US3033767A - Preparation of fluorocarbons - Google Patents

Description

May 8, 1962 F. OLSTOWSKI ET AL PREPARATION OF FLUOROCARBONS Filed sept. 2, 1958 700 800 E/ecff-o/y/e Tempera/arg, C

000 Owwf Unite States atent 3,933,767 PREPARAHN F FLURCONS Franciszek (blstowski, Freeport, and .lohn I. Newport El, Lake Jackson, Tex., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed Sept. 2, 1958, Ser. No. 753,438 Claims. (Cl. MA1-62) This invention relates to a process for the preparation of iiuorocarbons, and more particularly, to the electrolysis of non-volatile molten metal iiuorides to prepare these compounds.

This application is a continuation-in-part of patent application Serial No. 663,966, tiled June 6, 1957, now abandoned.

Presently, the preparation of ilumine-containing compounds has been mainly limited to fluorination of chlorinated or unsaturated hydrocarbons by the use of iluorimating agents, such as hydrogen fluoride, or fluorinating of saturated hydrocarbons by elemental iluorine. These processes involve handling hazardous materials which are expensive and require special equipment. Certain metal uorides are cheap raw materials and a process whereby tluorocarbons could be prepared by electrolysis of these fused metal uorides would considerably reduce the production cost of these compounds.

In the electrolysis of molten metal tluorides a troublesome phenomenon known as anode effect occurs which Without any obvious external reason causes the voltage to increase suddenly and the amperage to decrease. Although this phenomenon may occur under many conditions, it is most often encountered when the electrolyte is at a high temperature and the cell operating at a high anode current density. During the anode effect, the anode seems to be entirely surrounded by gas ilm and the current is carried from the anode to the electrolyte through the gas lm mainly by a large number of shifting arcs. Once the gas lilm is established it tends to perpetuate itself, since the arcing generates localized heating which causes the gas to expand. Voltages which under normal operations are around 4 to 6 volts may increase up to over 60 volts during this period, and the cell can not be operated under these conditions. It is necessary to vigorously agitate the electrolyte to remove the gas iilm, raise the anodes from the melt, or reverse the current to overcome this effect. Sometimes the anode effect is accompanied by a loss in weight of the carbon anode and it has been speculated that some carbon halides are formed. Kroll in Metal lndustry, August 1953, pages 141-143, reported that in an aluminum cell the anode gas during the anode elect contained a small amount of carbon tetrailuoride. Thus, even though a small amount of fluorocarbons may be formed during the anode etlect, it is totally impractical to operate an electrolytic cell under anode effect conditions to prepare ilumine-containing compounds.

In United States Letters Patent No. 785,961, a process for the preparation of carbon tetrauoride by electrolysis of sodium or potassium fluoride at 1000 C. and at a voltage of 8 volts is described. An anode comprised of soft carbonaceous material surrounding a hard carbon or graphite rod is used. In the method described only carbon tetrafluoride may be produced. In a copending patent application of instant inventors, patent application Serial No. 750,270, iiled July 22, 1958, a process is described whereby hexauoroethane and higher molecular weight uorocarbons may be produced by using an anode of carbonaceous material in particulate form loosely confined. However, the current efficiencies and power etliciencies of a cell using a carbonaceous material in particulate form could be materially improved. Also, while other uorocarbons other than carbon tetrafluoride may ice be obtained with the anode of loosely confined carbon particles, low electrolyte temperatures and high anode current densities must be used. Even with a low temperature the amount of fluorocarbon obtained which have a higher molecular weight than hexafluoroethane is not great. A1- though hexatluoroethane and higher molecular weight uorocarbons generally may be more cheaply produced by electrolysis of a metal fluoride with an anode of loosely confined carbon particles than by iluorination of chlorinated or unsaturated hydrocarbons, a process is greatly desired whereby hexauoroethane and higher molecular iluorocarbons could be produced in larger amounts and more economically, especially fluorocarbons, such as octafluoropropane and higher.

It is, therefore, among the objects of this invention to provide an improved process for the preparation of fluorocarbons by the electrolysis of non-volatile molten metal uorides. A further object is to provide an improvement in the electrolysis of used metal iluorides so that relatively high portion of the fluorocarbon anode product is hexaiiuoroethane and higher molecular weight iluorocarbons. Another object is to provide a process for the electrolytic production of metals from iluorides.

