US2838582A

US2838582A - Hydrocarbon conversion process

Info

Publication number: US2838582A
Application number: US478974A
Authority: US
Inventors: Louis S Kassel; Haensel Vladimir
Original assignee: Universal Oil Products Co
Current assignee: Universal Oil Products Co
Priority date: 1954-12-31
Filing date: 1954-12-31
Publication date: 1958-06-10
Anticipated expiration: 1975-06-10
Also published as: ES225871A1; FR1145269A; GB787539A; NL99595C

Description

June 10, 1958` s. KASSEL ET AL 2,838,582

v HYDROCARBON CONVERSION PROCESS Filed Dec. 3l, 1954 7' TOR/V575! olv /N VEN TORS: Lou/'s .5T Kasse/ Vlad/'m/'r Haense/ ffm;

1940101 NHEE UnitedV State atenf f HYDROCARBN CONVERSION PROCESS Louis S. Kassel, Oak Park, and Vladimir Haensel, Hinsdale, Ill., assignors to Universal Oil Products Company, Des Plaines, lll., a corporation of Delaware Application December 31, 1954, Serial No. 478,974

Claims. (Cl. 260-673.5)

This invention relates to thev catalytic conversion of' hydrocarbons boiling within the gasoline range. It is more specifi-cally concerned with a novel combination of solvent extraction and catalytic reforming.

The recent developments in the automotive industry, especially in regard to the development of high compression ratio automotive engines, have increased the demand for high octane number gasolines and the petroleum industry has provided technological improvements to produce these high octane number gasolines. One process that has recently received commercial attention is the catalytic reforming process. The term reforming is well known in the Apetroleum industry and refers to the treatment of gasoline fractions to improve the anti-knock characteristics thereof. A highly successful and economical reforming process that has achieved wide commercial acceptance is described in U. S. Patent No. 2,479,110, issued to Vladimir Haensel. However, the present reforming processes are all limited by decreasing yields lat increasing octane numbers. There are also other limitations. For example, when a full boiling range straight-run gasoline or a -relatively wide boiling range nap'htha is reformed in the presence of a catalyst that :promotes dehydrogenation of naphthenes and hydrocracking of parains, relatively poor yields and considerable fouling of the catalyst are obtained when the operating conditions are selected to obtain large octane number appreciation. This apparently is due to the fact that the relatively severe operating conditions that must be maintained in order to satisfactorily upgrade the higher boiling -paratnic constituents of the feed are too severe for some of the other constituents. The result is that an appreciable part of the feed stock is undesirably converted to gases and to catalyst carbon. Therefore, under the usual conditions of operation the yield of liquid product and catalyst life are limited to a considerable extent by and primarily dependent on the decomposition and carbon forming tendencies of the higher boiling paraftinic constituents and the aromatic constituents. The higher boiling parat-linie constituents may decompose to form coke on the catalyst and the aromatic constituents" also deposit coke or carbonaceous material on the catalyst by reacting with each other and forming polynuclear aromatics which are the carbonaceous materials that foul the catalyst. We have invented a method of reforming which largely overcomes these objectionable features of the prior art reforming processes.

It is an object of the Ipresent invention lto treat a full boiling range straight-run gasoline or a fraction thereof in such a manner that increased yields of high octane number gasoline and aromatics and longer catalyst life are obtained.

In one embodiment the present invention relates to a process which comprises introducing a hydrocarbon :charge stock to a separation Zone withdrawing from said separation zone a fraction containing a substantial portion of aromatic hydrocarbon and a second fraction containing a substantial proportion of parainic hydrocarbons, sub- 2,838,582 Patented June 10, 1953 jecting at least a portion of said second fraction to contact with a dehydrocyclization catalyst at dehydrocyclization conditions thereby forming additional aromatic hydrocarbons, and introducing at least `a portion of the reaction product to said separation zone.

In another embodiment the present invention relates to a process which comprises introducing a hydrocarbon charge stock containing paraiiins and aromatics to a separation zone, withdrawing from said zone a fraction containing a substantial proportion of aromatic hydrocarbons `and a 'second fraction containing a large proportion of, parafnic hydrocarbons, subjecting said second fraction and hydrogen to dehydrocyclization at dehydro- -cyclization conditions in the presence of a dehydrocyclization catalyst thereby forming aromatic hydrocarbons, fractionating the resultant stream to remove normally gaseous components therefrom and introducing at least a portion of the resultant stream to said separation zone.

