Nov. 30, 1965 KAZUO OKAMURA ETAL 3,221,070 ISOLATION OF TETRAFLUOROETHYLENE AND HEXAFLUOROPROPENE FROM THE PYROLYZATES OF CHLORODIFIUOROMETHANE Filed Sept. 12, 1963

INVENTORS KAZUO OKAMURA YUTAKA KOMETAN MASAYOSH TATEMOTO

fast highATTORNEYS 3,221,070 United States Patent Office Patented Nov. 30, 1965 2 3,221,070 tion and therefore makes it difficult to obtain high purity ISOATION OF TETRAFLUOROETHYLENE AND tetrafluoroethylene from this distillate, even with preci HEXAFLUOROPROPENE FROM THE PYROLY. Sion fractionation equipment. Tetrafluoroethylene may ZATES OF CHLORODFLUOROMETHANE be separated from hexafluoropropene and unreacted chlo Kazuo Okamura, Suita-shi, Osaka, Yutaka Kometani, rodifluoromethane by further fractional distillation of Sanda-shi, Hyogo Prefecture, and Masayoshi Tatemoto, the high boiling distillation residue; however, hexafluoro Osaka, Japan, assignors, by mesne assignments, to Thio propene and chlorodifluoromethane form an azeotropic ko Chemical Corporation, Trenton, N.J., a corporation mixture containing 13 mole percent of hexafluoropropene of Delaware and 87 mole percent of chlorodifluoromethane, with any Filed Sept. 2, 1963, Ser. No. 308,496 eXcess chlorodifluoromethane remaining in the still resi 11 Caines. (C. 260-653.3) O due, and consequently high purity hexafluoropropene This invention relates to the separation and recovery cannot be readily recovered from the high boiling distilla of the two commercially important fluoroolefins which tion residue. As a practical matter, therefore, the nor are formed upon the pyrolysis of chlorodifluoromethane, mal work-up by distillation of chlorodifluoromethane and its principal object is to provide a process for the pyrolyzates is inadequate for the purpose of isolating isolation and recovery of substantially pure tetrafluoro high purity tetrafluoroethylene and hexafluoropropene ethylene and hexafluoropropene from chlorodifluorometh from the pyrolysis reaction products. ane pyrolyzates. The present invention provides an improved process Tetrafluoroethylene and hexafluoropropene are pro for the isolation and recovery of substantially pure tetra duced commercially by the pyrolytic decomposition of 20 fluoroethylene and hexafluoropropene from chlorodifluo chlorodifluoromethane at a temperature from about 600 romethane pyrolyzates. Employing various fractional C. to about 1000 C., which pyrolysis is believed to distillates and distillation residues from chlorodifluoro result in the formation of the difluoromethylene diradical, methane pyrolyzates, we have found that at a given tem which, in turn, is capable of undergoing dimerization to perature the solubilities in polar organic solvents of tetrafluoroethylene and of undergoing more complex reac 2 5 Several components of these pyrolyzates vary significantly tions to form hexafluoropropene. The pyrolysis of from each other, although there may be little difference chlorodifluoromethane is an exceedingly complex reac in the solubilities of the remaining components. More tion, however, for the pyrolyzates have been found to over, we have found that even though these latter com contain tetrafluoroethylene, hexafluoropropene, unreacted ponents possess similar solubilities in polar organic sol chlorodifluoromethane, as well as minor amounts of di vents at a particular temperature, varying the tempera fluoromethane, trifluoromethane, chlorotrifluoromethane, ture of the solvent disproportionately changes their rela hexafluoroethane, dichlorodifluoromethane octafluorocy tive solubilities. For example, at 20 C, the solubility clobutane, chlorotrifluoroethylene octafluoroisobutene, of hexafluoropropene in methanol is 2 percent by weight, hydrogen chloride, to cite but a few of the readily iden while that of chlorodifluoromethane is 17 percent by tifiable components of the pyrolyzate. Table I sets forth Weight; at the same temperature, however, the solubilities several of the compounds, in the order of their ascending in methanol of trifluoromethane and tetrafluoroethylene boiling points, which have been isolated and identified are 2 percent and 1.7 percent by weight, respectively. from chlorodifluoromethane pyrolyzates and which dis By lowering the temperature of the solvent to from -40° till, at atmospheric pressure, at temperatures below 10° C. C. to 10 C., the difference in solubilities between tri 40 fluoromethane and tetrafluoroethylene increases signifi