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US2979539.Pdf 2,979,539 United States Patent Office Patented Apr. 11, 1961 2 fluoride, vinylidene chloride, vinyl chloride, 1,1-difluoro dichloroethylene, propene, ethylene, 3,3,4,4,4-pentafluoro 2,979,539 buetene-1, perfluoropropene, and hexafluorobutene-1. DFLUOROCAR BENE FREE RADCALS IN THE Generally the ethylenes are preferred, particularly the SYNTHESS OF FLUORNATED OLEFNC COM fluorinated ethylenes. The use of tetrafluoroethylene in POUNDS this process, producing perfluoropropene, constitutes a Louis A. Errede, St. Paul, and Wesley R. Peterson, North particularly preferred embodiment. It may also be desir Oaks, Minn, assignors to Minnesota Mining and Man able to use other perhalogenated ethylenes, such as tri ufacturing Company, St. Paul, Minn., a corporation of fluorochloroethylene, as a reactant. Delaware - 0 Any method can be employed to produce the difluoro carbene radical, providing the free radical is available Filed Jan. 6, 1959, Ser, No. 785,246 for the addition reaction. Such methods include the 7 Claims. (CI. 260-653.3) production of difluorocarbene during the pyrolysis of CHCIF, as described in U.S. 2,551,573. It is also pos - This invention relates to a process for the manufacture 15 sible to obtain the difluorocarbene free radical during of unsaturated fluorine-containing compounds. In one the pyrolysis of tetrafluoroethylene at temperatures above aspect, this invention relates to the addition of a difluoro 750° C. However, for the purposes of this invention, carbene radical to an ethylenically unsaturated compound the method of producing difluorocarbene is not critical. to produce higher molecular weight fluorine-containing Because of the relatively short life of the difluoro compounds. 20 carbene free radical, it is essential that it and the ethyl Fluorinated ethylenically unsaturated compounds are enically unsaturated compound be brought into contact highly valuable and useful intermediates and monomers during the period in which the free radical exists, i.e., in the manufacture of fluorinated polymers. Such poly before the difluorocarbene radicals are consumed by self mers have found wide application where resistance to . condensation, and at a temperature at which the addi chemical and thermal attack are desired. Perfluoropro 25 tion reaction can proceed, usually above about 100° C. pene, for example, has been copolymerized with tetra The reaction can ba advantageously performed in a fluoroethylene to produce a high molecular weight reaction tube similar to that appearing in Figure 1, al interpolymer (U.S. 2,598,283). However, the methods though the process of this invention is not necessarily generally employed for the preparation of fluorinated limited to a particular apparatus. Such tube is con ethylenically unsaturated compounds with three or more 30 structed of Monel, silver, alloy steel, or other material carbon atoms have been costly and inefficient, particu Substantially inert to the reactants and reaction products larly in high capacity production. and which will withstand the temperatures employed. It is an object of this invention to provide a method Where the difluorocarbene radical is produced by the for the production of fluorinated, ethylenically unsatu pyrolysis of CF2HCl, the CF2HCl gas is introduced into rated compounds in high yield. 35 one end of this tubular reactor and is heated therein It is another object of this invention to provide an to pyrolysis temperature as it flows through a pyrolysis efficient process for the production of fluorinated ethyl Zone. Heat may be applied by electric coils or other emically unsaturated organic compounds with a minimum conventional heating means, and temperatures may be production of less desirable by-products. measured by thermocouples located on the tube wall or Still another object of this invention is to provide a 40 in the moving gas stream. A smaller tube inserted into novel and commercially attractive method for the pro the opposite end of the reactor tube and positioned co duction of fluorinated propenes, particularly perfluoro axially therein introduces the ethylenically unsaturated propene. organic compound into that section of the reaction zone According to this invention, an ethylenically unsatu in which difluorocarbene exists as a reactive free radical. rated compound is reacted with difluorocarbene radical 45 The particular point of contact between the two reactants to produce a fluorinated ethylenically unsaturated or is determined experimentally and is related to the pyroly ganic compound having at least three carbon atoms per sis temperature, pressure, and residence time of the molecule. This reaction involves the addition of the CFHCl or difluorocarbene producing material. How free radical :CF to an ethylenically unsaturated com ever, if the ethylenically unsaturated compound contacts pound and can be conducted either with or without the 50 the moving gas stream at a point upstream of the region presence of a catalyst or a diluent. The reaction gener in which difluorocarbene radical exists, it