which might comprise straight chain and non-straight chain hydrocarbons, such as C4 hydrocarbons up to about C5 or C6, inclusive, hydrocarbons and which may Ibe derived as a separate stream during the feed preparation and fractionation operation as indicated in FIG. l.

The straight chain hydrocarbons adsorbed on the adsorbent material are desorbed or displaced therefrom by the application of heat and/ or a suitable desorbing fluid (gas or liquid), and the resulting desorbed or regenerated adsorbent material contacted with additional fresh feed. The resulting desorbed straight chain hydrocarbons may be separately recovered as product or subjected to a suitable treatment such as isomerization.

The recovered straight chain hydrocarbons are advantageously subsequently treated or converted, e.g., isomerized or reformed such as by thermal reforming methods, catalytic or non-catalytic, to produce an isomerate or reformate having Va substantial non-straight chain hydrocarbon content. This material now containing straight chain hydrocarbons together with a substantial amount of non-straight chain hydrocarbons is advantageously blended with the reformate product recovered from the first mentioned treatment or catalytic reforming of the non-straight chain hydrocarbons. If desired, the isomerate or reformate resulting from the conversion or reforming of the desorbed straight chain hydrocarbons may be subjected to another adsorption operation for the substantially complete removal of straight chain hydrocarbons therefrom. The resulting material recovered from this last mentioned other adsorption operation is then blended with the Afirst mentioned reformate to produce a finished product of improved quality. The straight chain hydrocarbons adsorbed during said other adsorption operation are recovered vand subsequently recycled to the above-mentioned straight chain hydrocarbon isomerization or reforming operation to produce additional non-straight chain hydrocarbons. ln the the above-indicated manner it is seen that substantially all of the straight chain hydrocarbons in the original fresh feed' petroleum fraction can, if desired, be converted to nonstraight chain hydrocarbons. Moreover, if desired, a fraction of the desorbed straight chain hydrocarbons originally in the fresh feed, particularly the low molecular weight C4 and C5 hydrocarbons, may be blended in the finished converted or reformed product in order to meet volatility requirements as a motor fucl without at the same time unduly decreasing the octane number of the finished product since these low molecular weight straight chain hydrocarbons possess a rather high octane number.

In FIG. 2 of the drawing there are schematically illustrated various embodiments of the practice of this invention. As indicated hereinabove, the adsorption operation as applied to the separation of straight chain hydrocarbons from a hydrocarbon fraction containing the same together with non-straight chain hydrocarbons may be carried out in either the vapor or liquid phase, followed by the recovery of the non-straight chain hydrocarbons as a separate stream which is subsequently passed to a conversion operation such as a catalytic reforming operation for the production of a high quality or improved motor fuel or gasoline. The adsorbed straight chain hydrocarbons are separately recovered from the selective adsorbent as a special product, e.g., for use as an industrial solvent, motor or jet fuel, such as a fraction boiling in the range l75400 F., or separately treated or reformed for the production of additional non-straight chain hydrocarbons which advantageously are recovered as a separate product or blended with the reformate produced by the catalytic reforming of the non-straight chain hydrocarbons. Such operations as outlined above are carried out in the practice of this invention as follows.

Referring now to FIG. 2 of the drawing a fresh feed petroleum fraction from tank 10 is passed via line 11 into feed preparation unit 12 for the removal of undesirable hydrocarbons or polar or polarizable components, eg., sulfur-containing compounds. The resulting prepared feed is passed via line 13 to a fractionating column 14 wherein it is fractionated to produce overhead the relatively low molecular weight constituents thereof such as C4, or C5 or C6 fraction or mixtures thereof via line 16 comprising a selected naplitha fraction, such as a heavy straight run Vnaphtha fraction. A heavy straight run naphtha fraction removed via line 16 might have the composition set forth in Table I.

