US3703473A - Sequestering agents for metal ion contamination of alkyl-aromatic hydrocarbons - Google Patents

Abstract

METAL ION CONTAMINATION IN ALKYL-AROMATIC HYDROCARBONS, SUCH AS TRACE AMOUNTS OF IRON IN P-XYLENE, IS SEQUESTERED WITH A SYNERGISTIC MIXTURE OF AGENTS. THIS MIXTURE CONTAINS A PHOSPHORUS HALIDE PLUS AN ORGANIC PHOSPHATE. SUCH SEQUESTRATION PERMITS SUCCESSFUL SIDE-CHAIN HALOGENATION OF EVEN VISIBLY CONTAMINATED HYDROCARBONS. THE ORGANIC PHOSPHATE IS PROVIDED BY AN ARYL PHOSPHATE, AN ALKYL PHOSPHATE, OR THEIR MIXTURES.

Description

United States Patent ABSTRACT OF THE DISCLOSURE Metal ion contamination in alkyl-aromatic hydrocarbons, such as trace amounts of iron in p-xylene, is sequestered with a synergistic mixture of agents. This mixture contains a phosphorus halide plus an organic phosphate. Such sequestration permits successful side-chain halogenation of even visibly contaminated hydrocarbons. The organic phosphate is provided by an aryl phosphate, an alkyl phosphate, or their mixtures.

CROSS-REFERENCE TO RELATED APPLICATION This application is a divisional application of Ser. No. 561,340, filed June 29, 1966, now Pat. No. 3,580,854.

This invention relates to a combination of sequestering agents for metal-ion-contaminated, alkyl-aromatic hydrocarbons, and additionally relates to a process for sequestering such contamination and to compositions resulting therefrom.

Heretofore it has been known that trace amounts of substances such as ferric halides, acting as Lewis acids, form ions during the halogenation of benzene, e.g., the tetrachloroferrate anion from ferric chloride, and thereby catalyze ring halogenation. Similarly it has been disclosed in U.S. Pat. No. 2,994,653 that in order to avoid ring chlorination of alkylaromatic hydrocarbons such as xylenes, side chain chlorination must be carried out in the absence of metallic ions, or by first sequestering such ions, and particularly those formed from iron, aluminum, and zinc. For convenience, all such substances and/or their respective ions are generally referred to herein as metal ion contaminants.

US. Pat. No. 2,994,653 further teaches that these ions, in amounts up to 4 p.p.m., for example, in the xylenes, can be effectively sequestered with an aryl phosphate or an alkyl phosphate. In my co-pending application, Ser. No. 543,819, now US. Pat. 3,350,467, it has been shown that contaminating metal ions in xylene can be sequestered by using phosphorous chlorides or phosphorous bromides, thus permitting side chain chlorination or bromination.

It has now been found that these phosphorous halides when used in conjunction with the previously disclosed aryl phosphates or alkyl phosphates produce a synergistic sequestration of the metal ion contamination, providing an unexpected enhancement in the amount of side chain halogenation, and a virtual elimination of ring chlorination. Moreover, the joint use of these sequestering agents combines the desirably low volatility of the organic phosphates with the attractive economy of the phosphorous halides.

Additionally where side chain cleavage of alkyl radicals from the aromatic nucleus is promoted by such contamination during halogenation at elevated temperature, such cleavage is effectively suppressed by the sequestrant combination. Dissolved or entrained oxygen can hinder the activity of the catalyst, as can water, thereby slowing the reaction rate. The phosphorous halide portion of the sequestrant can desirably retard the action of gaseous oxy- Patented Nov. 21, 1972 gen contained in the xylene and additionally can dehydrate the xylene, thereby reducing to eliminating the effect of water contamination.

Broadly, the present invention is directed to a sequestering agent for metal ion contaminants contained in an alkyl-aromatic hydrocarbon, which sequestering agent comprises a mixture of phosphorous halide with organic phosphate, i.e., aryl phosphate, alkyl phosphate, or their mixtures, where the halogen in the phosphorous halide has atomic weight between about 35-80.

One aspect of the invention is a composition comprising a metal-ion-contaminated, alkyharomatic hydrocarbon, a phosphorous halide, and an organic phosphate, where the hydrocarbon contains a sequestering amount of the phosphorous halide plus organic phosphate.

Another aspect of this invention is the method of sequestering metal ion contamination in an alkyl-aromatic hydrocarbon which comprises mixing such hydrocarbon with a sequestering amount of an organic phosphate and phosphorous halide.

