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 liquefaction to obtain two liquid phases and then separating it 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, that increases an additional step and so as the cost. The extracting agent may also increase in impurities contribution in 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 a process for preparation of tetrafluoropropene in vapour phase that is simple, economical and commercially viable.
OBJECTIVE OF THE INVENTION
The main object of present invention is to provide a process for purification of 2,3,3,3-tetrafluoropropene.

SUMMARY OF THE INVENTION
The present invention provides a process for purification of 2,3,3,3-tetrafluoropropene, comprising the steps of:
a) feeding a reaction mixture 1 comprising 2,3,3,3-tetrafluoropropene, hydrogen fluoride, hydrogen chloride 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) distilling the reaction mixture 1 to obtain a vapour stream 1 comprising hydrogen chloride, a vapour stream 2 comprising 2,3,3,3-tetrafluoropropene and hydrogen fluoride and a vapour stream 3 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 2 with a scrubber to obtain a vapour stream 4 comprising 2,3,3,3-tetrafluoropropene;
d) optionally, distilling vapour stream 4 to isolate pure 2,3,3,3-tetrafluoropropene.

DETAILED DESCRIPTION OF THE INVENTION
As used herein, hydrofluoropropenes is selected from a group consisting of 2,3,3,3-tetrafluoropropene or 1,3,3,3-tetrafluoropropene.
As used herein, the reaction mixture 1 comprises of 2,3,3,3-tetrafluoropropene, hydrogen fluoride, hydrogen chloride 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.
In an embodiment, reaction mixture 1 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.
The reaction mixture 1 of the present invention is obtained by dehydrohalogenation of trichlorodifluoropropane using hydrogen fluoride in presence of chromium oxyfluoride in vapour phase.
As used herein, the vapour stream 2 comprises of 2,3,3,3-tetrafluoropropene and hydrogen fluoride. The vapour stream 2 is obtained at a temperature of 50 to 100°C and at a pressure of 15 to 30 bar.
The vapour stream 2 comprises mainly of 2,3,3,3-tetrafluoropropene and hydrogen fluoride. The vapour stream 2 comprises of 2,3,3,3-tetrafluoropropene and hydrogen fluoride, may further be comprised of 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, the vapour stream 2 comprises of 80-95% of 2,3,3,3-tetrafluoropropene and 5-20% and more preferably 6-15% of hydrogen fluoride and is obtained at a temperature of 50 to 100°C and at a pressure of 15 to 30 bar.
As used herein, vapour stream 1 comprises of mainly hydrogen chloride
As used herein, the vapour stream 3 comprises of 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.
The vapour stream 3 comprises of 50-80% of hydrogen fluoride and 20-30% of one or more component 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.
In an embodiment, the vapour stream 3 comprises of 50-80% of hydrogen fluoride, preferably 55-80% of hydrogen fluoride.
As used herein, the vapour stream 4 comprising mainly of 2,3,3,3-tetrafluoropropene.
The distillation and re-distillation of vapour stream 4 is carried out at a temperature in the range 75-90°C and pressure in the range of 20-30 bar.
As used herein, the scrubber is selected from a group selected a group consisting of dichloropropene, potassium fluoride, and sodium fluoride. The most preferred dichloropropene is 2,3-dichloropropene.
The present invention does not use any extractive agent to obtain 2,3,3,3-tetrafluoropropene from the reaction mixture.
The present invention primarily involves using sequential distillation for separation of 2,3,3,3-tetrafluoropropene.
The present invention also provides a method to isolate pure 1234yf by contacting through a scrubber.
In an embodiment, vapour stream 2 comprising 2,3,3,3-tetrafluoropropene and hydrogen fluoride is contacted with a scrubber. The scrubber is used to remove hydrogen fluoride present in vapour stream 2.
The present invention process is highly efficient as the unwanted hydrogen fluoride present in vapour stream 2 is used for fluorination of dichloropropene and help in separation of 2,3,3,3-tetrafluoropropene from azeotropic mixture of hydrogen fluoride and 2,3,3,3-tetrafluoropropene.
In an embodiment, the vapour stream 2 comprising 2,3,3,3-tetrafluoropropene is contacted with a dichloropropene scrubber to obtain a vapour stream 4.
In another embodiment, the vapour stream 2 comprising 2,3,3,3-tetrafluoropropene is contacted with solid sodium fluoride scrubber to obtain a vapour stream 4.
The scrubber is contacted with the vapour stream 2 at a temperature of -10 to 50°C.
In a specific embodiment, the vapour stream 2 is contacted with dichloropropene at a temperature of -10 to 0°C.
In another specific embodiment, the vapour stream 2 is contacted with sodium fluoride at a temperature of 10 to 40°C, preferably at a temperature of 20 to 30°C.
The vapour stream 4 is comprises essentially of 2,3,3,3-tetrafluoropropene. The vapour stream 4 comprises of 99 to 99.1% of 2,3,3,3-tetrafluoropropene.
In an embodiment, vapour stream 4 comprises essentially of 2,3,3,3-tetrafluoropene is distilled to obtain pure 2,3,3,3-tetrafluoropropene. The pure 2,3,3,3-tetrafluoropene is isolated in bottom composition of second distillation.
