US3114684A

US3114684A - Preparation of halofluorocarbons

Info

Publication number: US3114684A
Application number: US762399A
Authority: US
Inventors: Olstowski Franciszek; Lloyd G Dean
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1958-09-22
Filing date: 1958-09-22
Publication date: 1963-12-17
Anticipated expiration: 1980-12-17

Description

Dec- 17, 1963 F. oLsrowsKl ETAL 3,114,634

PREPARATION OF HALOFLUOROCARBONS Filed Sept. 22, 1958 INVENTORS. Franc/33e* 0/5 fo nfs/w' /oya/GZ Dean BY @2206 TOR/VEY United States Patent O 3,ll4,684 PREPARATIN F HALGFLURCARBNS Franciszelr lstowslri, Freeport, and Lloyd G. Dean, Lahe Erickson, Tex., assignors to The Dow Chemical Company, Midland, Mich., a corporation ot Delaware Filed Sept. 22, 1953, Ser, No. 762,399 14 Claims. (6l. 20d-62) This invention relates to `a process for preparation of haloiiuorocarbons, and more particularly, to the preparation of these compounds by the electrolysis of a non-volatile molten metal fluoride `containing a metal halide other than a iuoride.

This application is a continuation-in-part of patent application Serial No. 663,966, filed on June 6, l957, now abandoned.

Presently, the preparation of chloroiluoirocarbons is mainly limited to partial iluorination of chlorinated hydrocarbons by the use of iiuorinating agents, such as hydrogen fluoride and luorine. Bromine containing iluorocarbons have been prepared by birornination of unsaturated iluorocaubons or saturated uorocarbons at high temperatures. These processes involve handling hazardous ma terials which `are expensive `and require special equipment. Metal uoridcs yand metal halides are cheap raw materials and a process whereby substituted uorocarbons could be prepared by ithe electrolysis of these fused metal salts would considerably reduce the production cost of there compounds. Heretoiore, no practical process Was known whereby haloiluorocarbons could be prepared by electrolysis of a fused metal fluoride electrolyte.

It is, therefore, among the objects of this invention to provide a process for the preparation of hatlolluorocarb ons by electrolysis of a fused metal huoride containing a metal halide other than a liuoride.

The above and other objects are attained by passing an electric current through `a molten electrolyte between a porous carbon `anode and ian insoluble cathode where the electrolyte consists essentially of a mixture of a metal fluoride which is non-volatile and stable at the electrolysis temperature selected from the `group consisting of alkali metal iluorides, alkaline earth ymetal iluorides, earth metal uorides, and mixtures thereof and a metal halide of a halogen having :an atomic nuxmlber in the range of 17 to 36 which is nonvolatile and stable at the electrolysis .emperature, such as a rneftal chloride and a metal bromide.

-lt has been discovered that when la porous carbon anode is used in the electrolysis of .an electrolyte consisting es sentially of the particular metal iluoride or iluorides and a metal salt, such as a chloride or bromide, an anode product is obtained containing halolluorocarbons. The anode product rnay contain `a ninnber of ilumine-containing compounds including lboth saturated md unsaturated cornpounds and may also contain products other ythan the haloiluorocarbons. The anode product is gaseous at the electrolysis temperature but higher molecular weight conipounds which are oils at room temperature may also be obtained.

ilhe porous carbon anode used rnay .be an intimately combined solid mass type which is made by combining amorphous carbon, such `as petroleum coke, coal, carbon black and the like or allotropic carbon, such as graphite, with a binder `and sintering the rninture to form an intimately combined solid rnass having a prescribed permeability, Also, the porous `anode may consist of carbonaceous material in particulate ionm conlined so that the individual particles are in electrical Contact with each other. A porous caobon anode which is intimately combined by sintering to [form la solid porous cohered mass is generally preferred.

A solid mass type porous anode lhav-ing a permeability of at least one `and not greater than 40 is generally used.

fil

3,114,534 Patented Dec.. 17, 1963 ICC lt is preiierxred that the permeability be in the range of 4 to 20. While an anode having 1a permeability less than one may be used in special cases, no benecial advantage is obtained. Where relatively low current densities are to be employed an anode having la permeability as low as 0.2 may be used, if desired. An anode having -a permeability greater tbian 40 is seldom used. The structural strength of tlie anode decreases with the porosity which rnakes it less desirable than a less porous anode.