A still further aspect of the invention is directed to a method of halogenating alkyl-aromatic hydrocarbon contaminated with metal ions, which method comprises chemically reacting, under catalytic influence, the hydrocarbon with chlorine or bromine in the presence of phosphorous halide and an organic phosphate.

The suppression of side chain cleavage of alkyl groups from the aromatic nucleus, e.g., cleavage of methyl groups from xylene, is usually referred to hereinafter as the suppression of either chlorinolysis, for such cleavage during chlorination, or of brominolysis, for cleavage during bromination. As disclosed hereinabove and as specified in the claims, the halogen of the phosphorous halide, as Well as the halogen for reaction with the alkyl-aromatic hydrocarbon, has atomic weight between about 35-80, i.e., chlorine and/ or bromine. Thus, it is to be understood that the use of the term halogen in the specification is employed for convenience to refer to chlorine and/or bromine, and the term halogenation to conveniently refer to reacting chlorine and/or bromine.

Also, the expression phosphorous halide sequestering agent is meant to include phosphorous trichloride, phosphorous pentachloride, phosphorous bromide, phosphorous pentabromide, and their mixtures. For efficiency these agents are preferably used in their commercially available, essentially anhydrous form since addition with solvents such as water can retard the initiation of halogenation. Phosphorous trichloride is the preferred phosphorous halide for economy as well as efiiciency.

Organic phosphate as emyployed in the specification and claims is intended to refer broadly to compounds of the structure:

wherein R R and R are selected from the group conchlorophenyl, 2bromophenyl, and Z-chloronaphthyl radicals, hydroxyalkyl radicals, e.g., 2 hydroxyethyl, dihydroxypropyl, and trihydroxyoctyl radicals. An aryl phosphate is intended to refer broadly to the structure set forth above wherein at least two of the R groups are aryl, hydroxyaryl, haloaryl, or their mixtures. Further, an alkyl phosphate is intended to refer broadly to the above structure wherein at least two of the R groups are alkyl, hydroxyalkyl, or their mixtures.

As used herein, the term alkyl-aromatic hydrocarbon is meant to include hydrocarbons having an aromatic ring which contains one or more methyl, ethyl, propyl, isopropyl, vinyl, propenyl, chloroor bromomethyl, chloroor bromoethyl, or like radical, also referred to herein as side chains; generally such side chains are lower alkyl, i.e., have 8 carbon atoms or less. The hydrocarbons can, in addition to having partial side chain halogenation, have partial to complete ring halogenation (needing suppression of further ring halogenation and/or side chain cleavage) such as a,m'-2-trichloro-p-xylene and a,ot'2,4,5,6 hexachloro-m-xylene.

Further illustrative alkyl-aromatic hydrocarbons are: ortho-, meta-, and para-xylene, toluene, durene, rnesitylene, e'thylbenzene, diethylbenzene, triethylbenzene, diiso propylbenzene, and cymene. For convenience, all of these substances are also referred to herein simply as hydrocarbons or as hydrocarbon compounds. Also, the general term xylene is used herein for convenience to refer to any of the three structurally different types of xylene as well as to any mixture of two or more of such types.

Thus the alkyl-arotnatic hydrocarbons are those which are halogen-free, or have partial halogenation but are capable of further side chain halogenation. This latter group consists of compounds possessing some side chain halogenation, with partial (or without any) ring halogenation, compounds that are partly ring halogenated but are free from side chain halogenation, for example 4,6-dibromo-rn-xylene, and compounds which are exhaustively ring halogenated. These latter compounds can have some side chain halogenation, e.g., a 2,3,5,6-heptachloro-pxylene.

Of these compounds, those which are halogen free, and those which have some side chain halogenation but no ring halogens such as a,a-dichloro-p-xylene, generally become contaminated by contact with dust, dirt, or metallic containers or feed lines and accumulate minute amounts of metal ion contamination, i.e., typically between about 0.125 ppm. or more of contaminants, but usually less than about 0.01 weight percent. The partly ring halogenated materials having some, or having no side chain halogens, are usually prepared in the presence of contamination to catalyze ring halogenation. However, such a reaction usually yields a mixture, and upon separation of one or more reaction products from the mixture these products become substantially isolated from the catalyst. Thus these compounds often possess less than about one weight percent, and usually less than about 0.1 weight percent, of contamination. Hydrocarbons having exhaustive ring halogenation, as well as unpurified mixtures of partially ring halogenated hydrocarbons, often contain materials used to catalyze ring halogenation, which are contaminants in amounts up to about weight percent or more.

