2,981,761 United States Patent Office Patented Apr. 25, 1961 1 2 with carbon in a combined form, which comprises heat ing to a temperature of at least 1500 C. a mixture of (a) 2,981,761 a fluoride of a non-metallic element of groups IV, V, VI METHOD FORTHE PREPARATION OF and VII of the periodic table having an atomic number FLUOROCARBONS 5 from 6 to 53, inclusive, and (b) a hydro carbon boiling Mark Wendel Farlow, Wilmington, Delassignor to E.I. below 300° C. at atmospheric pressure, and cooling the du Pont de Nemours and Company, Wilmington, Del, gaseous reaction product within not more than one second a corporation of Delaware to a temperature below 500 C. - In this reaction, most or all of the hydrogen that may No Drawing. Filed Oct. 6, 1958, Ser. No. 765,332 O be present in the system is converted to hydrogen fluo ride, thus consuming part of the available fluorine. This 20 Claims. (C. 260-653.3) side reaction is unavoidable since the carbon-supplying compound contains hydrogen, but it should be minimized to the extent possible. For this reason, as well as for This invention relates to an improved method of Syn 5 reasons of better operability, the fluoride employed should thesizing fluorocarbons, particularly tetrafluoroethylene. contain no hydrogen. For the same reason, the hydro The technical importance of fluorocarbons is con carbon should contain a minimum amount of hydrogen stantly increasing. Tetrafluoroethylene in particular is and the reactants should be anhydrous or substantial of such high industrial interest that new and improved ly so. - methods of synthesizing it are actively being sought. A 20 It should be mentioned in this connection that the hy recent technical advance in this field is the discovery that drogen fluoride which may be formed does not repre fluorocarbons can be prepared by reacting certain organic sent a loss of fluorine, since it can readily be recovered or inorganic fluorides with elemental carbon at high as Sodium fluoride by scrubbing the gaseous reaction temperature, e.g., in a carbon arc, and that tetrafluoro product with aqueous sodium hydroxide or sodium car ethylene is present in very substantial amounts in the 25 bonate. The sodium fluoride so obtained is convertible fluorocarbon product when the reaction temperature is to carbon tetrafluoride in excellent yields by reacting it high enough (generally above 1500 C.) and the gaseous with carbon and chlorine at a temperature in the range reaction product is rapidly cooled, preferably to below of 1200-1700 C., and the carbon tetrafluoride can be 500° C., immediately following contact with the hot car recycled to give tetrafluoroethylene by the process of this bon. These developments have been published in a series 30 invention, or by reaction with hot elemental carbon as of United States patents, principally 2,709,182 issued to disclosed in U.S. Patent 2,709,192 issued May 24, 1955 M. W. Farlow on May 24, 1955; 2,709,186 to 2,709,191, to M. W. Farlow. inclusive, issued to M. W. Farlow et al. on May 24, The fluorides suitable for use in this process are the 1955; 2,709,192 issued to M. W. Farlow on May 24, hydrogen-free-fluorides of those non-metallic elements of 1955; 2,725,410 issued to Farlow et al. on November 29, groups IV to VII of the periodic table which have atomic uary1955 24,and 1956. 2,732,410-11, issued to Farlow et al. on Jan numbers from 6 to 53, inclusive. These non-metallic ele These high temperature processes constitute a major ments are found in subgroup A of groups IV to VII of improvement in the field of fluorocarbon synthesis. How the periodic table. Reference is made here to Deming's ever, they are not free of technical difficulties, especially Periodic Table, as given in Deming's “General Chemistry' with respect to continuous operation. When elemental 40 (John Wiley & Sons, Inc., 5th ed., pp. 11-13) and in carbon is consumed in a continuous process, it must be many other reference books such as the Handbook of replaced continuously. This requirement is difficult to Chemistry and Physics published by the Chemical Rub meet, particularly when the source of heat is a carbon ber Publishing Co. This table shows that the non-metal arc, a preferred embodiment of these processes because lic elements are, besides the rare gases, the elements of . of the very high temperatures which are readily attain 45 group VII-A (i.e., the halogens); those in group VI-A able by means of an arc. With a carbon arc, some or having atomic numbers 8 to 52; those in group V-A hav all of the necessary carbon is supplied by the electrodes ing atomic numbers 7 to 33; those in group IV-A having themselves, and consumption of carbon from the elec atomic numbers 6 to 14; and boron in group III-A. Of trodes presents difficult engineering problems which inter these non-metallic elements, those in groups IV to VII fere with continuous operation on a large scale. Even 50 which have atomic numbers 6 to 53 (i.e., carbon, silicon, when the operation is carried out in an externally heated nitrogen, phosphorus, arsenic, oxygen, sulfur, selenium, reactor, such as a tube of refractory material heated in tellurium, fluorine, chlorine, bromine and iodine) are the a suitable furnace, the use of elemental carbon is not elements whose fluorides are operable in this process. entirely satisfactory since the carbon must also be con Thus, for example, the suitable fluorides include the car tinuously replaced in this type of apparatus. Moreover, 55 bon fluorides (fluorocarbons) free from aliphatic unsat contact between the gaseous or vaporized fluoride and uration, particularly CF4 and CF6; the silicon fluorides, the solid carbon may not be adequate, and the operator particularly SiF; nitrogen trifluoride, phosphorus penta has little or no control over the proportion of carbon fluoride, arsenic trifluoride, the sulfur fluorides (SF and relative to the fluoride at any given moment, and thus is SFs), fluorine itself, chlorine trifluoride, iodine penta notable to create the most favorable conditions for the 60 fluoride, etc. Fluorides in which more than one of the information of the desired fluorocarbons. above listed elements are combined with the fluorine such There was therefore a need for an improvement in as carbonyl fluoride, sulfuryl fluoride and thionyl fluoride, the high temperature process of synthesizing fluorocar are also suitable. bons, especially tetrafluoroethylene, from carbon and For reasons of accessibility, ease of handling and good 65 results, the preferred starting materials are elemental fluorides, whereby the necessary carbon would not be fluorine and the binary fluorides of the non-metallic ele present in elemental form, but would be supplied instead ments in groups TV-A, V-A and VI-A of the periodic by an added volatile reactant capable of making inti table. The most useful and preferred fluorides are the relativemate contact proportions. with the gaseous fluoride in any desired aliphatic, saturated fluorocarbons of one to two carbon atoms (carbon tetrafluoride and hexafluoroethane), sili This invention is a process of preparing fluorocarbons 70 contetrafluoride, phosphorus pentafluoride, arsenic tri particularly tetrafluoroethylene, by reaction of a fluoride fluoride, sulfur tetrafluoride and sulfur hexafluoride, 2,981,761 3 4. -- The other reactant can be any volatile hydrocarbon, ture range of the electric arc, which is estimated to be i.e., any hydrocarbon boiling below about 300° C. at at 2500-4000 C. or even higher. mospheric pressure (760 mm. mercury). It is desirable The absolute pressure of the reactant gases during the that the carbon-supplying reactant contain as much car pyrolysis is not critical. In general, however, it is much bon, as possible, both because a high carbon content preferred to operate at reduced pressures, which can be favors a higher rae of fluorocarbon formation per unit as low at 1 mm. of mercury but are desirably in the range volume and because the formation of hydrogen fluoride, of 10-300 mm. of mercury. This is especially desirable which consumes part of the available fluorine is thereby when an electric arc is used as the source of heat, since minimized. For these reasons, the preferred carbon the operation of the arc becomes more difficult with in supplying reactants are those in which the atomic ratio 10 crease in pressure. With other types of reactors, e.g., ex of carbon to hydrogen is at least 0.3:1, preferably at least ternally heated tubular reactors, the absolute pressure is 0.5:1. However, hydrocarbons which are poorer in car also much preferably sub-atmospheric, e.g., in the range bon, such as methane, are fully operable and in some of 10-300 mm., but it can be atmospheric or even Super cases may be desirable for economic reasons. atmospheric. Among the suitable hydrocarbons may be mentioned 15 Practical conversions to tetrafluoroethylene can be ob saturated aliphatic hydrocarbons such as methane, ethane, tained only if the product emerging from the hot reaction propane, n-hexane, n-octane, commercial mixtures of ali zone is cooled very rapidly (quenched) to a temperature phatic hydrocarbons (e.g., kerosene, gasoline, fuel oils); not exceeding 500 C., preferably of the order of 400° C. unsaturated aliphatic hydrocarbons such as ethylene, pro or lower. The time required to cool the gaseous reaction pene, isobutylene, allene, butadiene-1,3, acetylene, methyl 20 product, that is, the time of transition from the reaction acetylene; saturated or unsaturated cyclic hydrocarbons temperature to a temperature of about 400-500 C., such as cyclohexane, cyclohexene, naphthas, benzene, should not exceed one second. Preferably, it is in the toluene, and the xylenes, styrene, etc. For reasons of ac range of 0.001 to 0.1 second. The optimum rate of flow cessibility and economy, the most useful hydrocarbons through the hot reaction zone of the gaseous reactants are those containing from one to eight carbon atoms. 