FIELD OF INVENTION:
The present invention relates to a process for selective removal of impurities from 1,1,1,2-tetrafluoroethane. In particular, the invention relates to removal of 1,1,2,2-tetrafluoroethane and 2-chloro-1,1,1,2-tetrafluoroethane from 1,1,1,2-tetrafluoroethane by contacting the impure HFA 134a with polyethylene glycol.
BACKGROUND OF INVENTION:
HFA 134a (tetrafluoroethane; Norflurane), was developed by the chemical industry as CFC substitutes in the eighties, now have been used by the pharmaceutical industry as propellants for medical aerosols, particularly for asthma sprays, for approximately 10 years.
In recent years chlorofluorocarbons (CFCs), which are used on a large scale around the world, have been perceived as having an adverse effect on the ozone layer and/or as contributing to global warming. CFCs are used, for example, as refrigerants,as foam blowing agents, as cleaning solvents and as propellants for aerosol sprays in which the variety of applications is virtually unlimited. Consequently, attempts have been made to find suitable replacements which will perform satisfactorily in the many applications in which CFCs are used but which will not have the aforementioned damage in effect on the ozone layer. The search for suitable replacements which will perform satisfactorily in the many applications in which CFCs are used but which will not have the aforementioned damaging effect on the ozone layer. The "search for suitable replacements has in general centered on fluorocarbons which do not contain chlorine. The hydrofluorocarbon, 1,1,1,2-tetrafluoroethane, also known as HFA 134a, has been of particular interest as one such replacement, in particular as a replacement for dichlorofluoromethane (CFC 12) in refrigeration applications.
HFA 134a may be produced in a variety of ways, amongst which may be mentioned hydrogenation of a cholorofluorocarbon with hydrogen fluoride or an alkali metal fluoride; a catalyst such as chromia,
halogenated chromia or chromium oxyhalide may be employed to facilitate the reaction.
However, a characteristic of known processes for the production of HFA 134a is that many by-products tend to be produced. Some of the by-products are easy to separate by distillation. However a byproduct which it is desirable to remove, or at least reduce to low levels, for example below 50 ppm, is 1,1,2,2-tetrafluoroethane HFA 134). HFA 134 has a boiling point close to that of HFA 134a, making them difficult to separate by distillation.
U.S 4906790 discloses a method of removal of HCFC 1122 from HFA 134a in which HFA 134 a stream is phased over a molecular sieve. The sieve may be of carbon or a zeolite 4A or calcium chabazite. The sieve has little or no capacity for other impurities, including other hydrofluoroalkanes, making the adsorption of HCFC 1122 very selective. The invention is suitable for use of HFA 134a comprising 100 to about 1000 ppm HFA 134. Use of the zeolite allows removal of HFA 134 from HFA 134a to a very low level. Generally below 50 ppm and even below 20 ppm, depending to some extent on the initial HFA 134a content of the HFA 134a.
U.S 5211020 teaches a method for separating HFA 134a from an HFA 134a-rich mixture thereof with HF and/or CFC 1122 which comprises feeding the mixture to a distillation column to separate an azeotrope or near-azeotrope of HFA 134a and HF and/or CFC 1122 from a residue comprising substantially pure HFA 134a. Starting from an HF-rich mixture of HFA 134a such as a typical product stream in HFA 134a production, the method includes a first distillation step to separate HF from the initial mixture and produce an azeotrope or near azeotrope of HFA 134a and HF which is an HFA 134a-rich mixture.
Therefore, there arise a need for a process which is economic and reduce the impurities providing the desired HFA 134a, without the need of tedious distillation and complex set up of apparatus.
OBJECTIVES
The objective of the present invention is to provide a process which can reduce the impurity of 1,1,2,2-
tetrafluoroethane and 2-chloro-1,1,1,2-tetrafluoroethane without the need of tedious distillation.
Yet another objective of the present invention is to provide a process which is simple and economic.
STATEMENT OF INVENTION:
The present invention relates to a process for purification of HFA 134a comprising contacting HFA
134a with polyethylene glycol.
SUMMARY OF THE INVENTION
1,1,1,2-tetrafluoroethane is structurally similar to 1,1,2,2-tetrafluoroethane. The boiling point of both
these compounds are very close and difficult to remove by ordinary separation process. The present
invention relates to a process for selective removal of impurities from 1,1,1,2-tetrafluoroethane. The
invention relates to removal of 1,1,2,2-tetrafluoroethane and 2-chloro-1,1,1,2-tetrafluoroethane from
1,1,1,2-tetrafluoroethane. The process comprises of contacting impure 1,1,1,2-tetrafluoroethane with
polyethylene glycol. The gas can then be collected by any conventional means.
In a preferred embodiment, the gas after treatment with polyethylene glycol may optionally be
liquefied and stirred with absolute alcohol.
In another embodiment of the present invention, HFA 134a after contacting with polyethylene glycol is dried before liquefaction, prior to stirring with ethanol.
In an another embodiment the gas after treatment with polyethylene glycol alone or after treatment with polyethylene glycol followed by treatment with ethanol can be recycled back to be contacted with polyethylene glycol.
DETAILED DESCRIPTION
The invention relates to removal of 1,1,2,2-tetrafluoroethane and 2-chloro-l,l,l,2-tetrafluoroethane from 1,1,1,2-tetrafluoroethane. The process comprises of contacting a gas with polyethylene glycol. The ratio of impure HFA 134a to polyethylene glycol is 1:2 to 1: 25, preferably to 1:5 to 1:15, most preferably 1:10. The gas is then collected after contacting with polyethylene glycol.
Contacting the gas with polyethylene glycol can be done in various ways like bubbling the gas through a container comprising polyethylene'glycol or scrubbing the gas with polyethylene glycol.
The scrubbing can be performed in columns comprising polyethylene glycol.
In an embodiment, the gas can also be treated with absolute ethanol after treatment with polyethylene glycol. For treatment with absolute ethanol the gas is liquefied prior to stirring with ethanol. The process then comprises of following steps:
contacting HFA 134a with polyethylene glycol;
liquefying HFA 134a obtained from step (a);
stirring liquefied HFA134a obtained in step (b) with ethanol under pressure;
collecting purified HFA 134a obtained from step (c).
The gas after liquefaction is stirred for three to four hrs. with absolute ethanol. The ratio of ethanol to that of liquefied HFA 134a obtained in step (b) is 2:1 to 10:1, preferably to 3:1 to 7:1 most preferably 5:1.
In a preferred embodiment HFA 134a after contacting with polyethylene glycol is dried by passing the contacted gas through a trap comprising moisture absorbing agents to remove the moisture. Any moisture absorbing agents which does not react with the gas, like calcium chloride can be used for this purpose. The dried and liquefied HFA 134a is then stirred for three to four hrs. with absolute ethanol.
The ratio of ethanol to that of dried and liquefied HFA 134a obtained in step (b) is 2:1 to 10:1 preferably to 3:1 to 7:1 most preferably 5:1.
The gas can be liquefied by cooling to -27 degree C and lower or can be liquefied by compression . The gas can also be liquefied by combination of both cooling and compression. The gas in liquid form is treated with ethanol under pressure of 8-10 Kg/cm2, on decreasing pressure, it is released as a gas.
The purified gas is collected and analyzed for the the amount of 1,1,2,2-tetrafluoroethane and 2-chloro-1,1,1,2-tetrafluoroethane.
Polyethylene glycol used for present invention is PEG-600 and PEG-400. Polyethylene Glycol 400 is a low molecular weight grade of polyethylene glycol. It is a clear, colorless, viscous liquid.
The process of the present invention reduces the impurity of 1,1,2,2-tetrafluoroethane and 2-chloro-1,1,1,2-tetrafluoroethane without the need of tedious distillation.
The process is economic and efficient and without the need of tedious distillation and complex set up of apparatus.
The ratio of the impure gas to that of polyethylene glycol used for a cycle is 1:2 to 1:25, preferably 1:5 to 1:15, more preferably 1:10. After- sometime polyethylene glycol can be recycled after regenerating it. The polyethylene glycol can be regenerated by heating at 50 degree C for 3-6 hrs.
The gas after treatment with PEG can also be recycled back to be contacted with PEG.
EXAMPLE 1:
100 gms of HFA 134a is scrubbed with 2 L of PEG 400. The scrubbing is performed in two columns of height of 1.5 meter and diameter 1 inch. After scrubbing the gas is collected and analyzed for the
impurities. Initially 961.29 ppm of 1,1,2,2-tetrafluroethane and 59.469 ppm of 2-chloro-1,1,1,2-tetrafluoroethane were present in the sample prior to treatment with PEG 400. After the scrubbbing with PEG 400 the sample contain 217.569 ppm of 1,1,2,2-tetrafluoroethane and 22.885 ppm of 2-chlpro-1,1,1,2-tetrafluoroethane.

(Table removed)

EXAMPLE 2:
The 1,1,1,2-tetrafluoroethane (109 gm) containing 277 pm of 1,1,2,2-tetrafluoroethane impurity and 14.6 ppm of 2-chloro-1,1,1,2-tetrafluoroethane is scrubbed with polyethylene glycol-400 (1000 ml) in two columns. The height of column being used in lab is 1.5 meter and diameter is 1 inch. Material of construction is SS316. The scrubbed gas is passed through a calcium chloride trap to remove the moisture. The dried gas is liquefied at a pressure of 11 Kg/cm2 at 45 °C and stirred with absolute ethanol (150 ml) for 4 hrs. The purified gas is collected in a bomb. The purified gas contains 30 ppm of 1,1,1,2-tetrafluoroethane and 1.84 ppm of 2-chloro-1,1,1,2-tetrafluoroethane.

We Claim:
1. A process for purification of HFA 134a comprising contacting HFA 134a with polyethylene glycol.
2. The process as claimed in claim 1, wherein the contacting is done by bubbling or scrubbing HFA 134a with polyethylene glycol.
3. The process as claimed in claim 1 or 2, wherein the HFA 134a is liquefied and stirred with absolute ethanol.
4. The process as claimed in claim 1, wherein ratio of HFA 134a to that of polyethylene glycol is 1:2 to 1: 25 preferably 1:5 to 1:15.
5. The process as claimed in any one of the preceding claims, wherein polyethylene glycol is PEG-400 or PEG 600 .
6. The process as claimed in any one of the preceding claims, wherein ratio of HFA 134a to that of polyethylene glycol is preferably 1:10.
7. The process as claimed in claim 3, wherein HFA 134a is dried prior to liquefaction by passing the HFA 134a after contacting with polyethylene glycol through a trap comprising moisture absorbing agent.
8. The process as claimed in claim 7, wherein the moisture absorbing agent is calcium chloride.
9. The process as claimed in claim 3, wherein liquefaction is done by cooling HFA 134a to -27 degree C and lower or can be liquefied by compressing the HFA 134a.
10. The process as claimed in claim 3, wherein liquefaction is done by combination of both cooling and compression.
11. The process as claimed in claim 3, wherein ratio of ethanol to that of liquefied HFA 134a is 2:1 to 10:1 preferably 3:1 to 7:1 most preferably to 5:1.
12. The process as claimed in claim 3 or 11, wherein stirring with ethanol is done under pressure of 8-10 kg/cm2 for 3 to 4 hours.
13. The process as claimed in any of the preceding claims, wherein polyethylene glycol after contacting is regenerated by heating at 50 degree C for 3-6 hrs.
14. The process as claimed in claim 1, wherein contacting comprises contacting HFA 134a with polyethylene glycol to obtain treated HFA134a followed by recycling the treated HFA 134a for again contacting with polyethylene glycol.
15. The process as claimed in any of the preceding claim, wherein HFA 134a after contacting with
polyethylene glycol followed by treatment with alcohol is recycled back for again contacting
with polyethylene glycol.
16. The process for purification of HFA 134a such as herein described with reference to the foregoing examples.