The present invention provides a process of removal of hydrogen fluoride from a gas stream for purification of hydrofluoropropenes.

BACKGROUND OF THE INVENTION
Hydrofluoropropenes possess zero ozone depletion potential (ODP) and low global warming potential (GWP) which make them an important class of compounds and find application in various fields such as heat transfer, refrigerants, foaming industry, solvents, cleaning, propellants, and fire extinguishers etc.
Hydrofluoropropenes, such 2,3,3,3-tetrafluoropropene (1234yf) and 1,3,3,3-tetrafluoropropene (1234ze) are of significant commercial value as low GWP refrigerants and blowing agents. Most of the method known for their preparation either require or generate corrosive hydrogen fluoride gas that needs to be removed to obtain hydrofluoropropenes of appropriate industrial standard.
Many methods are known in the art for removal of hydrogen fluoride from hydrofluoropropenes.
U.S Patent No. 8658846 provides a process for purification of 1234yf and hydrogen fluoride mixture by azeotropic distillation.
U.S Patent No. 8975456 provides a process for purification of mixture of 1234yf and hydrogen fluoride by liquefactions to obtain two liquid phases and then separating them by distillation to obtain 1234yf.
European Patent No. 2247561 provides a process for separation of tetrafluoropropene and hydrogen fluoride by azeotropic distillation, followed by condensation.
Japanese Patent No. 5626345 provides a process for purification of 1234yf from a mixture of tetrafluoropropene and hydrogen fluoride by condensing the composition of tetrafluoropropene and hydrogen fluoride at -5 to 0°C followed by distillation to obtain 1234yf.
U.S Patent No. 9051231 and Japanese Patent No. 5338240 provide method for removing hydrogen fluoride using sulphuric acid. This method generates highly corrosive hydrogen fluoride that is detrimental to the equipment used and thus increase the manufacturing cost.
PCT Publication No. 2008/008519 provides a process for separation of hydrofluoropropene though extractive distillation using an extracting agent. The extracting agent needs to be removed from 1234yf after use, which makes the process cumbersome and add to the cost of running such process.
Owing to corrosive nature of hydrofluoric acid, many applications require tetrafluoropropenes to be completely free of hydrogen fluoride. Therefore, there is a need in the art to develop a process for continuously and efficiently remove hydrogen fluoride from tetrafluoropropenes.

OBJECT OF THE INVENTION
The main object of the present invention is to provide a continuous and an efficient process for purification of tetrafluoropropenes, contaminated with hydrogen fluoride.

SUMMARY OF THE INVENTION
A process of removing hydrogen fluoride from a gas stream containing 1234yf and hydrogen fluoride, comprising a step of contacting the gas stream with one or more metal salts and optionally recovering hydrogen fluoride.

