sign in sign up
<<
Home , Chlorodifluoromethane, Hydrogen fluoride

Patented May 26, 1953 2,640,086 UNITED STATES PATENT of FICE 2,640,086 PROCESS FOR SEPARATING FROM CHLORODFLUORO Robert H. Baldwin, Chadds Ford, Pa., assignor to E. H. du Pont de Nemours and Company, Wi inington, Del, a corporation of Delaware No Drawing. Application December 15, 1951, Serial No. 261,929 9 Claims. (C. 260-653) 2 This invention relates to a process for Sep These objects are accomplished essentially by arating from monochlorodi Subjecting a mixture of hydrogen fluoride and fluoronethane, and more particularly, separat Inonochlorodifluoromethane in the liquid phase ing these components from the reaction mixture to temperatures below 0° C., preferably at about obtained in the fluorination of with -30° C. to -50° C., at either atmospheric or hydrogen fluoride, Super-atmospheric pressures, together with from In the fluorination of chloroform in the prest about 0.25 mol to about 2.5 mols of chloroform ence Of a Catalyst, a reaction mixture is pro per mol of chlorodifluoronethane contained in duced which consists essentially of HCl, HF, the mixture and separating an upper layer rich CHCIF2, CHCl2F, CHCls, and CHF3. A method O in HF from a lower organic layer. The proceSS of Separating these components is disclosed in is operative with mixtures containing up to 77% U. S. Patent No. 2,450,414 which involves sep by weight of HF. arating the components by a special fractional It has been found that chloroform is substan distillation under appropriate temperatures and tially immiscible With EIF at temperatures be pressures. In this method, the components sep 5 low 0° C., and that at -50° C., HF is soluble in arate Satisfactorily except monochlorodifluoro chloroform to the extent of only 0.063% by methane and hydrogen fluoride which, unfor Weight. and hydrogen tunately, form an azeotrope containing from fioride are completely miscible at temperatures about 1% to 2.2% by Weight of HF. The two at least down to -50° C., and at this tempera Components of this azeotrope are separated by 20 ture a 50% by weight solution of HF in the Scrubbing in wherein hydrofluoric is Chlorodifuoromethane is homogeneous. In the formed and removed from the monochlorodifill preferred method, temperatures of about -30 Oronethane. In this method of separation, a C. to -50 C. are preferred for the separation. Serious less of HE in the Wash Water is involved However, considerable extension of either side and represets an important economic factor in 25 of this range is permissible. the cost of the fluorination process, In Carrying Out the invention, chloroform is Several Suggestions have been made for re added to the mixture of hydrogen fluoride and COvering the HF from the above-mentioned Sys chlorodifiuoromethane preferably in the ratio of tenn. According to U. S. Patent No. 2,374,89, about from 0.25 to about 2.5 mols of chloroform the HF is absorbed on activated charcoal from 30 per mol of monochlorodifluoromethane. How Which it is. Subsequently recovered. This methin ever, a Somewhat Smaller amount of chloroform Gd, however, is cumbersome and involves the in may be used, Since the limiting Value is the stallation of Specialized equipment which adds approach to the formation of the HFCCFa considerably to the cost of the recovery of the azeotrope. On the other hand, amounts of HF. Moreover, it is a batch process which is 35 chloroform greater than the upper limit of the inconvenient in that it requires a bank of ab range may be used, but HF has a solubility in SOrbing beds of activated charcoal if the recovery chloroform of 0.063% by weight at -50° C., and of HF is to be continuous. as the amount of chloroform is increased, more Another method of recovering the HF con HF would be dissolved in the organic layer of Sists of forming an adduct between it and so chloroform and chlorodifluoromethane. The dium fluoride or potassium fiuoride. This proc 40 preferred ratio of chloroform is between and ess likewise is costly and requires considerable 2 mols permol of CHCIF2. SuperVision. With respect to the concentration of hydrogen It is an object of this invention, therefore, to fluoride, this may vary from as low as 0.5% provide a process for separating HF and CHCIF2 45 up to about 77% by Weight in the HF-CHCIF economically. Another object is the provision mixture. The normal amount of hydrogen of a method of Separating these two components fluoride in the HF-organic liquid after removal without the use of special or expensive equip of HCl from the products of the fluorination ment. A still further object is the provision of mentioned above is usually about 3% by weight. a method by which the hydrogen fluoride re 50 covered is in a form usable for further reac EXAMPLES ITO WI tion with chloroform. A still further object is A pressure cylinder was filled with HF, CHCIF, the provision of a method which may be cons and CHCl3 in the amounts required to make up ducted continually with a minimum of atten a total charge. The cylinder was held at -509 tion. Other objects will appear as the descrip 55 C. for one hour with frequent shaking. After a tion of the invention proceeds. Settling time of about two minutes, a sample 2,640,086 3 4 of the upper layer which contained the HF and This overhead fraction was then scrubbed to re the lower organic layer which was made up of move the acidic constituents. CHClF2 and CHCl3 was taken, care being taken An alternative method of treating the lower to prevent mixing between the layers. Each liquid is to remove the HF, HCl, SO2, and COCl2 layer was vaporized and the gases scrubbed with 5 and then separate the CHClF2 and CHCl3 by dis Water, and the organic layer was recondensed. tillation. The chloroform so obtained is then The scrubber water was titrated for acidity and either returned to the HF-CHCIF2 separation sys the content was computed. ten or to the reaction chamber where it is re The organic fractions were collected over carbon acted with HF catalytically. dioxide ice, Weighed, and their compositions eS O The present invention offers many advantages, timated from initial and boiling the chief of which is that no extraneous reagents range measurements. The results from the are added to effect the separation. The chloro above experiments are tabulated below, each of form used is one of the reactants of the main which was carried out in identical manner ex reaction which produces the mixture with which cept as indicated in the table. 5 the present invention is concerned. Another ad Table CBICIF-HF-CHCls PBASE EQUILIBRIA Composition, Wt. Percent Mol Ratio Temp., Example CHCIF, HF CHO, QE2. ' 2 CHCF,

