US3309413A - Aromatic desulfurization - Google Patents

Description

United States Patent 3,309,413 AROMATIC DESULFURIZATION John M. Ferrara, Chicago, and Robert R. Burns, Naperville, Ill., assignors to Howe-Baker Engineers, Inc., Tyler, Tex., a corporation of Texas No Drawing. Filed Mar. 4, 1963, Ser. No. 262,322 8 Claims. (Cl. 260674) This invention, in general, relates to the treatment of benzene, xylene and/ or toluene to remove therefrom sulfur-containing compounds. The invention is especially applicable to the treatment of coke oven benzene to remove thiophene and carbon disulfide, but it is also applicable to thiophene removal from aromatics of petroleum origin, e.g., benzene-toluene-xylene mixtures.

Coke oven benzene is a byproduct of the coke-making industry. The thiophene and carbon disulfide content of coke oven benzene is usually in the order of 100 to 450 p.-p.m. sulfur. The usual thiophene content is in the order of 100-350 p.p.m. sulfur, and the usual carbon disulfide content ranges from 0 up to 150 ppm. sulfur. Benzene of petroleum origin is usually low in sulfur content, e.g., l-50 p.p.m. sulfur as thiophene and thiophene homologs.

There are instances where the coke oven benzene or petroleum aromatics must be purified of their sulfur content before they can be marketed for use in certain instances. For example, when benzene is used in the manufacture of nylon intermediates and other chemicals, low sulfur benzene (not more than 1 ppm. sulfur) is highly desired because high contents of sulfur in the benzene decrease yields and adversely affect the purity of the product. Also, the sulfur has an adverse effect on the catalysts used in converting benzene to the nylon intermediates or other chemicals.

This invention is primarily concerned with the provision of economical processes for removing thiophene and carbon disulfide impurities from benzene, toluene and/or xylene.

It is a primary objective of the invention to provide processes for the treatment of benzene in which the treated benzene has a very low residual sulfur content, e.g., less than 1 ppm.

Still another object of the invention is to provide improvements in the treatment of benzene, as well as related aroma-tic hydrocarbons, such as toluene, xylene, or mixtures thereof, for the efficient removal of thiophene and its homologs from these aromatic hydrocarbons or mixtures thereof.

A still further object of the invention is to provide improvements in the removal of thiophene and carbon disulfide from coke oven benzene.

Coke oven benzene The removal of thiophene is achieved, in accordance with the invention, by the treatment of a thiophene-containing coke oven benzene with strong sulfuric acid (98100% H 80 or oleum up to about 30% strength. The conditions of treatment must be controlled carefully in order to obtain efficient thiophene removal with low total product loss resulting from the treatment.

The concentrated sulfuric acid or oleum is thoroughly mixed with the thiophene-containing coke oven benzene. The total contact time between the acid or oleum and the benzene is held to a period of approximately 12 to 30 minutes, preferably about 12 to 20 minutes. In the case of 98-100% sulfuric acid, the amount of the sulfuric acid mixed with the benzene is in the order of about 3 to 6 volume percent of the acid based on the volume of the benzene being treated. In the case of oleum, the volume percent decreases with increasing oleum strength. In general, with oleum strengths ranging from 30%, the volume percent of oleum based on the volume of the agitator and electrodes having a 1-inch spacing.

benzene being treated, will be in the order of l-5 volume percent. With 20-30% oleum, the volume percent preferably does not exceed about 2.5 volume percent, above which relatively high product losses are encountered. Twenty to thirty percent oleum is the most efficient of the acid-treating agents because good results can be obtained with as little as 1 volume percent of oleum.

The temperature of the acid treatment of the thiophenecontaining benzene is also critical in order to obtain good thiophene removal and low product loss. A treating temperature in the range of about 50-100 F. is essential to obtain an optimum thiophene removal with a minimum of total product loss. Carbon disulfide remains essentially unaffected by the concentrated sulfuric acid or oleum treatment of coke oven benzene and the like.