1l'n a further embodiment the present invention relates to a process which comprises introducing a hydrocarbon charge stock containing paratiins and aromatics to an extraction zone wherein said charge stock is treated with a lselective solvent having a relatively higher solvent power for aromatics, separately removing from said extraction zone an extract containing said solvent and a substantial amount of the aromatics in said charge and a raflinate containing a substantial amount of paraflinic hydrocarbons, treating said extract to separate the solvent from the aromatics, reforming at least a portion of said raffinate with a dehydrocyclization catalyst at dehydrocyclization conditions in the presence of hydrogen thereby forming aromatics, introducing the reformate from the reforming zone to a first fractionation zone to remove normally gaseous components therefrom, introducing the remaining liquid reformate to a second fractionation zone, fractionating said liquid reformate into a low boiling parainic stock containing components lighter than normalhexane 'and a high boiling fraction, introducing at least a portion of said low boiling parainic stock to said extraction zone, and introducing said high boiling fraction to said extraction zone.

Briey stated, our process comprises solvent extracting a hydrocarbon charge stock to produce a railinate containing a major proportion of parafns and an extract containing chiefly aromatic hydrocarbons. At least a portion of the raffinate from the extraction zone is subjected to dehydrocyclization to convert a substantial portion 0f the paraflins in the rainate to aromatics. However, in catalytic reforming there occurs some hydrocracking and, therefore, the reformate is fractionated to reject the gaseous hydrocarbons produced in the reforming and the resultant liquid is fractionated to remove-a fraction boiling lower than normal hexane since these lighter components are usually high in octane number.

All or a portion of the higher boiling fraction is then passed to the same extraction zone that the charge stock is introduced to. The fraction boiling lower than normal hexane is also passed to the extraction zone to provide reux to the extraction column.

A feature of our process is that the conditions in the reforming zone may be severe enough to convert a substantial portion of the parail'ins to aromatics while at the s ame time minimizing undesirable side reactions which otherwise reduce yields of useful gasoline products. As hereinbefore mentioned, one of the chief reasons for deposit of carbon or carbonaceous material on the catalyst is the reaction of aromatics to form polynuclear aromatics. In our process, however, the aromatics lare removed and, therefore, substantially less carbon is formed on the catalyst with resultant longer catalyst life. High severity operation, in the presence of aromatics, is also not desirable from considerations of the chemical equiasaassz libria involved, as in such operations the aromatics in the feed limit the extent to which such aromatics can be formed from naphthenes and paraflins. ln contrast, however, the use of our 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 isomerization of Vlow octane rating straight chain parains to higher octane quality branched chain structure paraflins 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 Vdehydrocyclization at reasonable operating conditions, a feature of our process is that the isohexanes may be continuously removed and the normal hexane recycled to the reaction zone in the rainate thus obtaining substantial conversion of low octane normal hexane to much higher quality isohexanes with almost no restrictions in yield due to chemical equilibrium considerations.

Therefore, it is preferred to separate the aromatic hydrocarbons from the parafns and naphthenes in the charge for several reasons. One reason is that reforming the aromatics results in lower over-all yields of reformate presumably due to conversion of some of the aromatics to gaseous hydrocarbons and to hydrocarbons boiling above the gasoline range. Another reason is that high concentrations of aromatics in the reaction zone tend to result in a greater carbon deposition and consequently a shorter process period. Still another reason is that high concentrations of aromatics in the reaction zone tend to suppress the dehydrogenation of naphthenes to aromatics and to suppress the dehydrocyclization of parafiins to aromatics, said dehydrogenation and said dehydrocyclization being equilibrium reactions. By eliminating low octane number high boiling parafiins from the final product the end product is of high quality.

