EP0516690A4

EP0516690A4 - Halogen exchange fluorination

Info

Publication number: EP0516690A4
Application number: EP19910904787
Authority: EP
Inventors: Richard Edward Fernandez; William Henry Gumprecht
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1990-03-02
Filing date: 1991-01-29
Publication date: 1993-06-16
Also published as: CA2077455A1; AU7332991A; BR9108099A; CN1054582A; ZA911522B; WO1991013048A1; JPH05504963A; CS53291A2; EP0516690A1

Abstract

A process for halogen exchange fluorination by contacting a solid composition of alkali metal fluoride with a gaseous halocarbon having a replaceable halogen other than fluorine to produce a fluorinated hydrocarbon having at least one more fluorine than the starting halocarbon and, optionally, regenerating the alkali metal fluoride with HF, in the feed.

Description

TITLE HALOGEN EXCHANGE FLUORINATION

Field of Invention This invention relates to the halogen exchange fluorination of saturated halocarbons to the corresponding halocarbon having at least one additional fluorine-substitution than the original halocarbon. More particularly, the invention relates to the conversion of a saturated halocarbon having at least one chlorine or bromine substitution to the corresponding halocarbon having at least one fluorine substitution replacing the "at least one chlorine or bromine substitution." Of greatest interest is the invented process for improving the conversion of

2-chloro- or 2-bromo-l,1,1-trifluorethane, CF₃CH₂CI or CF₃CH2Br, hereinafter referred to as "HCFC-133a" and "HBFC-133aBl" respectively, to 1,1,1,2-tetra-fluoroethane, CF3CH2F, hereinafter referred to as "HFC-134a" and, optionally, recovering the resulting metal chloride or bromide as the metal fluoride for recycling into the conversion process.

Background of the Invention HFC-134a and its isomer, 1,1,2,2- tetrafluoroethane, CHF2-CHF2, hereinafter referred to as "HFC-134", are potentially useful as aerosol propellants and as refrigerants. They are of particular interest as replacements for Freon^® 12, the commercial refrigerant currently used in substantially all automotive air conditioning systems.

Heretofore, however, the production of HFC-134 and HFC-134a has not been commercially attractive. In particular, a definite need exists for converting HCFC-133a to HFC-134a by a process that is readily adaptable to continuous operation, that minimizes the need for hydrogen fluoride as a fluorine source, that provides the desired tetrafluoro compound at high conversion and selectivity levels and that provides the desired compound in a high state of purity.

Prior Art

As stated in U. S. Patent 4,311.863, (column 1, lines 26 ff.) "It is apparent from the prior art that the chlorine atom of the -CH₂CI group (as in CFC-133a) is highly resistant to halogen exchange with HF." As "prior art," the inventor in this patent discloses the following references: U. S. Patent 2,885,427; U. S. Patent 3,664,545; U. S. Patent 4,129,603; and in a book by Hudlicky p. 93 of "Chemistry of Organic Fluorine Compounds", MacMillan Co., New York, N.Y. (1962).

U. S. Patent 2.885.427 discloses the preparation of HFC-134a by the vapor phase reaction of trichloroethylene with HF in the presence of a catalyst prepared by heating hydrated chromium fluoride in the presence of oxygen. The resultant product is a mixture of fluorocarbons in which HFC-134a is reported as being present in an amount of 3 mol %.

Hudlick in his book and U. S. Patent 3.644.545 disclose the difficulty of fluorine exchange on -CH2CI groups with HF in an antimony-catalyzed liquid phase reaction and in a vapor phase reaction, respectively.

U. S. Patent 4.129.603 discloses the vapor phase reaction of CFC-133a with HF in the presence of chromium oxide catalyst to produce a flu rocarbon mixture in which the HFC-134a is reported as 18.2% by volume.

U. S. Patent 1,914.135; Australian Patent 3.141; U. S. Patent 2.739.989: and U.S. Patent 3 ,843.546 disclose halogen exchange fluorination using alkali metal or alkaline earth metal fluorides. However, these metal fluorides have relatively low orders of reactivity; and processes involving them are generally best conducted in the vapor phase at elevated temperature of 350 to 550*C by passing the gaseous halocarbon over or through a bed of the solid metal fluoride. The metal halide by-product tends to coat the metal fluoride as reaction progresses so that the reaction rate is retarded; frequent changes of metal fluoride are necessitated; and other expedients, as set forth in these patents, must be imposed to ameliorate the problem.