25 depends in large part on this quenching requirement, that The relative proportions of fluoride and hydrocarbon is, on the efficiency of the quenching system. Reduced are not critical. They are important only to the extent presures facilities rapid quenching in any given form of that maximum utilization of the fluoride, and at the same apparatus. time minimum formation of non-fluorocarbon by-prod The necessary quenching can be achieved in various lucts, are desired. In practice, the relative amounts of 30 ways. For example, the off-gas upon leaving the hot re fluoride and hydrocarbon are chosen so that the atomic action zone can be made to pass over the outside wall ratio of total combined carbon to total fluorine in the of a metal vessel containing a coolant material such as reacting system is at least 0.1:1, preferably at least 0.25:1. water, solid carbon dioxide or liquid nitrogen and located At the same time, in order to minimize the formation of a short distance from the reaction zone, or the off-gas can hydrogen fluoride, it is desirable that the ratio of the 35 be passed through a double walled hollow cylinder with total fluorine to the total combined hydrogen in the re or without radial fins, cooled with circulating water. In acting system be at least 1.5:1, preferably at least 3:1. another modification, the off-gas is carried immediately Optimum yields of tetrafluoroethylene are generally from the hot zone into a suitably designed quench reactor obtained when the fluoride and a hydrocarbon CHy are where it comes in intimate contact with a finely divided employed in such relative proportions that fluorine is 40 (fluidized) solid, which is advantageously carbon. present in an amount approximately equal to 2x-y. Apparatus of any suitable design can be used to carry Thus, when the reacting system contains only C, F and out the process of this invention. For example, the re H, these proportions are established, for example, in the actor can be a tube of refractory material, if desired following mixtures: packed with particles of an appropriate infusible sub 45 stance to improve contact between the reactants, through which is passed a mixture in the desired proportions of the gaseous or vaporized fluoride and hydrocarbon. The tube is heated to at least 1500 C. in a resistance furnace or induction furnace, and appropriate means are provided With fluorides of elements other than carbon, optimum 50 to quench the off-gas and collect the reaction products. results will again be obtained with the same C/H/F In this type of equipment, however, in view of the ratio, but allowance should be made for the fact that, corrosive nature of many fluorides and reaction products in some cases, not all the fluorine atoms in the fluoride at the high temperatures involved, it is often desirable to are equally reactive, i.e., available. Thus, for example, use carbon or graphite as the material of construction for phosphorous pentafluoride contains two especially readily 55 the hot parts of the reactor and as the contact masses. available fluorine atoms, since phosphorus trifluoride is a Some of this carbon participates in the reactiin, in spite major product of the reaction, and the optimum C/H/F of the fact that most of the carbon will be furnished ratio should be adjusted on the basis of the more readily by the added volatile hydrocarbon. Thus, while the use available fluorine. of a carbon-supplying reactant is advantagtous even in an However, it is by no means essential to adhere to these 60 apparatus made of, or containing carbon, the full ad theoretically optimum ratios, since considerable devia . vantages of this process are not realized in Such a case. tions from them are permissible. It can be observed as A preferred device for carrying out the process is a guide that a deficiency of carbon results in preferential the electric arc, which produces extremely high tempera formation of carbon tetrafluoride at the expense of tetra tures. In this type of apparatus, the electrodes can be fluoroethylene, while an excess of carbon tends to appear made of a heat- and corrosion-resistant metal, such as as waste carbon. An excess of hydrogen results in the copper or tungsten, thereby contributing no carbon to formation of larger amounts of hydrogen fluoride at the the reaction. In addition, metal electrodes can be kept expense of fluorocarbons, while a deficiency of hydrogen relatively cool through internal circulation of a cooling favors carbon tetrafluoride formation at the expense of liquid, and under such conditions they remain substan tetrafluoroethylene. tially unattacked for considerable periods of time. Car The reaction conditions are essentially those described bon electrodes are also entirely suitable, and a carbon in the patents already referred to for the synthesis of tetra arc can be used even without special provisions for pre fluoroethylene. Thus, the reaction temperature should venting or decreasing electrode consumption, since even be at least 1500 C., and it can be as high as can be in such a case a very substantial amount of the neces obtained by practical means, for example, in the tempera 75 sary carbon is supplied by the added hydrocarbon rather

