US3513213A - Hydrocarbon separation - Google Patents

Description

y ,1970 R. D. BECKHAM ETAL 3,513,213

- HYDROCARBON SEPARATION Filed April 24, 1968 I NVENTOR. RODNEY D- BECKHAM BYHERBERT a. GEBHART, JR

EARLE c. MAKIN,JR.

Affornlj United States Patent 3,513,213 HYDROCARBON SEPARATION Rodney D. Beckham, Bridgeton, Herbert J. Gebhart, .lr.,

Ferguson, and Earle C. Makin, Jr., St. Louis, Mo., as-

signors to Monsanto Company, St. Louis, Mo., a corporation of Delaware Filed Apr. 24, 1968, Ser. No. 723,858 Int. Cl. C07c 7/10, /10

US. Cl. 260-674 10 Claims ABSTRACT OF THE DISCLOSURE A process for separating vinyl aromatic hydrocarbons from alkyl aromatic hydrocarbons employing a substantially anhydrous silver salt. The vinyl aromatic hydrocarbons are recovered from admixture with the silver salt by contacting the mixture with an olefin and/ or diole| fin hydrocarbon.

BACKGROUND OF THE INVENTION The term vinyl aromatic hydrocarbons, as used herein, refers to aromatic hydrocarbons containing a monoethylenically unsaturated aliphatic substituent, e.g., styrene, a-methylstyrene, b-methylstyrene, vinyl toluene. Alkyl aromatic hydrocarbons, as used herein, refers to those aromatic hydrocarbons having saturated aliphatic substituents, e.g., xylene, ethylbenzene and the like.

One of the most difiicult separations problems existing in industry today is that of separating vinyl aromatic hydrocarbons from close boiling alkyl aromatic hydrocarbons. In most instances, separation of such hydrocarbons is difficult at best by distillation. However, to render the problem more difiicult, the unsaturated vinyl aromatic hydrocarbons are usually easily polymerized and thus tend to polymerize and foul the equipment used for separation by distillation. Probably the most exemplary and commonly encountered difficultly separable vinyl aromatic hydrocarbons and alkyl aromatic hydrocarbons are styrene and o-xylene. These two compounds are very difficult to separate one from another and because of the entirely different uses of the two, either one of these is an undesirable contaminant in the other and, therefore, it is desired to have means for effectively separating the two.

In addition to distillation, it is known that such compounds as mercuric chloride, mercuric acetate, and the like, will complex With styrene. Such complex formation offers a means of separating styrene from o-xylene. However, it is often quite difficult to recover the vinyl aromatic hydrocarbons from the complex. Severe conditions usually necessary for recovering the complexed vinyl aromatic hydrocarbons from the complex often result in substantial polymerization and loss of the vinyl aromatic hydrocarbons.

An additional means of separating alkyl aromatic hydrocarbons from vinyl aromatic hydrocarbons which has recently been proposed is a separations process employing aqueous solutions of such silver salts as silver fiuoroice borate and silver fiuorosilicates. Such a separations process is disclosed and claimed in copending application Ser. No. 587,930, filed Oct. 16, 1966, now Pat. No.

' 3,427,362. While this means of separating alkyl aromatic hydrocarbons from vinyl aromatic hydrocarbons represents a significant advancement in such separation, it has been found desirable to find a means for increasing the effectiveness of the usage of the silver salt in effecting such separation.

It is now an object of the present invention to provide a new and improved process for the separation of aromatic hydrocarbons. A further object of the present invention is to provide a new and improved process for the separation of vinyl aromatic hydrocarbons from alkyl aromatic hydrocarbons. An additional object of the present invention is to provide a new and improved process for the separation of vinyl aromatic hydrocarbons from alkyl aromatic hydrocarbons wherein the vinyl aromatic hydrocarbons can be substantially totally recovered. Yet another object of the present invention is to provide a process for the separation of vinyl aromatic hydrocarbons from alkyl aromatic hydrocarbons which as a benefit thereof provides a means whereby olefins and/ or conjugated diolefins may be effectively removed from admixture with non-conjugated diolefins and saturated hydrocarbons. Another object of the present invention is to provide a new and improved process for the separation of styrene from o-xylene. A particular object of the present invention is to provide a new and improved process for the separation of alkyl aromatic hydrocarbons from vinyl aromatic hydrocarbons with a silver salt such as silver fluoroborate and silver fluorosilicate wherein substantially more effective use of the silver salts is obtained. Additional objects will become apparent from the following description of the invention herein disclosed.

