US2464520A - Process for desulfurizing an aromatic hydrocarbon containing thiophene - Google Patents

Description

Patented. Mar. 15, 1949 PROCESS FOR DESULFURIZiNG' AN ARO- MATIC HYDROCARBON CONTAINING THIOPHENE Arthur P. Lien, Hammond, Ind., and Bernard L. Evering, Chicago, Ill., assignors to Standard Oil Company, Chicago, Ill., a corporation of Indiana No Drawing.

Application February 12, 1945, Serial No. 577,580

.6 Claims. (01. 260-674) This invention relates to a process for the treatment of aromatic hydrocarbons containing heterocyclic sulfur compounds with hydrogen fluoride. More particularly it relates to a process for the chemical conversion and extraction of sulfur compounds. In one embodiment the invention relates to the removal of thiophenes from aromatic hydrocarbons, such as benzene, benzol and the like.

One of the most'difficultly removable constituents from aromatic hydrocarbons such as benzene and benzols is thiophene. Thiophene so closely resembles benzene in its chemical and physical properties that for a long timeit escaped detection in small quantities in benzenes derived from coal tars. Thiophene may be present in commercial benzenes in proportions up to about 0.5% by weight, usually in the range of about 0.1 to about 0.5 weight percent.

Benzols may contain from a trace to as much as 1.5 or 2 weight percent of thiophene, depending on the source and treatment of the benzols. Benzols derived from low temperature conversions, for example, low temperature coal carbonization, have been found in some cases to contain no appreciable quantity of thiophene. Benzols are derived from light oil fractions obtained by thedistillation of coal tar and also from coal and town gases obtained from cokin or gasifyin coal, e. g., to make carbureted water gas. Benzols contain benzene, toluene, xylenes, and relatively small proportions of uns'aturates, paraffins and naphthenes. Normally, the aromatics constitute about 50 to 90 volume percent of benzol; The aromatics are present in variable proportions, but normally the predominating aromatic is benzene, followed in turn by toluene and xylenes. careful fractionation of benzols to produce commercial benzene, thiophene distills with the benzene fraction and must be removed to provide chemically pure benzene or nitration grade benzene.

One of the objects of our invention is to provide an improved process for the removal of heterocyclic. sulfur compounds from aromatic hydrocarbons. Another object is to provide a new process for thepreparation of a synthetic resin from thiophene. A further object is to remove thiophene from association with aromatic hydrocarbons, particularly monocyclic aromatic hydrocarbons, such as benzene, or hydrocarbon mixtures containing benzene, e. g., motor benzol. An additional object is to provide a process for the preparation of benzene in a substantially chemically pure condition. Further objects of our in- In the c I drogen fluoride.

vention will become apparent as the description thereof proceeds.

We have discovered a process for desulfurizing aromatic hydrocarbons which are contaminated by thiophene, which process comprises treating said aromatic hydrocarbons with liquid hydrogen fluoride in quantity sufficient at least to form a distinct liquid phase. By, the term desulfurizing, we mean a process of substantially reducing or eliminating sulfur or sulfur compounds. Briefly, we have found that at room temperature (about F.) or higher temperatures, thiophene undergoes a complex chemical conver-e sion upon contact with liquid hydrogen fluoride. This conversion results in the formation of hydrogen sulfide and the production of a resin which is soluble or dispersible in the liquid hy- At' temperatures below room temperature, liquid hydrogen fluoride may efiect substantial extraction of thiophene and the like from aromatic hydrocarbons accompanied by a reduced extent of chemical conversion of the thiophene or by substantially no conversion at low temperatures. It is preferred to eiiect the conversion of the thiophene-in the presence of a diluent, such as an aromatic hydrocarbon or mixture of aromatic hydrocarbons, which diluent is sparingly solublein liquid hydrogen fluoride.