2,981,761. 5 6. than by the electrodes. However, here again the full current. A direct current is greatly preferred, since only advantages of the process are realized only when essen with a direct-current is it possible to obtain a truly con tially non-consumable carbon electrodes are used. A tinuous rotating arc resulting in uniform heating and carbon anode can be made essentially non-consumable high stability. Current intensities in the range of 20 to by maintaining it at a relatively low temperature, in 500 amperes are generally used. practice below about 1500 C. This can be accomplished As in the already described synthesis of tetrafluoro by using a relatively thin anode supported by, and in ethylene from elemental carbon, the reaction in this intimate contact with, a water-cooled, metallic holder, process normally gives a mixture of fluorocarbons, the this device providing very efficient external cooling of the preponderant constituents of which are carbon tetra carbon anode. In a low tension arc the cathode cannot 0 fluoride and tetrafluoroethylene, with in general lesser be similarly cooled since its temperature must be high amounts of hexafluoroethane, and sometimes still lesser enough to sustain thermal emission of electrons, but the amounts of other saturated or unsaturated fluorocarbons. cathode normally furnishes, little or no carbon. With a The crude reaction product may also contain some un cool anode, a carbon electrode system loses substantially reacted fluoride, which can be recycled, and the free ele no carbon, as can be demonstrated by weighing the elec ment whose fluoride was employed, or compounds there trodes before and after operating the arc. of. As already mentioned, the reaction product will Improved forms of carbon arc, well adapted to the contain hydrogen fluoride, which can be recovered as synthesis of fluorocarbons, are described in the afore sodium fluoride by scrubbing the reaction product with mentioned U.S. Patent 2,709,192 and in other patents. aqueous sodium hydroxide, the sodium fluoride in turn These are suitable for use in the present process, with 20 being readily convertible to carbon tetrafluoride in ex such appropriate modifications as may be required for cellent yields. Another method of removing the hydro the cooling of the electrodes, if this is desired, and for gen fluoride consists in bringing the reaction product in the introduction of the carbon-supplying reactant. The contact with an alkali metal fluoride such as sodium fluo latter is preferably introduced in the gaseous or vaporized ride which absorbs hydrogen fluoride with formation o form, if desired premixed with the gaseous or vaporized 25 a non-volatile acid fluoride. . . " . . . . fluoride in the desired proportions, but it can also be With or without prior removal of the hydrogen fluoride delivered as a liquid or even as a solid into the reactor, and any other alkali-soluble products which may be where it vaporizes before entering the arc zone. A sub present, the fluorocarbons can be isolated by passing the stantially inert carrier gas such as nitrogen or helium gaseous reaction product through cold condensers and can be used if desired. 30 An especially suitable type of electric arc for use in fractionating the condensate through efficient distilling this process is a magnetically rotated arc. In comparison columns. In this way, tetrafluoroethylene can be readily with static arcs of conventional design or even with the separated from carbon tetrafluoride. Its separation improved arcs of the kind mentioned above, a rotating from hexafluoroethane requires more efficient fractiona arc is far more efficient by virtue of its much greater 35 tion, or it can be carried out by selective solvent extrac: stability and of the far better contact between arc and tion or by selective absorption on solids. However, in reactants that it permits. The examples which follow most cases it is not at all essential for the tetrafluoro were carried out using an arc of this type. ethylene to be completely free of hexafluoroethane. A particularly efficient type of rotating carbon arc. The fluorocarbons other than tetrafluoroethylene which operates as follows: The reactants (in this case, the hy 40 are produced in the process can be used as such (carbon drocarbon and the fluoride) pass through a symmetrical tetrafluoride, for example, is a useful chemical) or they annular gap formed by a substantially cylindrical solid can be in turn converted to tetrafluoroethylene by reac graphite cathode and a substantially cylindrical hollow tion with hot carbon in accordance with the published graphite anode, wherein a