FIELD OF THE INVENTION
The present invention provides a process for purification of 1,3,3,3-tetrafluoropropene.

BACKGROUND OF THE INVENTION
Hydrofluorocarbons (HFCs) such as 1,3,3,3-tetrafluoropropene (R1234ze) have found widespread use in many commercial and industrial applications including as refrigerants, aerosol propellants, blowing agents, heat transfer media, gaseous dielectrics and as working fluids in air conditioning, heat pump and refrigeration systems.
The manufacturing processes of trans-1,3,3,3-tetrafluoropropene commonly results in one or more undesired products alongside a desired E-1234ze, therefore necessitating purification.
PCT Pub. No. 2021043989 provides a process for purification of hydrohalocarbon by compressing and converting it to liquid form and then carrying out distillation in a pressurized distillation device comprising one or more rotary-packed bed. The use of distillation column equipped with rotary-packed bed makes the process complex and tedious at commercial scale.
European Pat. No. 2054361 provides a complex process for removing HF and R245fa from R1234ze by distilling its mixture to form azeotrope of HF and R1234ze and condensing azeotrope of HF and R1234ze to separate into two liquid phases, one enriched in HF is recycled back and the other enriched in R1234ze is separated.
The present invention provides an alternative process for purifying trans-1,3,3,3-tetrafluoropropene to obtain the propellant grade trans-1,3,3,3-tetrafluoropropene of very high purity.

OBJECT OF THE INVENTION
The object of the present invention is to provide a simple, cost effective and commercially viable process for purifying trans-1,3,3,3-tetrafluoropropene to produce the propellant grade trans-1,3,3,3-tetrafluoropropene.

SUMMARY OF THE INVENTION
In an aspect, the present invention provides trans-1,3,3,3-tetrafluoropropene of propellent grade comprising one or more additional component selected from a group consisting of 1,1,1,2,2-pentafluoroethane (R125); 1,1,1,2-tetrafluoroethane (R134a); 2,3,3,3-tetrafluoropropene (R1234yf); 1,1,3,3,3-pentafluoropropene (R1225zc); trifluoropropyne; 3,3,3-trifluoropropene (R1243zf); cis-1,3,3,3-tetrafluoropropene (R1234ze(Z)); trans-1-chloro-3,3,3-trifluoropropene (R1233zd(E)) and cis-1-chloro-3,3,3-trifluoropropene (R1233zd(Z)), wherein the additional components are present in a range of 5 ppm (parts per million) to 1000 ppm.
In another aspect, the present invention provides a process for purifying trans-1,3,3,3-tetrafluoropropene, comprising the steps of:
a) providing a composition comprising trans-1,3,3,3-tetrafluoropropene, low boiling components and high boiling components in a distillation column;
b) maintaining a high reflux ratio in the range of 5 to 100 at the head of the distillation column;
c) allowing removal of a fraction of low boiling components from the top of distillation column;
d) repeating step b) and c) till the low boiling component become substantially nil; and
e) distilling the remaining composition in distillation column to separate pure trans-1,3,3,3-tetrafluoropropene from the top of distillation column by maintaining a reflux ratio in the range of 5 to 100.

