US2810002A - Separation of alkyl aromatic hydrocarbons with an aluminum halide and a group i or ii metal halide - Google Patents

Description

OC- 15, 1957 c. B. scoTT ET AL SEPARATION oF ALKYL ARoMATIc HYDRocARBoNs WITH AN ALUMINUM HALIDE AND A GROUP I 0R II METAL HALIDE Filed March 22, 1954 2,810,002 n SEPARATION or ALKYL ARoMgA'ric HYnRocAR- BONS WITH AN ALUMINUM HALIDE AND A GROUP I OR II METAL HALIDE Carleton B. Scott, Pomona, William D. Schaeffer, Berkeley, aud John D. Wordie, Fullerton, Calif., assignors to Union Oil Company of California, Los Angeles, Calif., a corporation of California Application March z2, 1954, seria1o.'417,930

1s claims. (c1. 2150-474) This invention relates to a method for separating aromatic hydrocarbons, and in particular concerns a method for separating one or more specific isomers from isomeric mixtures of dialkylbenzenes, e. g. xylenes. i

Certain aromatic hydrocarbon compounds, particularly the lower dialkylbenzenes, are ordinarily obtained in the form of isomeric mixtures from which the individual isomers cannot beV separated by conventional fractional distillation procedures. For example, the Cs fracton obtained in petroleum hydrocarbon reforming operations contains ortho-, meta, and para-xylenes and ethylbenzene, all of which have boiling points within about 8 C. of each other. Two of the isomers, metaand para-xylenes, boil within about 0.8 C. of each other. Various methods have been proposed for resolving isomeric mixtures of this type, e. g., fractional crystallization and selective chemical reaction, but none of such methods has proved entirely satisfactory for large-scale operation.

It is accordingly an object of the present invention to provide an improved method for resolving mixtures cornprising isomericlower dialkylbenzenes.

Another object is to provide a commercially attractive method for the separation of mixed xylenes.

A further object is to provide an improved method for separating individualV isomers from the Ca fraction of pe-V troleum hydrocarbon reformates.

Other and related objects will be apparent from the following detailed description of the invention, and various advantages not specically referred to herein Will occur to those skilled in the art upon employment of the invention in practice.

We have found that the foregoing objects and attendant advantages may be realized in a process which comprises treating the isomeric mixture with an aluminum halide and certain other metallic halides. More particularly, we have found that the laddition of an aluminum halide and a halideof a metal of group I or Il of the periodic system to hydrocarbon mixtures comprising isomeric lower dialkylbenzenes results in the formation of a liquid complex comprising the metallic halides and one particular hydrocarbon isomer. When the isomeric mixture comprises mixed xylenes, the complex is formed with the meta isomer. In some instances the liquid complex l 2,810,002 Patented ct. 15, 1957 ice p adapted to produce either of the non-complexed isomers is substantially immiscible with the non-complexed isomers, and may be separated therefrom by simple settling and decantation. Alternatively, the non-complexed isomers may be separated from the complex by selective solvent extraction with a liquid aliphatic hydrocarbon such as pentane, hexane, heptane, iso-octane, decane, etc. In its simplest embodiment the invention thus comprises the steps of adding an aluminum halide and one of the aforementioned metal halides to a mixture of lower dialkylbenzene isomers, whereby one of said isomers is selectively complexed with the metallic halides, and thereafter separating the complex from the non-complexed isomers. The` fully explained it maybe employed directly inra process as Ythe ultimate product.

For convenience, the invention is herein described as it is applied to the treatment of various mixtures comprising mixed xylenes, but it is to be understood that the principle of the nvention'may be similarly applied to the treatment of any hydrocarbon mixture comprising lower dialkylbenzenes. The term lower dialkylbenzene is herein employed to designate'dialkylbenzenes in which each alkyl group contains from 1 to 4 carbon atoms, and

thus includes within its scope xylenes, di-ethylbenzenes,`

di-n-propylbenzenes, di-n-butylbenzenes, butyltoluenes, cymenes, ethyl-cumenes, tert-butyl-ethylbenzenes, etc.

The following examples will illustrate practice of the.- invention in its simplest form, but are not to be con-nA strued as limiting the same.

