FIELD OF THE INVENTION
The present invention relates to a process for purification of 2,3,3,3-tetrafluoropropene. The 2,3,3,3-tetrafluoropropene is used in many fields of applications such as refrigeration, blowing agents, solvents and aerosols.

BACKGROUND OF THE INVENTION
Hydrofluoro-olefins (HFOs), such as 2,3,3,3-tetrafluoropropene (HFO 1234yf) are compounds that are known for their properties as coolants and heat-exchange fluids, extinguishing agents, propellants, foaming agents, etc. Unlike CFCs (chlorofluorocarbons) and HCFCs (hydrochloroflurocarbons), that are potentially hazardous to the ozone layer. HFOs do not contain chlorine and thus pose no problem to the ozone layer (low ODP) and have low global warming potential (GWP). Owing to their low ODP and GWP, there has been a recent rise in the demand of pure HFOs.
US Patent No. 8,252,964 describes a process for purification of 2,3,3,3-tetrafluoropropene containing saturated halogenated impurities using molecular sieves of size 5 Å to 11 Å, preferably between 5 and 9 Å. The saturated halogenated impurities mentioned are 236ea, 245eb, R254. Such impurities are bulky in nature and therefore requires molecular sieves of size greater than 7.5 Å.
US Patent No. 10,130,909 describes a process of drying a fluid comprising 2,3,3,3-tetrafluoropropene and water using molecular sieve of size 3 Å to 5 Å.
European Patent No. 1278714 discloses a process for removing a (hydro)haloalkene impurity by contacting a product stream with a solid adsorbent comprising pores having openings which have a size across their largest dimension in the range of from about 7 Å to less than 10 Å.
The reference above disclose the removal of (hydro)haloalkenes including 1234yf using molecular sieves, there is a need to devise a process using molecular sieves that selectively adsorb the saturated and unsaturated halogenated hydrocarbon impurities from the product stream comprising HFO1234yf thereby giving 1234yf of high purity.

OBJECT OF THE INVENTION
The main object of the present invention is to provide a simple and safe process for purification of 2,3,3,3-tetrafluoropropene, which are of use in many fields of application such as refrigeration, blowing agents, solvents and aerosols.

SUMMARY OF THE INVENTION
In an aspect, the present invention provides a process for purification of 2,3,3,3-tetrafluoropropene comprising a step of contacting crude 2,3,3,3-tetrafluoropropene having saturated and unsaturated halogenated hydrocarbon impurities with an adsorbent.

DETAILED DESCRIPTION OF THE INVENTION
In an embodiment, the present invention provides a process for purification of 2,3,3,3-tetrafluoropropene comprising a step of contacting crude 2,3,3,3-tetrafluoropropene having saturated and unsaturated halogenated hydrocarbon impurities with an adsorbent.
As used herein, the ‘saturated and unsaturated halogenated hydrocarbon impurities” refer to hexafluoropropene, 1,1,1,3-tetrafluoropropene (1234ze), 2-chloro-3,3,3-trifluoropropene (1233xf), 1-chloro-3,3,3-trifluoropropene (1233zd), 1,1,1-1,1,1,2-tetrafluoroethane (R134a), 1,1,2,2-tetrafluoroethane (R134), 1,1-difluoroethane (152a), 3,3,3-trifluoropropene (1243), chlorodifluoromethane (R22), methyl chloride (R40), fluorochloroethene, chlorodifluoroethene and vinyl chloride.
As used herein, the adsorbent is a molecular sieve. Molecular sieves, also known as synthetic zeolites, are chemical compounds widely used in the industry as adsorbents, especially for drying gases or liquids. They are metal aluminosilicates that have a three-dimensional crystal structure formed from an assembly of tetrahedral. These tetrahedral are formed by four oxygen atoms that occupy the apices, and which surround either a silicon atom or an aluminium atom placed at the centre. These structures generally contain cations to make the system electrically neutral. Such as those derived from sodium, potassium or calcium.
In an embodiment, the adsorbent used in the present invention is preferably those of the type A and of the type X and advantageously those of the type X.
In an embodiment, the adsorbent used in the present invention is ‘13x’ which has a pore diameter of 10 Å.
The sodium based molecular sieve 13x is based on the molecular from type X crystalline form which has the larger pore size than other type of A crystalline forms like 3a, 4a and 5a.
The crude stream of HFO 1234yf in present invention is passed through molecular sieve bed at a feed rate selected in the range of 100 g/hour to 500g/hour and preferably in a range of 100 g/hour to 500g/hour.
In an embodiment, the feed rate is 100g/hour. In another embodiment, the feed rate is 180g/hour.
It has been found that saturated and unsaturated halogenated hydrocarbon impurities present in HFO 1234yf can be removed (partially or totally) by placing a crude HFO 1234yf in contact with an adsorbent. The purification process according to the present invention is characterized in that the HFO 1234yf, comprising saturated and unsaturated halogenated hydrocarbon impurities is placed in contact with an adsorbent, preferably molecular sieves and advantageously molecular sieves with a mean pore diameter of 10 Å.
The crude HFO 1234yf is subjected to the purification step may originate directly from the effluent obtained from the manufacturing step, after optional separation such as decantation or distillation.
The anhydrous mixture comprising HFO 1234yf having saturated and unsaturated hydrocarbon impurities is contacted with molecular sieve of size 10 Å to obtain HFO 1234yf free of saturated and unsaturated hydrocarbon impurities.
The process according to the invention is suitable for the purification of a crude HFO 1234yf with a purity of at least 99.9% by weight.
While the present invention has been described in terms of its specific embodiments, certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention.
The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention.
GENERATION OF CRUDE STREAM OF 2,3,3,3-TETRAFLUOROPROPENE:
A mixture of tetrafluoroethylene and methylchloride in the molar ratio of 1:1.16 respectively is preheated and then superheated to 350oC and was fed to the Inconel reactor which is maintained at 650oC by electrical heater. The obtained composition feed was passed to a several distillation columns to obtain crude 1234yf of purity ranging from 80% to 95%.
EXAMPLE-1: Process for the purification of 2,3,3,3-tetrafluoropropene.
A bed of 10 Å molecular sieve (4 kg) was formed and crude stream of 2,3,3,3-tetrafluoropropene was passed through this molecular sieve bed at a rate of 100 g/hour to obtain pure stream of 2,3,3,3-tetrafluoropropene.

