US3001928A

US3001928A - Reforming process

Info

Publication number: US3001928A
Application number: US832887A
Authority: US
Inventors: Henry W Grote
Original assignee: Universal Oil Products Co
Current assignee: Universal Oil Products Co
Priority date: 1959-08-07
Filing date: 1959-08-07
Publication date: 1961-09-26
Anticipated expiration: 1978-09-26

Description

Sept. 26, 1961 H. w. GROTE 3,001,928

REFORMING PROCESS Filed Aug. 7, 1959 l F racf/ ana/or TTR/VEYS:

United we,

3,001,928 REFRMING PROCESS Henry W. Grote, Hinsdale, Ill., assignor to Universal Gil Products Company, Des Plaines, Ill., a corporation of Delaware l Filed Aug. 7, 1959, Ser. No. 832,887 9 Claims. (Cl. 20S-65) The present application is a continuation-impart of my copending application, Serial Number 563,075, led February 6, 1956, as a continuation-impart of application, Serial Number 277,980, filed March 22, 1952, and application Serial No. 478,968, tiled December 31, v1954, all of said earlier applications being now abandoned.

The presen-t invention relates, in its most broad scope, to a novel method for obtaining high yields of aromatic hydrocarbons from various hydrocarbon mixtures and fractions. More specifically, the invention is directed toward an integrated, two-stage catalytic reforming process which affords high yields of aromatic hydrocarbons while converting an otherwise low-octane parainic hydrocarbon into its` high-octane isomer and providing for the removal thereof from said integrated process.

Recent developments in the automotive industry have greatly increased the demand for possessing unusually high octane ratings, and the petroleum industry has been striving constantly to keep up with these demands. One process that has achieved Widespread commercial lacceptance is the catalytic reforming process. .The usual method of eecting catalytic reforming of straight-run gasoline or a straight-run gasoline fraction, inorderto produce aromatics and other high octanev gasoline components, suitable for aviation and motor fuels, lsuffers from the almost impossible .task of obtaining complete dehydrogenation and arornatization ofthe naphthenic hydrocarbons, within the particularly chosen charge stock, to aromatics; for example, the conversion of'substa'ntially all the cyclohexane and methylcyclopentane to benzene. Also, it is not generally possible by conventional methods to-convert any substantial proportion of the straight chain parafns to aromatics by dehydrocycliza-tion, or to iso-paraflins by isomeriza-tion, as for example, the, conversion of normal hexane to benzene, ortofiso-hexane. There has recently been disclosed, and provided ,commercially, an improved reforming operation which utilizes a platinum-alumina-com'bined halogen 'catalyst under conditions that permit extended periods'of continuous operation without the necessity of regenerating or replacing the catalyst, providing thereby a substantially non-regenerative process. This improved catalyst yand operation has been set forth .in a patent to Vladimir 2 and which permits obtaining high octane products suita-. b-le for aviation as well as motor fuels.

It is a particular object of the present invention to provide an integrated process with means for convertingv six-carbon atom hydrocarbons into isoparaflins and benzene while affording a method for the recovery of isoparafiins from the process, avoiding thereby the destruction of a substantial portion thereof.

In its most broad embodiment, the present invention relates to a process which comprises catalytically reforming a gasoline fraction at a pressure of from about 200 to about 1000 pounds per square inch, separating from the resultant products a low-boiling fraction containing isohexane and lighter hydrocarbons and a heavier fraction containing aromatics, normal hexane nad five-membered ring naphthenes, subjecting said heavier fraction to solvent extraction fto separate the aromatics therefrom, and catalytically reforming the remaining non-aromatic rafnate, comprising normal hexane and live-membered ring naphthenes, at a pressure at least 75 pounds per square inch lower than that in the rst-mentioned reforming'step to form a product containing additional aromatics and isohexane.

In another embodiment, the present invention relates to a process for effecting an improved yield of aromatic hydrocarbons from a hydrocarbon stream boiling within the gasoline boiling-range which comprises subjecting said stream and hydrogen to reforming in the presence of a catalyst that promotes dehydrogenation of naphthenes and hydrocracking of parains, subsequently cooling the resulting reformed stream and effecting the separation thereof to provide a gaseous hydrogen-containing stream and an Varomatic-rich hydrocarbon stream, passing the latter toa fractionating zone and removing normally gaseous components therefrom, treating the remaining fraction in a separation zone, withdrawing from said separationzone a fraction containing a substantial portion of aromatics an'd a second fraction containing a large proportion of parainic hydrocarbons, subjecting at least a portion of said second fraction to contact with a dehydrocyclization catalyst in the presence of hydrogen and effecting the conversion thereof to form additional aro- Haensel, Patent No. 2,479,110, issued August 16, 1949.

However, in connection with this improved reforming process it is generally desirable to process full boiling range gasoline or gasoline fractions at -a pressure within the range of from about 400 to 1000 pounds per square inch to insure a substantially non-regenerative operation with. a minimum of carbon formation and the resulting catalyst deactivation.. At this Ihigh pressure level, .the conversion of various of the naphthenic hydrocarbons, more specially the lower boiling naphthenes to aromatics and the parati-ins to aromatics, is limited, as set forth hereinabove, and therefore, there is not obtained a maximum production of aromatics.

lt is, therefore, the principal object of the present invention to provide an improved combined operation effooting a high yield of aromatics from a hydrocarbon fraction boiling lwithin the gasoline boiling range.v

lt is also an object of the invention to provide a multiple-stage operation which is particularly suitable for the 7 production of aromatics from naphtheneshand parains matic hydrocarbons, separating the -resulting stream to provide a gaseous hydrogen stream and a hydrocarbon stream and recycling at least a portion of the latter stream to the rst mentioned fractionating Zone. In a more specific embodiment, the present invention relates to a reforming process which comprises subjecting gasoline to catalytic aromatization at a pressure in excess of about 500 pounds per square inch, fractionating theresultant hydrocarbon products in a fractionating zone to separate isohexanes and lighter hydrocarbons boiling below about F. from normal hexane and heavier hydrocarbons, subjecting said normal hexane and heavier hydrocarbons tosolvent extraction to separate aromatic hydrocarbons from non-aromatic hydrocarbons, recovering the separated aromatics, fractionating said non-aromatic hydrocarbons in a second fractionating zone to separate therefrom a C6 hydrocarbon fraction having an atmospheric boiling range of from about 150 F. to about F. and containing five-membered ring naphthenes, subjecting said C6 fraction to catalytic isomerization and aromatization at a pressure below about 300 pounds per square inch to form additional aromatic hydrocarbons and isohexanes, supplying the resultant hydrocarbon conversion products to the first-mentioned fraction-ating zone for fractionation therein Itogether with the first-mentioned hydrocarbon products, and recovering as an overhead product from said first-mentioned fractionating zone lthe commingled isohexane and lighter hydrocarbons boiling below about 150 F.

