Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C17/00—Preparation of halogenated hydrocarbons
  • C07C17/093—Preparation of halogenated hydrocarbons by replacement by halogens
  • C07C17/20—Preparation of halogenated hydrocarbons by replacement by halogens of halogen atoms by other halogen atoms
  • C07C17/202—Preparation of halogenated hydrocarbons by replacement by halogens of halogen atoms by other halogen atoms two or more compounds being involved in the reaction
  • C07C17/208—Preparation of halogenated hydrocarbons by replacement by halogens of halogen atoms by other halogen atoms two or more compounds being involved in the reaction the other compound being MX
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/50—Improvements relating to the production of bulk chemicals
  • Y02P20/582—Recycling of unreacted starting or intermediate materials

Definitions

• 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
• HCFC-133a 2-chloro- or 2-bromo-l,1,1-trifluorethane, CF 3 CH 2 CI or CF 3 CH2Br, 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.
• 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.
• HFC-134 and HFC-134a have not been commercially attractive.
• 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.
• 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 ⁇ C 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.
• the present invention is a process for the halogen exchange fluorination of a saturated halo carbon, preferably a continuous process, comprising the following steps:
• the reaction can be readily controlled to produce the -CH2F compound substantially exclusively, that is, substantially without replacement of Cl of the -CX 3 group.
• -CX 3 is -CF3 the product is CF 3 CH2F; i.e., HFC-134a.
• 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.
• the -CX3 could be -CH3, -CR 3 , or any combination between these extremes.
• 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 CX 3 CH2CI reactant, the net effect being the conversion of CX 3 CH2CI to CX3CH2F by HF, as shown in equation (2) .
• MCI alkali metal chloride
• HF gaseous hydrogen fluoride
• 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.
• 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 ⁇ C- ⁇ e 5' form the corresponding
• 1,1,l-trihalo-2-fluoroethane 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,
• the process of the invention is preferably conducted for the preparation of HFC-134a.
• the process is capable of producing HFC-134a in high yields (selectivities) at high conversions of CF 3 CH2CI.
• HFC-134a can be obtained substantially uncontaminated by 1,1-difluoro- 2-chloroethylene or other impurities difficult to separate by ordinary methods.
• HFC-134a (b.p.
• 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 AIF 3 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 CX 3 CH2CI 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 CX 3 CH 2 CI 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 reactant ⁇ , 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) .
• 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)
• MF + HF MHF 2
• the temperature will be at least 100 ⁇ C 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.
• M 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 ⁇ C, 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 CX3CH 2 CI 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.
• CX 3 CH2CI, and by-products, if any, can be handled in any of the various ways known to the art.
• 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.
• fluorinated reaction products that can be prepared by the process of this invention are CCI 3 CH2F, CCI 2 FCH2F, CC1F 2 CH 2 F and CF 3 CH2F, depending upon the starting material. ⁇ nreacted 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.
• the fluorinated products 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.
• 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.
• Example 1 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 CF 3 CH2CI was less than 11% throughout the reaction.
• 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 ⁇ C with a stream of dry N 2 passing through it.
• a gaseous CF 3 CH2CI feed replaced the N2 feed at a flow rate of 31 ml./min. over a 432 in. period.
• the conversion of CF3CH2CI decreased to less than about 1% with yields of CF 3 CH 2 F remaining high in the 80 to 90% range.
• Example 3 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°.
• Example 5 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. CF 3 CH2F 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 3 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.
• Example 7 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 CCIF 2 CH2F 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.
• This example illustrates the preparation of CF 3 CH2F from CF3CH2CI with KF, the regeneration of spent KF by reaction with HF and continued production of CF 3 CH2F.
• Example 3 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°.
• the N2 flow was replaced by a stream of CF3CH2CI at 50 ml/min over a 944 minute period.
• the CF 3 CH2CI conversion rose from 16% with selectivity to CF 3 CH2F of 89% at the 3 minute mark to approximately 60% conversion with 99% selectivity to CF 3 CH2F at the end of 10 minutes. Thereafter conversion decreased progressively to below 1%, attributed to decrease in available KF with time, but selectivity to CF 3 CH2F remained high at 98-99%.
• the CF3CH 2 CI 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 CF 3 CH 2 CI was then resumed at 250° for 368 minutes. Conversion of CF 3 CH 2 CI 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.
• This example illustrates the preparation of CF 3 CH2F by reaction of CF3CH 2 CI 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 CF 3 CH 2 F at a combined flow rate of approximately 62 ml./min. and the temperature was raised to 300°.
• After 50 minutes the conversion of CF 3 CH2CI was 2%, the selectivity to CF3CH2F 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 CF 3 CH2CI was 57%, the selectivity CF 3 CH2F 75%.
• 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 CF 3 CH2F selectivity approximately 84%. Both conversion and selectivity decreased with time and eventually levelled off at 2% and 80%, respectively.
• 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.

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• 1991
  • 1991-01-29 CA CA002077455A patent/CA2077455A1/en not_active Abandoned
  • 1991-01-29 AU AU73329/91A patent/AU7332991A/en not_active Abandoned
  • 1991-01-29 WO PCT/US1991/000442 patent/WO1991013048A1/en not_active Application Discontinuation
  • 1991-01-29 BR BR919108099A patent/BR9108099A/pt unknown
  • 1991-01-29 EP EP19910904787 patent/EP0516690A4/en not_active Withdrawn
  • 1991-01-29 JP JP3505541A patent/JPH05504963A/ja active Pending
  • 1991-02-28 CS CS91532A patent/CS53291A2/cs unknown
  • 1991-03-01 ZA ZA911522A patent/ZA911522B/xx unknown
  • 1991-03-02 CN CN91101282A patent/CN1054582A/zh active Pending

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