The charge stocks that may be reformed in accordance with our process comprise hydrocarbon fractions that boil within the gasoline range and that contain aromatics and parains. The preferred stocks are those consisting predominantlyv of aromatics, naphthenes and parafns, although minor amounts of olefins may be present. This preferred class includes straight-run gasoline, natural gasoline and the like. The gasoline fraction may be a full boiling range gasoline having an initial boiling point within the range of'from about 50 F. to about 100 F., and an end boiling point within the range of from about 350 F. to about 425 F., or it may be a selected fraction thereof which usually is a higher boiling fraction commonly referred to as naphtha and having an initial boiling point within the range of from about 150 F. to about 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 also be used as charging stock, however, when these unsaturated gasoline fractions are used, it is preferred that they be used in admixture'with a straight-run or natural gasoline fraction orY hydrogenatedV before use in our process. v f

The catalyst that may be used in our invention comprises those reforming catalystsV that promote dehydrogenation of naphthenic hydrocarbons and hydrocracking of parafnic hydrocarbons. Starting with a paraffinic hydrocarbon from a yield-octane standpoint it is preferable to upgrade the parainic hydrocarbon by dehydrocyclicizing the same to an aromatic than by cracking the parainic hydrocarbon. Since the raffinate char-ge tothe reforming zone consists of predominantly paraflinic constituents it is best to upgrade this recycle stream bydehydrocyclization. Therefore it is preferredthat the catalyst in the reforming zone be such that it has a substantial amount of dehydrocyclization activity. It isalso preferred that the catalyst has paraffin isomerization activity to isomerize normal hexane to isohexanes. 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 comprises a platinum-alumina-combincd halogen catalyst of the type described in U. S. Patent No. 2,479,109, issued August 16, 1949. Other catalysts such as molybdenum-alumina, chromia-alumina, and platinum on a cracking catalyst base may be used, however they are not as preferredas the rst two mentioned catalysts. As hereinbefore mentioned, it is preferred that the catalyst has substantial dehydrocyclicizing activity. We have found that catalysts of the platinum-alumina-combined halogen type, especially those that contain about 0.01% to about 1% by weight of platinum and from about 0.1% to about 1% combined iiuorine or those that contain about 0.1% to about 3.0% combined chlorine are especially effective and economical to use in our process because of the long life they exhibit and also they promote dehydrogenation reactions and dehydrocyclization reactions as well as the naphthene dehydrogenation, parafiin hydrocracking and paraffin isomerization reactions.

The operating conditions maintained in the reforming step of our process should be such that substantial conversion of naphthenes to aromatics and relatively mild hydrocracking of paraffins are induced. Further, the operating conditions should be such that there is substantial conversion of paraiiinic compounds to aromatics by dehydrocyclizaticn. When employing platinum-alumina-combined halogen catalysts the reforming process will be effected at a temperature within the range of from about 600 F. to about 1000" F., pressure within the range of from about 50 to about 1000 pounds per square inch, 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 hour per weight of catalyst in the reaction Zone. It is preferred that the reforming reaction be conducted in the presence of hydrogen. In one embodiment of the process sufficient hydrogen will be produced in the reforming reaction 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 in the beginning of the operation, and to recycle hydrogen within the process in order to be assured of a sufficient hydrogen atmosphere in the reaction zone. The hydrogen present in the reaction zone will be within the range of from about.0.5 to about 20 mols of hydrogen per mol of hydrocarbon. In some cases the gas to be recycled will contain hydrogen sulfide 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 efuent from the reforming zone is usually passed to a stabilizer which effects separation of the normally gaseous material which comprises hydrogen, hydrogen sulfide, ammonia, and hydrocarbons containing from one to four carbon atoms per molecule, from the normally liquid hydrocarbons. A more concentrated aromatic fraction is then obtained in accordance with the present invention by fractionating the stabilizer bottoms to produce fractions of greater and lesser volatility and passing both fractions to a solvent extraction process.

Solvent extraction processes are used to separate certain components in a mixture from other components thereof by a separation process based upon a difference in solubility ofthe components in a particular solvent. It is frequently desirable to separate various substances by solvent extraction when the substances to be separated have similar boiling points, are unstable at temperatures at which fractionation is effected, form constant boiling mixtures, etc. It is particularly desirable to separate-arof ratic hydrocarbons from a petroleum fraction containing these aromatic hydrocarbons by solvent extractron because a petroleum fraction is normally a continuous mixture of hydrocarbons whose boiling points are extremely close together and because the petroleum fraction contains numerous cyclic compounds which tend to form constant boiling or azeotropic mixtures. As herembefore stated, the basis of a solvent extraction separa-- tion is the difference in solubility in a given solvent of one of the substances to be separated from the other. It may be, therefore, seen that the more extreme this.- difference, the easier the separation will be and an easier separation reiects it, process-wise, in less extensive 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. Thus, 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 fewer contacting stages required to obtain a given purity of product; however, a greater through-put 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 w-ater, 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 alcohol, glycols, aldehydes, etc. Particularly preferred solvents are diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, and mixtures thereof containing from about 2% to about 30% by weight of water.