DETAILED DESCRIPTION OF THE INVENTION
As used herein, metal salt is selected a metal fluoride selected from a group consisting of sodium fluoride, potassium fluoride or an inorganic sulphate selected from a group consisting of potassium sulphate, potassium bisulphate or the like. The inorganic sulphate for present invention is used in solid and liquid state.
A molecule of a metal salt absorbs molecules of hydrogen fluoride from a gas stream. A molecule of a metal fluoride may absorb one molecule of hydrogen fluoride from a gas stream and on desorption may desorb one molecule of hydrogen fluoride.
In an embodiment of the present invention, the inlet gas stream is contacted with metal fluoride at a temperature range of 0 to 40°C and more preferably 20-40°C.
In a specific embodiment, an inlet gas stream is contacted with a solid sodium fluoride bed at 30°C to obtain outlet gas stream.
The inorganic sulphate molecule absorbs 1-14 molecules of hydrogen fluoride from a gas stream. An inorganic sulphate molecule may absorb 1-14 molecules of hydrogen fluoride from a gas stream and on desorption may desorb greater than 10-14 molecules of hydrogen fluoride and preferably desorbs 10-11 molecules. Inorganic sulphate absorbs hydrogen fluoride and forms inorganic sulphate hydrogen fluoride complex.
“Liquid inorganic sulphate” refers to a solution of inorganic sulphate in hydrogen fluoride. The absorption of hydrogen fluoride from a gas stream using inorganic sulphate, coverts solid inorganic sulphate to a liquid solution comprising inorganic sulphate and hydrogen fluoride. The liquid inorganic sulphate may have 2-5 molecules of hydrogen fluoride per inorganic sulphate molecule. The liquid inorganic sulphate salt is also used for removal of hydrogen fluoride.
In an embodiment of the present invention, the inlet gas stream is contacted with the inorganic sulphate at a temperature range of -10 to 40°C and more preferably 0-30°C.
In a specific embodiment, a gas stream comprising hydrogen fluoride is contacted with a solid potassium hydrogen sulphate bed at 30°C to obtain outlet gas stream.
The metal salt can be activated for reuse after several absorption cycles by heating at a temperature range from 60-300°C.
The inorganic sulphate is activated by heating at a temperature of 60-90°C and more preferably at a temperature of 70-90°C.
The inorganic sulphate is very effective in absorbing hydrogen fluoride from a gas stream comprising of hydrogen fluoride. The absorbed inorganic sulphate salt forms metal salt-hydrogen fluoride complex that is heated at high temperature for desorption of hydrogen fluoride to recover hydrogen fluoride.
The metal fluoride forms metal salt-hydrogen fluoride complex after absorption cycle and is activated for reuse after several absorption cycles by heating at a temperature range from 200-300°C and more preferably in the range 200-280°C.
As used herein 2,3,3,3-tetrafluoropropene gas stream may contain one or more of compounds 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, 2-chloro-1,1,1,2-tetrafluoropropane and difluoromethane
As used herein, the inlet gas stream refers to a gas stream containing 2,3,3,3-tetrafluoropropene contaminated with hydrogen fluoride. The inlet gas stream-1 may contain hydrogen fluoride in the range of 0.1-99%.
As used herein, the outlet gas stream refers to the gas stream obtained after passing tetrafluoropropene contaminated with hydrogen fluoride through an inorganic sulphate or metal fluoride. The outlet gas stream may contain hydrogen fluoride in the range of 0.001 to 20%, preferably in the range of 0.001-5%, more preferably in the range of 0.001-2%.
Further, the outlet gas stream may comprise 2,3,3,3-tetrafluoropropene in the range of 20-90%.
In an embodiment, the gas stream comprising 1234yf and hydrogen fluoride is sequentially contacted with one metal salt followed by another metal salt.
In an embodiment, outlet gas stream obtained by passing inlet gas stream through inorganic sulphate is contacted with metal fluoride bed to obtain another outlet gas stream essentially free of hydrogen fluoride.
In a specific embodiment, outlet gas stream obtained through inorganic sulphate is passed through a metal fluoride to further remove hydrogen fluoride and to obtain an outlet gas stream having hydrogen fluoride in range of 0.001 to 0.1%.
In another embodiment, an inlet gas stream comprising of 1234yf contaminated with hydrogen fluoride is first passed through a metal fluoride followed by inorganic sulphate.
In an embodiment, the outlet gas stream comprises mainly of 2,3,3,3-tetrafluoropropene, and hydrogen fluoride in the range of 0.001 to 0.5%. Outlet gas stream has concentration of 2,3,3,3-tetrafluoropropene in the range of 60-95%, and hydrogen fluoride less than 0.5%, preferably in the range of 0.001-0.5%.
The outlet streams may contain some content of hydrogen fluoride and can be passed again successively through the metal salt or inorganic sulphate till the concentration of hydrogen fluoride reaches <2%. Complete removal of hydrogen fluoride may require 2-5 absorption cycles.