Broadly, for efiective sequestration of the contaminants a sufficient amount of phosphorous halide plus organic phosphate is used to prepare a composition containing from about 0.01 to about 5 weight percent of phosphorous, based on the weight of the hydrocarbon. To enhance suppression of contaminants, sequestered compositions should usually have enough of the sequestering agents for the composition to contain at least about 0.01 weight percent of phosphorous; generally, it is uneconomical to prepare compositions having sequestering agents in such amounts that the composition contains more than about 5 weight percent of phosphorous. More particularly, halogen-free material such as rn-xylene, and those having some side chain halogenation but no ring halogens, both of which usually have less than about 0.01 weight percent contamination, advantageously contain, for economy, a combination of sequestering agents such that from about 0.01 to about 3 weight percent of phosphorous is present in the material. Additionally, although exhaustively ring halogenated compounds often contain about 5 weight percent or more of contaminants, only side chain cleavage is the deleterious reaction to be suppressed. Thus these compounds, like halogen-free materials, advantageously contain, for economy, a combination of sequestering agents such that from about 0.01 to about 3 Weight percent of phosphorous is present in the compound.

Partly ring halogenated substances possessing little or no side chain halogenation and which, through separation from a reaction mixture, typically have less than about 0.1 weight percent of contamination, are advantageously admixed, for economy, with a combination of sequestering agents so that from about 0.01 to about 4 weight percent of phosphorous is contained in such substances. Thus, those substances wherein up to about 5 weight percent of phosphorous is contained therein, are most often the unpurified mixtures of partially ring halogenated hydrocarbons.

Generally the sequestering agents are employed to provide a molar proportion of phosphorous halide to organic phosphate between about 10:1 and about 1:10. A combination of sequestering agents having a molar proportion of phosphorous halide organic phosphate of greater than about 10:1 usually will not provide sufiicient organic phosphate to obtain enhanced suppression of ring halogenation, compared to the use of phosphorous halide alone. A combination of sequestering agents containing a molar proportion of phosphorous halide to organic phosphate of less than about 1:10 can be uneconomical. Advantageously, for enhanced economy with excellent suppression of ring halogenation, the sequestering agents are used to provide a molar proportion of phosphorous halide to organic phosphate of between about 5:1 to about 2:1.

Halogenation of these hydrocarbon compounds is typically carried out in a steel reactor or one formed from iron or other conventional material, and these are lined, e.g., with a glass liner, to prevent any contaminating contact between the metal reactor and the reaction medium. The reactor is equipped, typically, with agitation means, halogen inlet means, hydrocarbon inlet, temperature control means, and product outlet. If desired, several reactors can be sequentially arranged particularly in the prep aration of hydrocarbons containing more than one halogen per side chain, with essentially only the first halogen being chemically reacted with each side chain in the initial reactor.

Since a liquid reaction medium free from solid portions of alkyl-aromatic hydrocarbon is advantageous to promote the rate of halogenation, reactions are usually carried out at a temperature above the melting point of the hydrocarbon at the pressure of the reaction. For halogenation at temperatures below the hydrocarbon melting point, a liquid dispersant can be used in sufficient amount to prepare a liquid reaction medium, and the solid hydrocarbon dispersed therein. The halogenation generally is carried out at temperatures within the range from about 10 to about 350 C. Although halogenation can be exothermic, reaction temperatures are generally maintained above about 10 C. to promote reaction rates, and advantageously to further enhance reaction rates are maintained above about 40 C. For economy, halogenation temperatures are advantageously not in excess of about 350 C.

Low halogenation temperatures, i.e., about 10 to about C., are usually employed at the outset in reacting halogen-free hydrocarbons. This initial use of low temperatures retards deleterious side reactiions, e.g., condensation of xylene forming diphenylmethane derivatives, although initial temperatures as high as about C. can be employed when halogenating xylene, without uneconomical formation of side reaction products, when continuous, careful control is exercised over reactant feed rates and the reaction temperature.