Permeability as used herein, refers to the porous anodes which are intimately combined in a solid mass by sintering and is expressed as the arnobnt of air passing through the porous carbon ianode in cubic Jreet per minute per square foot per inc-h thickness at `a pressure differential ofi Z inches of water. rThe term perou-s, as used herein, means gas permeable.

While the current eiliciency land the yield of haloiluorocarbone may not be as great, a porous anode comprising of carbonaceous material in particulate 'form loosely conlined is less costly and thus may be desirable in some cases. Practically any cambonaceous material in particulate form rnay be used. Charcoal, coke, lamp black, powdered graphite, and powdered carbon are illustrative examples of some ofthe carbonaceous materials which are operative. Due to its availability petroleum coke in particulate form is preferred. Generally particles of the carbonaiceous material larger than one inch are not used eXpt in a large unit Where a large bed is employed. Parti-cles as small as those passing through a No. 200 -standard mesh screen and being lretained on la No. 300 mesh tscreen are operative. However, it is preferred to use carbonaceous material which will pass through ya No. 6 standard mesh screen and be retained on a No. 40.

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

'FIGURE l diagrammatically illustrates an electrolytic cell employing a porous anode comprising of carbonaceous material in particulate form loosely confined which may be used in carrying out the invention, and

FlGURES

2 and 3 show different types of porous anode assemblie-s which may be used in the cell shown in FIGURE l when a solid mass type porous anode is used.

The electrolytic cell diagrammatically shown in lFIG- URE l comprises a metal tank l having a cover plate 2 and an electrical non-conducting cylindrical liner 3 in which the electrolyte i is placed, and a carbon lead 5 extending part way into the tank through an opening in cover plate 2. As shown, cover plate Z is fastened to tank l. by means of a muliplicity of screws 6 -to form a gas tight seal. Clamps or other means may be used. A pipe 7 is inserted in an opening 8 in cover plate 2 and provides a passageway through which the anode gas produced as a product inside of tank l may be withdrawn from the tank. The attachment of pipe 7 to cover plate 2 is gas tight and may be obtained by welding the outer periphery of the pipe to the cover plate or by having the end which is inserted in the cover plate threaded and the opening 8 also threaded to receive the pipe. Where the carbon lead 5 passes through cover plate 2, an electrical insulating seal 9 is used so that the gas tight seal is obtained. An electrical lead 1t) through which the current is supplied to the cell is attached to the carbon lead at the end :which is not inserted into the tank. Another lead il is electrically connected to the surface of the tank 'which through a molten cathode l2 at the bottom of the tank completes the circuit for the current ilow :through the electrolytic cell. A molten cathode of an inert metal, such as lead, heavier than the electrolyte is generally used where the metal deposited at the cathode is lighter than the electrolyte.

This simplifies the cell construction, since no provisions have to be made to entrap or remove the metal deposited from the surface of the electrolyte. Carbonaceous material 13 in particulate form being lighter than the molten electrolyte floats on the surface surrounding and in contact with carbon lead 5. Carbon lead is not immersed in the electrolyte itself.

In the operation of the cell, the cell is placed in a furnace where it is heated to ,the desired temperature. When the desired temperature is obtained, an electrical potential is applied to leads i@ and il to provide a current flow through the electrolyte. The anode product which may be substantially all lgas is drawn from within the tank through pipe 7 after which it is further processed by known methods to recover and separate the particular halofluorocarbons obtained. The metal depositing out from the electrolyte is deposited in the molten cathode and later recovered by known methods.

FIGURES 2 and 3 illustrate a porous anode assembly wherein a solid mass type of a porous anode is used. As shown in FIGURE 2 the anode assembly comprises a cylindrical carbon or graphite anode holder Ztl having a passageway 2i extending through the center along its longitudinal axis. The hollow-cup shaped piece of porous carbon 22 is attached to the lower end of holder Ztl with passageway 21 communicating with a hollow inside area 23 of the porous cup 22. At the upper end of holder Ztl, a pipe 24 is inserted in passageway 2l and thus provides a means by which the anode product forming at the porous cup may be removed from the cell. A lead 25 is attached to holder 2t) and thus supplies the current to the :anode and provides a means for cornpleting the circuit in the cell.