SUMMARY OF THE INVENTION The present invention which fulfills these and other objects, in one of its embodiments, is a process for the separation of vinyl aromatic hydrocarbons from aromatic hydrocarbon mixtures containing vinyl aromatic hydrocarbons in admixture with alkyl aromatic hydrocarbons. This process comprises contacting such aromatic hydrocarbon mixtures With a substantially anhydrous silver salt selected from the group consisting of silver fiuoroborate, silver fluorosilicate and mixtures thereof, separating an extract fraction containing said silver salt and aromatic hydrocarbons in solution therewith, and a rafflnate fraction containing aromatic hydrocarbons not in solution with said silver salt, and recovering from said extract fraction an aromatic hydrocarbon fraction sub; stantially richer in vinyl aromatic hydrocarbons than the initial aromatic hydrocarbon mixture. To facilitate the use of the substantially anhydrous silver salts used in the process of the present invention, the silver salt most often is used in solution with an organic solubilizing agent for such silver salt.

As a useful mode of operating the process of the present invention, the aromatic hydrocarbon mixture containing vinyl aromatic hydrocarbons and alkyl aromatic hydrocarbons is contacted with the substantially anhydrous silver salt and the resulting mixture of silver salt and aromatic hydrocarbons then contacted with a saturated aliphatic hydrocarbon of 3 to 15 carbon atoms. When the saturated aliphatic hydrocarbons are contacted with the mixture of aromatic hydrocarbons and silver salt in accordance with the process defined herein, extract and raffinate phases are more readily formed and the efficiency of the separation of alkyl aromatic hydrocarbons from vinyl aromatic hydrocarbons is thereby improved.

The recovery of the vinyl aromatic hydrocarbons from the extract phase may be accomplished by any available means. The vinyl aromatic hydrocarbons may be distilled from the extract phase. However, it is generally desired to carry out such a distillation under reduced pressure to avoid high temperatures which would likely cause polymerization of the vinyl aromatic hydrocarbons as well as decomposition of the silver salt. When distillation is used as the means of recovering the vinyl aromatic hydrocarbons from the extract phase, reduced pressures within the range of 75 to 300 mm. Hg are preferred.

A particularly useful method of recovering the vinyl aromatic hydrocarbons from the silver salt containing extract phase comprises contacting such extract phase with an unsaturated aliphatic hydrocarbon selected from the group consisting of olefins, diolefins and mixtures thereof. It has been found that the olefins and/ or diolefins when in molar excess will displace vinyl aromatic hydrocarbons from the extract phase and are in turn preferentially absorbed and retained therein. The olefins and/ or diolefins may be removed from the new extract phase by distillation under significantly less stringent conditions of temperature and pressure than those required for the removal of vinyl aromatic hydrocarbons. However, quite surprisingly, the olefins and/or diolefins, as the case may be, may in turn be displaced from the extract phase by contact with at least an equimolar quantity of vinyl aromatic hydrocarbons. In view of the ability of the olefins and/or diolefins to displace the vinyl aromatic hydrocarbons and in turn the vinyl aromatic hydrocarbons to displace the olefins and/or diolefins from the silver salt containing phase, the present invention in a particularly useful embodiment provides a dual process whereby vinyl aromatic hydrocarbons may be separated from alkyl aromatic hydrocarbons and olefins and/or diolefins such as isoprene, may be separated from saturated hydrocarbons, etc., using the same solvent solution and, if desired, the same or substantially the same equipment. In addition, conjugated diolefins may be separated from non-conjugated diolefins in this step. Such a dual process comprises (1) contacting a mixture of aromatic hydrocarbons containing vinyl aromatic hydrocarbons and alkyl aromatic hydrocarbons with a substantially anhydrous silver salt selected from the group consisting of silver fluoroborate, silver fiuorosilicate and mixtures thereof, (2) separating first raffinate fraction and a first extract fraction, (3) contacting said first extract fraction with a mixture of hydrocarbons containing olefins and/or diolefins in admixture with saturated hydrocarbons and/or other hydrocarbons or a mixture of conjugated and non-conjugated diolefins, the quantity of said mixture of hydrocarbons being such that the olefins and/ or diolefins are in molar excess to said vinyl aromatic hydrocarbons contained in said first extract fraction, thereby displacing aromatic hydrocarbons from said first extract fraction and forming a second extract fraction comprising said silver salt and unsaturated aliphatic hydrocarbons and a second raffinate fraction comprising the hydrocarbons not absorbed in said second extract fraction and the aromatic hydrocarbons displaced from said first extract fraction, (4) separating said second rafiinate fraction and said second extract fraction and (5) recycling at least a part of said second extract fraction to step (1) above as a substitute for at least a part of said substantially anhydrous silver salt and thereafter continuously repeating the above steps.