BRIEF DESCRIPTION OF DRAWING
Figure 1 and Figure 2 describes the flow of the process.
Figure 1: A stream ‘1’ is charged in a distillation column ‘D1’ and allowed venting of non-condensable components ‘2’ through metering valve ‘V1’. After removal of ‘2’, total reflux is maintained for 2 hours in ‘D1’ and allowed removal of a fraction of low boiling components ‘3’ from the top through condenser ‘C1’ and metering valve ‘V1’. The draw rate of ‘3’ is maintained using the mass flow meters ‘MFM-1 and MFM-3’, so that the reflux ratio is 10. The total reflux is maintained again for 2 hours in ‘D1’ and allowed removal of another fraction of ‘3’ from the top. The total reflux is maintained again for 2 hours in ‘D1’ and allowed removal of remaining fraction of ‘3’ from the top. The remaining mixture in ‘D1’ is distilled to obtain pure 1, 1-difluoroethane ‘4’ from the top and high boiling components ‘5’ are removed from the bottom re-boiler ‘RB1’ passing from ‘MFM-2’.
Figure 2: A stream ‘1’ is charged in a distillation column ‘D1’ and allowed venting of non-condensable components ‘2’ through metering valve ‘V1’. After removal of ‘2’, total reflux is maintained for 2 hours in ‘D1’ and allowed removal of a fraction of low boiling components ‘3’ from the top through ‘C1’ and ‘V1’. The draw rate of ‘3’ is maintained using the mass flow meters ‘MFM-1 and MFM-3’ respectively, so that the reflux ratio is 10. The total reflux is maintained again for 2 hours in ‘D1’ and allowed removal of another fraction of ‘3’ from the top. The total reflux is maintained again for 2 hours in ‘D1’ and allowed removal of remaining fraction of ‘3’ from the top. The remaining mixture in re-boiler ‘RB1’ of distillation column ‘D1’ is charged into re-boiler ‘RB2’ of distillation column ‘D2’ controlled via ‘MFM-2’ and distilled to obtain pure 1, 1-difluoroethane ‘4’ from the top of ‘D2’ through condenser ‘C2’ and metering valve ‘V2’ and mass flow meter ‘MFM-5’. The reflux ratio in “D2’ is maintained using MFM-4 and high boiling components ‘5’ are removed from the bottom of ‘D2’ through ‘MFM-6’.