In classifying hydrocarbon and hydrocarbon type compounds according to increasing solubility in such a solvent, it is found that the solubility of the various classes increases in the following manner: the least soluble are the paraftins followed in increasing order of solubility by naphthenes, olens, dioleiins, acetylenes, sulfur, nitrogen, and oxygen-containing 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 parafns and aromatics in solubility. Further difficulty in having unsaturated compounds in the feed is that they tend to polymerize at higher temperatures to form sludges and other undesirable materials which causes great difficulty in processingequipment. It may Vbe seen that an ideal charge to solvent extraction is one co-ntaining paraffinic and aromatic hydrocarbons exclusively. The paraiiinic compounds also differ in their relative solubility in the solvent. The solubility appears to be a function of the boiling point of the paraiin, with the lower boiling or lighter paraliins being mo-re soluble than the higher boiling or heavier paraliins. Therefore, when heavy paraflins are dissolved in the solvent, they may be displaced from theV solvent by adding lighter parafins thereto which displace the heavier parains. In an embodiment of this invention it is preferred to recycle the heavier parains to the reforming zone and, therefore, a light paraffin is charged to the extraction Zone to displace these heavier paraflins from the solvent by putting the heavier paraftins into the raiiinate phase.

The light that is charged to the extraction zone to displace the heavier paraflns may be provided for by removing the light paraflins that are removed from the Y extraction zone along with the extract. The reformate from the dehydrocyclization zone also may provide a source of light parafins. In a preferred operationthe reformate from the dehydrocyclization zone is fractionated or stabilized to remove normally gaseous parains tionation zone wherein an isohexane and lighter fraction is removed as overhead and the isohexane and lighter fraction is the light paraiiin fraction that is introduced to the extraction zone to displace heavier parains from the solvent.

Additional features and advantages of our invention will be apparent from the following description of the attached drawing which illustrates la particular method for conducting a gasoline upgrading operation in accordance with the present invention.

Referring to the drawing a straight-run gasoline fracti-on having an initial boiling point of F. and an end point of 425 F. is passed through line 1 into a lower portion of extractor 2. In extractor 2 the hydrocarbon material rises and is countercurrently contacted with a descending stream of selective solvent entering the upper portion of extractor 2 through line 4. Water may also be introduced into extractor 2 through line 32 which is shown as entering the top of extractor 2, however, the water may also be added directly to line 4. As hereinbefore mentioned the water is `added to increase the selectivity of the lean solvent in line 4.

As a result of the countercurrent contact of the selective solvent and hydrocarbon charge stock, the aromatic hydrocarbons contained in the charge stock are selectively dissolved in the solvent forming an extract stream containing the solvent and aromatic hydrocarbons, and a rafiinate stream containing the paraflinic hydrocarbons. The

raffinate stream passes from the upper portion of extractor 2 through line 9 While the extract stream passes through the lower portion of extractor 2 through line 8. Line 8 passes to flash drum 19. Flash drum 19 is maintained at a pressure lower than the extractor pressure and preferably is kept at about atmospheric pressure. In the ash drum some of the light paraftinic components are flashed overhead and are removed through line 10. The remainder of the liquid is withdrawn from ash drum 19 through line 11 and introduced to an upper portion of stripper 12 wherein the dissolved aromatic .hydrocarbons and dissolved paraftins are separated from the selective solvent. Line 11 is preferably introduced to stripper 12 at a point in the upper half of the column. The separation in stripper 12 is not difficult in that the aromatic hydrocarbons and light parains 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 parains passes overhead through line 13 and combines with the overhead from the ash drum 19 in line 10 and the combined stream in line 14 may be passed to extract rectifier 15. Heat is provided for the stripping operation by reboiler 17 and connecting

line

16 and 18. The solvent stream is taken from the bottom of stripper 12 through line 4 and passes through before-mentioned line 4 into the upper portion of extractorZ.

