FIELD OF INVENTION
The present invention relates to a process for removal of impurities from 1,1,1,2-tetrafluoroethane. In particular, the invention relates to a process for removal of 1,1,2,2-tetrafluoroethane from 1,1,1,2-tetrafluoroethane.
BACKGROUND OF INVENTION:
HFA 134a (tetrafluoroethane), was developed by the chemical industry as CFC substitutes in the
eighties. Now the compound HFA 134a is widely used by the pharmaceutical industry as propellants
for medical aerosols, particularly for ^-dima sprays.
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. 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, for example, 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 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. 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.
SUMMARY OF THE INVENTION
1,1,1,2-tetrafluoroethane is structurally similar 1,1,2,2-terafluoroethane. The b.p. 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. The process comprises of passing 1,1,1,2-tetrafluoroethane with a column packed with molecular sieves. The impurity is absorbed and pure product is obtained. The process is environmental friendly as no waste is generated.
STATEMENT OF INVENTION:
The present invention relates to a process for the removal of 1,1,2,2-tetrafluoroethane from 1,1,1,2-tetrafluoroethane which comprises contacting 1,1,1,2-tetrafluoroethane comprising 1,1,2,2-tetrafluoroethane with a sodium aluminosilicate molecular sieve having a mean pore size in the range of 3 A to 13A. The process of the present invention is highly efficient-reduces the level of impurity near to Zero. There is no material process as the selectivity of the sieve for impurity is very high. The sieves can be easily recycled thereby making the process very economic. Also, no chemical treatment is required neither any costly and complicated apparatuses are employed.
DESCRIPTION OF INVENTION:
The present invention related to a process for purification of 1,1,1,2-tetrafluoroethane. The impure 1,1,1,2-tetrafluoroethane is passed over a column packed with molecular sieves. The molecular sieves used for the present invention oje made up of sodium aluminium silicate, with mean pore size of 3.0 to 13.0 A. The general formula for the molecular sieve is 14SiO2.Al2O3.Na2O.3H2O, (Na2Al2Si14 O32.3H2O). The amount of molecular sieve for treatment of impure 1,1,1,2-tetrafluoroethane comprising as much as 800 to 1100 ppm of impurity mainly 1,1,2,2-tetrafluoroethane is in the ratio of 1:0.5 to 1:3 with respect to the total amount of impure 1,1,1,2-tetrafluoroethane. The impure gas when passed over column packed with sodiumalumino silicate molecular sieve, the impurity gets absorbed and the pure gas with upto 99% purity is obtained.
1,1,1,2-tetrafluoroethane vapour is passed over the molecular sieve with a gas hourly space velocity of
15-20 gm hr . The reaction can be operated at ambient conditions at normal temperature and pressure. No severe conditions of temperature and pressure are required.
The molecular sieve after use in reaction is exhausted and recovered by any process known to a person
skilled in the art. The process of the present invention is highly efficient-reduces the level of impurity near to Zero. The sieves can be easily recycled thereby making the process very economic. Also, no chemical treatment is required neither any costly and complicated apparatuses are employed.
The process is environmental friendly as no waste is generated.
EXAMPLE -1:
The 1,1,1,2-tetrafluoroethane (220 gm) containing 818 pm of 1,1,2,2-tetrafluoroethane impurity was passed through a column containing 440 gm of molecular sieve (5 A). The unabsorbed gas is liquefied and is collected. The purified gas (175 gm) contains 1.687 ppm of 1,1,2,2-tetrafluoroethane.
Results:

(Table Removed)
EXAMPLE -2:
The 1,1,1,2-tetrafluoroethane (100 gm) containing 1059 pm of 1,1,2,2-terafluoroethane impurity was passed through a column containing 200 gm of molecular sieve (10 A). The unabsorbed gas is liquefied and is collected. The purified gas (79 gm) contains 1.687 ppm of 1,1,2,2-tetrafluoroethane
Results:
(Table Removed)

We Claim:
1. A process for the removal of 1,1,2,2-tetrafluoroethane from 1,1,1,2-tetrafluoroethane, the process comprising contacting 1,1,1,2-tetrafluoroethane comprising 1,1,2,2-tetrafluoroethane with a sodium alumino silicate molecular sieve having a mean pore size in the range of 3 A to 13A.
2. The process as claimed in claim 1, wherein the pore of molecular sieve is 5 to 10 A.
3. The process as claimed in claim 1, wherein the impure 1,1,1,2-tetrafluoroethane comprises 800 to 1100 ppm 1,1,2,2-tetrafluoroethane.
4. The process as claimed in claim 1, wherein the ratio of molecular sieve to the impure 1,1,1,2-tetrafluoroethane is 1:0.5 to 1:3.
5. A process as claimed in claim 1 wherein 1,1,1,2-tetrafluoroethane vapour is passed over the molecular sieve with a gas hourly space velocity of 15 to 20 gms hr .
6. A process for purification of 1,1,1,2-tetrafluoroethane such as herein described with respect to foregoing examples.