As halogenation proceeds, these side reaction problems abate and reaction temperatures can be increased to promote the rate of halogenation without enhancing the rate of side reactions. For example in the halogenation of xylene, after the reaction of about 0.5-3 moles of halogen per mole of xylene, but before more exhaustive xylene halogenation is conducted, the reaction temperature can be elevated to between about 170-250 C. For partially ring halogenated hydrocarbons having partial to no side chain halogenation or for hydrocarbons having exhaustive ring halogenation, where chlorinolysis or brominolysis is an important deleterious side reaction, elevated temperatures, e.g., above about 150 C., can nevertheless be employed at the'outset without'promoting deleterious condensation side reactions. For example u,a',2,4,5,6h6Xachloro-m-xylene can be efiectively chlorinated to a,a,a',a', 2,4,5,6 octachloro-m-xylene at a temperature between about 215-235 C. with concomitant suppression of chlorinolysis.

In exhaustive halogenation, e.g., in the preparation of t,06,0t,0L',OL',0t'-h6XflCh1OIO-P-XY16I1C from p-xylene, separate reactors can be used for sequential chlorination from the initial p-xylene. Such reactors can be separately main tained at different temperatures, i.e., a low temperature reactor can be used for initial chlorination of p-xylene with about 0.5-3 moles of chlorine to thus prepare a substantial amount of a,a-dichloro-p-xylene, and so on.

Although subatmospheric, atmospheric or higher pressure can be used, where gaseous halogens are employed for a part to all of the halogenation (as opposed to employing essentially all solid or liquid halogenating agent, e.g., sulphuryl chloride or liquid bromide) a pressure above atmospheric is advantageously used to promote the solubility of the gaseous halogen in the reaction mixture. For chlorination, gaseous chlorine is preferred for economy and advantageously the reaction is carried out at a pressure between about 3 to about 45 p.s.i.g. Pressures below about 3 p.s.i.g. do not generally promote rapid solubility of the gaseous chlorine in the reaction medium whereas pressures above about 45 p.s.i.g. are usually not economical. If desired, the gaseous chlorine can be diluted with an inert gas such as nitrogen, e.g., to assist in controlling the rate of chlorination.

Catalysis of the halogenation is essential and can be initiated by any conventional free radical initiator such as an actinic light source, thermal initiation, or by the addition of a conventional free radical initiating chemical such as benzoyl peroxide. Preferably, for economy and efficiency a visible light source is used with any sequestrant. Such a source can be a mercury vapor lamp which can be maintained in a cooled immersion well, fluorescent lamps either white, blue, black or clear, or unfrosted incandescent lamps.

In addition to simply employing the hydrocarbon for the reaction medium, such hydrocarbon can be dispersed in suitable liquid dispersant, i.e., one which is unreactive to the halogen, such as carbon tetrachloride, benzene, or acetic acid. Where the dispersant is used to dissolve hydrocarbons which are not readily soluble, the resulting reaction medium can be preponderantly liquid dispersant, e.g., up to 95 volume percent or more carbon tetrachloride solvent can be used to dissolve a balance of a,a',2,3, 5,6-hexachloro-p-xylene. During elevated temperature halogenation, i.e., above the boiling point of the diluent at the pressure of the reaction, any vaporized diluent can be condensed and recycled back to the reaction medium, or some to all of this vapor loss can be made up by a fresh feed of diluent to the reaction medium.

In reaction, the halogenation is normally carried out to completion as determined by evolution of the desired amount of hydrogen halide. The product desired will dictate the amount of halogen to be added in view of the fact that essentially the stoichiometric amount or a slight excess is normally used. A substantial excess of halogen may be advantageous in certain instances where a highly halogenated material is desired, as in the chlorination of p-xylene to O6,d,a,ot',0t',Ot'-heXaCh1OIO-P-XylI16. However, by employing less than the theoretical amount of halogen required, over-halogenated products will be substantially avoided such as the formation of a,a,a-trichloro-p-xylene in the chlorination of p-xylene to produce a,a-dichlorop-xylene.

During elevated temperature halogenation, i.e., above the boiling point of any agent in the sequestrant combination at the pressure of the reaction, sequestering agents which fume from the reaction medium can be replaced by feeding fresh sequestrant to such medium. When the desired halogenation is terminated, removal of virtually all sequestrant from the reaction product can generally be accomplished by crystallizing out halogenated product and decanting the sequestering agents with the mother liquor. Alternatively the phosphorus halide sequestrant can be removed from the halogenated product by extraction with a suitable solvent such as water and the reaction product then isolated through distillation, preferably at reduced pressure for efiiciency, to remove the organic phosphate.

The following examples show ways in which the invention has been practiced, but should not be construed as limiting the invention. In the examples all parts are parts by weight and all degrees are in degrees centigrade unless otherwise specified. The dichloro-p-xylene of the examples is a,ot-dichloro-p-xylene, and the hexachloro-pxylene is a,a,a,a',ct,a-hexachloro-p-xylene.

