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3,592,593 United States Patent 0 F” CC, Patented July 13, 1971

1 2 Progress was made by the introduction of a process 3,592,593 PURIFICATION OF THIONYL according to which is added to the re?ux stream Benno Bohm, Leverkusen, Germany, assignor t0 Farben at the head of a column in which is evap fabriken Bayer Aktiengesellschaft, Leverkusen, Ger orated under a fractional distillation. The sulfur in the many re?ux stream reacts with the thereby No Drawing. Filed Dec. 6, 1967, Ser. No. 688,358 reducing the amount of the dichloride in the distillate. Claims priority, application 9Ggrmany, Dec. 10, 1966, The reaction according to Equation 2 however proceeds 50 slowly. Therefore the sulfur dichloride is only uncom Int. Cl. c0’1b 17/45 pletely removed from the vapors. The last parts of the US. Cl. 23—-203 6 Claims 10 sulfur dichloride are to be removed by repeated distilla tion under reflux. This however is hazardous as thionyl chloride forms itself sulfur dichloride under the condi~ ABSTRACT OF THE DISCLOSURE tions of prolonged re?ux-temperatures: Pure thionyl chloride can be obtained from a crude product containing besides and\ mainly sulfur contaminates by evaporating the It has now been found in accordance with the present in thionyl chloride at a temperature below the vention an improved process for the puri?cation of thionyl of sulfur monochloride () and contact chloride by fractionally distilling oif thionyl chloride from ing the gaseous thionyl chloride with sulfur containing an sulfur chlorides impurities at a temperature lower than effective amount of iron or iron-compounds to convert the boiling point of sulfur monochloride whereby the gas any sulfur dichloride contaminating the gaseous thionyl eous thionyl chloride being distilled is contacted with sul chloride to liquid sulfur monochloride. fur to convert to liquid sulfur monochloride the sulfur dichloride contained in said gaseous thionyl chloride, conducting the liquid sulfur monochloride to the still of The present invention is concerned with a process for 25 the column and taking off puri?ed thionyl chloride at the the puri?cation of thionyl chloride. More particularly the head of the column the improvement which comprises present invention relates to a process for the removal of contacting said gaseous thionyl chloride with sulfur con sulfur chlorides from thionyl chloride. taining an elfective amount of an active iron product. On a technical scale thionyl chloride usually is obtained Suitable active products which can be used in accord by a process wherein sulfur dioxide or is 30 ance with the present invention are the sul?des such as reacted with chlorine and sulfur chlorides. Other known FeS, Fe2S3 and the like, the such as F6203, Fe3O4, processes for the production of thionyl chloride are the FeO, ?nely divided iron powder, the inorganic iron salts direct synthesis from the elements sulfur, and such as the chlorides, , phosphates, nitrates and chlorine and the reaction of with sulfur the like. Preferably the active iron products are used in ?nely chlorides. 35 The end-product of all these known processes is a crude divided form in an amount of between 0.01 to 10‘, pref thionyl chloride containing besides sulfur chlorides, sulfur erably of about 0.02 to 1 gram calculated as elementary dioxide and chlorine as impurities dissolved in the thionyl iron per 100 grams of sulfur. For obtaining a highly chloride. Sulfur dioxide and chlorine can be easily re active material the ?nely divided active iron products moved by distillation. The recontamination of the thionyl are suspended as homogeneously as possible in molten chloride with sulfur dioxide is usually avoided by hot sulfur which is then molded or merely chilled and dis condensation of the distillate in a so called ascending integrated into pieces. The size and form of sulfur pieces cooler, i.e. in counter?ow to the steam, and by chilling is not important. It must be possible to apply the sulfur the distillate to ambient temperature (IS-30° C.) sepa lumps into the head of the column on a suitable carrier rately from the steam. 