1. Total charge------29.4 38.8 31.8 78 Organic layer.-- 44.9 0.28 55.8 0.9 -50 HF layer. -- 13 81 6 ------2. Total charge- 58.6 21.2 20.2 0.25 Organic layer 72.5 0.96 26.6 0.264 -50 EIF layer--- - 32.4 59.5 8.2 ------3. Total charge------13.1 44.2 42.7 2.4 Organic layer------2.8 0.5 78.0 2.5 -50 HF layer---- 4.1 92.5 3. 4------4. Total charge------47.1 Organic layer------0.063 -50 HF layer------95.4 5. Total charge------29.6 38.4 Organic layer 0.32 - 40 HF layer---- 6. S.rganic E; layer -- 50 HF layer.---

EXAMPLE WI vantage of the present invention is that the hy drogen fluoride recovered is in an anhydrous form "This example illustrates a continuous opera Suitable for use in the fluorination process. tiun of the invention. Chloroform flowing at the It is apparent that many widely different em rate of 936 parts per hour, was reacted With 33 bodiments of this invention may be made without parts per hour of hydrogen fluoride in the pres 45 departing from the Spirit and scope thereof, and ence of an antimony chloride catalyst. The HCl therefore it is not intended to be limited except formed was removed from the remaining reac as indicated in the appended claims. tion products by distillation. The effluent liquid I claim: Inixture from the fluorination chamber minus 1. The process of separating a mixture of hy the HCl was drawn off at a temperature of i8 50 drogen fluoride and monochlorodifluoromethane C. under a gage preSSure of 110 p. S. i. at the rate which comprises adding chloroform to the mix of 645 parts per hour of CHClF2, 24 parts per ture and subjecting the same to a temperature hour of HF, 2.1 parts per hour of COCl2, and below 0° C., allowing two layers to form and Small amounts of SO2, CHCl2F, CHF3, and a trace thereafter separating the said layers, the ratio of of HCl, Into this stream, 893 parts per hour of 55 the chloroform to the monochlorodifluorometh chloroform was injected and the resulting mix ane being from 0.25 mol to 2.5 mols of chloro ture was cooled to -50 C. by passing it through form per mol of monochlorodifluoromethane. a heat exchanger. The cooled liquid was allowed 2. The process of claim 1 in which the tem to Separate in two layers in a separation tank perature is from about -30° C. to about -50° C. at a gage preSSure of about 90 p.s. i. The top 60 3. The process of claim 1 in which the chloro layer was withdrawn continuously and analyzed form is added in the amount of from 1 molto 1.4 parts pel' hour of chloroform, 3.0 parts per about 2 mols of chloroform per mol of mono chlorodifluoromethane. hour of CHClF2, 20 parts per hour of HF and 4. The process of claim 1 in which the hydro a trace of SO2, COCl2, and HC1. This stream 65 gen fluoride is present up to 77%, by Weight of was then recycled for further reaction with chlo the HF-CHClF2 mixture. roform in the catalytic chamber. 5. In the process of reacting hydrogen fluoride The bottom layer was also continuously with and chloroform in the presence of a Catalyst and drawn and analyzed 642 parts per hour of CHClF2, separating the resulting products, one of which 891 parts per hour of CHCl3, 3.6 parts per hour 70 is a mixture of hydrogen fluoride and mono of HF and Small amounts of COCl2, SO2 and chlorodifluoromethane, the improvement which HCl. This mixture was distilled to separate the comprises adding chloroform thereto, Subjecting chloroform from the other compounds present. the same to a temperature below 0° C., allowing The overhead fraction was principally CHCIF the cooled mixture to form two immiscible layers. with the minor portions of acidic constituents. s and thereafter separating the Same, the ratio of 2,640,086 s the chloroform to the monochlorodifuorometh provement which comprises separating the hy ane being from 0.25 mol to 2.5 mols of chloroform drogen fluoride from the monochlorodifluoro per mol of monochlorodifiuoromethane. methane by adding from about 0.25 mol to about 6. The process of claim 5 in which the tem 2.5 nois of chloroform thereto for each mol of perature is from about -30° C. to about -50° C. monochlorodifluoromethane, subjecting the mix 7. The process of claim 5 in which the chloro ture to a temperature below 0° C., separating the form is added in the amount of from 1 mol to two layers so formed, returning the upper HF about 2 mols of chloroform per mol of mono layer to the reaction mixture and recovering chlo chlorodifluoromethane. roform from the lower layer and returning it to 8. The process of claim 5 in which the hydro 10 the said mixture. gen fluoride is present in amount less than 77% by weight of the HF-CHClF2 mixture. ROBERT H. BALOWIN. 9. In a continuous process of fluorinating chlo References Cited in the file of this patent loform by passing a mixture of hydrogen fluoride UNITED STATES PATENTS and chloroform over a catalyst wherein a product s containing unreacted hydrogen fluoride and Number Name Date monochlorodifluoromethane is obtained, the im 2005,710 Daudt ------June 18, 1935