US2425559A - Catalytic conversion of alkyl aromatic hydrocarbons - Google Patents

Description

Aug. 12, 1947. H. J. PAsslNo ETAL 2,425,559

CATALYTIC CONVERSION OF ALKYL AROMATIG HYDROGARBONS med umn 11. 194s /Zff Phe/ro! /26 SWW-)mawV l l v l came //4 l .E I l Mena INVENTORS HERBERT J. PASS/NO Jv/m HENRY G. Mc GRATH,

Patented Aug. 12, 1947 CATALYTIC CONVERSION OF ALKYLv AROMATIC HYDROCARBON S Herbert J. Passino,

Grath, Elizabeth, N. J.

Kellogg Company, ration of Delaware Englewood, and Henry G. Mc-

assignors to The M. W. Jersey City, N. J., a corpo- Applieation March 11, 1943, Serial No. 478,814

14 claims. (o1. zsofsss) This invention relates to improved methods for the production of motor fuel of the highest antiknock value. More particularly the invention relates to the production of cyclic hydrocarbon motor fuel constituents, or fractions rich in such constituents, which are of the highest anti-knock value. Still more particularly the invention relates to an improved process for the production of aviation motor fuel constituents of high antiknock value by selective isomerization of polyalkylated aromatic hydrocarbons. The invention relates also to improved methods for the isomerization of poly-alkylated cyclic hydrocarbons, such as aromatic and naphthenic hydrocarbons, for any purpose whatever.

In the preparation of aviation motor fuel, particularly for military use, it is desirable to restrict the hydrocarbon constituents which are included in the motor fuel to those of the highest antiknock value because of the necessity for producing composite fuel of the highest value and because the variations in anti-knock value of the various hydrocarbons increase in degree under the severe operating conditions in which military aviation motor fuel is employed. Necessarily these considerations are important inthe preparation of motor fuel for general use, if to a lesser degree.

It is an object of this invention to provide an improved process for the production of motor fuel constituents of the highest anti-knock value. It is a further object of the invention to provide a process for isomerizing poly-alkylated cyclic hydrocarbons which isk an improved process by reason of the employment therein of an isomerizing catalyst of superior qualities. It is a further object of the invention to provide an improved process for the treatment of. a mixture of polyalkylated aromatic hydrocarbons to produce therefrom, in the most expeditious and efficient manner, aviation motor fuel constituents of the highest anti-knock value. Other objects include the provision of improved methods for the isomerization of poly-alkylated cyclic hydrocarbons in general for any purpose. t

Aromatic hydrocarbons boiling below approximately 400 F. are in general valuable ingredients of motor fuel. However, there is considera-ble variation in the anti-knock value of these cornpounds, Within a relatively high range, particularly among theA members of each group of isomers. In the preparation of aromatic motor fuel constituents for use in aviation gasoline these variations in anti-knock value, particularly in the poly-alkylated aromatic hydrocarbons boil- 2 ing within the range of 250 F. to 350o F., are highly important considerations.

The invention will be described with particular application to the treatment of poly-alkylated aromatic hydrocarbons containing 8 to l0 carbon atoms per molecule since these include the polyalkylated aromatic hydrocarbons boiling within the aviation motor fuel boiling range. It is ro be` understood, however, that the invention is applicable to the treatment of any mixture of poly-alkylated aromatic hydrocarbons or any individual poly-alkylated aromatic hydrocarbon. Furthermore the invention is applicable to the treatment of any poly-alkylated cyclic hydrocarbon for the production of motor fuel or for other purposes, For example. poly-alkylated naphthenes may be isomerized.

The invention will be described also with reference to the accompanying drawing which represents diagrammatically apparatus suitable for carrying out a specific embodiment of the invention which involves the treatment of xylenes. It is to be understood, however, that the process of the invention whichis thus illustrated is applicable in the treatment of other poly-alkylated cyclic hydrocarbons which may require somewhat different arrangements of apparatus than are thus provided for the treatment of the xylenes.

Aside from the relatively small amounts of aromatic hydrocarbons which are obtainable in coal tar and certain aromatic petroleum oils. the principal sources of such hydrocarbons are. the conversion of cyclic non-aromatic hydrocarbons, such'as cyclo-parailins and cyclo-olens, to the corresponding aromatic hydrocarbons by dehydrogenation and the conversion of aliphatic hydrocarbons to aromatic hydrocarbons by catalytic cyclization and dehydrogenation reactions, and the thermal and catalytic cracking of higher boiling oils, such as gas oil and reduced crude.-

While the invention, in certain aspects, is applicable to the treatment of poly-alkylated hydrocarbons from any source an important modification of the invention involves its use in combination with methods for the conversion of aliphatic and cyclic hydrocarbons to aromatic hydrocarbons by dehydrogenation. Consequently the following description of the invention includes the application of the invention to the treatment of poly-alkylated aromatic hydrocarbons produced by dehydrogenation and cyclization of charging stocks which are carefully selected with reference to boiling characteristics.

Referring to the drawing a non-aromatic charging stock is introduced into the system through reactor 6 aliphatic 3 through line l. While this material is referred to as non-aromatic, in a relative sense, it may contain a. substantial proportion of aromatic hydrocarbons since these are not detrimental to the cyclization process. The non-aromatic hydrocarbons to be cyclized may be cyclic or aliphatic, unsaturated or saturated. Ordinarily the charging stocks available will contain all these materials, differing only in the relative proportions. For the production of poly-alkylated aromatic hydrocarbons it is necessary that the charging stock comprise aliphatic hydrocarbons containing at least eight carbon atoms per molecule and which are convertible to aromatichydrocarbons. or poly-alkyiated hexacarbocyclic hydrocarbons, such as dimethyl cyclohexane.

The non-aromatic feed is transferred through line I by pump 2 to the entrance of a heating coil I suitably located in heater I. In heating coil 3 the hydrocarbon feed is heated to an outlet temperature. generally within the range of: 850

to 1050 F., which is selected with reference to the character of the feed and the degree of conversion desired. The outlet of heating coil 3 connects by line 5 with reactor 6 whereby the heated hydrocarbon feed is introduced into the reactor at the desired temperature.

Reactor 6 is provided with suitable dehydrogenating catalytic material for effecting the desired aromatization reactions which may involve dehydrogenation of cyclic hydrocarbons or cyclization and dehydrogenation of aliphatic hydrocarbons, or both. A representative catalyst for such reactions is one comprising principally the activated alumina of commerce and containing, as an activating ingredient, 6 to 12 weight per cent of molybdenum oxide. Other dehydrogenating catalysts, such as chromium oxide, alone, or mounted on a suitable support such as alumina, also may be used.