Table I-Low boiling compounds identified in cantly, thereby facilitating their separation by selective chlorodifluoromethane pyrolyzates Solvent absorption. This phenomenon has been observed with many highly polar organic Solvents, thereby per Compound: Boiling point ( C.) mitting these solvents to be employed in the selective Hydrogen chloride ------85 45 Solvent absorption of chlorodifluoromethane from a mix Trifluoromethane ------82.4 ture of chlorodifluoromethane and hexafluoropropene, or Chlorotrifluoromethane ------81.1 for the absorption of hexafluoroethane, trifluoromethane, Hexafluoroethane ------78.4 chiorotrifluoromethane and other low boiling compo Tetrafluoroethylene ------76.6 nents from a distillate containing tetrafluoroethylene and Chlorodifluoromethane ------40.8 50 these low boiling compounds. When the techniques of Hexafluoropropene ------29.4 multiple fractional distillation and selective solvent ab Octafluorocyclobutane ------5.5 sorption with polar organic solvents are effectively em Octafluoroisobutene ------7 ployed in the processing of chlorodifluoromethane pyrol Since the presence of minute traces of impurities in 55 yZates, it is possible to isolate and recover substantially tetrafluoroethylene or hexafluoropropene tend to de pure tetrafluoroethylene and hexafluoropropene from crease the thermal stability of homopolymers and co these pyrolyzates. Based on these discoveries, the invention provides a polymers produced from these fluoroolefins, careful puri processes for the isolation and recovery of substantially fication of tetrafluoroethylene and hexafluoropropene pure tetrafluoroethylene and hexafluoropropene from prepared by the pyrolysis of chlorodifluoromethane or 60 other halofluoroalkanes is required prior to their use in chlorodifluoromethane pyrolyzates which comprises (a) any polymerization process. Although the crude gaseous washing a pyrolyzate formed upon the pyrolysis of chlorodifluoromethane and containing tetrafluoroethylene, pyrolyzate of chlorodifluoromethane may be washed with hexafluoropropene, unreacted chlorodifluoromethane, and water to remove acid, dried, and then fractionally dis other components, with water to remove any water tilled in a conventional fractionation column to separate 65 it into two fractions, namely a low boiling distillate con soluble acids which were concurrently formed during taining trifluoromethane, chlorotrifluoromethane, hexa the pyrolysis reaction and which remain in the pyrolyzate; fluoroethane, and part of the tetrafluoroethylene, and a (b) subjecting the water-washed pyrolyzate to fractional distillation residue containing all of the remaining com distillation to separate the pyrolyzate into (i) a first dis ponents of the pyrolyzate, the close proximity of the tillate containing part of the tetrafluoroethylene and sub boiling points of all of the components in the low boiling 70 stantially all of the low boiling components of the distillate precludes their separation by fractional distilla pyrolyzate, and (ii) a first distillation residue; (c) con 3,221,070 3. 4. tacting the first distillate with a polar organic solvent at Table I, the difference in the solubilities of chlorodi a temperature in the range from about -40° C. to about fluoromethane and hexafluoropropene in methanol at 20 10° C. to dissolve by absorption substantially almost all C. is sufficiently large to permit the selective solvent ab of the low boiling components from the first distillate sorption of chlorodifluoromethane. At 20 C., the dif in the polar organic solvent while leaving undissolved 5 ference in solubility of trifluoromethane and tetrafluoro substantially all of the tetrafluoroethylene contained in ethylene in methanol is minute, thereby precluding the the first distillate; (d) combining the tetrafluoroethylene separation of these compounds by methanolic absorp remaining undissolved from the solvent absorption of tion at this temperature. By lowering the temperature of the first distillate with the first distillation residue and then the solvent to form -40° C. to 10 C., and preferably subjecting the resultant mixture to fractional distillation IO from -20° C. to 0° C., the solubility of trifluoromethane to separate it into (i) a second distillate consisting es is greatly increased without any substantial increase in sentially of substantially pure tetrafluoroethylene, there the solubility of