The mixing of the concentrated sulfuric acid or oleum with the thiophene-containing benzene may be done in a first stage, and the separation of the sulfuric acid or oleum and benzene may be done in a second stage which includes the electrostatic treatment in a vessel containing electrodes. The agitation of the two-phase mixture should be sufiicient to disperse the sulfuric acid or oleum in small droplets throughout the body of the benzene. The total contact time between the acid or oleum and benzene should be held to 130 minutes, preferably 12-20 minutes.

The mixing of the concentrated sulfuric acid or oleum with the thiophene-containing benzene preferably is done as a multi-stage mixing. The agitation is sufiicient to insure a thorough dispersion of the sulfuric acid or oleum in benzene. The residence time of the thiophene-containing benzene and the concentrated sulfuric acid or oleum in the mixing stages is important in the practice of the invention. As aforesaid, the total contact time between the acid or oleum and the benzene should be held to 12 to 30 minutes, preferably 12 to 20 minutes.

In the preferred practice of the invention, con-tinuous multi-stage process is employed. In the last stage, the

action of the thiophene and sulfuric acid or oleum and,

at the same time, to improve the process of separation of the dispersed droplets of acid or oleum and the reaction products and promote separation thereof from the henzene, resulting in less acid carryover in the benzene phase. The two phases separate in a settling tank into Which the continuous streams of mixed sulfuric acid or oleum and benzene or other aromatic are fed. The electrodes preferably are placed in the settling tank, but they also may be placed in a vessel preceding the settling tank.

The direct current electrical field created by the electrodes is in the order of 20006000 volts per inch of electrode spacing. A field potential of about 4,000 volts has been found to be excellent with an electrode spacing of 1 inch.

A residence time for the acid or oleum-benzene dispersion in the electrical treating and settling stage of the process of S to minutes is desirable. The over-all time of mixing plus settling is in the range of 1090 minutes.

The advantages of the invention will be further appreciated from the following examples of the invention,

which examples are provided for the purpose of illustra- EXAMPLE I A single-stage treatment of thiophene-containing benzene is conducted in a small vessel equipped with an The field potential was maintained at 4 kv. The results of experiments conducted with benzene containing various concentrations of thiophene, with various acid and oleum concentrations, and with variations in the volume percent of acid or oleum added, mixing time and temperature are recorded in the following table.

TABLE I in the effective treatment of benzene with 300 p.p.m. thiophene and from 4 volume percent to 1 volume percent in the effective treatment of benzene with 200 p.p.m. thiophene.

Some of the results relating to the foregoing conclusions are set forth in the following tables.

Mixing Tim Min.

Sample Vol. Percent No. Acid Acid Field Thiophene Potfintial, in Prod.,

p.p.m.

Prod. Loss. Percent =00 t mww t t w-menuumiuwzomenummupgegpwmomrenenenm 'A-Teclmical grade benzene with 300 p.p.m. thio hene 0ne degree coke oven benzene U3, Steel ory, Indiana. Heme as A, but only 200 p.p.m. thiophene added.

' optimum value as mixing time increased. Under these conditions, 15 minutes was the minimum mixing time needed to reduce thiophene from 300 to 1 p.p.m. When the acid concentration (98% H 50 the mixing time (15 minutes) and the temperature (77 F.) were held constant, the effectiveness in thiophene removal improved as the acid volume increased. Under these conditions, 5 volume percent acid was the minimum quantity needed to reduce the thiophene content from 300 p.p.m. to less than 1 p.p.m. About 4 volume percent was the minimum quantity of the acid required to reduce the thiophene content from 200 p.p.m. to less than 1 p.p.m.

When the acid concentration (98% H 80 the acid quantity (5 volume percent) and the mixing time minutes) were held constant, thicphene removal reached an optimum value at 75 to 78 F. At temperatures significantly above or below the aforesaid temperatures, there resulted thiophene content in the treated benzene greater than 1 p.p.m.

When oleum was used in place of 93% H 50 and the mixing time (l5 minutes) and temperature (77 F.) were held constant, the quantity of oleum needed to reduce the thiophcnc content to less than 1 p.p.m. was reduced-from 5 volume percent to 1.5 volume percent (200 p.p.m. thiophene).