The above and other objects are attained according to the invention by passing an electric current through a molten electrolyte at a temperature of at least 600 C. between a porous carbon anode having a permeability in the range of 1 to 40 and an insoluble cathode. The molten electrolyte consists essentially of at least metal fluoride which is stable and non-volatile at the electrolysis temperature and is non-wetting in respect to the anode selected from the group consisting of alkali metal uorides, alkaline metal earth uorides, and earth metal fluorides. Upon the electrolysis, an anode product containing a series of homologous uorocarbons including both saturated and unsaturated is obtained. The anode product is gaseous at the electrolysis temperature and will come oit as the anode gas, but may contain higher molecular weight compounds, such as perlluorobenzene, peruorotoluene, and perliuoronaphthalene, as well as aliphatic fluorocarbons which are oils at room temperature.

The invention may be more easily understood when the detailed discussion is considered in conjunction with :the drawings, in which:

`FIIGURE 1 diagrammatically illustrates an electrolytic cell in which the invention can be carried out, and

FIGURE 2 shows the effect of temperature of the electrolyte on the composition of the anode product Obtained from the electrolysis. l

The electrolytic cell diagrammatically shown in FIG- URE 1 comprises a metaltank 1 having a cover plate 2, an electrical non-conducting cylindrical liner 3, and an anode assembly indicated generally as 4. The cover plate is fastened to tank 1 by means of a multiplicity of screws 5 but other means, such as clamps, may be used. The anode assembly comprises a cylindrical graphite or carbon anode holder 6 having a passageway 7 in the center of the holder extending along the longitudinal axis. At the lower end of holder 6 a hollow-cup porous anode Si is attached to the holder. At the other end of the holder, a pipe line 9 is attached so that the pipeline communicates with the passageway 7. A lead 11 is electrically attached to the outer surface of tank 1 and another lead 12 is attached to holder 6 through which the current to the cell is supplied. The anode assembly is inserted into tank 1 with holder 6 passing through an opening in cover plate 2 in which an electrical non-conducting seal `13: forms a gas tight seal between the holder yand the cover plates. The hollow-cup porous anode 8 is immersed in the molten iluoride placed in the tank and indicated by number 14 in the drawing. A metal 15 inert to the lluoride electrolyte and having a melting. point below the electrolysis temperature, such as lead, is placed inthe cell lwhich settles to the bottom of the tank con- 'the metal Vdeposited at the cathode is lighter than Vthe electrolyte. This simplies the Vcell construction, since -no arrangement is necessary to remove `the metal deposited 'fromthe surface of the electrolyte. In the operation of the cell, the cover plate is tightened down to form a :gas :tight seal andthe cell is placedin a furnace and 'heateduntil the electrolyte has attained the desired temperature. The current isthen passed through the electrolyte. The iluorocarbons formed during the electrolysis pass from fthe surface of the porous anode 8 into the opening ofthe anode and then discharge through passageway 7 and pipeline 9. The anode product obtained from -the cell is then further processed by known methods to separate the particular fluorocarbons obtained.

The composition of the anode gas or the amounts of `the dierent uorocarbons obtained as an anode product is aected by the temperature and somewhat by the anode `current: density. FIGURE 2 illustrates the eiect of temperature upon the composition of the fluorocarbon product obtained 'in the electrolysis of a lithium fluoridesodium uoride mixture as a function of the temperature .of-the electrolyte. The details of the tests and data on which the figure is based are set forth in Example HI below. 4In `FIGURE .2, theabscissa represents the temperature ofthe electrolyte at which the electrolysis was effected and the ordinate represents a composition of the uorocarbon product obtained atthe anode in mole percent. To obtain the plot shown in FIGUREAZ, relatively low anode currentdensities in the range of l to 5 amperes per square inch were used.