tetrafluoroethylene, thereby permitting by isolating substantially pure tetrafluoroethylene from the selective solvent absorption of the low boiling com the pyrolyzate, and (ii) a second distillation residue; ponents from the chlorodifluoromethane pyrolyzates and recovering the resultant substantially pure tetrafluoro while leaving undissolved the tetrafluoroethylene. When ethylene from this fractional distillation; (e) subjecting these techniques of selective solvent absorption by polar the second distillation residue to fractional distillation organic solvents of certain components of the pyrolyzate to separate it into (i) a third distillate consisting essen are combined in a process employing fractional distilla tially of hexafluoropropene and chlorodifluoromethane, tion in accordance with the invention, it is possible to and (ii) a third distillation residue; (f) contacting the 20 isolate and recover tetrafluoroethylene and hexafluoropro third distillate with a polar organic solvent to dissolve by pene having a purity of 99 percent, or higher. More absorption substantially all of the chlorodifluoromethane over, the process may be made continuous and automated from the third distillate in the polar organic solvent while such that tetrafluoroethylene and hexafluoropropene are leaving undissolved substantially pure hexafluoropropene, isolated and recovered in high purity from the pyrolysis thereby isolating substantially pure hexafluoropropene reaction products of chlorodifiuoromethane, while the un from the pyrolyzate; and recovering the resultant sub reacted chlorodifluoromethane may be recovered and re santially pure hexafluoropropene from this selective sol cycled back to the pyrolysis reaction. vent absorption; and (g) recovering the chlorodifiuoro TABLE III.-Effect of temperature on the solubilities of methane remaining in the polar organic solvent employed chlorodifluoromethane, hexafluoropropene, trifloro in the solvent absorption of the third distillate. As used 30 herein, the phrase "low boiling components of the pyroly methane and tetrafluoroethylene in methanol and di zate' refers to those fluorocarbon compounds such as formanide trifluoromethane, chlorotrifluoromethane, and hexa Solubility in fluoroethane, which are formed upon the pyrolysis of Solubility in Methanol (Percent) Dimethyl chlorodifluoromethane and which possess a boiling point, Temperature formanide at atmospheric pressure, lower than that of tetrafluoro (° C.) (Percent) ethylene (-76.6° C.). The solvolytic selectivity exhibited by polar organic CIClF2 C3F8 CHF3 C2F4 CHF3 CF4 solvents for certain but not all components of the chlorodi

20------17 2 2 1.7 5 1,3 fluoromethane pyrolyzates may be illustrated by a com 40 0------4. 6 5 2 8.5 1.7 parison of the relative solubilities of hexafluoropropene 20 13 O 2.5 20 1.7 and chlorodifluoromethane in various highly polarized 80------15 2.5 28 1. and non-polar solvents. Table II sets forth the solubili ties, at 25 C., of hexafluoropropene and chlorodifuoro For illustrative purposes, a preferred practical embodi methane in various organic polar and non-polar solvents. 45 ment of the process of the invention is described below Table II.-Soltibilities of hexafluoropropene and with reference to the accompanying drawing, the single figure of which sets forth a schematic flow-sheet for the chlorodifiutoronethane continuous isolation and recovery of high purity tetra fluoroethylene and hexafluoropropene from chlorodiflu Solubility of Solubility of oromethane pyrolyzates: Solvent Hexafluoro- Chlorodifloro propene netlane Chlorodifluoromethane (B.P. -41. C.) was continu (Percent) (Percent) ously pyrolyzed in a reactor at a temperature in the range from about 600° C. to about 1000° C., using a Dimethylformamide------2.0 29, residence time in the reaction zone of the reactor 1 in the Acetone------3.8 20.0 Methanol----- 2.0 7.0 55 range from about 0.005 to about 0.2 second. The gaseous Ethanol.------2.6 2.0 Isopropanol- 2.6 10.0 pyrolyzate was scrubbed with water in an acid removal Belzele------... 3 6.0 tower 2 to dissolve hydrogen chloride, and the wet gas Dodecane.