3,377,391 United States Patent Office Patented Apr. 9, 1968 2 3,377,391 As earlier stated, in combination with the high pyrolysis HIGH TEMPERATURE, SHORT-CONTACT temperatures employed in accordance with this invention, TIME PYROLYSS OF CHLOROTREFLU OROMETHANE very short contact times of the CCF at such temper John Richard Soulen, Narberth, and William Ford atures are used, that is, contact times on the order of about Schwartz, King of Prussia, Pa., assignors to Penn 0.0002 to 0.05 second, preferably in the range of about salt Cemicals Corporation, Philadelphia, Pa., a cor 0.0006 to about 0.01 second. At contact times of the usual poration of Pennsylvania order of magnitude used in pyrolyses of this type, i.e., of No Drawing. Filed Oct. 20, 1965, Ser. No. 499,084 the order of about 10 seconds and higher, the process of 6 Claims. (Cl. 260-653) this invention is inoperative because of considerable de 10 gradation of the reactant and reaction products. As used herein, contact time is defined as follows: ABSTRACT OF THE DISCLOSURE Chlorotrifluoromethane (CCIF) is pyrolyzed at a tem contact time (seconds)= perature within the range of about 1200° C. to about heated reactor volume 2000 C. for a period of from 0.0002 to 0.05 second to volume of gas per second (calculated produce, as the major products, 1,2-dichlorotetrafluoro at reaction temperature and pressure) ethane, carbon tetrafluoride, and dichlorodifluoromethane. fed to reactor

20 The short contact times indicated above for the pyrol This invention relates to the preparation of other or ysis of this invention correspond to very high space velo ganic fluoro and fluorochloro compounds by the pyrolysis cities ranging from about 500 to about 120,000 per hour of chlorotrifluoromethane. More particularly, this inven which permit a high rate of feed and reduce reactor vol tion concerns pyrolyzing chlorotrifluoromethane (CCIF) ume needed. Space velocity is defined as volumes of react to produce, as the major products, 1,2-dichlorotetrafluoro ant (measured at standard temperature and pressure ethane (CClF2CClF2), carbon tetrafluoride (CFA), and (STP), i.e., 0° C. and 760 mm. Hg) per volume of dichlorodifluoromethane (CCF). By "pyrolysis” is heated reactor per hour. This is in sharp contrast to the meant the trasformation of a compound into another com much lower space velocities previously employed in the pound or other compounds through the agency of heat pyrolysis of CCIFs, on the order of about 9 per hour. For alone, and therefore the term includes not only the re 30 example, A. B. Trenwith and R. H. Watson, J. Chem. arrangement of a compound but also the making of more Soc., ibid., used the extended reaction times of about 100 complex compounds. to 115 seconds for pyrolyzing CCIF at 700° C. to 850° C. A. B. Trenwith and R. H. Watson, J. Chem. Soc., 1957, The reaction pressure in the present process is not pp. 2368-2372, describe the pyrolysis of CCIF at tem critical and may be atmospheric, subatmospheric, or peratures ranging from 700 to 850° C., whereby the prin superatomspheres. Superatomspheric pressure may range, cipal products were CO2 and chlorine, with a smaller e.g., up to about 10 atmospheres. However, atmospheric amount of CF2Cl2 and a trace amount of CFA being pro and subatmospheric pressure operation will generally be duced. CCIFCCF2 was not found in the reaction pro found most convenient. As a practical limit, pressures ducts. N. V. Thornton, A. B. Burg and H. I. Schlesinger, lower than about one mm. Hg abs. are not recommended. JACS, 55 (1933), pp. 3177-3182, decomposed CCF in 40 Preferred operating pressures will generally range from a high tension electric discharge to produce CF and about 10 mm. Hg to atmospheric pressure. - Smaller quantities of CCl2F2; however, no chlorofluoro The reaction is conveniently carried out by continuously ethanes were produced