CA1119202A

CA1119202A - Manufacture of halogenated compounds

Info

Publication number: CA1119202A
Application number: CA000297242A
Authority: CA
Inventors: John I. Darragh; Richard L. Powell
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1977-02-17
Filing date: 1978-02-17
Publication date: 1982-03-02
Also published as: IT1095355B; JPS53105404A; AU3311878A; DE2806865A1; GR65299B; FR2381006A1; NL7801741A; AR216937A1; ES467081A1; BR7800944A; AU518050B2; IT7820257A0

Abstract

ABSTRACT OF THE DISCLOSURE
1,1,1,2-tetrafluoroethane is prepared by reacting 1,1,1-trifluoro-2-chloroethane with hydrogen fluoride in the vapour phase in the presence of a chromium oxide catalyst.
The method permits high selectivities to be obtained for the desired tetrafluoroethane.

Description

This invention relates to a process for the manufacture of l,1,1,2-tetrafluoroethane and in particular to such a process wherein said tetrafluoroethane of a high degree of purity is obtained.
S According to the present invention there is provided a : process for the manufacture of 1,1,1,2-tetrafluoroethane which comprises reacting in the vapour phase at elevated temperature a haloethane of formula CX3CH2Y wherein X
is bromine, chlorine or fluorine and Y is either bromine or chlorine with hydrogen fluoride in the presence of a catalyst which is chromium oxide or which is at least in part basic chromium fluoride.

, . . .

In the haloethane starting material X may be chlorine only, fluorine only, bromine only or a combination of two or three of said halogens.
Preferably X is chlorine and or fluorine and Y is chlorine. Preferably also at least one of the X
substituents is fluorine. A very suitable haloethane is one having three fluorine atoms, more particularly, 1,1,1-trifluoro-2-chloroethane.
The chromium oxide catalyst may consist of chromium oxide alone. The chromium oxide may be activated by heating in an inert atmosphere. Again the catalyst may comprise a basic chromium fluoride in which chromium is associated with oxygen and fluorine atoms. We find that by employing a chromium oxide catalyst prepared by heating a readily-decomposable salt of chromium e.g.
chromic hydroxide in air or oxygen as described in our UK Patent Specification 976883 in the present process that useful yields of the desired l,1,1,2-tetrafluoro-ethane may be obtained.
It is particularly preferred in the present process to employ a chromium oxide catalyst which is obtained by treating a chromium hydroxide paste with steam as is more fully described and claimed in our UK Patent Specification 1,302,224. The catalyst may be compressed into pellets and used in a fixed bed. Alternatively the catalyst of appropriate particle size may be used in a fluidised bed.

' 1119Z~Z

The pelleted or non pelleted catalyst may be given a prefluo-rination treatment by passing hydrogen fluoride over the catalyst at 250C to 450C for at least 30 minutes. In any event the catalyst may take up variable amounts of fluorine when used in the present process.
The amount of hydrogen fluoride employed in the process depends to a great extent on the haloethane starting material. At least the stoichiometric amount of hydrogen fluoride is usually employed per mole of haloethane starting material. We prefer to employ an excess of the stoichiometric amount but not greater than six times the stoic~iometric amount of hydrogen fluoride in the present process. We prefer to employ at least two moles but not greater than six moles of hydrogen fluoride per mole of said organic starting material, e.g. l,l,l-trifluoro-2-chloroethane.
Preferred temperatures in the present process are in the range 300C to 400C for example 325C to 375C.
Preferred contact times are in the range 2 to 60 seconds.
Atmospheric or superatmospheric pressures may be employed.
Unreacted organic starting material, hydrogen fluoride and by-products e.g. haloethanes containing chlorine atoms in the CX3 group may be recycled to the process for further reaction to give the desired compound.

, In the present process particularly when operating under preferred process conditions very high selectivities to the desired 1,1,1,2-tetrafluoroethane product are obtained.
When the Y substituent in the haloethane starting material is chlorine there may be formed in addition to the desired product asym tetrafluoroethane (CF3 CH2F) a small amount of 1,1-difluoro-2-chloroethylene (CF2=CHCl) as by-product. This occurs when the organic starting material in the hydrofluorination reaction is 1,1,1-trifluoro-2-chloroethane.
It is desirable to reduce further even small amounts of said difluorochloroethylene but this is extremely difficult to achieve by conventional methods, for example, by fractional distillation.
We find that difluorochloroethylene contained in asym tetrafluoroethane may be reduced in content by treating the impure asym tetrafluoroethane either with hydrogen fluoride in the presence of catalysts used in the present process for manufacture of asym tetrafluoro-ethane but at much lower temperatures or by intimately contacting said impure asym tetrafluoro-ethane at much lower temperatures in the liquid phase with a metal permanganate.

~ ;

~9~

6.

According to a further feature of the present invention we provide a process for the manufacture of 1,1,1,2-tetrafluoroethane as hereinbefore described wherein the Y
substituent in the haloethane starting material is chlorine and wherein the 1,1,1,2-tetrafluoroethane product containing 1,1-difluoro-2-chloro-ethylene as impurity is brought together with hydrogen fluoride into contact with a catalyst which is chromium oxide or which is at least in part basic chromium fluoride at a temperature in the range 100C to 275C whereby the said haloethylene content is reduced.
The impure asym tetrafluoroethane to be treated to remove the haloethylene impurity may be the crude product which is associated with other haloethanes containing fluorine including one or more of 1,1,1,2,2-pentafluoroethane (CF3 CHF2), 1,1,1,2-tetrafluoro-

2-chloroethane (CF3 CHClF), l,l,l-trifluoroethane tCF3 CH3) and 1,1,1-trifluoro-2-chloroethane (CF3 CH2Cl).
Such a crude reaction product may be obtained by bringing 1,1,1-trifluoro-2-chloroethane into reaction with hydrogen fluoride at temperatures in the range 300C to 400C in the presence of a catalyst which is chromium oxide or which is at least in part basic chromium fluoride as is previously described.
The manner of carrying out the process of this further feature of the invention is capable of considerable variation. In one method the crude 1~19;Z0;i~
7.

impure reaction product obtained by the hydro-fluorination of 1,1,1-trifluoro-2-chloroethane comprising asym tetrafluoroethane, said other haloethanes containing fluorine and unreacted hydrogen fluoride leaving a reactor are passed into a second reactor containing a catalyst which is chromium oxide or within at least a part basic chromium fluoride and maintained at 100C to 275C whereby said impurity is almost completely removed. Such a crude reaction product will also be associated with hydrogen chloride derived by reaction of hydrogen fluoride with organic starting material, but such hydrogen chloride need not be removed before passing to the second reactor. In another variant the process is carried out in a single reactor having a first reaction zone containing a catalyst which is a chromium oxide or which is at least in part basic chromium fluoride maintained at a temperature (higher than that of the second zone) of 300C to 400C wherein the hydrofluorination of 1,1,1-trifluoro-2-chloroethane is effected. The crude impure organic product together with unreacted hydrogen fluoride (and hydrogen chloride) from the first reaction zone is fed to the second part of the reaction zone containing said chromium oxide or basic chromium fluoride catalyst maintained at a temperature of 100C to 275C whereby the amount of lll9Z~)Z

1,1-difluoro-2-chloroethvlene contaminant in the crude product is considerably reduced. Asym-tetrafluoroethane may be recovered from the reaction mixture leaving the reactor by conventional means, for example, by fractional distillation.
Preferred temperatures in the purification process are in the range 125C to 250C. Contact times are usually in the range 2 to 20 seconds and preferably in the range 3 to 15 seconds. Atmospheric or super-atmospheric pressures may be employed.
According to a still further feature of the presentinvention we provide a process for the manufacture of 1,1,1,2-tetrafluoroethane as hereinbefore described wherein the Y substituent in the haloethane starting material is chlorine and wherein the 1,1,1,2-tetrafluoroethane product containing l,l-difluoro-2-chloroethylene as impurity is intimately contacted with a metal permanganate The permanganate treatment is usually carried out in a liquid medium. Preferably there are used aqueous, or non-aqueous solvents for the permanganate particularly organic solvents or mixtures thereof, which are not appreciably attacked by permanganate. It is particularly suitable to use the permanganate in the form of an aqueous solution.

~.

lll9Z02 The permanganate may be in particular an alkali metal or alkaline earth metal permanganate and the permanganate solution may be acid, neutral or alkaline.
Of the latter a neutral or alkaline solution is preferred.
If the solution is to be alkaline this may be achieved most conveniently by addition of an alkali metal hydroxide although other bases may be used if desired, for example alkaline earth metal hydroxides or ammonia.
Useful results can be obtained when using from 0.1~ up to 10% by weight in the aqueous phase of sodium hydroxide or potassium hydroxide. Lower rather than higher proportions than 10% by weight of NaOH or KOH are preferred and it is particularly preferred to employ concentrations from 0.5% up to 2~ by weight NaOH
or KOH in the aqueous phase.
Sodium and potassium permanganates are particularly useful metal permanganates. Useful results may be obtained with various concentrations of permanaganate in the aqueous phase. For example good results are obtained ` 20 when using 20 g/l to 60 g/l potassium permanganate in the aqueous phase.
The temperature used in the treatment with aqueous permanganate is usually in the range 10C up to the boiling point of the mlxture, for example 15C to 40C.

.

~1~9ZOZ

10. i The contaminated asym tetrafluoroethane may be a crude product associated with the organic starting material and other haloethanes by-products containing fluorine as already described. However the crude product may be fractionally distilled to give a product consisting essentially of l,1,1,2-tetrafluoroethane and 1,1-difluoro-2-chloroethylene impurity.
The times of treatment with aqueous permanganate may vary according to the process conditions. For example treatment times in the range 5 minutes to 90 minutes can be employed.
The relative proportions of aqueous solution of permanganate to crude asym tetrafluoroethane may be varied considerably and the optimum proportions will depend on such factors as thoroughness of mixing, the amount of the impurity, the temperature of treatment and composition of the product. Thus the proportion by volume of aqueous permanganate to crude organic material is usually in the range l:0.1 to l:lO, for example 1:0.2 to 1:6.

.

'' : .: ~ , ~9zo~

- 11. ,1 i After agitation of the organic material with aqueous permanganate the mixture is allowed to separate into two distinct layers and the purified lower asym tetrafluoro-ethane can be fractionally distilled.
1,1,1,2-tetrafluoroethane which has a low boiling point (-26.5C) is useful as a refrigerant, for example, in food-freezing techniques. It is useful as an aerosol propellant and as a foam blowing agent.
The following Examples illustrate the invention.
A11 percentages are v/v unless otherwise stated.

Into a tubular nickel reactor 90 cms long and 2.5 cms internal diameter were placed 150 grams of a chromium oxide catalyst. The latter had been prepared by steam treatment of a chromium hydroxide paste at 95C for 18 hours, and subsequently calcined at 340C for 11 hours as described in our UX Patent Specification No 1,307,224. The catalyst was then pretreated with hydrogen fluoride at 350C for 4 hours.
The tubular reactor was heated by an electric furnace and the temperature inside the reactor was held at 350C.

1~192~)2 ~;i 12.

1827 grams of 1,1,1-trifluoro-2-chloroethane were passed together with an amount of hydrogen fluoride over the catalyst over a total period of 55 hours. The molar ratio of HF:CF3CH2Cl was 4:1. The contact time was 7 seconds.
The products were collected, washed with water, scrubbed with 2.5% w/w aqueous KOH solution and dried.
The organic product thus optained contained 18.2%
1,1,1,2-tetrafluoroethane, 1.65% of a mixture of pentafluoroethane with l,l,l-trifluoroethane, 0.12% 1,1-difluoro-2-chloroethylene and 80% 1,1,1-trifluoro-2-chloroethane which was available for recycling to the process. At the end of the run there was no evidence of deterioration of the activity of the catalyst. The carbon balance was 94%.

The procedure of Example 1 was repeated except that the contact time was 14 seconds. After 2 hours the exit gas stream was analysed and found to contain:-22.2% 1,1,1,2-tetrafluoroethane 1.94% of a mixture of pentafluoroethane with l,l,l-trifluoroethane 0.13% 1,1-difluoro-2-chloroethylene 75.7% 1,1,1-trifluoro-2 chloroethane 13.

IJ The procedure of Example 1 was repeated except that the contact time was 28 seconds. After 2 hours the exit gas stream was analysed and found to contain:-25.2% 1,1,1,2-tetrafluoroethane 2.4~ of a mixture of pentafluoroethane with l,l,l-trifluoroethane 0.08% 1,1-difluoro-2-chloroethylene 72.3% 1,1,1-trifluoro-2-chloroethane The procedure of Example 1 was repeated except that the molar ratio of l,l,l-trifluoro-2-chloroethane to hydrogen fluoride was 8.6:1. After 2 hours the exit gas stream was analysed and found to contain:-27.4% 1,1,1,2-tetrafluoroethane 1.4% of a mixture of pentafluoroethane with l,l,l-trifluoroethane 0.05~ 1,1-difluoro-2-chloroethylene 71.2% 1,1,1-trifluoro-2-chloroethane Into a tubular nickel reactor 90 cms long and 2.5 cms internal diameter were placed 130 grams of a chromium oxide catalyst. The latter had been prepared by steam treatment of a chromium hydroxide paste at 95C for 18 hours, and subsequently calcined at 340C as described in our UK
Patent Specification No 1,307,224. The catalyst was then pretreated with hydrogen fluoride at 350C for 4 hours. The tubular reactor was heated by an electric furnace and the temperature inside the reactor was - 30 maintained in the range 335C to 355C.

~9Z~2 14.
This reactor was connected to a second similar reactor containing the same amount of said catalyst but held at 160C.
89 grams of 1,1,1-trifluoro-2-chloroethane were passed together with an amount of hydrogen fluoride over the fixed catalyst bed over a total period of

3 hours. The molar ratio of HF:CF3CH2Cl was 3:1.
The contact time was 7 seconds. The exit gas leaving the reactor was analysed by gas/liquid chromatography and was found to contain (%).
CF3 CH2F 12.63 CF2 = CHCl 0 53 CF3CHClF 0.04 OTHERS 0.375 CF3CH3 0.17 CF3CHF2 0.02 CF3CH2Cl 86.23 Said exit gas containing hydrogen fluoride was passed to said second similar reactor the contact time being again 7 seconds. The exit gas leaving the second reactor was analysed by gas/liquid chromatography and was found to contain (%) ; CF3CH2F 12.63 CF2 = CHCl 0.0007 CF3CHClF 0.06 OTHER~ 0.1 CF3 C 3 0.18 CF3CH2C1 87.0 )2 15.

A crude organic product containing 16% 1,1,1,2-tetrafluoroethane, 83% 1,1,1-trifluoro-2-chloroethane, 0.8% pentafluoroethane and 1000 pp m of l,l,-difluoro-2-chloroethylene contaminant was obtained by a method substantially as described in Example 1.
Samples were taken of an aqueous solution of permanganate containing lOg NaOH, 60g KMnO4 and 1500g water.
These were placed together with said crude organic product in an autoclave in various ratios (v/v~
and were vigorously stirred at different temperatures under autogeneous pressure. After the runs the mixtures were allowed to settle and the lower organic layer was recovered and analysed for remaining l,l-difluoro-2-chloroethylene content. The results are indicated in the Table.
- TABLE

KMnO4/Organics Temp Time Remaining CF =CHCl ratio C Minsppm v/v in o~ganic product 1:1 30C 15 5 30C 90 Not detectable 1:5 20C 60 5 1:0.2 20C 20 10 30C 20 7.5 : .
:: . . ..
,, .: ' '

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the manufacture of 1,1,1,2-tetrafluoro-ethane which comprises reacting in the vapour phase at elevated temperature 1,1,1-trifluoro-2-chloroethane with hydrogen fluoride in the presence of a catalyst which is chromium oxide or which is at least in part basic chromium fluoride.

2. A process as claimed in Claim 1 wherein the chromium oxide catalyst is obtained by treating a chromium hydroxide paste with steam.

3. A process as claimed in Claim 1 in which there is employed at least the stoichiometric amount of hydrogen fluoride required for conversion of the haloethane starting material to 1,1,1,2-tetrafluoroethane.

4. A process as claimed in Claim 3 in which there is employed at least two moles but not greater than six moles of hydrogen fluoride per mole of said organic starting material.

5. A process as claimed in Claim 1 which is carried out at a reaction temperature in the range 300°C to 400°C,

6. A process as claimed in Claim 5 in which the re-action temperature is in the range 325°C to 375°C.