----- 1.3 4.0 was dried by passing it through a water-gas separator Carbon tetrachlorid 1... O 1.5 3 and then through a drying tower 4 packed with a suita 60 ble drying agent. Gas chromatographic analysis of the As shown in Table II, the solubility of hexafluoropro dry gas existing from the drying tower 4 indicated that ene in various organic solvents is below 4 percent by for every 100 parts by weight of tetrafluoroethylene, the weight, while the solubility of chlorodifluoromethane in Water-washed pyrolyzate contained from about 70 to highly polar organic solvents, such as dimethylformamide, about 250 parts by weight of unreacted chlorodifiuoro acetone, and alkanols with short carbon chains (e.g., 65 methane, from about 0 to about 2 parts by weight of tri lower alkanols), is from five to twenty times that of hexa fluoromethane, from about 0 to about 0.5 part by weight fluoropropene. Consequently, the chlorodifluoromethane of chlorotrifluoromethane, from about 0 to about 0.5 contained in an azeotropic mixture of hexafluoropropene part by weight of hexafluoroethane, from about 0 to 2 and chlorodifluoromethane may be selectively dissolved parts by weight of hexafluoropropene, and a small amount in a highly polar organic solvent without substantially dis O of a high boiling fraction, the variances in concentration solving the hexafluoropropene. of the components in the pyrolyzate being dependent upon The disproportionate effect of temperature on the solu tahe particular reaction conditions employed during the bilities of various components of chlorodifluoromethane pyrolysis. pyrolyzates in methanol and dimethylformamide is illus The dry gaseous pyrolyzate exiting from the drying trated by the data set forth in Table III. As shown in 5 toWer 4 was introduced into a first fractionation column 3,221,070 5 6 5 (bubble cap type) and continuously fractionally dis packing material. Methanol from the solvent storage tank tilled at a pressure in the range from 14 to 16 kilograms 8 was introduced into the top of the separation column 15 per square centimeter (gauge), with the over-head tem where it was sprayed downwardly to effect countercurrent perature of the column 5 maintained at about -5° C. absorption of the azeotropic mixture of hexafluoropropene to about -8 C. and chlorodifluoromethane rising upwardly through the The overhead distillate, which contained part of the column 17. At ambient temperatures (20 C. to 25 C.), tetrafluoroethylene, as well as the major portion of all methanol dissolved substantially all of the chlorodifluoro of the low boiling components of the pyrolyzate, such methane contained in the azeotropic mixture while leaving as trifluoromethane, chlorotrifluoromethane, hexafluoro the hexafluoropropene undissolved. ethane, and other compounds, was continuously recovered The undissolved hexafluoropropene exiting from the from the top of the first fractionation column 5 and col top of the second separation column 17 was passed lected in a storage tank 6, from which this distillate was through a stripper 18 to remove any entrained methanol, introduced into the bottom of a first separation column and then into a hexafluoropropene storage tank 19 from 7 packed with Raschig rings. Methanol from a solvent which it was recovered for use. Gas chromatographic storage tank 8 was pumped through a heat eXchanger 9, 5 analysis indicated that this hexafluoropropene had a which cooled the solvent to a temperature from -20° C. purity of more than 99 percent. to 0° C., and the cold methanol introduced into the top The methanol solution of chlorodifluoromethane exit of the separation column 7, where it was sprayed down ing from the bottom of the second separation column 17 wardly to effect countercurrent absorption of the distillate was pumped into a second solvent regenerator 20 where (B.P. -5° C. to -8° C.) flowing upwardly through the 20 chlorodifluoromethane was stripped from solution, recov separation column 7. At temperatures in the range from ered from the overhead of the solvent regenerator 20, and -20° C. to 0° C., the methanol selectively dissolved sub passed through a stripper 21 to remove any entrained stantially all of the low boiling components from the methanol. Although not shown in the accompanying distillate while leaving substantially undissolved the tetra flow-sheet, this chlorodifluoromethane was recycled back fluoroethylene contained in the distillate. to the pyrolysis reactor 1. Methanol was recovered from Methanol containing all of the low boiling components the bottom of the solvent regenerator 20 and recycled extracted from the low boiling distillate was continuously back to the solvent storage tank 8 for reuse. recovered