by this electric discharge tech passing a stream of the CClF3 feed through an elongated n1cque. tube preferably having a high ratio of wall area to cross It has now been discovered that high temperature sectional area so that heat may be rapidly and continuous pyrolysis of CCF, i.e., in the range of about 1200° C. ly transferred from the heated reactor walls to the gaseous to about 2000 C., unexpectedly produces CCFCCF, reactant. The reactor should be constructed of a material CF4 and CCl2F2 in relatively high yields as principal resistant to attack by the reactant and reaction products reaction products, and as minor products, CFFCF, at the high operating temperatures. Materials of this type CClF and CCl2FCClF2. However, the period of the 50 include for example, inert graphite, boron nitride, and pyrolysis reaction embodied herein is very short and like inert materials. The reactor can be heated to the de should not exceed about 0.05 second. sired pyrolysis temperatures in any suitable manner such The product CF is useful as a dielectric fluid and as as by electrical induction heating or by placing the reactor a component of aerosol and refrigerant compositions. The in an electrically heated furnace. product CClFCClF2 is a valuable refrigerant used 55 The products of the pyrolysis passing from the reactor mainly in systems having centrifugal rotary compressors. are cooled and usually will be scrubbed in caustic solution The product CCl2F also is a kell known refrigerant. The or other alkaline solution to remove acidic inorganic by minor product CFFCF is a starting material for prepar products (e.g., chlorine and fluorine). The organic pro ing useful polymers. The minor product CCl3F also is a ducts are separated from the reaction mixture in a con well-known refrigerant and, moreover, CCl2F and CCF 60 ventional manner by fractional distillation. The unreacted each can be pyrolyzed at high temperatures to produce CCF can, of course, be recovered for recycling purposes. additional CClFCClF2, as set forth in our copending applications, Ser. No. 497,535, filed Oct. 18, 1965 and EXAMPLES 1-5 Ser. No. 495,348, filed Oct. 12, 1965, respectively. In the experiments herein described, specific embodi As stated above, the pyrolysis of CClF3 is carried out 65 ments of the invention are set forth to illustrate and according to this invention at a temperature within the clarify the invention. range of about 1200° C. to about 2000 C. The preferred Gaseous CCIF is passed continuously at a measured temperature range, with regard to obtaining the highest rate through a V8' I.D. x /2' O.D. x 13' long, inert conversion of the CCF and best yields of CClFCClF2 graphite tube reactor centered within a 2' diameter and CF, therefrom, is from about 1450° C. to about 70 "Vycor' high-silica glass tube, 15' long. The reactor is 1850° C. inductively heated with a 3/4' long load coil of 12 turns 3,377,391 3 4. of 4' copper tubing about the “Vycor' tube, the power scope of the invention which is defined by the appended for said coil supplied by a high frequency generator with claims. ABLE I Pyrolvsis Conditions Percent Exampic RateFeed of Imm.Pressure Hg, Tenn., ContactTime, Conversionof CCF Weight percent in recovered converted product of - gmis.jmin.CCF. Abs. oC. Seconds CCFCC1F, CF CCF, CF = CF, C.C.F CCF CCF, l------0.449 3. 1, 450 ), O24 21.8 8.8 46.3 2.8 0. Ni c 2 0.465 35 129 0.0024 68.2 4.5 56.2 - 18.3 7.5 (), 7 (...) 3. 0.352 38 s Q.933 7.9 8. A $9.2 25.3 2.7 9 (), 9 4. 0.204 44 1279) 0.005) 8.3 7.4 3. 8s. 4.4 9 2, 4 5 - 0. i47 2 2850 0.004 85.0 28.4 34.8 22 2.3 5.9 ... 