The combined stream in line 14 may be used as the final product, however, 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 14 is introduced to an intermediate portion `of extract rectier 15. In extract rectilier 15, the lighter cornponents, chiefly the dissolved light paraiiins, are removed overhead through line 2o while the aromatics are removed through line 39. The gaseous material in line 20 passes through cooler 2l wherein the gaseous fraction is liquefied and from cooler 21 the fraction passes through line 22 into receiver 23. A portion of the liquefied overhead stream is passed through lineV 24 and line 25 into the upper portion of extract rectifier 15 as reflux, and a portion of the liquefied product is withdrawn from receiver 23 through lines 24 and 7 which portion is introduced to the extractor 2 at a point in the lower portion thereof and at a point belowl the points where linesul lhydrocracked to lower boiling paraiins.

7 and 3 enter extractor 2. Heat is provided to extract rectiier by reboiler 23 and connecting lines 27 and 29.

The ratiinate stream from extract-or 2 which is withdrawn through line 9 may be reformed without further treatment, however, it is preferred that the raffinate stream be further treated in order `to improve its suitability for reforming. The raffinate contains dissolved solvent and further the raffinate contains components which may be heavier than are suitable for reforming.

In the drawing the rainate in line 9 is introduced into glycol separator 35. Separator may be a type of holding or settling tank wherein the glycol entrained in the rainate is allowed to settle out of the rafiinate phase. Separated solvent is removed from separator 35 through line 36 and the remaining raffinate stream is withdrawn from separator 35 through line 37 and subjected .to a water-wash in vessel 3S. Water-wash column 38 is illustrated as a vertically elongated vessel in which the raflinate is introduced at a lower portion thereof and is counter-currently contacted with a descending stream of water introduced to column 38 in the upper portion thereof through line 39. Water and solvent are removed from vessel 38 through line 40 and the washed raffinate is removed from the upper portion of the vessel through line 41 and introduced to fractionator or rerun column 45.

Rerun column 45 is provided to remove heavy components from the charge to the reforming reactor, however, when the charge does not contain heavy components that are deleterious to the catalyst the rerun column may be eliminated entirely. In the drawing rerun column 45 is provided and heat provided thereto by reboiler 48 land connecting lines 47 and 49. The heavy undesirable components are removed from rerun column 45 through line 50. The overhead from rerun column 45 which comprises the charge stock to the dehydrocyclization zone is removed through line 46 and passes through cooler 51 and line 52 into overhead receiver 53. A portion of the liquid in receiver 53 is withdrawn through line 54 and passes to an upper portion of rerun column 45 through line 55 as reflux. The charge to the dehydrocyclization reaction is removed from receiver 53 through

lines

54 and 56, is picked up by charge pump 33 and passed through line 34, combines with hydrogen recycled in line 71, and the combined stream is passed through heater v5'7 and thence line 58 into reactor 59.

Reforming reactor 59 contains a bed of spherical catalyst of approximately l/s average .diameter containing 0.3 platinum, 0.5% combined uorine, and 0.1% com- `bined chlorine. The pressure in the reactor is 500 pounds per square inch, the weight hourly space velocity.

is 4, and the hydrogen to hydrocarbon mol ratio is 6 to l.

carbon atoms in the ring are dehydrogenated to the corresponding aromatics and a portion of the parafrins are Some isomeri* zatio-n of the paratins also takes place. The important octane number increasing reaction of dehydrocyclization also occurs in reactor 59. By this reaction, a considerable portion of the parains .are converted into 'aromatica` This reaction is extremely important in increasing the octane number of the paraii'ins which are recycled to the reforming reactor. The effluent from reactor 59 passes through line 6i?, cooler 61, line 62 and into separator 63. Hydrogen is withdrawn from the top of receiver 63 through line 64 and is picked up by compressor and discharged into line 7l and combines with the charge stream in line 34 and passes into furnace 57. Make-up hydrogen may be added to the system through line 65 containing valve 66, or excess hydrogen may be withdrawn from the system through said line.