FIGURE 3 shows a modication of the porous anode assembly shown in FIGURE 2. It comprises a carbon or Igraphite carbon holder Eil which at its lower end 31 is enlarged. The holder has a passageway 32 in the center extending along its longitudinal axis which becomes enlarged at the lower end. The porous anode 33 in the shape of a plug is inserted in the lower end of the anode holder Sil in the enlarged area of the passageway. A pipe 34 is inserted in passageway 32 at the upper end of the anode holder. In the operation of the cell the porous anode portion of the anode assembly as shown in FIGURES 2 and 3 are immersed in the electrolyte.

The shape of the porous carbon anode used is immaterial. The hollow-cup type as shown in FIGURE 2 or the plug type as shown in 'FIGURE 3 are preferred especially where higher molecular weight fluorocarbons or haloiluorocarbons are obtained. ri'hese compounds may be readily drawn through the porous anode and removed from the system through the passageway in the holder'. Instead of using a hollow-cup type porous anode as shown in |`FIGURE 2 or a plug as shown in FIGURE 3, a solid cylindrical piece or the porous carbon material may be used as an anode. It may be necessary in some cases to use a hood or shield to enclose the solid anode to entrap the anode gases as they are formed and released in order to remove them from the system. `Other types of anode assemblies which are apparent to those skilled in the art may also be used.

Illustrative examples of the alkali metal, alkaline earth metal, and earth metal liuorides which may be used as the iluoride constituent of the electrolyte are magnesium uoride, aluminum iluoride, sodium Iluoride, barium iluoride, strontium fluoride, calcium fluoride, lithium iluoride, and cesium iluoride. rhese metal 'lluorides are nonvolatile and stable at electrolysis temperature. Generally in the electrolysis the same haloiiuorocarbons are obtained regardless of the particular metal iluoride used as the iluoride constituent in the electrolyte. However, the ratio of the particular compounds obtained in the anode product may vary somewhat with the metal tluoride employed.

Although only one of the alkali metal iluorides, alkaline earth metal iluorides, or earth metal uorides may be used as the fluoride constituent of the electrolyte, a mixture of these metal iluorides is often used to increase the conductivity or lower the melt-ing point of the bath. For this purpose, lithium iluoride is most commonly added to the other metal iluorides, but other mixtures and combinations may also be used. When other iluorides are added to either increase conductivity or lower the melting point of a particular metal fluoride bath, the fluorides of metals whidh are higher in the electromotive series or more electronegaitive than the metal to be extracted at the cathode from the particular bath are preferred. By using iluorides of metals more eleotronegative, these metals will not deposit out at the cathode with the desired metal except at exceptionally high cathode current densities. Thus, the cathode yproduct is not contaminated under normal operation conditions. Also in continuous operation of the cell, the metal iluoride added to the electrolyte is not depleted by the electrolysis and only the uoride of the particular metal being deposited at the cathode has to tbe Iadded continuously. For example, when lithium iluoride is added to a magnesium ouride bath, the lithium is more electrone'gative 'than magnesium and thus will not deposit out at the cathode. Once the lithium lluoride is added to the bath it will riot be depleted lby 'the electrolysis and only magnesium flouride has to be added for continuous operation.

Illustrative examples of the metal Fluoride mixtures that may be used and the metal preferentially deposited out Iat the cathode are shown in the ltable below.