45 such as a perforated plate or the like. The bed of Sulfur dichloride has a boiling point of about twenty solid sulfur is then contacted with the thionyl chloride degrees below the boiling point of thionyl chloride (79° vapors, whereby a solution of sulfur in thionyl chloride C.) whereas sulfur monochloride boils at about 138° C. is formed ?owing in counter-current direction to the thi Therefore, one should expect both sulfur chlorides to be onyl chloride vapors. separable from the thionyl chloride by fractional distil 50 The iron containing sulfur reacts very rapidly with the lation. At least a part of the sulfur dichloride‘ is removed sulfur dichloride present, thereby avoiding sulfur di with the low boiling fraction of the distillate however chloride contamination of the thionyl chloride which is during distillation some sulfur dichloride undergoes the taken off at the head of the column. reaction A sufficiently pure thionyl chloride thus can be pro 2SCl2z2S2C1+ C12 ( l ) 55 duced by a single step distillation, wherein the crude whereby sulfur monochloride is formed. The sulfur mono product containing the thionyl chloride and the impuri chloride on the other hand disproportionates according to ties mainly S02, chlorine and sulfur chlorides is evapo the reaction rated in a distillation column thereby contacting the szcipsclmts (2) vapors with the iron containing sulfur bed provided in 60 the top of the column. From the thionyl chloride vapor As the chlorine escapes at the head of the column equi the volatile sulfur dichloride is thus removed and a librium conditions are not established and a pure thionyl substantially pure‘ product is obtained. According to an chloride cannot be obtained as long as sulfur chlorides are other embodiment of the present invention the process present. A pure product therefore results only after re can be performed also in two steps to yield a still purer moving the major part of the sulfur dichloride and de 65 product and to improve the efficiency. stroying the removing sulfur chlorides under re?ux to In this two-step-process the vapor of the crude thionyl sulfur and chlorine. chloride is at ?rst fed into a column having a bed of In order to overcome this drawback it has been pro sulfur pieces as known per se, thereafter the fractional posed to add sulfur to heated liquid thionyl chloride. By distillation is repeated in a second smaller column con this method however only a poor yield of pure thionyl 70 taining a bed of the iron-modi?ed sulfur pieces. chloride can be obtained in the form of a distillate for By this preferred embodiment of the known process reason of the foregoing discussion. the larger part of the volatile sulfur dichlorides as well 3,592,593 3 4 as of the sulfur monochloride is removed already in the which was prepared by melting together 0.4 g. of FeCla ?rst step. To remove the smaller amounts of the sulfur and 400 g. of sulfur. dichloride remaining in the distillation product of the 37.9 kg./h. of a crude thionyl chloride product con ?rst column only a small amount of the iron-modi?ed taining 80.0% of SOCIZ, 14.5% of SClg, 4.3% of SZCIZ sulfur is necessary. This has the advantage that only and 1.1% of S02 were continually introduced into the small amounts of the iron compounds are brought into distillation vessel. In the continuous operation the mix the distillation residue containing mainly sulfur mono ture in the vessel, which boiled at 92° C., contained chloride, sulfur and thionyl chloride. The residues of 41.5% of SOCl2, 56.3% of SZCIZ and 2% of sulfur both steps can be used as starting material for the produc dissolved in the mixture; 15.8 kg./h. of the mixture ?ew tion of thionyl chloride. The process can be performed in off via the over?ow trap. 1.49 kg./h. of sulfur were the known types of fractional distilling columns, the consumed in the ?rst column and periodically replenished, invention lies in the process and not in a particular while 0.35 kg./h. of the iron-containing sulfur prepara apparatus. tion was consumed in the second column and replenished. The invention is further illustrated by the following At the same time, 23.4 kg. of the puri?ed product which examples without being restricted thereto. 