The modification of the invention illustrated by the drawing includes the use of the catalyst as a stationary consolidated granular mass through which the hydrocarbon reactants are passed at the reaction temperature. In this method of operation the passage of the heated hydrocarbons through the reactor is continued until the catalyst is deactivated for further effective use, after which the hydrocarbon stream is diverted to an' other reactor while the catalyst in the first reactor is regenerated or replaced'. This method of operation is continuous with respect to the 'hydrocarbons but is discontinuous or intermittent with respect to the catalyst. The invention includes, however, the use of dehydrogenation processes in which the catalyst is moved continuously through the reaction zone. In such methods of operation the catalyst is dropped by gravity through the reaction zone in contact with the vaporized hydrocarbon reactants or is suspended as a finely divided powder in the hydrocarbon stream passing through the reaction zone. By another method of operation the catalyst may be maintained in the reactor as a fluidized mass with continuous withdrawal and replacement of a portion of the mass to maintain the activity of the whole mass at a uniform level.

During the passage of the hydrocarbons hydrocarbons having six or more carbon atoms per molecule are .converted to aromatic hydrocarbons having corresponding numbers of carbon atoms per molecule, such as benzene, toluene, xylenes, ethyl benzene, propyl benzenes, methyl ethyl benzenes, trimethyl benzenes, methyl propyl benzenes, di-

methyl ethyl benzenes, and butyl benzenes. In addition cyclic non-aromatic hydrocarbons, such as cyclohexane, methyl cyclohexane, ethyl cyclohexane, dimethyl cyclohexanes, propyl cyclohexanes, trimethyl cyclohexanes, methyl ethyl cyclohexanes, butyl cyclohexanes, methyl propyl cyclohexanes, dimethyl ethyl cyclohexanes, diethyl cyclohexanes, and the corresponding cyclo-olefins and cyclo di-oleiins, are converted to corresponding aromatic hydrocarbons by dehydrogenation. Aromatic hydrocarbons which may be present in the mixture apparently do not react undesirably to an appreciable extent in reactor 6 and these may be present in substantial proportions.

'I'he degree of conversion of the non-aromatic hydrocarbons to aromatic hydrocarbons in reactor 6 is controlled by suitable regulation of temperature and space velocity. Substantial conversion of non-aromatic hydrocarbons to aromatic hydrocarbons, particularly the conversion of aliphatic to aromatic hydrocarbons, is associated with high temperatures and relatively low space velocities. Within the temperature range of 850 to 1050 F. space velocities of 0.1 to 3.0 volumes of liquid per volume of catalyst space perr hour are employed advantageously. For 'example, at an operating temperature of 950 ,F. a space velocity of 0.5 volume of liquid per volume of catalyst space may beemployed.

The reactants are withdrawn .from reactor 6 through line 1 which passes through cooling means B'and connects with a separator 9. Cooling at 8 is suilcient to condense the normally liquid constituents of the reaction mixture. In separator 9 the uncondensed gases, which consist principally of hydrogen, are disengaged from the liquid condensate and are withdrawn through line I0. It is desired ordinarily to recycle hydrogen to the reaction zone in the amount of 0.5 to 9,

it is desirable to remove at least a portion of such gases from the hydrogen stream prior to recycling it to the reaction zone. Consequently line I0 is connected to the lower portion of an absorber Il. Since it is desirable to maintain absorber Il at relatively high pressure a compressor I2 is providedinline I0.

In absorber l I the gases pass upwardly through and around gas and liquid contact elements and are contacted with a. hydrocarbon absorber oil, such as naphtha or gas oil, which flows downwardly through absorber Il. Such gas oil or naphtha selectively absorbs a suicient proportion of the iight hydrocarbon gases from the. gases passing upwardly through absorber II. Preferably absorption is suflciently complete to include in the absorber oil-substantially all the hydrocarbon gas and hydrogen gas in an amount equal to the excess which is not used for recycling.

The hydrogen gas is absorber il through withdrawn overhead from line I3 which connects tem through line 23.

are flashed from the absorbent which is passed through line I8, provided with pump I1, to the upper portion of absoberml I, torre-use. The gases separated at Iirenwithdrawn tti refrom through linsg which 'connects wit bilizer I9. Since stabilizer' I9 is maintained dinarily at a higher pressure than separatv a compressor 28 is provided in line I8 to the gases to the desired stabilizer pressure.4

The liquefied product separated in gas Sep arator 9 is withdrawnV therefrom through line 2l, which is provided with a pump 22, and connects with stabilizer I9.

In stabilizer I9 theA liquid introduced through line 2I and the compressed gases introducedv through line I8 are subjected to fractionating conditions of temperature andk pressure to separate overhead substantially all normally gaseous l constituents of themixture. The gases pass overhead through line 23, are cooled at 24` to condense a vportion thereof sufficient for reiluxing stabilizer I 9 and the resulting mixture is dellvered to separator 25. Reflux liquids are returned from separator 25 to stabilizer I9 through line 28 and vpump 21. Uncondensed gases are withdrawn from separator 25 and from the sys- I The liquid product separated as a condensate in the bottom of stabilizer I9 'is transferred to rerun tower 28 by means of line 30. In rerun tower 29 the liquids are fractionated to separate high boiling condensation products.

.The hydrocarbons vaporizedin tower 29 pass overhead through line 32 which is provided with 'cooling means 33 and connects with reflux drum 34. vAt 33 the vapors are' cooled to effect condensation thereof and the condensate thus obtained is withdrawn from drum 34 through line 3,5 by means of pump 38 for transfer to subsequent fractionating means for theseparation of a narrow boiling cut suitable for further treatment. A portion of the condensate flowing through line 35 is diverted through line 31 and returned to the upper portion of tower 29 as reflux.

Since the modification here illustrated relates specifically tothe treatment of xylenes the subsequent fractionation of the liquids flowing through line is conducted in a manner effective to separate a. narrow boiling fraction including xylenes and to separate the remainder of the liquids in a manner which may be desired for the further handling of such material. In the specific modification illustrated in the drawing these liquids are fractionated, in two separate fractionators, to separate a xylenecut, a prexylene cut containing the 'lower boiling hydrocarbons and a post-xylene cut containing the higher boiling hydrocarbons. ,L

In carrying out this separation line 35 is connected to a` fractionator 38 which is maintained underA fractionating conditions of temperature and pressure effective to separate overhead, as vapors, the hydrocarbons lower boilingV than xylene. .'I'he overhead vapors are withdrawn from fractionator 38 throughl line 39 which connects with reflux drum 40 and is provided with cooling means 4I. Atv4I the vapors.. are cooled sufficiently to effect condensation thereof. Thecondensate which accumulates at 40 is withdrawn therefrom through line 4'2, provided with'pump 43, as the pre-xylene cut. A part of this cut is returned to the upper portion of fractionator 38 as reux through line 44 which connects line 42 with fractionator 38. The pre-xylene cut flowing through line 42 may be withdrawn thereby from the system or all or a portion of this material may be recycled to the aromatization treatment for further conversion thereof. Such recycling may be effected conveniently by line 45 which connects line 42 with line I.