British Patent 941,144 discloses that the elevated temperatures required in the gas-solid processes can be reduced and the yields improved by employing a gas-liquid process. A gaseous chlorocarbon is passed through a metal fluoride-metal chloride melt at a temperature of about 300 to 375°C. The metal fluorides disclosed are, inter alia, sodium, potassium and calcium fluorides. The molten metal chloride which functions as a solvent for the fluoride may be ferric or zinc chloride or mixtures thereof or these mixtures with sodium chloride.

U. S. Patent 4,311. 863 discloses a gas-liquid halogen exchange process in an aqueous medium. Specifically, the process involves converting HCFC-133a to HFC-134a by reaction with potassium, cesium or rubidium fluoride in a 25 to 65 weight % aqueous solution at about 200 to 300^βC under autogenous pressure. Although the process can provide adequate yields of HFC-134a, it is not readily adaptable to low cost, economic, continuous operation, particularly in view of the higher pressures required to maintain the aqueous mixture in the liquid state at the operating temperatures required and the excessive corrosion of the reactor materials under process conditions. It should be noted that at column 5, line 34 ff. of this patent, it is disclosed that "HF in the absence of water does not further the reaction. ...2-chloro-l,1,1-trifluoroethane (CFC-133a) was contacted with fused KF.HF with no water present. No reaction occurred." (Underline added).

Summary of Invention The present invention is a process for the halogen exchange fluorination of a saturated halo carbon, preferably a continuous process, comprising the following steps:

1. Contacting a solid composition consisting essentially of an alkali metal fluoride having the formula MF preferably wherein "M" is at least one alkali metal having an atomic number 19 through 55, i.e. Potassium, K, or Cesium, Cs, or Rubidium, Rb, preferably Cs with a gaseous halocarbon having at least one replaceable halogen other than fluorine, i.e., chlorine or bromine, in the molecule preferably CX₃CH₂CI wherein X is at least one of Cl or F, at a temperature where both the original halocarbon and the fluorinated product(s) are in the gaseous state to a temperature just below the lower of the decomposition temperature of the original halocarbon or that of the fluorinated product, preferably about 150"C to about 450^βC, at a subatmospheric or superatmospheric pressure as high as 2000 psi, preferably the latter for increased productivity. usually 14.7 psi to about 1500 psi, for a period of a few seconds to several hours, usually 0.5 minute to two hours, i.e., a pressure and time sufficient to provide at least one reaction product having at least one more fluorine atom in the molecule than the original halocarbon, preferably CX₃CH2F, and a residual solid composition of MF at least partially depleted in fluoride content and enriched in its other-than-fluoride halide content, i.e., MCI; 2. Isolating and recovering the fluorinated reaction product from the residual composition; and, optionally,

3. Contacting the residual composition with gaseous anhydrous HF in the presence or absence of the halocarbon to convert the other-than-fluoride halide content to HX wherein X is chlorine or bromine, and separating the gaseous HX from the solid composition enriched in MF.

The invention process can be represented by equation 1 below,

(1) CX₃CH₂C1 + MF —^7* CX3CH2F S'MCl where X and M are as defined previously.

Surprisingly, where at least one of the X groups is Cl, as in -CCI₃, -CCI2F and -CCIF2, the reaction can be readily controlled to produce the -CH2F compound substantially exclusively, that is, substantially without replacement of Cl of the -CX₃ group. Where -CX₃ is -CF3 the product is CF₃CH2F; i.e., HFC-134a. It should be noted that while X can be halogen, as in -CC1F2, X can also be H or R; where R is an alkyl or aryl group optionally containing halogen. Thus the -CX3 could be -CH3, -CR₃, or any combination between these extremes. In another aspect of the invention, the alkali metal fluoride, MF of equation (1) , may be produced in situ by reaction of an alkali metal chloride, MCI, which may be fresh or the MCI by-product of equation (1) , with gaseous hydrogen fluoride, HF, used either alone or in conjunction with the gaseous CX₃CH2CI reactant, the net effect being the conversion of CX₃CH2CI to CX3CH2F by HF, as shown in equation (2) . (2) CX₃CH2CI + HF CX₃CH₂F + HCl (2)

In still another aspect of the invention, gaseous CX3CH2CI and HF may be co-fed continuously or intermittently in contact with the alkali metal fluoride under controlled conditions of temperature, whereby the alkali metal fluoride is continuously or intermittently regenerated in situ from the alkali metal chloride by-product of the reaction.