In FIGURE. 2 it will be noted'that the amount of hexatiuoroethane.increasedfrorn approximately 35 mole ercent at 700 C. as the temperature of the electrolysis increased to av point of .around 66' mole percent at 900 C. It then decreased as the temperature was increased. At 41000u C., the uorocarbonzproduct obtained contained only around 45 percent hexafluoroethane. The amount of octafluoropropane decreased with increase in temperature of the electrolysis. At 700 C. the Vproduct obtained contained approximately 14 percent octauoropropane which decreased to approximately l2 percent at 800 C. and then down toabout3 percent at 900 C.

Ata relativelylow anode current density, the'ternperature has considerable effect upon the `composition of the uorocarbon product obtained as shown in FIGURE 2. However at Vhigh, anode current densities, such as l2 amperes per square inch and above, the composition of the fluorocarbon product obtained does not diler greatly for temperatures in the range of 700 to 900 C. This is especially truefor the Vhigher molecular weight fluoro` carbons. At ahigh anode current density, a lluorocarbon product containing'about 12 mole percent octatluoropropane and over `2 mole percent of octaiiuorobutenemay be obtained at temperatures as high as 900 C.

VWhile the. amounts of carbon tetrafluoride, hexafluoroethane, and the higher molecular Weight fluorocarbons will vary somewhat with the particular metal lluoride or iluorides employed, vsimilar results as those shown in FIGURE i?.V are obtained with the other metal fluoride or fluorides. Alkali metal `iiuorides, alkaline earth metal uorides, .and earth metal uorides which do not wet the anode-'and are non-volatile and stable at the electrolysis temperature and mixtures thereof may be used as the electrolyte in the production of these fluorocarbons. illustrative examples of'these metal uorides are magnesium fluoride, aluminum fluoride, Vsodium fluoride, barium fluoride, strontium fluoride, calcium fluoride, lithium uoride, cesium fluoride, and a yttriu-rniluoride. An example of a non-volatile,'stable metal uoride which wets .the anode is potassium 'u'oride Thus, potassium fluoride cannot be used as main constituent of the electrolyte but may be tolerated in small amounts up rtoaround 5 percent.

Although only one of the alkali metal fluorides, alkaline earth metal uorides, or earth metal liuorides may be used as the electrolyte, a mixture of these metal uorides is often used to increase the conductivity or lower the melting point of the bath. For this purpose, lithium fluoride is most commonly added to the other metal uorides,

but other mixtures and combinations may also be used. When other 'lluorides are added to-either increase the conductivity or lower the melting point or" a particular metal :iluoride bath, the uorides of metals which are higher in the electromotive series or more electronegative than the metal to be extracted at the cathode from the .particular bath are preferred. By using iluorides of metals more electronegative, these metals will not deposit out `at the cathode with the desired metal except at exceptionally high cathode current densities. Thus, the cathode product is not contaminated under normal operating conditions. Also in continuous operation of the cell, the metal fluoride added to the electrolyte is not depleted by the electrolysis and only the lluoride of the particular metal being deposited at the cathode has tobe added continuously. For example, when lithium iluoride is added to a magnesium uoride bath, the lithium is more electronegative than magnesium and thus will not deposit out at the cathode. Once the lithium iluoride is added to the bath it will not be depleted bythe electrolysis and only magnesium -uoride has to be added for continuous operation.

Illustrative examples of the mixtures that may be used with the metal which will be preferentially deposited at the cathode are shown in the table below.

Metal preferentially deposited at the Bath composition:

`Y'Fa'Lil-i Y Similar procedure of electrolysis may be employed regardless of the metal iiuoride or fluorides used as electrolyte. However, the optimumY conditions for particular electrolytes used may vary to a certain degree. The temperature of the bath must be at least at the melting point of the bath so that the electrolyte is in a molten state. The maximum emperature that may be used is either limited by the cell structure, the stability and volatility of the particular electrolyte employed, or the fluorocar- -bon desired. Since at a lower temperature the construction of the cell is simplied and also a greater amount of the higher molecular Weight fluorocarbons is obtained, a temperature in the range of 700 to l000 C. is preferred for all the electrolytes, except for a LiF-NaFAlF3 bath where the preferred temperature is in the range of 650 C. to 800 C. When it is desirable to obtain the maximum amount of octofluoropropane, a temperature in the range of`650 C. to 850 C. is used.

