The present invention provides a process for purification of hydrofluoropropenes.

BACKGROUND OF THE INVENTION
Hydrofluoroolefins especially hydrofluoropropenes are important compounds and find applications as refrigerants, blowing agent, solvents owing to their zero ozone depletion potential (ODP) and low global warming potential (GWP).
U.S. Pat. No. 2996555 provides a process for preparation of 2,3,3,3-tetrafluoropropene (1234yf) by reacting trichlorodifluoropropane and hydrogen fluoride in presence of chromium oxyfluoride catalyst in vapour phase.
U.S. Pat. No. 8658846 provides a process for purification of 1234yf and hydrogen fluoride mixture by azeotropic distillation, followed by condensation or extractive distillation.
U.S. Pat. No. 8975456 provides a process for purification of a mixture of tetrafluoropropene and hydrogen fluoride by liquefication to obtain two liquid phases and then separating them by distillation to obtain 1234yf.
PCT No. 2008/008519 provides a process for separation of hydrofluoroolefins through extractive distillation. The extracting agent needs to be removed from 1234yf after removal of hydrogen fluoride, which increases an additional step and the cost. The extracting agent may also increase impurities in the product mixture.
The known processes either involve use of an extracting agent for purification of tetrafluoropropene and/or require multiple operations that increase the cost of running the process at commercial scale.
Therefore, there is a need in the art to develop an alternative process for purification of tetrafluoropropene viz., simple, economical and commercially viable.

OBJECTIVE OF THE INVENTION
The main object of present invention is to provide an economical and commercially viable process for purification of tetrafluoropropene.

SUMMARY OF THE INVENTION
The present invention provides a process for purification of 2,3,3,3-tetrafluoropropene, comprising the steps of:
a) condensing a feed gas mixture comprising 2,3,3,3-tetrafluoropropene, hydrogen fluoride and at least one compound selected from hydrogen chloride, 2-chloro-3,3,3-trifluoropropene, 1,1,1,2,2-pentafluoropropane, 1,1-dichloro-1,2,2-trifluoropropane, 1-chloro-1,1,2,2-tetrafluoropropane, and 2-chloro-1,1,1,2-tetrafluoropropane at a temperature to obtain a vapour stream 1 comprising 2,3,3,3-tetrafluoropropene and a liquid stream comprising hydrogen fluoride and at least one compound selected from 2-chloro-3,3,3-trifluoropropene, 1,1,1,2,2-pentafluoropropane, 1,1-dichloro-1,2,2-trifluoropropane, 1-chloro-1,1,2,2-tetrafluoropropane and 2-chloro-1,1,1,2-tetrafluoropropane;
b) contacting vapour stream 1 with a scrubber to obtain a vapour stream 2 comprising 2,3,3,3-tetrafluoropropene; and
c) optionally, distilling vapour stream 2 to isolate pure 2,3,3,3-tetrafluoropropene.