During the passage of the charging stock throughV reactor 59, the bulk of the naphthenes containing six The liquid hydrocarbons, comprising the reformate and the bulk of the normally gaseous hydrocarbons produced in the process, are withdrawn from receiver 63 through line 75 and passed into fractionator or stabilizer 76. Normally gaseous hydrocarbons are removed overhead through line 77. In stabilizer 76 the normally gaseous material, which includes hydrogen, ammonia, hydrogen sulfide, :and hydrocarbon gases containing from 1 to 4 carbon atoms per molecule, is separated from the hydrocarbon liquid comprising substantial aromatic hydrocarbons and parafnic hydrocarbons. The conditions in the reforming zone or reactor 59 are maintained so that there is substantially no oleflnic substances produced. At the conditions hereinbefore specified and in the presence of hydrogen and the catalyst of this invention, olenic materials will not be produced in any appreciable amounts. The gaseous material passes overhead to line 77 into cooler 78 wherein a portion of the material is condensed and the entire stream passes through line 79 into receiver 80. In receiver 80 the liquid phase and the gaseous phase of the overhead material separate, the gaseous phase passes through line 82 from which it may be vented to the atmosphere or used as fuel or else may be further used in the present process or other processes. The stabilizer has heat provided thereto by reboiler 84 and connecting lines 83 and 85. The conditions in the stabilizer may be such that the gasoline therein is cut deeper, that is C5 or C6 hydrocarbons may be removed through overhead line 77, however, in the usual operation only C4 and lighter components are removed as overhead. It is contemplated that the stabilizer and receiver will operate lat a sufficient pressure to liquefy at least a portion of the overhead material so that a liquid reflux stream may be available for return through line 31 to improve the separation in stabilizer 76. The stabilizer bottoms are removed through line 86 and introduced 'to fractionator 90.

Infractionator 90 the stabilizer bottoms are separated into a light overhead and a heavier bottoms fraction which is fed to the extraction zone 2 through line 3. The conditions in fractionator 90 are maintained so that components which are lighter than those which it is preferred to reform in reactor 59 are removed as an overhead fraction. In the embodiment shown in the drawing the overhead comprises components boiling from the boiling point of isohexane and lighter. The column 9o may be referred to as a de isohexanizer. Components boiling from the boiling point of isohexane and lighter are removed from the deisohexanizer 90 through line 91 and passed into cooler 92 wherein the material is condensed and the entire stream passes through line 93 into receiver 94. The liquid in receiver 94 is withdrawn through line 95. ,Line 95 splits up into several streams. A portion of the stream in line 95 passes through line 96 into the upper portion of deisohexanizer 90 as reflux. A portion of the liquid in line 95 may be withdrawn through line 97 as product and in some instances may be combined with the product in line 30. A portion of the liquefied stream in line 95, however, is withdrawn through line 6 and passed to a lower portion of extractor 2 as light paraiiin reflux. Line 6 enters extractor 2 preferably at a point below which the fresh feed enters through line 1 and preferably below the point wherein line 3, through which the bottoms from fractionator 90, enters extractor 2. This use of the isohexane and lighter fraction in line 6, that is as a reflux to extractor 2, is a preferred feature of the invention. The use of this isohexane and lighter' fraction enables much of the heavier para'lins to be displaced into the raffinate and to be recycled to the reforming reactor 59, and thus the combined operation provides a greater utilizing of the product streams and ultimately increases the yield of .aromatics and octane number of the final product. Heat is provided to deisohexanizer 90 by reboiler 101 and connecting lines 100 and 102. Bottoms are removed from the deisohexanizer 90 through line 3 and introduced to a lower portion of extractor 2.

Although the process illustrated in the drawing represents one of the preferred forms of our invention, it is to be understood that our invention is not to be limited thereto. A number of variations may be introduced into the process without departing from the spirit and scope of said invention.

We claim as our invention:

1. A process which comprises introducing a virgin hydrocarbon charge stock containing paraiins and aromatics to a solvent extraction zone wherein said charge stock is treatedpwith 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 containing said solvent and a substantial amount of aromatics and a raffinate containing a substantial amount of parafns, treating said extract to separate the solvent from the aromatics, reforming at least a portion of said ratl'inate with a dehydrocyclization catalyst at dehydrocyclization conditions in the presence of hydrogen thereby forming additional aromatics, introducing the reformate from said reforming zone to a first fractionation zone to remove normally gaseous components therefrom, introducing the remaining liquid reformate to a second fractionation zone and therein fractionating said liquid reformate into a low boiling paraffinic fraction containing isohexanes and lighter components and a high boiling fraction containing aromatics, introducing at least a portion of said low boiling parafl'lnic fraction to said extraction zone, and introducing said high boiling fraction to said extraction zone.