from the bottom of the first separation column We claim: 7 and introduced into a first solvent regenerator 10, in 1. A process for the isolation and recovery of substan which the dissolved vapors were stripped from the meth 30 tially pure tetrafluoroethylene and hexafluoropropene anol and discarded. Solvent recovered from the bottom from chlorodifluoromethane pyrolyzates which comprises of the stripper 10 was recycled back to the solvent stor (a) washing a pyrolyzate formed upon the pyrolysis age tank 8. of chlorodifluoromethane and containing tetrafluoro Tetrafluoroethylene, which remained undissolved from ethylene, hexafluoropropene, unreacted chlorodifluo the methanol absorption of the low boiling distillate, romethane, and other components, with water to was continuously recovered from the top of the first remove any water-soluble acids which were con separation column 7, passed through a stripper 11 to re currently formed during the pyrolysis reaction and move any entrained methanol, and then stored in a which remain in the pyrolyzate; tetrafluoroethylene hold tank 12. This tetrafluoroethylene (b) subjecting the water-washed pyrolyzate to frac was combined with the distillation residue from the bot 40 tional distillation to separate the pyrolyzate into (i) tom of the first fractionation column 5 and the combined a first distillate containing part of the tetrafluoro feedstock introduced into a second fractionation column ethylene and substantially all of the low boiling com 13 (bubble cap type) where it was continuously frac ponents of the pyrolyzate, and (ii) a first distillation tionally distilled at a pressure from 7.5 to 9 kilograms residue; per square centimeter (gauge) with the temperature at (c) contacting the first distillate with a polar organic the top of the column 13 being maintained at -25 C. 45 solvent of the group consisting of methanol, ethanol, to -20° C. to recover tetrafluoroethylene having a purity isopropanol, acetone, and dimethylformamide at a of more than 99 percent as the overhead distillate. temperature in the range from about -40° C. to The distillation residue at the bottom of the second about 10 C. to dissolve by absorption substantially fractionation column 3 was continuously introduced into all of the low boiling components from the first dis a third fractionation column 14, where it was continuously 50 tillate in the polar organic solvent while leaving un fractionally distilled at a pressure of 4 to 5 kilograms dissolved substantially all of the tetrafluoroethylene per square centimeter (gauge) with the overhead tempera contained in the first distillate; ture of the column 14 being maintained at from 0 C. (d) combining the tetrafluoroethylene remaining un to 5° C. The overhead distillate was a two-component 55 dissolved from the solvent absorption of the first mixture of hexafluoropropene and chlorodifluoromethane, distillate with the first distillation residue and then while the bottoms were a high boiling residue which was subjecting the resultant mixture to fractional distilla discarded. tion to separate it into (i) a second distillate con The overhead distillate which exited from the third sisting essentially of substantially pure tetrafluoro fractionation column 14 was introduced into a fourth 60 ethylene, thereby isolating substantially pure tetra fractionation column 15 maintained at a pressure between fluoroethylene from the pyrolyzate, and (ii) a second 4 and 5 kilograms per square centimeter (gauge) and distillation residue; and recovering the resultant sub an overhead temperature of from 0° C. to 5 C. to sepa stantially pure tetrafluoroethylene; rate this mixture into an azeotrope consisting of 13 mole (e) subjecting the second distillation residue to frac percent of hexafluoropropene and 87 mole percent chloro tional distillation to separate it into (i) a third difluoromethane as the overhead distillate and excess 65 distillate consisting essentially of hexafluoropropene chlorodifluoromethane as the residue. The bottoms from and chlorodifluoromethane, and (ii) a third distilla the fourth fractionation column 15, consisting essentially tion residue; of chlorodifluoromethane, were recycled back to the pyro (f) contacting the third distillate with a polar organic lytic reactor 1 for further reaction. 