DESCRIPTION OF THE DRAWING The accompanying drawing is a diagrammatic representation of a particularly useful and practical method of carrying out the dual process of the present invention.

4 DESCRIPTION OF THE PREFERRED EMBODIMENTS To further describe the above disclosed dual process of the present invention which provides for the separation of vinyl aromatic hydrocarbons from alkyl aromatic hydrocarbons and also for the separation of olefins and/ or conjugated diolefins from non-conjugated diolefins and other hydrocarbons, reference is made to the drawing. With reference to the drawing, an aromatic hydrocarbon mixture containing vinyl aromatic hydrocarbons and alkyl aromatic hydrocarbons is introduced into a liquid-liquid extraction column 10 by means of feed entry line 11. Concurrently with the introduction of the aromatic mixture by line 11, a solvent comprised of a substantially anhydrous silver salt which is either silver fluoroborate, silver fiuorosilicate, or a combination thereof, and an organic solubilizing compound capable of dissolving the silver salt, is introduced into column 10 by means of solvent entry line 12. Lines 11 and 12 are shown intersecting column 10 at a point near but below the top of column 10 and at substantially the same distance from the top of column 10. In this embodiment, lines 11 and 12 should be so arranged that the compositions introduced thereby will intimately co-mingle one with another, almost immediately upon entering column 10. Any arrangement which will accomplish this end may be substituted for that shown in the drawing. To facilitate such co-mingling, it is desirable to provide mechanical means with the column to aid in such co-mingling. Examples of such means are trays, rotating discs, packings, etc. Concurrently with the introduction of the aromatic hydrocarbons via line 11 and solvent via line 12, a saturated aliphatic hydrocarbon of 3 to 15 carbon atoms is introduced into column 10 by means of line 13. This aliphatic hydrocarbon flows upwardly through column 10 countercurrently contacting descending solvent and aromatic hydrocarbon feed. A raffinate phase is continuously taken overhead from column 10 by line 14 through which the raflinate phase is passed to distillation or other recovery means (not shown) whereby the components of the rafiinate are separated. The components of the raflinate in continuous operation include the aliphatic hydrocarbon, the aromatic hydrocarbons not absorbed by the solvent and any unsaturated aliphatic hydrocarbons which were contained in the solvent at the time of its entering column 10 by line 12.

An extract phase is continuously taken from column 10 by line 15. This extract phase, referred to as the first extract phase, contains the silver salt and aromatic hydrocarbons of the feed mixture which go into solution therewith.

The first extract phase is introduced into a second extraction column 16 in which the first extract phase passes downwardly countercurrently contacting upfiowing unsaturated aliphatic hydrocarbons comprised of olefins and/or diolefins and/or other hydrocarbons which enter column 16 by unsaturated hydrocarbon feed line 17, and upfiowing saturated aliphatic hydrocarbons of 3 to 15 carbon atoms which enter column 16 by line 18. A second raffinate phase is continuously taken overhead from column 16 by line 19. This second rafiinate phase is carried by line 19 to distillation or other recovery means (not shown) whereby the components of the second raffinate phase are separated. The components of the second rafiinate phase comprise the saturated aliphatic hydrocarbon, the non-absorbed portion of the unsaturated hydrocarbons, and the aromatic hydrocarbons which were contained in the first extract phase at the time it entered column 16 by line 15.

By means of line 20, an extract phase, referred to as the second extract phase, is removed from column 16 and at least a portion thereof is returned through line 20 to line 12 for re-use in column 10. This second extract phase contains the silver salt and unsaturated aliphatic hydrocarbons absorbed therein.

The solubilizing organic compound used to obtain the substantially anhydrous silver salt solution is found in the first rafiinate phase or in the first extract phase or partially in both phases, depending upon the particular solubilizing organic compound used, the particular components of the feed material, the ratio of the components of the feed material to the solubilizing organic compound and other factors. If a portion of the solubilizing agent is present in the first extract phase, then the solubilizing agent also may be found in the second rafiinate phase, the second extract phase or partially in both. As will be further discussed herein below, consideration should be given to the ease with which the materials of the feeds can be separated from the solubilizing organic compounds in selecting such compounds for dissolving the anhydrous silver salt.

Those skilled in the art will readily appreciate that many modifications of the above-described dual process of the present invention and the arrangement of equipment therefor, may be made. However, so long as such modifications depend upon the principles and concepts above discussed, such modifications may be practiced without departing from the spirit and scope of the present invention.