2. A process which comprises introducing a hydrocarbon charge stock containing paraflins and aromatics to a solvent extraction zone wherein said charge stock 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 containing said solvent and a substantial amount of the aromatics in said charge and a raffinate containing a substantial amount of the parafns in said charge, fractionating said extract to separate the solvent from the aromatics leaving a lean solvent, re-

cycling said lean solvent to said extraction zone, reforming at least a portion of said raffinate with a catalyst comprising alumina, from about 0.01% to about 1% by weight of platinum and from about 0.1% to about 3%. by weight of combined halogen at a temperature of from about 600 F. to about l000 F., a pressure of from about 50 to about 1000 pounds per square inch, a weight hourly space velocity of from about 0.5 to about and in the presence of hydrogen at a hydrogen to hydrocarbon mol ratio of from about 0.5 to about 20 mols of hydrogen per mol `of hydrocarbon thereby forming additional aro matics, introducing the reformate from said reforming zone to a rst fractionation zone to remove normally gaseous components therefrom, introducing the remaining liquid reformate to a second fractionation zone and therein fractionating said liquid reformate into a low boiling parafnic fraction containing isohexanes and lighter components and a high-boiling fraction containing 'aromatics, introducing said high boiling fraction to said extraction zone and introducing at least a portion of said low boiling paraflinic fraction to said extraction zone at a point below the point of introduction of said high boiling fraction.

3. A process which comprises subjecting a virgin gasoline fraction containing aromatic and parainic hydrocarbons to solvent extraction with a polyalkylene glycol solvent in an extraction Zone to separate the same into an aromatic extract and a paratnic raiiinate, subjecting the rainatc to dehydrocyclization in the presence of a dehydrocyclizationrcatalyst, fractionating the resultant products and separating therefrom a liquid fraction containing isohexane and lighter hydrocarbons, and introducing at least a portion of said liquid fraction to the lower portion of said extraction zone.

4. A process which comprises subjecting a straight-run gasoline fraction containing aromatic and parafinic hydrocarbons to solvent extraction with a polyalkylene glycol solvent in an extraction zone to separate the same into an aromatic extract and a paranic raffinate, subjecting the ranateto dehydrocyclization in the presence of a dehydrocyclization catalyst, fractionating the resultant products to separate therefrom a liquid fraction containing isohexane and lighter hydrocarbons and a heavier fractioncontaining aromatics, introducing at least a portion of said liquid fraction to the lower portion of said extraction zone, and introducing said heavier fraction to the extraction zone at a higher elevation therein.

5. The process of claim 3 further characterized in that said polyalkylene glycol solvent is selected from the group consisting of diethylene glycol, triethylene glycol, dipropylene glycol and tripropylene glycol.

References Cited in the file of this patent UNITED STATES PATENTS 2,391,962 Goldsby Jan. l, 1946 2,405,660 Linn Aug. 13, 1946 2,409,695 Lcughlin Oct. 22, 1946 2,479,109 Haensel Aug. 16, 1949 2,510,673 Annable June 6, 1950 2,522,696 Watson Sept. l9, 1950 2,700,638 Friedman Jan. 25, 1955 FOREIGN PATENTS 513,051 Belgium Oct. 14, 1952

Claims

1. A PROCESS WHICH COMPRISES INTRODUCING A VIRGIN HYDROCARBON CHARGE STOCK CONTAINING PARAFFINS AND AROMATICS TO A SOLVENT EXTRACTION ZONE WHEREIN SAID CHARGE STOCK IS TREATED 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 CONTAINING SAID SOLVENT AND A SUBSTANTIAL AMOUNT OF AROMATICS AND A RAFFINATE CONTAINING A SUBSTANTIAL AMOUNT OF PARAFFINS, TREATING SAID EXTRACT TO SEPARATE THE SOLVENT FROM THE AROMATICS, REFORMING AT LEAST A PORTION OF SAID RAFFINATE WITH A DEHYDROCYCLIZATION CATALYST AT DEHYDROCYCLIZATION CONDITIONS IN THE PRESENCE OF HYDROGEN THEREBY FORMING ADDITIONAL AROMATICS, INTRODUCING THE REFORMATE FROM SAID REFORMING ZONE TO A FIRST