vIn its most specific embodiment, the present invention provides a catalytic reforming process which comprises subjecting a gasoline fraction to reforming at a temperature of from about 600 F. to about 1000 F. and a pressure of from about 500 to about 800 pounds per square inch, with hydrogen at a hydrogen to hydrocarbon mol ratio of from about 5:1 to about 20:1, said conditions in the reforming zone being selected to minimizc the production of olenic hydrocarbons, in the presence of a catalyst comprising alumina, 0.01% to about 1% by weight of platinum and from about 0.1% to about 3% by weight of combined halogen, subsequently cooling the resultant reformed stream and eiecting the separation thereof to provide a gaseous hydrogen-containing stream and an aromatic-rich hydrocarbon stream, introducing said aromatic-rich stream to a first fractionating zone to remove normally gaseous components therefrom, passing the remaining aromatic-rich hydrocarbon stream from the first fractionation zone to a second fractionation zone and fractionating said stream to separate a low-boiling stream containing isohexanes and lighter hydrocarbons, having a boiling point below about 150 P., from the aromatic-rich portion of said stream, passing the resulting fractionated aromatic-rich stream from the second fractionation zone to an extraction zone wherein said stream is countercurrently contacted with a selective solvent containing diethylene glycol and from about 2% to about 30% by weight of water, separately removing from said extraction zone an extract stream containing said solvent and a substantial amount of the aromatics in said portion, and a rainate stream containing a substantial amount of parainic hydrocarbons, introducing said extract to a stripping column, removing as overhead from said column an aromatic-containing stream, removing as bottoms from said column a solvent stream and recycling said stream to said extraction zone, fractionating said raliinate to separate therefrom a C6 hydrocarbon fraction having an atmospheric boiling range of from about 150 F. to about 185 F. and containing tivernembered ring naphthenes, subjecting said C@ fraction together with hydrogen to contact with a dehydrocyclization catalyst at a pressure below 300 pounds per square inch, effecting thereby the conversion thereof to form additional aromatic hydrocarbons, separating the resulting stream to provide a gaseous hydrogen-containing stream and a hydrocarbon stream and recycling at least a portion of this latter stream to the first fractionation zone.

Briefly, the present invention provides a method for effecting an improved yield of aromatic hydrocarbons from a hydrocarbon stream boiling substantially within the gasoline range which comprises subjecting the hydrocarbon stream to reforming in the presence of hydrogen and a suitable reforming catalyst. In the rst reforming zone, the principal reactions are those by which naphthenes are dehydrogenated to aromatics, and the heavy paraflins are hydrocracked to lower-boiling paraftins. It is also preferred that the conditions and catalyst in the first reaction zone be such that the catalyst will also exhibit a significant degree of isomerization and dehydrocyclization activity. Therefore, the catalyst preferably isomerizes normal paraflins to isoparatiins and converts C, hydrocarbons containing tive-membercd ring naphthenes to aromatics. The resulting reformed stream is cooled and a separation thereof effected to provide a gaseous hydrogen-containing stream and an aromaticrich hydrocarbon stream containing paraflinic hydrocarbons. The aromatic-rich hydrocarbon stream is fractionated to reject the normally gaseous hydrocarbons produced in the process and the resultant liquid is further fractionated to separate a low boiling stream containing isohexane and lighter hydrocarbons from the aromaticrich portion of the stream. Therefore, the reformed efuent stream from the reaction zone is fractionated to separate a low boiling hydrocarbon stream, having a boiling point below about 150 F. and containing isohexanes and lighter hydrocarbons, from the aromatic- 4 rich portion of the stream. The aromatic-rich portion of the stream, containing normal hexane and higher boiling paratiins and aromatics, is passed to an extraction zone in which the recovery of aromatic hydrocarbons is effected. At least a portion ofthe resulting non-aromatic or paratnic hydrocarbon stream from the extraction zone is passed to a second reforming zone wherein it is contacted with a catalyst having dehydrocyclization, aromatization and isomerizing activities while in the presence of hydrogen. In a specific embodiment of my invention the non-aromatic hydrocarbon stream from the extraction zone is passed to a fractionation zone and fractionated to provide a gasoline stream boiling above about 185"a F. and a C-hydrocarbon stream having an atmospheric boiling range of from about 150 F. to about 185 F. This latter C-hydrocarbon fraction is passed to the second reforming zone wherein it is contacted with a catalyst having dehydrocyclization, aromatizing, and isomerization activities, while in the presence of hydrogen. The second reforming zone is at pressure at least pounds per square inch lower than the first reforming zone and preferably at least pounds per square inch lower than the pressure in the first reforming zone. In one specific mode of operation, the pressure in the rst reforming zone is in excess of 500 pounds per square inch gauge and the pressure in the second reforming zone is below about 300 pounds per square inch gauge. Generally the pressure in the first catalytic reforming zone is within the range of from about 500 to about 800 p.s.i.g. and the pressure in the second catalytic reforming zone is below about 300 p.s.i.g. In the second reaction zone the temperature is preferably higher than the temperature in the iirst reforming zone The product from the second reaction zone is passed to the first fractionation zone and from there the stream follows the same route as the effluent from the first reforming zone.

A feature of my process is that mild hydrocracking conditions may be employed in the first reforming step. Generally more severe conditions are necessary to dehydrocyclicize a straight chain parain to form an aromatic, than to dehydrogenate a cycloparatiin or naphthene to form an aromatic hydrocarbon. Reforming of the low-octane number paratlins in a separate reaction zone results in their being dehydrocyclicized to aromatics and/or their being converted to lower boiling high octane number parains without the excessive production of gaseous hydrocarbons that would result were these higher boiling paratiins substantially completely reacted in the rst reforming reactor continued at conditions of high severity. Therefore, a feature of my process is that the conditions in the second reforming zone may be severe enough to convert a substantial portion of the parafns to aromatics while at the same time minimizing undesirable side reactions which otherwise reduce yields of useful gasoline products. As hereinbefore set forth, one of the major causes of excessive coke deposition, which inherently results in rapid catalyst deactivation, is the reaction of various aromatic hydrocarbons to form heavy, carbonaceous polynuclear aromatics. Excessive carbon deposition is also facilitated through the accumulation of certain parainic hydrocarbons which, in a process employing recycle of a portion of the reaction products, either pass unaffected through the reaction zone, or react in a detrimental manner to form coke and other carbonaceous material. In my process, however, the aromatic hydrocarbons are withdrawn in a substantially pure stream through the use of a solvent extraction procedure, and a provision is made whereby the paralinic hydrocarbons are converted to a valuable product and also withdrawn from the process.