To the metal uoride or fluoride mixture, a metal halide of a halogen having an atomic number irr the range of 17 to 36, such as a metal chloride and a metal bromide, which is non-volatile and stable at the electrolysis temperature is added. By the electrolysis of the resulting electrolyte consisting essentially of the metal fluoride or metal iluorides and the metal halide, haloiluiorocarbons are obtained. With metal chlorides chlonouorocarbons are obtained, and by the additionv of metal bromides bromoiluorocarbons are produced. It is preferred to add the halide of the same metal as that of the fluoride constituent of the electrolyte which is being deposited at the cathode in the bath. Tlhus, the cell can be continuously operated by just adding the metal iluoride electrolyte and the particular halide. A non-volatile and stable halide or the same metals as the alkali metals, alkaline earth metals, or earth metals of the fluoride which may Ibe used other than tlhe particular metal utilized in the bath may also be used. However, the metal of the halide `may continuously increase in the cell, if it is higher in the electromotive series, or deposit out at the cathode with the desired rnetal of the bath, if lower. In special cases, non-volatile and stable halides of metals other than those of the iluorides which may be used in the electrolyte may also be used. Most of these other metals are lower on the series and will deposit tout at the cathode in conjunction with the electrolyte metal. Illustrative examples of these other metal chloride and bromide are ouprous chloride, cuprous bromide, chromic chloride, molybdenum dichloride, lead chloride, manganese chloride, lead bromide, cadmium bromide, `and cadmium chloride.

Although the non-volatile stable metal halide is added to `the electrolyte bath mainly to effect the formation of halouorocarbons, the salt may also function as melting point depressor. For example, calcium chloride may be added to calcium fluoride to lower the melting point of the calcium fluoride as weil as to effect the formation of chlorofluorooarbons.

The concentration of metal halide salt added to the fluoride bath will vary with the particular salt used. The energy required for the production of the fluorine-containing compound is generally higher than for the production of chlorine or bromine. Consequently, a higher concentration of the fluoride in Ithe bath is generally maintained to `obtain a *greater formation of the fluorine-containing compounds and thus minimize the formation of chlorine or bromine. Generally, an electrochemical equivalent ratio of the fluoride anion to the chloride or bromide anion in the range of :1 to 40:1 is used, although the ratio may be `as low las 1:1. With chloride salts, an electrochemical equivalent ratio of fluoride to chloride in the range of 10:1 to 20:1 is preferred, while for ithe production of bromoiirrorocarb-ons, the preferred electrochemical equivalent ratio of uoride to bromide is in the range of :1 to 40:1. However, in an electrolyte comprising essentially calcium liuc-ride and calcium chloride, an electrochemical equivalent ratio of fluoride to chloride of as low as 1:1 may be fused and a ratio in the range of 1.5 :1 to 5:1 is generally employed.

While an anode product containing a higher percentage of haloiluorocarbons is normally obtained at lower temperatures, an electrolysis temperature in the range of 700o to 1000 C. is generally used. The optimum of the temperature for a particular electrolyte may vary somewhat. The minimum temperature that may be employed is the melting point of the electrolyte used, since the electrolyte must be in the molten state. The maximum temperature is either limited by cell structure, the stability and volatility of the particular` electrolyte employed or metal halide added to the bath, or the thermal stability of the particular halofluorocarbon desired at the anode. For eX- ample, in the electrolysis of calcium fluoride to which calcium chloride has been added, temperatures up to the boiling point of the calcium fluoride are operative providing the cell structure will withstand these high temperatures. These temperatures cannot be used where magnesium chloride is added to the bath due to the higher volatility of the magnesium chloride. Since at a lower temperature the construction of the cell is simplified, a temperature in the range of 700 to 1000 C. is thus generally preferred within which range an anode product containing a high percentage of halofluorocarbons is obtained. However for an electrolyte containing a LiFNaFAlF3 mixture as the fluoride constituent, the optimum temperature is somewhat lower being in the range of 650 to 800 C.

Although anode current density below l and up to 100 amperes per square inch may be used with certain porous anodes, an anode density in the range of 1 to 40 amperes is generally employed, preferably in the range of 1 to 10 amperes per square inch. Generally, at a higher anode current density, the anode product contains a higher percentage of halofluorocarbons. With an anode of carbonaceous material in particulate form loosely confined, an anode current density of over 5 amperes per square inch is seldom used due to the high Voltage required. The cathode current density is generally in the range of 1 to amperes per square inch. To obtain the current densities desired a voltage up to 30 Volts may be employed, but a voltage in the range of 4 to l() is preferred. For the loosely confined anode, a higher voltage may be required to obtain the desired anode current density.

Various electrolytic cell construction and various types of anodes which are apparent to those skilled in the art may be used. The particular anode adopted will generally depend upon the metal being deposited in the cell.