Components Crude stream Pure stream
2,3,3,3-Tetrafluoropropene 99.7099% 99.9778%
By-products
1,3,3,3-Tetrafluoropropene 0.0221% 0.0000%
2-chloro-3,3,3-trifluoropropene 0.0011% 0.0000%
1-chloro-3,3,3-trifluoropropene 0.0101% 0.0000%
Hexafluoropropene 0.0078% 0.0038%
1,1,1,2-Tetrafluoroethane 0.0481% 0.0000%
1,1-Difluoroethane 0.0260% 0.0000%
1,1,2,2-Tetrafluoroethane 0.1127% 0.0181%
3,3,3-Trifluoropropene 0.0013% 0.0000%
Chlorodifluoromethane 0.0294% 0.0000%
Methyl chloride 0.0093% 0.0003%
Fluorochloroethene 0.0010% 0.0000%
Chlorodifluoroethene 0.0000% 0.0000%
Vinyl chloride 0.0212% 0.0000%
Total impurities 2901ppm 222

EXAMPLE-2: Process for the purification of 2,3,3,3-tetrafluoropropene.
A bed of 10 Å molecular sieve (4 kg) was formed and crude stream of 2,3,3,3-tetrafluoropropene was passed through this molecular sieve bed at a rate of 180 g/hour to obtain pure stream of 2,3,3,3-tetrafluoropropene.
Molecular sieved used 10 Å
Components Before Adsorber After Adsorber
2,3,3,3-Tetrafluoropropene 99.9885% 99.9986%
By-products
Hexafluoropropene 0.0008% 0.0004%
1,1,1,2-Tetrafluoroethane 0.0016% 0.0000%
1,1-Difluoroethane 0.0005% 0.0000%
1,1,2,2-Tetrafluoroethane 0.0023% 0.0000%
3,3,3-Trifluoropropene 0.0003% 0.0008%
Chlorodifluoromethane 0.0006% 0.0000%
Methyl chloride 0.0025% 0.0002%
Fluorochloroethene 0.0003% 0.0000%
Chlorodifluoroethene 0.0002% 0.0000%
Vinyl chloride 0.0024% 0.0000%
Total impurities 0.0115 14ppm

CLAIMS:WE CLAIM:
1. A process for purification of 2,3,3,3-tetrafluoropropene comprising a step of contacting crude 2,3,3,3-tetrafluoropropene having saturated and unsaturated halogenated hydrocarbon impurities with an adsorbent having a pore diameter of 10 Å.
2. The process as claimed in claim 1, wherein the ‘saturated and unsaturated halogenated hydrocarbon impurities” refer to hexafluoropropene, 1,1,1,3-tetrafluoropropene (1234ze), 2-chloro-3,3,3-trifluoropropene (1233xf), 1-chloro-3,3,3-trifluoropropene (1233zd), 1,1,1-1,1,1,2-tetrafluoroethane (R134a), 1,1,2,2-tetrafluoroethane (R134), 1,1-difluoroethane (152a), 3,3,3-trifluoropropene (1243), chlorodifluoromethane (R22), methyl chloride (R40), fluorochloroethene, chlorodifluoroethene and vinyl chloride.
3. The process as claimed in claim 1, wherein the adsorbent is a molecular sieve.
4. The process as claimed in claim 3, wherein the molecular sieves used are of the type A and of the type X.
5. The process as claimed in claim 1, wherein, the adsorbent used is a molecular sieve ‘13x’ which has a pore diameter of 10 Å.
6. The process as claimed in claim 1, wherein 2,3,3,3-tetrafluoropropene is obtained with a purity of greater than 99.9% by weight.
7. The process as claimed in claim 1, wherein impurities in pure 2,3,3,3-tetrafluoropropene are less than 250 ppm.
8. The process as claimed in claim 1, wherein impurities in pure 2,3,3,3-tetrafluoropropene are less than 50 ppm.

9. The process as claimed in claim 1, wherein the crude stream of 2,3,3,3-tetrafluoropropene is passed through molecular sieve bed at a feed rate selected in the range of 100 g/hour to 500g/hour.