High severity operation, in the presence of aromatics, is also not desirable from considerations of the chemical equilibria involved, as in such operations the aromatics in the feed limit the extent to which such aromatics can be formed from naphthenes and paraiins. In contrast, however, the use of my process involves the removal of a substantial portion of the aromatics from the charge to the reaction zone which thus permits the formation of additional aromatics unrestricted by the limitations of chemical equilibria. Similarly, the isomer-ization of low octane number rating straight chain paraflins to higher octane quality branched chain structure paraffins is -an equilibrium chemical reaction. As the isomerization of normal hexane is important to achieve in upgrading gasolines, due to the very limited extent that it undergoes dehydrocyclization at reasonable operating conditions, a feature of my process 4is that .high-octane isohexanes may be continuously removed, and the normal hexane recycled to the reaction zone in the raffinate thus obtaining substantial conversion of low octane normal hexane to much higher quality isohexanes, accompanied by almost no restrictions in yield due to chemical equilibrium considerations. Accordingly, the aromatics are separated from the parafns and naphthenes in the reformate from the first reaction zone for several reasons. One reason is that if the aromatics were introduced to the second reaction zone, there Would result a lower overall yield of reformate, presumably due to the conversion of the aromatics to gaseous hydrocarbons and to hydrocarbons boiling above the gasoline range, primarily polynuclear aromatics. Another reason is that high concentrations of aromatics in the reaction zone tend to result in a greater carbon deposition and consequently-a shorter catalyst life. Still another reason, which has hereinbefore been mentioned, is that high concentrations of aromatcs in the reaction zone tend to suppress the dehydrogenation of naphthenes to aromatics and to suppress the dehydrocyclization of parains to aromatics, said dehydrogenation and said dehydrocyclization beingequilibrium reactions. By eliminating low octane number, high boiling paraflins from the final product the end product is a reformate of high quality even though the low boiling portions of the charging stock have never been subjected to the relatively severe operating conditions that previously have been thought to be necessary to produce high quality reformate.

Similarly, the reaction products from the first reaction zone are subjected to a sep-aration to remove therefrom the normally gaseous hydrogen-containing stream which is recycled to the reaction zone, and those normally liquid, low-molecular weight hydrocarbons boiling below about 150 F., and which hydrocarbons are rich in isohexane. The rem-aining reaction products are then subje'cted to a solvent extraction procedure to effect removal of the aromatic hydrocarbons, and to provide a raflinate 'stream containing normal hexane and five-membered ring napthenes. The rainate is fractionated to produce a particular hydrocarbon fraction having an atmospheric Iboiling range of about 150 F. to about 185 F. and rich in normal hexane and the five-membered ring naphthenes. This hydrocarbon fraction is passed into a separately distinct reforming zone to effect the formation of additional aromatics and to convert the normal hexane into high-octane isohexane. The resulting product is recycled to combine with the reaction product from the first-mentioned reaction zone, and the -additional isoh'exane is subsequently removed from the process with those low molecular weight hydrocarbons boiling below 150 F., the additional aromatics'being removed wia the solvent extraction procedure, In this manner, the normal hexane can be advantageously utilized to produce isohexane, and the latter is not permitted to accumulate within the process, nor is it subject to detrimental cokefo-rming reactions.

The charge stocks which may be reformed, in accordance with my process, comprise hydrocarbon fractions that boil Within the gasoline range and contain naphthenes and parains. The preferred stocks are those consisting essentially of naphthenes and parans, although aro- 6 matics'and :minor amounts of oletins may be presenti This preferred class includes straight-run gasoline, natural gasoline and the like. The gasolinefraction may be a full boiling range gasoline having an initial boiling point within the range of from about 50 F. to about,l F. and an end boiling point within the range of from about 350 F. to about 425 F. or it may be aselected fraction thereof which usually is a higher boi-ling` fraction commonly referred to as naphtha, having an ini-A tial boiling point within the range of from about F. to rabout 250 F. and an end boiling point within the range of from about 350 F. to about 425 F. Mixtures of the various gasolines and/or gasoline fractions may also be used, and thermally cracked and/or catalytically cracked gasolines may be employed. However, when these unsaturated gasoline .fractions are used, it is preferred that they be used either in admixture with a straight-run or natural gasoline fraction, or else hydro-- gneated prior to use.

In a preferred operation in the iirst reforming step, wherein the charge is subjected to hydrocracking and aromatization, the catalytic contact is made at a pressure of from about 200 to about 1000 pounds per square inch. -In the subsequent catalytic contacting step, the C8 plus hydrocarbon fraction contacts the catalyst at a lower pressure, said pressure being at least 75 poundsY per square inch and preferably at least 100 pounds per square inch lower than the pressure in the first reform-1 ing step. It is also to be noted that certain of the fivemembered naphthenes, such as methylcyclopentane, are not completely converted to benzene in the first reform-v ing step so that a subsequent contact after removal of aromatics permits Ifurther dehydrogenation and conversion of such fractions to benzene and other arom-atics while the normal hexane fraction is subjected to dehydrocyclization to produce aromatics of higher octane number, and isomerization to isohexane and other branched parains of higher octane number. -It is also a feature of the improved operation to effect the recycling of the resultnig hydrocarbon stream after contact with a dehydrocyclization catalyst, so that resulting aromatics land isohexanes are admixed with the reformed stream' entering the first fractionation zone. In the first fractionation zone, the normally gaseous components are taken off overhead and the remaining stream is passed to a second fractionation zone wherein isohexanes and lighter hydrocarbons boiling below 150 F. are taken oif overhead and removed as such. i

A preferred operation effects the recycle of the hydrogen stream being separated `from the reformed gasoline stream into contact with the charge stream in order to provide added hydrogen to the catalytic reforming zone.l Similarly, hydrogen separated from the second stage dehydrocyclization zone may ibe recycled to the latter to provide the presence of additional hydrogen during the catalytic contact of the parains.

