WO2003091188A1

WO2003091188A1 - Separation process of 1,1,1,2-tetrafluoro-2-chloroethane (hcfc-124) from 1,1,2,2-tetrafluoro-1-chloroethane (hcfc-124a)

Info

Publication number: WO2003091188A1
Application number: PCT/EP2003/004201
Authority: WO
Inventors: Paolo Cuzzato
Original assignee: Solvay Solexis SpA
Current assignee: Solvay Specialty Polymers Italy SpA
Priority date: 2002-04-23
Filing date: 2003-04-22
Publication date: 2003-11-06
Anticipated expiration: 2004-10-23
Also published as: ITMI20020873A0; AU2003222305A1; ITMI20020873A1

Abstract

A process for the separation of HCFC-124 from its isomer HCFC-124a, comprising the continuous feeding of a mixture of the two isomers on molecular sieves having sizes comprised between 4Å and 10Å, and the desorption of HCFC-124 by heating the molecular sieves at a temperature preferably in the range 50° C-200° C.

Description

Separation process of l,l,l,2-tetrafluoro-2-chloroethane (HCFC-124) from 1 , 1 ,2,2-tetrafluoro- 1 -chloroethane (HCFC- 124a)

The present invention relates to a process for the separation of 1,1, 1,2- tetrafl.uoro-2-chloroethane (HCFC-124) from 1,1,2,2 tetrafluoro-1-chloroethane (HCFC-124a) to obtain HCFC-124 free from the isomer HCFC-124a.

The process commonly used for preparing HCFC-124, i.e. the fluorination of perchloroethylene (PCE) with anhydrous HF, in the presence of suitable catalysts, produces a mixture of HCFCs-124 contairring from 2 to 10% of the isomer HCFC- 124a. Due to the small difference of about 2 degrees centigrade of the boiling point of the two isomers, it is extremely difficult to separate them by fractional distillation.

HCFC-124 is a compound of remarkable industrial interest since it can be used for the chlorotrifluoroethylene monomer (CF =CFC1) preparation largely used for the synthesis of fluoropolymers or it can be used as such or in admixture with one or more of the following compounds HFC, HCFC, hydrocarbons or ethers, in replacement of chlorofluorocarbons (CFCs), banned by the Montreal Protocol due to their environmental impact, in applications such for example refrigerant, heat exchange fluid.

For the above uses it is necessary that HCFC-124 is substantially pure i.e. free from HCFC-124a which is less stable. The need was therefore felt to have available a process capable to separate HCFC-124 from its isomer HCFC- 124a in a simple, effective and cheap way to obtain HCFC-124 substantially pure.

It has been unexpectedly and surprisingly found by the Applicant a process capable to solve the above technical problem. An object of the present invention is therefore a process for the separation of

HCFC-124 from its isomer HCFC-124a, comprising: a) the continuous feeding of a mixture of the two isomers through a molecular sieve bed having sizes comprised between 4A and lOA, until HCFC-124 appears in the outflowing HCFC- 124a, then feeding is interrupted, and b) the heating of the molecular sieve bed to desorb and recover HCFC-124.

The invention concerns in particular a process for the separation in gaseous phase of HCFC-124 from its isomer HCFC-124a, comprising: a) the continuous feeding of a gaseous mixture of the two isomers through a molecular sieve bed having sizes comprised between 4A and lOA, preferably between 5A and 8A, at a temperature from 5°C to 35°C, preferably from 15°C to 25°C, using a mixture flow comprised between 0.1 and 101/h per liter of molecular sieves, until HCFC-124 appears in the outflowing HCFC-124a, then the feeding is interrupted, and b) the heating of the molecular sieve bed at a temperature in the range 50°C- 200°C, preferably 100°C-150°C to desorb and recover HCFC-124.

With the present process it is possible.to separate HCFC-124 with a purity up to at least 99% from HCFC-124/124a mixtures. The HCFC-124/124a mixture is preferably in the gaseous state.

HCFC-124 obtained with the present process can further be purified by recycling it in the process since the molecular sieves maintain their separation capability for many cycles thus making it possible to obtain an extremely pure HCFC-124. At any rate it is possible to recycle the obtained monomer on new or purified molecular sieves.

The pressure used in the process is not critical: it is possible to work at atmospheric or higher pressure, but preferably at a pressure at which the HCFC-124/124a mixture remains gaseous. The mixture HCFC-124/124a can also be fed to the molecular sieve bed diluted with an inert gas for example helium or nitrogen.

When the HCFC- 124/ 124a mixture contains water in amounts higher than some ppm it is preferable to dehydrate it by passing it on CaCl₂ or silica gel before feeding it to the molecular sieves. The molecular sieves are generally activated before the use by heating to 250°-300°C in anhydrous helium or nitrogen flow.

Also a HCFC- 124/124a mixture containing small amounts of other compounds as dichlorotetrafluoroethane (CFC-114 and/or 114a) can be treated with the process of the present invention obtaining HCFC-124 substantially free from CFC-114 and/or 114a. This represents a frirther advantage of the present invention since HCFC-124 obtained by PCE fluorination or by hydrogenation of 1,1,1,2- tetrafluoroethane (HFC-134a), can contain small amounts of CFC-114 and/or 114a hardly separable by distillation. The latter compounds are completely removed by means of the present method. According to a preferred embodiment the mixture HCFC- 124/124a, optionally containing CFC-114/114a, is let continuously pass through a dehydration system, and subsequently fed to a molecular sieve bed contained in a metal pipe equipped with devices for the temperature control. The outflowing fraction is analyzed by gaschromatography; first the only HCFC- 124a and the possible CFC-114/114a flows out and when HCFC-124 begins to flow out it means that the molecular sieve saturation with HCFC-124 is ended. At this point the mixture feeding is interrupted, the system is purged with an inert gas to remove the mixture still present in the pipe and then one begins to heat the molecular sieve bed to cause the HCFC-124 release; when the release is ended, a further inert gas flow is let pass to complete the HCFC-124 collection. Alternatively, at the place of the inert gas, vacuum can be used to remove

HCFC-124 from the molecular sieves thus making it easier its recovery by condensation.

. The invention concerns also a process for the manufacture of isomerically pure HCFC- 123 (l,l,l-trifluoro-2,2-dichloroethane) comprising (a) the manufacture of isomerically pure HCFC-124 according to the process of the invention (b) the dismutation of the isomerically pure HCFC-124.

The dismutation of HCFC-124 can be carried out according to the process described in US patent 5,345,014 whose content with regard to the manufacture of isomerically pure HCFC- 123 is incorporated by reference into the present application.

The isomerically pure HCFC- 123 obtainable according to the invention is useful, for example, as intermediate for the manufacture of trifluoromethyl compounds such as trifluoroacetylchloride.

Some Examples follow for illustrative but not limitative purposes of the present invention.

Examples

Example 1

A HCFC-124/124a mixture containing 10% ofHCFC-124a, traces of other compounds and about 130 ppm of water, is let pass through a cartridge containing calcium chloride, and subsequently through a second cartridge containing silcia gel, then it is fed to a pipe containing about 150 cc of molecular sieves 5A, Aldrich 5X product, in pellets having a diameter of 1.6 mm, previously dried for some hours in muffle at 300°C.

The whole apparatus is at room temperature; the mixture is fed with a flow of 20 cc/rnin, measured at 25°C and at atmospheric pressure. After about 110 minutes one begins to notice the HCFC-124 outflowing, then feeding is interrupted and the molecular sieve bed is purged with anhydrous nitrogen and then heated up to 150°C.

The desorbed gas is analyzed by gaschromatography and results to be formed by:

HCFC-124 99.33 % HCFC-124a 0.57 % others 0.10 %

Example 2 A HCFC-124/124a mixture containing:

HCFC-124 93.4 %

HCFC-124a 6.4 %

CFC-114 0.05 % others 0.15 % is let pass through calcium chloride and silica gel cartridges, and fed to a metal pipe having a diameter of 5 cm, containing about 900 cc (714 g) of molecular sieves 5 A in pellets having a diameter of 1.6 mm (Aldrich 5X). The mixture flow- rate is 1.3 1/h at 25 °C.

After 16 hours one begins to notice the HCFC-124 by gaschromatography of the outflowing gases.

At this point the feeding is interrupted, one purges with nitrogen and starts to heat the sieve bed up to 150°C to desorb HCFC-124 which is collected in a cold trap at about -30°C.

The analysis of the desorbed gas results to be: HCFC-124 99.0 %

HCFC-124a 0.88 % others 0.12 %

CFC-114 absent.

Example 3 The desorbed gas obtained in Example 2 is treated again in the same apparatus containing the same sieves used in Example 1 and under the same conditions.

The gas after treatment results to contain:

HCFC-124 99.87 % HCFC-124a 0.13 % It is therefore possible to further purify the HCFC-124 by treating it again in more absorption/desorption cycles on the same molecular sieves which maintain their separation efficiency for more cycles.

Example 4 (comparative) A HCFC 124/124a mixture containing 9.5% of HCFC-124a, is dried as in

Example 1 and then fed to a pipe containing 114 cc (76.4 g) of molecular sieves 13A, marketed by Aldrich as 13X, under the form of pellets having a diameter of 3.2 mm, previously treated under anhydrous nitrogen flow at 300°C for 4 hours. The whole apparatus is at room temperature; the mixture to be separated is fed with a flow of 20 cc/min, measured at 25°C and at atmospheric pressure.. In the first 4 hours all the inlet gas flow is absorbed by the sieves, then a gaseous flow having a composition very similar to the initial composition starts to flow out. At this point feeding is interrupted and the molecular sieve bed is purged with helium and then heated to 250°C to make the adsorbed gas to be released. The HCFC-124/124a ratio in the desorbed gas is substantially equal to that of the initial mixture but a 3% of products initially not present results present, likely due to the decomposition of the HCFC-124/124a mixture. The sieves after the use result visually greyed.

Example 5 (comparative) Example 4 is exactly repeated except that 120 cc (88.5 g) of 3 A molecular sieves, marketed by Aldrich, are used.

In the first 3 hours all the inlet flow is absorbed by the sieves, then a gaseous flow having the initial composition starts to flow out. By operating then as in

Example 4, one proceeds to the sieve heating at 100°C obtaining the release of a gaseous mixture having the same composition as that initially fed.

Claims

C LAIM S

1 - A process for the separation of HCFC-124 from its isomer HCFC- 124a, comprising: a) the continuous feeding of a mixture of the two isomers through a molecular sieve bed having sizes comprised between 4A and 1 OA, until HCFC-124 appears in the outflowing HCFC-124a, then feeding is interrupted, and b) the heating of the molecular sieve bed to desorb and recover HCFC-124.

2 - The process according to claim 1, wherein the mixture HCFC-124/124a is in the gaseous state.

3 - The process according to claim 2, wherein the gas outflowing from the phase b) is recycled in the process feeding it on the same molecular sieves of step a).

4 - The process according to claims 1-3 wherein the HCFC-124/124a mixture is dehydrated by passing it on CaCl or silica gel before being fed to the molecular sieves.

5 - The process according to claims 1-4, wherein the HCFC-124/124a mixture contains small amounts of mcUorotefrafluoroethane (CFC-114 and/or 114a).

6 - The process according to any one of claims 1-5 wherein the molecular sieve bed has sizes comprised between 5 A and 8A.

7 - The process according to any one of claims 1-6 wherein step (a) is carried out at a temperature from 5°C to 35°C, preferably from 15°C to 25°C.

8 - The process according to any one of claims 1-7 wherein step (a) is carried out using a mixture flow comprised between 0.1 and 101/h per hter of molecular sieves.

9 - The process according to any one of claims 1-6 wherein step (b) is carried out at a temperature in the range 50°C-200°C, preferably 100°C-150°C. 10 - Process for the manufacture of isomerically pure HCFC-123 comprising (a) the manufacture of isomerically pure HCFC-124 according to the process of anyone of claims 1-9 (b) tlie dismutation of the isomerically pure HCFC-124.