The present invention relates to a process for purifying olefin feed comprising R-22, R-1234yf, R-40, R-134a, R-134, R-1225zc, and OFCB. BACKGROUND OF THE INVENTION
Refrigerant is the substance which is used as working fluid in a thermodynamic cycle, undergoes a phase change from liquid to vapour and produces cooling. These are used in refrigeration, air conditioning, and heat pumping systems. They absorb heat from one area, such as an air conditioned space, and reject it into another, such as outdoors, usually through evaporation and condensation, respectively. These phase changes occur both in absorption and mechanical vapour compression refrigeration systems, but they do not occur in systems operating on a gas cycle using a fluid such as air.
Fluorocarbon based fluids have found widespread use in industry in a number of applications, including as refrigerants, aerosol propellants, blowing agents, heat transfer media, and gaseous dielectrics. Tetrafluoropropenes, having zero ozone depletion and low global warming potential, have been identified as favorable refrigerant over other refrigerants. One tetrafluoropropene having valuable properties is 2,3,3,3-tetrafluoropropene (R-1234yf).
However, the production of these and other organofluorine compounds often require substantial separation steps to isolate the compounds from other components present in the reaction product, including unreacted feedstock, undesirable byproducts, and coproducts.
Production of organofluorine compounds often results in the formation of other organofluorine compounds, organochlorines, and chlorofluorocarbons (collectively referred to herein as 'coproducts of organofluorine production' or simply

'coproducts'), as both intermediate products and coproducts that appear in the final reaction mixture.
In prior art several methods have been disclosed for preparing R-1234yf, wherein by-products have been removed by using several techniques such as distillation, azeotropic distillation, adsorption, absorption, membrane separation and a like or combination thereof to achieve high yield.
U.S. Pat. No. 2,931,840 describes a reaction involving the pyrolysis of chloromethane with tetrafluoroethylene, or alternatively chloromethane with chlorodifluoromethane. It is very difficult to remove unreacted chloromethane and the side products from the reaction product stream. It does not mention the process for removing unreacted chloromethane and the side products from the reaction mixture.
U.S. Pat. No. 9,302,964 discloses a method for producing 2,3,3,3-tetrafluoropropene, the method comprising contacting an azeotropic composition or azeotrope-like composition of 2,3,3,3-tetrafluoropropene and chloromethane with an extraction solvent to obtain 2,3,3,3-tetrafluoropropene containing substantially no chloromethane.
PCT publication no. 2017/108519 discloses a process for purifying 2,3,3,3-tetrafluoro-1-propene (R-1234yf) from a first composition comprising 2,3,3,3-tetrafluoro-1-propene, 3,3,3-trifluoropropene (R-1243zf), trans-1, 3,3,3-tetrafluoro-l-propene (R-1234ze-E) and optionally or not at least one compound selected from the group consisting of chloromethane (R-40), 1,1-difluoroethane (R-152a), chloropentafluoroethane (R-115), 1,1,1,2-tetrafluoroethane (R-134a), trans-1,2,3,3,3-pentafluoropropene (R-1225ye-E); wherein the said process involves solvent extraction and extractive distillation methods.
PCT publication no. 2017/108522 discloses a process for purifying 2,3,3,3-tetrafluoro-1-propene (R-1234yf) from a first composition comprising 2,3,3,3-tetrafluoro-1-propene and chloromethane (R-40); wherein the said process involves solvent extraction and extractive distillation methods.

PCT publication no. 2017/108524 discloses a process for purifying 2,3,3,3-tetrafluoro-1-propene (R-1234yf) from a first composition comprising 2,3,3,3-tetrafluoro-1-propene, 1,1,1,2 , 2-pentafluoropropane (R-245cb) and trans-1, 3,3,3-tetrafluoro-1-propene (R-1234ze-E); ); wherein the said process involves solvent extraction and extractive distillation methods.
Compounds having close boiling point to 2,3,3,3-tetrafluoropropene are 1,1,1,2-tetrafluoroethane (R-134a), 1,1,3,3,3-pentafluoropropene (R-1225zc), 1,1,2,2-tetrafluoroethane (R-134), chlorotrifluoroethene (CTFE) and chloromethane (R-40). Separation of these compounds by normal distillation is very difficult.
There is therefore a need to develop a process for purifying olefin feed by removing compounds having close boiling point to 2,3,3,3-tetrafluoropropene by mean of binary or ternary azeotrope or azeotrope like formation.
SUMMARY OF THE INVENTION
A first aspect of the present invention provides a process for purification of R-1234yf feed comprising R-22, R-1234yf, R-40, R-134a, R-134, R-1225zc, and OFCB, the process comprising the steps of:
a) passing the feed to a distillation column to separate top composition comprising R-22, OFCB, R-1234yf, R-40 and R-134a;
b) optionally passing the top composition comprising R-22, OFCB, R-1234yf, R-40 and R-134a through an absorption tower;
c) optionally passing the top composition or the composition obtained from step a) and/or step b) through adsorption tower;
d) optionally passing the top composition or the composition obtained from step a) and/or step b) and/or step c) through semipermeable membrane;
e) passing the composition obtained from step b) and/or step c) and/or step d) to another distillation column to separate top composition of binary