Various types of desirable 4and suitable catalystsV may be utilized within each stage of theprocess, however, the preferred operation utilizes the improved platinumalumina-combined halogen catalyst in each of the contact zones. The catalysts that may be used in the first re-` forming zone of my invention comprise thosereforming catalysts that permit dehydrogenation of naphthenic hydrocarbons, hydrocracking of parainic hydrocarbons and isomerization of parainic hydrocarbons. A satisfactory catalyst comprises a platinum-alumina-silica catalyst of the type described in U.S. Patent No. 2,478,916, issued August 16, 1949. A preferred catalyst is the type described in U.S. Patent No. 2,479,109, issued August 16, 1949. Other catalsts such as molybdena-alumina, chromia-alumina and platinum on a cracking catalyst base may be used. In the second reforming zone, as well as in the first reforming zone, the platinum concentration in the catalyst may range up to about 10% by YWeight or more of the alumina, but a desirable catalyst may be.

provided to contain as low as from `about 0.01% to about 1% by weight of platinum. The halogen ions may be present in an amount of from about 0.1% to about 8% Yby weight of the catalyst but preferably are present in an amount of from Iabout 0.1% to about 3% by weight of the alumina on a dry basis. Also, while any of the halogen ions provide a desirable catalyst, the uoride ions'are particularly preferred and next in order are the chloride ions, the bromide ions and iodide ions. In the second stage of catalyst contact, wherein the non aromatic Ca-plus fraction undergoes dehydrocyclization, and wherein C8 hydrocarbons containing livemembered ring naphthenes undergo isomerization and dehydrogenation, there may be a lesser quantity of platinum present in the catalyst.

Except for pressure level, the operating conditions maintained in each of the two reforming zones of my process are essentially the same. Generally the pressure in the rst reforming zone is within the range of from about 200 to about 1000 p.s.i.g. and the pressure in the second reforming zone is at least 75 p.s.i. lower. Genorally the pressure in the rst reforming zone is in excess of 500 p.s.i.g. and the pressure in the second reforming zone is below about 300 p.s.i.g. More specically, the pressure in the iirst reforming zone is within the range of from about 500 to about 800 p.s.i.g. and the pressure in the second reforming zone is from about 25 p.s.i.g. to about 300 p.s.i.g. The conditions in the rst zone should be such that substantial conversion of naphthenes to aromatics, and relatively mild hydrocracking of parans are induced, and further the operating conditions in the second zone should be such that there is a substantial conversion of parafflnic compounds to lomtics by dchydroyclization as well as isomerization of paramos such as the isomerization of normal hexane to isohexane. When employing platinum-alumina-combined halogen catalyst in both of the reforming zones, the conditions in cach are usually a temperature within the range of from about 600 l?. to about 1000" F., and a weight hourly space velocity of from about 0.5 to about 20. The weight hourly space velocity is defined as the weight of Oil per hout per weight of catalyst in the reaction zone. It is preferred that the reforming reaction in both of the reaction zones be conducted in the presome of hydrogen. In one embodiment of the process, sucient hydrogen Will be produced as a result of the various reactions to furnish the hydrogen required in the process, and, therefore, it may be unnecessary to introduce hydrogen from an extraneous source or to recycle hydrogen within the process. However, it will be preferred to introduce hydrogen from an extraneous source generally at the beginning of the operation and to recycle hydrogen within the process in order to be assured of a sucient hydrogen atmosphere in each of the reaction zones. The hydrogen present in each of the reaction zones will be within the range of from about 0.5 to about 2() mols of hydrogen per mol of hydrocarbon. In some cases, the gas to be recycled will contain hydrogen sulde introduced with the charge or liberated by the catalyst, and it is within the scope of the present invention to treat the hydrogen-containing gas to remove hydrogen sulfide or other impurities before recycling the hydrogen to the reforming zone. The pressure in the first reaction zone is from about 200 to about 1000 pounds per square inch. The pressure in the second reaction zone is lower, and is at least 75 pounds per square inch lower and preferably at least about 100 pounds per square inch lower. The temperature in the second reaction zone is preferably higher than that employed in the rst reaction zone. The conditions are further selected that there are substantially no olens present in the product streams from the tirst and second reaction zones.

The eluent from the rst reforming zone is usually passed to a stabilizer which elects a separation of the normally gaseous material which comprises hydrogen; hydrogen sulfide, and hydrocarbons containing from 1 to 4 carbon atoms per molecule from the normally liquid hydrocarbons. rthe liquid from the stabilizer is then passed to a fractionation zone which effects separation of isohexane and lighter hydrocarbons having boiling points below about F. from the liquid charge. The doohexanzed hydrocarbon stream is then passed to an extraction z one to produce a more concentrated aromatic fraction.

Solvent extraction processes are utilized to separate certain desired components in a mixture from the other components thereof by a separation based upon u dfference in solubility of the components in a particular solvent. It is frequently desirable to separate various substances by solvent extraction; for example, when the Substances to be separated have similar boiling points, arc unstable at temperatures at which fractionation is cffected, forrn constant boiling mixtures, ctc. It is particularly desirable to separate aromatic hydrocarbons rom a petroleum fraction containing these aromatic hydrocarbons by solvent extraction because a petroleum fraction is normally a complex mixture of hydrocarbons whose boiling points are extremely close together and because the petroleum fraction contains numerous cyclic compunds which tend to form constant-boiling or azeotropic mixtures. As hereinbefore stated, the basis of a solvent extraction separation is the difference in solubility in a given solvent of one of the substances to be separated from the other. It may, therefore, be seen that the more extreme this difference the easier the separation will be and an easier separation reflects itself processwise in less expensive equipment and greater yields per pass in the use of processing equipment as well as in higher purity of product.

A particularly preferred solvent for separating aromatic hydrocarbons from non-aromatic hydrocarbons is a mixture of water and a hydrophilic organic solvent. Such a solvent may have its solubility regulated by adding more or less water thereto. rFhus, by adding more water to the solvent, the solubility of all components in the hydrocarbon mixture are reduced, but the solubility difference between the components is increased. This effect is reflected process-wise in less contacting stages required to obtain a product of given purity. However, a greater throughput of solvent must be used in order to obtain the same amount of material dissolved.

As hereinbefore stated, the solvent to be used in this invention is preferably a mixture of a hydrophilic organic solvent and water, wherein the amount of water contained in the mixture is selected to regulate the solubility in the solvent of the materials to be separated. Suitable hydrophilic organic solvents include alcohols, glycols, aldehydes, glycerine, phenol, etc. Particular preferred solvents are diethylene glycol, triethylene glycol, dipropylcnc glycol, tripropylene glycol and mixtures thereof containing from about 2% to about 30% by weight of water.