In the examples, solution A is filtered p-xylene containing, after filtration, about 0.1 p.p.m. iron. Solution B is a more highly iron contaminated solution prepared by dissolving ferric chloride into distilled p-xylene, with agitation, and allowing the solution to stand for two days followed by filtering to remove insolubles. Solution B contains 20 p.p.m. iron.

The iron content of these solutions is determined by the thiocyanate test method described in Colorimetric Determinations of Traces of Metals, by E. B. 'Sandel-l, vol. III, 1950, page 363. Ring chlorination, production of dichloro-p-xylene, and production of hexachloro-p-xylene, all expressed in mole or weight percent of respective product, are determined by analysis of each product by total area vapor phase chromotography.

Example 1 A reaction mixture containing about 3.1 p.p.m. iron is prepared from 84.9 parts of solution A mixed with 15.1 parts of solution B and the resulting mixture is nominated as portion C. A second reaction mixture, designated as portion D and containing about 3.2 p.p.m. iron is made from 83.9 parts of solution A mixed with 16.1 parts of solution B. A third reaction mixture containing about 5.1 p.p.m. iron is prepared from 74.9 parts of solution A mixed with 25.1 parts of solution B, and the mixture thus prepared is designated portion E, and a third reaction mixture containing about 7.1 parts p.p.m. iron is prepared from 64.8 parts of solution A mixed with 35.2 parts of solution B and the resulting mixture is separated into two aliquot portions F and G. sequestering agents are admixed with all portions C, D, E, F and G as shown in the tables below. Each portion is then separately treated at atmospheric pressure by first heating to a temperature of and then chlorinating, while catalyzed by a 22-watt fluorescent lamp, by passing gaseous chlorine into the reaction mixture until 1.8 moles of chlorine are reacted per mole of p-xylene, as measured by the amount of hydrogen chloride evolved. Dichloro-p-xylene product determinations are run on the reaction mixtures C, D, and E and the determinations are set forth in Table 1 below.

Thereafter, portions F and G are further chlorinated by passing gaseous chlorine into the reaction mixture,

accompanied by heating through a temperature gradient of 85-135 i.e., the initial temperature of 85 is gradually raised to reach 135 when addition of chlorine is stopped. Chlorine addition is terminated when the presence of a,u,a,u,a'-pentachloro-p-xylene is virtually eliminated from the reaction mixture, as determined by monitoring the reaction mixture with vapor phase chromotography.

TABLE 1 Total weight Moles Moles Total parts PC]; 'IPP 1 moles phos- Mole Portion sequessequessequesphorous percent (iron trant trant trant in dichloroin 1 -1 (x100) (x100) (x100) portion p-xylene z l Triphenyl phosphate. 1 Measured after 1.8 moles of chlorine are reacted per mole of p-xylene starting material.

TABLE 2 Total weight Moles Moles Total parts Weight PC1 TPP 1 moles phospercent Portion sequessequessequesphorous hexa- (iron in trant trant trout in chlorop.p.m.) (X100) (X100) (X100) portion p-xylene 1 Triphenyl phosphate.

1 Maximum product obtainable, as calculated from ring chlorination and condensation products formed after 1.8 moles of chlorine reacted per mole of p-xylene starting material.

1 Measured after termination of chlorine addition.

Hexachl-oro-p-xylene determinations. are then run on these further chlorinated portions F and G and the determinations are set forth in Table 2 above.

For portions C, D, and E the balance of the reaction products consist essentially of u-monochloro-, 0t,Ol.-dlChlO- ro-, and a,a,a-trichloro-p-xylene.

As is readily seen from Table 1, after 1.8 moles of chlorine are reacted per mole of p-xylene, the E portion possessing the combination of sequestrants, but the smallest amount of total sequestrant and total weight of phosphorous, demonstrates a significant increase in dichloro-pxylene yield. Moreover, this excellent yield of dichlorop-xylene is achieved with the most contaminated (5.1 ppm.) portion of the C, D, and E portions.

In Table 2, the 79 weight percent hexachloro-p-xylene obtained with the triphenyl phosphate sequestering agent, is the maximum amount obtainable calculated from the analysis of the C portion after 1.8 moles of chlorine are reacted. At this point of chlorine addition, vapor phase chromotography analysis already shows the presence of 4 weight percent ring chlorinated product and 17 weight percent of xylene condensation product. Thus further chlorination is terminated since the maximum achievable yield of 79 weight percent hexachloro-p-xylene is undesirable.