To further describe and to specifically illustrate the present invention, the following examples are presented. These examples are not to be construed as in any manner limiting the present invention.

Example I Eight grams of a mixture consisting of 4.0 grams of styrene and 4.0 grams of a substantially pure o-xylene, were agitated with approximately ml. of a silver fluoroborate solution at a temperature of 25 C. The silver fiuoroborate solution consisted of 2.04 grams of silver fluoroborate dissolved in 8.0 grams of toluene. The agitation was stopped and a raffinate and extract phase allowed to form. The extract and raffinate phases were then separated. This extract phase was then agitated with 12 grams of petroleum ether and a second extract and rafiinate phase allowed to form. These phases were separated and the second raffinate phase combined with the first raffinate phase to form a total raffinate phase. The second extract phase and the total raflinate phase were each analyzed. The following table represents the weight percent toluene in each phase and the composition on a toluene-free basis of the aromatic hydrocarbon feed, the total rafiinate, and the extract.

TABLE Feed Rafiinate Styrene 50. 0 41. 55 O-xylene 50. 0 58. 45 Toluene 54. 15

Component (wt. percent) The amount of styrene in the extract represents a 116.3% utilization of all of the available silver fluoroborate.

Example 11 Four grams of a mixture containing 2 grams of styrene and 2 grams of substantially pure ethylbenzene, were agitated with approximately 4 ml. of a silver fiuoroborate solution at C. The silver fiuoroborate solution consisted of 1.0 gram of silver fluoroborate dissolved in 5.0

grams sulfolane. On stopping agitation, no phasing oc- TABLE Feed Ratfinate Extract Component (wt. percent) Styrene Ethylbenzene r Extract The amount of styrene in the extract represents a 102.8% utilization of all of the available silver fluoroborate.

Example III The extract (6.6 grams) of Example II was intimately contacted with 3 grams of n-pentene-l to form an extract and a raffinate phase. These phases were separated and the extract phase contacted with an additional 3 grams of n-pentene-l to form a second extract and rafiinate phase. This second extract and raffinate phase was separated and the first and second rafiinate phases combined to form a total raffinate phase. These phases were analyzed for hydrocarbon composition. The following table presents the hydrocarbon composition of the extract from Example II and the extract and total ratfinate formed in this Example III.

Sixteen grams of a mixture containing 8.0 grams of styrene and 8.0 grams of substantially pure o-xylene, were agitated with 8 ml. of a silver fiuoroborate solution at 25 C. The silver fluoroborate solution consisted of 4.0 grams of silver fluoroborate dissolved in 4.0 grams of a mixture of 3.2 grams of sulfolane and 0.8 gram of Water. Agitation was stopped and a raffinate and extract phase allowed to form. These phases were separated and the extract phase agitated with approximately 30 mls. of petroleum ether to form a second extract and raffinate phase. The second raffinate phase was combined with the first raffinate phase to form. a total rafiinate phase which, along with the second extract phase, was analyzed. The following table presents the weight percent o-xylene and styrene in the feed and the extract and rafiinate phases.

The amount of styrene in the extract represents a 47.0% utilization of all of the available silver fluoroborate.

Example V Eight grams of a mixture consisting of 4.0 grams of styrene and 4.0 grams of substantially pure o-xylene, were agitated with approximately 10 mls. of a silver fluoroborate solution at 25 C. The silver fiuoroborate solution consisted of 2.0 grams of silver fiuoroborate dissolved in a mixture of 6.4 grams of sulfolane and 1.6 grams of water. Agitation was stopped and a raffinate and extract phase allowed to form. The extract and raffinate phases were separated and the extract phase agitated with petroleum ether to form second extract and raffinate phases. The second raffinate phase was combined with the first raffinate phase to form a total raffinate phase and this total ratfinate phase and second extract phase were analyzed. The following table presents the weight percent of styrene and o-xylene in the extract and raifinate phases.

The amount of styrene in the extract represents a 14.0% utilization of all of the available silver fluoroborate.

A comparison of Examples I, II, IV and V with respect to the efficiency of utilization of the silver fluoroborate clearly illustrates the importance of using a substantially anhydrous silver salt in the practice of the present invention. While the use of silver salt solvent solutions containing water does bring about the desired separation, the quantity of silver salt required to separate and recover a given quantity of styrene becomes much greater as the water content increases. Comparison of Examples IV and V also indicates the effect of concentration of the silver salt. The higher the concentration, the more effectively the silver salt is utilized.