In classifying hydrocarbon type compounds according to increasing solubility in such a solvent, it is found that the solubility of the various classes increases in the fo1- lowing manner: the least soluble are the parains followed in increasing order of solubility by naphthcncs, olens, diolefins, acetylenes, sulfur, nitrogen and oxygen-contaiu ing compounds and aromatic hydrocarbons. It may thus be seen that a charge stock which is rich in unsaturated compounds will present a greater problem in solvent extraction than a saturated charge stock since the unsaturated compounds fall between the paraiins and aromatics in solubility. Further diiculty, in having unsaturated compounds in the feed, is that they tend to polymerize at higher temperatures to form sludges and other undesirable materials. It may be seen that an ideal charge to solvent extraction is one containing paratiinic and aromatic hydrocarbons exclusively.

The -parainic compounds also differ among themselves in their relative solubility in the solvent. appears to be a function of the boiling point of thevparafiin with the lower boiling or lighter parans being more soluble than the higher boiling or heavier parains. Therefore, when heavy parains are dissolved in the solvent they may be displaced from the solvent by adding lighter parains thereto.

At least a portion of the raina-te from the extraction zone is passed to the second reforming zone in which it is contacted with a catalyst having dehydrocyclization and isomerizing activity. The second zone is maintained at aromatization and isomerizing conditions. In a preferred embodiment of this invention the raiiinate, that is the nonaromatic hydrocarbons separated from the extraction Zone, is fractionated in a fractionation zone to separate therefrom a C@ hydrocarbon fraction boiling in the range of from about 150 F. to about 185 F. and containing tive-membered ring naphthenes, and this fraction is subjected in the second reforming zone to catalytic .isomerization and aromatization at a pressure below about 300 pounds per square inch to form additional aromatic hydrocarbons and isohexanes. As hereinbefore mentioned, the use of a second catalytic reaction zone is preferred since the conditions in the second zone may be selected so as to produce the highest possible yield of aromatics from the charge stock to the second zone. The eluent from the second reaction zone is passed to the rst mentioned fractionation zone, or stabilizer,ffor fractionation therein together with the eluent from the first catalytic reforming zone. As hereinbefore mentioned, the commingled isohexane and lighter hydrocarbons boiling below about 150 F. are recovered as anoverhead product i'n such fractionation zone.

r Additional features and advantages of my invention, will be apparent from the following description of the accompanying drawing which illustrates a particular method for conducting a gasoline reforming operation in accordance with the present invention. The drawing is described in conjunction with a specific example of the production of a highly aromatic product. For the purpose of simplicity, many valves, pumps, heat exchangers, etc. have been omitted from thedrawing, since their illustration is not necessary for a complete understanding of the invention'.

vReferring now to the drawing, there is indicated a 150 F. to 400 F. gasoline charge stream being passed by way of line 1 and valve 2 into a heater 3 while in admixture with a hydrogen stream being introduced by way` of line 4. This gasoline stream may be a straightrun gasoline, natural gasoline or other relatively low octane number stream Which is to undergo reforming to provide a high yield of aromatic hydrocarbons, together with desirable high octane number aviation and motor fuels. A heated stream, at a temperature of the order of about 920 F., or within the range of 900 F. to 950 F., while at a pressure of the order of 600 pounds per square inch or Within the range of from about 300 to about 1000 pounds per square inch, is introduced by way of line 5 into reactor 6. Reforming'reactor 6 contains a bed of spherical catalyst of approximately 1s-inch average diameter, containing about 0.375% platinum, 0.5% combined fluorine, and 0.1% combined chlorine. During the passage of the chargingstock through the rst reactor 6, the bulk of the naphthenes containing six or more carbon atoms per molecule, are dehydrogenated to the corresponding aromatics and a portion of the parafns are hydrocracked to lower boiling paraiiins. lsomerization of the parains and .dehydrocyclization of theparafns in the charge preferably also take place. The drawing indicates a single conversionk zone 6, however, it is to be understood that one or more zones may be utilized in series, with interheaters therebetween if desired, so that there may be accomplished a substantial degree of aromatization of the charge stream. The conditions inthe reforming zone,

The solubilityy 10 or reactor 6, are selected so that Vsubstantially no oleni substances are produced.

catalyst of this process, oleiinic materials will not be pro duced in any appreciable amounts.

The resulting reformed stream passes from the first reaction zone 6 by way of line 7, cooler 8, line 9 and. subsequently enters a separating zone 10'. A resultingv hydrogen-containing gaseous stream is discharged fromA the upper portion of separating zone l10 by way of line is passed 4from separator 10 by Way of yline 16 and valve 17 and enters a rst fractionation zone or stabilizer 18. ln accordance with the present invention, normally gaseous hydrocarbons are removed overhead through line Z0. ln stabilizer 18, the normally gaseousy material, which includes hydrogen, ammonia, hydrogen su-lde, and hydrocarbon gases containing from 1 to 4 carbon atoms per molecule, is separated from the hydrocarbon liquid` comprising aromatic hydrocarbons and paraffinic hydro' carbons.

The gaseous material passes overhead through line 20y into cooler 21, wherein a portion of the material is condensed, and the entire stream passes through line 22 into receiver 23. ln receiver23, the liquid phase and the gaseous phase of the overhead material separate; thel gaseous material passes through line 25; from which it may be vented to the atmosphere or used as fuel, or may' be further used in the present process or other processes. The stabilizer has heat provided thereto by reboiler 27 and connecting lines 26 and 28. The stabilizer and receiver are 'operated at a sufficient pressure to liquefy at least a portion of the overhead material so that a liquid reflux stream may be availabe-to improve the separation in stabilizer 18. The liquid redux is removed from receiver 23 through line 24 and passes into an upper portion of stabilizer 18. l

The stabilizer bottoms, which as hereinbefore stated, comprises substantially parainic and aromatic hydro* carbons, are withdrawn from stabilizer 18 through line 29 and are passed to an intermediate portion of a second fractionation zone or fractionator 30. In fractionator 30, the stabilizer bottoms is separated into a light overhead and heavier bottoms fraction. The conditions in fractionator 30 are maintained so that components which are lighter than those which are preferred to be reformed in a second reactor zone are removed as an overhead fraction. ln the embodiment of the drawing, the overhead` comprises components boiling below normal hexane or from the boiling point of isohexanes and lighter hydrocarbons, i.e.' boiling below about 150 F.; column 30 may be referred to as a deisohexanizer. The light hydrocar bon stream is removed from fractionator 30 and passes throughl line 31 into cooler 32 wherein the material is condensed and the entire stream passes through line 33 into receiver 34. The liquid in receiver 34 is withdrawn through line 35. Line 35 splits up into several streams. A portion of the stream in line 35 passes through line 36 into the upper portion of :fractionator 30 as redux. A

portion of the liquid in line 35 may be withdrawn as product through line 37 and in some instances may be combined with the product in line 113. Heat is provided to the fractionator 30 by reboiler 41 and connecting

lines

40 and 42. The bottoms, which are substantially free of components boiling below normal hexane, are removed` from the fractionator 30 through line 44 and are introduced to a lower portion of extractor 38.