Detailed Description of the Invention in the preferred process of the invention iβ» the alkali metal fluoride is contacted intermittently or continuously with a gaseous tetrahaloethane, optionally in the presence of gaseous HF at an effective temperature of from about 150° to about 450^βC-^e 5' form the corresponding

1,1,l-trihalo-2-fluoroethane, and the fluorinated product is recovered from the resulting product stream.

The 1,1,l-trihalogeno-2-chloroethane starting material may be CCI3CH2CI, CCI2FCH2CI,

CCIF2CH2CI, CF₃CH₂CI or a mixture of any two or more thereof. CF₃CH₂CI is the preferred starting material; and CF₃CH2F, the preferred trihalogeno-2-fluoroethane, because of the latter's .greater economic importance. Accordingly, the process of the invention is preferably conducted for the preparation of HFC-134a. As illustrated in the accompanying examples, the process is capable of producing HFC-134a in high yields (selectivities) at high conversions of CF₃CH2CI. Moreover, HFC-134a can be obtained substantially uncontaminated by 1,1-difluoro- 2-chloroethylene or other impurities difficult to separate by ordinary methods. Thus, HFC-134a (b.p. -26.5'C) can be recovered in a high degree of purity by simple means, such as fractional distillation. Unreacted CF3CH2CI (b.p. 6.1"C) is likewise recoverable in a high degree of purity, and can be recycled for further production of the tetrafluoroethane by the invention process.

That CF₃CH2CI and other CX₃CH₂CI materials can be converted to the corresponding -CH2F derivative under relatively mild gas phase conditions is surprising in view of the difficulties experienced by the prior art in converting -CH2CI to -CH2F compounds.

The alkali metal fluoride composition consists essentially of an alkali metal fluoride where the alkali metal may be Na, Li, K, Rb and Cs, but preferably where the atomic number is 19 though 55, i.e., K, Rb and Cs. Mixtures of these alkali metal fluorides may also be employed, including mixtures containing minor amounts of the lower atomic number alkali metal fluorides or alkaline earth metal fluorides. The alkali metal fluoride may be unsupported, e.g. as granules, finely divided powder or other particulate form, or carried on a suitable support, such as carbon, calcium fluoride or other alkaline earth metal fluoride, or aluminum fluoride. The latter may be a highly fluorinated alumina obtained by the reaction of HF with alumina wherein the fluorine content corresponds to an AIF₃ content of at least about 85%, preferably at least about 95%.

The reaction temperature may range widely. Normally it will be in the range of from about 150° to about 450°C, preferably from about 200" to about 400"C, depending on the CX₃CH2CI and the alkali metal fluoride. In general, the greater the fluorine content of the starting material the higher will be the minimum reaction temperature. Also the higher the atomic number of the alkali metal of the alkali metal fluoride the lower can be the operating temperature. At temperatures lower than these limits, the conversions tend to be too low for commercial production, while at temperatures above these limits, the selectivity of the reaction to produce the desired -CH2F compound is decreased by dilution in the side reactions.

Reaction pressure is not critical provided it is not so high as to result in condensation of the gaseous CX₃CH₂CI reactant during the course of the reaction at the desired operating temperature.

Reaction time can vary widely - from several seconds to many hours - depending on the reactantε, the temperature and the result desired. It will be appreciated that in general, as the reaction proceeds according to equation (1) above, the alkali metal fluoride reactant will eventually become substantially spent, i.e. converted to the corresponding alkali metal chloride.

Reaction time can be prolonged and product production rate maintained through in situ conversion of by-product alkali metal chloride to the fluoride with HF (equation 3) . (3) MCI + HF =>MF + HCl The temperature for this conversion should be above the melting point of the corresponding bifluoride, MHF2, formed by further reaction of MF with HF (equation 4) (4) MF + HF = MHF₂

