AU650333B2

AU650333B2 - Process for separating hydrogen fluoride from its mixtures with 1,1,1-trifluoro-2-chloroethane

Info

Publication number: AU650333B2
Application number: AU14971/92A
Authority: AU
Inventors: Bernard Berthe
Original assignee: Elf Atochem SA
Current assignee: Arkema France SA
Priority date: 1991-04-17
Filing date: 1992-04-16
Publication date: 1994-06-16
Anticipated expiration: 2012-04-16
Also published as: ES2088114T3; CA2065952A1; GR3020642T3; AU1497192A; JPH06135867A; ATE139513T1; EP0509885A3; FR2675496A1; EP0509885B1; FR2675496B1; EP0509885A2; MX9201720A

Abstract

Separation of hydrogen fluoride (HF) from its mixtures with 1,1,1-trifluoro-2-chloroethane (F133a). By settling the mixture of HF and F133a at a temperature below 0 DEG C, there is obtained a lower organic phase which is poor in HF and an upper phase which is rich in HF. The latter can be directly recycled to the fluorination reactor or subjected to a distillation to separate the HF/F133a azeotrope at the head, which is sent back to the settler, and to recover practically pure HF at the base. By distillation of the lower phase, the HF/F133a azeotrope is separated at the head, which is sent back to the settler, and F133a is recovered at the base.

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: Elf Atochem S.A.

4 8 Cours Michelet La Defense 92800 Puteaux

FRANCE

Bernard Berthe Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Process for Separating Hydrogen Fluoride from its Mixtures with 1,1,1-trifluoro-2-chloroethane The following statement is a full description best method of performing it known to me/us:of this invention, including the 2 The invention relates to the separation of hydrogen fluoride (HF) from its mixtures with l,l,l-trifluoro-2chloroethane (F133a), which is an important synthesis intermediate capable of being employed especially for the manufacture of 1,1,1,2-tetrafluoroethane (F134a).

The process according to the invention applies more particularly to the separation of the unconverted HF present in mixtures originating from the manufacture of F133a by fluorination of trichloroethylene or of symmetrical or unsymmetrical tetrachloroethane. For economic reasons, HF must be recovered in anhydrous form to allow it to be recycled to the fluorination reactor.

Various techniques for performing this separation Sof HF and chlorofluorohydrocarbons have already been described. There may be mentioned, for example: US Patent Specification 2,640,086, which relates to the separation of HF and of chlorodifluoromethane and employs chloroform to promote the separation into two phases, an HF-rich phase and an HF-poor phase; I 20 US Patent Specification 3,873,629, relates to a continuous process for the separation of HF and of chlorodifluoromethane which consists in bringing the -gaseous mixture of the two constituents into countercurrentwise contact with the sulphuric acid;

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3 US Patent Specification 3,976,447, which proposes a separation of HF from gaseous effluents by absorptiondesorption on calcium, barium or strontium chloride particles; US Patent Specification 4,209,470, which describes a process for separating HF from its mixtures with 1chloro-l,l-difluoroethane, in which, to improve the phase separation, an auxiliary liquid is added, consisting wholly or predominantly of l,l-dichloro-l-fluoroethane; European Patent Application EP 0,353,970, relating to the separation of HF from its mixtures with 2,2dichloro-l,1,1-trifluoroethane and/or 2-chloro-1,1,1,2tetrafluoroethane by phase separation and distillation.

In the case of mixtures of HF and F133a, a simple distillation does not enable them to be separated because HF and F133a form an azeotrope which is more volatile than HF or F133a; the HF content of this azeotrope is approximately 60 mol% (20 by weight). There are no data in the literature on the phase separation of mixtures of HF and F133a; at room temperature and whatever the HF and F133a concentrations, mixtures of HF and F133a do not separate into two phases.

It has now been found that it is possible to obtain an excellent separation of a mixture of HF and 4 F133a, provided that it is cooled to a temperature below 0°C, preferably of between -40 C and -10 0 C. Thus, for example at -20°C, the phase separation of the HF-F133a azeotrope mixture yields an organic lower phase which contains only 2.7% by weight of HF (14 mol%) and an acidic upper phase containing 60% by weight of HF (90 mol%).

Consequently, by combining phase separation and distillation it has been found possible to obtain, if need be, a complete separation of HF and of F133a.

The process for separating HF and F133a according to the invention is therefore characterised in that: a) the mixture of HF and F133a is subjected to a phase separation at a temperature below -0°C, b) the HF-poor organic lower phase thus obtained is distilled in a distillation column so as to separate off at the head the HF present in this phase, in the form of HF- F133a azeotrope which is returned to the phase separator, and to recover the excess I F133a at the foot.

The terminology "the head" and "the foot" as used herein clearly refers to the head and the foot of the distillation column.

Preferably either the HF and F133a mixture is obtained from a fluorination reaction and the HF-rich upper phase is recycled directly to the fluorination reactor, or the HFrich upper phase is subjected to a distillation so as to separate at the head the F133a present in this phase, in the form of HF-F133a azeotrope which is returned to the phase separator, and to recover practically pure HF at the foot.

The operation of the process according to the \lbff LMM invention will be understood better by referrin4"to the diagrams shown in Figures 1 and 2, which are appended.

The mixture to be separated, consisting essentially of HF and F133a, cooled beforehand by means of an exchanger 2, is fed by the conduit 1 into the phase separator 3 maintained at a temperature below 0 0 C, preferably between -40 0 C and -10°C. When demixing takes place, an HF-poor organic lower phase 4 and an HF-rich upper phase 5 are then obtained in the phase separator. The organic phase 4 originating from the phase separator 3 feeds via 6 a distillation column 7, at the top of which an effluent 9 composed of the HF and F133a azeotrope is taken off; this effluent 9 is returned to the phase separator 3 upstream of the exchanger 2 for separation into two phases. At the foot of the column 7 a stream 8 of pure F133a is recovered.

The HF-rich upper phase 5 leaving by the conduit 10 can be recycled as it is directly to the 4a 4 fluorination reactor for the production of F133a (Figure However, according to Figure 2, corresponding to the preferred embodiment of the process according to the invention, the HF-rich upper phase 5 is delivered by the conduit 10 to a distillation column 11, at the head of which an effluent 13 composed of the HF and F133a azeotrope is taken off, and this, like the effluent 9, is returned to the phase separator 3 upstream of the exchanger 2 for separation into two phases. At the foot of the -6column 11 practically pure HF is then recovered-'at 12.

The transfer from the phase separator to the distillation columns and from the latter towards the phase separator takes place through the intermediacy of expansion valves or pumps, depending on the operating pressures of the phase separator and of the distillation columns. The temperature of the streams feeding the distillation columns via 6 and 10 can be adjusted by means of exchangers to obtain an optimum distillation.

By way of example, the following table gives the molar compositions, temperatures and pressures of the various streams obtained when proceeding in accordance with the diagram of Figure 2, starting with a mixture of HF and F133a containing from 14 to mol% of IF and from 10 to 86 mol% of Fi33a.

Table I Organic HF Head Foot Foot phase phase of the of of columns column column (9 and 13) 7 11 (12) HF (mol%) 14 90 60 100' F133a (mol%) 86 10 40 100 Temperature -20 -20 +17 +27 +43 Pressure (bars absolute) 15 15 2.2 2.2 2.2 I_ iC__ I(Erl -7- Tests at different pressures 10, -15 and bars) have shown that this parameter has no appreciable influence on the phase separation of the mixture of HF and F133a. Its influence on the temperatures at the foot and at the head of columns 7 and 11 is illustrated in the following Tables II and

III:

Table II Organic HF Head Foot Foot phase phase of the of of columns column column (9 and 13) Z 11 (12) HF (mol%) 14 90 60 100 F133a (mol%) 86 10 40 100 Temperature -20 -20 +42 +54 Pressure (bars absolute) 15 15 5 5 Table III Organic HF Head Foot Foot phase phase of the of of columns column column (9 and 13) Z 11 (12) HF (mol%) 14 90 60 100 F133a (mol%) 86 10 40 100 Temperature -20 -20 +66 +81 +96 Pressure (bars absolute) 15 15 10 10 L L -I

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1 i 8 The temperature is the essential parameter for the phase separation. In fact, above 15'C no phase separation is observed, whatever the composition of the HF-F133a mixture. At -20°C the separated HF phase contains 60 by weight of HF; this content goes down to at a phase separation temperature of At this latter temperature the separated organic phase contains by weight of HF; this content drops to 2.7 when the phase separation is performed at -20°C. Good control of the temperature in the phase separator is therefore important for obtaining an optimum phase separation.

In the mixture of HF and F133a fed to the phase separator, the HF content can range from 14 to 90 mol%; in most cases it is between 25 and 75 When F133a is prepared by fluorination of trichloroethylene or of a tetrachloroethane, the effluents from the fluorination reactor generally contain, in addition to F133a and to unconverted HF, hydrochloric acid, which can be easily removed by distillation, and a small proportion (up to 20 by weight relative to F133a) of other organic compounds such as, for example, trichloroethylene, monofluorotrichloroethane and difluorodichloroethane. Phase separation tests have shown that the presence'of these organic compounds is in no case detrimental to the phase separation and can even promote it. By way of example, Table IV below shows the molar streams 1__1 -R il 9 obtained by proceeding in accordance with the diagram of Figure 2, starting with the effluent from a reactor for the fluorination of trichloroethylene to F133a.

This effluent, which contains a little 1,1-difluoro- 1,2-dichloroethane (F132b), is predistilled to remove the byproduct hydrochloric acid and feeds the phase separator 3 via the conduit 1. This effluent is cooled to -20°C by the exchanger 2 and the phase separator is maintained at Table IV FLOWS IN MOLES/HOUR: Feed (1) Organic phase (4) HF phase Head of column I (13) Head of column 1 (9) Foot of column 11 (12) Foot of column Z (8) The foot, of the column 11, containing chiefly HP and traces of F132b, can be returned as such to the fluorination reactor.

The foot of the column 7, containing F133a

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and most of the F132b fed to the phase separator, is then distilled to obtain pure F133a at the head of the column. The foot of this distillation column, very rich in F132b, is then returned to the fluorination reactor.

It is found that the molar content of HF of the organic phase thus obtained is only 11 which should be compared with that (14 obtained in the absence of F132b.

The separation process according to the invention applies, therefore, not only to HF-Fl33a binary mixtures but also to the crude fluorination mixtures after removal of the byproduct HCj.

Claims

1. A process for separating hydrogen fluoride (HF) from its mixtures with 1,1,1- trifluoro-2-chloroethane (F133a), which process comprises: a) subjecting the mixture of HF and F133a to phase separation at a temperature below 0°C, and b) distilling in a diotillation column the HF-poor organic lower phase thus obtained so as to separate off at the head, as herein defined, the HF present in this phase, in the form of HF-F133a azeotrope which is returned to the phase separator, and to recover the excess F133a at the foot, as herein defined.

2. A process according to claim 1 in which the HF-rich upper phase obtained is distilled so as to separate at the head the F133a present in this phase, in the form of HF- F133a azeotrope which is returned to the phase separator, and to recover practically pure HF at the foot.

3. A process according to claim 1 in which the mixture of HF and F133a to be treated is obtained from a fluorination reaction and the HF-rich upper phase is recycled directly to the fluorination reactor.

4. A process according to any one of the preceding claims, in which the temperature of phase separation is between -40°C and -10 0 C. S

5. A process according to any one of the preceding claims, in which the HF content of 20 the mixture to be treated is between 14 and 90 mol%.

6. A process according to any one of claims 1 to 4 in which the HF content of the mixture to be treated is between 25 and 75 mol%.

7. A process according to any one of the preceding claims, in which the mixture of HF and F133a to be treated also contains up to 20% by weight of other organic compounds expressed relative to F133a).

8. A process for separating hydrogen fluoride from its mixtures with 1,1,1-trifluoro-2- i chloroethane substantially as described with reference to Figure 1 or 2 of the accompanying drawings.

9. Hydrogen fluoride obtained by the process claimed in any one of the preceding claims. Dated 5 April, 1994 Eif Atochem S.A. Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON I 4 0 3 .:t[llbffO0140:LMM l~ ABSTRACT PROCESS FOR SEPARATING HYDROGEN FLUORIDE FROM ITS MIXTURES WITH 1,1,1-TRIFLUORO-2-CHLOROETHANE The invention relates to the separation of hydrogen fluoride (HF) from its mixtures with 1,1,l-trifluoro-2- chloroethane (F133a). The phase separation of the mixture of HF and F133a at a temperature below 0°C yields an HF-poor organic lower Sphase and an HF-rich upper phase. The latter can be recycled directly to the fluorination reactor or subjected to a distillation to separate, off at the head the HF-F133a azeotrope which is returned to the phase separator and to recover practically pure HF at the foot. When the lower phase is distilled, the HF-F133a azeotrope is separated off at the head and is returned to the phase separator, and F133a is recovered at the foot. Figure 1 -i