DETAILED DESCRIPTION OF THE INVENTION
In an embodiment, the propellant grade trans-R1234ze has a purity of at least 99.95%.
The various terms used in Figures 1 & 2 are as described below.
As used herein, stream ‘1’ refers to a crude mixture of R1234ze, non-condensable, low boiling and high boiling components.
As used herein, ‘2’ refers to non-condensable components.
As used herein, ‘3’ refers to low boiling components.
As used herein, ‘4’ refers to pure R1234ze.
As used herein, ‘5’ refers to high boiling components.
As used herein, ‘D1’ refers to first distillation column and ‘D2’ refers to second distillation column.
As used herein, ‘C1’ refers to first condenser and ‘C2’ refers to second condenser.
As used herein, ‘V1’ refers to first metering valve and ‘V2’ refers to second metering valve.
As used herein, ‘RB1’ refers to first re-boiler and ‘RB2’ refers to second re-boiler.
As used herein, ‘MFM-1’, ‘MFM-2’, ‘MFM-3’, ‘MFM-4’, ‘MFM-5’ and ‘MFM-6’ refers to first, second, third, fourth, fifth and sixth mass flow meters respectively.
As used herein, the substantially nil amount refers 5-100 ppm of that component, when analyzed by GCMS analysis.
As used herein, the low boiling component refers to a component having boiling point lower than trans-1,3,3,3-tetrafluoropropene, ranging from -70 to -25°C. The low boiling component is selected from a group consisting of pentafluoroethane; 2,3,3,3-tetrafluoropropene; 1,1,1,2-tetrafluoroethane, 1,2,3,3,3-pentafluoropropene; 1,1-difluoroethane; trifluoromethane; 3,3,3-trifluoropropene; dichlorodifluoromethane and chlorodifluoromethane. Preferably, the low boiling component includes pentafluoroethane; 2,3,3,3-tetrafluoropropene; 1,1,1,2-tetrafluoroethane; 1,2,3,3,3-pentafluoropropene; 3,3,3-trifluoropropene; dichlorodifluoromethane and chlorodifluoromethane.
As used hereinabove, the high boiling component refers to a component having boiling point higher than trans-1,3,3,3-tetrafluoropropene, ranging from -20 to 80°C. The high boiling component is selected from a group consisting of 1,1,1,3,3,3-hexafluoro propane (HFC-236fa); 1,3,3,3-tetrafluoroprop-1-ene (HFC-1234ze) cis-isomer; 1,1-dichloro-1,2,2,2-tetrafluoroethane (CFC-114a); 1,2-dichloro-1,1,2,2-tetrafluoroethane (CFC-114); 1-chloro-1,1,2,2-tetrafluoroethane (CFC-124a); 2-chloro-1,1,1,2-tetrafluoroethane (CFC-124); vinyl chloride (VCM); 1-chloro-3,3,3-trifluoropropene (HFO-1233zd); 1-chloro-3,3,3-trifluoropropene (HFO-1233zd) cis-isomer; methylene chloride (HCC-30); 1,1-dichloroethane; carbontetrachloride; 1,2-dichloroethane (HCC 150) and trichloroethylene. Preferably the high boiling component includes 1,3,3,3-tetrafluoroprop-1-ene (HFC-1234ze) cis-isomer, 1,1-dichloro-1,2,2,2-tetrafluoroethane (CFC-114a); 1,2-dichloro-1,1,2,2-tetrafluoroethane (CFC-114); 1-chloro-1,1,2,2-tetrafluoroethane (CFC-124a); 2-chloro-1,1,1,2-tetrafluoroethane (CFC-124); 1-chloro-3,3,3-trifluoropropene (HFO-1233zd); and 1-chloro-3,3,3-trifluoropropene (HFO-1233zd) cis-isomer.
The composition of trans-1,3,3,3-tetrafluoropropene to be purified may additionally contains one or more of non-condensable components.
As used herein, the non-condensable components have very low boiling point of less than -80°C or range from -170 to -80°C and are selected from a group consisting of acetylene, nitrogen, air or the like.
In an embodiment, the non-condensable impurities having very low boiling point as compared to trans-1,3,3,3-tetrafluoropropene even lower than low boiling components are removed at the top of distillation column before high reflux is maintained. After removal of non-condensable impurities, the high reflux is maintained to enrich low boiling components at the top of distillation column and thus removed from the top. After the complete removal of low boiling component, the remaining mixture is distilled to enrich pure trans-1,3,3,3-tetrafluoropropene at the top and thus is isolated from the top of distillation column. The remaining high boiling component is separated from the bottom of distillation column.
As used herein, the reflux ratio refers to L/V ratio, wherein L is the flow rate of the liquid in Kg/hour and V is the flow rate of the vapor in Kg/hour. In other words, the reflux ratio is the ratio of amount of liquid returning in distillation column to the liquid removed from the column.
As used herein, the total reflux ratio refers reflux ratio when nothing is withdrawn from the column. In other words, the total reflux ratio refers to L/V ratio = 8, wherein L is the flow rate of the liquid in Kg/hour and V is the flow rate of the vapor in Kg/hour.
In an embodiment, the process is carried out while maintaining a total reflux ratio for some time prior to maintaining high reflux ratio.
In an embodiment, the high reflux is achieved by maintaining reflux ratio in the range of from 5-100. In a preferred embodiment, the high reflux is achieved by maintaining reflux ratio in the range of from 10-50. In other words, the high reflux ratio means that more liquid that has returned to the distillation column compared to the amount of liquid removed. The reflux ratio is measured through mass flow metres which is placed in reflux line and another in product removal line.
In an embodiment, the total reflux, the high reflux, and distillation steps are carried out in a single distillation column or sequential distillation columns.
In another embodiment, the high reflux and distillation steps are carried out in a separate distillation column connected to each other.
In another embodiment, the distillation is carried out continuously in two or more columns connected to each other for sequential separation of non-condensable components, low boiling components and high boiling components.
The composition feed which is subjected to purification in the present invention comprises the following composition. The analysis was carried out in GCMS.
Compounds Boiling Points
(°C) Input feed (ppm) Output
(ppm)
1,1,1,2,2-Pentafluoroethane (R-125) -48 51 1.8
2,3,3,3-Tetrafluoropropene (R-1234yf) -29 611 1.5
1,1,1,2-Tetrafluoroethne(R-134a) -26 1344 1.5
Trifluoropropyne -48 92 0
3,3,3-Trifluoroprop-1-ene (R-1243zf) -23 2632 0
1,3,3,3-Tetrafluoroprop-1-ene (E-isomer) (R-1234ze E) -18 97.8392 % 99.99894 %
Dichlorodifluoromethane (R-12) -29 10 0
E-1,1,1,4,4,4-HexafluoroBut-2-ene (R-1336mzzz) 33.4 3 0
1,1,1,3,3,3-Hexafluoropropane (R-236fa) -1.4 168 0
E-1,2,3,3-Tetrafluoropropene (R-1234ye) 19 0
1,2-Dichlorotetrafluoroethnae (R-114) 3.2 800 0
1-Chloro-1,1,2,2-Tetrafluoroethane (R-124a) -8 28 0
1,1,1,3,3-Pentafluoropropane (R-245fa) 15.3 3403 0
1-Chloro1,2,2,2-Tetrafluoroethane (R-124) -11.9 272 0
1,3,3,3-Tetrafluoroprop-1-ene (Z-isomer) (R-1234ze- Z) 9.8 1.1461% 0
E 1-chloro-3,3,3-Trifluoropropene (R-1233zd E ) 18.5 59 0
Z 1-Chloro-3,3,3-Trifluoropropene (R-1233zd Z ) 39.6 60 0

