The present invention relates to a process for purifying olefin feed.
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 other 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-tetrafruoroethane (R-134a), 1,1,3,3,3-pentafluoropropene (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-1234yf, R-40, R-134a, R-134, R-1225zc, and OFCB, comprises a step of separating a ternary azeotrope composition comprising R-1234yf, R-40 and R-13 4a.
An embodiment of present invention provides a process for purification of R-1234yf feed comprising R-1234yf, R-40, R-134a, R-134, R-1225zc, and OFCB, comprises a step of separating a binary azeotrope composition comprising of 10 mole % to 35 mole % of R-134a and 60 mole % to 90 mole % of 1234yf
Another embodiment of first aspect of the present invention provides a process for purification of R-1234yf feed comprising 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 of ternary azeotrope containing R-1234yf, R-40 and R-134a;

b) passing the ternary azeotrope containing R-1234yf, R-40 and R-134a through 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 containing R-1234yf and R-134a and bottom composition comprising substantially pure R-1234yf.
A second aspect of the present invention provides a process for purification of R-1234yf feed comprising 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 of ternary azeotrope containing R-1234yf, R-40 and R-134a;
b) passing the ternary azeotrope containing R-1234yf, R-40 and R-134a through an absorption tower;
c) passing the ternary composition or the composition obtained from step b) through an adsorption tower;
d) passing the composition obtained from step c) to another distillation column to separate top composition of binary azeotrope containing R-1234yf and R-134a and bottom composition comprising substantially pure R-1234yf.
A third aspect of the present invention provides a process for purification of R-1234yf feed comprising R-1234yf, R-40, R-134a, R-134, R-1225zc, and OFCB, the process comprising the steps of:
a) passing the feed to the distillation column to separate top composition of ternary azeotrope containing R-1234yf, R-40 and R-134a;
b) passing the ternary azeotrope containing R-1234yf, R-40 and R-134a through an absorption tower;

c) optionally passing the ternary composition or the composition obtained from step b) through semipermeable membrane;
d) passing the composition obtained from step c) to another distillation column to separate top composition of binary azeotrope containing R-1234yf and R-134a and bottom composition comprising substantially pure R-1234yf.
A fourth aspect of the present invention provides a process for purification of R-1234yf feed comprising R-1234yf, R-40, R-134a, R-134, R-1225zc, and OFCB, the process comprising the steps of:
a) passing the feed to the distillation column to separate top composition of ternary azeotrope containing R-1234yf, R-40 and R-134a;
b) passing the ternary composition obtained from step a) through a semipermeable membrane;
c) passing the composition obtained from step b) to another distillation column to separate top composition of binary azeotrope containing R-1234yf and R-134a and bottom composition comprising substantially pure R-1234yf.
A fifth aspect of the present invention provides a process for purification of R-1234yf feed comprising R-1234yf, R-40, R-134a, R-134, R-1225zc, and OFCB, the process comprising the steps of:
a) passing the feed to the distillation column to separate top composition of ternary azeotrope containing R-1234yf, R-40 and R-134a;
b) passing the ternary azeotrope containing R-1234yf, R-40 and R-134a through an adsorption tower;
c) passing the composition obtained from step b) through semipermeable membrane;
d) passing the composition obtained from step c) to another distillation column to separate top composition of binary azeotrope containing R-

1234yf and R-134a and bottom composition comprising substantially pure R-1234yf.
BRIEF DESCRIPTION OF DRAWINGS:
Figure 1 illustrates the process for 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, 1,1,2-
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 methylchloride/methane, through three successive distillation columns.
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, 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 600°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 and comprising tetrafluoroethene (TFE), R-32, R-40, VdF, R-23, R-1234yf, HFP, OFCB, R-1225zc, R-134a, R-134, R-22, CTFE, R-236ca, R-236ea, R-1122, R-227ca, R-227ea, heavies and 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 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 an 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 semi-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-1234yf, R-40, R-134a, R-1225zc, R-134, and OFCB.
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 20 mole% to about 35 mole % of R-1234yf, about 5 mole % to about 15 mole % of R-40, of about 0.5 mole % to about 20 mole % of R-134a, about 1 mole % to about 4 mole % of R-1225zc, about 1 mole % to about

4 mole % of R-134, about 20 mole % to about 45 mole % of OFCB and about 5 mole % to about 10 mole % of heavies and lights.
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, chloroform, 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 or 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 12A.
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.

As used herein, the ternary azeotropic composition essentially contains R-1234yf, R-134a and R-40. The ternary azeotropic composition may contain less than about 5 mole % of other components selected from the group consisting of R-134, R-22 and OFCB.
In an embodiment of present invention, the ternary azeotropic composition contains about 52 mole % to about 62 mole % of R-1234yf, about 25 mole % to about 34 mole % of R-40 and about 2 mole % to about 25 mole % of R-134a.
In an embodiment of present invention, the ternary composition contains about 51.5 mole % of R-1234yf, about 30 mole % of R-40 and about 16 mole % of R-134a.
In an embodiment of present invention, the ternary composition contains about 52.5 mole % of R-1234yf, about 27.2 mole % of R-40 and about 17.5 mole % of R-134a.
In another embodiment of the present invention, R-134a may be added to the distillation column to obtain the ternary azeotrope composition.
In another embodiment of the present invention, R-134a may be recovered through pressure swing distillation.
In an embodiment of the present invention, the mixture collected at the bottom of the distillation column after the separation of ternary composition, is recycled back to one of the initial distillation columns.
As used herein, the binary azeotropic composition 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 azeotropic composition 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.