This selected heavy naphtha fraction is passed from fractionator 14 via line 16 to heater 19 wherein its temperature is increased to a temperature in the range 20G-600 F., usually in the range 3D0-500 F. This naphtha fraction leaves heater 19 via line 20 in the liquid or vapor phase depending upon the operating pressure and/ or naphtha boiling point and is introduced via line 21 into the top of adsorber 22 which contains a fixed bed of solid particle-form selective adsorbent for straight chain hydrocarbons. The adsorber 22 is operated at a temperature such that substantially all of the straight chain hydrocarbons, such as the normal parafns in the naphtha fraction introduced into the adsorber 22, are adsorbed by the adsorbent material therein and there issues from the bottom of adsorber 22 via line 23 naphtha fraction now substantially free of straight chain hydrocarbons. Adsorption conditions within adsorber 22 are to some extent dependent upon the composition of the petroleum fraction undergoing treatment, e.g. the greater the amount of straight chain hydrocarbons therein the longer the adsorption or processing period required to effect substantially complete adsorption of the straight chain hydrocarbons therefrom or the desired composition of the effluent issuing from adsorber 22. Generally, processing periods in the range 2 to S minutes up to about 11/2-2 hrs. at throughputs in the range it-V2 v./hr./v. up to about 3-5 and higher v./hr./v. are satisfactory before the adsorbent material within adsorber 22 is substantially saturated with straight chain hydrocarbons or to effect the removal of the straight chain hydrocarbons to the desired extent. Particularly satisfactory results have been obtained at an adsorption temperature in the range 200-600 F. and at a space velocity of about l v./hr./v.

After the adsorbent material in adsorber 22 is substantially saturated with straight chain hydrocarbon it is taken off stream and the straight chain hydrocarbons desorbed therefrom and the adsorbent material thereby regenerated. After desorption-regeneration of the adsorbent it is again contacted with additional feed to effect the removal of the straight chain hydrocarbons therefrom.

The naphtha fraction issuing from adsorber 22 Via line 23, now substantially free of straight chain hydrocarbons, is passed through heater 24 wherein it is vaporized and its temperature is increased to a value in the range 500-1000" F. and then via line 25 introduced into a reformer 26. Reformer 26 contains a solid particle reforming catalyst, such as a platinum-containing catalyst which may be regenerable or non-regenerable, or a chromia-alumina catalyst or a molybdena-alumina catalyst or a cobalt-molybdate catalyst. Typical operating conditions for reformer 26 when employing a platinum-containing catalyst are as follows: temperature about 875 F., pressure about 250 p.s.i.g., space Velocity about 3 v./hr./v. with a recycle of 8000 c.f./ bbl. of charge naphtha of a gas containing about 97 mol percent hydrogen. Two or more of these catalytic reformers 26 may be employed in series or in parallel.

The reformed naphtha fraction issues from a reformer 26 via line 29 and is then passed through a cooler 30 and via line 31 into separator 32 with the resultant separation of a gas phase and a liquid phase. A portion, predominantly hydrogen, of the gas phase recovered from separator 32 is recycled in the conventional manner via lines 33 and 51 to reformer 26 to provide the desired hydrogen atmosphere therein. Another portion, such as a C3 or C4 or C5 fraction or mixture thereof may be withdrawn and employed, as subsequently described, to desorb the adsorbed straight chain hydrocarbons from the adsorbent. The liquid reformate is withdrawn from separator 32 via line 34 and a portion thereof may be withdrawn as product of improved quality via line 35. Another portion of the reformate withdrawn from separator 32 via line 34 may be recycled to adsorber 22 via line 36 and lines 39 to serve as an internal coolant by direct or indirect heat exchange with the adsorbent therein and/or as a diluent therein so as to control better the adsorption temperature within adsorber 22, or to cool the hot desorbed regenerated adsorbent following the desorption operation described hereinafter, the resulting hot recycled reformate then being passed by means not illustrated in indirect heat exchange with the feed to reformer 26 to supply at least a portion of the heat necessary to bring the feed up to reforming temperature. t

The heat of adsorption of straight chain hydrocarbons on the selective adsorbent materials is considerable and if not controlled may lead to unduly high adsorption temperatures and adversely affect the operation of the adsorber 22. Since this recycled reformate is for the most part substantially free of straight chain hydrocarbons, its reintroduction into adsorber 22 during adsorption does not unduly aect the adsorption operation.

Liquid fresh feed or relatively cool feed introduced into adsorber 22 via lines 81 and Ztl and line 21 may also be used to cool the hot desorbed adsorbent. Advantageously, heat exchange means 40 is provided Within adsorber 22 to serve as temperature control means during the adsorption operation and as a heating means, if desired, during the desorption of the straight chain hydrocarbons from the adsorbent material contained within adsorber 22.