The distillation provides 2,3,3,3-tetrafluoropropene of purity 99 to 99.9%.
In specific embodiment, present invention provides a process for purification of 2,3,3,3-tetrafluoropropene, comprising the steps of:
a) feeding a reaction mixture 1 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;
b) distilling reaction mixture 1 at a temperature of 50 to 100°C and pressure of 15 to 30 bar to obtain a vapour stream 1 comprising hydrogen chloride, vapour stream 2 comprising 2,3,3,3-tetrafluoropropene and hydrogen fluoride and vapour stream 3 comprising mainly of 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 2 comprising 2,3,3,3-tetrafluoropropene and hydrogen fluoride with dichloropropene scrubber to obtain a vapour stream 4; and
d) optionally, distilling vapour stream 4 comprising 2,3,3,3-tetrafluoropropene to isolate pure 2,3,3,3-tetrafluoropropene.
In a more specific embodiment, present invention provides a process for purification of 2,3,3,3-tetrafluoropropene, comprising the steps of:
a) feeding a reaction mixture 1 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;
b) distilling reaction mixture 1 at a temperature of 50 to 100°C and pressure of 15 to 30 bar to obtain a vapour stream 1 comprising hydrogen chloride, vapour stream 2 comprising 2,3,3,3-tetrafluoropropene and hydrogen fluoride and vapour stream 3 comprising mainly of 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 2 comprising 80 to 85% of 2,3,3,3-tetrafluoropropene and 15 to 20% of hydrogen fluoride with a dichloropropene scrubber to obtain a vapour stream 4; and
d) optionally, distilling vapour stream 4 comprising 2,3,3,3-tetrafluoropropene at a temperature of 75 to 90°C and pressure of 20 to 30 bar to isolate pure 2,3,3,3-tetrafluoropropene.
In specific embodiment, 2,3,3,3-terafluoropropene of purity between the range of 95 to 99.99%.
In specific embodiment, present invention provides a process for purification of 2,3,3,3-tetrafluoropropene, comprising the steps of:
a) feeding a reaction mixture 1 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;
b) distilling reaction mixture 1 at a temperature of 50 to 100°C and at a pressure of 15 to 30 bar to obtain a vapour stream 1 comprising hydrogen chloride, vapour stream 2 comprising 2,3,3,3-tetrafluoropropene and hydrogen fluoride and vapour stream 3 comprising mainly of 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) re-distilling vapour stream 2 comprising 2,3,3,3-tetrafluoropropene at a temperature of 75 to 90°C and pressure of 20 to 30 bar to isolate pure 2,3,3,3-tetrafluoropropene.
In an embodiment, the reaction mixture 1 of the present invention is obtained by following the example of U.S. Pat. No. 2996555 involving dehydrohalogenation 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 fluoride, hydrogen chloride, 1,1,1,2,2,-pentafluoropropane, 2-chloro-3,3,3-trifluoropropene is distilled at a temperature of 50 to 100°C and at a pressure of 15 to 30 bar to obtain a vapour stream 2. The vapour stream 2, mainly comprises of hydrogen fluoride and 2,3,3,3-tetrafluoropropene was contacted with a 2,3-dichloropropene scrubber. The hydrogen fluoride present in vapour stream 2 reacted with dichloropropene giving a vapour stream 4 comprising mainly of 2,3,3,3-tetrafluoropropene. The vapour stream 4 was distilled at 80°C and 25 bar and pure 2,3,3,3-tetrafluoropropene is isolated as bottom composition. R1234yf (Purity): 99.6%
Example 2: Purification of 2,3,3,3-tetrafluoropropene.
A reaction mixture comprising 2,3,3,3-tetrafluoropropene, hydrogen fluoride, hydrogen chloride, 1,1,1,2,2,-pentafluoropropane, and 2-chloro-3,3,3-trifluoropropene is distilled at a temperature of 50 to 100°C and at a pressure of 15 to 30 bar to obtain vapour stream 2. The vapour stream 2 mainly comprises of hydrogen fluoride and 2,3,3,3-tetrafluoropropene is contacted with sodium fluoride scrubber. The hydrogen fluoride from vapour stream 2 reacted with sodium fluoride giving a vapour stream 4 comprising essentially of 2,3,3,3-tetrafluoropropene. The vapour stream 4 was re-distilled to obtain pure 2,3,3,3-tetrafluoropropene as bottom composition. 1234yf (Purity): 99.5%

WE CLAIM:

1. A process for purification of 2,3,3,3-tetrafluoropropene, comprising the steps of:
a) feeding a reaction mixture 1 comprising 2,3,3,3-tetrafluoropropene, hydrogen fluoride, hydrogen chloride and at least one compound selected from a group consisting of 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) distilling reaction mixture 1 to obtain a vapour stream 1 comprising of hydrogen chloride, a vapour stream 2 comprising 2,3,3,3-tetrafluoropropene and hydrogen fluoride and a vapour stream 3 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 2 with a scrubber to obtain a vapour stream 4 comprising 2,3,3,3-tetrafluoropropene;
d) optionally, distilling vapour stream 4 to isolate pure 2,3,3,3-tetrafluoropropene.

2. The process as claimed in claim 1, wherein the distillation of reaction mixture 1 in step b) is carried out at a temperature of 50 to 100°C and at a pressure of 15 to 30 bar.

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

4. The process as claimed in claim 1, wherein step c) is carried out at a temperature of 75-90°C and a pressure of 20-30 bar.
5. The process as claimed in claim 1, wherein the 2,3,3,3-tetrafluoropropene is obtained with a purity in the range of 99 to 99.99%.