TABLE IL-E flect of Sulfuric Acid Concentration on Thiophene Removal ma Benzene Loss [All Acids Used at 5 Volume Percent, Mixing Time 15 Min., sample A] Acid Concentration Residual Thiophene Benzene Loss (percent) (p.p.m.) (percent) 93 27. 3 Nil 96 12. 6 Nil 98- 0.6 0. 48 100 0.5 1. 17 101.13 (5% oleum)--- 0. 14 1. 29 104.5 (20% 0leum) Nil 2. 61 106.75 (30% 0leum) Nil 3. 59

TABLE III-EFFECT OF MIXING TIME (5 VOLUME PER es msor) ON THIOPHENE REMOVAL AND BEN- [Temperatuie constant at 77 F. sample No. A]

Mixing Time Residual Thiophenc Benzene Loss (m1n.) (p.p.m.) (percent) 35. 1 Nil 9. 3 Nil 2. 63 Nil 0. 0. 48 0. 88 0. 55 0. 86 0.73

TABLE IV.-EFFECT OF ACID VOLUME 98 E O I THIOPHENE REMOVAL AND BENZE N] LO SS 4) l [Mixing time 15 minutes, temperature 77 F., sample N o. A]

Acid Volume (percent) Residual Thiophene Benzene Loss (percent) (ppm) 0. 6 0. 48 1.8 0. l4 2. 1 Nil 10. 0 Nil [Mixing time 15 minutes, sample No. A]

Benzene Loss Residual Thiophene (percent) Temperature F.) (p.p.m.)

TABLE VI.EFFECT OF ACID VOLUME (30% OLEUM) ON THIOPHENE REMOVAL AND BENZENE LOSS [Mixing time minutes, temperature 77 F., sample No. B] 15 Benzene Loss (percent) Acid Volume (percent) Residual Thiophene p.p.m.)

HOG

EXAMPLE II Three streams of coke oven benzene containing about 200 p.p.m. sulfur as thiophene are mixed with streams of oleum at a volume ratio of 100:1, respectively. Each stream is mixed in a mixing stage by mechanical agitators at a total residence time in the mixing stage of about 15 minutes. The streams are discharged into one of a group of settling tanks and collected therein.

The settling tankseach contain electrodes spaced at about one inch. The collected oleum-benzene mixture is subjected to electrical treatment of about 4 kv. field potential for 15-20 minutes, and then the mixture of the oleum phase and the benzene phase are separated. The resultant benzene phase has less than one p.p.m. sulfur in the form of thiophene.

Carbon disulfide removal from coke oven benzene The concentrated sulfuric acid and oleum treatments of sulfur-containing coke oven benzene has little effect on the carbon disulfide content. Accordingly, the acid or oleum-treated benzene must be further treated to reduce the carbon disulfide content to an acceptable value, i.e., a value providing a residual sulfur content of less than 1 p.p.m. The carbon disulfide removal is effected by mixing the benzene with dimethylamine and sulfuric acid. This treatment provides carbon disulfide removal which is better than can be achieved by distillation of benzene. Distillation leaves about 2.5 p.p.m. residual carbon disulfide even with a 25 plate column at a reflux ratio of 25:1.

The dimethylamine treatment is accomplished by mix ing 0.2-0.6 volume percent of dimethylamine with the carbon disulfide-containing benzene. There is also incor-porated with the dimethylamine 1 to 3 volume percent of aqueous sulfuric acid, which may be dilute or concentrated sulfuric acid. The volume percents are based on the volume of the benzene being treated. After a mixing period of 5 to 60 minutes, the purified benzene is recovered by separating the acid and benzene phases by allowing the mixture to stand as in the case of the thiophene removal process, above described. The carbon disulfide is reacted and/or complexed, and is removed with the acid phase from the benzene.

The following examples illustrate dimethylamine treatment of benzene.

