US2917449A

US2917449A - Method of upgrading a petroleum naphtha

Info

Publication number: US2917449A
Application number: US483998A
Authority: US
Inventors: Edward R Christensen; Howard V Hess
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1955-01-25
Filing date: 1955-01-25
Publication date: 1959-12-15
Anticipated expiration: 1976-12-15

Description

Dec. l5, 1959 E. R. cHRlsTENsEN Erm. 2,917,449

METHOD OF UPGRADING A PETROLEUM NAPHTHA Filed Jan. 25, 1955 2 Sheets-Sheet 1 ma/Malay Dec. l5, 1959 E. R. cHRlsTENsl-:N .a1-Ax'.`

METHOD oF UPGRADING A PETROLEUM NAPHTHA Filed Jan. 25, 1955 2 Sheets-Sheet 2 ..N-WHP United States Patent METHOD F UPGRADING A PETROLEUM NAPHTHA Edward R. Christensen, Beacon, and Howard V. Hess, Glenllam, N.Y., assignors to Texaco Inc., a corpora, tion of Delaware Application January 25, 1955, Serial No. 483,998

4 Claims. (Cl. 208-64) 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 petroleum fractions in the naphtha or gasoline boiling range to improve their quality. Still more particularly this invention is directed to the treatment of petroleum fractions 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 3-30% by volume and higher.

Various converting and catalytic reforming processes have been proposed for the treatment of naphtha stocks to produce a high quality, high octane motor fuel. These processes call for the vapor phase treatment of petroleum fractions in the gasoline boiling range by contact with an active converting catalyst such as a platinum-containing catalyst, a chromia-alumina catalyst, a molybd'enaalumina catalyst or the like. During treatment of these selected petroleum fractions, a number of reactions take place substantially simultaneously. For example, in a catalytic reforming operation employing a platinum-containing catalyst in contact with a naphtha fraction containing aromatcs, naphthenes, isoparaliins and n-parains, dehydrogenation of the naphthenes to aromatics occurs. Substantially at the same time, especially when operating under more severe treating conditions, isomerization and dehydrogenation of the para'inic hydrocarbons take place. Ad-ditionally under these conditions aromatization or dehydrocyclization of the paraflinic hydrocarbons also takes place. Concurrently with these reactions, particularly under the more severe treating or conversion conditions, a certain amount of cracking and gas formation (C4 and lighter) takes place together with deposition of carbon upon the catalyst thereby resulting in a reduction in the recoverable yield of the more valuable normally liquid hydrocarbons. Cracking, as evidenced by gas formation and carbon deposition is particularly noticeable when the aforesaid conversion of catalytic reforming reactions are carried out under the more severe catalytic reforming conditions in order to produce a high octane motor fuel or motor fuel component.

The platinum-containing treating catalysts employed in present day commercial catalytic reforming 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 or a catalytic reforming catalyst, particularly a platinum-containing catalyst, is the amount of carbon deposited or laid down upon a catalyst. Carbon deposition in turn is usually governed or dependent upon the severity of the converting or reforming conditions in which the catalyst is employed. The replacement of a spent treating catalyst, particularly a platinum-containing catalyst, is expensive. Moreover the regeneration of a spent regenerable catalyst is an expensive operation possess side chain branching. Representative straight and time consuming, all the more so in a refinery operation when for purposes of regeneration it is .necessary to take a catalyst case olf stream for catalystregenera` tion.

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

It is another object of this invention to provide a flexible petroleum converting operation which is capable of handling a wide variety of petroleum fractions containing straight chain hydrocarbons and non-straight chain hydrocarbons.

Still another object of this invention is to-providea treating process wherein the useful on-stream life of a treating catalyst, especially a platinum-containing catalyst, is substantially increased, particularly when compared with the useful catalyst life of the same catalyst employed in the same catalytic conversion operation in the conventional manner to produce a petroleum fraction or gasoline component having the same octane number as produced by the combination treating process in accordance with this invention.

Yet another object of the invention is to provide a combination treating operation employing a catalytic converting or catalytic reforming operation for the production of a high octane motor fuel not otherwise obtainable save at the expense of a prohibitively shortened catalyst life.

Yet another object of this invention is to provide a combination process for increasing the yield of a given high octane number motor fuel obtainable from a given naphtha fraction as compared to the yield obtainable by employing conventional operations.

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

How these and other objects in this invention yare achieved will become apparent with reference to the accompanying disclosure and drawing wherein:

Fig. l is a block iiow diagram broadly outlining the process of this invention, and

Fig. 2 is a schematic ow diagram illustrating various embodiments of the practice of this invention.

In accordance with our invention We have provided an improved process for treating or converting a petroleum fraction containing straight chain hydrocarbons andnonstraight chain hydrocarbons, which comprises subjecting the petroleum fraction to a treating or converting operation, such as a catalytic reforming operation, to produce a petroleum fraction of improved quality, such as an improved or higher octane motor fuel, subjecting the resulting improved petroleum fraction to contact with a solid absorbent which selectively adsorbs straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons,-to adsorb straight chain hydrocarbons from said fraction, thereby producing a further improved petroleum fraction. The practice of this invention is particularly applicable to any petroleum fraction suitable for use in a catalytic reforming operation or suitable for the production of aromatics or improved naphthas or motor fuels in the gasoline boiling range, provided, of course, said petroleum fraction contains straight chain hydrocarbons and non-straight chainhydrocarbons.