DETAILED DESCRIPTION OF THE INVENTION
As used herein, the tetrafluoropropene is selected from a group consisting of 2,3,3,3-tetrafluoropropene or 1,3,3,3-tetrafluoropropene.
As used herein, a feed gas mixture comprises of 2,3,3,3-tetrafluoropropene, hydrogen fluoride and at least one compound selected from hydrogen chloride, 2-chloro-3,3,3-trifluoropropene, 1,1,1,2,2-pentafluoropropane, 1,1-dichloro-1,2,2-trifluoropropane, 1-chloro-1,1,2,2-tetrafluoropropane and 2-chloro-1,1,1,2-tetrafluoropropane.
In an embodiment, feed gas mixture comprises of 15-35% of 2,3,3,3-tetrafluoropropene, 35-55% of hydrogen fluoride, 10-25% of hydrogen chloride, 1-2% of 1,1,1,2,2-pentafluoropropane, and 1-2% of 2-chloro-3,3,3-trifluoropropene 1-2%.
In an embodiment, the feed gas mixture of the present invention is obtained by dehydrohalogenation and fluorination of trichlorodifluoropropane using hydrogen fluoride in presence of chromium oxyfluoride in vapour phase.
In an embodiment, purification comprises condensing a feed gas mixture at a temperature to obtain a vapour stream 1 comprising of 2,3,3,3-tetrafluoropropene and a liquid stream comprises mainly of hydrogen fluoride.
The condensation of feed gas mixture is carried out at a temperature of -15 to 10 °C and more preferably at a temperature of -10 to 0°C.
In a specific embodiment, feed gas mixture is condensed at -10 to -5°C to obtain a vapour stream 1 and liquid stream.
As used herein, a vapour stream 1 comprises mainly of 2,3,3,3-tetrafluoropropene and hydrogen chloride. The vapour 1 stream may further be comprised of hydrogen fluoride, 2-chloro-3,3,3-trifluoropropene, 1,1,1,2,2-pentafluoropropane, intermediates such as 1,1-dichloro-1,2,2-trifluoropropane, 1-chloro-1,1,2,2-tetrafluoropropane, and 2-chloro-1,1,1,2-tetrafluoropropane. The vapour stream 1 comprises of 40-45% of 2,3,3,3-tetrafluoropropene, 40-45% of hydrogen chloride and 10-20% of any one or more component selected from of hydrogen fluoride, 2-chloro-3,3,3-trifluoropropene, 1,1,1,2,2-pentafluoropropane, 1,1-dichloro-1,2,2-trifluoropropane, 1-chloro-1,1,2,2-tetrafluoropropane, and 2-chloro-1,1,1,2-tetrafluoropropane.
In an embodiment, the vapour stream 1 comprises of 2,3,3,3-tetrafluoropropene and hydrogen chloride. The concentration of 2,3,3,3-tetrafluoropropene and hydrogen chloride in the range of 10-90%, preferably 50-90%.
The vapour stream may further comprise hydrogen fluoride in the range of less than 10% and more preferably in the range of 1-2%.
In an embodiment, vapour stream 1 comprises of 40-45% of 2,3,3,3-tetrafluoropropene, 40-45% of hydrogen chloride and 1-10% of hydrogen fluoride collected at a temperature of -10 to 10°C.
In an embodiment, vapour stream 1 may comprise of 1-10% of at least one compound selected from hydrogen fluoride, 2-chloro-3,3,3-trifluoropropene, 1,1,1,2,2-pentafluoropropane, 1,1-dichloro-1,2,2-trifluoropropane, 1-chloro-1,1,2,2-tetrafluoropropane, and 2-chloro-1,1,1,2-tetrafluoropropane.
As used herein, the liquid stream mainly comprises of hydrogen fluoride and at least one compound selected from 2,3,3,3-tetrafluoropropene, hydrogen chloride, 2-chloro-3,3,3-trifluoropropene, 1,1,1,2,2-pentafluoropropane, 1,1-dichloro-1,2,2-trifluoropropane, 1-chloro-1,1,2,2-tetrafluoropropane, and 2-chloro-1,1,1,2-tetrafluoropropane. The liquid stream comprises of 50-90% of hydrogen fluoride.
As used herein, a scrubber is selected from a group selected a group consisting of dichloropropene, sodium fluoride and potassium fluoride.
In an embodiment, vapour stream 1 comprising 2,3,3,3-tetrafluoropropene is contacted with a scrubber. The scrubber is used to remove hydrogen fluoride present in vapour stream.
The process is highly efficient as hydrogen fluoride is used for fluorination of dichloropropene and prevent formation of azeotrope of hydrogen fluoride and 2,3,3,3-tetrafluoropropene.
In an embodiment, the vapour stream 1 comprising 2,3,3,3-tetrafluoropropene is contacted with a dichloropropene scrubber to obtain a vapour stream 2.
In another embodiment, the vapour stream 1 comprising 2,3,3,3-tetrafluoropropene is contacted with solid sodium fluoride to obtain a vapour stream 2.
The vapour stream 2 comprises mainly of 2,3,3,3-tetrafluoropropene and concentration of 2,3,3,3-tetrafluoropropene is in the range of 85-99% and more preferably in the range of 90-99%.
In another embodiment, vapour stream 1 is contacted with a carbon bed, before a scrubber.
In another embodiment, vapour stream 1 is contacted with any two different scrubbers successively.
In an embodiment, vapour stream 2 comprising of 2,3,3,3-tetrafluoropene is distilled to obtain pure 2,3,3,3-tetrafluoropropene. The distillation is carried out at a temperature of 75-90°C and pressure of 20-28bar.
The distillation provides 2,3,3,3-tetrafluoropropene of purity greater than 99% and more preferably in the range of 99.1 to 99.99%.
In specific embodiment, present invention provides a process for purification of 2,3,3,3-tetrafluoropropene, comprising the steps of:
a) taking a feed gas mixture comprising 2,3,3,3-tetrafluoropropene, hydrogen fluoride and at least one compound selected from hydrogen chloride, 2-chloro-3,3,3-trifluoropropene, 1,1,1,2,2-pentafluoropropane, 1,1-dichloro-1,2,2-trifluoropropane, 1-chloro-1,1,2,2-tetrafluoropropane, and 2-chloro-1,1,1,2-tetrafluoropropane;
b) condensing the feed mixture at a temperature of -10 to 0°C to obtain a vapour stream 1 comprising 2,3,3,3-tetrafluoropropene and a liquid stream 1 comprising hydrogen fluoride and at least one compound selected from 2-chloro-3,3,3-trifluoropropene, 1,1,1,2,2-pentafluoropropane, 1,1-dichloro-1,2,2-trifluoropropane, 1-chloro-1,1,2,2-tetrafluoropropane, and 2-chloro-1,1,1,2-tetrafluoropropane;
c) contacting vapour stream 1 through a scrubber to obtain a vapour stream 2 comprising 2,3,3,3-tetrafluoropropene;
d) optionally, distilling the vapour stream 2 comprising 2,3,3,3-tetrafluoropropene at a temperature of 75-90°C and at a pressure of 20-28 bar to isolate pure 2,3,3,3-tetrafluoropropene.
In an embodiment, the feed gas mixture of the present invention is obtained by following the example of U.S. Pat. No. 2996555 involving dehydrohalogenation and fluorination of trichlorodifluoropropane using hydrogen fluoride in presence of chromium oxyfluoride in vapour phase.
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 following example is given by way of illustration and therefore should not be construed to limit the scope of the present invention.