The silver salts used in the process of the present invention include silver tetrafluoroborate, more commonly known as silver fluoroborate, and silver tetrafluorosilicate, more commonly known as silver fluorosilicate. These silver salts may be used alone or in combination. The preferred silver salt is the silver fluoroborate.

By substantially anhydrous as used herein, is meant a silver salt in admixture With or containing less than 15% by weight of water in admixture with the silver salt. Most often, the substantially anhydrous silver salt contains less than 10% Water, preferably, less than by weight.

In utilizing the silver salt in solution with an organic solubilizing agent, the silver salt solution will contain the silver salt in a concentration of to 90% by weight of the solution. Preferred, however, are concentrations of to 60% by weight.

In carrying out the process of the present invention, most often about 0.2 to 20 parts by weight of silver salt per part by weight of vinyl aromatic hydrocarbons the aromatic hydrocarbon mixture to be separated are employed. Preferably, however, the amount of silver salt used is Within the range of 0.5 to 10 parts by weight per part by weight of vinyl aromatic hydrocarbons.

When olefins and/or diolefins are employed to displace the vinyl aromatic hydrocarbons from the silver salt containing extract or the process of the present invention is operated as a dual process, as above described, it is generally desirable that the amount of olefins and/or diolefins contacted with the vinyl aromatic hydrocarbon silver salt containing extract be in weight ratio to the silver salt within the range of from 5:1 to 70:1, preferably within the range of from 10:1 to :1. Within these ranges, however, it is necessary that the amount of olefin and/or diolefin employed always be greater on a molar basis, than the amount of vinyl aromatic hydrocarbons contained in the silver salt containing extract.

The organic solubilizing agents useful in the practice of the present invention include aromatic hydrocarbons, non-aromatic unsaturated hydrocarbons and oxygenated compounds. The aromatic hydrocarbons useful as solubilizing agents may contain a single aromatic ring or may contain two or more aromatic rings, either condensed or noncondensed. In addition, the aromatic hydrocarbons may have substituents to the ring or may be condensed with one or more other ring structures which are paraffinic or olefinic in nature. Non-limiting examples of aromatic hydrocarbons suitable as solubilizing agents in the practice of the present invention are benzene, toluene, the xylenes, various other polymethylbenzenes, such as mesitylene, isodurene, tri-, tetra-, penta-, and hexamethylbenzenes; ethylbenzene and the various poly ethylbenzenes, isopropylbenzene, propylbenzene and the various polyisopropyl and polypropyl benzenes, the various butyl and pentyl benzenes and the like; the substituted benzenes containing two or more different substituents such as ethyltoluene isopropyltoluene and ethylxylenes; the various methylnaphthalenes, and polymethylnaphthalenes, ethylnaphthalene and the various polyethylnaphthalenes, the naphthalenes containing propyl, isopropyl, butyl, and pentyl substituents; the substituted naphthalenes containing two or more different substituents such as methylethyl naphthalene, methylpropyl naphthalene, and the like; the various indanes such as methylindane, ethylindanes, isopropylindanes, and the like; the dihydronaphthalenes such as methyl, ethyl, propyl, and butyl substituted dihydronaphthalenes; the tetrahydronaphthalenes such as methyl, ethyl, propyl, and pentyl substituted tetrahydronaphthalenes and the like; the vinyl aromatic hydrocarbons such as styrene, alpha-methyl styrene, vinyl toluene, and the like. In the preferred practice of the present invention utilizing aromatic hydrocarbons as the solubilizing agent for the silver salt, the aromatic hydrocarbons are the mononuclear aromatics containing 6 to 12 carbon atoms. The substituents to such aromatic hydrocarbons may be straight-chain, branched chain or cyclic and may be saturated or unsaturated.