By straight chain hydrocarbons is meant any aliphatic or acyclic or open chain hydrocarbon which does not chain hydrocarbons are, of course, the normal parafins and the normal olens, monoor polyolelins, including the straight chain acetylenic hydrocarbons. The nonstraight chain hydrocarbons `comprise the aromatic and naphthenic hydrocarbons as well as the isoparaflinic and isooleiinic hydrocarbons and the like. A petroleum frac- Patiented Dec. 15, 1959,

tion 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 a range 20G-475 F., more or less, Furthermore, a petroleumA fraction suitable for use in the practice of this invention vmust contain both straight chain and non-straight chain hydrocarbons and might have the following composition:

Hydrocarbon type: Percent by volume The straight. chain hydrocarbons, e.g. the n-paraln content of petroleum fractions suitable for use in the practice of this invention is frequently in the range 3'50% by volume. Typical refinery stocks or fractions which are applicable to the practice of this invention are a.wide boiling straight run naphtha, a light straight run naphtha, a heavy straight run naphtha, a catalytic cracked naphtha, a thermally cracked or thermally reformed naphtha. This invention, however, is particularly applicable to the treatment of catalytic reformates in the naphtha boiling range such as a Platformate, an Ultraformate, a Hydroformate and the like.

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 alumina-silicate which exhibit the property of amolecular sieve, that is adsorbents made up of porous matter or crystals wherein the pores are of molecular dimension and are of uniform size. A particularly suitable solidadsorbent for straight chain hydrocarbons to the substantial exclusion'of. non- `straight chain hydrocarbons is a calcium aluminosilicate manufacturedr by Linde Air Products Company and designated type 5A molecular sieve. The crystals f this particular calcium alumino-silicate, apparently actually a sodium calcium alumino-silicate, have a pore size or diameter of about Angstrom units, a pore size suicient to admit straightchain hydrocarbons, such as then-parafns, to the substantial exclusion of the nonstraight chain hydrocarbons, such as the naphthenic, aromatic and the isoparans and isoolenic hydrocarbons, e.g. isobutane and higher. This particular selective adsorbent s-available in various sizes such as IAG" and 1A in diameter pellets aswell as in a nely divided powder orm.

Other selective adsorbents may be employed in the practice of this invention. For example, 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 ofa 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 networkl and having interstitial dimensions sufficiently large to adsorb straight chain hydrocarbons but sufficiently small to exclude the non-straight chain hydrocarbons. The naturally occurring zeolite, chabazite, exhibits such desirable properties. Another suitable naturally occurring` zeolite is analcite NaA1Si2O5.H2O. which,. whenv dehydrated, and. when` all or part ofthe sodium is replaced by an alkaline earth metal, such as calcium, yields a material which may be represented by the formula (Ca,Na)Al2Si4O'12.2H2O and which after suitable conditioning will adsorb. straight chain hydrocarbons mA the. substantial exclusion.w of 1191istraight chain hydrocarbons. Naturally occurring or synthetically prepared phacolite, gmelimite, harmotome and the like, or suitable modifications of these products by base exchange, are also applicable in the practice of this invention.

Other solid adsorbentswhich selectively adsorb straight chain hydrocarbons such as n-paratiins and the n-olens to the` substantial exclusion of the non-straight chain hydrocarbons, includingvthe aromatic and naphthenic hydrocarbons, are known.

Referring now to Figure l ofthe drawing which sets forth in a block ow diagram various embodiments of the practice of this invention, a fresh lfeed petroleum fraction which may have a wide or narrow boiling range, containing straight chain hydrocarbons (n-paraflins and/ or n-olens) in admixture with non-straight chain hydrocarbons (aromatic and/or naphthenic and/or isoparaflinie and/or isoolefnic hydrocarbons) is supplied to a suitable feed fractionation and/or preparation unit. Should the fresh feed contain substantial amounts of undesirable polar or polarizable compounds such as sulphur-containing compound, 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 treatment in accordance with this invention. The removal of these polar or polarizable materials may be accomplished by solvent extraction, extractive distillation, hydrogenation, dehydrogenation, acid or caustic washing. and the like or by' any suitable combination thereof. Processes for removal of or for effectively neutralizing the above-mentioned polar and polarizable materials in a petroleum fraction are well known in the art and form no part of this invention.

A typical feed preparation operation particularly suitablefor naphtha fraction prior to catalytic reforming, such as Platforming, is the so-called Hydrobon treatment which essentially is a mild hydrogenation operation for the purpose of removing the heavy metal content of the naphtha stream as well as for the removal of substantially all ofthe sulfur-containing compounds therefrom.