EXAMPLES
Example 1: Purification of 2,3,3,3-tetrafluoropropene
A gas mixture comprising 2,3,3,3-tetrafluoropropene, hydrogen chloride, hydrogen fluoride, 1,1,1,2,2-pentafluoropropane and 2-chloro-3,3,3-trifluoropropene was condensed at a temperature of -10 to 0°C to obtain a liquid and vapour stream. The liquid stream mainly comprised of hydrogen fluoride along with 1,1,1,2,2-pentafluoropropane, 2-chloro-3,3,3-trifluoropropene and minor quantity of 2,3,3,3-tetrafluoropropene and the vapour stream comprised of 2,3,3,3-tetrafluoropropene and hydrogen chloride. The vapour stream was contacted with a dichloropropene scrubber. The hydrogen fluoride from vapour stream reacted with dichloropropene giving a vapour stream 2 comprising mainly of 2,3,3,3-tetrafluoropropene. The vapour stream 2 was distilled at 80°C and 25 bar to obtain pure 2,3,3,3-tetrafluoropropene.
1234yf (Purity): 99.6%
Example 2: Purification of 2,3,3,3-tetrafluoropropene
A mixture comprising 2,3,3,3-tetrafluoropropene, hydrogen fluoride, 1,1,1,2,2,-pentafluoropropane and 2-chloro-3,3,3-trifluoropropene was condensed at a temperature of -10 to 0°C to obtain liquid and vapour stream 1. The liquid stream mainly comprised of hydrogen fluoride along with 1,1,1,2,2-pentafluoropropane, 2-chloro-3,3,3-trifluoropropene and minor quantity of 2,3,3,3-tetrafluoropropene and the vapour stream 1 comprising 2,3,3,3-tetrafluoropropene. The vapour stream 1 was contacted with a sodium fluoride scrubber to obtain a vapour stream 2 comprising mainly of 2,3,3,3-tetrafluoropropene. The vapour stream 2 was distilled at 80°C and 25 bar to obtain pure 2,3,3,3-tetrafluoropropene.
1234yf (Purity): 99.5%
Example 3: Purification of 2,3,3,3-tetrafluoropropene
A mixture comprising 2,3,3,3-tetrafluoropropene, hydrogen fluoride, 1,1,1,2,2,-pentafluoropropane and 2-chloro-3,3,3-trifluoropropene was condensed at a temperature of -10 to 0°C to obtain liquid and vapour stream 1. The liquid stream mainly comprised of hydrogen fluoride along with 1,1,1,2,2-pentafluoropropane, 2-chloro-3,3,3-trifluoropropene and minor quantity of 2,3,3,3-tetrafluoropropene. The vapour stream 1 comprising 2,3,3,3-tetrafluoropropene was contacted with a dichloropropene scrubber after passing through carbon bed giving a vapour stream 2 comprising mainly of 2,3,3,3-tetrafluoropropene. The vapour stream 2 was distilled at 80°C and 25 bar to obtain pure 2,3,3,3-tetrafluoropropene.
1234yf (Purity): 99.7%
Example 4: Purification of 2,3,3,3-tetrafluoropropene
A mixture comprising 2,3,3,3-tetrafluoropropene, hydrogen fluoride, 1,1,1,2,2,-pentafluoropropane and 2-chloro-3,3,3-trifluoropropene was condensed at a temperature of -10 to 0°C to obtain liquid and vapour stream 1. The liquid stream mainly comprised of hydrogen fluoride along with 1,1,1,2,2-pentafluoropropane, 2-chloro-3,3,3-trifluoropropene and minor quantity of 2,3,3,3-tetrafluoropropene. The vapour stream 1 comprising 2,3,3,3-tetrafluoropropene was contacted with a dichloropropene scrubber after passing through sodium fluoride giving a vapour stream 2 comprising mainly of 2,3,3,3-tetrafluoropropene. The vapour stream 2 was distilled at 80°C and 25 bar to obtain pure 2,3,3,3-tetrafluoropropene.
1234yf (Purity): 99.99%