The desorption of the straight chain hydrocarbons from the adsorbent material within adsorber 22 is effected by supplying thereto a desorbing fluid such as a gas or liquid, preferably a gas or liquid containing components having a molecular diameter sutliciently small to penetrate the pores of the adsorbent, e.g. flue gas, methane, hydrogen, nitrogen, a straight chain hydrocarbon such as n-butane introduced via line 17 into line 16. Advantageously, when steam is employed as the desorbing uid it is followed by a ho-t purge gas such as methane, nitrogen and the like to displace the steam from the pores of the adsorbent prior to contact with additional fresh feed. Within heater 19 the desorbing medium is, if necessary, brought up to the desired desorption temperature (which may be the same as the adsorption temperature) such as a temperature in the range 20G-900 F., usually 100- 300 F. higher than the adsorption temperature. 'Ihe desorption temperature should 'be such that the adsorbed straight chain hydrocarbons are relatively quickly desorbed without at the same time causing destruction of the solid adsorbent or decomposition or cracking of the adsorbed straight chain hydrocarbons. The desorbing fluid issues from heater 19 via line 20 and is introduced via line 21into the top of adsorber 22 wherein upon passing through 4the adsorbent material therein it effectively strips and displaces the adsorbed straight chain hydrocarbons.

The desorbing Huid together with desorbed straight chain hydrocarbons leave `adsorber 22 in the above-described operation via line 42 and passed via line 85 through a suitable cooler 43 and gas-liquid separator 44. The desorbed straight chain hydrocarbons are recovered from separator 44 via line 45 and introduced into heater 46 where they are heated to a suita-ble temperature for a subsequent converting or treating operation, such as a reforming or isomerization operation, e.g. a catalytic reforming or isomerization or thermal reforming or cracking operation. The desorbing iluid is returned to the desorption zone via lines 47, 60, 16, heater 19 and lines 20 and 21.

The heated straight chain hydrocarbons issue from heater 46 via line 49 and are introduced into a converter vessel 50. As schematically indicated in FIG. 2 the converter or reformer Vessel is provided with. a uid bed of reforming lcatalyst such as a chromia-alumina reforming catalyst preferably containing ceria and potassia. The reforming catalyst is maintained in the uidized condition by the up-flowing stream of vaporized straight chain hydrocarbons introduced into converter 50 via line 49. Reformer 50 may be operated at a temperature of 900'- 1000 F., more or less, and at superattnospheric pressure with a space velocity of 0.4 v./hr./v. and a gas recycle rate of 1250 c.f./ bbl. of feed. It is desirable to maintain in catalytic converter 5t) a hydrogen atmosphere. Advantageously to provide such a hydrogen atmosphere hydrogen gas recovered from separator 32 is injected into a converter 50 via lines 51, 52 and 49 together with the feed to converter 50.

Because of the more severe reforming conditions employed in converter 50 and due to the fac-t that the straight chain hydrocarbons converted or reformed therein are prone to lay down or deposit carbon upon the catalyst surface, thereby adversely affecting the converting or reforming operation, a continuous stream of spent catalyst is removed from converter vessel 40 via line 53 and passed into catalyst regenerator 54 wherein the carbon content of the catalyst is burned by introducing air or other oxygen-containing gas in suitable quantities via lines 55 and 53. Hot regenerated catalyst is recycled to converter 50 via line 56. The flue gas issuing from regenerator 54 via line 59 may be employed, as indicated, via line 59 as a desorbing or stripping or drying medium. Moreover, as stated hereinbefore, if desired a portion of the hydrogen or normally gaseous hydrocarbons such as the C4 hydrocarbons recovered from separator 32 may be recycled as desorbing uid in the gaseous or liquid phase to adsorber 22 via lines 5'1 and 60. By employing gaseous hydrogen instead of the normally gaseous hydrocarbons as a stripping medium for the straight chain hydrocarbons there is produced a very suitable feed for converter 50 via lines 42, S7 and 45 and obviates the necessity for separately recovering the desorbed straight chain hydrocarbons from the desorbing lluid such as would be the case if an inert gas or Hue gas or natural gas or a gaseous or liqueed normally gaseous hydrocarbon and the like were employed as the desorbing fluid.