Advantageously, preferably prior to feed preparation, the fresh feed is subjected to fractionation to produce a petroleum fraction having they boiling point range most suitable for subsequent treatment in accordance with this invention. If the fresh feed contains components which have a boiling point below about F., it is desirable to remove substantially all of these feed components. Hydrocarbons which have a boiling point below 100 F. are n-butane, isobutane, isopentane and neopentanc, all of which possess a rather high octane number and for this reason alone would be desirable components in a motor fuel or gasoline. Normal pentane, having a boiling point of about 97 F., has a lower octane number (about 6l) and accordingly its presence in a motor fuel is lessv desirable. The removal of these low boiling hydrocarbons is desirable since these hydrocarbons are refractory and do` not readilyundergo catalytic reforming. Accordingly, when these low boiling hydrocarbons are passed to a catalytic reforming operation, such as a Platforming operation, they pass through substantially unchanged and in effect act as a diluent. Accordingly, the low boiling C5 or C4 and lighter hydrocarbons are advantageously fractionated from the feed undergoing treatment in accordance with this invention. All or a portion of these low boiling hydrocarbons, however, may advantageously be blended back into the final treated petroleum fraction in accordance with this invention.

Following the: feed fractionation and/or preparation operationsas indicated in Figure 3, the naphtha feed is sentito a catalytic reformer wherein it is contacted with an active reforming catalyst under reformingconditions of temperature and pressure to upgrade the feed into an improved motor fuelor high octane motor fuel component..

Various converting and catalytic reforming operations and processes particularly suitable for upgrading a petroleum fraction in a naphtha boiling range may be employed in thc combination treating process in accordance with this invention. The reforming processes may be suiciently identified and described to those skilled in the art my merely mentioning their descriptive name, namely such reforming processes as Platforming, Ultraforming, Houdriforming, Catalytic Reforming, Catforming, Cycloversion, Fixed 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 gasolines, or for producing high octane motor fuel components from selective naphthas or petroleum fractions, or for producing a high yield of aromatic or petrochemicals or high quality motor fuel components. These catalytic reforming operations may be carried out by employing a fixed bed of catalyst, a moving bed of catalyst or a liuidized catalyst, or any combination thereof and are generally operated at a temperature in the range 800- 1000 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 the product desired. The various catalysts suitable for reforming hydrocarbons may be employed, e.g. platinumcontaining catalysts (Platforming catalyst) molybdenaalumina catalysts, chromia-alumina catalysts and cobalt molybdate catalysts; the particular reforming process sometimes being adequately defined merely by describing the particular catalyst employed therein. As a result of the reforming operation, there is produced and recovered a reformate having improved qualities as a motor fuel.

Depending upon the composition of the fresh feed other converting processes, in place of catalytic reforming, may be employed, e.g. thermal cracking, thermal reforming (essentially non-catalytic processes), isomerization, etc., particularly when the fresh feed contains a lsubstantial amount, in the range -50 and higher percent by vol., straight chain hydrocarbons.

The effluent from the reforming or converting operation is treated to separate the normally gaseous materials therefrom, e.g. hydrogen, methane, ethane and propane. At least a portion of the separated and recovered hydrogen is recycled to the reforming or converting operation. The normally liquid components of the effluent are then contacted with the solid selective adsorbent material in powdered, beaded, microspheroidal, granular or pelleted form to selectively adsorb the `straight chain hydrocarbons therefrom. Although it is preferred to remove substantially all of the straight chain hydrocarbons from the eiiluent it is realized that it is not necessary in the practice of this invention to adsorb or separate all of the straight chain hydrocarbons. The extent or degree of straight chain hydrocarbon removal, especially octane number improvement, in order to produce a high octane gasoline is governed by various factors, economic and otherwise, including capacity of the available equipment, the quality desired in the finished treated product, yield considerations, the composition of the eluent and the like.

The eiuent undergoing treatment for the removal of the straight chain hydrocarbons therefrom may be present either in the liquid phase or in a 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 hydrocarbons in contact therewith, provided, of course, suficient time is allowed to substantially saturate the adsorbent. It is preferred in the practice of this invention to maintain the eiuent in a vapor phase While in contact with the solid adsorbent. Contacting of the effluent with the solid adsorbent may be effected by any suitable means for effecting gas-solid or liquid-solid contacting and the selective adsorbent may be maintained as a fixed bed, a moving bed or a uid bed.

When liquid phase contacting is carried out for'the removal of the straight chain hydrocarbons from the efliuent, it is preferred to carry out the adsorption operation at a temperature in the range 50-500 F. or higher, suiiicient pressure being applied, if necessary, to maintain the eluent in the liquid phase. In vapor phase adsorption it is preferred to carry out the adsorption operation at a temperature at least sufficient to maintain substantially all of the effluent undergoing treatment in the vapor phase, such as a temperature in the range 300- 700 F. or higher, satisfactory adsorption operations having been carried out at temperatures in the range 35065O F.

The efduent undergoing treatment is maintained in contact With the selective adsorbent until substantially all of the straight chain hydrocarbons have been removed therefrom, or until the selective adsorbent has become substantially saturated with respect to straight chain hydrocarbons. When the adsorbent is substantially saturated, so that straight chain hydrocarbon adsorption is no longer possible, the petroleum fraction or effluent undergoing treatment is contacted with additional fresh or regenerated adsorbent.