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

The term stable, as used herein in reference to the metal fluoride and metal halides, means salts which are thermally stable and will not decompose due to temperature itself.

The term non-volatile, as used herein in reference to the metal fluoride and metal halide, means salts which do not have a vapor pressure in excess of 20 mm. of Hg at the electrolysis temperature.

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

EXAMPLE I An electrolytic cell comprising a steel Crucible With an alumina liner, a porous anode having permeability of 4, as per manufacturers specifications and similar in construction to the anode assembly shown in FIGURE 2, and a molten lead cathode in which the calcium metal was deposited was operated with an electrolyte of calcium fluoride and calcium chloride.

To the electrolytic cell, 600 grams calcium fluoride and 400 grams of calcium chloride were added. The electrolyte was heated to 985 and 514 grams of lead were added to act as a molten cathode. The porous anode assembly was placed in the cell and current passed through the cell at about 30 amperes at a potential of 6.1 volts which gave an average anode current density of about 8 amperes per square inch. After passing approximately amperehours through the cell, the run was discontinued.

The anode gas was collected in the glass sampling bomb by displacement of air. The gas was analyzed by infrared and found to contain the following in mole percent.

Component: Percent or., 18 Crzci2 5 Craci 36 ci2 40 The lead cathode was analyzed by chemical wet methods for percent of calcium. The cathode contained 8.8 percent calcium which corresponded to a current eiciency of 83 percent.

The anode efficiency was assumed to be at least 83 percent, since the anode products could only react with the metal calcium produced.

The cell was also operated at a 1,000 C. and under different anode current densities. The anode gases obtained in mole percent under the different current densities are given below:

An electrolytic cell similar to the one described in EX- ample I was used in the preparation of chlorouorocarbons. To the cell, 500 grams of lithium uoride and 500 grams of magnesium fluoride were added. These constitutents were heated to 850 and 100 grams of magnesium chloride were then added to the molten bath. The cell was operated at an average current of 30 amperes at a potential of 8,0 volts. The average anode current density obtained was 3 amperes per square inch. The anode gases were collected in a glass bomb and infra-red analysis showed that the gases contained the following in mole percent.

7 Component: Percent CFaCl 44.5 CEZCIZ 4.4 CFC13 0.4 GF4 16.2

A chemical analysis showed the gas to also contain 34.4 volume percent of chlorine.

ln a manner similar to above chloroliuorocarbons are obtained by the electrolysis of LiF-LiCl, NaF-NaCl, MgFZ-MgClz, LiF-NaCl-NaF, LiENaECaClZ and LiF NaFMnCl2- EXAMPLE III An electrolytic cell similar t0 the one described in Example l was used in the preparation of bromotluorocarbons. To the cell were added 1500 grams of a mixture containing 32.5 weight percent calcium fluoride, 41.5 weight percent magnesium iluoride and 26.0 Weight percent of lithium fluoride. This mixture was heated to 800 C. and 35 grams of sodium bromide were added. A potential of 8 to 9 volts was used which gave a current flow of l5 to 25 amps. through the cell, or a current density of 3.75 to 6.25 amperes per square inch.

The anode gases generated were collected in a 250 milliliter glass bomb. These gases was analyzed by infra-red and found to contain the following in mole percent.

Component: Mole percent CFgEr 56 GF4 22 C2F6 4 A chemical wet analysis showed that the gas also contained about 18 percent bromine.

ln a manner similar to above bromoliuorocarbons are obtained by the electrolysis of LiF'LiBr, NaFNaBr, LiF NaF-NaBr, LiF-NaF-CaF2'NaBr, and

An anode comprising petroleum coke loosely confined was used in the preparation of halofluorocarbons. A cell similar to that shown in FIGURE 1 was used. The tank Was approximately 6 inches in diameter and an alumina liner was inserted which was 3 inches in diameter and 5 inches high. The carbon lead extending through the cover of the tank was a 3A inch graphite rod.