'Ihe reformed product issuing from converter 50 via line 61 is cooled by means of cooler 62 to liquefy the normally liquid hydrocarbons therein. The resulting cooled mixture is passed via line 63 through gas-liquid separator 64. A portion of the gas from gas-liquid separator 64 may be recycled to converter 50 via lines 65, 52 and 49 to the extent determined Iby the hydrogen content of this gas. If desired, a portion of this gas recovered from separator 64 via line 65 may be recovered via line 66 as a fuel gas for steam generation, power generation, ue gas generation and the like. The liquid reformate product recovered from separator 64 via line 69 may be separately withdrawn via `line 70 as a liquid reformate product, such as a petroleum fraction in theV gasoline boiling range having an improved octane number. If desired, the liquid reformate product from separator 64 may be transferred via line 69 to the reformate blending tank 71 Where it may be blended with at least a portion of the liquid reform'ate product recovered from separator 32 via line 34 to produce a blended product of improved quality.

After the adsorbent material in adsorber 22 has undergone a number of adsorption, desorption and regeneration cycies the effectiveness or adsorptive capacity of the adsorbent material sometimes becomes decreased apparently due to the accumulation of carbonaceous material on the surface of the adsorbent and/or within its pores deposited on the adsorbent during the desorption and regeneration lof the adsorbent. This material can be removed by controlled burning. In accordance with one embodiment of this invention high temperature oxygencontaining gas or air is supplied to adsorber Z2 via lines 17 and 16, heater 19 and lines 20 and 2,1 or controlled amount of air added via line 27 into iiue gas line 59' and eventually into adsorbe'r 2,2 at a controlled temperature in the range 600--1l00 F., such as a temperature in the range 7G0900 F., to burn ccntrolledly this carbonaceous material from the adsorbent without at the same time eX- posing the adsorbent to too high a temperature, such as 1300 F., which would adversely affect or destroy the adsorptive properties of the adsorbent. After regeneration in this manner it has been observed that the adsorptive capacity of the selective adsorbent, such as in the case of a calcium alumino-silicate molecular sieve type adsorbent, is restored to its original capacity. By regularly employing an oxygen-containing hot stripping gas (oxygen content of about 3% by volume) in the above described manner the adsorbent contained within adsorber 22 can be maintained at its original high adsorptive capacity.

Example N o. 1

The following is exemplary of Aa practice of this invention wherein a straight run naphtha is contacted with a solid alumino-silicate molecular sieve type adsorbent for straight chain hydrocarbons and wherein the recovered non-straight chain hydrocarbons are reformed catalytically, including the catalytic reforming or isomerization of the desorbed recovered straight chain hydrocarbons such as may be separated from the straight run' naphtha feed. More particularly, Xa straight run naphtha fraction containing about 28.5% by volume straight chain hydrocarbons, the remaining being non-straight chain hydrocarbons comprising naphthenic, aromatic and i-soparainic hydrocarbons, said fraction having a research octane number of 44.1 clear, +3 cc. TEL 66.4, was contacted with the above-identified solid adsorbent to produce a catalytic reformer feed having an octane number research clear 62.8, and +3 ce. TEL 79.7. This feed was subjected to reforming by contact with a platinum-containing catalyst ata temperature of about 900 F. and at a pressure of 500 p.s.i.g. employing a space velocity of 3 v./hr./v. There was produced a liquid reformate at a yield of 93.6% by vol. based on the feed substantially free of straight chain hydrocarbons and having a research octane number clear of 90, +3 cc. TEL 98.1.

A straight chain hydrocarbon fraction comparable to the desorbed straight chain hydrocarbons which are recovered from the above-mentioned adsorption operation and having a composition of about 24% by vol. n-pentane, 56% by vol. n-hexane and 20% by vol. n-heptane and exhibiting an octane number of 28 was passed into contact with a platinum isomerization catalyst lat a temperature of 800 F. and a space velocity of 1.0 v./hr./v. to produce an isomerate at a yield amounting to at least about 95% by vol., based on the charge to the isorrieiization reaction, and having an octane number of 58. This isomeratc was subsequently contacted with a selective adsorbent for straight chain hydrocarbons to produce a finished isomerate at a yield of 61.5% by vol., substantially free of straight chain hydrocarbons, based on the charge to the isomerization reaction having an octane number clear of 77.1, +3 cc. TEL 94. 'The straight chain hydrocarbons comprising substantially all n-parafns in the feed to the isomerization reaction and amounting to about 34% by vol. of the original charge thereto are advantageously recycled to the isomerization reaction together with additional fresh charge. By operating in the above-indicated manner substantially 'all of the straight chain hydrocarbon constituents of the initial naphtha fraction are charged to non-straight chain hydrocarbons.