The bottoms in fractionator 38, which include "--the xylenes, are transferred from fractionator 38 to fractionator 48 by means of line 41. In fractionator 48 fractionating conditions of temperature and pressure are maintained effective to separate overhead vapors containing the xylenes and substantially free from higher boiling aromatic hydrocarbons. These vapors, which constitute the xylene cut, are withdrawn through line 48 which is provided with cooling means 49 and connects with reflux drum 50. The vapors are cooled at 49 to eiTect condensation thereofv and the condensate is withdrawn from drum 50 through line 5I ywhich is provided withpump 52. A portion of the condensate is returned to fractionator 48 as reflux by passage through line 53 which connects line 5I with the upper portion of fractionator 48. The bottoms separated in fractionator` 48, which constitute the post-xylene cut, are withdrawn from fractionator 46, and from the system, through line 54.

The further treatment of the xylene cut nowing through line 5I in accordance with this invention depends upon the proportion of non-aro.. matic hydrocarbons contained therein and upon the character of the isomerizing treatment to be employed. Since certain isomerizing catalysts react with paraflinic and naphthenic hydrocarbons it is desirable, when employing such cata.- lysts t-o isomerize the poly-alkylated aromatic hydrocarbons, to restrict theproportion of such parafflnic and naphthenic hydrocarbons in the aromatic fraction as much as possible. Other isomerizing catalysts are not subject to this disability so that a larger proportion of nonaromatic hydrocarbons can be tolerated.

In operations whichrequire an aromatic cut which is free, or substantially free, from nonaromatic hydrocarbons the isomerization feed may be prepared by suitable regulation of the charging stock to the aromatization process, by solvent extraction of non-aromatic hydrocarbons from the aromatized product or other mixture of aromatic and non-aromatic hydrocarbons by a combination ,of these two methods, or by any other suitable means. For example in thepreparation of a xylene cut which is `to be substantially free from non-aromatic hydrocarbons it is advantageous to fractionate the non-aromaticA feed lintroduced through line I' to eliminate substantia'lly constituents higher` boiling than ap-` Since it is an object of this invention'toproduce hydrocarbon fractions of the highest octane value the elimination of non-'aromatic hydrocarl bons from the productby such control ofv the feed to the aromatization operation is desirable as a relatively simple method of excluding lsuch hydrocarbons from the product. Consequently it is a preferred modification of this invention to regulate the end boiling point of the non-aromatic feed passing through line I at about 260 F., when the production of xylenes of the highest anti-knock value is an object of the process. This method of operation may be employed advantageously in connection with the production of toluene by aromatization operations, in which case the toluene productv is included in the prexylene cut passing through line 42. In such a method of voperation the post-xylene cut with drawn at line 54 is relatively small in quantity and comprises principally high boiling alkylated aromatic hydrocarbons resulting from alkylation reactions occurring during the aromatization treatment. i

The further handling of a xylene cut produce by the above described preferred modification depends upon the relative proportions of the various xylenes therein and the proportion of orthoxylene which ls tolerable in the product of the process. If the xylene cut flowing through line l predominates in meta-xylene and para-xylene preliminary fractionation to separate a cut predominating in ortho-xylene is desirable, if only for the purpose of reducing the load on the isomerization operation. However. if the xylene cut flowing through line 5I predominates in orthoxylene, or if the amount of ortho-xylene which is tolerable in the product of the process is greater than the equilibrium amount of this constituent, it may be desirable to pass the xylene cut flowing through line 5I directly to the isomerization treatment. The relative proportions of the xylene isomers in the aromatization product depend primarily on the composition of the feed stock. For example, if the xylenes are formed by dehydrogenation of dimethylated cyclic hydrocarbons, their structures apparently govern those of the xylenes formed therefrom. Similarly the location of methyl groups on aliphatic starting compounds appears to aifect the structure of the poly-alkylated aromatic hydrocarbon formed therefrom.

As it is a preferred modification of the invention to produce a product containing less than the equilibrium proportion of ortho-xylene, which is about 10% at room temperature, it is preferable to subject the xylene cut to a preliminary fractionation to recover meta and para-xylenes therefrom without further treatment, since this can be effected in the same fractionation equipment which is required to separate excess orthoxylene from the isomerized product. In accordance with this preferred modification line 5| `is connected with a xylene fractionator 55.

`It is the function of fractionator 55 to provide a product which is free, or vsubstantially free, from ortho-xylene and at the same time prepare a feed for the isomerization treatment which predominates in ortho-xylene. The feed to fractionator 55 may be -supplied entirely from the source to which it is connected by line 5I or it may be supplied, from any suitable source of xylenes, with a similar relatively narrow boiling range xylene cut through line-56, or xylenes may -be introduced into fractionator 55 from both of lines 5I and 56.

In xylene rfractiona'tor 55 fractionating conditions of temperature and pressure are maintained which are effective to separate overhead a vapor mixture comprising meta-inflene and para-xylene and substantially free fromk ortho-xylene. The degree of fractionation necessary in fractionator 55 depends somewhat upon the amount of orthoxylene which may be tolerated in the xylene product of the process. Somewhat greater latitude is permissible in the constitution of the bottoms sel) arated in fractionator 55 since any mixture of the xylen'es containing more than the equilibrium proportion of the ortho-xylene may be employed as feed to the isomerization treatment. However, eflicient use of the isomerization apparatus indicates the desirability of an isomerization feed predominating in ortho-xylene. It is desired ordinarily to take overhead a xylene product substantially free from ortho-xylene while withdrawing a bottoms which contains an appreciable, if minor, amount of metaand para-xylenes. The reduction in cost of the fractionation operation which results from permitting inclusion of meta.- and para-xylenes in the bottoms may justify the increased size of the isomerization apparatus made necessary by the inclusion of these relatively inert materials in the feed thereto.

The xylene vapors passing overhead in fractionator 55 are withdrawn therefrom through line I5l which is provided with cooling means 53 and connects with reflux drum 59. Thevapors are condensed at 56 and the condensate accu- 4 mulates in drum 59 from which it is withdrawn through line 50 provided with pump 6I. 'I'he poly-alkylated hydrocarbons flowing through thev 60 consists essentially of meta-xylene and paraxylene and represent motor fuel constituents of the highest anti-knock value, particularly for use in military aviation. .A portion of the material flowing through line 60 may be returned to the upper portion of fractionator 55 as reflux by line 62 which connects line 60 with fractionator 55.

The bottoms separated in fractionator 55 predominate in ortho-xylene but may include appreciable amounts of meta-xylenev and paraxylene and are withdrawn through line 63 provided with pump 64. Line 63 connects with isomerization reactor 65 and is provided, if necessary,I

with heating or cooling means 66 to bring the isomerization charge to the desired reaction temperature. If the isomerization charge flowing through line 63 contains an amount of water which is detrimental in the isomerization reaction zone or other subsequent parts of the apparatus it may be diverted from line 63 through line 61 fwhich connects with drier 66. Drier 66 suitably is lled with granular drying medium, such as alumina, for absorbing the water contained in the hydrocarbon mixture passing therethrough. The dried mixture is withdrawn from drier 66 by line 69 which connects with line 63. To prevent injury to the drying medium and to assist that operation it may be necessary o desirable to provide cooling means I0 in line 61.

