WO1995015300A1

WO1995015300A1 - Production of 1,1,1,2-tetrafluoroethane

Info

Publication number: WO1995015300A1
Application number: PCT/GB1994/002500
Authority: WO
Inventors: Paul Nicholas Ewing
Original assignee: Imperial Chemical Industries Plc
Priority date: 1993-12-03
Filing date: 1994-11-14
Publication date: 1995-06-08
Also published as: GB9324814D0

Abstract

A process for the production of 1,1,1,2-tetrafluoroethane which comprises contacting 1,1,2,2,-tetrafluoroethane with a fluorination catalyst at an elevated temperature in the presence of a source of chloride ion. The source of chloride ion, which may be hydrogen chloride, may be generated in situ from a chlorocarbon such as 1-chloro-2,2,2,-trifluoroethane and hydrogen fluoride.

Description

PRODUCTION OF 1.1.1.2-TETRAFLUOROETHANE.

This invention relates to a process for the production of 1, 1, 1,2-tetrafluoroethane. 1,1,1,2-tetrafluoroethane, otherwise known as HFA 134a, is manufactured and sold as a non ozone depleting replacement for chlorofluorocarbons (CFC's), in particular dichlorodifluoromethane (CFC 12), in the many applications in which CFC's are employed, in particular in refrigeration and air-conditioning applications.

Amongst the many processes which have been proposed for the production of HFA 134a, catalytic isomerisation of 1,1,2.2-tetrafluoroethane (HFA 134) has been described. In US 4,950,815 there is described a process for the preparation of 1,1,1,2-tetrafluoroethane which comprises contacting 1, 1,2,2-tetrafluoroethane with a fluorination catalyst at an elevated temperature. The temperatures required to achieve satisfactory conversion of 1,1,2,2-tetrafluoroethane may be as high as 400°C or even higher; the use of such high temperatures increases the cost of the process and may have a deleterious effect on the lifetime of the catalyst employed. According to the present invention there is provided a process for the production of

1,1,1,2-tetrafluoroethane which comprises contacting 1, 1,2.2-tetrafluoroethane with a fluorination catalyst at an elevated temperature in the presence of a source of chloride ion. By a "source of chloride ion" there is meant a compound or molecule which under the conditions of the process provides chloride ion. CI^". We prefer that the source of CI^' is hydrogen chloride and in a preferred embodiment of the process the isomerisation is carried out in the presence of hydrogen chloride. The hydrogen chloride may be generated in situ, for example by carrying out the isomerisation in the presence of chlorine which reacts with 1,1,2.2-tetrafluoroethane to produce hydrogen chloride, or in the presence of a chlorocarbon which under the conditions of the process yields hydrogen chloride.

Thus, for example, the isomerisation may be carried out in the presence of hydrogen fluoride and a chlorocarbon which under the conditions of the process react to produce hydrogen chloride. The chlorocarbon may be a hydrochlorocarbon or hydrochlorofluorocarbon, for example 1 -chloro-2.2.2-trifluoroethane or 2-chloro-l,l,l,2-tetrafluoroethane. In this embodiment of the process wherein hydrogen chloride is produced in situ by feeding a chlorocarbon and hydrogen fluoride to the process, we particularly prefer that the chlorocarbon is 1 -chloro-2.2,2-trifluoroethane. / 2 00

Hydrogen fluoride is preferably also present in embodiments of the process in which it is not required to generate hydrogen chloride in situ.

The amount of hydrogen fluoride employed may vary within a wide range but generally a molar excess of hydrogen fluoride to 1,1,2,2-tetrafluoroethane is employed. The molar ratio of hydrogen fluoride to 1 , 1 ,2,2-tetrafluoroethane may be within the range from about 0.5: 1 to about 20:1, preferably from about 2: 1 to about 10: 1.

The temperature at which the isomerisation is effected may be within the range of temperatures for which the isomerisation of 1,1,2,2-tetrafluoroethane has been previously described. However, the increased conversions of l,l,2_T2-tetrafluoroethane which are achieved by the present invention allow the process to be conducted either with comparable conversions but at significantly lower temperatures, or with greater conversions of 1,1,2,2-tetrafluoroethane at comparable temperatures. The temperature may be in the range from about 250°C to about 500°C, preferably from about 280°C to about 380°C.

The process is conveniently effected at atmospheric pressure although subatmospheric or superatmospheric pressures, say up to about 20 bar, may be employed if desired.

Where the source of chloride ion is hydrogen chloride, the amount of hydrogen chloride present is preferably as small as possible, consistent with providing the advantage of increased 1,1,2,2-tetrafluoroethane conversion since the presence of more hydrogen chloride than is required to achieve the increased 1, 1,2,2-tetrafluoroethane conversions may serve to enhance the unwanted reaction of the 1,1,1,2-tetrafluoroethane with hydrogen chloride to produce l-chloro-2,2,2-trifluoroethane. The molar ratio of hydrogen chloride to 1, 1,2,2-tetrafluoroethane may be in the range from about 1 : 100 to about 1 :2, preferably from about 1:50 to about 1:2. Where hydrogen chloride is generated in situ, then sufficient of the chlorocarbon from which the hydrogen chloride is produced is fed to provide an amount of hydrogen chloride within the above range. The precise amount of chlorocarbon required will depend upon the particular chlorocarbon employed and the conversion of the chlorocarbon achieved under the conditions of the process. Where the chlorocarbon is l-chloro-2,2,2-trifluoroethane, one mole of hydrogen chloride is produced for each mole of l-chloro-2,2,2-trifluoroethane which reacts with hydrogen fluoride. However, under typical isomerisation conditions, only 1% to 20% of the l-chloro-2,2,2-trifluoroethane fed to the process reacts with hydrogen fluoride. Consequently, the molar ratio of l-chloro-2,2,2,-trifluoroethane to 1,1,2,2-tetrafluoroethane may be in the range from about 1 :20 to about 10: 1, preferably from about 1 : 10 to about 2: 1.

Suitable fluorination catalysts are well known in the art and include for example aluminium fluoride, sodium fluoride, alumina and especially catalysts based on chromia or chromium oxyfluoride. Activity promoting amounts of other metals, for example zinc or nickel, may also be present. We especially prefer to employ a chromia catalyst which has been pre-fluorinated by contact with hydrogen fluoride at elevated temperature, for example from about 200°C to about 400°C for several hours.

1,1,2,2-tetrafluoroethane may be produced by the hydrofluorination of 1,1 ,2,2-tetrachloroethane as is described in our International Patent Application No .

PCT/GB93/01208. Furthermore the product of the process described in PCT/GB93/01208 is a mixture of 1,1,2,2-tetrafluoroethane and l-chloro-2,2,2-trifluoroethane which is suitable for use directly in the process of the present invention.

According to a preferred embodiment of the invention there is provided a process for the production of 1 , 1 , 1 ,2-tetrafluoroethane which comprises the steps of (i) contacting 1 , 1 ,2,2- tetrachloroethane with hydrogen fluoride in the presence of a fluorination agent/catalyst whereby to form 1,1,2,2-tetrafluoroethane and l-chloro-2,2,2-trifluoroethane and (ii) contacting the 1,1,2,2-tetrafluoroethane and l-chloro-2,2,2-trifluoroethane from step (i) with hydrogen fluoride in the presence of a fluorination catalyst at elevated temperature whereby to effect isomerisation of 1 , 1 ,2,2-tetrafluoroethane to 1,1,1 ,2-tetrafluoroethane.

Conditions of temperature and pressure and suitable catalysts for step (i) of the process are described in PCT/GB93/01208, the contents of which are incorporated herein by reference.

The two steps may be performed in a single reaction vessel although the optimum conditions for steps (i) and (ii) may be different and we prefer that each step is performed in a separate reaction vessel.

In an embodiment of the two step process, the two reaction vessels are arranged in parallel, the product stream from each reaction vessel being passed to the same purification system, for example a series of distillation operations by which l-chloro-2,2,2-trifluoroethane, 1,1,2,2-tetrafluoroethane, 1,1,1,2-tetrafluoroethane and

1,1,2,2-tetrachloroethane are separated from each other, the l-chloro-2,2,2-trifluoroethane and 1,1,2,2-tetrafluoroethane streams being recycled to the step (ii) reaction vessel and 1,1,2,2-tetrachloroethane being recycled to the step (i) reaction vessel.

In an alternative embodiment of the two-step process, the reaction vessels may be arranged in series, and unconverted 1,1,2,2-tetrafluoroethane and l-chloro-2,2,2-trifluoroethane from step (ii) may be recycled to step (i). In this embodiment we prefer that 1,1,1,2-tetrafluoroethane product and hydrogen chloride are separated from the process after step (i). Thus according to a preferred form of this alternative embodiment of the invention there is provided a process for the production of 1,1,1,2-tetrafluoroethane which comprises (i) contacting 1,1,2,2-tetrachloroethane with hydrogen fluoride in the presence of a fluorination agent/catalyst whereby to form 1 , 1 ,2,2-tetrafluoroethane and l-chloro-2,2,2-trifluoroethane and (ii) contacting the 1,1,2,2-tetrafluoroethane and l-chloro-2,2,2-trifluoroethane from step (i) with hydrogen fluoride in the presence of a fluorination catalyst at elevated temperature whereby to effect isomerisation of 1,1,2,2-tetrafluoroethane to 1,1,1,2-tetrafluoroethane, wherein unconverted 1,1 ,2,2-tetrafluoroethane and 1 -chloro-2,2,2-trifluoroethane, and 1,1, 1 ,2-tetrafluoroethane product from step (ii) are recycled to step (i) of the process and hydrogen chloride and 1,1,1,2-tetrafluoroethane are separated from the product stream from step (i) of the process prior to step (ii) of the process.

Separation of hydrogen chloride and 1,1,1,2-tetrafluoroethane from the other components of the product stream from step (i) of the process may be achieved by conventional techniques, for example distillation.

The invention is illustrated but not limited by the following examples in which:

134 is 1 , 1 ,2,2-tetrafluoroethane, 134a is 1,1,1,2-tetrafluoroethane, 133a is l-chloro-2,2,2-trifluoroethane,

124 is 2-chloro-l,l,l,2-tetrafluoroethane and

125 is pentafluoroethane. Example 1.

43 mis of a catalyst comprising 8% zinc on chromia (prepared by co-precipitation from a solution of zinc and chromium hydroxides as described in EP 502605) was charged to a 1/2" outside diameter Inconel reactor tube, dried at 300°C for 16 hours and pre-fluorinated in a stream of hydrogen fluoride at 250°C for 16 hours.

Hydrogen fluoride, nitrogen and 1,1,2,2-tetrafluoroethane were then fed over the catalyst at 326°C and with flow rates of 20mls/minute, 10 mis/minute and 7mls/minute respectively. The reactor off gas was sampled, scrubbed to remove acids and analysed by Gas Chromatography.

Whilst maintaining the feeds of hydrogen fluoride, nitrogen and 1,1,2,2-tetrafluoroethane, hydrogen chloride was passed over the catalyst at a flow rate of 2 mis minute and the reactor off gases were again sampled, scrubbed and analysed by gas chromatography.

The results are shown in Table 1.

TABLE 1.

Reactor off gas composition (mole %)

134 134a 133a

WITHOUT HC1 99.1 0.2 0.1

WITH HCl 95.9 2 0.7

Example 2.

The procedure of example 1 was repeated except that instead of feeding hydrogen chloride in addition to 134, a mixed organic feed comprising 82 mole % 1,1,2,2-tetrafluoroethane and 18 mole % 2-chloro-l,l,l,2-tetrafluoroethane was passed over the catalyst. The results are shown in table 2. TABLE 2.

FEED GAS TEMP REACTOR OFF-GAS COMPOSITION (MOLE %) COMPOSITION (°C) 134 134a 133a 124 125

100% 134 325 99.3 0.1 0.1 - -

82% 134 325 75.6 3.1 3.2 0.6 17 18% 124

Example 3.

30 mis of a chromia catalyst was charged to a 1/2" external diameter Inconel reactor tube, dried at 300°C for 16 hours and pre-fluorinated in hydrogen fluoride at 250°C for 16 hours. Hydrogen fluoride and an organic feed comprising a mixture of 134 and 133a (see Table 3) were then fed over the catalyst in a molar ratio of 3.3:1. The reactor feed gas and reactor off gas were sampled and analysed by gas chromatography for a range of different temperatures and contact times and the results are shown in Table 3. For comparison, an organic feed comprising 100% 134 was also passed over the catalyst.

TABLE 3.

Temp Contact Feed Gas Reactor Off-Gas 134 (°C) Time Composition. Composition. (Mole %) Conversion (sees) (Mole %) (%)

134 133a 134 133a 134a

300 6.8 100 0 99 - 0.7 0.7

300 6.8 71.6 27.7 60 24.2 14.2 16.9

300 25.5 66.5 32.7 50.8 30.1 16.7 23.6

325 24.5 69.3 30 47.7 28.2 22.7 31.5

325 3.7 69.3 30 34.5 19.2 33.8 50.1

350 23.5 67.1 31.9 37.5 29.1 31.1 44.1

Example 4.

43 mis of a chromia catalyst was charged to a 1/2" external diameter Inconel reactor tube, dried at 300°C for 16 hours and pre-fluorinated in hydrogen fluoride at 250°C for 16 hours.

Hydrogen fluoride, nitrogen and 1,1,2,2-tetrafluoroethane were then fed over the catalyst at 336°C and with flow rates of 20mls/minute, 10 mis/minute and 7mls/minute respectively for 24 hours. The catalyst was then regenerated by passing a mixture of air, hydrogen fluoride and nitrogen (in the molar ratio 20:2: 10) over the catalyst at 380°C for 16 hours.

Hydrogen fluoride, nitrogen and 1,1,2,2-tetrafluoroethane were then passed over the catalyst at 333°C with the flow rates given above. The reactor off gas was sampled, scrubbed to remove acids and analysed by Gas Chromatography.

Whilst maintaining the feeds of hydrogen fluoride, nitrogen and 1,1,2,2-tetrafluoroethane, hydrogen chloride was passed over the catalyst at a flow rate of 0.5 mis/minute and the reactor off gas was again sampled, scrubbed and analysed by gas chromatography. The results are shown in Table 4.

TABLE 4.

Reactor off gas composition (mole %)

134 134a 133a

WITHOUT HCl 84.7 14.8 0.1

WITH HCl 72.5 23.3 3.5

Claims

CLAIMS.

1. A process for the production of 1,1,1, 2-tetrafluoroethane which comprises contacting 1,1,2,2-tetrafluoroethane with a fluorination catalyst at an elevated temperature and in the presence of a source of chloride ion.

2. A process as claimed in claim 1 in which the source of chloride ion is hydrogen chloride.

3. A process as claimed in claim 2 in which the molar ratio of hydrogen chloride to 1 , 1 ,2,2-tetrafluoroethane is in the range of from 1 : 100 to about 2 : 1

4. A process as claimed in claim 2 or 3 in which the hydrogen chloride is generated in situ.

5. A process as claimed in claim 4 in which hydrogen chloride is generated by effecting the process in the presence of chlorine or a chlorocarbon.

6. A process as claimed in claim 5 in which the process is effected in the presence of a chlorocarbon and hydrogen fluoride which under the conditions of the process react to produce hydrogen chloride.

7. A process as claimed in claim 6 in which the chlorocarbon is a hydrochlorocarbon or hydrochlorofluorocarbon.

8. A process as claimed in claim 7 in which the chlorocarbon is l-chloro-2,2,2-trifluoroethane.

9. A process as claimed in claim 8 in which the molar ratio of l-chloro-2,2,2-trifluoroethane to 1,1,2,2-tetrafluoroethane is in the range of from about 1:20 to about 10:1.

10. A process as claimed in claim 7 which comprises the steps of (i) contacting 1,1,2,2- tetrachloroethane with hydrogen fluoride in the presence of a fluorination agent/catalyst whereby to form 1,1,2,2-tetrafluoroethane and l-chloro-2,2,2-trifluoroethane and (ii) contacting the 1,1,2,2-tetrafluoroethane and l-chloro-2,2,2-trifluoroethane from step (i) with hydrogen fluoride in the presence of a fluorination catalyst at elevated temperature whereby to effect isomerisation of 1,1,2,2-tetrafluoroethane to 1,1,1,2-tetrafluoroethane.