In an embodiment, trans-1,3,3,3-tetrafluoropropene is obtained with a purity greater than 99.99%, having low boiling component less than 100 ppm preferably between 10 to 100 ppm and high boiling components less than 100 ppm, preferably between 10 to 100 ppm.
In another embodiment, trans-1,3,3,3-tetrafluoropropene obtained by the process of present invention has purity of 99.99% to 99.999% having total content of low and high boiling components of less than 100 ppm, preferably 10 to 100 ppm.
In an embodiment, the pure trans-1,3,3,3-tetrafluoropropene contains substantially nil amount of non-condensable components.
In an embodiment, the pure trans-1,3,3,3-tetrafluoropropene contains substantially nil amount of any other impurity component.
In an embodiment, the present invention provides a process for purifying trans-1,3,3,3-tetrafluoropropene, comprising the steps of:
a) providing a composition comprising trans-1,3,3,3-tetrafluoropropene, low boiling components and high boiling components in a distillation column;
b) maintaining a higher reflux ratio in the range of 5 to 100 in the distillation head;
c) allowing removal of a fraction of low boiling components from the top of distillation column;
d) repeating step b) and c) more than one time; and
e) distilling the remaining composition to separate pure trans-1,3,3,3-tetrafluoropropene from the top of distillation column by maintaining a reflux ratio in the range of 5 to 100.
In another embodiment, the low boiling components are removed at a rate of 10g/hr to 500g/hr from the top of distillation column through metered valve.
In a specific embodiment, the low boiling components are removed at a rate of 15g/hr to 300g/hr from the top of distillation column through metered valve.
In another embodiment, the reflux ratio is measured at the head of the distillation column. The high reflux ratio enables enrichment of low boiling components, which can be later withdrawn in small portions. In a smaller scale, the low boilers can be enriched by maintaining total reflux for certain specific time and then withdrawing a small portion.
In another embodiment of the present invention, the distillation column is maintained at a temperature gradient of 1 to 5°C. The temperature gradient is the difference in the temperature of the top and the bottom of the distillation column.
In another embodiment of the present invention the process is carried out as illustrated in Figure 1.
In another embodiment of the present invention, the process is carried out as illustrated in Figure 2.
The pure product i.e., trans-1,3,3,3-tetrafluoropropene is monitored by gas chromatography (GC).
Unless stated to the contrary, any of the words “comprising”, “comprises” and includes mean “including without limitation” and shall not be construed to limit any general statement that it follows to the specific or similar items or matters immediately following it.
Embodiments of the invention are not mutually exclusive but may be implemented in various combinations. The described embodiments of the invention and the disclosed examples are given for the purpose of illustration rather than limitation of the invention as set forth in the appended claims.
The crude trans-1,3,3,3-tetrafluoropropene as used herein as composition feed can be prepared by any of the methods known in the art.
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: Purification of crude trans-1,3,3,3-tetrafluoropropene.
A crude mixture containing trans-1,3,3,3-tetrafluoropropene, non-condensable, low boiling and high boiling components was charged in a distillation column and allowed venting of non-condensable components. After removal of non-condensable components, the mixture was refluxed for 2 hours and allowed removal of a fraction of low boiling components from the top. The remaining mixture was refluxed for another 2 hours and allowed removal of another fraction of low boiling components from the top. The remaining mixture in distillation column was again refluxed for 2 hours and allowed removal of remaining fraction of low boiling components from the top.
The remaining mixture in distillation column was distilled to obtain pure trans-1,3,3,3-tetrafluoropropene from the top and high boiling components were removed from the bottom.
GCMS analysis data
Components Output
ppm
1,1,1,2,2-Pentafluoroethane (HFC-125) 1.8
2,3,3,3-Tetrafluoroprop-1-ene (HFC-1234yf) 1.5
1,1,1,2-Tetrafluoroethane (HFC-134a) 1.5
R-1225ye (m/z 113) 0.7
1,1-Difluoroethane (HFC-152a) 0
3,3,3-Trifluoropropene (HFC-1243zf) 0
1,3,3,3-Tetrafluoroprop-1-ene (HFC-1234ze) 99.99894 %
1,3,3,3-Tetrafluoroprop-1-ene (HFC-1234ze) Isomer 0
1,3,3,3-Tetrafluoroprop-1-ene (HFC-1234ze) Isomer 0
1-Chloro-3,3,3-trifluoro Propene (HFO-1233zd) 0
1-Chloro-3,3,3-trifluoro Propene (HFO-1233zd) Isomer 0