is subjected to pyrolysis temperatures which may, depending on such ally is believed to proceed as follows: factors as residence time, etc., promote excessive pyroly sis of the -ethylenically unsaturated compound, and thereby reduce the yield of the desired addition product. wherein X is hydrogen, fluorine or chlorine, and R is 55 Conversely, if the ethylenically unsaturated compound hydrogen, fluorine, chlorine, or alkyl having no more ... is introduced into the moving gas stream at a point down than 2 C atoms, including halogenated alkyl. Prefer - a stream of that region at which the difluorocarbene radi ably at least one, usually every, X is halogen and most cal exists, the addition-reaction cannot occur. preferably fluorine. R preferably comprises fluorine or For purposes of more completely illustrating the prac chlorine. tice of this invention, the process of producing perfluoro The ethylenically unsaturated organic compound to propene from CF.HCl and CFFCF will be described which the difluorocarbene free radical is added is termi with reference to the figures. It is to be understood nally unsaturated and contains from 2 to 4 carbon atoms. that similar procedures can be employed with the other Included are compounds such as trifluorochloroethylene, reactants described herein and with other operating con tetrafluoroethylene, butene-1, vinylidene fluoride, vinyl ditions, within the scope of this disclosure. - 2,979,589 3. 4. Figure 1 shows the temperature profile of a 1' I.D. select the temperature and pyrolysis zone residence time Monel reactor tube with the passage of one mole per of the tetrafluoroethylene so as to prevent pyrolysis of minute flow of CFHCI. The pyrolysis zone is heated the CF=CF. Figure 3 relates the mole concentration to a temperature of about 700° C., selected in conjunc of the various components along the length of reactor tion with the pressure and CF.HCl residence time in 5 tube, measured from the CF2HCl inlet end, with tetra the pyrolysis zone so as to optimize production of di- fluoroethylene introduction at the 9%' point. fluorocarbene radical. Generally, in the case of mono- Figure 4 is a plot of the total mole concentration chlorodifluoromethane, temperatures above about 600 along the length of the reactor tube. C., and below about 1,000° C., may be used, the higher Figure 5 is a plot of total residence time and instan temperatures tending to increase pyrolysis and forma 10 taneous residence time (average residence time in one tion of difluorocarbene at a given residence time in the inch intervals) as related to the distance from the pyrolysis zone. Pressures may range between 0.0i and CFHC) inlet end. 10 atmospheres absolute, but are preferably below 0.5 Figure 6 is a plot of the molar concentration of the atmospheres for increased formation of reactive free recovered products as related to the blend point or point radicals. For the purposes of the present illustration, 15 of introduction of the tetrafluoroethylene... It will be a pressure of 130 mm. Hg or 0.171 atmospheres has been noted that the 9/2'-10' blend point region produces in employed. Further data on the effect of temperature this instance the optimum perfluoropropene with a mini and pressure on pyrolysis of CF.HCl is found in Indus- mum tetrafluoroethylene residence time in the pyrolysis trial and Engineering Chemistry, vol. 39, No. 3, pp. zone. This corresponds to a conversion of about 90%, 354,358. 20 based on HCl produced, and to a yield of 85/95 or about Figure 2 is a plot showing the profile of the moles 90% of perfluoropropene. The mixture leaving the reac of the various reactants and products at Yarious points tion tube is washed with water, cooled to about -70 compoundalong the reactor is introduced tube when through no ethylenically the coaxially unsaturated positioned lict.C., and fractionally distilled to recover the desired prod tube. The difluorocarbene radical concentration rises 25. Referring to the illustrative data appearing in the afore to a maximum and then decreases as the radicals con- mentioned figures, it is observed that the CFHC dense to form. CF=CF. Measuring from the end of residence time in the pyrolysis zone is about 0.44 second the reactor tube through which the CF.HCl is intro- and the CF=CF residence time in the pyrolysis zone is Zoneduced extends at a flow generally rate of frommoleper 5% tominut, 11' andthe thepyrolysis opt 30 doesabout not 0.05 become second. important Furthermore, because pyrolysis of the short of theresidence latter. mum concentration of difluorocarbene free radical exists time, usually below about 0.5 second. in the 94" to 12" range. The blend point or point of As mentioned earlier, the process of this invention is introduction of the ethylenically unsaturated compound, not limited to the use of any one ethylenically unsatu hereinafter used interchangeably with tetrafluoroethylen, rated monomer. Thus, a variety of compounds of com is coincident with this optirim and appeas a 2 - 8 pounds can be produced by the reaction of difluorocar.
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