Further, as is seen from Table 2, the sequestrant combination provides an excellent increase in hexachloro-pxylene yield compared with the use of phosphorous trichloride sequestrant alone. The increase of 4.9 weight percent of hexachloro-p-xylene for the sequestrant combination compared to the phosphorous trichloride alone, is especially desirable since it is an increase achieved at a level of reaction, i.e., above the 90 percent conversion level, where even a lesser increase has been impossible, or economically impractical, to obtain. Now, however, this nearly complete conversion, to the exhaustively chlorinated p-xylene is economically and simply achieved.

Example 2 A p-xylene having readily visible particles of ferric oxide is analyzed for iron content according to the abovementioned method and found to contain 25 p.p.m. iron. To a part portion of this p-xylene is admixed 0.00 727 mole of phosphorous trichloride and 0.00215 mole of triphenyl phosphate. The resulting mixture is chlorinated in the manner of Example 1.

On analysis of the reaction product by total area vapor phase chromotography, such product is found to have only 1.7 mole percent ring chlorination and an excellent 42.2 mole percent yield of dichloro-p-xylene, thus demonstrating the powerful sequestering ability of the sequestrant combination, even for severe contamination.

It is to be understood that although the invention has been described with specific reference to particular embodiments thereof, it is not to be so limited, since changes and alterations therein may be made which are within the full intended scope of this invention as defined by the appended claims.

What is claimed is:

1. A composition consisting essentially of a metal ion contaminated alkyl-aromatic hydrocarbon, and a sequestering amount of a synergistic combination of a phosphorous halide and an organic phosphate, said synergistic com-bination containing a molar proportion of phosphorous halide to organic phosphate between about 10:1 and about 1:10, wherein said organic phosphate is selected from the group consisting of aryl phosphates, alkyl phosphates, and their mixtures, and the halogen in said phosphorous halide has atomic weight between about 35-80.

2. The composition of claim 1 wherein the sequestering amount of said phosphorous halide together with said organic phosphate provide a composition containing from about 0.01 to about 5 weight percent of phosphorus, based on the weight of said hydrocarbon.

3. The composition of claim 1 wherein said organic phosphate is triphenyl phosphate and said phosphorous halide is selected from the group consisting of phosphorous trich-loride and phosphorous pentachloride.

4. The composition of claim 1 wherein said alkylaromatic hydrocarbon contains less than about 5 weight percent of contaminants and is selected from the group consisting of toluene, xylene, and their mixtures.

5. The composition of claim 1 wherein the contaminated alkyl-aromatic hydrocarbon together with said phosphorous halide and organic phosphate, are about 5-995 volume percent of a liquid reaction medium, and the balance of said liquid reaction medium is a liquid dispersant selected from the group consisting of benzene, carbon tetrachloride, acetic acid, and their mixtures.

6. The method of sequestering metal ion contamination of an alkyl-aromatic hydrocarbon which contamination promotes ring activity of the hydrocarbon during liquid phase, catalyzed halogenation of said hydrocarbon, which method compriser mixing said hydrocarbon with a sequestering amount of a synergistic combination of organic phosphate and phosphorous halide, wherein said organic phosphate is selected from the group consisting of aryl phosphates, alkyl phosphates, and their mixtures, and the halogen in said phosphorous halide as well as the halogen employed for said halogenation, has atomic weight between about 35-80.

7. The method of claim 6 wherein said sequestering amount of organic phosphate and phosphorous halide provide a mixture containing from about 0.01 to about 5 weight percent phosphorous, based on the weight of said hydrocarbon.

8. The method of claim 6 wherein said organic phosphate is triphenyl phosphate and said phosphorous halide is selected from the group consisting of phosphorous trichloride and phosphorous pentachloride.

9. The method of claim 6 wherein said alkyl-aromatic hydrocarbon is selected from the group consisting of toluene, xylene, and their mixtures.

10. The method of claim 6 wherein said alkyl-aromatic hydrocarbon contains less than about 5 weight percent of References Cited UNITED STATES PATENTS 4/1961 Miller 260651 R 8/1961 Miller 260651 R 10 3,230,268 1/ 1966 Kobayashi 260651 R 3,350,467 10/ 1967 Lasco 260-651 R MAYER WEINBLATI, Primary Examiner 5 IRWIN GLUCK, Assistant Examiner US. Cl. XJR.