continuous electrical discharge methods, or recycled in the process of this invention. is rotated by magnetic lines of flux essentially parallel 45 greaterThe detail.following examples: illustrate the invention in to the axis of rotation of the annular arc. This causes the arc to move at right angle to the magnetic field lines. Example. I The magnetic field is created by surrounding the arc A gaseous mixture of carbon tetrafluoride and benzene chamber with a coil through which a current (preferably in the molar ratio CF:CHs of 9:1 was passed through a direct current) passes. A field strength suitable to 50 a magnetically rotated carbon arc at an absolute pressure cause rotation is 100-200 gauss. The arc rotates ex within the arc chamber of 20 mm. of mercury. The tremely rapidly in the annular gap between the elec cathode was a graphite rod, 3A6' in diameter, and the trodes, its speed being estimated at 1000-10,000 revolu anode was a hollow graphite cylinder having an internal tions per second, and it heats the reactants very uniform diameter of 0.5', mounted on a water-cooled ring-shaped ly to extremely high temperatures as they pass through 55 copper holder which served to keep the anode cool. The the gap. The gaseous reaction product leaves the arc arc was operated at 30 volts and 40-50 amperes. The chamber through the hollow anode and is immediately reactant gases, after passing through the arc flame in the cooled by contact with cold portions of the apparatus annular space between the electrodes, left the hot reac or with a specially designed quenching unit. tion zone through the hollow anode and impinged on a The electrical characteristics of the rotating arc are 60 water-cooled copper surface about one inch downstream essentially similar to those of the static arc. Thus, from the arc Zone, where the gaseous reaction product operating conditions of the arc may be varied over a wide was quenched to below 500 C. within a few microsec range from the minimum voltage required to maintain onds following contact with the arc flame. the arc to very high voltages, e.g., in the range of 10 The reaction product, formed at the rate of about 31 to 75 volts. In general, for a given current the required 65 g. per hour, was then led into a copper trap cooled in voltage of the arc is determined by the pressure in the liquid nitrogen, where it condensed. The trap contained system, the width of the arc gap, and the nature of the sodium fluoride which served to absorb the hydrogen gases present in the arc chamber. The power require fluoride by reacting with it to form the non-volatile so ments will, of course, depend on the quantity of reactants dium acid fluoride. The volatile, hydrogen fluoride-free passed through the rotating arc and the temperature to 70 reaction product was found by mass spectroscopy analysis which they are to be heated. to contain, on a molar basis, 46% of tetrafluoroethylene, The arc may be operated with a direct current or with 43% of carbon tetrafluoride, 7% of hexafluoroethane and an alternating current if the alternating current is of small amounts of fluorocarbons containing 3 or more high frequency and is employed in combination with an carbon atoms per molecule. Analysis of the non-volatile alternating magnetic field which is in phase with the arc 75 sodium fluoride-sodium acid fluoride mixture for hydro 2,981,761 7 8 gen ion showed that hydrogen fluoride had been produced gaseous reaction product to a temperature below 500 at the rate of about 4.4 g/hr. Examination of the C. in less than one second. graphite anode after the operation showed that it was 3. The process as set forth in claim 2 wherein the non virtually unchanged in shape or size and that its Weight metallic element is carbon. had diminished by less than 0.1 g/hr. of operation. This 5 4. The process as set forth in claim 3 wherein the car bon fluoride is carbon tetrafluoride. showed that practically all of the necessary carbon had 5. The process as set forth in claim 3 wherein the car been supplied by the benzene. bon fluoride is hexafluoroethane. Example II 6. The process as set forth in claim 2 wherein the ele Using the apparatus and procedure of Example I, a O ment is silicon. gaseous mixture of carbon tetrafluoride and methane in 7. A process for the preparation of fluorocarbons which the molar ratio CFA:CH4 of 3:1 was passed through the comprises heating to a temperature of at least 1500° C. arc at such a rate that 38 g. of reaction product was a mixture of (a) a fluoride of a non-metallic element of formed per hour. The product, after removal of the group V of the periodic table having an atomic number hydrogen fluoride, was found to contain on a molar basis of 7 to 33, inclusive, and (b) a hydrocarbon boiling be 52% of tetrafluoroethylene, 32% of carbon tetrafluoride, low 300 C. at atmospheric pressure, and cooling the 11% of hexafluoroethane and small percentages of gaseous reaction product to a temperature below 500 C. in less than one second. higher fluorocarbons. 