azeotrope comprising R-1234yf and R-134a and bottom composition comprising pure R-1234yf
BRIEF DESCRIPTION OF DRAWINGS:
Figure 1 illustrates the preparation of feed.
Figure 2 illustrates one of the aspect of the present invention.
DETAILED DESCRIPTION
As used herein, the term 'azeotrope or azeotrope like' is intended in its broad sense to include both compositions that are strictly azeotropic and compositions that behave like azeotropic mixtures. An azeotropic mixture is a system of two or more components in which the liquid composition and vapor composition are equal at the stated pressure and temperature. In practice, this means that the components of an azeotropic mixture are constant boiling and cannot be separated during a phase change.
As used herein, the term 'heavies' refers to a mixture comprising mainly of
high boiling components having boiling points greater than R40 such as
octafluorocyclobutane (OFCB), tetrafluorochloroethane, tetrafluoroethane, R-1224zc
(3-chloro-l,l,3,3-tetrafluoropropene), R-l 112 (2,2-dichloro-l,l-difluororoethene),
R-236ca (1,1,2,2,3,3-Hexafluoropropane), R-236ea (1,1,1,2,3,3-Hexafluoropropane),
R-l 122 (2-chloro-l,l-difluoroethene), R-227ca (1,1,1,2,2,3,3-Heptafluoropropane),
R-227ea (1,1,1,2,3,3,3-Heptafluoropropane), R-124 (2-chloro-l,l,l,2-
tetrafluoroethane) which are recycled back to the reactor may be sent to incinerator.
As used herein, the term 'lights' refers to component having boiling points lower than R1234yf such as R22 which are recycled back to the reactor.
As used herein, the term 'feed' used in the present invention refers to crude composition obtained by the reaction of tetrafluoroethylene/ chlorodifluoromethane with chloromethane/methane, optionally in presence of initiator or catalyst known in the art.

As used herein, feed contains components selected from VdF
(Vinylidenefluoride), tetrafluoroethene (TFE), R-32 (Difluoromethane), R-40
(chloromethane), R-1234yf (2,3,3,3-tetrafluoropropene), HFP (Hexafluoropropene),
OFCB (octafluorocyclobutane), R-1225zc (1,1,3,3,3-pentafluoropropene), R-134a
(1,1,1,2-tetrafluoroethane), R-134 (1,1,2,2-tetrafluoroethane), R-22
(Chlorodifluoromethane), CTFE (chlorotrifluoroethene), and heavies.
The feed can also be obtained by following the process disclosed in PCT publication PCT/IN2017/050006 and/or PCT publication PCT/IN2017/050555 filed by the same applicant.
In an embodiment of the present invention, the feed is a non-azeotrope mixture obtained by passing the product obtained by the reaction of tetrafluoroethylene/ chlorodifluoromethane and chloromethane/methane, through three successive distillation columns, heat quencher, alkali scrubber, and/or sulfuric acid to remove moisture and/or alumina to remove moisture/acid to obtain a stream of gases free from moisture and acid.
In another embodiment of the present invention, the feed is obtained from the process illustrated in Figure 1. '10' of Figure 1 represent chlorodifluoromethane being charged to the reactor '20' maintained at a temperature of about 700°C to about 800°C using an electric heater or steam. The stream of gases '30' mainly comprising tetrafluoroethene, along with '40' comprising of R-40 and an initiator such as carbon tetrachloride/hexachloroethane/trichloroacetylchloride/chloroform is fed to another reactor '50' maintained at a temperature of about 500°C to about 800°C using electrical heater or fired furnace. The stream '60' recovered from '50' is passed through quencher (heat quencher), alkali scrubber, sulfuric acid and alumina to obtain a stream of gases free of acid and moisture is fed to the distillation column '70'. '80', the lower boiling fractions recovered from '70' are fed back to the reactor '50', and the higher boiling fractions '90' comprising R-40, R-1234yf, HFP, OFCB, R-1225zc, R-134a, R-134, R-22, CTFE, and heavies are fed to the next distillation column '100'.