Our process will hereinafter be described with reference to a solution of thiophene in an aromatic hydrocarbon, e. g., as in commercial benzene or benzols. The process hereinafter described may be carried out batchwise or in multistage or continuous operations. In multistage operations, hydrogen fluoride may be added in increments with or without resin'separation between stages. In our process we employ substantially anhydrous liquid hydrogen fluoride asa conversion catalyst and extraction solvent; accordingly, we prefer to effect our process under substantially anhydrous conditions. Suitable processing temperatures fall within the range of about 30 F. to 300 F.-, preferably 60 F. to F. Commercial benzenes are advantageously treated at temperatures between about 45 and 180 F., preferably about 60 F. to about 120 F. We employ pressures in the hydrogen fluoride treating zone suflicient to maintain the hydrocarbon and the hydrogen fluoride in the liquid phase. Operations may be effected at substantially atmospheric pressures when using room temperatures or lower temperatures. However, in

commercial operations, it is sometimes desirable to use pressures somewhat above atmospheric,

e. g., about 25 to about 50 p. s. 1. Of course, at

on the amount of thiophene present, larger volumes of hydrogen fluoride being required at high concentrations of thiophene. The necessary time of contact between the hydrogen fluoride and the feed stock will vary to some extent, depending upon the particular aromatic hydrocarbon, the content of thiophene and other sulfur compounds in the feed, the volume of hydrogen fluoride employed per volume of feed stock, and the particular temperature at which treating is effected. However, suitable contact times will usually fall within the range of about 1 to about 120 minutes, preferably about 5 to about 60 minutes.

The thiophene in solution in an aromatic hydrocarbon is vigorously agitated or otherwise con-' tacted with liquid hydrogen fluoride. After contactlng, the reaction mixture is allowed to settle in order to form a distinct hydrogen fluoride extract phase. Conventional mixing devices may be employed, e. g., the reaction mixture may be agitated with paddle stirrers, propellers, or turbomixers or the reaction mixture may be pumped at high velocity through tubular conduits containing orifice mixers (baflles) or the like. Alternatively, aromatic hydrocarbons containing thiophene may be passed upwardly throu h a tower countercurrently to liquid hydrogen fluoride. The tower may be provided with a zone containing suitable packing materials resistant to the action of hydrogen fluoride. A hydrogen fluoride extract phase separates in the lower portion of the tower and the treated aromatic hydrocarbons pass from the upper portion of the tower. The hydrogen fluoride extract phase is a distinct liquid phase containing all or a substantial proportion of the materials produced by the extraction and/ or chemical conversion of the thiophene and other compounds which may react. In addition, the hydrogen fluoride extract phase also contains sulfur compounds other than thiophene, e. g., mercaptans, and organic sulfides and disulfldes if such compounds were present in the feed stock. A portion of the hydrogen fluoride extract phase may be recycled to the conversion zone.

The aromatic hydrocarbons derived from the hydrogen fluoride conversion are treated to remove small amounts of hydrogen fluoride which remain dissolved or dispersed therein. The removal of hydrogen fluoride from the raf'finate may be accomplished by heating and stripping ofi the hydrogen fluoride, which may be recycled. Stripping aids such as inert gases or low boiling liquids may be used. Any traces of or anic fluorides can be removed by passing over. bauxite. Alternatively, the removal of hydrogen fluoride and organic fluorides may be accomplished by passing the aromatic hydrocarbons over material which may selectively absorb or react with hydrogen fluoride and decompose organic fluorides, e. g., activated alumina, bauxite, solid CaFz, KF, NaF, and the like. Alternatively, or in addition, the aromatic hydrocarbons may be washed with an aqueous or alcoholic solution of an alkaline material, such as ammonia or caustic, and then with water. After the separation of hydrogen fluoride, the treated aromatic hydrocarbons may be subjected to fractionation, if desired. Where the feed stock to the hydrogen fluoride conversion and extraction process is benzol, the processed benzol may be carefully fractionated to separate a benzene fraction of high purity suitable for nitration or other operations requiring the use of pure benzene.

The liquid hydrogen fluoride extract phase, may be variously treated to recover hydrogen fluoride for re-use in the conversion and extraction process and a solid resinous material derived from thiophene and, in part, from certain reactive aromatics and unsaturates which may be present in the feed stock. Thus hydrogen fluoride may be flash vaporized from the extract phase. In another method of operation, the extract may be subjected to distillation in a tower, hydrogen fluoride passing overhead. A carrier liquid may be introduced into the tower at an intermediate point to maintain the resin in pumpable form. A suitable carrier liquid is hydrocarbon oil which is not reactive with liquid hydrogen fluoride, for example, a hydrocarbon oil which has been treated with hydrogen fluoride under conditions similar to those prevailing in the distillation tower to remove constituents reactive with liquid hydrogen fluoride. It is preferable to use a low viscosity hydrocarbon oil for injection into the distillation tower, for example, a heavy naphtha, kerosene, or a light lubricating oil.