Example I Approximately 40 parts by weight (3 moles) of anhydrous aluminum chloride is added to about 53.5 parts. by weight (5 moles) of a mixture comprising the three,- xylene isomers and ethylbenzene. The aluminum chlo-` ride does not dissolve in the hydrocarbon mixture, but remains at the bottom of the vessel as a separate solidi phase. Approximately 12.7 parts by weight (3 moles) of lithium chloride is then added to the two-phase mixture.A Upon shaking, the metal halides dissolve in the, hydrocarbon phase with the evolution of heat to form a brown; liquid. This product is then extrated with n-heptane, and the extract phase is poured into ice water to hydrolyze any aluminum chloride which might be present. However, theabsence of any appreciable amount of aluminum hydroxide in the hydrolyzed extract indicates that substantially none of the aluminum chloride is in the extract phase. The rainate, i. e., the product not removed by the extraction with heptane, is also poured into ice water. The hydrocarbon portion of each of the two hydrolysis products is then analyzed for individual xylene isomers and ethylbenzene, with the following results beingrobtained:

The procedure of Example I is repeated, employing 16.5 parts (1.5 mole) of cuprous chloride in place of the lithium chloride. During solution of the cuprous chloride in the hydrocarbon-aluminum mixture artificial cooling is supplied to prevent the temperature from exceeding about 25 C. The following analytical results are obtained:

pmo- Ethyl- Xylene, Xylene, Xylene, ben- Ratio, Sample perperperzene, m-/pcent cent cent percent Feed Mixture 22.3 49.5 13.7 14.5 2.22 Hydrolyzed Extract 281.6 38. 8 9. 7 22. 9 1. 36 Hydrolyzed Ralfmate `25.0 55.8 10.9 8.3 2.22

Example III Approximately 3 moles of aluminum bromide and 1.5 l moles of potassium bromide are shaken with 3 moles of a mixture of xylenes'and ethylbenzene at a temperature` of about 100" C.I Ihe resulting mixture is extracted with 3 n-heptane and the extract and rafnatephases were hy drolyzed asin Example I. The following analytical results were obtained:

pmvo- A, :Ecrire Xylene, Xylene, Xylene, ben- Ratio, Sample vper- .per- .perzene, m-/pcent cent cent percent Feed LMixture 22. 3 49. 5 I3. 7 14. 5 2.22 Hydrolyzed Extract 22:7 49.0 13. 7 14. 6 2.16 Hydrolyzed Rainate 19. 9 57. 9 10. 3 11. 9 2.81

Similar results are obtained Vwhenalurninumchloride and sodium chloride are employed.

Example I V The procedure of Example I is repeated, employing 2 moles of aluminum chloride and 0.4 mole of mercuric chloride per mole of hydrocarbon and a somewhat different feed composition. The following results are A xylene mixture containing 54 percent by volume of para-xylene and 46 percent by volume of meta-xylene (ratio, m-/p=0.85) is treated with one molecular equivalent of aluminum chloride and 0.16 molecular equivalent of cadmium chloride, and the resulting mixture is extracted with n-heptane as in Example I. The extract and rainate phases are hydrolyzed with ice water, and the hydrocarbon phases of the hydrolysate are found to contain:

Hydrolyzed Hydrolyze Extract, Rafnate, Percent Percent by Vol. by Vol.

m-Xylene 25. 5 65. 2 p-Xylene.- 71. 9 27. 0 o-Xylene 2. 6 7.8 Ratio, m-/p- 0.34 2. 42

The small amount of ortho-Xylene formed is due to the isomerizing influence of Ythe metal halides and can be reduced by operating at a lower temperature. VWhen 0.2

molecular equivalent of mercurous chloride is substituted for the cadmium chloride the ratio of meta-to-para is 0.35 in the hydrolyzed extract and 1.58 in the hydrolyzed rainate.

The aluminum halide which is employed in accordance f with the invention is anhydrous aluminum chloride, bromide or iodide, and the other metallic halide is a chloride, bromide or iodide of one of the metals of groups I or II of the periodic system, e. g., sodium chloride, potassium bromide, lithium chloride, calcium iodide, magnesium chloride, cadmium bromide, mercurio iodide, beryllium chloride, barium bromide, gold chloride, cupric iodide, strontium chloride, etc. Ammonium halides are also operable, and the ammonium ion is herein considered as a group I metal. are preferred by reason of their lower cost and general availability. It is not necessary that the halogen atom be the same, i. e., aluminum chloride may be employed with sodium bromide or potassium iodide, aluminum bromide maybe employed with cadmium chloride, etc.