CLAIMS:

WE CLAIM:
1. Trans-1,3,3,3-tetrafluoropropene of propellent grade comprising one or more additional components selected from a group consisting of 1,1,1,2,2-pentafluoroethane; 1,1,1,2-tetrafluoroethane; 2,3,3,3-tetrafluoropropene; 1,1,3,3,3-pentafluoropropene; trifluoropropyne; 3,3,3-trifluoropropene; cis-1,3,3,3-tetrafluoropropene; trans-1-chloro-3,3,3-trifluoropropene and cis-1-chloro-3,3,3-trifluoropropene, wherein the additional components are present in a range of 5 ppm (parts per million) to 1000 ppm.
2. A process for purifying trans-1,3,3,3-tetrafluoropropene, comprising the steps of:
a) providing a composition comprising trans-1,3,3,3-tetrafluoropropene, low boiling components and high boiling components in a distillation column;
b) maintaining a high reflux ratio in the range of 5 to 100 at the head of the distillation column;
c) allowing removal of a fraction of low boiling components from the top of distillation column;
d) repeating step b) and c) till the low boiling component becomes 5-100 ppm; and
e) distilling the remaining composition in distillation column to separate pure trans-1,3,3,3-tetrafluoropropene from the top of distillation column by maintaining a reflux ratio in the range of 5 to 100.
3. The process as claimed in claim 2, wherein the step b) of maintaining a high reflux ratio in the range of 5 to 100 at the head of the distillation column and step c) of allowing removal of a fraction of low boiling components from the top of distillation column are repeated at least twice.
4. The process as claimed in claim 2, wherein the low boiling component used in step a) refers to a component having boiling point lower than trans-1,3,3,3-tetrafluoropropene, ranging from -70 to -25°C selected from a group consisting of pentafluoroethane; 2,3,3,3-tetrafluoropropene; 1,1,1,2-tetrafluoroethane, 1,2,3,3,3-pentafluoropropene; 1,1-difluoroethane; trifluoromethane; 3,3,3-trifluoropropene; dichlorodifluoromethane and chlorodifluoromethane.
5. The process as claimed in claim 2, wherein the high boiling component used in step a) refers to a component having boiling point higher than trans-1,3,3,3-tetrafluoropropene, ranging from -20 to 80°C selected from a group consisting of 1,1,1,3,3,3-hexafluoro propane; 1,3,3,3-tetrafluoroprop-1-ene (cis-isomer); 1,1-dichloro-1,2,2,2-tetrafluoroethane; 1,2-dichloro-1,1,2,2-tetrafluoroethane; 1-chloro-1,1,2,2-tetrafluoroethane; 2-chloro-1,1,1,2-tetrafluoroethane; vinyl chloride; 1-chloro-3,3,3-trifluoropropene; 1-chloro-3,3,3-trifluoropropene cis-isomer; methylene chloride; 1,1-dichloroethane; carbontetrachloride; 1,2-dichloroethane; and trichloroethylene.
6. The process as claimed in claim 2, wherein the composition of trans-1,3,3,3-tetrafluoropropene to be purified contains one or more of non-condensable components selected from a group consisting of acetylene, nitrogen and air or a mixture thereof.
7. The process as claimed in claim 2, wherein the high reflux is achieved by maintaining reflux ratio in the range of from 10-50.
8. The process as claimed in claim 2, wherein the distillation column is maintained at a temperature gradient of 1 to 5°C.
9. The process as claimed in claim 2, wherein the low boiling components are removed at a rate of 10g/hr to 500g/hr from the top of distillation column through metered valve.

10. The process as claimed in claim 2, wherein the flow of the process is as illustrated in Figure 1 and Figure 2.