Exemplary of the advantages to be obtained from the practice of this invention it was determined that when a reformer feed having a composition as set forth hereinabove, i.e. 28.5% normal parailins, was passed directly to a catalytic reforming operation it was necessary to carry out the reforming operation at a higher temperature, namely 925 F., in order to achieve a liquid reformate product having the same clear) octane number as is produced in an above-described combination adsorptionreforming operation employing a substantially n-parain free reformer feed and carrying out the reforming operation at a temperature of 900 F. Moreover because of the fact that it is necessary to carry out the reforming operation in the instance of the untreated reformer feed at a higher temperature (925 F.) and because of the presence in the reformer feed of straight chain hydrocarbons the effectiveness or efliciency of the reforming catalyst is reduced because of the deposition ofV carbon upon the catalyst brought about by the degradation or cracking of the straight chain hydrocarbons or n-parathn content of the reformer feed. Moreover it was observed that the total yield of liquid reformate in an operation in accordance with this invention for the production of a motor fuel of given octane number, is increased by about 1.5 volume percent, a significant improvement when it is realized that in a days operation in a single reforming unit upwards of 20,000 barrels per day of a naphtha fraction are treated or reformed.

Moreover it is pointed out that should the catalytic reforming operation be carried out at the same temperature, 900 F., but without the benefit of treating the reformer feed in accordance with this invention for the removal of the straight chain hydrocarbons, there was produced a liquid reformate pnoduct having a research octane number clear of 82, +3 cc. TEL 93.7, each, respectively, 8 yand 4.4 octane numbers less than a liquid reformate produced by employing the combination treating operation of this invention. Moreover, by operating in accordance with this invention a yield advantage of 6% by volume is obtained in this instance.

In accordance with another embodiment of this invention employing in combination the removal of straight chain hydrocarbons from a naphtha fraction, especially a naphtha fraction containing 10% or more by vol. straight chain hydrocarbons, and at least about 10% by vol. naphthenes, followed by catalytic reforming of the remaining non-straight chain hydrocarbons together with the reforming or isomerization of the straight chain hydrocarbons recovered from the adsorption step, the catalytic reforming of the remaining non-straight chain hydrocarbons is carried out at such a level that substantially only the naphthenic hydrocarbons therein are dehydrogenated with the resulting production of additional aromatic hydrocarbons. The conditions of reforming are such that the isoparaflinic constituents are substantially unaffected or are not reformed or isomerized to any significant degree. More particularly, the reforming of the non-straight chain hydrocarbons under relatively mild conditions is conducted under pressures of about 20G-700 p.s.i.'g. or higher at a temperature in the range 750-975" F. in the presence of a reforming, predominantly dehydrogenating catalyst, preferably a platinum-containing catalyst, with a space velocity in the range 3-20 liquid volumes per hour per volume of catalyst. The operation is carried out in the presence of hydrogen by recycling gas containing 95% or higher of hydrogen, recovered from the reforming operation itself, at a rate of about 300C-9000 cu. ft. per bbl. of liquid charge. This light reforming operation is preferably carried out in a fixed bed operation with .the charge stock being preheated to approximately the reforming temperature and then contacted with the catalyst.

In a specific typical operation the naphtha, yafter removal of substantially all of the straight chain hydrocarbons, is contacted with the catalyst at a temperature in the range S70-925 F., at a pressure of about 250 p.s.i.g. with a space velocity of 3 v./hr./v. and with a recycle of 6000 cu. ft. of hydrogen-containing gas per bbl. of naphtha.