70 solvent of the group consisting of methanol, ethanol, The azeotropic mixture of hexafluoropropene and isopropanol, acetone, and dimethylformamide to dis chlorodifluoromethane recovered as the overhead distillate solve by absorption substantially all of the chloro from the fourth separation column i5 was collected in a difluoromethane from the third distillate in the polar hold tank 6, from which it was pumped into the bottom organic solvent while leaving undissolved sub of a second separation column 17 packed with suitable stantially pure hexafluoropropene, thereby isolating 3,221,070 7 substantially pure hexafluoropropene from the pyro (c) contacting the first distillate with a lower alkanol lyZate, and recovering the resultant substantially pure at a temperature in the range from about -40° C. hexafluoropropene; and to about 10° C. to dissolve by absorption substan (g) recovering the chlorodifiuoromethane remaining in tially all of the low boiling components from the the polar organic solvent employed in the solvent first distillate in the alkanol while leaving undis absorption of the third distillate. solved substantially all of the tetrafluoroethylene 2. A process for the isolation and recovery of substan contained in the first distillate; tially pure tetrafluoroethylene and hexafluoropropene (d) combining the tetrafluoroethylene remaining un from chlorodifluoromethane pyrolyzates which comprises dissolved from the solvent absorption of the first (a) washing a pyrolyzate formed upon the pyrolysis O distiliate with the first distillation residue and then of chlorodifluoromethane and containing tetrafluoro Subjecting the resultant mixture to fractional dis ethylene, hexafluoropropene, unreacted chlorodifluo tillation at a pressure in the range from about 7.5 romethane, and other components, with water to re to about 9 kilograms per square centimeter gauge move any water-soluble acids which were concur to separate it into (i) a second distillate boiling in rently formed during the pyrolysis reaction and which the range from about -25 C. to about -20° C. remain in the pyrolyzate; and consisting essentially of substantially pure tetra (b) subjecting the water-washed pyrolyzate to frac fluoroethylene, thereby isolating substantially pure tional distillation to separate the pyrolyzate into (i) tetrafluoroethylene from the pyrolyzate, and (ii) a a first distillate containing part of the tetrafluoro Second distillation residue; and recovering the re ethylene and substantially all of the low boiling com 20 Sultant substantially pure tetrafluoroethylene; ponents of the pyrolyzate, and (ii) a first distillation (e) subjecting the second distillation residue to frac residue; tional distillation at a pressure in the range from (c) contacting the first distillate with a lower alkanol about 4 to about 5 kilograms per square centimeter at a temperature in the range from -20° C. to 0 C. gauge to separate it into (i) a third distillate boiling to dissolve by absorption substantially all of the low 25 in the range from about 0° C. to about 5° C. and boiling components from the first distiilate in the consisting essentially of a mixture containing hexa alkanol while leaving undissolved substantially all of fluoropropene and chlorodifluoromethane, and (ii) the tetrafluoroethylene contained in the first distillate; a third distillation residue; (d) combining the tetrafluoroethylene remaining un (f) contacting the third distillate with a lower alkanol dissolved from the solvent absorption of the first 30 in which the solubility of chlorodifluoromethane, distillate with the first distillation residue and then at 25 C., is at least five times greater than that of subjecting the resultant mixture to fractional distilla hexafluoropropene at the same temperature, to dis tion to separate it into (i) a second distillate solve by absorption substantially all of the chlorodi consisting essentially of substantially pure tetrafluo fluoromethane from the third distillate in the alkanol roethylene, thereby isolating substantially pure 35 while leaving undissolved substantially pure hexa tetrafluoroethylene from the pyrolyzate, and (ii) a fluoropropene, thereby isolating substantially pure second distillation residue; and recovering the re hexafluoropropene from the pyrolyzate; and recov sultant substantially pure tetrafluoroethylene; ering the resultant substantially pure hexofluoropro (e) subjecting the second distillation residue to frac pene; and tional distillation to separate it into (i) a