In extractor 38, the hydrocarbon material rises and is countercurrently contacted at an elevated temperature` At the conditions herein-1v before specified, and in the presence of hydrogen and the" 1 1 of 250 F. with a descending stream of selective solvent. In this embodiment 92.5% diethylene glycol and 7.5% water is used, with the solvent stream entering the upper portion of extractor 3S through line 46. Water may also be introduced into extractor 38 through line 69 and valve 70 which is shown as being added to the glycol stream in line 46; however, the water may also be added to eX- tractor 38 independently of line 46, that is, it may be separately fed into extractor 38. As hereinbefore mentioned, the water is added to increase the selectivity of the solvent. The pressure on the column is l() p.s.i.g. The solvent to feed ratio is 5:1.

As a result of the countercurrent contact of the selective solvent and the hydrocarbon charge stock, the aromatic hydrocarbons contained in the charge to the extractor are selectively dissolved in the solvent, thereby forming an extract stream containing the solvent and aromatic hydrocarbons, and a ranate stream containing the paratfrnic hydrocarbons. The rafinate stream passes from the upper portion of extractor 38 through line 4S while the extract stream passes through the lower portion of extractor 38 through line 47. Line 47 passes to flash drum 48. Flash drum 48 is maintained at a pressure lower than the extractor and preferably is kept atV about atmospheric pressure. In the flash drum, some of the light parafnic components are flashed overhead and are removed through line 49. The remainder of the liquid is withdrawn from ash drum 48 through line 50 and introduced to stripper 51 wherein the dissolved aromatic yhydrocarbons and dissolved paraflns are separated from the selective solvent. Line 50 is preferably connected to the stripper 51 at a point in the upper half of the column. The separation in stripper 51 is not dicult due to the fact that the aromatic hydrocarbons are substantially different in nature from the selective solvent as well as having a substantially different boiling point. The aromatic hydrocarbon stream along with some light paraflins passes overhead from the stripper 51 through line 52 and combines with the overhead from the ash drum in line 49 and the combined stream in line 53 may be passed to extract rectier 54. Heat is provided for the stripping operation by reboiler 56 and connecting lines 5S and 57. The solvent stream is taken from the bottom of stripper 51 through line 46 and is passed into the upper portion of extractor 38 as hereinbefore mentioned.

The combined stream in line 53 may be used as the final product or it may be subjected to further treatment in order to produce a product of higher quality. In the present illustration the combined stream in line 53 is introduced to an intermediate portion of extract rectilier 54. In extract rectiiier 54 the lighter components, chiefly the dissolved light parans, are removed overhead through line 53 while the aromatics are removed from the lower portion through line 113. The gaseous material in line 58 passes through cooler 59 wherein the gaseous fraction is liqueed, and from the cooler 59 the fraction passes through line 60 and into receiver 61. A portion of the liquefied overhead stream in receiver 61 is withdrawn through line 62 and passed through line 63 into the upper portion of extract rectifier 54 as reux, and a portion of the liquefied product is withdrawn from receiver 61 through

lines

62 and 64, which portion is recycled and introduced to the extractor 38 at a point inthe lower half thereof. A portion of the liqueed product in line 62 may also be removed as product through line 62. Heat is provided to extract rectifier 54 by reboiler 111 with connecting

lines

110 and 112.

The rainate stream from extractor 3S, which is withdrawn through line 45, may be passed directly t0 the second reforming operation in reactor 91. However, it is preferred that the rainate stream be further treated in order to improve its suitability for recycling to the reforming reactor. The rainate contains dissolved and entrained solvent and further the raffinate may contain 12 components which may be heavier than are suitable for reforming.

In the drawing the ranate in line 45 is introduced into glycol separator 72. Separator 72 may be a type of holding or settling tank wherein the glycol Aentrained in the raffinate is allowed to settle out of the rainate phase. Separated solvent is removed from separator 72 by way of line 73 and the remaining rainate stream is withdrawn from separator 72 through line 74 and subjected to a water wash in vessel 75. The water was column 7S is illustrated as a vertical vessel in which the rainate is introduced at a lower portion thereof, and is couutercurrently contacted with a descending stream of water introduced to column 75 in the upper portion thereof through line 76. The water and solvent are removed frorn vessel 75 through line 78, and the washed raffinate is removed from the upper portion of the vessel through line 77. A portion of the washed rafnate may be removed from the system through line 77a containing valve 78b. In one embodiment of the invention, valve 78' in line 77 is maintained closed and valve 78" inline 77' is maintained open. The raffinate in line '77 thereby continues through line 77' and open valve 73" into line' 85. In a preferred embodiment hereinbefore described, valve 78" is maintained closed and valve 78 is maintained open. The raiinate in line 77 thereby continues through open valve 78 and into fractionator 79. Fractionator 79 has heat provided thereto by reboiler 87 and connecting lines 86 and 88. In fractionator 79 the non aromatic hydrocarbon stream undergoes separation to provide an overhead stream having an atmospheric b0iling range of F. to 185 F., and in view of the previous separation made in fractionator 50, this overhead fraction comprises primarily selected C6 hydrocarbons. The overhead material is withdrawn through line 80, passes through cooler 81 and line 82 into overhead receiver 83. The receiver 83 and fractionator 79 are operated so as to liquefy the overhead material. At least a portion of the 15G-185 F. fraction in receiver 83 is returned to an upper portion of fractionator 79 through line 84 as redux. The bottoms from the column 79, which -boil above about F., provides a gasoline stream suitable for motor fuel blending. This latter stream is indicated as being withdrawn by way of line 89.