In accordance with a preferred modification of the invention the `ortho-xylene is isomerized by contact thereof with a catalyst comprising hydrogen fluoride as the essential ingredient. Preferably the isomerization treatment is effected by a liquid phase contact of the hydrocarbons and liquefied hydrogen fluoride at the desired isomerization reaction temperature. The xylene fraction passing through line 63 is intimately mixed with liquefied hydrogen fluoride which may be introduced into line 53 by means of line 1I, by which lt is recycled from a subsequent point-in the process. 'Ihe resulting mixture .passes through reactor'65 in contact with suitable mixing means (not shown) and is maintained therein for the desired length of time.

In reactor 65 the mixture of hydrocarbons and hydrogen fluoride is maintained for a length of 9 time which depends upon the degree oi' conversion desired and the operating temperature. At relatively low temperatures, such as room temperature or lower,`relatively long contact times time to produce a xylene product containing more than the equilibrium proportion of the ortho-xylene especially if the isomerized product is to be fractionated for the separation of orthoxylene from its isomers.

The isomerized product is withdrawn from reactor 65 through line 12 which is provided with cooling means 13 and which connects with separator 14. In separator 14 the mixture of hydrogen fluoride and hydrocarbons is permitted to separate into an upper, or hydrocarbon, layer and a lower, or hydrogen fluoride, layer. The hydrogen fluoride is withdrawn through line 1| which, as mentioned above, connect with line 63 for recycling the hydrogen fluoride for further use. Line 1| is provided with a pump 15 to facilitate recycling the hyrogen fluoride and withdrawing a portion thereof through line 16 which connects with line 1|. A portion of the hydrogen fluoride may be withdrawn intermittently or continuously through line 16, and replaced by fresh or regenerated hydrogen fluoride which is introduced through line 11 provided with pump 18. The hydrogen fluoride may react with certain portions of the hydrocarbon reactants with the formation of complexes which are absorbed in the hydrogen fluoride and tend to lower its activity. The effect of the formation `of such complexes is compensated for by withdrawing a portion of the recycled hydrogen fluoride at 16 and replacing'it at 11. The complex withdrawn at 16 may |be treated to regenerate the hydrogen fluoride.

The hydrocarbons separated as the upper layer in separator 14 are withdrawn therefrom through line 19 which connects with a hydrogen fluoride stripper 80. In stripper 80 the hydrocarbon mixture is subjected to fractionatingv conditions of temperature and pressure effective to separate overhead hydrogen fluoride vapors. The hydrogen iiuoride vapors are withdrawn overhead through line 8| which is provided with cooling means 82 and connects with accumulator 83. The hydrogen fluoride is condensed at 82 and the liquefied material thus obtained is returned for;y

re-use through line 84, provided with pump 85,

which connects accumulator 83 with line 1I. A portion of the liquefied hydrogen fluoride may be returned to the upper portion of stripper 8|! as reflux by means of line 86.

The isomerized product, or isomate, which collects in the -bottom of stripper 80 is withdrawn therefrom through line 81 which connects with treater 88. Treater 88 is a suitable receptacle containing granular treating material. such as bauxite for absorbing residual quantities of hydrogen fluoride from the isomate. The treated isomate is then withdrawn from treater 88 through line 88 which connects with rerun tower 80.

10 In tower'll the-isomate is subjected to fractionating conditions of temperature and pressure effective to pass overhead the xylene product as a vapor while retaining as a bottoms any heavy constituents which may be formed in reactor by alkylation reactions. These bottoms are withdrawn from tower 80, and from the system, through line 8|.

The vapors passing overhead in tower 80. which comprise the isomate, are withdrawn through line 82 which is provided with cooling means 83 and connects with accumulator drum 84. 'I'he vapor is cooled at 88 to effect complete condensation and the condensate thus obtained collects in drum 84. The isomate is withdrawn from drum 84 through line 85 provided with pump 86. Preferably line 85 is connected to xylene fractionator 55 in order to include the Daraxylene and meta-xylene formed in the isomerizetion treatment in the overhead product of fractionator 55, as described, and to permit recycling the unconverted ortho-xylene to the isomerization treatment. However, if the proportion of ortho-xylene left in the isomate is not greater than the amount which is tolerable in the desired product the isomate flowing through line 85 may be withdrawn from the process, as a product thereof, through line 81, A portion of the liquid flowing through line 85 may be returned to tower 88 as reflux through line 88.

In connection with the operation of xylene fractionator 55 on a feed from a. source indicated by line 5| it may be desirable to divert a portion of the bottoms in line 53 to prevent the accumulation in the lsomerization system of parafilnic and naphthenic hydrocarbons boiling approximately in the boiling range of ortho-xylene. Hydrocarbons of this character whichy may be included inthe aromatization products supplied through line 5| or which may be included in the xylene stream supplied through line 56 are largely unaffected by the isomerization treatment. Consequently these materials may tend to accumulate in the system when all, or substantially all, of the isomate in line 85 is recycled to fractionator 55. Since some of these paraillnic and naphthenic hydrocarbons may be convertible to aromatic hydrocarbons the hydrocarbons to be diverted from line 63 conveniently may be recycled to the aromatization process for further treatment therein. Line |8a, which connects line 63 with line -I is provided for this purpose.

In the foregoing description of the isomerization treatment the feed to the isomerization treatment is prepared in fractionator 55, as bottoms. However, it may be desirable to pass the feed to the isomerization reaction without preliminary fractionation particularly if 4it contains a predominating amount of ortho-xylene. Indeed it may be desirable to eliminate the use of xylene fractionator 55 altogether if the feed predominates in ortho-xylene and if the proportion of ortho-xylene left in the isomate is no more than the maximum amount thereof which is tolerable in the product. In accordance with this modification the xylenes passing through line 5| may be diverted wholly or partly through line 88 which connects line 5| with line 63. Likewise mixtures of aromatic hydrocarbons which are susceptible to the isomerization treatmentA may be introducedfrom an external source through line |00 which connects with line 63 near the entrance of heater or cooler 66. In this method of operation the isomate may be further lfractionated at 55 to separate a highly purified product and an ortho-xylene fraction for recycling 'or the isomate may be employed as such Without further fractionation.

It may be desirable. or necessary, to subject the hydrocarbon mixture containing the poly-alkylated hydrocarbons to an extraction treatment designed to remove therefrom aliphatic and naphthenic hydrocarbons. This preliminary treatment of the feed to the isomerization process may be necessary when employing a catalyst which is highly susceptible to the deactivating e'fect'sof such aliphatic and naphthenic hydrocarbons. Ordinarily the preliminary separation of nonaromatic hydrocarbons is necessary in the treatment of the product of the aromatization of a feed stock having an end boiling point within the boiling range of the desired aromatic hydrocarbons. For example, the charge to the aromatization treatment may be fractionated to an end boiling point of approximately 300 F. to produce a mixture containing poly-alkylatedhydrocarbons having 8 and v9 or more carbon atoms per molecule. Under these circumstances it is necessary ordinarily to remove accompanying aliphatic and naphthenic hydrocarbons and other` nonaromatic hydrocarbons from the mixture containing the poly-allwlated aromatic hydrocarbons prior to isomerization treatment thereof.