Preferably, the temperature will be at least 100^βC higher, more preferably at least 150"C higher than the melting point of the bifluoride, which is much less active than MF for the present purpose. Thus, where M is K the temperature will be preferably at least about 330"C, more preferably at least about 380"C; where M is Rb, it will preferably be at least 310°C, more preferably at least about 360"C; where M is Cs, it will preferably be at least 280^βC, more preferably at least about 330"C. The temperature for the conversion of MCI to MF is preferably kept below about 400"C when CX3CH2CI starting material is present along with HF in the gaseous reactant stream, in order to minimize thermal decomposition and other side reactions of the CX3CH₂CI starting material and its fluorinated reaction product. In the absence of the starting material, the temperature for the conversion of MCI to MF may be higher, up to 500"C, for example. The normally gaseous reaction product mixture containing the CX₃CH2F product, unreacted

CX₃CH2CI, and by-products, if any, can be handled in any of the various ways known to the art. For example, the mixture can be scrubbed with water, aqueous caustic or aqueous acid to remove any acid or water-soluble material that may be present. One convenient scrubbing solution is 20.7% aqueous HCl precooled to -60"C. This scrubbing permits low-boiling organics to be collected as liquids, and further purified by fractional distillation. Among the fluorinated reaction products that can be prepared by the process of this invention are CCI₃CH2F, CCI₂FCH2F, CC1F₂CH₂F and CF₃CH2F, depending upon the starting material. ϋnreacted starting material can be recycled to the reactor. By-products that may also be formed include those arising from such side reactions as dehydrohalogenation and carbon-carbon cleavage.

As stated previously, the fluorinated products, CX₃CH₂F, are useful as refrigerants, solvents, blowing agents and intermediates for preparing other useful products. Since they contain hydrogen, they have a reduced impact on the environment. The reaction vessel is not critical and may be any of those normally employed for effecting gas-solid reactions. It is conveniently and preferably tubular with the solid alkali metal fluoride disposed therein so as to provide high surface area for reaction with gaseous CX3CH2CI compound. The reactor is constructed of materials resistant to the action of the halogenated materials, including HF and HCl. Suitable materials of con¬ struction include stainless steels, high nickel alloys, such as "Monel", "Hastalloy" and "Inconel", and plastics such polyethylene, polypropylene; poly- chlorotrifluoroethylene and polytetrafluoroethylene. Specific embodiments of this invention are illustrated in the examples which follow. Example 6 being the best mode contemplated for performing the invention.

The examples were conducted in a 1" OD by 13" long stainless steel reactor tube equipped with a gas feed tube, an outlet tube, and an electric tube furance controlled by a thermocouple centered within - li ¬ the reactor. The outlet tube was connected in series with a primary gas scrubber containing aqueous caustic, a similarly constituted back-up scrubber, and a gas chromatograph (GC) adapted to automatically sample and analyze gaseous effluent from the reactor. In some examples, the GC results were confirmed with a mass spectrometer (MS) . All reactants employed were anhydrous. The gas chromatograph (GC) was a "Hewlett Packard" 5880 model utilizing a flame ionization detector and a customized 4-component column.

Analyses of the scrubber solution(s) were carried out using fluoride and chloride specific ion electrodes.

Example 1 87 grams of powdered reagent grade potassium fluoride containing about 7 grams of water waε placed in a 1" by .13_." 316 stainless steel reactor tube contained within an electrically heated furnace. The metal fluoride was dried in place by passing dry N₂ gas through it at 305" for 25 hours. Gaseous CF2CH2CI was then fed to the reactor from a cylinder at an initial rate of 18 ml./minute over a 422 minute period at around 300°. The CF₃CH₂CI feed rate gradually diminished to 6.8 ml/min during the reaction period as the cylinder gradually emptied. The reaction product stream was periodically sampled and found to consist essentially of CF₃CH2F, CF2=CH2 CF2=CHC1 and unreacted CF₃CH2CI.

During the first 5 to 77 minutes of reaction, the conversion of CF3CH2CI to products varied between about 10 and 24%, the selectivity (or yield on conversion) of CF₃CH2F ranged from a low of about 2 to a high of about 73%, that of CF2=CH2 ranged from 16 to 28%, and that of CF2=CHC1 ranged from 9 to 77%. Thereafter, the conversion of CF₃CH2CI levelled out to about 15 to 17% with product yields varying as follows: CF₃CH₂F, 72 to 75%; CF₂=CH₂, 21 TO 25%; CF₂=CHC1, 3 to 5%.