EXAMPLE III One degree coke oven benzene (US. Steel, Gary, Ind.) containing 130 p.p.m. carbon disulfide was treated with 0.3 volume percent of dimethylamine and 2 volume percent of 0.02 N sulfuric acid for 15 minutes. The resultant treated benzene had a residual carbon disulfide content of 1.1 p.p.m.

6 EXAMPLE 1v One degree coke oven benzene (US. Steel, Gary, Ind.) containing 130 p.p.m. carbon disulfide was treated with 0.3 volume percent of dimethylamine and 2 volume percent of 98% sulfuric acid for 15 minutes. The resultant treated benzene had a residual carbon disulfide content of 0.1 p.p.m.

The use of concentrated sulfuric acid provides more effective carbon disulfide removal than does the dilute acid. Accordingly, the sulfuric acid used in conjunction with the dimethylamine preferably is concentrated sulfuric acid, i.e., 50100% H or even oleum up to 30% strength.

In addition to coke oven benzene, the dimethylamine treatment can be used effectively on aromatic hydrocarbons of petroleum origin to remove carbon disulfide therefrom.

The dimethylamine treatment for carbon disulfide removal can be coupled or combined with the sulfuric acid or oleum treatment for thiophene removal by adding the dimethylamine in the latter process. The 98l00% sulfuric acid or the oleum then performs the dual function of reacting with the thiophene and also coacting with the dimethylamine to react and/or complex with the carbon disulfide. This gives a process combining both carbon disulfide removal and thiophene removal into a single treatment.

EXAMPLE V tively. The streams are agitated with mechanical agitators at about 12-15 minutes residence time in the mixing stage, and are discharged into one of a group of setting tanks and collected therein.

The settling tanks each contain electrodes spaced at about one inch. The collected oleum-benzene mixture is subjected to electrical treatment of about 4 kv. field potential for 15-20 minutes, and then the mixture of the oleum phase and the benzene phase are separated. The resultant benzene phase has less than one p.p.m. sulfur in the form of thiophene.

EXAMPLE VI The process of Example V is repeated with petroleum BTX, a mixture of benzene, toluene and xylene, with 1.5 volume percent of acid at 100 F. The treated BTX has less than one p.p.m. residual sulfur.

Thus, it will be seen that the 98100% sulfuric acid or oleum treatment aforedescribed may be employed to reduce high sulfur content (e.g., 100-450 p.p.m.) as thiophene and thiophene homologs in coke oven benzene to values less than 1 p.p.m. sulfur as thiophene. The term thiophene in the foregoing description embraces the compound thiophene as well as lower alkyl thiophene homologs such as 3-methyl thiophene, 2,5-dimethyl thiophene, methyl ethyl thiophene, diethyl thiophene, npropyl thiophene, etc. The 98l00% H SO or oleum treatment may also be used to reduce lower thiophene contents of petroleum benzene (e.g. 5-50 p.p.m.) or of petroleum BTX (e.g., 5-50 p.p.m.) to values less than 1 p.p.m. The dimethylamine-sulfuric acid or oleum treatment to reduce carbon disulfide content is applicable to aromatic hydrocarbons in general, e.g., benzene, toluene and/or xylene, or naphthalene. The most important industrial application of the latter is in the removal of carbon disulfide from coke oven benzene.

Removal 0 thiophene from petroleum BT X and other petroleum hydrocarbon aromatics Petroleum aromatic hydrocarbon fractions such as benzene, toluene and xylene mixtures (BTX) usually concontent. Ae cordingly the former are handled somewhat differentlyin sulfur removal treatment, especially in the volume "percent sulfuric acid used to remove thiophene. 'Benzenc-tolucne-xylene'(BTX) refinery streams can be treated with 98100% sulfuric acid in a single-stage or multistage electrostatic treatment process. -The multi- 'stagefp'roce'sses givebetter over-all results than the singlestage process. The multi-stage process may be one in which fresh 98-100% sulfuric acid is added to the thiophene-containing BTX in two or more stages. The multi-stage process may also be a counter current process in which the BTX is treated in a series of stages wherein spent acid effluent from a later stage of the process is used as the treating acid in the earlier stage or stages. The last stage may be an aqueous caustic neutralization step.