The amount of aluminum halide employed depends upon. the proportion of the selectively complexed isomer in the mixture -being treated andv upon the degree of selectivity desired. On a molar basis, such amount'is usually between about 0.5/1 and about 5/1. Thus, 4in Y Of these metal halides, the chlorides cent of the meta isomer, the aluminum halide will be employed in an amount representing between about 0.25 and about 2.5 moles per mole of the isomeric mixture.

The metal halide otherV than the aluminum halide is employed in an amount suiiicient to promote solution of substantially all vof the aluminum halide in the hydrocarbon mixture. Such amount is usually between about 0.2 and about 1.5 moles of metal halide per mole of aluminum halide.

The treatment of isomeric mixtures with metal halides in accordance with the invention Vis preferably effected at atmospheric temperatures and/or pressures, although if desired somewhat elevated temperatures and/or pressures may be employed. However, since the metal halides promote isomerization at elevated temperatures, the temperature should be controlled so as not to exceed the temperature at which substantial isomerization occurs. In general, the temperature should be maintained below about C.

As will be apparentto those skilled in the art, the operation may be carried out batch-wise, semi-continuously or continuously by any .of the conventional means for contacting solids and liquids. The following example illustrates 'one form which a continuous process may take:

Example Vl Percent by volume p-Xylene .M 26.5 m-Xylene v Y Y 45.9 o-Xylene 1 Y 15.3 Ethylbenzene 12.3

VThe mole-ratios of aluminum chloride and cadmium chloride to meta-xylene are about 2/1 and l/ l, repectively. Solution of the feed stream in the recycle stream is effected, and the solution is passed to a continuous multi-stage liquid-liquidextraction column wherein it passes countercurrent to a Vstream of n-decane. The extract phase is` passed to a distillation column wherein an overhead stream comprising Cs aromatic' hydrocarbons lean in meta-xylene VisV taken off, and a bottoms stream comprising n-decarie is returned tothe extraction column. The raliinate phase is passed from the extraction column to a continuous vacuum distillation column operating at 20-100 mm. pressure. This column is operated to produce an overhead stream comprising meta-xylene in an `amount substantially equal to the meta-xylene content of the feed stream and a bottoms fraction comprising C hydrocarbons richin meta-xylene, aluminum chloride and cadmium chloride. Said bottoms fraction constitutes the aforesaid recycle stream, and is continuously returned to the initial step of the operation for admixing with a further quantity of the feed.

In the foregoing example, the complexed and noncomplexed hydrocarbons are separated by selective solvent extraction. Relatively low-boilingv aliphatic hydrocarbons, e. g., hexane, heptane, octane, etc., are preferred solvents for this purpose by reason of their low cost and ready availability, but any solvent which is selective with respect to the complexed and the non-complexed hydrocarbons may kbe employed. Any of the conventional techniques generally applied to selective solvent extraction processes'may beV employed. In some instances, deu'e'riding upon the nature'ofthe isomeric 'feedA mixture arid the amount of metal' halides employed, the complex is immiscible with the non-complexed hydrocarbons; and the separation ofthe two may-'be effected simply by allowing' the mixture to settle followedby mechanical separation of the two liquid phases.

As will be apparent to those skilled in the ar't, the process of the invention may be carried out in a plurality of stages arranged in cascade fashion. Thus, from an initial separation stage may be passed to a second separation stage wherein it is `r'e-treatedwith the metal halides to obtain 'a secondary raffinate and a secondary extract. The latter may be recycled back to the initial stage, and the raffinate may be' passed to a tertiary stage and again treated'with the metal halides'. By providing an appropriate number of stages and feeding the raffinate from each stage to the next succeeding Vstage while returning the extract from each stage to the feed stream of each preceding stage,visomers of any desired degree of purity may be separated `from the feed mixture.

The principle of the invention may be applied in various ways to provide a number of integrated processes adapted to the production of substantially pure isomeric hydrocarbons. For example, a mixture of ortho, metaand para-xylenes may be treated as hereinabove explained to obtain substantially pure meta-xylene Aand a mixture of the ortho and para isomers. The latter mixture may then be fractionally distilled to obtain substantially pure paraxylene as an overhead product and substantially pure ortho-xylene as distillation bottoms. Alternatively, the ortho and para mixture may be separated by fractional crystallization or by selective chemical reaction.

The process of the invention may also be carried out as a combination separation-isomerization process to produce any one of the isomers as the major product. As previously stated, the mixed metal halides of thepresent class promote the isomerization of lower dialkylbenzenes at temperatures in excess of about 80 C. Accordingly, a mixture of ortho,` metaand para-xylenes may be treated with an aluminum halide and a halide of a metal of group I or II of the periodic system at a non-isomerizing ternperature, e. g., 30-50 C., as hereinabove described to obtain the ortho and para isomers in non-complexed form and the meta isomer in the form of a complex with the metal halides. The complex is then directly subjected to isomerizing temperatures, e. g., 809-150 C. or higher, whereby the meta isomer is isomerized to form an equilibrium mixture of ortho, metaand para-xylenes. VSaid mixture is then recycled back to the initial separation operation whereby a further quantity of the ortho-para mixture and a further quantity of the complexed meta isomer is obtained.

The following examples will illustrate the use of the metal halides of the present class as isomerization catalysts, but are not to be construed as limiting the invention: Example VII A mixture of ortho, metaand para-xylene is treated with aluminum bromide and sodium chloride and is extracted with n-decane asf above explained, while maintaining a temperature of about 40 C. The hydrocarbon component of the raflinate phase comprises about 90.5 percent by volume. of meta-xylene, 8.8 percent by volume of para-xylene and 0.7 percent of ortho xylene. The raflinate, which contains about 0.4 mole each of aluminum bromide and sodium chloride per mole of hydrocarbons, is then heated at a temperature of about 140 C. for a period of about two hours, after which the product is distilled to separate the isomerized hydrocarbons from the metal halides. The distilled product comprises 73.0 percent by volume of meta-xylene, 17.5 percent by volume of para-xylene and 9.5 percent by volume of ortho-xylene. When aluminum bromide alone is employed as the isomerization catalyst, 45.8 percent of the xylenes are dealkylated to benzene and toluene, and the volume recovery is only 2 3 percent.

' `Example VIII the r'ainatetracted with n-heptane as previously explained. ,The extract phase, comprising the heptane solvent and a xylen'e mixture lean in the meta isomer, is fractionally distilled to obtain an overhead fraction comprising the heptane solvent, an intermediate fraction rich in paraxylene, and a bottoms fraction having the following composition:

Thev bottoms fraction is admixed with 0.3 molecular equivalents each of aluminum bromide and sodium chlo ride, and the mixture is heated at -90 C. for 1.5 hours. After filtering to remove the metal salts the isomerized product is found to contain:

Percent by e h volume o-Xylene 46.6 m-Xylene 40.7 p-Xylcne 8.3 Benzene 0.2 Toluene 2.3 Residue 1.9

` 100.0 This product is treated, as by fractional crystallization, to separate the para-xylene therefrom, `and the remainder is recycled to the separation step for removal of the rneta-xylene. By repeating this procedure metaand para-xylenes are obtained as substantially the sole products. If desired, the meta and ortho isomer streams may be combined prior to the isomerization step, whereby para-xylene is obtained as substantially the sole product.

The drawing which accompanies and constitutes a part of this application is in the form of a flowsheet illustrating several ways of practicing the process of the invention. In said drawing, Figure l illustrates the simplest embodiment of the invention wherein the complexed m-xylene is separated from its non-complexed isomers by simple phase separation or, alternatively, by extraction with a suitable solvent, followed by decomposition of the complex to obtain free m-xylene. When solvent extraction is employed` the extract is distilled or otherwise treated to separate the solvent, and the latter is recycled to the extraction step. y Figure 2 illustrates a more complexembodiment wherein the m-xylene complex is separated from the non-complexed isomers by solvent f extraction and is decomposed to obtain free m-xylene, and the extract consisting of solvent and non-complexed xylene isomers is isomerized, with the isomerizate being separated from the solvent and recycled back to the initial step of the process wherein the isomeric mixture is admixed with the complexing agent.

Other modes of applying the principle of our invention may be employed instead of those explained, change being made as regards the methods or materials employed provided the step or steps stated by any of the following claims, or the equivalent of such stated step or steps, be employed.