The straight chain hydrocarbons recovered from the selective adsorbent are separately subjected to a second, more severe reforming operation to promote isomerization, dehydrocyclization and the like of the straight chain hydrocarbons. The straight chain hydrocarbons are usually predominantly comprised of normal paraffns. The reforming conditions in this second stage are more severe than the relatively mild reforming or dehydrogenation conditions employed inthe treatment of non-straight chain hydrocarbon fractions. Although the same catalyst may be employed in both operations it is preferred to employ in the second stage reforming operation a catalyst which can be regenerated. As a suitable regenerable reforming catalyst, the catalyst in the second stage is a chromiaalumina catalyst preferably containing mino-r amounts of ceria and potassia. This catalyst is readily commercially available and usually contains about l-20% chromia on alumina. It is desirable to exclude from the second stage reforming catalyst components which may promote cracking. The second stage reforming catalyst is preferably cartried out in a hydrogenating atmosphere, preferably in the presence of a predominantly hydrogen atmosphere. Hydrogen gas for use in the second stage reforming operation may be obtained by the recovery of hydrogen gas from the first stage reforming operation.

By operating in the above-described manner, especially when the nonstraight chain hydrocarbon fraction recovered from the adsorber is treatedunder relatively mild reforming conditions to effect substantially only dehydrogenation of Ithe naphthenic hydrocarbons, the useful life of this reforming catalyst can be greatly extended, almost to an indefinite length of time. This is especially beneficial when a platinum-containing catalyst is employed in the first stage reforming of the non-straight chain hydrocarbon fraction.

As disclosed hereinbefore the treatment of a hydrocarbon fraction containing both straight chain hydrocarbons and non-straight chain hydrocarbons for the removal of straight chain hydrocarbons therefrom may be carried out in either the liquid or vapor phase. When operating in the liquid phase, land after suitable feed preparation, referring again to FIG. 2 of the drawing, a liquid naphtha fraction at a temperature below its initial boiling point or substantially above its boiling point provided sutiicient pressure, such as a pressure in the range 100-800 p.s.i.'g., more or less depending upon the composition of the naphtha undergoing treatment and/or adsorption temperature Iand/or desorbing fluid employed, is employed to maintain it in the liquid phase, is introduced via lines 13, 81, 20 and 21 into Ithe top of adsorber 22 wherein it flows downwardly in contact with the selective adsorbent material for the straight chain hydrocarbons. A liquid fraction is recovered from the bottom of adsorber 22 via line 23 from which it passes into heater 24 and line 25 into reformer 26 and treated in the manner already described.

The desorption of the surface adsorbed hydrocarbons and the pore adsorbed straight chain hydrocarbons from the adsorbent within adsorber 22 in this operation may be effected in the manner already described, that is employing a hot stripping or regenerating gas such as hydrogen or gaseous or liquefied normally gaseous hydrocarbons such as n-butane. The desorption conditions of temperature and pressure `may be substantially the same as those employed during the adsorption operation (isothermal and/or isobaric adsorption `and desorption) or may be higher or lower, depending upon the molecular weight of the straight chain hydrocarbons to be desorbed, the desorbing fluid employed and whether or not it is desired to carry out the desorption operation with the desorbing fluid in `the liquid phase and/or the desorbed straight chain hydrocarbons in the liquid or gaseous phase.

Instead of a liquid or vapor feed downflow Within adsorber 22 the liquid or vaporized naphtha fraction introduced into adsorber 22 for the removal of straight chain hydrocarbons therefrom may flow upwardly within adsorber 22 by introducing the liquid or vapor naphtha fraction into the bottom of adsorber 22 by means of line 91, after the feed has undergone suitable preparation or fractionation as already described. A fraction substantially free of straight chain rhydrocarbons leaves adsorber 22 via line 83 for introduction into reformer 26 via lines 92, 23, heater 24 and line 25.

The straight chain hydrocarbons are desorbed by introducing a desorbing fiuid into the bottom of adsorber 22 via line 91 which is supplied with the desorbing fluid in the manner indicated hereinabove with respect to FIG. 2. The desorbed straight chain hydrocarbons are recovered from the top of adsorber 22 by means of line 83 and may be transferred in the manner already described to converter 50 to eect conversion or reforming of the desorbed straight chain hydrocarbons.