When employing the preliminary extraction treatment of the feed to the isomerization process the xylene cut iiowing through line 5| is diverted therefrom through line I| which connects with a suitable extraction apparatus such as phenol extractor |02. Likewise mixtures containing polyalkylated hydrocarbons from an external source may be introduced into phenol extractor |02 by means of line |03.

The hydrocarbon mixtures from lines |0| or |03 are introduced into extractor |02 at a point approximately one-third the length of the extractor |02 from the bottom thereof. In extractor |02 the hydrocarbon mixtures are mixed with downwardly flowing liquid phenol and the aromatic hydrocarbons are absorbed thereby. In addition a portion of the non-aromatic hydrocarbons are also absorbed by the phenol. The mixture ows downwardly in extractor |02 and is heated by contact with hot vapors and by suitable re-boiling means in the bottom of extractor |02 to vaporize unabsorbed non-aromatic hydrocarbons and to strip from the extract non-aromatic hydrocarbons previously absorbed. Such heat treatment ordinarily strips the extract of a portion of the absorbed aromatic hydrocarbons also and these are continuously contacted with the downwardly flowing phenol solvent as the vapors flow-upwardly from the bottom of tower |02, or from points adjacent the bottom thereof, to the point, approximately two-thirds the distance up tower |02,A at which the phenol solvent is introduced. In this manner aromatic hydrocarbons which are stripped from the bottoms are reabsorbed, The unabsorbed vapors rise above the point of introduction of the phenol in the approximately upper one-third of tower |02 in which they are reuxed under suitable conditions to effect condensation of phenol and absorbed hydrocarbons.

The non-aromatic hydrocarbons which pass overhead in extractor |02 as vapors are withdrawn therefrom through line |04 which is provided with cooling means |05 and connects with' withdrawn from line |05 through line |01 pro- #an acid to absorb such phenol.

, line |21 connects.

12 vided with pump |00. Hydrocarbons thus ob tained may be withdrawn through line |01 fromy the process and may be wholly or partly recycled,

. by means not shown, from line |01 to the entrance of the` aromatization process. A portion of this condensate also. is returned to the upper portion oi' extract |02 as reflux through line |09 which connects line |01 withextractor |02.

The extract collected in the bottom of extractor |02 is withdrawn therefrom through line I I0, provided with pump III and transferred to phenol stripper I |2.`-In stripper I I2 the extract is heated to a temperature suiiiciently high to strip absorbed hydrocarbons from the phenol solvent.

The latter is withdrawn from the bottom of stripper I I2 through line I I3 provided with pump I I4, which connects with extractor |02. at a point. approximately two-thirds the way up. as described above. A portion of the phenol solvent which circulates through line I|3 may be withdrawn intermittently or continuously, through line ||5, and replaced with fresh phenol, through line |I6, to maintain the quality of the solvent at the desired level.

The hydrocarbon vapors which are substantially entirely aromatic in character are withdrawn woverhead from stripper ||2 through line which connects line |20 with the upper portion of stripper I I2.

To remove residual quantities of lphenol which may be entrained in the aromatic liquids flowing through line |20 the liquids may be treated with For example a suitable acid may be introduced into the system through line |23 which connects with line |20. The resulting mixture is further mixed by passage through mixer I24 which is interposed in line I 20 and the mixture is then permitted to settle in a suitable drum |25, to which line |20 is connected. A

In drum |25 the acid containing absorbed phenol settles out as a lower phase and is withdrawn through line |26. 'I'he acid treated hydrocarbons pass overhead from drum |25 through line |21. To remove acid entrained in such liquids caustic may be introduced into line |21 through line |28. The resulting mixture may be taining absorbed acid separates as alower phase and is withdrawn through line I3I, The treated hydrocarbons pass overhead from settler |30 through line |32 which connects with rerun tower |33.

In rerun tower |33 the treated aromatic hydrocarbons are fractionated to separate as bottoms high boiling hydrocarbons resulting from polymerization of unsaturates by means of the acid treating agent. Such bottoms are withdrawn from tower |33 and from ,the system through line y |34. The rerun tower yI 33 is operated under fractionating conditions of temperature and pressure tolseparate overhead a vapor mixture containing the aromatic hydrocarbons to be isomerized.

Such vapors are withdrawn through line |35y In settler |30 the caustic con-l portionoftthis condensatemay be returned.'l

throughline |40, tolthe upper portion off tower llasrefluir.y n

' 'kIfit is desiredl tosubject the aromatic` hydro-5 carbons flowingl .through line |3Bto :preliminary -fractionationprior to isomerization,line v|38 isl connected to fractionator 55 in the :manner shown.` However, i for certain .reasons ...which have been discussed above Ait may .be idesired to. subject the whole mixture of aromatic hydrocarbonsy directly to isomerization prior to any fractionation thereof. For example, a portionv of the hydrocarbons flowing throughline I38'lmay be diverted through line lMI. Sincefthe hydrocar:` bon mixture flowing through line |4| may contain water asa result of .the treatments=at|25 and |30 it is preferred ordinarily to connect line HI with linevlGl `asishown in yorder to pass the hydrocarbons through 'drier v68. However, if such ldrying is not necessarythe hydrocarbons maybe introduced from line |4| directly into line 63 by means of line |42. Y f y In the above description of the invention there are numerous references for illustration to the treatmentof the polyalkylated aromatic hydro-` carbons having ,8 carbon .atoms per molecule, that is, the xylenes. The `invention is applicable, however, to the production of gasoline constituentsof highland-knock value having 9, and 11 carbon atoms permolecule. i

The aromatization treatment of a feedstock-v fractionated to an end boiling point of approximately 300` F. permits `the recovery by fractionation, of an aromatized product, of a substantially pure aromaticfraction boiling above` 300 F., and consisting essentially-of aromatic hydrocarbons having 9 carbon atoms. per molecule. 'Ihese apparently consist principally vof the :trimethyl benzenes. Furthermore that portion ofthe aro-y matized product boiling between 260 and'300 F. is highly aromatic in character.. and contains the xylenes .fraction isl treated in laccordance t with the method outlined above, preferably after an extraction treatment to remove non-aromatic hydrocarbons. v-.-. i g

The 300-350. F. y.fraction of the aromatized product of a feed having anend pointfof 300 tion, boiling betweenx300 and-350 F. may be obtained ff in, :'thejf fractionation.. of the aromatized product .andpassedthroughline il, instead of' they xylenes..In'fractionatorfi the C aromatic hydrocarbons are fractionated to separate an overhead\product boiling between 300 and 333 F.

` as described abovew The bottoms thus obtained aresublected to isomerizationyin the manner described'for ortho-xylene', `and the isomerized product isrefractio'nated fin fractionator 55 to separate-the low boiling visomer,r 1,3,5 trimethyl benzene. `In thismanner an'av'iation motor fuel fraction of highanti-knock value is obtained as the overhead productor fractionator 55.