third 40 (g) recovering the chlorodifluoromethane remaining distillate consisting essentially of hexafluoropropene in the alkanol employed in the solvent absorption of and chlorodifluoromethane and (ii) a third distilla the third distillate. tion residue; 4. A process for the isolation and recovery of sub (f) contacting the third distillate with a lower al stantially pure tetrafluoroethylene and hexafluoropropene kanol to dissolve by absorption substantially all of 45 from chlorodifluoromethane pyrolyzates which comprises the chlorodifluoromethane from the third distillate (a) washing a pyrolyzate formed upon the pyrolysis while leaving undissolved substantially pure hexa of chlorodifluoromethane and containing tetraflu fluoropropene, thereby isolating substantially pure Oroethylene, hexafluoropropene, unreacted chlorodi hexafluoropropene from the pyrolyzate; and recov fluoromethane, and other components, with water ering the resultant substantially pure hexafluoropro 50 to remove any water-soluble acids which were con pene; and currently formed during the pyrolysis reaction and (g) recovering the chlorodifluoromethane remaining which remain in the pyrolyzate; in the alkanol employed in the solvent absorption (b) Subjecting the water-washed pyrolyzate to frac of the third distillate. tional distillation at a pressure in the range from 3. A process for the isolation and recovery of sub 55 about 14 to about 16 kilograms per square centimeter stantially pure tetrafluoroethylene and hexafluoro gauge to separate the pyrolyzate into (i) a first dis propene from chlorodifluoromethane pyrolyzates tillate boiling in the range from about -5° C. to which comprises about -8 C. and containing part of the tetrafluoro (a) washing a pyrolyzate formed upon the pyrolysis ethylene and substantially all of the low boiling com of chlorodifluoromethane and containing tetraflu 60 ponents of the pyrolyzate, and (ii) a first distillation residue; oroethylene, hexafluoropropene, unreacted chlorodi (c) contacting the first distillate with methanol at a fluoromethane, and other components, with water temperature in the rang from -20° C. to 0° C. to to remove any water-soluble acids which were con dissolve by absorption substantially all of the low currently formed during the pyrolysis reaction and 65 boiling components from the first distillate in the which remain in the pyrolyzate; methanol while leaving undissolved substantially all (b) subjecting the water-washed pyrolyzate to frac of the tetrafluoroethylene contained in the first dis tional distillation at a pressure in the range from tillate; about 14 to about 16 kilograms per square centi (d) combining the tetrafluoroethylene remaining un meter gauge to separate the pyrolyzate into (i) a 70 dissolved from the solvent absorption of the first first distillate boiling in the range from about -5 distillate with the first distillation residue and then C. to about -8 C. and containing part of the tetra Subjecting the resultant mixture to fractional dis fluoroethylene and substantially all of the low boil tillation at a pressure in the range from about 7.5 ing components of the pyrolyzate, and (ii) a first to about 9 kilograms per square centimeter gauge distillation residue; 75 to Separate it into (i) a second distillate boiling 3,221,070 9 O in the range from about -25 C. to about -20° C. ponents which comprises contacting the distillate with and consisting essentially of substantially pure tetra methanol at a temperature in the range from -20 C. to fluoroethylene, thereby isolating substantially pure 0° C. to dissolve substantially all of the low boiling com tetrafluoroethylene from the pyrolyzate, and (ii) a ponents from the distillate in the methanol while leaving second distillation residue; and recovering the re undissolved substantially all of the tetrafluoroethylene, sultant substantially pure tetrafluoroethylene; thereby isolating tetrafluoroethylene from the distillate. (e) subjecting the second distillation residue to frac 8. The method of isolating hexafluoropropene from a tional distillation at a pressure in the range from mixture of hexafluoropropene and chlorodifluorometh about 4 to about 5 kilograms per square centimeter ane which comprises contacting the mixture with a lower gauge to separate it into (i) a third distillate boil O alkanol to dissolve substantially all of the chlorodifluoro ing in the range from about 