' 110', low boiling fraction comprising R-22 is fed to the reactor '20'. ' 120', the high boiling fraction comprising R-40, R-1234yf, OFCB, R-1225zc, R-134a, R-134, and heavies is fed to the next distillation column '130'. '140', the lower boiling fraction comprising R-1234yf, R-1225zc, R-134a, R-134, R-40, and OFCB is passed through absorption tower '160' to obtain feed '170'. '150', the higher boiling fractions comprising heavies is recycled back to the reactor '50'.
In another embodiment, the feed "170" may additionally contain R-22.
In another embodiment of the present invention, the feed is a non-azeotrope mixture obtained from the distillation column maintained at a temperature range of -29°C to -23°C at atmospheric pressure.
In another embodiment of the present invention, the reaction of tetrafluoroethylene/chlorodifluoromethane with chloromethane/methane can be done in a batch reactor or continuous reactor.
In a preferred embodiment of the present invention, the process of purification is performed in a continuous reactor.
In an embodiment of the present invention, the feed comprises non-azeotrope mixture comprises of R-22, R-1234yf, R-40, R-134a, R-1225zc, R-134, OFCB and heavies.
In another embodiment of the present invention, R-22 may be added to the feed additionally before feeding it to the distillation column.
In an embodiment of the present invention, the feed may contain heavies.
In another embodiment of the present invention, the feed comprises non-azeotrope mixture comprises of about 5 mole % to about 25 mole % of R-22, of about 15 mole% to about 35 mole % of R-1234yf, about 20 mole % to about 45 mole % of R-40, of about 0.5 mole % to about 10 mole % of R-134a, about 0.1 mole % to about 10 mole % of R-1225zc, about 0.1 mole % to about 10 mole % of R-134, about 5 mole % to about 45 mole % of OFCB and about 3 mole % to about 5 mole % of heavies.

As used herein, the term absorption tower refers to the tower containing adsorption solvent selected from an alcohol, nitrile, chlorinated hydrocarbon, amides, ethers or esters.
In an embodiment of the present invention the absorption tower contains a solvent selected from a group consisting of dichloromethane, chloromethane, carbon tetrachloride, methanol, ethanol, isopropanol, diethyl ether, tetrahydrofuran, dioxane, acetonitrile, ethyl acetate, dimethylformamide, or the like.
In a preferred embodiment of the present invention the absorption tower contains chloroform and methanol.
In another embodiment of the present invention the adsorption tower contains molecular sieves having mean pore diameter of the size ranging from 3 A to 1 lA.
In another embodiment of the present invention the adsorption tower contains molecular sieves having mean pore diameter of the size ranging from 3 A to 5 A.
As used herein, the term semipermeable membrane refers to polymeric membrane that allows selective permeability of one compound over the other in the feed. Examples of polymeric membrane include polyethene, polypropylene, polyester, polyamide, nylon, nitrile rubber, neoprene, polydimethylsiloxane (silicone rubber), chlorosulfonated polyethylene, polysilicone-carbonate copolymers, fluoroelastomer, polyvinylchloride, plasticized polyvinylchloride, polyurethane, cis-polybutadiene, cis-polyisoprene, poly(butene-l), polystyrene-butadiene copolymers, styrene/butadiene/styrene block copolymers, styrene/ethylene/butylene block copolymers, thermoplastic polyolefin elastomers, and block copolymers of polyethers and polyesters.
In another embodiment of the present invention, the semipermeable membrane includes polyethene or polypropylene.
In one embodiment of the present invention, the top composition comprises about 0.2 mole % to about 10 mole % of OFCB, about 1 mole % to about 10 mole %

of R-134a, about 35 mole % to about 55 mole % of R-1234yf, about 12 mole % to about 40 mole % of R-22 and about 10 mole % to about 40 mole % of R-40.
In one embodiment of the present invention, the R-22 may be added to the feed before passing to the distillation column.
In another embodiment of the present invention, the top composition has less than 500 ppm of R-1225zc and R-134.
In another embodiment of the present invention, R-1225zc and R-134 are completely not detectable in the top composition.
It has been observed by the present inventors that R-22 improves separation of R-1234yf from R-1225zc and R-134 by increasing the relative volatility of R-1234yf. Thus enabling 1234yf, R-40 and R-134a to boil along with R-22 without the close boiling components such as R-1225zc and R-134.
In the presence of R-22, ternary azeotrope of R-1234yf, R40 and R-134a comes along with binary azeotrope of OFCB and R40 which leads to the suppression of close boiling components like R-1225zc and R-134.
In an embodiment of the present invention, the mixture collected at the bottom of the distillation column after the separation of top composition, is recycled back to one of the initial distillation columns.
As used herein, the binary azeotrope essentially contains R-1234yf and R-134a. The binary azeotrope may contain less than about 5 mole % of other components selected from a group consisting of R-134, OFCB, R-1225zc and R-22.
In an embodiment of the present invention, the binary azeotrope contains about 10 mole % to about 35 mole % of R-134a and about 60 mole % to about 90 mole % of 1234yf.
In another embodiment of the present invention, the binary azeotrope is recycled back to the initial distillation columns.