By fractionating the feed to the aromatization processl tol anend pointbetween 300 and 350 F. more or less aromaticlhydrocarbons having 10 or more carbon atoms per molecule are obtained in By fractionating the aromatized product to separate hydrocarbons boiling above the point of the feed an aromatic fraction free. or substantially free, of non-aromatic hydrocarbons is obtained. That portion of or a similar mixture from any source, may be treated to produce fractions of improved antiknock value. I This fraction- 1 is .substantially uen.- tirely aromaticy and contains `poly-,alkylated .aro' matic hydrocarbonsvjwhich are principally tri-1 methyl benzenes.k I i' thisfraction predominatesl in,the `1,2,3 and 1,2,4 trlmethyll benzenes it may be' subjected tohisomerization treatment-'to imr proveits anti-knockvalue by converting :these 1 compounds to 1,3,5 trimethylbenzene whichisv of superior antifknock value. If the fractional# ready contains an appreciable amount .of "1,3,5

trimethyl benzene it isv further sub-dividedv into a fraction boiling4 between 30,0and-2333f.-F.,and

a fraction boilingiabove 333 The ,higherf boiling fraction is thenssubjected to yisomerizaition treatment in the manner described abovefafterY which it `may be combined'withlthe lowboiling fraction' .or,may,` be .subjected tov further'frac-eA tienati te vSchermatethe1 lower boilinsfi l trif methyllbenzene' asia product. Fvnexmpla finthis product boiling between `333 F. and 350 F. may be subjected to isomerization in the manner describedabove to produce a product of improved anti-knock value. This fraction contains 1,2,4 trimethyl benzene and 1,2,3 trimethyl benzeneas described, above andmay include also the methyl isopropyl benzenes, as well as 1,2 diethyl benzene, isobutyl benzene and secondary butyl benzene. Isomerization of this fraction converts trimethyl benzenes contained therein to 1,3,5 trimethyl benzene which is lower boiling and can be separated fromwtheproduct lby fractionation if desired. f Isomerization of thisfraction also converts 1,2 diethylbenzene to its isomers which are higher boiling and substantially superior in antiknock value. While theisomers of 1,2 diethyl benzene boil above the aviation gasoline boiling range theyare valuable ingredients in ordinary motor fuel and the conversion permits the removal ci a constituent of relatively low anti-knock value from ,the fraction being isomerized. 'I'he isomerization of this fraction also -establishes equilibrium proportions among the methyl isopropyl benzenes. A.Since the equilibrium proportion'of orthomethyl isopropyl Ibenzene is rather low, and since the anti-knock value of this compound is substantially lower than that of its isomers, any change in the proportions of the methyl isopropyl benzenesv ordinarily represents a substantial improvement in the anti-knock value ofthemixture. t

"trimethylr benzenes tmthe rbenzene or toluene molecules to -producegalkylated benzenes of lower boiling point. For. exampleftrimethyl benzenes oflow anti-.knock value, such as 1,2,3 trimethyl benzene may.y bereacted with toluene in the alkylation'reactionzonefto produce xylenes which may be treated,linthe mannerxdescribed above, in a subsequent operation', or Awith benzene to produce toluene and xylenes.;sAlso rbenzene may be reacted Withmethyl isopropyl benzenes to produceI toluene.'alldfgisopropyl` benzene, or with toluene v tofprocluce xylenesand isopropyl benzene. -In carrying-v.:outsuchralkylation-dealkylationy treatments relatively higli temperatures,

,.qwithint the frange.: suitable ifor'ithe isomerlzation Vof 300 to 1000 pounds per square inch, also is a desirable operative condition.

'I'he isomerization treatment of poly-alkylated aromatic hydrocarbons may be carried out, With or without the presence of benzene or toluene, at relatively high temperatures which effect cracking in the alkyl groups of relatively high boiling aromatic hydrocarbons particularly in alkyl groups of more than two carbon atoms. For example, Ain the S33-350 F. fraction mentioned above there may occur methyl isopropyl benzenes, secondary butyl benzene. isobutyl benzene and tertiary butyl benzene. These compounds may be cracked advantageously by the removal of a methyl group from `a side chain to produce lower boiling hydrocarbons of high anti-knock value. This modication of the invention thus providesk for simultaneous isomerization of polyalkylated hydrocarbons to isomers of maximum anti-knock valueand treatment of either polyalkylated or mono-alkylated hydrocarbons having side chains of two or more carbon atoms to produce lower boiling products of high antiknock value. In addition there may be eii'ected simultaneous transfer of alkyl groups from a polyalkylated aromatic hydrocarbon to a mono-alkylated or non-alkylated hydrocarbon with beneficial results. To effect cracking of side chains in the manner described, or the removal of side y chains entirely, while isomerizing in the presence of hydrogen fluoride, temperatures of 300 to 800 F.'may be employed. The foregoing specific application of the invention is directed particularly to the treatment'of aromatic hydrocarbons boiling up to 350 F. since higher boiling hydrocarbons ordinarily are not included in aviation motor fuel intended for miltary use. However, the invention may be employed with advantage in the preparation of aromatic hydrocarbons of high anti-knock value for use in motor fuel for nonrnilitary aviation use or for non-aviation use. For example, isomerization of the ortho diethyl benzene to its isomers has been mentioned above. The meta and para forms of this compound boil above the end point of military aviation fuel but represent valuable high boiling ingredients of motor fuel for other purposes. In addition the compounds boiling within the range of 350 to 400 F. include other poly-alkylated hydrocarbons which may be isomerized to forms of maximum antiknock value. For example, ortho methyl propyl benzene may be isomerized to the meta. or -para forms which are of higher value. In addition the tetra-methyl benzenes and the dimethyl ethyl benzenes also may be subjected to isomerization treatment. with suitable fractionation if desired,

to obtain the isomers of highest anti-knock value. In the last-mentioned groups of isomers those which are free of ortho relationships of the side chains are of superior anti-knock value.

The 35o-400 F. fraction also may be treated with advantage to obtain lower boiling aromatic hydrocarbons by the methods, described above, which include dealkylation and cracking in the alkyl groups. For example, the tetramethyl benzenes and the dimethyl ethyl benzenes may be dealkylated with advantage, preferably in the presence of benzene or toluene to obtain transfer of methyl groups to the lower boiling hydrocar- Vbons. The methyl propyl benzenes may bev treated likewise or may be subjected to cracking products. Similarly diethyl benzenes may be cracked or dealkylated. Butyl benzene, boiling at 361 F., preferably is cracked in the alkyl groups. The lower boiling products obtained by these various treatments may be subjected to isomerization and fractionation in the manner described above, if necessary, to obtain products of maximum anti-knock value. The residual hydrocarbons boiling in the original boiling range may be recycled for further-treatment or may be taken as a motor fuel constituent of improved anti-knock value by reason of the isomerization reactions.