0° C. to about 5 C. and methane from the mixture in the alkanol while leaving consisting essentially of a mixture containing hexa undissolved substantially all of the hexafluoropropene, fluoropropene and chlorodifluoromethane, and (ii) thereby isolating hexafluoropropene from the mixture. a third distillation residue; 9. The method of isolating substantially pure hexo (f) contacting the third distillate with methanol to 5 fluoropropene from an azeotropic mixture of hexafluoro dissolve by absorption substantially all of the chlor propene and chlorodifluoromethane which comprises odifluoromethane from the third distillate in the contacting the azeotropic mixture with a lower alkanol methanol while leaving undissolved substantially in which the solubility of chlorodifluoromethane, at 25 pure hexafluoropropene, thereby isolating Substan C., is at least five times greater than that of hexafluoro tially pure hexafluoropropene from the pyrolyzate; 20 propene at the same temperature, to dissolve substan and recovering the resultant substantially pure hexa tially all of the chlorodifluoromethane from the azeo fluoropropene; and tropic mixture in the alkanol while leaving undissolved (g) recovering the chlorodifluoromethane remaining substantially all of the hexafluoropropene, thereby isolat in the methanol employed in the solvent absorption ing substantially pure hexafluoropropene from the azeo of the third distilate. 25 tropic mixture. 5. The method of isolating tetrafluoroethylene from a 10. The method of isolating substantially pure hexa distillate containing tetrafluoroethylene, hexafluoropro fluoropropene from an azeotropic mixture of hexafluoro pene, chlorodifluoromethane, and other low boiling com propene and chlorodifluoromethane which comprises ponents which comprises contacting the distillate at a contacting the azeotropic mixture with methanol to dis temperature in the range from -40 C. to 10 C. with 30 solve substantially all of the chlorodifluoromethane from a lower alkanol to dissolve substantially all of the low the azeotropic mixture in the methanol while leaving boiling components from the distillate in the alkanol undissolved substantially all of the hexafluoropropene, while leaving undissolved substantially all of the tetra thereby isolating substantially pure hexafluoropropene fluoroethylene, thereby isolating tetrafluoroethylene from from the azeotropic mixture. the distillate. 35 11. The method of isolating substantially pure hexa 6. The method of isolating tetrafluoroethylene from fluoropropene from an azeotropic mixture of hexafluoro a distillate containing tetrafluoroethylene, hexafluoropro propene and chlorodifluoromethane which comprises con pene, chlorodifluoromethane and other low boiling com tacting the azeotropic mixture with dimethylformamide ponents which comprises contacting the distillate at a to dissolve substantially all of the chlorodifluoromethane temperature in the range from -20° C. to 0 C. with a 40 from the azeotropic mixture in the dimethylformamide lower alkanol to dissolve substantially all of the low boil while leaving undissolved substantially all of the hexa ing components from the distillate in the alkanol while fluoropropene, thereby isolating substantially pure hexa leaving undissolved substantially all of the tetrafluoro fluoropropene from the azeotropic mixture. ethylene, thereby isolating tetrafluoroethylene from the distillate. 45 No references cited. 7. The method of isolating tetrafluoroethylene from a distillate containing tetrafluoroethylene, hexafluoropro LEON ZITVER, Primary Examiner. pene, chlorodifluoromethane and other low boiling com DANIEL D. HORWITZ, Examiner. UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 221,070 November 30, 1965 Kazuo Okamura et al. It is hereby certified that error appears in the above numbered pat ent requiring correction and that the said Letters Patent should read as corrected below. Column 2, line 58, for 'processes' read - - process - -; column 4, line 9, for 'form' read -- from - -; TABLE III, in the heading for 'diformamide', in italics, read -- dimethylformamide - -, in italics; line 72, for "tahe" read -- the - -; column 5, lines 9 and 10, for "hexa fluoroethane' read -- hexafluoro ethane - - ; column 8, line 63, for "rang" read -- range -- . Signed and sealed this 27th day of September 1966.

(SEAL) Attest: ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents