CA2082844A1

CA2082844A1 - Process for the separation of a mixture containing hydrogen fluoride and 1-chloro-2,2,2-trifluoroethane

Info

Publication number: CA2082844A1
Application number: CA 2082844
Authority: CA
Inventors: Wolfgang Dukat; Bernd Kutzner; Gunter Siegemund; Wolfgang Wanzke
Original assignee: Individual
Current assignee: Solvay SA
Priority date: 1991-11-15
Filing date: 1992-11-13
Publication date: 1993-05-16
Also published as: EP0542290A1; JPH05255144A

Abstract

Abstract of the Disclosure Process for the separation of a mixture containing hydrogen fluoride and 1-chloro-2,2,2-trifluoroethane The invention relates to a process for the separation of a mixture containing hydrogen fluoride and 1-chloro-2,2,2-trifluoroethane, in which the mixture is cooled to a temperature of -80°C to -20°C in a separation zone, an organic phase having an HF content of less than 10 molar % being formed as the lower phase and an HF
phase having an HF content of more than 95 molar % being formed as the upper phase in the separation zone.

Description

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Description Process for the separation of a mixture containing hydrogen fluoride and l-chloro-2,2,2-trifluoroethane 5 The invention relates to a process for the separation of a mixture containing hydrogen fluoride (HF) and l-chloro-2,2,2-trifluoroethane (R 133a).

R 133a is a versatile intermediate in the preparation of partially halogenated fluorocarbons (H-FCs) and chloro-10 fluorocarbons (H-CFCs), which act as replacements for completely halogenated CFCs in different sectors of use and are ecologically superior to these. R 133a can be converted by further reactions both into R 134a (1, 1, 1,2-tetrafluoroethane) and into R 123 (1,1-dichloro-2,2,2-trifluoroethane), R 124 (1-chloro-1,2,2,2-tetrafluoroethane) and R 125 (penta-fluoroethane)~ It can likewise be used as a precursor for the synthesis of the inhalation anaesthetic 1-bromo-1-chloro-2,2,2-trifluoroethane and for the preparation of 20 trifluoroacetic acid derivatives.

For an industrial process for the preparation of alipha-tic fluorocarbons from chlorocarbons by reaction with hydrogen fluoride, the recovery of excess HF, and its return into the cour~e of the reaction is significant for 25 several reasons. On the one hand, economic considerations favor as complete as possible a utilization of the anhydrous hydrogen fluoride in the process, since the conversion into aqueous hydrofluoric acid or fluoride solutions represents a significant 108s in value. On the 30 other hand, fluoride-containing waste waters are to be avoided for reasons of waste water protection.

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It is already known that liquid hydrogen fluoride is miscible only to a limited extent with many aliphatic fluorocarbons. This fact has also already been industri-ally exploited, in that the heterogeneous mixtures have been separated in a phase separator to give a high-HF and a low-HF phase, so that the two phases can then be further processed separately.

US Patent 2 450 415, for example, describes a phase separation between dichlorodifluoromethane (R 12) and HF.
The R 12 phase with low HF content is then worked up under aqueous conditions, while the high-HF phase is returned to the reaction.

US Patent 2 478 362 describes the phase separation between HF and the fluorination products of tetrachloro-ethene in a continuous production proces The high-HF
phase is also here returned to the reactor.

US Patent 3 947 558 describes a sequence of two phase separations, in which HF is recovered as completely as possible from a fluorination process for C1-C3 fluoro-carbons. A low-HF organic phase is first separated off, to which a monoglycol is then added, in which the or-ganofluorine compounds are virtually insoluble. After the second phase separation, HF is almost exclu3ively located in the glycol phase and can be recovered therefrom by distillation.

EP-B 98 341 describes the recovery of HF from mixtures thereof with pentafluorobutane and 1-chloro-1,1-difluoro-ethane by phase separation and distillation.

US Patent 4 911 792 (= EP-A 0 353 970) describes the separation of mixtures of HF, 2,2-dichloro-1,1,1-tri-fluoroethane and/or 2-chloro-1,1,1,2-tetrafluoroethane by phase separation and subsequent distillation of both phases.

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The catalytic preparation of R 133a from trichloroetheneand HF is described in EP-A 0 407 961. The product m:ixture obtained from thi~ reaction, in addition to R 133a and excess HF, still contains hydrogen chloride, which can be separated off by distillation. However, separation of R 133a and HF is not possible by simple distillation.

The present invention relates to a process for the separation of a mixture containing hydrogen fluoride and 1-chloro-2,2,2-trifluoroéthane, which comprises cooling the mixture to a temperature of -80C to -20C in a separation zone, an organic phase having an HF content of less than 10 molar % being formed as the lower phase and an HF phase having an HF content of more than 95 molar % being formed as the upper phase in the separation zone.

As a result of the low temperature selected, the two phases have a composition which allows a complete separa-tion of HF and R 133a by subsequent distillation of the phases.

It is true that two phases are already formed at 0C
under atmospheric pressure, while a corresponding mixture is still homogeneous at 20C. However, the composition of the two phases at 0C is not yet so far removed from the concentrations in the crude mixture introduced that a complete separation of the components R 133a and HF would be possible by separate distillation of the two phases.

In contrast, at -20C, the concentration differences between the phases at atmospheric pressure are already great enough. The phase separation produces an R 133a phase having less than 10 molar % of HF and an HF phase having less than 5 molar % of R 133a. The phase separation is preferably carried out at -40C to -80C:
in this case, less than 2% of HF only is found in the . .
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R 133a phase and in the HF phase, less than 1~ of R 133a.

The pressure is generally-0.1 to 10 bar, preferably 1 -5 bar.
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As a result of the phase separation at low temperature according to the invention, an upper HF phase having high HF content and low R 133a content i6 obtained, as is a lower organic phase having low HF content and high R 133a content.

The HF phase is preferably removed from the separation zone, transferred into a distillation column and HF i8 withdrawn at the bottom thereof, while an azeotrope of HF and l-chloro-2,2,2-trifluoroethane is recovered at the head of the column. The temperature at the column head in this case i6 generally -40C to +80C, preferably 0C to lS +50C. The pressure in the column is generally 0.1 bar to 10 bar, preferably 1 bar to 5 bar (absolute pressures in each case). The azeotrope i~ then preferably returned to the separation zone.

Alternatively, the HF phase, instead of separation by distillation into HF and azeotrope, can also be returned to the reactor in which the reaction of trichloroethene with HF to give R 133a takes place.

In a particularly preferred embodiment, additionally to the HF phase, the organic phase is also worked up by distillation, by removing it from the separation zone, transferring it into a distillation col D and withdrawing l-chloro-2,2,2-trifluoroethane at the bottom thereof, while recovering an azeotrope of HF and 1-chloro-2,2,2-trifluoroethane at the head of the column.
The temperature at the head of this column in this case is ~enerally -50C to +80C, preferably 0C to +50C. The pressure in the column is generally 0.1 to 10 bar, preferably 1 to 5 bar (absolute pressures in each case, , .

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as for all other pressures cited in the present deQcrip-tion). The azeotrope i8 preferably returned to the separation zone.

By continuously returning the azeotrope of HF and R 133a obtained as head product of the two di6tillations to the separation zone and combining it there with fresh starting mixture (containing ~F and R 133a), complete separation of HF and R 133a iæ achieved in continuous operation.

To use the product mixture obtained according to EP-A 0 407 961 (see above), thi~ is firct freed from HCl by distillation. The mixture thus obtained generally still contains small amounts of higher boiling compounds, such as unreacted trichloroethene and 1,2-dichloro-l,1-difluoroethane (R 132b), which do not adversely affect the course of the process according to the invention. Low boiling impurities, for example penta-fluoroethane (R 125) are previously distilled off to-gether with HCl, 80 that only a mixture of R 133a and HF
with a small fraction (less than 3%) of the abovemen-tioned higher boiling compounds is present in the separa-tion zone.

Figure 1 is a schematic representation of a preferred embodiment of the invention.

A product mixture essentially comprising R 133a and HF
(with small amounts of unreacted trichloroethene and minor impurities, ~uch as 1,2-dichloro-l,1-difluoro-ethane) flows via line (1) and (2) via the cooler (3) and line (4) to the phase separator (separation zone) (5). In the phase separator (5), an upper high-HF phase (6) and a lower high-R 133a phase (7) form. The ~F phase (6) is withdrawn from the phase separator (5) and fed into the distillation column (9) via line (8). Pure hydrogen fluoride is recovered via line (10) at the bottom of the .. .. : .. . .

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In order to recover R 133a from the lower organic phase (7), this i8 withdrawn from the phase separator (5) and fed via line (13) to a second distillation column (14).
An azeotrope comprising HF and R 133a is withdrawn at the column head via line (15), liquefied in the condenser (12) and fed via the cooler (3) to the phase separator (5). R 133a is withdrawn at the bottom of column (14) via line (16). All or some of the upper phase (6) from the phase separator (5) can be returned via line (17) into the reactor, which is not preferred, however. The columns (9) and (14) are driven by the two rotary evaporators . (18) and (19).

The following Examples describe the invention.

Examples Comparison Example 1 10 g of HF (0.5 mol) and 56.2 g of R 133a (0.47 mol) are placed in a gas-tight ve~sel made of transparent fluoro-plastic (polychlorotrifluoroethylene PCTFE). After heating the vessel to 20C, no phase separation was observable. Even after 24 h, the mixture was homogeneous.
Analytical samples from the lower and upper part of the mixture contained the same molar concentration of HF and R 133a.

Comparison example 2 504 g of HF (25.2 mol) and 496 g of R 133a (4.2 mol) were 3~ mixed in a steel cylinder and heated at 20C. After 5 h, 50 g each were removed from the lower and upper part of the mixture and analyzed. The measured HF and R 133a concentrations agreed with the ratio of amounts weighed . . .

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out, so that at a molar ratio HF/R 133a of 6:1, phase ~eparation had likewise not proceeded.

Comparison Example 3 The mixture from Comparison Example 1 was cooled to a temperature of 0C. Within a few minutes, the formation of 2 phases was observed. Samples were removed from both phases and the concentrations of ~F and R 133a were determined.

Analysis:
Upper phase Lower phase HF 58 molar % 46 molar %
R 133a 42 molar % 54 molar %

phase separation did occur in this case, but the two phases still have almost the same composition.

Example 1 The mixture from Comparison Example 1 was cooled to a temperature of -40C. The two phases were then re-analyzed.
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Upper phase Lower phase 20 HF 99 molar % 2 molar R 133a 1 molar % 98 molar %

Example 2 For a continuous separation apparatus according toFiqure 1, the rates of R 133a and ~F which would occur at the positions (8), (10), (11), (13), (15) and (16) of the separating apparatus if defined hypothetical quantities of R 133a and HF were fed in at the inlet (1) were calculated. For the separation efficiency of the distillation columns (9) and (14), 10 theoretical plates were assumed in each case. The hypothetical rates in (1) and the rates calculated in the other positions are listed in the following Table; this contains, moreover, .. .
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Moreover, measured and calculated thermodynamic data of R 133a and ~F and mixture6 thereof were used in the calculation, in particular the result of Example relating to the phase separation at -40C.

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Claims

1. A process for the separation of a mixture containing hydrogen fluoride and 1-chloro-2,2,2-trifluoro-ethane, which comprises cooling the mixture to a temperature of -80°C to -20°C in a separation zone, an organic phase having an HF content of less than 10 molar % being formed as the lower phase and an HF
phase having an HF content of more than 95 molar %
being formed as the upper phase in the separation zone.

2. The process as claimed in claim 1, wherein the mixture is cooled to -40°C to -80°C.

3. The process as claimed in claim 1 or 2, wherein the HF phase is removed from the separation zone, transferred into a distillation column and HF is withdrawn at the bottom thereof, while an azeotrope of HF and 1-chloro-2,2,2-trifluoroethane is recovered at the head of the column.

4. The process as claimed in claim 3, wherein the temperature at the column head is -40°C to +80°C.

5. The process as claimed in claim 3 or 4, wherein the azeotrope is returned to the separation zone.

6. The process as claimed in one of claims 1 to 5, wherein the organic phase is removed from the separation zone, transferred into a distillation column and 1-chloro-2,2,2-trifluoroethane is withdrawn at the bottom thereof, while at the head of the column an azeotrope of HF and 1-chloro-2,2,2-trifluoroethane is recovered.

7. The process as claimed in claim 6, wherein the temperature at the column head is -50°C to +80°C.

8. The process as claimed in claim 6 or 7, wherein the azeotrope is returned to the separation zone.