The acid used in BTX thiophene removal is 98-10096 sulfuric acid, or oleunt as aforedescribed, at 50-120 F. It is employed in amounts front about 0.25 volume percent to 2 volume percent, based on the BTX. The acid volume required is a direct function of the thiophene concentration of the feed stream BTX. For example, with 98% ill TABLE VII 'Ihlopheue 1n B'IX Fractions, p.p.m. Total 11,801, Vol.

Percent Benzene Toluene Xylene 0. 3d 0. 76 N11 t). 30 t). 6': N 11 0. 73 t). 74 0. H 0. 73 0. 9 N11 EXAMPLE Vlll A three-stage countcreurrent treatment was set up on a pilot plant scale. The first stage was an acid-treatment with spent acid from the second stage. The second stage was an acid-treatment with fresh 98% H 50 added at a rate equal to about 1.5 volume percent of the refinery stream BTX, which had about 30 p.p.m. thiophene content and was fed initially into the first stage. The third stage was a neutralization stage provided by the addition of 20 B. caustic. An electrostatic treatment was used in each stage with 1 inch electrode spacing. Data observed during a continuous couatercurrent run for about four and one-half hours are reported below:

'1i\1t 1.1; Vtli 'Itme 1,005 1.030 1.11 1.130 1,200 1,230 1,300 1,330 1.400 1.430 Feed Rate. ce./m 1S0 171) 181 181 131 181 181 180 Additive Rate, ee.lm.:

1st Stage" '2. 7 '2. 7 2. 7 2. 7 L. 7 2. i '2. 78 J. 77 2. 8 2 75 2nd Stage. 2. 7 3. 1 l. 3 '2. 7 2. 8 2. S l. 84 2. 8 'J. 8 2. 8 3rd Stage l0. 10. T 10. H 111. 0 1d. 0 13.0 13. 4 l3 l3. 3 13. 3 Tempemtur l-eel ill-'1 104 H 101 104 104 104 102 10'! 1st Stage" at M tn- 97 as \N tttl as 2nd Stagetit) 113 tttl 117 1011 1011 ltttl 1011 3rd Stngeu- 57 J1 tr. M 15 Uti 9d Mixers. r.t|.m.:

1st Stage I. 000 1, 000 1,000 l. 000 1,000 l 000 1,000 1.000 1.000 1,000 2nd Stage. l, mu 1, out) 1, 1.0110 1,000 l mu 1, 00d 1, uuu 1,000 1, (III Zlt'tl Btttgo 350 350 325 000 tit!) titlti 000 000 titltl d Voltages. kv

lat Stage ll 5 5 .'i (1 ft 5 5 .'1 2nd Stage. 1'1 6 5 5 t: b a t- .l 3rd Stage 6 5 5 5 5 b 5 5 ti carryover, Total:

1st Stage p.p.m..... 1. 900 2,100 2nd Stage p.p.m.-.. it, we 4, ton 3rd Stage p.p.m.... 1 Nut) 1 Nut) Miscellaneous:

Soluble acid. lat

Kluge 1. 0 1.02.: 1.850 P.p.m. 2nd Stage... 8. 0 3.600 :1, but) .A

H in a single-stage treatment at F., about 0.5

'volume percent was required to reduce to less than 1.0

that small amounts of olefin's, e.g., (ll-1.5%, are removed by the acid-treatment.

EXAMPLE VII A refinery benzene-toluene-xylene stream was provided with thiophene and thiophene homologs. i.e., 3-methyl thiophene and 2',5-dimethy1 thiophene, at concentrations of 3.33 p.p.m: each-making a total thiophene and thiophene homolog concentration of 10 p.p.m. The ll'lX .wastreated countcrcurrcntly in two stages with equal volume amounts of 98% sulfuric acid at a temperature of 'l0l)'-.F. The electrostatic treatment in each stage was at about 5 kv. The results of tests at various total sulfuric acid volume percents were:

in the foregoing run, the acid data was: (a) first stage. 749 cc. acid in at 1.591 sp. gr. and 23.48 meq./ml. and 605 cc. acid out at 1.6505 sp. gr. and 26.4 meq./ml. ant (b) second stage. 770 cc. acid in at 1.837 sp. gr. and 37.5 meq./ml. and 893 cc. acid out at 1.591 sp. gr. and 23.4t mcq./ml.