WE CLAIM:
1. A process for purification of 2,3,3,3-tetrafluoropropene, comprising the steps of:
a) condensing a feed gas mixture comprising 2,3,3,3-tetrafluoropropene, hydrogen fluoride and at least one compound selected from hydrogen chloride, 2-chloro-3,3,3-trifluoropropene, 1,1,1,2,2-pentafluoropropane, 1,1-dichloro-1,2,2-trifluoropropane, 1-chloro-1,1,2,2-tetrafluoropropane, and 2-chloro-1,1,1,2-tetrafluoropropane at a temperature to obtain a vapour stream 1 comprising 2,3,3,3-tetrafluoropropene and a liquid stream comprising hydrogen fluoride and at least one compound selected from 2-chloro-3,3,3-trifluoropropene, 1,1,1,2,2-pentafluoropropane, 1,1-dichloro-1,2,2-trifluoropropane, 1-chloro-1,1,2,2-tetrafluoropropane and 2-chloro-1,1,1,2-tetrafluoropropane;
b) contacting vapour stream 1 with a scrubber to obtain a vapour stream 2 comprising 2,3,3,3-tetrafluoropropene;
c) distilling vapour stream 2 to isolate pure 2,3,3,3-tetrafluoropropene.

2. The process as claimed in claim 1, wherein the condensation of feed gas mixture is carried out at a temperature of -15 to 10°C.

3. The process as claimed in claim 1, wherein the scrubber is selected from a group consisting of dichloropropene, sodium fluoride and potassium fluoride or a combination thereof.

4. The process as claimed in claim 1, wherein the step c) is distilled out at 75-90°C and pressure of 20-28bar.

5. The process as claimed in claim 1, wherein 2,3,3,3-tetrafluoropropene is obtained with a purity in the range of 99.1 to 99.99%.

Dated this 23rd day of July 2020.