While anode current densities from 4below l and up to amperes per square inch may be used with certain porous anodes, anode current densities in the range of l to 40 amperes per square inch are generally employed, preferably in the range of 2 to 15 amperes per square inch especially if it is desired to obtain higher molecular weight uorocarbon than carbon tetratluoride. The

cathode current density is generally in the range of 1 to 30 amperes per square inch. To obtain these current densities, a voltage up to 20 volts may be employed, but a voltage in the range of 4 to 10 volts is preferred.

Porous carbon anodes generally used in the electrolysis of the metal fluorides and in the preparation of the iluorocarbons are those having a permeability of at least l and not greater than 40, preferably in the range of 4 to 20. While anodes having a permeability greater than l may be used in special cases, no benecial advantage is obtained. The maximum anode current density which may be used without encountering anode elect is proportional to the permeability, increasing with an increase in permeability. With the permeabilities generally used, normally all practical anode current densities may be used without encountering the objectionable phenomenon. In special cases, however, where relatively low current densities are to lbe employed, an anode having a permeability as low as 0.2 may be used, if desired. Likewise, an anode having a permeability greater than 40 may also be used, but the amount of the higher molecular weight uorocarbons obtained decreases.

Permeability, as used herein, is expressed as the amount of air passing through the porous carbon anode in cubic feet per minute per square foot per one inch thickness at a pressure differential of 2 inches of water. The term carbon anode, as used herein, means anodes made by combining ne carbon particles with a binder and sintering to form a cohered mass and includes anodes made from amorphous carbon, such as petroleum coke, coal, carbon black, etc. and allotropic carbon, such as graphite. The term porous, as used herein, means gas permeable.

The shape of the anode is immaterial. A hollow-cup type anode as shown in FIGURE 1 may be preferred where high molecular weight iluorocarbons are obtained. These compounds may `be readily drawn into the hollow anode and easily removed from the system. When a solid porous anode is used, it may be necessary in some cases to use a hood or shield to enclose the anode to entrap the anode gases as they are formed and released. Other types and shapes of porous anode assemblies which are apparent to those skilled in the art may be used.

Various known electrolytic cell construction and various known types of cathodes may be used. The particular cathode adopted will depend upon the metal being deposited.

The term earth metals, as used herein, means the elements aluminum, scandium, yttrium, and lanthanum of the third group of the periodic system.

The following examples further illustrate the invention but are not to be construed as limiting it thereto.

Example I An electrolytic cell similar to the one shown in the attached drawing and equipped with a porous graphite anode was used in the electrolysis of an aluminum iluoride-lithium fluoride electrolyte. The permeability of the porous anode as rated by the manufacturer was 4. However, in testing the anode -by a method similar to that used by the manufacturer, an air rate of 3.7 cubic feet per minute per square foot per inch at a dilerential pressure of one inch of water was obtained. The cell was placed in a furnace and the electrolyte was maintained at 900 C. A voltage of 4.6 volts was used and an average anode current density of 2 amperes per square inch was obtained. Molten aluminum in the bottom of the cell served as the cathode.

The anode gases were passed through an oil trap and collected in a glass sampling bomb. The gases were analyzed by infra-red and found to contain 2.2 grams of carbon tetrauoride, 8.4 grams of C2126 and 1.6 grams of higher gaseous uorocarbons having the formula, CnFzMg. In the oil trap, 2.25 grams of liuorocarbon oil were obtained which had a molecular weight of around 410. The porous anode had a weight loss of 13.7 grams and 3.4 grams of aluminum were produced. The above run was repeated with an electrolyte comprising 62 weight percent aluminum fluoride and 38 weight percent sodium fluoride. Approximately the same results as above were obtained.

In a manner similar to above, luorocarbons are obtained by the electrolysis of LiF, NaF, MgF2, NaF-Lil, BaFLiF, SrFz-LiF, NaF-LiF-AlF3, etc.

Example 1I To show the eiect of a porous anode on anode effect, an electrolysis similar to that in Example I was carried out at a current density of 4 amperes per square inch at a voltage of 5.45 volts for about 3 hours. The cell operated smoothly and the anode gas contained approximately 16 percent of carbon tetrauoride, 70 weight percent of perlluoroethane and higher gaseous fluorocarbons, and 14 weight percent of oil and tar.