The non-aromatic unsaturated hydrocarbons useful in practicing the present invention include olefins, both acyclic and alicyclic, and diolefins. Among the acyclic olefins useful as solubilizing agents are such compounds as hexene-l, hexene-Z, methylhexenes, dimethylhexenes, heptenes, methylheptenes, dimethylheptenes, ethylheptenes, nonenes, methylnonenes, dimethylnonenes, ethylnonenes, methylethylnonenes, diethylnonenes, propylnonenes, decenes, ethyldecenes, dimethyldecenes, methyldecenes, diethyldecenes, methylethyldecenes, propyldecenes, dipropyldecenes, methylpropyldecenes, and the like on up to and including such acyclic compounds having 15 carbon atoms. The alicyclic olefins useful in the practice of the present invention include such compounds as cyclohexene, methylcyclohexene, dimethylcyclohexenes, ethylcyclohexenes, cycloheptene, methylcycloheptene, dimethylcycloheptenes, ethylcycloheptenes, diethylcycloheptenes, methylethylcycloheptenes, cyclooctene, methylcyclooctene, dimethylcyclooctenes, trimethylcyclooctenes, ethylcyclooctene, and the like up to and including alicyclic olefins having up to 10 carbon atoms in one or more substituents to the ring. In addition, such alicyclic olefins as those containing two or more rings in which only one of the rings contains olefinic unsaturation may be used as a solubilizing agent in the practice of the present invention. The diolefinic hydrocarbons useful as solubilizing agents include both the cyclic and noncyclic diolefinic hydrocarbons and include such compounds as pentadienes, hexadienes, heptadienes, octadienes, on up to and including those containing as high as 15 carbon atoms and higher. These diolefins include both those having no substituents as well as those having one or more alkyl substituents. In the preferred practice of the present invention utilizing non-aromatic unsaturated hydrocarbons as the solubilizing agent for the silver salt, olefin hydrocarbons of 6 to 15 carbon atoms are employed. These may be either cyclic or non-cyclic.

The oxygenated compounds which may be used as solubilizing agents in the practice of the present invention include ethers, ketones, alcohols, glycols, sulfones and the like. The ethers useful include acylic ethers, alicyclic ethers, aryl ethers and alkyl aryl ethers. The acyclic ethers include such compounds as diethyl ether, di-npropyl ether, di-n-butyl ether, di-isopropyl ether, di-isobutyl ether, di-tert-butyl ether, di-n-octyl ether and the like. Among the alicyclic ethers are such compounds as tetrahydrofuran, 1,4-dioxane, 1,3-dioxane, alkyl-substituted ethylene oxides, and the like. Useful aryl and alkyl aryl ethers include such compounds as diphenyl ether, ditolyl ether, methyl phenyl ether, methyl tolyl ether and the like.

Among the ketones useful in the practice of the present invention are the alkyl ketones such as dimethyl, diethyl, di-n-propyl, di-n-butyl, di-n-pentyl, di-n-hexyl and corresponding di-iso-alkyl or mixed iso-normal alkyl ketones. Particularly useful among the ketones are those in which the alkyl radicals contain 1 to 6 carbon atoms. Among this useful group are such compoundsas dimethyl, diethyl, di-nand isopropyl, di-n-, iso-, and sec-butyl, di-n-, iso-, and sec-pentyl ketone, di-n-, iso-, hexyl ketone, etc.

The alcohols useful as solubilizing agents in carrying out the present invention include the acyclic, alicyclic, and the aryl alcohols. Several nonlimiting examples of such alcohols are methyl alcohol, ethyl alcohol, cyclohexanol, benzyl alcohol and the like. When using alcohols as solubilizing agents, it is usually somewhat preferred to use those having no geater than 8 carbon atoms with the acyclic alcohols being somewhat preferred over the alicyclic and aryl alcohols. Particularly useful are nonaromatic alcohols having 1 to 6 carbon atoms and including such alcohols as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol and the isomeric butyl alcohols.

The glycols useful in the practice of the present invention are most often those having 2 to 6 carbon atoms. Several non-limiting examples of such alcohols are ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, and the like. Particularly useful, are such glycols as ethylene glycol and propylene glycol and other such glycols containing 2 to 4 carbon atoms.

Another useful group of oxygenated compounds useful as solubilizing agents in the practice of the present invention are the sulfones. Within this group are both the alkyl and aryl sulfones. Particularly useful are the aryl sulfones such as tetramethylene sulfone (sulfolane) and its alkyl substituted derivatives wherein the alkyl group or groups has 1 to 6 carbon atoms.

The aromatic hydrocarbon mixture containing vinyl aromatic hydrocarbons and alkyl aromatic hydrocarbons which is to be separated in accordance with the present invention generally is contacted with the silver salt at a temperature within the range of -30- to 70 C., preferably -20 to 50 C. Pressure does not appear to be critical in the separation and recovery of the vinyl aromatic hydrocarbons by means of the substantially anhydrous silver salt. Therefore, the pressure at which the process of the present invention is operated is generally based upon practicality.

The period of contact of the aromatic hydrocarbon mixture to be separated with the silver salt may be very short. As a practical matter, the period of contact will vary considerably depending upon the elliciency of the means employed for contacting the aromatic hydrocarbons with the silver salt. The determination of the optimum periods of contact are well within the ability of those skilled in the art and thus require no discussion herein.

When the process of the present invention is operated as a dual process and olefins and/ or diolefins are used to displace and recover the vinyl aromatic hydrocarbons from the silver salt, the same conditions as to temperatures, pressures and contact time may be used as are used for contact of the aromatic hydrocarbons with the silver salt.

It has been found particularly useful in carrying out the process of the present invention to use saturated aliphatic hydrocarbons of 3 to carbon atoms per molecule to aid in separating aromatic hydrocarbons which are not absorbed by the silver salt from such silver salt. As noted above, the use of the saturated aliphatic hydrocarbons of 3 to 15 carbon atoms greatly facilitates the formation of an extract and rafiinate phase and thereby considerably simplifies the present separations process. Non-limiting examples of such hydrocarbons are propane, n-butane, npentane, n-hexane, n-heptane, n-octane, n-nonane, ndecane, n-undecane, n-dodecane, n-tridecane, isobutane, isopentane, isoheptanes, isodecanes, isododecanes, isotridecane, cyclopentane, cyclohexane, methylcyclohexane, cycloheptane, and the like. Most often, the saturated aliphatic hydrocarbons are paraffinic hydrocarbons and may be straight-chain or branched-chain. Petroleum ether is a very practical and useful fraction for use in the present process. The most useful saturated aliphatic hydrocarbons are the parafiinic hydrocarbons of 4 to 7 carbon atoms per molecule.

The amount of saturated aliphatic hydrocarbons of 3 to 15 carbon atoms used in the process of the present invention may vary considerably. The actual amount of such aliphatic hydrocarbons used will depend to a large extent on the amount of alkyl aromatic hydrocarbons in the aromatic hydrocarbon mixture and the degree of separation desired, etc. Usually, however, about 0.5 to 10 volumes of saturated aliphatic hydrocarbon will be used per volume of alkyl aromatic hydrocarbon in the aromatic hydrocarbon feed mixture to be separated. Preferably, however, about 1 to 3 volumes of the saturated aliphatic hydrocarbon will be used per volume of alkyl aromatic hydrocarbons in the feed mixture.

In employing the saturated aliphatic hydrocarbons of 3 to 15 carbon atoms to remove unabsorbed alkyl aromatic hydrocarbons from the silver salt, these aliphatic hydrocarbons may be contacted with the mixture of silver salt and aromatic hydrocarbons absorbed therein after the initial contact and agitation of the aromatic hydrocarbon feed with the silver salt has ceased or the saturated aliphatic hydrocarbon may be brought into contact with the silver salt simultaneously with the aromatic hydrocarbon feed which is to be separated. Further, the saturated aliphatic hydrocarbon may be introduced concurrently with the aromatic hydrocarbon mixture to be separated and into countercurernt contact with the silver. Instead, however, the saturated aliphatic hydrocarbons may be contacted countercurrently with the aromatic hydrocarbon mixture to be separated and the silver salt.

The aromatic hydrocarbon mixtures which may be separated in accordance with the present invention are those containing vinyl aromatic hydrocarbons and alkyl aromatic hydrocarbons. While the hydrocarbons, it is most practical for the separation of aromatic hydrocarbon mixtures containing vinyl aromatic hydrocarbons and alkyl aromatic hydrocarbons within the C to C range. The present invention is particularly useful and practical for the separation of styrene from close boiling o-xylene and for the separation of a-methylstyrene and/ or vinyl toluene from close boiling alkyl aromatic hydrocarbons.

The olefins and/or diolefins useful in displacing absorbed vinyl aromatic hydrocarbons from the silver salt are preferably those containing 2 to 8 carbon atoms per molecule though those having higher numbers of carbon atoms may be used. These olefins and/or diolefins may be in relatively pure state or may be in admixture with other hydrocarbons such as paraffins, naphthenes or even alkyl aromatic hydrocarbons. Additionally, the present invention provides a means for separating conjugated diolefins from non-conjugated diolefins since the conjungated diolefins are preferentially absorbed in the silver salt solution. Therefore, mixtures of these diolefins may be employed. In choosing the olefin or diolefin or a mixture of such unsaturated compounds with one another or with saturated compounds to be used for displacing the vinyl aromatic hydrocarbons, care should be taken that these compounds are not so similar in boiling point or so capable of forming an azeotope with the vinyl aromatic hydrocarbons as to present new separation problems in recovering the vinyl aromatics. While the olefins and/or diolefins may be cyclic, straight-chain or branched-chain in structure, it is preferable that they be straight or branched-chain. When the present invention is operated with a C to C aromatic hydrocarbon feed mixture containing vinyl aromatic hydrocarbons, isoprene or other conjugated diolefins of 5 to 7 carbon atoms are particularly useful.

What is claimed is:

1. A process for the separation of vinyl aromatic hydrocarbons from aromatic hydrocarbon mixtures containing vinyl aromatic hydrocarbons, in admixture with alkyl aromatic hydrocarbons, which comprises contacting said aromatic hydrocarbon mixture with a substantially anhydrous silver fluoroborate, separating an extract fraction containing said silver fluoroborate and the aromatic hydrocarbons in solution therewith, and a raffinate fraction containing aromatic hydrocarbons not in solution 11 with said silver fluoroborate, and recovering from said extract fraction an aromatic hydrocarbon fraction substantially richer in vinyl aromatic hydrocarbons than the initial aromatic hydrocarbon mixture.

2. The process of claim 1 wherein the substantially anhydrous silver fluoroborate is in solution with an organic solubilizing agent, the amount of silver fluoroborate in said solution being within the range of to 90% by weight of said solution.

3. The process of claim 1 wherein the amount of silver fiuoroborate contacted with said aromatic hydrocarbon mixture is such as to cause a ratio by weight of silver fiuoroborate to vinyl aromatic hydrocarbons in said aromatic hydrocarbon mixture within the range of about 0.2:1 to 20: 1.

4. The process of claim 1 wherein the aromatic hydrocarbon mixture is one containing vinyl aromatic hydrocarbons and alkyl aromatic hydrocarbons within the C to C range.

5. The process of claim 1 wherein the aromatic hydrocarbon mixture is contacted with the silver fluoroborate at a temperature within the range of 30 to 70 C.

6. The process of claim 1 wherein the mixture resulting from the contacting of the aromatic hydrocarbon mixture with the silver fluoroborate is contacted with a saturated aliphatic hydrocarbon of 3 to carbon atoms.

7. The process of claim 6 wherein about 0.5 to 10 volumes of said saturated aliphatic hydrocarbon is used per volume of alkyl aromatic hydrocarbon in the aromatic hydrocarbon mixture which is contacted with the silver fluoroborate.

8. The process of claim 6 wherein the saturated aliphatic hydrocarbon is a non-cyclic parafiinic hydrocarbon of 4 to 7 carbon atoms per molecule.

9. The process of claim 1 wherein said aromatic hydrocarbon fraction substantially richer in vinyl aromatic hydrocarbons than the initial aromatic hydrocarbon mixture is recovered from said extract fraction by contacting said extract fraction with an amount of an unsaturated aliphatic hydrocarbon selected from the group consisting of olefins and conjugated diolefins such that said unsaturated aliphatic hydrocarbon is in molar excess to the vinyl aromatic hydrocarbons contained within said extract fraction.

10. A process for the separation of vinyl aromatic hydrocarbons from alkyl aromatic hydrocarbons and unsaturated aliphatic hydrocarbons selected from the group consisting of olefins and conjugated diolefins from mixtures of such unsaturated hydrocarbons with other hydrocarbons which comprises (1) contacting a mixture of aromatic hydrocarbons containing vinyl aromatic hydrocarbons and alkyl aromatic hydrocarbons with substantially anhydrous silver fluoroborate, (2) separating a first raffinate fraction containing the nonabsorbed aromatic hydrocarbons and a first extract fraction containing the silver fluoroborate and the aromatic hydrocarbons in solution therewith, (3) contacting said first'extract fraction with a mixture of hydrocarbons containing unsaturated aliphatic hydrocarbons selected from the group consisting of olefins and conjugated diolefins, the quantity of said mixture of hydrocarbons being such that said unsaturated aliphatic hydrocarbons contained in said first extract fraction, thereby displacing the aromatic hydrocarbons absorbed in said first extract fraction and forming a second extract fraction comprising said silver fluoroborate and said unsaturated aliphatic hydrocarbons in solution therewith and a second ratfinate fraction comprising the hydrocarbons not in solution with said silver fluoroborate and the aromatic hydrocarbons displaced from said first extract fraction, (4) separating said second r'aflinate fraction and said second extract fraction,and (5) recycling at least a part of said second extract fraction to step (1) above as a substitute for at least a part of said silver fluoroborate and thereafter continuously repeating the above steps.

References Cited UNITED STATES PATENTS 2,391,404 12/1945 Friedman et a1. 260--669 XR 2,458,067 1/ 1949 Friedman et a1. 260-669 XR 3,427,362 2/ 1969 Beckham et a1. 260-674 DELBERT E. GANTZ, Primary Examiner C. R. DAVIS, Assistant Examiner US. Cl. X.R. 260-669

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