ln the operation of the cell, lead which was to act as a molten cathode and 1000 grams of a mixture containing 48 weight percent of lithium fluoride and 52 weight percent of sodium fluoride were placed within the alumina liner in the cell. Sodium chloride in amount of 42 grams was also added. The cell was placed in a furnace and heated until the lithium Fluoride-sodium lluoride and sodium chloride mixture were in molten state. The cell was then removed from the furnace and the 3A inch graphite rod was extended into the cell until Ait almost touched the surface of the electrolyte. Carbonaceous material comprising crushed petroleum colte passing through 1A inch mesh screen and being retained on a 40 mesh standard screen was placed on top of the electrolyte to form a bed 2 inches thick within the alumina linear and surrounding the 3%: inch graphite rod. The cover was then placed on the tank which was tightened to obtain a gas tight seal.

rl`he cell was then placed in a furnace where the cell was heated to a temperature of 800 C. While the electrolyte was at 800 C. a voltage of 19 volts was applied across the cell which resulted in a current flow of 30 amperes. The anode current density was approximately 4 amperes per square inch. To determine the anode current density the anode area was considered to be equal to the area of the electrolyte upon which the petroleum coke floated. Thus the total cell current in ampercs l was divided by the area of the electrolyte subjected to the petroleum coke.

The cell was thus operated for one hour and the gaseous anode product issuing from the cell was collected in a 500 ml. gas bomb by displacement of air. The gaseous product obtained in the bomb was analyzed by infra-red and found to contain the following7 in mole ercent.

Component: Percent CF,C1 33.4 CF2C12 0.6 GF4 7.3

A run similar to that above was made wherein sodium bromide in an amount of 30 grams was added as a constituent in the electrolyte. The cell was operated at a temperature of 750 C. and at an anode current density of about 5 amperes per square inch. The anode product obtained was found to contain the following in mole percent.

Component: Percent CF3Br 1.6 CE1 9.9 CEFG 4.8 CSFB 0.4

What is claimed is:

1. Process for the preparation of a halolluorocarbon containing in addition to tluorine at least one of the other halogens which comprises passing an electric current through an electrolyte between a carbon anode and an insoluble cathode at a temperature suiicient to melt the electrolyte to obtain an anode product containing said halolluorocarbon, said electrolyte consisting essentially of a mixture of at least one metal lluoride and a metal halide corresponding to one of said other halogens, the metals of the mixture of halides being selected from the group consisting of alkali and alkaline earth metals, the halide corresponding to said other halogens in said electrolyte being present in a minor proportion and recovering the haloiluorocarbon from the anode products.

2. A process for the preparation of halouorocarbon, which comprises passing an electric current at a suiliciently low voltage to prevent anode effect through an electrolyte between a porous carbon anode and an insoluble cathode at a temperature sufficient to melt the electrolyte to obtain an anode product containing a halouorocarbon, said electrolyte consisting essentially of a mixture containing at least one metal lluoride which is non-volatile and stable at the electrolysis temperature selected from the group consisting of alkali metal fluorides, alkaline earth metal liuorides, and earth metal lluorides and a metal halide of a halogen having an atomic number of from 17 to 36 which is non-volatile and stable at the electrolysis temperature in an amount such that the electrochemical equivalent ratio of the uoride anions to the anions of the metal halide in the electrolyte is in the range of 1:1 to 40:1, and recovering the halofluorocarbon from the anode product.

3. A process according to claim 2 wherein the metal uoride in the electrolyte consists essentially of at least one alkali metal fluoride which is non-volatile and stable at electrolysis temperature, and a metal halide of a halogen having an atomic number in the range of 17 to 36 which is non-volatile and stable at electrolysis temperature.

4. A process according to claim 2 wherein the metal fluoride in the electrolyte consists essentially of at least one alkaline earth metal lluoride which is non-volatile and stable at electrolysis temperature and a metal halide of a halogen having an atomic number in the range of 17 to 36 which s non-volatile and stable at electrolysis temperature.

5. A process according to claim 2 wherein the metal fluoride in the electrolyte consists essentially of at least one earth metal fluoride which is non-volatile and stable at electrolysis temperature and a metal halide of a halogen having an atomic number in the range of 17 to 36 which is non-volatile and stable at electrolysis temperature.

6. A process according to claim 2 wherein the metal uoride is a mixture of an alkali metal fluoride and an alkaline earth metal uoride.