The straight chain hydrocarbons are desorbed from the adsorbent, thereby regeneratingk the adsorbent, by contacting the adsorbent with a stripping medium which displaces, purges or sweeps out the adsorbed straight chain hydrocarbons from within the pores of the selective adsorbent. Exemplary of a suitable gaseous stripping medium are nitrogen methane, hydrogen ue gas, carbon dioxide, substantially dry natural gas and steam, preferably superheated steam. In general, any normal gaseous material is suitable as a stripping medium provided, of course, the molecules thereof are sufficiently small to enter the pores of the adsorbent. Superheated steam is particularly suitable in the practice of this invention as a stripping medium since not only does it effectively displace the adsorbed straight chain hydrocarbons, but also it can be readily and conveniently separated from the desorbed straight chain hydrocarbons by cooling and condensation. Desirably when superheated steam is employed as the stripping medium, it is followed by an additional normally gaseous stripping medium such as an inert purge g-as, e.g., nitrogen, methane, natural gas, hot

, air hydrogen or flue gas, and the like, in order to sweep the steam from Within the pores ofthe adsorbent. The

desorption operation may be carried out at any suitable.

temperature. A desorption temperature in the range S00- 1100" F. has been found to be satisfactory. Although the desorption temperature is usually 10G-300 F. higher than the adsorption temperature, such as a temperature in the range 700-1000 F., the desorption operation may be carried out at substantially the same temperature as the adsorption temperature. Desorption of the straight chain hydrocarbons may also be effected in the liquid phase by contacting the adsorbent with a polar liquid, eijg. water, at a suitable elevated temperature, as indicated a ove.

After the straight chain hydrocarbons have been desorbed, the straight chain hydrocarbons are recovered and subjected to a suitable conversion operation such as catalytic reforming or isomerization, or thermal cracking or reforming in order to upgrade the desorbed straight chain hydrocarbons into more Valuable higher octane hydrocarbons, e.g. normal paraflins to normal olefins and/or to their corresponding branched chain isomers. The resulting converted product can be directly blended with the straight chain hydrocarbon-free efiluent from the adsorber or, if desired, may be contacted with selective adsorbent to remove lthe `straight chain hydrocarbons therefrom` and the ren'ianingl straight chain hydrocarbon-4 free-con'verted product blended with the above mentioned efuent. n

In Fig. 2 of the drawing there is schematically illustrated an embodiment of the practice of this invention. Referring now in greater detail to Fig. 2 a fresh feed petroleum fraction, such as a petroleum fraction in the naphtha boiling range, is subjected to fractionation and/ or preparation, as indicated by unit 11. During fractionation and/ or preparation of the fresh feed to yield a petroleum fraction having a suitable boiling point range for subse quent treating in accordance with this invention, the lightercomponents of the fresh feed, such as the hydrocarbons having a molecular weight in the range C5 and lower, especially substantially all of the isopentane and butane contained in the fresh feed, are advantageously removed overhead as a separate fraction via line 12. The remaining fresh feed, substantially free of C5 and lower molecular weight hydrocarbons, and having the desired boiling point range, such as a boiling point range in the range 15G-450 F., is subjected to a feed preparation operation which` might involve Ia mild hydrogenation, e.g. a so'- called/ Hydrob'on' Treatment or hydrogen rening operation to saturate the unsaturated hydrocarbons therein, for removal of more polar compounds therefrom, e.g. sulfur-containing compounds and the like. Application of the above-described operations of fresh feed fractionation and/or preparation to a straight run naphtha fraction would produce a fheavy straight run naphtha fraction which might have the composition set forth in Table I. A naphthafraction possessing these properties would be suitable for subsequent treatment in accordance with this invention- Following suitable feed fractionation and preparation treatment the prepared feed issues via line 13 into heater 14"where it is brought up to a sufficiently high temperature, such as a temperature in the range 800-1000 F., for

introduction via line 1S into catalytic reforming unit 16. Catalytic reforming'unit 16fis suitably provided with an active reforming catalyst or' a platinum-containing catalyst which may be regenerable or non-regenerable, e.g. Platforming catalyst, or a chromia-alumina catalyst or a molybdena-alumina catalyst or a cobalt molybdate catalyst. Typical operating conditions for refonner 16 when employing afplatinum-containing catalyst are as follows: inlet temperature 875 F., pressure 250 p.s.i.g., space velocity `3 v./hr./v. with a recycle of 8,000 cu. ft./ bbl. of prepared feed of a gas containing at least about 90 mol percent hydrogen. Two or more of catalytic reforming units 16 may be employed in series or in parallel.

Within catalytic reforming'unit 16 certain hydrocarbon components present in the treated feed are upgraded into higher octane hydrocarbons with a resultingv net production of hydrogen. For example, `the naphthenic hydrocarbons are dehydrogenatedy to form corresponding aromatic hydrocarbons. Substantially simultaneously therewith the isoparafnic andl normal paranic hydro- .carbons undergov isomerization, dehydrocyclization and ya certain amount of cracking with resulting gas formation (C4l audilower niolecularweightAv hydrocarbons) depending 8 upon the severity' of the reforming. operation.- In'v any event the efuent issuing from reformer 16 has an in creased aromatic hydrocarbon content and has improved qualities as a motor fuel and a higher octane rating, as compared to the feed supplied to reforming unit 16.

The eifiuent issuing from reforming unit 16 via lineA 19 is passed to a gas-liquid separator 21 wherein hydrogen produced during the reforming operation is separated therefrom. At least part of this separated hydrogen is`- recycled Via line 20 to reformer 16 to provide the desired hydrogen recycle. The remaining reformer effluent or reformate is advantageously passed from gas-liquid sep`- arator 21 via line 22 into fractionator 23 wherein an overhead fraction comprising substantially all of the C5 and/ or C4 and lighter hydrocarbons are removed overhead as a' separate fraction via line 24. The remaining high molecular weight, higher boiling hydrocarbons, comprising substantially all of theV normally liquid hydrocarbons in' the reformer etlluent, are passed via line' 25 to heater 26 wherein the eluent, if not already in the vapor phase. is Vaporized. The eluent is introduced from heater V26 into adsorber 29 by means of line 30. If heater 26 is unnecessary or if it is desired to carry out liquid phase" adsorption heater 26 may be by-passed via line 17.

If desired, the reformer eluent in fractionator 23, after removal of the C5 and/ or lighter hydrocarbons is further fractionated to procure a side cut via line 28 having a boiling point not greater than about 250 F. `1t has been observed that the remaining higher boiling fraction, such as a platformate having a boiling point range of Z50-450 F., is less susceptible to upgrading as regards octane number increase by subsequent treatment in accordance with this invention. This higher boiling fraction accordingly may be separately removed from fractionator 23 as a bottoms fractionvia line 27 for subsequent blending with the blended product in line 61.

Adsorber 29 is provided with a xed bed of solid particle selective adsorbent. Suitable adsorbents for straight chain hydrocarbons are the alkaline earth metal aluminosilicates, more particularly the calcium alumino-silicates, e.g. sodium calcium alumino-silicate sold under the trade name Linde 5A molecular sieve by the Linde Air Products Company. This material has the following approximate analysis: Na 3.0%, Al 20.4%, Cal8.8% and Si 18.2%. The adsorber 29 is operated at a temperature such that substantially all of the straight chain hydrocarbons, such as the normal parains in the vaporized effluent introduced into adsorber 29 via line 30 are adsorbed by the adsorbent material therein with the result that there issues from the bottom of adsorber 29 via line 31 a treated or finished fraction substantially free of straight chain hydrocarbons.

The adsorption conditions within adsorber 29 are to some extent dependent upon the composition of the hydrocarbon fraction undergoing treatment or finishing therein, e.g. the greater the amount of straight chain hydrocarbons the longer the adsorption or finishing period required to effect substantially complete adsorption of the straight chain hydrocarbons. Removal of the straight chain hydrocarbons, especially the straight chain paraflinic hydrocarbons, is desirable since these hydrocarbons possess a very low octane number. For example, normal hexane has anV octane number of 24, normal heptane an octane number of 0, normal octane an octane number of 17. The removal of the normal parafns is desirable when it is desired to produce a highquality, high octane motor fuel. The branched chain hydrocarbons, such as the branched chain isomeric parafiinic hydrocarbons, in a motor fuel are not undesirable since branched chain hydrocarbons in general possess a relatively high octane number. For example, isohexane has an octane number of about 73.

Processing or finishing periods of the eiuent undergoing treatment in adsorbei 29 in the range-2 minutes u p toY aboutv llz-Z hours at throughputs iii the range V4 v./hr./v. up to about 20 v./hr./v. are satisfactory and suitable in order to effect the desired removal of the straight chain hydrocarbons or before the adsorbent material Within adsorber 29 is substantially saturated with straight chain hydrocarbons. The nished effluent issuing from adsorber 29 via line 31 may be Withdrawn as a separate reformate product via line 32 or blended with additional hydrocarbons in amanner to be described hereinafter.

After a period of time the adsorbent material within adsorber 29 becomes substantially saturated with respect to straight chain hydrocarbons and regeneration of the adsorbent by desorption of the straight chain hydrocarbons is necessary. The straight chain hydrocarbons are desorbed from the adsorbent by contacting the adsorbent with a hot gaseous stripping medium, such as nitrogen, methane, natural gas, liue gas, carbon dioxide, oxygencontaining gas, hydrogen, steam, preferably superheated steam and the like. The hot gaseous stripping medium is introduced into adsorber 29 via line 33 or by multi-point injection via lines 33a, having been supplied from suitable sources via line 34 or line 35, the hydrogen ernployed as a stripping medium advantageously being supplied from gas-liquid separator 21 via

lines

20, 35 and 39.

The desorption operation may be carried out at substantially the same temperature as the adsorption operation, it is preferred to employ a desorption temperature suflicient to maintain the materials being treated or desorbed in the vapor phase, e.g. temperature in the range 3D0-700 F. during adsorption and a temperature in the range 400-ll F. during desorption. Usually, however, the desorption temperature is about U-300 F. higher than the adsorption temperature, generally in the range 500-l000 F. As a general rule the desorption temperature should be such that the adsorbed straight chain hydrocarbons are relatively quickly desorbed Without at the same time causing destruction of the adsorbent or decomposition or cracking of the adsorbed-desorbed hydrocarbons. The desorbed straight chain hydrocarbons together wtih their accompanying stripping medium issue from adsorber 29 via line 40 and are introduced into gas-liquid separator 41. When a normally gaseous stripping medium, such as hydrogen, flue gas, nitrogen 'and the like is employed as a stripping medium the separation of the normally gaseous materials and the desorbed straight chain hydrocarbons is effected within separator 41, the normally gaseous stripping medium being removed via line 42 and the straight chain hydrocarbons being removed via line 43. When steam is employed as the desorbing medium the stripping steam, in the form of water, is removed from separator 41 via line 44.