Most of the hydrogen fluoride contained in the extract phase is readily distillable therefrom. However, a minor proportion of the hydrogen fluoride appears to be' absorbed quite strongly by resinous materials which may be present and another minor proportion of the hydrogen fluoride may be bound in the form of organic fluorides. In order to separate or regenerate the hydrogen fluoride bound in the resinous materials or in organic fluorides, it is desirable to maintain bottoms temperatures in the distillation tower of the order of about 200 to about 500 F. Closely bound hydrogen fluoride need not be removed in the hydrogen fluoride extract distillation tower, but may be removed in a separate tower operating at a desired high temperature. A slurry or dispersion of resin in the carrier liquid is withdrawn from the bottom of the distillation tower, cooled, and filtered to separate the ersin and carrier liquid for recycle to the distillation tower.

Many benzols contain unsaturates, i. e., olefinic hydrocarbons, in addition to thiophene and other sulfur compounds. These compounds appear to take part in the reaction resulting in the formation of resins from thiophene. However, commercialbenzenes which contain thiophene may contain little or no unsaturates. In order to enhance thiophene removal and to increase the yield of resins, as well as to influence their properties, it may be desirable to add a small proportion, i. e., about 0.1 to about 1% by volume based on the benzene, of an unsaturated hydrocarbon. Suitable unsaturated hydrocarbons include amylenes, styrene, indene, isoprene, cyclopentadiene, dicyclopentadiene, and the like.

The following examples are tabulated t0 illustrate but not to limit our invention. In these examples the feed stock was a synthetic blend of chemically pure benzene and added thiophene, the blend containing 1.78 weight percent of sulfur as determined by the A. S. T. M. Lamp method. The feed stock (1000 cc.) and liquid hydrogen fluoride were mechanically stirred at about 1700 of 1510 cc.

. 8 provided with separate conduits for the removal of hydrocarbon and hydrogen fluoride liquid extract phases. Sulfur contents were determined by the Lamp method (A. S. T. M.

- 1288!; D-9041T described in A. S. T. M. Standards (1942), part 111, page 977).

. cc HF Contact Temp. Wt. Per Ex t. Added to Time p Reactor Min. e

In experiment 1, it was found that on opening the bottom valve of the reactor, hydrocarbon rather than hydrogen fluoride came out. In carrying out experiment 2, 150 cc. of additional fresh 6 urates with the feed to the hydrogen fluoride conversion and extraction process.

In the course of our process, sulfur compounds other than thiophene, particularly heterocyclic sulfur compounds, are chemically converted and/or extracted fromaromatic hydrocarbons.

, The sulfur compounds present in addition. tothiohydrogen, fluoride Was added to the contents reinate hydrogen fluoride, it was found that a large "amount of the solid material lined the reactor walls. The fact that a bottom HFlayer did not separate'after experiment 1is thus explained, in that the thiophene present reacted to form a thick, heavy condensation product, or resin, and the HF present was bound or dissolved in this product, the resulting mixture being so thick it adhered to the reactor walls on being thrown outward by action of the stirrer. In experiment 2, the additional HF brought about sufllcient fluidity of the HF-resin solution to give a separable bottom layer.

' The solid resins produced in the experiments were milled, refluxed with water and dried to obtain a light brown powder. The solid resins derived from thiophene are high melting and not soluble in the common solvents such as acetone, benzene, naphtha, alcohol, or carbon tetrachloride. These resins are thus adapted particularly well to uses requiring a high degree of thermal and solvent stability.

We have observed that the totalweight of resinous material recovered on treatment of a thiophene containing aromatic hydrocarbon with liquid hydrogen fluoride is in excess of the weight of thiophene present in the aromatic hydrocarbon. This gain in weight is all the more surprisin view of the fact that part of the original weight of the thiophene is lost as hydrogen sulfide as evidenced by the strong odor of hydrogen sulflde evolved from the reaction products. It is conceivable that part of the thiophene is converted by the catalytic reaction of hydrogen fluoride into diacetylene and hydrogen sulfide and that the diacetylene thus formed may undergo an 'alkylation'reaction with undestroyed thiophene and/or aromatic hydrocarbons. The participation of an aromatic hydrocarbon in the reaction might well explain'the gain in weight. It should phene may include alkyl thiophenes, such as methyl and dimethyl thiophenes, and various alkyl mercaptans, thioethers and disulfides.