Example 2

The procedure of Example 1 was repeated except that sodium fluoride (57.6 grams) was used in place of potassium fluoride and the reactor was heated in a sand bath to 250". CF3CH2CI was fed at a rate of 32 ml./min. and the reactor temperature was raised in 50" increments to 400" over a period of 1680 minutes. Conversion of CF₃CH2CI was less than 11% throughout the reaction.

Example 3

Carbon pellets (80 grams) , 6 to 8 mesh, in size, were soaked in 30% by weight aqueous KF. The wet pellets were placed in the 1" by 13" stainless steel reactor tube of Example 1, and were dried by purging with dry N2 at 300°C for 20 hours. After being cooled to room temperature, the tube was capped, weighed and found to contain 68.3 grams of the KF-treated pellets, 8 wt% KF.

The reactor was then heated to 253-257^βC with a stream of dry N₂ passing through it. A gaseous CF₃CH2CI feed replaced the N2 feed at a flow rate of 31 ml./min. over a 432 in. period. After the first 70 minutes, the CF₃CH2CI conversion was 63% and the yield (selectivity) of CF₃CH₂F 98%, of CF =CH₂ 0.9% and of CF₂=CHC1 1.1%. After 100 minutes the CF₃CH C1 had dropped to 7%, the yield of CF₃CH₂F remained high at 94%, that of CF₂=CH2 was unchanged while that of CF2=CHC1 increased to 6%. Thereafter, the conversion of CF3CH2CI decreased to less than about 1% with yields of CF₃CH₂F remaining high in the 80 to 90% range.

Repeating the above procedure at 200°C resulted in CF₃CH2CI conversions of less than 1% throughout; selectivity to CF₃CH₂F was 99-100%.

Example 4

Example 3 was repeated except that the support for KF consisted of chips of PCB carbon (61 grams). It contained 24.3 wt.% KF (80.3 grams) after soaking in the KF solution, and was dried at 261° in a stream of dry 2 gas. The reaction period at 261° was 560 minutes. Maximum conversion of CF₃CH2CI was 51% with selectivity to CF₃CH2F ranging between 70 and 80%. By-products included CHF₃ and CF₃CH₃ in addition to CF₂=CH₂.

Example 5

The procedure of Example 3 was again repeated except that (a) the carbon support was impregnated with a 38.5% by weight aqueous cesium fluoride solution, (b) 129 grams of the wet CsF-impregnated carbon was placed in the reactor and dried in ₂ while being heated to 250°, and (c) the CF3CH2CI feed rate was 50 ml./min at 250-252°.

59 samples of the product stream were taken over a period of 805 minutes. Conversion of CF₃CH2CI to products during the first 26 minutes was 99%; the yield of CF₃CH₂F was 75%, CF=CH₂ 22%, CF₂ ^a=CHF 3%, and CF2=CHC1 nil. Over the next 36 minutes, the CF₃CH2CI conversion had dropped to 73%, while the yield of CF3CH2F rose to.94%.

The conversion of CF₃CH2CI decreased further with time and around the 380 minute mark -leveled off at between 15 and 20%, while the yield of CF3CH2F remained at 98-99%. Yields of CHF₃, CF2=CH2, CF2=CHF and CF2=CHC1 were all below 1%, with that of CF2=CHC1 nil over the last 640 minutes of reaction time.

Example 6

The procedure of Example 5 was repeated except that (a) 69.3 grams of the carbon support (dry weight) containing 38.5% by wt. CsF was employed, (b) the reaction temperature was 200-202° and (c) reaction period was 555 minutes. CF₃CH2F was produced in quantitative yield over the first 56 minutes, which decreased gradually to 20% over the next 128 minutes and was essentially 10% over the last 371 minutes.

Example 7

The procedure of Example 3 was followed except that (a) the reactor tube was charged with 72.1 grams of KF on carbon (20% by wt. KF) , dry weight basis, previously dried with N2 at 200°, (b) the organic feed was 1,1,1,2-tetrachloroethane, fed at approx. 0.8 grams/min. into a steam-traced evaporator to provide a vapor flow of approx. 130 ml/min. , and (c) the reactor-temperature was initially 264°, was raised gradually to around 300° during the first 60 minutes, then gradually lowered to around 245° over the next 120 minutes.