As indicated in FIG. 2 an operation particularly suitable for the treatment of a wide boiling naphtha fraction such as a straight run naphtha fraction comprises fractionating a straight run naphtha feed introduced via line 11 into feed preparation unit 12 and line 13 into fractionator 14. A relatively heavy straight run fraction is separately recovered as a separate side stream via line 16 and treated in the manner described. lThe higher components, C4, C5 and C6, separately or mixtures thereof are removed overhead from a fractionator 14 via line 1S. All or a portion of the overhead fractions, particularly the C4 fraction, may be employed as desorbing fluid via lines 15 and 107 or may be transferred via lines 15 and 101 to line 25 to reformer 26 wherein, depending upon the severity of the reforming operations, they pass through relatively unchanged or are isomerized to some extent. The C5 and lighter parafinic hydrocarbons possess an octane number sufiiciently high that their presence in relatively small amounts in the reformate issuing from reformer 26 is tolerable, if not desirable. Additionally the C5 and lighter hydrocarbons impart desirable volatility characteristics to the reformate from reformer 26 when employed as a motor fuel. Moreover all or part of the C6 fraction recovered from fractionator 14 via line 15 may be transferred to converter 50 via line 102, line 45, heater 46 and line 49 for subsequent conversion into more valuable material, e.g. reforming by isomerization and dehydrogenation of the naphthenic constituents into a motor fuel component of improved quality. As indicated in the drawing, all or a portion of the C6 and lighter fraction may be admixed with the reformate product from reformer 26 by passage through cooler 103, if required, and line 104 into line 34. Moreover this same C6 and lighter fraction may be admixed with the product or reformate from converter 50 and, if desired, transferred along line 34 into line 69 which serves as thel inlet to the reformate blending tank 71. Line 47 is provided so that, if desired, the fresh feed in line 13 can be introduced directly into adsorber 22 via lines 81, 20 and 21 or via line 16, heater 19 and lines 20 and 21, bypassing fractionator 14.

The above-described operations with respect to straight chain hydrocarbon adsorption, reforming of the straight chain hydrocarbon-free material and isomerization or reforming of the desorbed straight chain hydrocarbon material can be carried out Substantially continuously by employing `a plurality of adsorbers 22, one or more adsorbers onstream and one or more adsorbers undergoing desorption and regeneration at the same time, likewise, if necessary, a plurality of converters 50. For purposes of simplicity and clarity only one adsorber Z2 and one 'reformer 26 and one converter 50 have been shown. The employment of Vone or more adsorbers `and reformers in the manner to eiect substantially continuous operation is well known to those skilled in the art and the applicability to the practice of this invention is deemed obvious. The adsorption and desorption operations in accordance with this invention may be carried out at desired temperature or a pressure commensurate with the operating conditions desired, i.e. liquid or vapor phase adsorption and/ or des'orption.

For purposes of simplicity and clarity the conventional control equipment, Valves, pumps, heaters, coolers, gasliquid separators, etc. have for the most part not been illustrated. The location and employment of these auxiliary pieces of equipment and the like in the practice of this invention are well known.

This application is a continuation-impart of our copending patent application Serial No. 478,426, tiled December 29, 1954, now U.S. Patent No. 2,886,502, issued May 12, 1959. The disclosures of the above-identified copending application are herein incorporated and made part of this disclosure.

As is vident to those skilled in the art many modifications, substitutions and changes are possible in the practice of this invention without departing from the spirit or scope thereof.

We claim:

1. A petroleum treating process which consists in fractionating a heavy naphtha into a light naphtha fraction containing substantially only C3 and lighter hydrocarbons and a heavy naphtha fraction containing substantially only C7 and heavier hydrocarbons, said naphtha fractions containing straight chain hydrocarbons and non-straight chain hydrocarbons, subjecting said light ynaphtha fraction to contact with a molecular sieve alumino-silicate adsorbent selectively adsorbing straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons from said light naphtha fraction, separately recovering the resulting treated light naphtha fraction substantially free of straight chain hydrocarbons, desorbing from said adsorbent straight 'chain hydrocarbons adsorbed from said light naphtha fraction, withdrawing said desorbed straight chain hydrocarbons as one product of the process, catalytically reforming said heavy naphtha fraction containing said C7 and heavier hydrocarbons to yield a catalytic reformate containing straight chain hydrocarbons and non-straight chain hydrocarbons, separating hydrogen and light hydrocarbons from said reformalte, subjecting reformatie containing lheavier hydrocarbons to contact with a separate alumino-silicate molecular sieve adsorbent selectively adsorbing straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons from said reformate and yielding a treated reformate substantially free of straight chain hydrocarbons, desorbing adsorbed straight chain hydrocarbons of the reformate from the aforesaid separate adsorbent, withdrawing said desorbed straight chain hydrocarbons as a second product of the process, blending the aforesaid treated light naphtha fraction and the aforesaid treated reforma-te to yield a blended product consisting of said two fractions, and withdrawing said blended product as a third product of the process.