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.
EXAMPLES
EXAMPLE 1: Process for purifying 1234yf through formation of top composition using R-22
Tetrafluoroethene and chloromethane was reacted in the presence of initiator at a temperature range of 500-750°C. Low boiling fractions were removed from the resulting reactor outlet stream. The reactor outlet feed have the following composition was transferred into distillation column.
The reactor outlet stream comprising 10 to 15 % R-22 is transferred into a distillation column. Presence of R-22 improves separation of R-1234yf from R-1225zc and R-134 by increasing the relative volatility as R-1234yf, R40 and R-134a comes along with R-22 without close boiling compounds like R-1225zc, R-134 etc.
Example 1 Distillation step 1:
Table 1

Components Top Cut composition (Percentage by mole) Bottom Cut composition (Percentage by mole)
OFCB 0.36 66.04
R-134a 2.18 0.021
R-1225zc Not detected 4.78
R-1234yf 41.14 2.49

R-134 Not detected 3.66
R-22 37.42 0.18
R-40 16.79 11.31
Example 2
Table 2

Components Top Cut composition (Percentage by weight) Bottom Cut composition (Percentage by weight)
OFCB 13.28 6.85
R-134a 1.19 0.0
R-1225zc 0.01 1.10
R-1234yf 31.35 0.18
R-134 0.01 1.55
R-22 16.58 0.14
R-40 36.68 22.45
Heavies 0.00 67.73
The results depicted in Tables 1 and 2 clearly indicates that impurities like R-1225zc and R-134 can be completely eliminated from the top composition. The product from the distillation column is then sent to a series of absorption, semipermeable membrane and adsorption tower. The product stream is then passed to a series of distillation column to remove R22, and the binary azeotrope containing R-134a and R-1234yf The top composition is sent back to the distillation column 1 and bottom composition is distilled at atmospheric to 15 bar to get R-1234yf of more than 99% purity.

We Claim:

1.A process for purification of R-1234yf feed comprising R-22, R-1234yf, R-40, R-134a, R-134, R-1225zc, and OFCB, comprises a step of separating a top composition comprising R-22, OFCB, R-1234yf, R-40 and R-134a.
2. A process for purification of R-1234yf feed comprising R-22, R-1234yf, R-40, R-134a, R-134, R-1225zc, and OFCB, the process comprising the steps of:

a) passing the feed to a distillation column to separate top composition comprising R-22, OFCB, R-1234yf, R-40 and R-134a;
b) passing the top composition comprising R-22, OFCB, R-1234yf, R-40 and R-134a through any one or more selected from an absorption tower, adsorption tower and semipermeable membrane;
c) passing the composition obtained from step b) to another distillation column to separate top composition of binary azeotrope comprising R-1234yf and R-134a and bottom composition comprising pure R-1234yf

3. The process as claimed in claim 1 wherein, absorption tower contains a solvent selected from a group consisting of dichloromethane, chloroform, chloromethane, carbon tetrachloride, methanol, ethanol, isopropanol, diethyl ether, tetrahydrofuran, dioxane, acetonitrile, ethyl acetate, dimethylformamide.
4. The process as claimed in claim 1 wherein, adsorption tower contains molecular sieves having mean pore diameter of the size ranging from 3 A to
5A.
5. The process as claimed in claim 1 wherein, semipermeable membrane is
selected from a group consisting of polyethene, polypropylene, polyester,

polyamide, nylon, nitrile rubber, neoprene, polydimethylsiloxane (silicone rubber), chlorosulfonated polyethylene, polysilicone-carbonate copolymers, fluoroelastomer, polyvinylchloride, plasticized polyvinylchloride, polyurethane, cis-polybutadiene, cis-polyisoprene, poly(butene-l), polystyrene-butadiene copolymers, styrene/butadiene/styrene block copolymers, styrene/ethylene/butylene block copolymers, thermoplastic polyolefin elastomers, and block copolymers of polyethers and polyesters.