Sampling of the reaction product stream was begun at the 75 minute mark - by condensing it at 0°C - and continued every 5 minutes for the remainder of the reaction period. The product mixture consisted essentially of CCI₃CH2F and CCl2=CHCl. Example 8

The procedure of Example 7 was followed except that (a) CCIF2CH2CI was the feedstock and (b) reaction temperature ranged from 235 to 241°. Sampling of the product stream was begun after the first 100 minutes of reaction, with samples taken every 5 minutes for the next 80 minutes. Conversion of CCIF2CH2CI was approximately 30% with selectivity to CCIF₂CH2F approximately 55% at the 100 minute mark. Both conversion and selectivity decreased to around 10% in the next 10 minutes, and thereafter ranged between 5 and 10% for the rest of the run.

Again it will be noted that replacement of Cl by F has unexpectedly taken place at the -CH₂CI and not the -CCIF2 group.

Example 9

This example illustrates the preparation of CF₃CH2F from CF3CH2CI with KF, the regeneration of spent KF by reaction with HF and continued production of CF₃CH2F.

The procedure of Example 3 was followed except that there was added to the reactor 86 grams of the carbon pellets that had been previously soaked for approximately 16 hours in 6 molar aqueous KF, filtered off and dried in a vacuum oven for approximately 16 hours at 200°. The KF-laden carbon was purged with dry N2 while being heated to 250°. Then the N2 flow was replaced by a stream of CF3CH2CI at 50 ml/min over a 944 minute period. During this period, the CF₃CH2CI conversion rose from 16% with selectivity to CF₃CH2F of 89% at the 3 minute mark to approximately 60% conversion with 99% selectivity to CF₃CH2F at the end of 10 minutes. Thereafter conversion decreased progressively to below 1%, attributed to decrease in available KF with time, but selectivity to CF₃CH2F remained high at 98-99%.

At the conclusion of the 944 minute period, the CF3CH₂CI feed was replaced by dry N2, and the reaction temperature was raised to 500° for approximately 50 minutes. The flow of N2 was then replaced by HF at a rate of 90-100 ml./min. for 134 minutes, when the HF flow was replaced by dry N2 and the temperature was allowed to decrease to 250°. The flow of CF₃CH₂CI was then resumed at 250° for 368 minutes. Conversion of CF₃CH₂CI rose to 7% in the first 18 minutes with selectivity to CF3CH2F at 100% then gradually decreased to less than 1% accompanied by a decrease in selectivity to CF3CH2F of about 26% during the rest of the run.

The results indicate that conversion of KC1 to KF occurred in situ but that the HF treatment time was too short to convert more than a minor proportion of the KC1 by-product to KF.

Example 10

This example illustrates the preparation of CF₃CH2F by reaction of CF3CH₂CI with HF and KC1. The procedure of Example 8 was followed except that the reactor tube was loaded with 70 grams (dry weight) of the carbon support impregnated with 11.2% by wt. KC1 (dry weight) . The reactor was heated to 250° with dry N2 flowing through it. The N2 was replaced by a gaseous mixture of 1 part by volume HF and 5 parts by volume of CF₃CH₂F at a combined flow rate of approximately 62 ml./min. and the temperature was raised to 300°. After 50 minutes the conversion of CF₃CH2CI was 2%, the selectivity to CF3CH2F 28%. Reaction was continued for another 400 minutes at temperatures between 250 and 300° and the HF/CF₃CH2CI mole ratio between 2/5 and 2.5/5 with little change in conversion or yield of CF₃CH2F. The temperature was raised to 350° and held there for 80 minutes during which time conversion of CF₃CH₂CI increased to 4-5%, with the CF₃CH2F yield at approximately 26%. Raising the temperature resulted in a further increase in conversion to 13%, which increased to 21% over the next 250 minutes with yield of CF₃CH2F between 16 and 19%. Raising the temperature to 400° and the HF/CF₃CH2CI mole ratio to 1/1 resulted in an increase in conversion to 31% and an increase in selectivity to CF3CH2F to 28%.

Example 11 The procedure of Example 9 was followed.

The reactor was loaded with 74.7 grams of the carbon support containing 20.5% by weight of KF, and heated to 300° under dry N2. The N2 sweep was replaced by gaseous CF3CH2CI at a flow rate of 50 ml/min. After 55 minutes the conversion of CF₃CH2CI was 57%, the selectivity CF₃CH2F 75%. At the 64 minute mark HF vapor was added at a flow rate of 50 ml./min. for a mole ratio of HF/CF3CH2CI of 1/1. After a total reaction time of 83 minutes the CF3CH2CI conversion was approximately 15% and the CF₃CH2F selectivity approximately 84%. Both conversion and selectivity decreased with time and eventually levelled off at 2% and 80%, respectively.