The removal of sulfur compounds from benzene, tol uene, xylene and mixtures thereof of petroleum origin i: conducted similarly to the treatment of coke oven ben zcne. The volume percent, based on the aromatic hydro carbon, of 98-100% sulfuric acid or oleum is 0.25-2.071 unless the thiophene content is unusually high. The mix lag time for the acid and the aromatic hydrocarbon i 1-30 minutes, preferably 12-20 minutes, at 50-120 F The electrostatic treatment of the mixture is done a 2000-6000 volts at electrode spacings of 1-12 inches preferably 1-3 inches. The elapsed time for electro static treatment and settling is 5-60 minutes. When de sirable, the dimethylamine treatment is conducted at th same volume ratios as aforedefined.

Taking sulfur-containing petroleum origin benzene, tol uene, and/or xylene and coke oven benzene as a class this invention embraces the treatment of these aromuti hydrocarbons to reduce the sulfur content to a low value e.g., less than 1 p.p.m., by intimately mixing with sal said aromatic hydrocarbons of 98-100% sulfuric aci or 0.25-% oleum for 1-30 minutes, preferably 12-20 minutes, at 50-120 The resultant mixture is electrostatically treated at 2000-6000 volts at electrode spacings of 1-12 inches, preferably 1-3 inches. The elapsed time of electrostatic treatment and settling is 5-60 minutes. The treatment may also include the addition of 0.2-0.6 volume percent of dimethylamine in the presence of sulfuric acid or oleum to remove carbon disulfide.

The invention is hereby claimed as follows:

1. A process for purifying a mixture of benzene, toluene and xylene to a residual sulfur content of less than one p.p.m. which comprises mixing with a mixture of benzene, toluene and zylene, said mixture containing a small amount of carbon disulfide and a member selected from the group consisting of thiophene and homologs of thiophene, 0.2 to 0.6 volume percent, based on said mixture, of dimethylamine and 0.25 to 6 volume percent, based on said mixture, of a member selected from the group consisting of 98-100% sulfuric acid and oleum of up to 30% strength, applying to the formed mixture an electric current between electrodes spaced 1-12 inches apart at a field of about 2000-6000 volts per inch, and separating the acid phase and the benzene, toluene and xylene phase, the latter containing less than one p.p.m. residual sulfur.

2. A process for purifying coke oven benzene to a residual sulfur content of less than one p.p.m. which comprises mixing with coke oven benzene containing thiophene and carbon disulfide with about 3-6 volume percent, based on said coke oven benzene, of 98-100% sulfuric acid and 0.2 to 0.6 volume percent, based on said coke oven benzene, of dimethylamine for 1-30 minutes, applying to the formed mixture an electric current between electrodes spaced 1-12 inches apart at a field of about 2000-6000 volts per inch, and separating the acid phase and the coke oven benzene phase, the latter phase containing less than one p.p.m. residual sulfur.

3. A process for purifying coke oven benzene to a "residual thiophene content of less than one p.p.m. which comprises mixing with coke oven benzene containing thiophene with about 1-5 volume percent, based on said coke oven benzene, of oleum of 5% to 30% strength for 1-30 minutes, applying to the formed mixture an electric current between electrodes spaced 1-12 inches apart at a field of about 2000-6000 volts per inch, and

separating the acid phase and the coke oven benzene phase, the latter phase containing thiophene in an amount less than one p.p.m. sulfur.

4. A process as claimed in claim 3 wherein said coke oven benzene is also mixed with 0.2 to 0.6 volume percent, based on said mixture, of dimethylamine, said coke oven benzene containing a small amount of a member selected from the group consisting of sulfuric acid and oleum to remove carbon disulfide.