The porous anode was replaced first with an ordinary graphite anode and then with an ordinary carbon anode and the cell again operated as above. 'With both of these anodes the cell immediately went into anode effect and very little current passed through the cell even at high voltages. When the ordinary anodes were replaced with the porous anode, the cell again operated smoothly producing lluorocarbons.

Example III To illustrate the eiect of electrolysis temperature upon the fluorocarbon composition in the anode Product, a series of runs was made where an electrolyte consisting essentially of 48 percent lithium iluoride and 52 weight percent sodium fluoride was subjected to electrolysis at relatively low anode current density at different temperatures.

An electrolytic cell similar to that shown in FIGURE l was used except that a diierent type of a porous carbon anode assembly was used. The porous carbon anode assembly consisted of a cylindrical graphite lead which was enlarged at the lower end and the passageway along the longitudinal axis of this lead was also enlarged at the. lower end. A cylindrical porous carbon plug 1 inch in diameter was inserted into the enlarged passageway leaving inch of the plug extending below the graphite lead. Thus the area of the porous carbon anode exposed to the electrolyte was approximately 3.5 square inches. The porous carbon plug had a permeability of 4 as per manufacturers speciication.

`In the operation of the cell, lead which was to act as a molten cathode and 1000 grams of a mixture containing 48 weight percent lithium fluoride and the remainder sodium fluoride were placed in the cell inside of an alumina liner which had an inside diameter of 3 inches and was 5 inches high. The cell was then placed in a furnace and heated to the predetermined temperature. When the electrolyte reached the desired temperature, the porous carbon anode assembly was inserted into the cell so that the porous plug was immersed in the electrolyte and the cover plate tightened down to form a gas tight seal. Current was applied to the cell and it was operated for l hour while the electrolyte was maintained at the desired temperature. The anode gas formed by the electrolysis was forced up the passageway of the carbon holder holding the porous anode and was collected in a 500 milliliter glass gas bomb by displacing the air in the bomb. The gaseous product in the bomb was analyzed by infrared to determine the composition of the fluorocarbon product obtained.

The pertinent data and results obtained which are plotted in FIGURE 2 are shown in the table below.

agossfrsv Small amounts of oily tars were obtained but were not analyzed.

In a manner similar to that described above the cell was operated atrrelatively high anode current densities at different temperatures.V

The pertinent data and results obtained are shown in the table below. Small amounts of oily tars were also obtained butwere not analyzed.

To show .the eiiect upon the composition of the uorocarbon product obtained with a porous carbon anode made by combining line carbon particles with a binder and cindering the mixture to form a porous solid mass as used in this invention as compared to the composition obtained with an anode made of carbonaceous material in particulate form loosely confined, a series of runs was made with an anode made of loosely conned particles of petroleum coke.

A cell similar to that shown in FIGURE 1 was Vused except .that a solid inch graphite rod was used instead of the carbon holder with a passageway shown in the drawing. Also, the cover plate had anadditional opening from that shown Vinthe drawing through which a pipe was Vextendeda short way into the tank. The anode gas formed in the cell was Withdrawn through this pipe.

Lead which was to act as a molten cathode and 1000 grams `of a mixture or" lithium fluoride and sodium uoride similar to that used above was placed inside of the 3 inch in diameter alumina liner. The cell was then placed in a furnace and heated until the lithium uoride and sodium l'luoride mixture was molten. The 3A inch graphite rod was thenextended into the cell until it almost touched the surface of the electrolyte. Petroleum coke in particulate form passing through a 'Vs inch mesh screen and being retained on'a 40 mesh standard screen was then placed on top ofthe electrolyte to form a bed 2 inches thick Within the alumina liner and surrounding the 3A inch graphite rod. Since the petroleum cokewas considerably lighter than the molten metal iluorides, itlloated upon the surface of the electrolyte.

The cover plate was bolted down and the cell was then further heated until the predetermined temperature was reached. Current was passed through the cell and the anode yproduct obtained within the cell collected in a bomb and analyzed -by intra-red from which the composion Vof the iluorocarbon product was determined.