In another modification a 333-400 F. aromatic fraction, which may contain or'more possible aromatic hydrocarbons, may be subjected t0 treatment at relatively high temperature in the presence of an isomerizing catalyst to effect isomerization, cracking of alkyl groups and dealkylatiorr Aromatic hydrocarbons having less than eight carbon atoms per molecule maybe added to effect simultaneous alkylation of these hydrocarbons. The product of this treatment is fractionated to separate material boilingbelow 350 F. for including in aviation motor fuel or forfurther treatment in the manner described above. The remainder, boiling in the range of 350400 F., may be retreated or employed asdi-alkylated benzenes and a lesser degree of con`y version in the case of benzenes' having attached thereto more than two alkyl groups. The former are represented by the xylenes. which may be treated without fractionation, as described, and the latter are represented by the trimethyl benzenes which may require fractionation to obtain a product of high anti-knock value.

In treatments involving cracking and dealkylation the isomerizing eect of the catalyst may be exerted on poly-alkylated aromatic hydrocarbons in the charge stock, or on poly-alkylated products, or both. For example, 1,2,3 trimethyl benzene may be converted to lower boiling products by isomerization or by deallqrlation to xylenes which are then subjected to the isomerizing effect of the catalyst. Similarly methyl isopropyl benzene may be isomerized and also reacted with toluene to producecumene and xylenes, the latter also subject to isomerization. Also the trimethyl benzenes and methyl isopropyl benzenes may be isomerized beneficially while close-boiling compounds such as butyl benzenes are cracked or dealkylated. Similarly tetramethyl benzenes are reacted with tolueneto producexylenes which are then isomerized'to form a product having the equilibrium proportion of the isomers.

In the foregoing description of the process refl of poly-alkylated hydrocarbonsl in which the alkyl groups are located adjacent each other to in the manner described to obtain lower boiling u produce poly-alkylated hydrocarbons on which laccomplished readily since .fthe ortho-xylene product is separated as a bottoms, from the isomerized product, while the meta-xylene and para-xylene are recycled. On'the other hand it may be desired to produce para-xylene from meta-xylene or ortho-xylene. 'I'his is accomplished -by isomerization in the manner described above since the para-xylene isomer is separated 4from the others by freezing, in which operation the meta-xylene and ortho-xylene may be recycled. The hydrogen fluoride catalyst employed in this invention is highly active in promoting the conversion of ahy poly-alkylated cyclic hydrocarbons or group of isomers to the equilibrium proportions ofvsuch hydrocanbon and its isomers. For example, it may be desired to isomerize polyalkylated naphthenes and cyclo-olefins having no alkyl groups attached to adjacent carbon. atoms in the ring to those having that arrangement, since the latter are superior in anti-knock value. By suitable fractionation in a manner analogous to the method described above in connection with the treatment of xylenes hydrogen fluoride isomerlzing catalyst may be employed toproduce almost any poly-alkylated cyclic hydrocarbon substantially free from its isomers.

As was indicated above the isomerization of the polyalkylated hydrocarbons by means of hydrogen fluoride can be effected at temperatures ranging from 32 F. to substantially high'er temperatures at which decomposition reactions occur. However, the optimum temperatures for effecting a maximum rate of conversion with minimum decomposition are in the range of 100 to 250 F. When cracking or dealkylation is desired higher temperatures may be employed.

The proportion of hydrogen uoride in the reaction zone should be substantially high. Ordinarily a volumetric ratio of one part of liquid' hydrogen fluoride to one part ofliquid hydrocarbons is satisfactory. In general a range of volumetric ratios of liqueed hydrogen fluoride to hydrocarbons in the reaction zone between 1:20 and 2:1 and may be employed with advantage.

While the isomerization with hydrogen fluoride is best carried out with both catalyst and hydrocarbon reactants in the liquid phase, vapor phase or mixed phase conditions may be employed. For example both hydrocarbons and hydrogen fluoride may be in the vapor phase if the temperature required is not so high as to produce excessive decomposition. Alternatively liquid hydrocarbons may be contacted with' vaporized hydrogen fluoride. However, it is preferred to maintain both hydrocarbons and hydrogen fluoride in the liquid phase since this reduces the size of the apparatus necessary.

The pressure on the isomerization reaction zone when employing hydrogen fluoride is without substantial effect except` as it may be required to maintain the desired liquid. phase Conditions.

18 When dealkylating in the presence of benzene or toluene higher pressures may be desired.

The time of contact of th'e hydrocarbons and hydrogen fluoride in the isomerization reaction zone depends upon the temperature, the degree of conversion desired, the-ratio yof catalysts to hydrocarbons and the eiiiciency of mixing. At relatively low temperatures a rather long time of contact, i. e., of an hour or more, may be required to achieve equilibrium proportions of the polyalkylated aromatic hydrocabons. At higher temperatures within the preferred range land with efficient mixing of the hydrocarbons with' a substantial proportion of catalyst a contact time of a few minutes is suillcient to achieve substantial isomerization.

While the preferred isomerization catalyst comprises hydrogen uoride as the essential ingredient, and while hydrogen fluoride alone is an effective catalyst for isomerizing poly-alkylated h'ydrocarbons, the catalyst may be promoted by the incorporation therein of a small amount of boron excess of. the amount which remains dissolved in the hydrogen fluoride. n 1

Other catalytic material may be employed in the process to isomerize the poly-alkylated aromatic hydrocarbons. These include activated clays, activated ch'arcoals, dihydroxyfluoboric` acid, boron fluoride and fluorosulfonic acid. In general any solid selective catalytic material which is capable of promoting cracking of hydrocarbons may be employed at non-cracking temperaturesv to isomerize the poly-alkylated aromatic hydrocarbons and at higher temperatures to effect both cracking and isomerization. These' include siliceous materials such as activated clays, metal silicates, such as aluminum silicate, and silica-alumina catalysts, such as silica gels activated with alumina. Other suitable materials include alumina promoted with a non-metallic reference is made specifically t0 the separation of aromatic hydrocarbons from non-aromatic hydrocarbons by absorption of the latter in phenol. It is to ,be understood, however, that any method for obtaining such separation may be employed. For example, oth'er solvents may be employed instead of phenol and other methods, such as azeotropic distillation, may be employed. For example, the xylene cut iiowing through line 10| can be mixed with methanol or other agents capable acantes tached to adjacent carbon atoms `in the benzene v ring to those having alkyl groups attached to non-adjacent carbon atoms is greater than in the original mixture, and .subjecting said separated portion to isomerization treatment with a catalyst comprising hydrogen fluoride as the essential ingredient to convert said poly-alkylated aromatic hydrocarbons to isomers thereof having no alkyl groups attached to adjacent carbon atoms in the benzene ring.

2.1A method for improving the motor fuel value of a mixture of poly-alkylated aromatic hydrocarbons which comprises separating a portion of said mixture in which the ratio of poly-alkylated aromatic hydrocarbons having alkyl groups attached to adjacent carbon atoms in the benzene ring to those having alkyl groups attached to non-adjacent carbon atoms is greater than in the original mixture, subjecting said separated portion to isomerization treatment with a catalyst comprising hydrogen uoride as the essential ingredient to convert said poly-alkylated aromatic hydrocarbons to isomers thereof having no alkyl groups attached to adjacent carbon atoms in the benzene ring, and recombining said isomerized hydrocarbons with the remainder of said mixture. J P

3. A method for improving the motor fuel value of a mixture of poly-alkylated aromatic hydrocarbons which comprises separating a portion of said mixture in which the poly-alkylated aromatic hydrocarbons predominate in those having alkyl groups attached to adjacent carbon atoms in the benzene ring, and subjecting said separated portion to isomerization treatment by contact thereof with an isomerization catalyst comprising hydrogen fluoride as the essential ingredient to convert said poly-alkylated aromatic hydrocarbons to isomers thereof having no alkyl groups attached to adjacent carbon atoms in the benzene ring.