2. The process of claim 1 wherein contacting of the respective fractions with the alumino-silicate selective adsorbent is carried out in the liquid phase.

3. A process in accordance with clairn 1 wherein the straight chain hydrocarbons adsorbed by the selective adsorbent contacted by said reformate are desorbed by contact with a desorbing medium, and separating said desorbingr medium from the desorption eiluent to yield a fraction consisting essentially of straight chain hydrocarbons as said second product of the process.

References Cited in the le of this patent UNITED STATES PATENTS 2,818,455 Ballard et al. Dec. 31, 1957 2,834,429 Kinsella et a1. May 13, 1958 2,850,549 Ray Sept. 2, 1958 2,891,902 Hess etal June 23, 1959

Claims (1)

1. A PETROLEUM TREATING PROCESS WHICH CONSISTS IN FRACTIONATING A HEAVY NAPHTHA INTO A LIGHT NAPHTHA FRACTION CONTAINING SUBSTANTIALLY ONLY C6 AND LIGHTER HYDROCARBONS AND A HEAVY NAPHTHA FRACTION CONTAINING SUBSTANTIALLY ONLY C7 AND HEAVIER HYDROCARBONS, SAID NAPHTHA FRACTIONS CONTAINING STRAIGHT CHAIN HYDROCARBONS AND NON-STRAIGHT CHAIN HYDROCARBONS, SUBJECTING SAID LIGHT NAPHTHA FRACTION TO CONTACT WITH A MOLECULAR SIEVE ALUMINO-SILICATE ADSORBENT SELECTIVELY ADSORBING STRAIGHT CHAIN HYDROCARBONS TO THE SUBSTANTIAL EXCLUSION OF NON-STRAIGHT CHAIN HYDROCARBONS FROM SAID LIGHT NAPHTHA FRACTION, SEPARATELY RECOVERING THE RESULTING TREATED LIGHT NAPHTHA FRACTION SUBSTANTIALLY FREE OF STRAIGHT CHAIN HYDROCARBONS, DESORBING FROM SAID ADSORBENT STRAIGHT CHAIN HYDROCARBONS ADSORBED FROM SAID LIGHT NAPHTHA FRACTION, WITHDRAWING SAID DESORBED STRAIGHT CHAIN HYDROCARBONS AS ONE PRODUCT OF THE PROCESS, CATALYTICALLY REFORMING SAID HEAVY NAPHTHA FRACTION CONTAINING SAID C7 AND HEAVIER HYDROCARBONS TO YIELD A CATALYTIC REFORMATE CONTAINING STRAIGHT CHAIN HYDROCARBONS AND NON-STRAIGHT CHAIN HYDROCARBONS, SEPARATING HYDROGEN AND LIGHT HYDROCARBONS FROM SAID REFORMATE, SUBJECTING REFORMATE CONTAINING HEAVIER HYDROCARBONS TO CONTACT WITH A SEPARATE ALUMINO-SILICATE MOLECULAR SIEVE ADSORBENT SELECTIVELY ADSORBING STRAIGHT CHAIN HYDROCARBONS TO THE SUBSTANTIAL EXCLUSION OF NON-STRAIGHT CHAIN HYDROCARBONS FROM SAID REFORMATE AND YIELDING A TREATED REFORMATE SUBSTANTIALLY FREE OF STRAIGHT CHAIN HYDROCARBONS, DESORBING ADSORBED STRAIGHT CHAIN HYDROCARBONS OF THE REFORMATE FROM THE AFORESAID SEPARATE ADSORBENT, WITHDRAWING SAID DESORBED STRAIGHT CHAIN HYDROCARBONS AS A SECOND PRODUCT OF THE PROCESS, BLENDING THE AFORESAID TREATED LIGHT NAPHTHA FRACTION AND THE AFORESAID TREATED REFORMATE TO YIELD A BLENDED PRODUCT CONSISTING OF SAID TWO FRACTIONS, AND WITHDRAWING SAID BLENDED PRODUCT AS A THIRD PRODUCT OF THE PROCESS.

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