In another embodiment of the present invention, the process is as depicted in Figure 2. As referred in Figure 2, the feed '170' is fed to the distillation column '180', to separate a low boiling fraction comprising a ternary azeotrope '190' and a high boiling fraction '200'. The ternary composition is fed to series of absorption tower, adsorption tower and semipermeable membranes '210'. The stream obtained through '210' is fed to another distillation column '220' to recover binary azeotrope composition '230', which is fed back to the distillation column '180' and '240' comprising substantially of 1234yf, which is optionally fed to a distillation column '250' to recover '260' containing pure 1234yf and '270' containing heavies which is fed back to the distillation column.
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 ternary azeotrope composition
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 after removal of low boiling fraction and heavies have the following composition was transferred into distillation column.
Distillation step 1:
Table 1 shows the composition of the feed sent to the distillation column.
Table 1 Component of reactor outlet Composition stream (after removal of lights) (Percentage by weight)

Octafluorocyclobutane 36.6
1,1,1,2-tetrafluoroethane (HFC-134a)* 0.9
1,1,3,3,3 -pentafluoropropene (HFO-1225zc) 1.8
2,3,3,3 -tetrafluoropropene (HFO-1234yf) 27.6
1,1,2,2-tetrafluoroethane (HFC-134) 1.5
Chloromethane (R-40) 10.1
Low boiling fractions 7.0
Heavies 14.0
* 134a was added to the above feed
Table 2 shows the composition of the different fractions in the distillation column 1.
Table 2

Component of reactor outlet stream (after removal of lights) Top Cut composition (Percentage by weight) Bottom Cut composition (Percentage by weight)
Octafluorocyclobutane (OFCB) Not detected 56.09%
1,1,1,2-tetrafluoroethane (HFC-134a) 17.5% 0.29%
1,1,1,2,3,3,3-Hepta fluoropropane (R-227ea) Not detected 1.31%
1,1,1,2,2,3,3-Heptafluoro propane(R-227ca) Not detected 2.14%
1,1,3,3,3 -pentafluoropropene (HFO-1225zc) Not detected 2.66%

2,3,3,3 -tetrafluoropropene (HFO-1234yf) 52.5% 15.03%
1,1,2,2-tetrafluoroethane (HFC-134) Not detected 1.87%
Chloromethane (R-40) 27.2% 1.22%
Lights 2.35% Not detected
Heavies Not detected 19.39%
It is clear from the table 2 that the separation of ternary azeotrope suppresses contamination like 1225zc and 134.
A ternary azeotropic or azeotrope-like composition comprising R-1234yf: 52.5 mol%; R-134a: 17.5 mol% and R-40: 27.2 mol% is sent to the absorption, adsorption tower, semipermeable membrane and the next distillation tower. Distillation step 2:
Table 3 shows the composition of the different fractions in the distillation column 2.
Table 3

Component of reactor outlet stream (after removal of lights) Top Cut composition (Percentage by weight)
Octafluorocyclobutane (OFCB) Not detected
1,1,1,2-tetrafluoroethane (HFC-134a) 10-35
1,1,3,3,3 -pentafluoropropene (HFO-1225zc) Not detected
2,3,3,3-tetrafluoropropene(HFO-1234yf) 60-89
1,1,2,2-tetrafluoroethane (HFC-134) 0-8
The top composition is sent back to the distillation column 1 and bottom composition contains R-1234yf of more than 99% purity.

We Claim

1.A process for purification of R-1234yf feed comprising R-1234yf, R-40, R-134a, R-134, R-1225zc, and OFCB, comprising a step of separating a ternary azeotrope composition comprising R-1234yf, R-40 and R-134a.
2. A process for purification of R-1234yf feed comprising R-1234yf, R-40, R-134a, R-134, R-1225zc, and OFCB, comprising a step of separating a binary azeotrope composition comprising of 10 mole % to 35 mole % of R-134a and 60 mole % to 90 mole % of 1234yf.
3. A process for purification of R-1234yf feed comprising R-1234yf, R-40, R-134a, R-134, R-1225zc, and OFCB, comprising the steps of:

a) passing the feed to a distillation column to separate top composition of ternary azeotrope composition comprising R-1234yf, R-40 and R-134a;
b) passing the ternary azeotrope containing R-1234yf, R-40 and R-134a through 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 a binary azeotrope containing R-1234yf and R-134a and bottom composition comprising substantially pure R-1234yf.
4. The process as claimed in claim 3 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.

5. The process as claimed in claim 3 wherein, adsorption tower contains
molecular sieves having mean pore diameter of the size ranging from 3 A to
5A.
6. The process as claimed in claim 3 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.
7. The process as claimed in claim 3 wherein, ternary composition comprises of 52 mole % to 62 mole % of R-1234yf, 25 mole % to 34 mole % of R-40 and 2 mole % to 25 mole % of R-134a.
8. The process as claimed in claim 2 and claim 3 wherein, binary composition comprises of 10 mole % to 35 mole % of R-134a and 60 mole % to 89 mole % of1234yf