The desorbed Straight chain hydrocarbons issuing from separator 41 via line 43 maybe recovered as a separate product via line 44 or sent to a subsequent conversion operation, to be described, via line 4S. Advantageously when'hydrogen is employed as a stripping medium and when the aforesaid subsequent conversion operation is a catalytic conversion operation or isomerization operation or the like wherein the presence of hydrogen during the conversion of the desorbed straight chain hydrocarbons is desirable, the vaporized desorbed straight chain hydrocarbons together with the hydrogen stripping medium are recycled directly from adsorber 29 via

lines

40, 46 and 47, gas-liquid separator being by-passed until the desired hydrocarbon concentration has been reached yat which time a portion of the hydrogen and hydrocarbon mixture in line 46 is introduced into line 4S as indicated and fresh hydrogen supplied as additional stripping medium via

lines

20, 36, 39 and 33 as indicated into line 45 via

lines

40 and 46, by-passing the gas-liquid separ'ator 41.

The desorbed straight chain hydrocarbons are supplied via line 45 to heater 49 where they are brought up to the lesired conversion temperature and introduced via line 50 into converter`51 wherein the desorbed straight chain hydrocarbons are converted into higher octane or` improved motor fuel components.

The conversion operation carried out within converter 51 may be thermal cracking, thermal reforming, catalytic cracking, catalytic reforming, isomerization and the like, depending upon the properties and composition of the desorbed straight chain hydrocarbons. Preferably the conversion operation within converter 51 is an isomerization operation'employing an isomerization catalyst such as a platinum-containing catalyst, e.g. U.O.P. Platforming catalyst. The upgraded eiiluent issuing from converter 51 via line 52 now possessing a higher octane number and now containing straight chain hydrocarbons and non-straight chain hydrocarbons may be removed as a separate converted product via line 53, or blended with the straight chain hydrocarbons free effluent issuing from adorber 29 via line 31 by means of line 54 or all or a portion of the efuent from converter 51 may be returned via

lines

52 and 55 and line 22 to fractionator 23 and adsorber 29 for additional treatment as previously described.

The overhead fractions in

lines

12 and 24 containing C5 and/or YC4 and lighter hydrocarbons, preferably containing substantially all of the isopentane and the C4 hydrocarbons present in the fresh feed and the efliuent issuing from catalytic reformer 16. are combined by

lines

56 and 59, respectively, into line 60 for blending with the combined adsorber-converter effluent in line 31 and removed as a separate finished blended converted reformate product via line 61. If desired, all or a portion of the admiXed overhead fraction combined in line 60 may be passed via line 62 to a liquefied petroleum gas recovery plant.

Exemplary of the advantages obtainable in the practice of this invention as applied to a 20,000 bbl. a day charge platforming unit, it has been determined that when such a unit is operated in the conventional manner, including a mild hydrogenation treatment of the feed thereto, to produce a catalytic reformed gasoline having an octane number of about 93 there is produced 16,140 barrels per day of a debutanized gasolinevhaving a research octane number clear of 92.9. Additionally there is produced a hydrogen and hydrocarbon-containing fuel gas in an amount equal to 21.42 MM standard cu. ft. This amount of gas represents an actual loss of hydrocarbons. However, when operating in accordance with the practice of this invention employing in combination a platforming unit followed by selective iinishing of the platformate to remove substantially all the straight chain hydrocarbons therefrom, it was determined that the platforming unit could be operated at a lesser degree of severity, as indicated by the recovery of 17,440 barrels per day of debutanized gasoline and the recovery of 15,003 MM cu. ft. of hydrogen and hydrocarbon-containing lgas. The increased recovery of debutanized gasoline amounts to about an 8% by volume increase over the conventional operation. The recovered debutanized catalytic reformed gasoline amounting to 17,440 barrels per day is then treated with a selective adsorbent for the removal of straight chain hydrocarbons therefrom and there is produced 16,272 barrels per day of catalytic reformed gasoline having a clear research octane number of 92.9 together with 1168 barrels per day of straight chain hydrocarbons which may be recovered and ernployed as such as a solvent or subjected to an isomerization or catalytic reforming operation to produce additional high octane motor fuel. The advantages of employing the practice of this invention are an increased recovery of high octane gasoline since, as indicated hereinabove, less of the treated hydrocarbons are converted to butanes and lighter hydrocarbons. Additionally since the platforming operation operated in the combination treating process in. accordance with this invention is carout under less severe conditions the useful' catalyst life isiextended atleast'two'fold, 150 days vs. 70 days.

Further indicative of the advantages obtainable in the practice of this invention a 85.9 CFRR (clear) catalytic reformed gasoline (platformate) was upgraded in accordance with the practice of this invention by vapor phase contact with a selective adsorbent, Linde A molecular sieve, for removal of the straight chain hydrocarbons therefrom. The results are summarized besearch Clear The above operationsV were carried out employing a finishing or adsorption time of about thirty minutes, a space velocity of about l v./hr./v. and a desorption or regeneration temperature, following adsorption, of about 700 F. employing natural gas as the stripping medium.