7. A process for the preparation of chloroiluorocarbons which comprises passing an electric current at a sui'liciently low voltage to prevent anode effect through an electrolyte between a porous carbon anode and an insoluble cathode at a temperature suicient to melt the electrolyte to obtain a product at the anode containing chlorolluorocarbons, said electrolyte consisting essentially of calcium iluoride and calcium chloride in an electrochemical equivalent ratio of iluoride to chloride in the range of 1.5 :1 to 5:1.

8. A process according to claim 7 wherein the porous carbon anode is an intimately combined solid mass having a permeability of at least 0.2 and the electrolyte is at a temperature in the range of 700 to 1000 C.

9. A process according to claim 8 wherein the permeability is in the range of 4 to 20.

10. A process for the preparation of chlorofluorocarbons, which comprises passing an electric current at a sufciently low voltage to prevent anode effect through an electrolyte between a porous carbon anode of an insoluble cathode at a temperature suficient to melt the electrolyte to obtain a product at the anode containing chlorouorocarbons, said electrolyte consisting essentially of magnesium uoride, lithium fluoride, and a metal chloride which is non-volatile and stable at the electrolysis temperature in an amount such that the electrochemical equivalent ratio of fluoride to chloride in the electrolyte is in the range of 10:1 to 20:1.

11. A process according to claim 10 wherein the metal 10 chloride is magnesium chloride, the porous carbon anode is an intimately combined solid mass having a permeability in the range of 4 to 20, and the electrolyte is at a temperature in the range of 700 to 1000 C.

12. A process for the preparation of a bromolluorocarbon, which comprises passing an electric current at a suiciently low voltage to prevent anode eiect through an electrolyte between a porous carbon anode and an insoluble cathode at a temperature sufficient to melt the electrolyte to obtain a product at the anode containing bromofluorocarbons, said electrolyte consisting essentially of magnesium fluoride, lithium fluoride, and a metal bromide which is non-volatile and stable at the electrolysis temperatures in an amount such that the electrochemical equivalent ratio of fluoride to bromide in the electrolyte is in the range of 10:1 to 40:1, and recovering the bromoiluorocarbon from the anode product.

13. A process according to claim 12 wherein the porous carbon anode is an intimately combined solid mass having a permeability of at least 0.2 and the electrolyte is at a temperature in the range of 700 to 1000c C.

14. A process according to claim 13 wherein the metal bromide is magnesium bromide, the ratio of fluoride to bromide in the electrolyte is in the range of 20:1 to 40: 1, and the permeability is in the range of 4 to 20.

References Cited in the le of this patent UNITED STATES PATENTS 785,961 Lyons et al Mar. 28, 1905 868,670 Kugelgen et al. Oct. 22, 1907 1,343,662 Danckwardt June 15, 1920 2,841,544 Radimer July 1, 1958 FOREIGN PATENTS 896,641 Germany Mar. 15, 1954

Claims

1. PROCESS FOR THE PREPARATION OF A HALOFLUOROCARBON CONTAINING IN ADDITION TO FLUORINE AT LEAST ONE OF THE OTHER HALOGENS WHICH COMPRISES PASSING AN ELECTRIC CURRENT THROUGH AN ELECTROLYTE BETWEEN A CARBON ANODE AND AN INSOLUBLE CATHODE AT A TEMPERATURE SUFFICIENT TO MELT THE ELECTROLYTE TO OBTAIN AN ANODE PRODUCT CONTAINING SAID HALOFLUOROCARBON, SAID ELECTROLYTE CONSISTING ESSENTIALLY OF A MIXTURE OF AT LEAST ONE METAL FLUORIDE AND A METAL HALIDE CORRESPONDING TO ONE OF SAID OTHER HALOGENS, THE METALS OF THE MIXTURE OF HALIDES BEING SELECTED FROM THE GROUP CONSISTING OF ALKALI AND ALKALINE EARTH METALS, THE HALIDE CORRESPONDING TO SAID OTHER HALOGENS IN SAID ELECTROLYTE BEING PRESENT IN A MINOR PROPORTION AND RECOVERING THE HALOFLUOROCARBON FROM THE ANODE PRODUCTS.