4. A method for improving the motor fuel value of a mixture of aromatic hydrocarbons which comprises separating a portion of saidmixture containing polyalkylated aromatic hydrocarbons and aromatic hydrocarbons having attached thereto alkyl groups of more than two carbon atoms, and subjecting said separated portion to simultaneous isomerization and cracking treatment in the presence of hydrogen fluoride at a temperature above 250 F. to isomerize poly-alkylated aromatic hydrocarbons and to effect cracking in said alkyl groups of more than two carbon atoms. I

5. A method for improving the motor fuel valu of a mixture of hydrocarbons containing polyalkylated aromatic hydrocarbons which comprises contacting said mixture with hydrogen uoride at a temperature of D-400 F. in the presence of aromatic hydrocarbons having less than eight carbon atoms per molecule to convert said poly-alkylated hydrocarbons to lower boiling poly-alkylated hydrocarbons in yWhih 11.9

20 f alkyl groups are attached to adjacent carbon atoms in the benzene ring, said treatment being carried out in the substantial absence of other reactive hydrocarbons and for a length of time whereby the formation of said last mentioned poly-alkylated hydrocarbons constitutes the principal reaction. n

6. A method for isomerizing poly-alkylated aromatic hydrocarbons4 which comprises `contacting said aromatic hydrocarbons with `hydrogen yfluoride at a temperature of 1D0-250 F. and in the substantial absence of other reactive hydrocarbons whereby isomerization of said polyalkylated aromatichydrocarbons is the principal reaction.

7. A method for isomerizing xylenes which comprises contacting said xylenes with hydrogen fluoride at a temperature of 1D0-250 F. andin the substantial absence of other reactive hydrocarbons whereby isomerization of xylenes is the principal reaction.

8. A method for isomerizing ortho-xylene which comprises contacting said ortho-xylene' with hydrogen fluoride at a temperature of 250 F. and in the substantial absence of other reactive hydrocarbons whereby isomerization of ortho xylene is the principal reaction.

9. A method for improving the motor fuel value of a mixture of xylenes including ortho-xylene which comprises contacting with hydrogen nuoride a portion of said mixture containing said.' ortho-xylene in a proportion greater than in said Y mixture and greater than the proportion of ortho A10D-250 F. and in the substantial absence of other reactive hydrocarbons whereby isomerization of xylenes constitutes the principal reaction.

10. A method for improving the motor fuel value of a mixture of xylenes including orthoxylene which comprises separating from said mixture a portion thereof containing orthoxylene in a proportion greater than the proportion thereof in said mixture," contacting said separated portion with hydrogen fluoride at a temperature of 10U-250 F. to isomerize ortho-xylene to the isomers thereof, and recombining the isomerized xylenes withsaid mixture.

11. A method for producing poly-alkylated aromatic hydrocarbons of high anti-knock value which comprises preparing a feed stock containingv non-aromatic hydrocarbons having eight carbon atoms Lper molecule and convertible to xylenes and substantially free of hydrocarbons boiling in the boiling range of the said xylenes,

subjecting said feed stock to aromatizing treatment in the presence of a dehydrogenating catalyst to effect conversion thereof to xylenes, fractionating the aromatized product to separate a fraction boiling above the end point of the feed stock andincluding said xylenes, and subjecting xylenes thus obtained tov isomerizationtreatment in the presence of a hydrogen fluoride catalyst to prises subjecting non-aromatic hydrocarbonsl having atleast eight carbon atoms per molecule to aromatization treatment in the presence of a dehydrogenating catalyst to effect conversion thereof to aromatic hydrocarbons having a corresponding number of carbon atoms per molecule including poly-alkylated aromatic hydrocarbons, separating from said aromatized product a fraction including the xylene products of aromatization, further fractionating said xylene fraction to separate an overhead product comprising meta-Xylene and para-xylene and substantially free from ortho-xylene and a bottoms product predominating in ortho-xylene, subjecting a portion of said bottoms product to isomerization treatment in the presence of a hydrogen fluoride catalyst to convert ortho-xylene to its isomers, combining at least a part of the isomerized product with the xylene fraction for fractionation as described, and recycling to the aromatization treatment a portion of said bottoms product.

13. A method for producing aviation motor fuel of high anti-knock value from a mixture of aromatic hydrocarbons boiling below and above 333 F. which comprises separating from said mixture a fraction comprising aromatic hydrocarbons boiling between 333 F. and approximately 400 F., subjecting said last-mentioned fraction to treatment in the presence of a hydrogen fluoride catalyst at elevated temperature to effect simultaneous isomerization of poly-alkylated benzenes and cracking of other aromatic constituents of the said fraction in the alkyl groups thereof, separating from the products of said treatment a fraction boiling below 350 F. and combining said last-mentioned fraction with constituents of said first-mentioned mixture boiling below 333 F.

14. A method for isomerizing poly-alkylated aromatic hydrocarbons which comprises contacting said aromatic hydrocarbons with hydrogen uoride promoted with boron trifiuoride at a temperature of D-250 F. and in the substantial absence of other reactive hydrocarbons whereby isomerization of said poly-alkylated aromatic hydrocarbons is the principal reaction.

HERBERT J. PASSINO. HENRY G. McGRATI-I.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,143,472 Boultbee Jan. 10, 1939 2,222,128 Wagner Nov. 19, 1940 2,241,393 Danner May 13, 1941 2,243,873 Lyman June 3, 1941 2,304,183 Layng et ai. Dec. 8, 1942 2,315,078 Pines et al. Mar. 30, 1943 2,325,379 Durrum July 27, 1943 1,953,702 Davidson Apr. 3, 1934 2,282,231 Mattox May 5, 1942 2,337,190 Greensfelder et al. Dec. 21, 1943 2,338,711 DOuville et al Jan. 11, 1944 2,347,317 Gibson Apr. 25, 1944 2,343,744 Burk I Mar. 7, 1944 2,378,763 Frey June 19, 1945 FOREIGN PATENTS Number Country Date 292,932 Great Britain I May 23, 1929 292,933 Great Britain II May 23, 1929 OTHER REFERENCES Zelinsky et al., Ind. and Eng. Chem. 27, 1209-11 (1935), 260-668.

Thomas, Anhydrous Aluminum Chloride in Organic Chemistry," Reinhold, 1941, pages 717-. 719. (Copy in Division 31.)

Grosse et al., Ind. and Eng. Chem. 32, 528-31 (1940). (Copy in 260-6735.)

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