Further indicative of the practice of this invention a catalytic reformed gasoline (platformate) having a research, octane number clear of 86.8 was upgraded by vapor phase contact with a selective solid adsorbent (Linde 5A molecular sieve), employing a space velocity of about l v./hr./v., for the removal of straight chain hydrocarbons therefrom. The adsorption and desorption was carried out at various temperatures, desorption being effected by natural gas comprising substantially only methane. The operating conditions and results obySince the straight' chain hydrocarbons removed from the eiuent undergoing finishing, such as a catalytic reformer effluent (Platformate), represents a substantial fraction thereof it is desirable in accordance with the practice of this invention to upgrade the straight chain hydrocarbons octanewise or otherwise to improve their quality as a motor fuel or motor fuel component or petrochemical. Accordingly in accordance with the practice of this invention a straight chain hydrocarbon fraction, comparable to the desorbed straight chain hydrocarbons which are recovered during the desorption operation, and having a composition of about 23% by volume normal pcntane, 56% by volume normal hexane and 21% by volume normal heptane and exhibiting a research clear octane number of 39 was contacted with a platinum isomerization catalyst at a temperature in the range 700-900 F., at a pressure of about 500 p.s.i.g., at a space velocity ofv about 1.0 v./hr./v., employing a hydrogen recycle rate of about 4,000 standard cu. ft. per barrel of charge. The resulting isomates were subsequently finished by removal of the straight chain hydrocarbons. The results obtained areset forth in TableIV.

l2 TABLE Iv Run No 1 2 3 4 By operating in the above-indicated manner substan-- tially all of the straight chain hydrocarbons in the initial feed fraction are charged to an improved high octane material or to branch chain hydrocarbons.

The practice of this invention is particularly applicable to catalytic reforming followed by finishing of the reformer effluent or reformate for the removal of straight chain hydrocarbons therefrom. Petroleum fractions in the naphtha boiling range, e.g. having an initial boiling point in the range 45-250 F. and an end point in the range -475" F. and containing a substantial amount of naphthenic hydrocarbons, for example containing at least about 5% by volume naphthenic hydrocarbons, e.g; in the range 5-50% by volume are particularly suited for treatment in accordance with this invention. In accordance with one embodiment of the invention the catalytic reforming operation is carried out under relatively mild conditions of temperature, pressure and throughout such that substantially only the naphthenic hydrocarbons contained in the naphtha fraction undergoing treatment are dehydrogenated during the catalytic reforming operation whereas the remaining straight chain and non-straight chain (branched acyclic and/ or aromatic) hydrocarbons pass through the catalytic reforming operation substantially unchanged. By operating in accordance with this embodiment of applicants invention the catalyst life of the catalyst employed in the catalytic reforming operation can be extended for an indefinite period of time. This is particularly advantageous when the catalytic reforming operation is a platforming operation employing a platinum-containing non-regenerable catalyst, so-called platforming catalyst.

Further exemplary of the practice of this invention a catalytic reformed gasoline, platformate, was finished in accordance with the practice of this invention by the removal of the straight chain hydrocarbons therefrom. There was procured a high octane finished gasoline having an octane number substantially greater than the initially charged platformate and having a value higher than that which could be economically reached by catalytic reforming (Platforming) alone. The results are indicated in Table No. V.

TABLE NO. V

Finished Naphtha API 50. 3 47. 5

RVP, lbs. ASTM Distillation,

IBP 5 percent EP Percent Rec 13 Yields, vol.' percent:

Finished naphtha 94.6 Desorbed material 5.0

Still further exemplary of the practice of this invention a catalytic reformed gasoline was separated into ten (10) close boiling fractions and finished by the removal of the straight chain hydrocarbons therefrom. The results set forth in Table No. VI indicate that fractions of a catalytic reformed gasoline having a boiling point above 249 F. exhibit a smaller octane number increase than the lower boiling fractions. Accordingly, for `economic reasons it may be more advantageous to iinish only the more responsive lower boiling fractions of a reformate, leaving the relatively less responsive high boiling fractions untreated, rather than to finish the whole reformate.

TABLE NO. VI

Selective finishing of close boiling fractions from a platformate [87.1 clear research Oct.]

Vol. ASTM Res. Oct. ASTM Res. Oct. Boiling percent Clear +3 cc. TEL Cut No. Range, Cumula- F. tive Raw Finished Raw Finished In accordance with still another embodiment of this invention employing the practice set forth in our copending patent application Serial No. 478,426, tiled December 29, 1954, of which this application is a continuation-in-part, the fresh feed petroleum fraction after suitable feed fraction and/or preparation, if desired, is contacted with a selective adsorbent for the removal of straight chain hydrocarbons therefrom. The resulting eiiluent now substantially free of straight chain hydrocarbons is passed to a catalytic reforming unit, such as a platforming unit, for upgrading into a higher octane motor fuel or valuable components thereof. The reformate issuing from the catalytic reforming unit is then contacted with the selective adsorbent for the removal of the straight chain hydrocarbons present in the reformate, which straight chain hydrocarbons may have been formed therein by isomerization of the isoparaiiinic or isooleinic constituents present in the feed to the catalytic reformer. The adsorbed straight chain hydrocarbons are desorbed from the adsorbent material and separately treated to produce an improved motor fuel or motor fuel cornponent.