3 a maximum output of 7.5 kilowatts operating at 450 kilo- We claim: cycles. The effective reaction zone in the tube is thus 34 lis 1. The method which comprises pyrolyzing chlorotri inches. The temperature of the reactor is measured with fluoromethane at a temperature of from about 1200° C. an optical pyrometer focused on the center of the heated to about 2000 C. wherein the pyrolysis time is from portion of the tube. Examination of the inert graphite re- about 0.0002 to about 0.05 second, a major product of actor after repeated runs therein reveals that its inner the pyrolysis being 1,2-dichlorotetrafluoroethane. surface is unaffected by the passage of the hot gases 20 2. The method of claim 1 wherein the pyrolysis tem therethrough. - perature is from about 1450° C. to about 1850° C. The product mixture passes from the reactor and is 3. The method of claim 1 wherein the pyrolysis time condensed in a trap cooled with liquid nitrogen. The con- is from about 0.0006 to about 0.01 second. - denser is vented to a mechanical vacuum pump which 4. The method which comprises pyrolyzing chlorotri maintains the subatmospheric reaction pressure employed 25 fluoromethane at a temperature of from about 1450° C. in these examples. After completion of the run, the reac- to about 1850° C. wherein the pyrolysis time is from tion products are warmed to room temperature and trans- about 0.0006 to 0.01 second, a major product of the ferred to an evacuated stainless steel cylinder. The reaction pyrolysis being 1,2-dichlorotetrafluoroethane. products are then passed through a series of scrubbers 5. The method of pyrolyzing chlorotrifluoromethane containing aqueous solutions of sodium hydroxide to re- 80 which comprises passing chlorotrifluoromethane through move inorganic by-products. The organic reaction prod- a tube heated to a temperature of from about 1200° C. ucts are analyzed using gas-liquid chromatographic and to about 2000° C., wherein the contact time is within infrared analyses techniques. the range of about 0.0002 to 0.05 second, a major prod The data from five runs are summarized in Table I. uct of the pyrolysis being 1,2-dichlorotetrafluoroethane. In addition to the components listed in the “Product” 8 6. The method of pyrolyzing chlorotrifluoromethane column of Table I, the reaction products contain unre- which comprises passing chlorotrifluoromethane through acted CCF and varying minor amounts of CFCF3, and a tube heated to a temperature of from about 1450° C. CC4. to about 1850° C., wherein the contact time is within the EXAMPLE 6 range of about 0.0006 to about 0.01 second, a major 40 product of the pyrolysis being 1,2-dichlorotetrafluoro The procedure of the preceding examples is repeated ethane. using an 80% platinum-20% rhodium alloy tube as the References Cited pyrolysis reactor. The pyrolysis temperature is about UNITED STATES PATENTS time1500 is C.,0.002 the secondpressure (space is 25 velocity-9390mm. Hg and theper contacthour). 45 3,009,966 11/1961 Hauptschein et al. 260-653.3 59% of the CCF fed is converted via the pyrolysis re- 3,188,356 6/1965 Hauptschein et al. -- 260-653.5 action. The principal reaction products are CF4 (70 weight FOREIGN PATENTS percent), CCIFCCIF (6%) and CCF (24%). 1,357,773 3/1964 France. It is to be understood that the foregoing illustrative 50 examples should not be construed as limitative of the DANIEL D. HORWITZ, Primary Examiner. UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,377,391 April 9, 1968 John Richard Soulen et a 1. 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 l, line 57, 'kell' should read -- well -- . Column 2, line 54, "superatmospheres" should read -- super tomospheric --. Columns 3 and 4, TABLE I, second Column, line 1 thereof, "O. 449" should read - - 0. 448 - - ; same TABLE, fourth column, lines 1, 2, 3, 4 and 5 thereof,

1, 450 1,450 12610 1, 610 1,705 Should read 1,705 12790 1,790 285 O 1,850 same TABLE I, ninth column, line 2 thereof, "18.3" should read - - 18.4 - - . Signed and sealed this 2nd day of September 1969.

(SEAL) At test: EDWARD M.FLETCHER, JR. WILLIAM E. SCHUYLER, JR. At testing Officer Commissioner of Patents