The aforementioned overhead cut, boiling inuthe range of from about 150 F. to about 185 F., is removed from receiver 83 through line 85. The hydrocarbon in line 85 mixes with hydrogen introduced in line 90 and the mixture of hydrocarbon and hydrogen in line 91 passes into heater 92 wherein the combined stream is heated to a temperature of the order of about 920 F. or within the range of 900 F. to 970 F. The pressure in the second reaction zone is 290 pounds per square inch.l

The combined stream in heater 92 passes through line 93 into reactor 94. Reforming reactor 94 contains a bed of spherical catalyst of the same composition as the catalyst in reactor 6. During the passage of the charge stock through the second reactor 94, a substantial portion of the parafins are hydrocracked to lower boiling parains. A substantial portion of the parafns are also isomerized; for example, normal hexane is isomerized to isohexane. Naphthenes are also dehydrogenated to aromatics, for example cyclohexane is dehydrogenated to benzene. C6 hydrocarbons containing ive-membered ring naphthenes are also isomerized and aromatized to aromatics, for example, methylcyclopentane is converted to benzene. The drawing indicates a single conversion zone 94, however, it is understood that one or more zones may be utilized in series with interheaters between as desired so that there may be accomplished a substantial degree 0f conversion of the charge stream. The conditions in the reforming zone or reactor 94 are selected so that there is substantial conversion of parains and cycloparains to aromatics and so that there are substantially no olenic substances'produced. At the conditions here-` inbefore specified, and in4 the presence of hydrogen. and' The resulting reformed stream passes from second re action zone 94 by way of line 95, cooler 96 and line 97 containing valve 987and subsequently enters a separating zone or receiver 99. A resulting hydrogen-containing gaseousfstream is discharged from the upper portion ofthe separating zone 99 by way of line 100 and a portion of this stream may ybe vented or withdrawn as fuel gas or process gas by way of line 101 containing valve 102, while the remaining portion passes into compressor 103. The compressor 103 provides a recycling of a portion of a hydrogen-containing stream by way of line 90. The condensed hydrocarbon stream is Iwithdrawn from separator 99 by way of line 104,-valve 105, and line 19. Line 19 introduces the liquid into the first Afractionation zone or stabilizer 18.

Although the-process illustrated in the drawing represents one of the preferred -forms of my invention, it i's to be understood that my invention is not limited thereby. A number of variations may be introduced into the process without departing from the spirit or scope of said invention.

I claim as my invention:

l. A process whichv comprises catalytically reforming a gasoline fraction at a pressure of from about 200 to about 1000 pounds per square inch, separating from the'resultant products a low-boiling fraction containing isohexane and lighter hydrocarbons and a heavier fraction containing aromatics, normal hexane and live-membered ring naphthenes, subjecting said heavier fraction to solvent extraction to separate the aromatics therefrom, and catalytically reforming the remaining non-aromatic raimate, comprising normal hexane and Ve-membered ring naphthenes, at a pressure at least 75 pounds per square inch lower than that in the iirst-mentioned reforming step to form a product containing additional aromatics and isohexane.

V2.. A process which comprises catalytically reforming a gasoline fraction-at a pressure of from about 200 to about 1000 pounds per square inch, separating from the resultant products a low-boiling fraction containing isohexane and lighter hydrocarbons and a heavier fraction containing iive-membered ring naphthenes, normal hexane and aromatics, subjecting said heavier fraction to solvent extraction to separate aromatics from paratiins, fractionating the resultant parainic raiiinate to separate therefrom a C6 fraction having an atmospheric boiling range of from about 150 F. to about 185 F. and containing normal hexane and ve-membered ring naphthenes, and catalytically reforming said C6 fraction at a pressure at least 75 pounds per square inch lower than that in the first-mentioned reforming step to form additional aromatics and isohexaue.

3. A process for effecting an improved yield of aromatic hydrocarbons from a hydrocarbon stream boiling within the gasoline boiling range which comprises subjecting said stream and hydrogen to reforming in the presence of a catalyst that promotes dehydrogenation of naphthenes and hydrocracking of paraflins, fractionating the resulting reformed stream and removing normally gaseous components therefrom in a lirst fractionating zone, passing the remaining stream from said first fractionating zone to a second fractionating zone and fractionating said stream to separate a low boiling stream containing isohexane and lighter hydrocarbons from the aromatic-rich portion of said stream, passing the remaining aromatic-rich portion to a solvent extraction zone, withdrawing from said extraction zone a fraction containing a substantial portion of aromatic hydrocarbons and a second fraction having an atmospheric boiling range of from about 150 F. to about 185 F. and containing normal hexane and ve-membered ring naphthenes, subjecting said second fraction to dehydrocycli'zation ir'ifthepesence of hydrogen and eifecting tlr'e conversion 'thereof to formA additional aromatichydrostream recycling at least a portion of this latter: stream to said rst fractionating zone to recover said additionalisohexane from said process.

4. A process for effecting an improved yield of aromatic hydrocarbons from a hydrocarbon stream boiling within the gasoline boiling range which comprises subjecting said stream and hydrogen to reforming in the` presence of a catalyst comprising platinum, alumina and combined halogen, at conditions that promote del hydrogenation of naphthenes and hydrocracking of parans, fractionating the resulting reformed stream and removing normally gaseous components therefrom ina rst fractionating zone, passing the remaining stream from said first fractionating zone to a second fractionating zone,- separating a low-boiling stream containing isohex-v ane and lighter hydrocarbons from the aromatic-rich portion of said stream,l passing the aromatic-rich portion. to a solvent extraction zone and countercurrently contacting said portion with a selective solvent vto remove a substantial portion vof the aromatics therefrom, subjecting the resulting parainic ranate, containing normal hexane and iive-membered ring naphthenes, to reforming in the presence of hydrogen and with a catalyst comprising platinum, alumina and combined halogen at dehydrocyclization conditions and a pressure at least k pounds per square inch lower than in the rstmentioned reforming zone, effecting the conversion thereof to form additional aromatic hydrocarbons and isohexane, separating the resulting stream to provide a gaseous hydrogen stream and a hydrocarbon stream and recycling at least a portion of this latter stream to said iirst rfractionating step to recover said additional isohexane from said process. 5. The'p'rocess of claim 4 further characterized in that said paraliinic rainate is subjected to reforming at highertemperatures than said gasoline fraction.