To determine the anode current density, the anode area was considered to be equal to the area of electrolyte upon which the petroleum coke iloated. Thus the total cell `current in amperes was divided by the area of the electrolyte subjected to the petroleum coke.

.8 The pertinent data-and resultsobtained are'shown in the table below.

Elec- Fluoroearbon analysis based trolyte anode Cell Cell on total uorocarbons, mole tempercurrent current, potenpercent ature, density amps. tial,

C. amps/in.2 volts GF4 .CiFi CsFs CaFe CiFs From the results obtained above, it can be seen that J with an anode of loosely Yconfined petroleum coke the amount of uorocarbons of higher molecular than hexaiiuoroethane which can only be obtained at temperatures below 800 C. is'considerably less than the 15 mole percent obtained with a porous carbon'anode. Also va considerably greater voltage is required.

What is claimed is:

1. A process for thepreparation of'iluorocarbons which comprises passing an electric current through a molten electrolyte at a temperature of from 600 C. to l000 C. between a cohered porous carbon anode having a permeability in the'range of l to 40 and an insoluble cathode at an anode current density in the range of from l to 100 amperes per square inch to `obtain an anode product containing iluorocarbons, said molten electrolyte consisting essentially of at least one metal uoride which is nonwetting in respect to the anode and stable and non-volatile at electrolysis temperature selected from the group consisting of alkali metal fluorides, alkaline earth metal iluorides, and earth metal uorides, and recovering the fluorocarbons from the `anode product.

2. A process according to claim'l wherein the tem perature isin the range of 700 to 1000 C. and at an anode current density of from 1 to 40 amperes per square inch.

3. A process according to claim '2 wherein the molten electrolyte is an alkali metal uoride which is stable and non-volatile at the operating temperature and is nonwetting in respect to the anode.

4. A process according to claim 2 wherein the molten electrolyte is a mixture of alkali metal iiuorides `which are stable and non-volatile at the electrolysis temperature and are non-wetting in respect to the anode.

5. A process according to claim 2 wherein Vthe molten electrolyte consists essentially of at least one alkali metal fluoride and one alkaline earth iluoride which are stable and non-volatile at the electrolysis temperature and are non-wetting in Yrespect to the anode.

6. A process according to claim 2 wherein the molten electrolyte consists essentially of at least one alkali metal fluoride and one earth metal Viluoridewhich are stable and non-volatile at the electrolysis temperature andnon-wetting in'respect to the anode.

7. A process for the preparation of iluorocarbons, which comprises passing an electric lcurrent through a molten electrolyte consisting essentially of sodium fluoride and lithium fluoride between a cohered porous carbon anode having a permeability in the range Vof 4 to 20 and an' insoluble cathode `at a temperature in the range of 700 to 1000D C. and at an anode current density in the range of from l to 40 amperes vper square inch to obtain an anode product containing iiuorocarbons, and recovering the tluorocarbons from the anode product.

8. A process for the preparation of iiuorocarbons which comprises passingan electric current .througha molten electrolyte consisting essentially of sodium uoride and lithium fluoride at a temperature in the range of 650 to 850 C. betweena cohered porous carbon anode having a permeability in the range of 4 to 20 and an insolublecathode at an anode current'density in the'range of 2 `to 15 amperes per square vinch to obtain anode product containing uorocarbcns, and recovering the uorocarbons from the anode product.

9. A process for the preparation of uorocarbons, which comprises passing an electric current through a molten electrolyte consisting essentially of magnesium fluoride and lithium fluoride between a cohered porous carbon anode having a permeability in the range of 4 to 20 and an insoluble cathode at a temperature in the range of 700 to 1000 C. and at an anode current density in the range of from 1 to 40 amperes per square inch to obtain an anode product containing iiuorocarbons, and recovering the tluorocarbons from the anode product.

10. A process for the preparation of uorocarbons which comprises passing an electric current through a molten electrolyte consisting essentially of magnesium fluoride and lithium uoride at a temperature in the range of 65 0 to 850 C. between a cohered porous carbon anode having a permeability in the range of 4 to 20 and an insoluble cathode at an anode current density in the range of 2 to 15 amperes per square inch to obtain anode product containing tluorocarbons, and recovering the fluorocarbons from the anode product.