5. A process as claimed in claim 3, wherein said oleum is 20-30% strength oleum which is used in a volume percent of 1-2.5%.

6. A process for removing carbon disulfide from a member selected from the group consisting of benzene, toulene, xylene and mixtures thereof which comprises mixing said member with about 0.2-0.6 volume percent, based on said member, of dimethylamine and 1-6 volume percent, on the same basis, of sulfuric acid, and separating the acid phase and the organic phase comprising said member.

a 7. A process as claimed in claim 6 wherein said member is coke oven benzene.

8. A process for removing sulfur compounds from an aromatic hydrocarbon selected from the group consisting of benzene, toluene, xylene, and mixtures thereof which comprises mixing with said aromatic hydrocarbon contain-ing sulfur compounds a small amount of an acid selected from the group consisting of 98-100% sulfuric acid and oleum of up to 30% strength, applying to the formed mixture an electric current between electrodes spaced 1-12 inches apart at a field of 2000-6000 volts per inch, and then separating the acid phase and the aromatic hydrocarbon phase, and also mixing with said aromatic hydrocarbon a small amount of dimethylamine, said aromatic hydrocanbon also containing a small amount of a member selected from the group consisting of sulfuric acid and oleum of up to 30% strength to remove the carbon disulfide content from said aromatic hydrocarbon.

References Cited by the Examiner UNITED STATES PATENTS 2,049,016 7/1936 'Morrell 208-224 2,247,927 7/1941 Smith 208-224 2,418,047 3/ 1947 Parkes et al. 208-236 2,948,764 8/1960 Oele et a1. 208-267 3,066,087 111/1962 Phillips 204- FOREIGN PATENTS 631, 873 11/1961 Canada.

DELBERT E. GANTZ, Primary Examiner.

C. E. SPRESSER, Assistant Examiner.

Claims (2)

1. A PROCESS FOR PURIFYING A MIXTURE OF BENZENE, TOLUENE AND XYLENE TO A RESIDUAL SULFUR CONTENT OF LESS THAN ONE P.P.M. WHICH COMPRISES MIXING WITH A MIXTURE OF BENZENE, TOLUENE AND ZYLENE, SAID MIXTURE CONTAINING A SMALL AMOUNT OF CARBON DISULFIDE AND A MEMBER SELECTED FROM THE GROUP CONSISTING OF THIOPHENE AND HOMOLOGS OF THIOPHENE, 0.2 TO 0.6 VOLUME PERCENT, BASED ON SAID MIXTURE, OF DIMETHYLAMINE AND 0.25 TO 6 VOLUME PERCENT, BASED ON SAID MIXTURE, OF A MEMBER SELECTED FROM THE GROUP CONSISTING OF 98-100% SULFURIC ACID AND OLEUM OF UP TO 30% STRENGTH, APPLYING TO THE FORMED MIXTURE AN ELECTRIC CURRENT BETWEEN ELECTRODES SPACED 1-12 INCHES APART AT A FIELD OF ABOUT 2000-6000 VOLTS PER INCH, AND SEPARATING THE ACID PHASE AND THE BENZENE, TOLUENE AND XYLENE PHASE, THE LATTER CONTAINING LESS THAN ONE P.P.M. RESIDUAL SULFUR.

6. A PROCESS FOR REMOVING CARBON DISULFIDE FROM A MEMBER SELECTED FROM THE GROUP CONSISTING OF BENZENE, TOULENE, XYLENE AND MIXTURES THEREOF WHICH COMPRISES MIXING SAID MEMBER WITH ABOUT 0.2-0.6 VOLUME PERCENT, BASED ON SAID MEMBER, OF DIMETHYLAMINE AND 1-6 VOLUME PERCENT, ON THE SAME BASIS, OF SULFURIC ACID, AND SEPARATING THE ACID PHASE AND THE ORGANIC PHASE COMPRISING SAID MEMBER.