8. The process as set forth in claim 7 wherein the non Example III 20 metallic element is nitrogen. Using the apparatus and procedure of Example I, a 9. The process as set forth in claim 7 wherein the non mixture of carbon tetrafluoride and acetylene in the molar metallic element is arsenic. ratio CF:CH of 3:1 was passed through the arc at 10. The process as set forth in claim 7 wherein the such a rate that 31 g. of product was formed per hour. non-metallic element is phosphorus. After removal of the hydrogen fluoride, the product was 25 11. The process as set forth in claim 10 wherein the found to contain on a molar basis 65% of tetrafluoro phosphorus fluoride is phosphorus pentafluoride. ethylene, 22% of carbon tetrafluoride, 7% of hexafluoro 12. A process for the preparation of fluorocarbons ethane, and small percentages of higher fluorocarbons. which comprises heating to a temperature of at least 1500 C. a mixture of (a) a fluoride of a non-metallic Example IV 30 element of group VI of the periodic table having an Using the apparatus and procedure of Example I, ex atomic number of 8 to 52, inclusive, and (b) a hydro cept that the arc had a water-cooled copper anode instead carbon boiling below 300° C. at atmospheric pressure, of a graphite anode and the pressure within the arc cham and cooling the gaseous reaction product to a temperature ber was 30 mmi. of mercury, a mixture of phosphorus below 500 C. in less than one second. . pentafluoride and 1,3-butadiene in the molar ratio 35 13. The process as set forth in claim 12 wherein the PF:CHs of 7:1 was passed through the arc. The flow non-metallic element is sulfur. rate was such that there was formed 84 g. of reaction 14. A process for the preparation of fluorocarbons product per hour. The product, after washing with which comprises heating to a temperature of at least aqueous alkali to remove hydrogen fluoride, phosphorus 1500 C, a mixture of (a) a fluoride of a non-metallic trifluoride and other alkali-soluble materials, was found 40 element of group VII of the periodic table having an to consist chiefly of tetrafluoroethylene and carbon tetra atomic number of 9 to 53, inclusive, and (b) a hydro fluoride. The carbon cathode was found to have lost no carbon boiling below 300° C. at atmospheric pressure, weight during this operation, showing that all of the and cooling the gaseous reaction product to a temperature necessary carbon had been supplied by the butadiene. below 500° C. in less than one second. - It is to be understood that the foregoing examples are 45 15. The process as set forth in claim 14 wherein the merely illustrative of the invention described and are not fiuoride of a non-metallic element is fluorine. intended to limit the invention. In essentially the same 16. A process for the preparation of tetrafluoroethylene way and giving rise to the same fluorocarbon reaction which comprises passing through an electric carbon arc products there may be used hexafluoroethane, silicon a mixture of (a) a fluoride of a non-metallic element of tetrafluoride, sulfur tetrafluoride, sulfur hexafluoride, 50 group IV to VII of the periodic table having an atomic fluorine, chlorine trifluoride, arsenic trifluoride or nitro number of 6 to 53, inclusive, and (b) a hydrocarbon gen trifluoride as the fluoride component in combination having from 1 to 8 carbons, and cooling the gaseous with such hydrocarbons as ethylene, propane, allene, reaction products to below 500° C. in less than one second. methylacetylene, toluene or styrene as the carbon Sup 55 17. The process as set forth in claim 16 wherein the plying coreactant. arc employed is a magnetically rotated arc. - I claim: - 18. The process as set forth in claim 16 wherein the 1. A process for the preparation of fluorocarbons which hydrocarbon is methane. comprises heating to a temperature of at least 1500 C. 19. The process as set forth in claim 16 wherein the a mixture of (a) a fluoride of a non-metallic element of hydrocarbon is acetylene. groups IV to VII of the periodic table having an atomic 60 20. The process as set forth in claim 16 wherein the number from 6 to 53, inclusive, and (b) a hydrocarbon hydrocarbon is benzene. boiling below 300° C. at atmospheric pressure, and cool ing the gaseous reaction product to a temperature below References Cited in the file of this patent 500° C. in less than one second. UNITED STATES PATENTS 2. A process for the preparation of fluorocarbons which comprises heating to a temperature of at least 1500° C. 2,709, 186 Farlow et al. ------May 24, 1955 a mixture of (a) a fluoride of a non-metallic element of 2,732,410 Farlow et al. ------Jan. 24, 1956 group IV of the periodic table having an atomic number 2,732,411 Farlow et al. ------Jan. 24, 1956 of 6 to 14 inclusive, and (b) a hydrocarbon boiling be 2,759,026 McCleary ------Aug. 14, 1956 low 300° C. at atmospheric pressure, and cooling the 70