We, therefore, particularly point out and distinctly claim as our invention:

l. The method of treating an aromatic hydrocarbon mixture comprising meta-xylene and at least one other xylene isomer which comprises adding to said mixture an aluminum halide selected from the class consisting of aluminum chloride, aluminum bromide and aluminum iodide and suflicient of a metal halide selected from the class consisting of the chlorides, bromides and iodides of the metals of groups I and II of the periodic system to cause said aluminum halide to dissolve in said aromatic hydrocarbon mixture while maintaining a tempe'ature below that at which isomerization of said ,dialkylbenzenes occurs to any substantial extent, and thereafter separatingfrom the mixture so treated a complex comprising the metallic halides and at least one of said dialkylbenzene isomers, the ratio of isomers in said complex being substantially different from the ratio of isomers in said aromatic hydrocarbon mixture.

2V. The method of claiml wherein said aromaticrhydrocarbon mixture comprises the Ca fraction of a petroleum hydrocarbon reformate and contains meta-xylene, orthoxylene, para-xylene, and ethylbenzene.

3. The method of claim 1 wherein said aluminum halide is aluminum chloride.

4. The method of claim 1 wherein said aluminum halide is aluminum chloride and said metal halide is cadmium chloride. A

,5. The method oftreating an aromatic hydrocarbon mixture comprising meta-xylene Vand at least one other xylene isomer which comprises adding to said mixture an aluminum halide selected from the class consisting of aluminum chloride, aluminum bromide and aluminum iodide and suiicientV of a metal halide selected from the kclass consisting ofthe chlorides, bromides and iodides of the metals of groups I and II of the periodic system to cause said aluminumhalide to dissolveV in said aromatic hydrocarbon mixture while maintaining a temperature below about 70 C., and thereafter separating from the mixture so treated a liquid complex comprising the metallic halides and at least one of said xylene isomers, the ratio of xylene isomers in said complex being substantially different from the ratio of isomers in said aromatic hydrocarbon mixture;

6. The method of claim 5 wherein said aluminum lialide is aluminum chloride.

7. The method of claim 5 wherein between about 0.5 and about 5 moles of aluminum halide are employed per mole of the isomer which forms the said complex. t

8. The method of claim 5 wherein the aromatic hydrocarbon mixture is an equilibrium mixture comprising ortho, metaand para-xylenes and ethylbenzene. l

9. The method of claim 5 wherein between about 0.2 and about 1.5, imolesrof the said metal halide is employed per mole of aluminumhalide'. y Y

10. The method of treating an aromatic hydrocarbon mixture comprising meta-'xylene and at least one other xylene Visornerlwhich comprises adding to said mixture an aluminum halide selected` from the class consisting of aluminum chloride, aluminum bromide and .aluminum iodide and suicient of a metal halide selected from the class consisting of the chlorides, bromides and iodides of the metals of groups I and II ofthe periodic system to cause aluminum halide to dissolve in said aromatic hydrocarbon mixture, subjecting the resulting mixture to selective solvent extraction with a liquidwsaturated aliphatic hydrocarbon at a temperature below that at which isome'rization of said isomeric xylenes occurs to any substantial extent, and separating a' raflinate phase comprising a complex containing the metallic halides andV at least one isomer of xylene from an extract phase comprising said aliphatic hydrocarbon and non-complexed xylene isomers, the ratio of xylene'isorners in the raffinate -phase being substantially dilerent from the ratio of xylene isomers in said aromatic hydrocarbon mixture. i l

11. The method of claim wherein the aluminum halide ,israluminum chloride.

12. The method of claim 10 wherein between about 0.5 and about 5 moles of aluminum chloride are employed per mole of that isomer which forms the said complex with metallic halides and between about0.25 about' 1.5 moles of .metal halide are' employed per of aluminum chloride. Y u Y 1 3. The method of'claim` 10 wherein the temperature is maintained below about 70 C.

14.A The method of treating an aromatic hydrocarbon mix ure comprising meta-xylene and at least one other mole carbon at a temperature xylene isomer which comprises adding to said mixture an aluminum halide selected from the class consisting of aluminum chloride, aluminum bromide Vland aluminum iodide and sufiieient of a metal halide selected from the class consisting ,of ythe chlorides, bromides and iodides of themetals of jgroups I Vand vII of the periodic system to cause aluminum halide to dissolve in said aromatic hydrocarbon mixturegvsubjecting the resulting mixture to selective'solvent' extraction with a liquid saturated aliphatic hydrocarbon at a-temperature below that at which isomerization of said visomeric xylenes occurs vto any substantial extent; separating ,aV rainate phase comprising a complex ,containing the metallic halides and at least one isomer vgofxylne from an extract phase comprising said aliphatic hydrocarbon andknon-complexed xylene isomers, the ratio of xylene isomers inthe ranate phase being substantially ditlerentl from the ratio of xyleneisomers in said aromatic hydrocarbon mixturegrecovering the noncomplexed isomers from said extract phase; and recovering the complexed isomers from the rainate phase.