-"It will be apparent that we have provided a novel process for the conversion of thiophene to a synthetic resin and also a process for the removal of thiophene from its solutions in aromatic hydrocarbons having very similar chemical and physical properties. We have also provided a novel, efficient, and economical process for the conversion of commercial benzene or benzol to pure benzene suitable for further chemical operations such as nitration or conversion to dyes.

We claim: 1 A process for desulfurizing an aromatic h drocarbon containin thiophene, which process comprises contacting said hydrocarbon with at least about 30 volume percent of anhydrous liquid hydrogen fluoride based on said aromatic hydro carbonin a contacting zone under sufiicient pres: sure to maintain the liquid phase whereby the thiophene is chemically converted to a resin dispersed in a distinct extract phase predominating in liquid hydrogen fluoride, separating said extract phase, subjecting said extract phase to distillation conditions of temperature and pressure in a distillation zone to vaporize hydrogen fiuoride from said extractphase, introducing into said distillation zone a hydrogen fluoride-treated hydrocarbon oil in quantity sufilcient to disperse resin which tends to separate in said distillation zone upon evaporation of hydrogen fluoride from said extract phase, liquefying hydrogen fluoride derived from said distillation zone and recycling said liquefied hydrogen fluoride to said contactin zone. T

2. A process for desulfurizing benzol which contains thiophene, which process comprises contacting said benzolwith at least 30 volume percent of substantially anhydrous liquid hydrogen fluoride, whereby hydrogen sulfide is generated and a resin derived from thiophene and an arcmatic hydrocarbon is produced, maintaining sufflcient liquid hydrogen fluoride in the reaction zone to disperse said resin and to form a distinct liquid phase, allowing the reaction mixture to stratify, and separating a desulfurized and deresined benzol layer from a layer of liquid hydrogen fluoride containing said resin.-

3. The process of claim 2 wherein said contacting is effected at a temperature between about 45- F. and about 180 F. under a pressure suflicient to maintain the liquid phase.

4. A process for desulfurizing an aromatic hydrocarbon which contains thiophene, which process comprises contacting. said aromatic hydrocarbon with at least 30 volume percent of subbe understood, however, that we do not intend .It will be appreciated that the resin as in the formulation of other plastics. In addition, it may be possible to increase the resin yield and influence the properties of the resin by the inclusion of co-reactive materials such asunsatl derived from thiophene may be compounded with plasticizers', fillers, pigments, antioxidants and the like,

be bound by any theory concerning the resini'iication reactions.

' hydrocarbon layer from a layer oi. liquid hydrogen fluoride containing said resin.

5. A process for desulfurizing an aromatic hy- 7 drocarbon which contains a heterocyclic sulfur compound selected from the group consisting of thiophene and an alkyl thiophene, which process comprises contacting said aromatic hydrocarbon with at least 30 volume percent of substantially anhydrous liquid hydrogen fluoride, whereby hydrogen sulfide is generated and a resin derived from said heterocyclic sulfur compound and an aromatic hydrocarbon is produced, maintaining sumcient liquid hydrogen fluoride in the reaction zone to disperse said resin and to form a distinct liquid phase, allowin the reaction mixture to stratify, and separating a desulfurized and deresined aromatic hydrocarbon layer from a layer of liquid hydrogen fluoride containing said resin.

6. A process for desulfurizing an aromatic hydrocarbon which contains an alkyl thiophene, which process comprises contacting said aromatic hydrocarbon with at least 30 volume percent of substantially anhydrous liquid hydrogen fluoride, whereby hydrogen sulfide is generated and a resin derived from said alkyl thiophene and an aromatic hydrocarbon is produced, maintaining sufflcient liquid hydrogen fluoride in the reaction zone to disperse said resin and to form a distinct liquid phase, allowing the reaction mixture to of liquid hydrogen fluoride containing said ARTHUR P. LIEN. BERNARD L. EVERING.

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

UNITED STATES'PATENTS Number Name Date 2,343,841 Burk Mar. 7, 1944 2,356,357 Schlesman Aug. 22, 1944 2,375,675 Matuszak May 8, 1945 2,378,762 Frey June 19, 1945 g FOREIGN PATENTS Number Country Date 292,932 Great Britain May 28, 1929 292,933 Great Britain May 23, 1929 501,725 Germany July 4, 1930 OTHER REFERENCES Whitehead, Benzol" (19 0), page 132, D. Van Nostrand Co., New York City.