15 was free from sulfur chlorides and which contained more than 99% of water-white SOClz were obtained from the EXAMPLE 1 condenser._ The process described below was carried out in a dis I claim: tillation equipment which consisted substantially of a 1. A process for recovering thionyl chloride from its ?ask of 1 litre capacity, which was equipped with an 20 admixture ‘with impurities including sulfur monochloride over?ow trap, a column of 5 cm. width and 67 cm. and sulfur dichloride, said process comprising the steps length and a re?ux condenser. The column was charged of fractionally distilling said mixture at a temperature at the lower 55 cm. of its length with Raschig rings of below the boiling point of sulfur monochloride and at 7 mm. diameter, at the upper 12 cm. with lumps of a which a gaseous mixture of thionyl chloride and sulfur sulfur preparation which was prepared by stirring 0.2 g. dichloride vaporizes, contacting said vapor mixture with of pyrite cinders into a melt of 300 g./hr. of sulfur. sulfur containing an effective amount of an active iron In the continuous operation 675 g. of a crude thionyl product and thereby converting sulfur dichloride of said chloride product containing 81% of SOCIZ, 14% of SCl2, vapor mixture to liquid sulfur monochloride, returning 2.3% of S2Cl2, and 2.4% of S02 was dropwise intro said liquid sulfur monochloride as re?ux to said mixture duced into a distillation ?ask so that the ?ask was 30 containing impurities and removing thionyl chloride as continually kept ?lled with 500 cm.3 of a mixture which overhead product. consisted of 47.3% of SOCl2, 50.4% of SZCIZ and 2.3% 2. Process according to claim 1, wherein said active of sulfur and which was boiled at 92-93“ C. 267 g./h. iron product is selected from the group consisting of of the mixture run off via the over?ow; the consumption iron sul?des, iron oxides, iron chlorides, iron nitrates, iron of sulfur in the column amounted to 39 g. per hour. 35 phosphates, ?nely divided iron and mixtures thereof. At the same time, 433 g. of the puri?ed product which 3. Process according to claim 1, wherein said active was free from sulfur chlorides and consisted of more iron product is present in an amount of about 0.01 to than 99% of water-white SOClz were obtained from the 10 grams, calculated as iron per 100 grams of sulfur. condenser, 4. Process according to claim 1, wherein said active EXAMPLE 2 40 iron product is present in an amount of about 0.02 to The process described below was carried out in a dis 1 gram, calculated as iron per 100 grams of sulfur. tillation equipment consisting of a gas-heated distilla 5. Process according to claim 1, wherein the sulfur tion vessel of 50 1. capacity, which was equipped with an is present in solid form containing said active iron product in ?nely divided form therein. over?ow trap, a ?rst column of 20 cm. vwidth and 220 45 cm. length, a second column of the same Width and 6. A process according to claim 1 wherein said gaseous 110 cm. length and a re?ux condenser. At the lower mixture containing thionyl chloride and sulfur dichloride 140 cm. of its length the ?rst column was ?lled with is contacted with sulfur prior to said contact with sulfur Raschig rings, at the upper 80 cm. with ordinary sulfur containing an effective amount of an active iron product. lumps. The vapor outlet means of the ?rst column was 50 connected to the vapor inlet means of the second column; References Cited the re?ux condenser of the second column was provided UNITED STATES PATENTS with a delivery pipe extending from the foot of the 2,539,679 l/l95l Trager ______23——203X second column to the center of the ?rst column. The 3,155,457 ll/l964 Kunkel ______23—203 second distillation column was charged with Raschig rings 55 at the lower 50 cm. of its length and, above that, at EARL C. THOMAS, Primary Examiner a height of 50 cm., with lumps of a sulfur preparation V_ 4______

F'O-IOSO UNITED STATES PATENT OFFICE ‘ 1 CERTIFICATE OF CORRECTION Patent No.“~~_A3+59-2+593\ DEtBdmLJ-ML InventoI-(s)~_LBenn° 18.02% T_\__~_N

Col. 1, line 55, "SgCl" should read -- S2612 --. 7 Col. 3, line 26, "g./hr. " should read -- g. - O

Signed and sealed this 11th day of January 1972.

(SEAL) Attest:

AttestingEDWARD M.F'LETCHER, Officer JR. ROBERT GO'I'TSCHALK Acting Commissioner of Patents