For purposes of simplicity and clarity, conventional control equipment, valves, pumps, compressors, heaters, coolers, gas-liquid separators, fractionators, etc. have for the most part not been illustrated in the drawing. The location and employment of these auxiliary pieces of equipment and the like in the practice of this invention are well known to those skilled in the art. Furthermore the above-described operations of catalytic reforming, straight chain hydrocarbon adsorption and desorption and isomerization or reforming or converting of the desorbed straight chain hydrocarbons can be carried out substantially continuously by employing a plurality of catalytic reforming units 16 and adsorbers 29 and converters l, one or more adsorbers 29 undergoing desorption-regeneration at the same time. For purposes of simplicity and clarity only one reformer unit 16, one adsorber Z9 and one converter 51 have been shown.

e "14 The employment of one or more of these units'in'th manner to effect substantially continuous operation is well known to those skilled in the art.

As is evident 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 combination treating operation for upgrading a heavy naphtha boiling in the range -425 F. and containing straight chain hydrocarbons and non-straight chain hydrocarbons which comprises subjecting said naphtha to catalytic reforming by contact with a reforming catalyst under reforming conditions of temperature and pressure to produce a reformate, said reformate containing straight chain hydrocarbons and non-straight chain hydrocarbons, fractionating said reformate to separate therefrom an overhead fraction containing C4 and C5 hydrocarbons, contacting the remaining reformate with a solid alumino-silicate molecular sieve selective adsorbent which selectively adsorbs straight chain hydro- Hydrocarbon type: Percent by vol.

Naphthenes 0-75 Aromatics 0-50 Paraiins, including normal paraftins and isoparains 3-90 Unsaturatcs, including normal oleiins and isooleiins 0-S0 3. A method in accordance with claim 1 wherein the straight chain hydrocarbons adsorbed by said selective adsorbent are desorbed therefrom, isomerized and blended with said resulting treated reformate and said overhead fraction.

4. A method of treating a heavy petroleum naphtha boiling in the range 175-425 F. and containing straight chain hydrocarbons and non-straight chain hydrocarbons which comprises catalytically reforming said naphtha to produce a reformate containing straight chain hydrocarbons and non-straight chain hydrocarbons together with a resulting net production of hydrogen, recovering hydrogen produced during said catalytic reforming operation, fractionating said reformate to separate therefrom an overhead fraction containing C4 and C5 hydrocarbons, contacting the remaining reformate with a solid alumino-silicate molecular sieve selective adsorbent which selectively adsorbs straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons to adsorb only substantially all of the straight chain hydrocarbons from said remaining reformate and to yield a resulting treated reformate substantially free of straight chain hydrocarbons, desorbing the adsorbed straight chain hydrocarbons from said adsorbent, subjecting the resulting desorbed straight chain hydrocarbons together with a portion of the hydrogen produced during and recovered from said reforming operation to isomerization to produce an isomate containing straight chain hydrocarbons and non-straight chain hydrocarbons, contacting said isomate with a solid alumino-silicate selective adsorbent which selectively adsorbs straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons to adsorb only straight chain hydrocarbons from said isomate and to yield a treated isomate substantially free of straight chain hydrocarbons and blending together said resulting treated reformate, said treated isomate now substantially free of straight chain hydrocarbons and the 'aforesaid overhead fraction con# taining C4 and C5 hydrocarbons to produce a petroleum product having improved qualities as a motor fuel.

References Cited in the le of this patent UNITED STATES PATNTS Houdry Mar. 16, 1937 Whiteley Feb. 7, 1939 Houdry Mar. 21, 1939 dOuville et a1 Oct. 21, 1941 Marschner Dec. 8, 1942 Ogorzaly Mar. 14, 1944

Claims

1. A COMBINATION TREATING OPERATION FOR UPGRADING A HEAVY NAPHTHA BOILING IN THE RANGE 175-425*F. AND CONTAINING STRAIGHT CHAIN HYDROCARBONS AND NON-STRAIGHT CHAIN HYDROCARBONS WHICH COMPRISES SUBJECTING SAID NAPHTHA TO CATALYTIC REFORMING BY CONTACT WITH A REFORMING CATALYST UNDER REFORMING CONDITIONS OF TEMPERATURE AND PRESSURE TO PRODUCE A REFORMATE, SAID REFORMATE CONTAINING STRAIGHT CHAIN HYDROCARBONS AND NON-STRAIGHT CHAIN HYDROCARBONS, FRACTIONATING SAID REFORMATE TO SEPARATE THEREFROM AN OVERHEAD FRACTION CONTAINING C4 AND C5 HYDROCARBONS, CONTACTING THE REMAINING REFORMATE WITH A SOLID ALUMINO-SILICATE MOLECULAR SIEVE SELECTIVE ADSORBENT WHICH SELECTIVELY ADSORBS STRAIGHT CHAIN HYDROCARBONS TO THE SUBSTANTIAL EXLUSION OF NON-STRAIGHT CHAIN HYDROCARBONS TO ADSORB ONLY STRAIGHT CHAIN HYDROCARBONS FROM SAID REMAINING REFORMATE, RECOVERING FROM THE AFORESAID SELECTIVE ADSORPTION OPERATION OF RESULTING TREATED REFORMATE SUBSTANTIALLY FREE OS STRAIGHT CHAN HYDROCARBONS AND BLENDING SAID RESULTING TREATED REFORMATE WITH SAID OVERHEAD FRACTION.