11. A process for the preparation of uorocarbons, which comprises passing an electric current through a molten electrolyte consisting essentially of magnesium uoride, calcium uoride and lithium fluoride between a cohered porous carbon anode having a permeability in the range of 4 to 20 and an insoluble cathode at a temperature in the range of 700 to 1000 C. and at an anode current density of from 1 to 40 amperes per square inch to obtain an anode product containing uorocarbons, and recovering the fluorocarbons from the anode product.

12. A process for the preparation of uorocarbons which comprises passing an electric current through a molten electrolyte consisting essentially of magnesium uoride, calcium fluoride, and lithium fluoride at a temperature in the range of 650 to 850 C. between a cohered porous carbon anode having a permeability in the range of 4 to 20 and an insoluble cathode at an anode current density in the range of 2 to 15 amperes per square inch to obtain anode product containing uorocarbons, and recovering the iiuorocarbons from the anode product.

13. A process for the preparation of uorocarbons, which comprises passing an electric current through a molten electrolyte consisting essentially of aluminum fluoride and lithium fluoride between a cohered porous carbon anode having a permeability in the range of 4 to 20 and an insoluble cathode at a temperature in the range of 700 to 1000 C. and at an anode current density in the range of from 1 to 40 amperes per square inch to obtain an anode product containing uorocarbons, and recovering the fluorocarbons from the anode product.

14. A process for the preparation of uorocarbons which comprises passing an electric current through a molten electrolyte consisting essentially of aluminum uoride and lithium fluoride at a temperature in the range of 650 C. to 850 C. between a cohered porous carbon anode having a permeability in the range of 4 to 20 and an insoluble cathode at an anode current density in the range of 2 to 15 amperes per square inch to obtain anode product containing iluorocarbons, and recovering the fluorocarbons from the anode product.

15. A process for the preparation of hexauoroethane and higher molecular weight uorocarbons which comprises passing an electric current through a molten electrolyte at a temperature in the range of 650 to 850 C. between a cohered porous carbon anode having a permeability in the range of 4 to 20 and an insoluble cathode at an anode current density in the range of 2 to 15 amperes per square inch to obtain an anode product containing hexauoroethane and higher molecular weight luorocarbons, said molten electrolyte consisting essentially of at least one lmetal fluoride which is non-wetting with respect to the anode, stable, and non-volatile at the electrolysis temperature selected from the group consisting of alkali metal fluorides, alkaline earth metal uorides, and earth metal fluorides, and recovering the fluorocarbons from the anode product.

References Cited in the file of this patent UNITED STATES PATENTS 785,961 Lyons et al Mar. 28, 1905 2,592,144 Howell et al Apr. 8, 1952 2,684,940 Rudge et al July 27, 1954 2,693,445 Howell et al Nov. 2, 1954 2,841,544 Radimer July l, 1958 FOREIGN PATENTS 896,641 Germany Mar. 15, 1954

Claims (1)

1. A PROCESS FOR THE PREPARATION OF FLUOROCARBONS WHICH COMPRISES PASSING AN ELECTRIC CURRENT THROUGH A MOLTEN ELECTROLYTE AT A TEMPERATURE OF FROM 600*C. TO 1000*C. BETWEEN A COHERED POROUS CARBON ANODE HAVING A PERMEABILITY IN THE RANGE OF 1 TO 40 AND AN INSOLUBLE CATHODE AT AN ANODE CURRENT DENSITY IN THE RANGE OF FROM 1 TO 100 AMPERES PER SQUARE INCH TO OBTAIN AN ANODE PRODUCT CONTAINING FLUOROCARBONS, SAID MOLTEN ELECTROLYTE CONSISTING ESSENTIALLY OF AT LEAST ONE METAL FLUORIDE WHICH IS NONWETTING IN RESPECTA TO THE ANODE AND STABLE AND NON-VOLATILE AT ELECTROLYSIS TEMPERATURE SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL FLUORIDES, ALKALINE EARTH METAL FLUORIDES, AND EARTH METAL FLUORIDES, AND RECOVERING THE FLUOROCARBONS FROM THE ANODE PRODUCT.

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