Example 12

Example 11 was repeated except that (a) the reaction temperature was increased to 400°C, (b) the spent metal halide-carbon charge (from Example 11) was used and dried at 300° for 16 hours (c) the HF cofeed was initiated at 75 minutes, and (d) reaction time was increased to 830 minutes.

Conversion of CF₃CH₂CI was 65% after the first 63 minutes with selectivity to CF₃CH₂F at about 70%. After 90 minutes, conversion had decreased to approximately 20% and selectivity to approximately 41%. Thereafter, for the rest of the run, the conversion of CF₃CH2CI gradually increased from a low of 17% at 120 minutes to about 30%, with selectivity to CF₃CH2F running from 31 to 37%.

With reference to Example 11, it will be noted that better results, in terms of conversion of CF₃CH2CI and selectivity to CF₃CH2F are obtained at 400°C than at 300°. It will be noted in this connection that the vapor pressure of HF over KHF₂ - the reaction product of KF and HF, which is much less active than KF for the present purpose - is approximately 0.564 atmospheres at 400° and only 0.052 atmospheres at 300°. In other words, the higher the degree of dissociation of the alkali metal bifluoride, MHF2, the higher the conversion of the organic halide and the better the desired result.

Claims

What is claimed:

1. A process for the halogen exchange fluorination of a saturated halocarbon having at least one replaceable halogen other than fluorine to a fluorinated product having at least one more fluorine in the molecule than the saturated halocarbon which comprises the following steps: (1) contacting the saturated halocarbon with a solid composition containing an alkali metal fluoride having the formula MF at a temperature where both the original halocarbon a,nd the fluorinated product are gaseous to a temperature below the decomposition temperature of said halocarbon or said fluorinated product, whichever is lower, at a pressure and for a time sufficient to yield at least one reaction product having at least one more fluorine in the molecule than said saturated halocarbon and a residual solid composition at least partially depleted in its fluoride content and enriched in its other-than-fluoride halide content;

(2) isolating and recovering the fluorinated reaction product.

2. A process for preparing a fluorinated ethane having the formula CX3CH2F, where X stands for Cl or F, which process comprises:

(i) continuously contacting a solid composition consisting essentially of an alkali metal fluoride, MF, where M is at least one alkali metal having an atomic number from 19 through 55, with; (ii) a gaseous stream of a haloethane, CX3CH2CI, where X is Cl or F, at an effective temperature in the range of about 150°C to about 450°C and for a time sufficient to result in (a) a gaseous product stream containing CX₃CH2F, where X is Cl or F and (b) an at least partially spent alkali metal fluoride composition containing alkali metal chloride, and

(iii) separating the gaseous product stream from the alkali metal composition.

3. The process of Claim 2 where the alkali metal fluoride is disposed on a solid support.

4. The process of Claim 3 where the support is a particulate carbon.

5. The process of Claim 2 where the alkali metal fluoride is potassium fluoride and the temperature is in the range of from about 250°C to about 400"C.

6. The process of Claim 2 where the alkali metal fluoride is cesium fluoride and the temperature is in the range of from about 200°C to about 350°C.

7. A process as in Claim 2 where the alkali metal fluoride is produced by reaction of hydrogen fluoride with the corresponding alkali metal chloride.

8. The process of Claim 2 where the at least partially spent alkali metal fluoride composition is regenerated by treatment with gaseous hydrogen fluoride at a temperature within the effective temperature range which is at least about 100°C higher than the melting temperature of an alkali metal bifluoride corresponding to the alkali metal fluoride. 9. A process as in Claim 8 wherein the hydrogen fluoride contacts said solid composition simultaneously with the CX₃CH2CI compound.

10. The process of Claim 2 where said haloethane is CF3CH2CI and said gaseous product stream contains CF₃CH2F.

11. The process of Claim 2 where said haloethane is CCIF2CH2CI and said gaseous product stream contains CCIF2CH2F.

12. The process of Claim 2 where said haloethane is CCI2FCH2CI and said gaseous product stream contains CCI2FCH2F.

13. The process of Claim 2 where said haloethane is CI₃CH2CI and said gaseous product stream contains CCI3CH2F.