6. A process forr eiecting an improved yield of aromatic hydrocarbons from a gasoline stream, which com-- prises, subjecting said gasoline stream to reforming in the presence of hydrogen and a platinum-alumina-combined halogen catalyst at a temperature of the order of about 900 F. and a pressure within the range of from about 500 p.s.i.g. to about 800 p.s.i.g., effecting the separation thereof to provide a normally gaseous hydrogencontaining stream and an aromatic-rich hydrocarbon stream, fractionating the latter to separate a low-boiling hydrocarbon stream having an end boiling point below about P. and containing isohexanes and lighter hydrocarbons from said aromatic-rich portion of the stream, passing a resulting aromatic-rich stream to an extraction zone and effecting the recovery of aromatic hydrocarbons therefrom, passing a resulting non-aromatic hydrocarbon stream from said extraction zone to a second fractionation zone and separating the non-aromatic stream to provide a gasoline stream boiling above about F. and a light hydrocarbon stream having an atmospheric boiling range of from about 150 F. to about 185 F. and containing ve-membered ring naphthenes, subjecting this later stream to contact with a platinum-alumina-combined halogen catalyst at a temperature within the range of from about 700 F. to about 850 F, and at a pressure of less than about 300 p.s.i.g. and forming thereby additional aromatic hydrocarbons and isohexanes, cooling and separating the latter hydrocarbon stream to provide a gasous hydrogen-containing stream and a liquid stream and recycling the latter to said iirst fractionation zone and into admixture with the reformed hydrocarbon stream passing thereto whereby said additional isohexanes may be recovered from said process and said additional aromatics may be introduced to said extraction zone.

7. A reforming process which comprises subjecting gasoline to catalytic aromatization at a pressure in excess of about 500 pounds per square inch, fractionating the resultant hydrocarbon products in a fractionating zone to separate isohexanes and lighter hydrocarbons boiling below about 150 F. from n-hexane and heavier hydrocarbons, subjecting said n-hexane and heavier hydrocarbons to solvent extraction to separate aromatic hydrocarbons from non-aromatic hydrocarbons, recovering the separated aromatics, fractionating said non-aromatic hydrocarbons in a second fractionating zone to separate therefrom a C hydrocarbon fraction having an atmospheric boiling range of from about 150 F. to about 185 F. and containing ve-membered ring naphthenes, subjecting said C3 fraction to catalytic isomerization and aromatization at a pressure below about 300 pounds per square inch to form additional aromatic hydrocarbons and isohexanes, supplying the resultant hydrocarbon conversion products to the first-mentioned fractionating zone for fractionation therein together with the first-mentioned hydrocarbon products, and recovering as an overhead product frompsaid first-mentioned fractionating zone the commingled isohexane and lighter hydrocarbons boiling below about 150 F.

8. The process of claim 7 further characterized in that the aromatizing and isomerizing reactions are eiected in the presence of a platinum-alumina-combined halogen catalyst.

9. A catalytic reforming process which comprises subjecting a gasoline fraction to reforming at a temperature of from about 600 F. to about 1000 F. and a pressure of from about 500 to about 800 pounds per square inch, with hydrogen at a hydrogen to hydrocarbon mol ratio of from about 5:1 to about 20:1, said conditions in the reforming zone being selected to minimize the production of olenic hydrocarbons, in the presence of a catalyst comprising alumina, 0.01% to about 1% by weight of platinum and from about 0.1% to about 3% by weight of combined halogen, subsequently cooling the resultant reformed stream and effecting the separation thereof to provide a gaseous hydrogen-containing stream and an aromatic-rich hydrocarbon stream, introducing said aromatic-rich stream to a first fractionating zone to remove maining aromatic-rich hydrocarbon stream from the first fractionation zone to a second fractionation zone and fractionating said stream to separate alow-boiling stream containing isohexanes and lighter hydrocarbons, having a boiling point below about F., from the aromatic-rich portion of said stream, passing the resulting fractionated aromatic-rich stream from the second fractionation zone to an extraction zone wherein said stream is countercurrently contacted with a selective solvent containing diethylene glycol and from about 2% to about 30% by weight of water, separately removing from said extraction zone an extract stream containing said solvent and a substantial amount of the aromatics in said portion, and a ramnate stream containing a substantial amount of parainic hydrocarbons, introducing said extract to a stripping column, removing as overhead from said column an aromatic-containing stream, removing as bottoms from said column a solvent stream and recycling said stream to said extraction zone, fractionating said ratlnate to separate therefrom a C5 hydrocarbon fraction having an atmospheric boiling range of from about 150 F. to about F. and containing iive-membered ring naphthenes, subjecting said C6 fraction together with hydrogen to con tact with a dehydrocyclization catalyst at a pressure below 300 pounds per square inch, effecting thereby the conversion thereof to form additional aromatic hydrocarbons, separating the resulting stream to provide a gaseous hydrogen-containing stream and a hydrocarbon stream and recycling at least a portion of this latter stream to the first fractionation zone.

References Cited in the le of this patent UNITED STATES PATENTS Schneider et al Oct. 13, 1959

Claims

4. A PROCESS FOR EFFECTING AN IMPROVED YIELD OF AROMATIC HYDROCARBONS FROM A HYDROCARBON STREAM BOILING WITHIN THE GASOLINE BOILING RANGE WHICH COMPRISES SUBJECTING SAID STREAM AND HYDROGENN TO REFORMING IN THE PRESENCE OF A CATALYST COMPRISING PLATINUM, ALUMINA AND COMBINED HALOGEN, AT CONDITIONS THAT PROMOTE DEHYDROGENATION OF NAPHTHENES AND HYDROCRACKING OF PARAFFINS, FRACTIONATING THE RESULTING REFORMED STREAM AND REMOVING NORMALLY GASEOUS COMPONENTS THEREFROM IN A FIRST FRACTIONATING ZONE, PASSING THE REMAINING STREAM FROM SAID FIRST FRACTIONATING ZONE TO A SECOND FRACTIONATING ZONE, SEPARATING A LOW-BOILING STREAM CONTAINING ISOHEXANE AND LIGHTER HYDROCARBONS FROM THE AROMATIC-RICH PORTION OF SAID STREAM, PASSING THE AROMATIC-RICH PORTION TO A SOLVENT EXTRACTION ZONE AND COUNTERCURRENTLY CONTACTING SAID PORTION WITH A SELECTIVE SOLVENT TO REMOVE TO A SUBSTRANTIAL PORTION OF THE AROMATICS THEREFROM, SUBJECTING THE RESULTING PARAFFINIC RAFFINATE, CONTAINING NORMAL HEXANE AND FIVE-MEMBERED RILNG NAPHTHENES, TO REFORMING IN THE PRESENCE OF HYDROGEN AND WITH A CATALYST