15. The method of claim 14 wherein the said aromatic hydrocarbon mixturewcomprises ortho-, metaand paraxylenes andfethylbenzene.

16. The methodof treating an aromatic hydrocarbon mixture comprising meta-xylene and at least one other xylene isomer which comprises adding to said mixture an aluminumvhalide selectedk from the class consisting of aluminum chloride, aluminum bromide and aluminum iodide and suiicientof a 'metal halide selected from the class consisting of the chlorides, bromides andiodides of the metals of groups I and II of the periodic system to cause aluminum halide to dissolve in said aromatic hydrocarbon mixture; subjecting the resulting mixture to selective solvent extraction -with a liquidsaturated aliphatic hydrobelow that at which isomerization` of said/ isomericrxylenes occurs to any substantial extent; separatingarainnate phase comprising a complex containing the metallic halides and at least one isomer of xylene from an extract phase comprising said aliphatic hydrocarbon and non-complexed xylene isomers, ,the ratio of, xylene isomers in the ratlinate phase being substantially dierent from the ratioof xylene isomers in said aromatic hydrocarbon mixture; and subjecting said rafiinate phase to an isomerizing temperature above about C.

17. The4 method of treating a mixture comprising isomcric xylenes including meta-xylene which comprises (l) adding to said mixture between about 0.5,.and about 5 moles of aluminum chloride per mole ofmeta-xylene and between about 0.25 and about 1.5 moles of a metal halide selected from the class consisting of the chlorides, bromides and iodides of the metals of groups I and II of the periodic system per mole of aluminum chloride while maintaining a temperature below about 70 C.; (2) extracting the resulting mixture with a liquid saturated al1'- phatichydrocarbon while maintaining a temperature below about 70 C.; (3) separatinga raffinate -phase comprising a complex containing .the metallic halides and meta-xylene from .an extract phase richl in xylenel isomers other than meta-xylene, the ratio of isomers in therainate phase differing substantially from Vthe ratio of isomers inthe extract phase; (4) recovering xylene isomers from saidl extract phase; (5) subjecting said raiiinat'e phase to anisome'rizing temperature above about 70C.; and (6) returningpthe isomerized product to step (l).Av

18. The methodof claim 17 wherein the original mixture comprises ortho, metaand para-xylenes and ethylbenzene.

References Cited in the tile of this patent UNITED STATES PATENTS Holi et a1. Lien et al'. A

2,564,073 Aug. 14, 1951 sept. 13, 1949

Claims (1)

1. THE METHOD OF TREATING AN AROMATIC HYDROCARBON MIXTURE COMPRISING META-XYLENE AND AT LEAST ONE OTHER XYLENE ISOMER WHICH COMPRISES ADDING TO SAID MIXTURE OF ALUMINUM HALIDE SELECTED FROM THE CLASS CONSISTING OF ALUMINUM HALIDE CHLORIDE, ALUMINUM BROMIDE AND ALUMINUM IODIDE AND SUFFICIENT OF A METAL HALIDE SELECTED FROM THE CLASS CONSISTING OF THE CHLORIDES, BROMIDES AND IODIDES OF THE METALS OF GROUPS 1 AND 11 OF THE PERIODIC SYSTEM TO CAUSE SAID ALUMINUM HALIDE TO DISSOLVE IN SAID AROMATIC HYDROCARBON MIXTURE WHILE MAINTAINING A TEMPERATURE BELOW THAT AT WHICH ISOMERIZATION OF SAID DIALKYLBENZENES OCCURS TO ANY SUBSTANTIAL EXTENT, AND THEREAFTER SEPARATING FROM THE MIXTURE SO TREATED A COMPLEX COMPRISING THE METALLIC HALIDES AND AT LEAST ONE OF SAID DIALKYLBENZENE ISOMERS, THE RATIO OF ISMOERS IN SAID COMPLEX BEING SUBSTANTIALLY DIFFERENT FROM THE RATIO OF ISOMERS IN SAID AROMATIC HYDROCARBON MIXTURE.

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