In another embodiment, the process for removal of hydrogen fluoride is followed by contacting the outlet stream with water scrubber or alkali scrubber and absorbent.
As used herein, the absorbent refers to a material used for absorbing moisture from the gas stream and is selected from alumina, carbon and molecular sieves.
The size of molecular sieves used for present invention is selected in the range of 3 to 10 Å and preferably in the range of 3-5 Å and more preferably in the range 3 to 4 Å.
In another embodiment, the process for removal of hydrogen fluoride is followed by a distillation step.
The outlet gas stream obtained from scrubber or absorbent is distilled to obtain an outlet gas stream having 1234yf with a purity of 99 to 99.9%.
The distillation is carried out at a temperature range of 75-90°C and pressure in the range 20-30bar.
In another embodiment, an outlet gas streams are contacted with water scrubber and adsorbent to obtain a gas stream containing 1234yf having hydrogen fluoride in the range of 0.001 to 0.1%.
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 gas stream containing 2,3,3,3-tetrafluoropropene can be obtained by following any process known in the art for preparation of 2,3,3,3-tetrafluoropropene.
For the purpose of this present invention, the gas stream containing 2,3,3,3-tetrafluoropropene is obtained by a process using trichlorodifluoropropane and hydrogen fluoride in presence of chromium oxyfluoride as catalyst in vapour phase as described in U.S. Pat. No. 2996555.
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: Recovery of hydrogen fluoride.
A gas stream comprising hydrogen fluoride is contacted with potassium hydrogen sulphate at 30°C to obtain an outlet stream. Later, desorption of potassium hydrogen sulphate obtained, is carried out at 80°C to recover hydrogen fluoride.
Recovery % of HF: 99%.
Example 2: Purification of 2,3,3,3-tetrafluoropropene.
A gas mixture containing 2,3,3,3-tetrafluoropropene (R1234yf), and hydrogen fluoride is passed through a potassium hydrogen sulphate.xHF scrubber to obtain outlet gas stream-1. The outlet gas stream-1 obtained was passed through a sodium fluoride bed to obtain outlet gas stream-2 containing of 2,3,3,3-tetrafluoropropene. The outlet gas stream-2 was distilled at 80 °C and 25 bar to obtain pure 2,3,3,3-tetrafluoropropene having HF content of 0.05%.
R1234yf (Purity): 99.5%
Example 3: Purification of 2,3,3,3-tetrafluoropropene.
A gas stream comprising 2,3,3,3-tetrafluoropropene, hydrogen fluoride, hydrogen chloride, 1,1,1,2,2-pentafluoropropane, and 2-chloro-3,3,3-trifluoropropene is passed through a potassium hydrogen sulphate bed to obtain outlet gas stream-1. The outlet gas stream-1 obtained was passed through a water scrubber and alumina bed to remove hydrogen fluoride and to obtain outlet gas stream-3 comprising 2,3,3,3-tetrafluoropropene which was distilled at 80 °C and 25 bar to obtain pure 2,3,3,3-tetrafluoropropene having HF content of 0.04%.
R1234yf (Purity): 99.2%
Example 4: Purification of 2,3,3,3-tetrafluoropropene.
A gas stream comprising 2,3,3,3-tetrafluoropropene and hydrogen fluoride is passed through a sodium fluoride bed to obtain an outlet gas stream-1. The outlet gas stream-1 obtained was passed through a potassium hydrogen sulphate bed to obtain an outlet stream-2 which was passed through a water scrubber and an alumina bed to remove hydrogen fluoride to obtain outlet gas stream-3 comprising 2,3,3,3-tetrafluoropropene which was distilled at 80 °C and 25 bar to obtain pure 2,3,3,3-tetrafluoropropene having HF content of 0.01%.
R1234yf (Purity): 99.6%
Example 5: Purification of 2,3,3,3-tetrafluoropropene.
A gas mixture comprising 2,3,3,3-tetrafluoropropene and hydrogen fluoride is passed through a potassium hydrogen sulphate or liquid potassium hydrogen sulphate.xHF scrubber. The outlet stream obtained was passed through a water scrubber and molecular sieve bed to obtain outlet gas stream comprising 2,3,3,3-tetrafluoropropene which was distilled at 80 °C and 25 bar to obtain pure 2,3,3,3-tetrafluoropropene having HF content of: 0.03%.
R1234yf (Purity): 99.4%
Example 6: Purification of 2,3,3,3-tetrafluoropropene.
A gas mixture comprising 2,3,3,3-tetrafluoropropene and hydrogen fluoride is passed through a sodium fluoride scrubber. The outlet stream obtained was passed through a water scrubber and molecular sieve bed to remove hydrogen fluoride and to obtain third gas stream comprising 2,3,3,3-tetrafluoropropene, which was distilled at 80 °C and 25 bar to obtain pure 2,3,3,3-tetrafluoropropene having HF content of 0.05%.
R1234yf (Purity): 99.2%.

WE CLAIM:

1. A process of removing hydrogen fluoride from a gas stream containing 2,3,3,3-tetrafluoropropene and hydrogen fluoride, comprising the step of:
a) contacting the gas stream with one or more metal salts; and
b) optionally recovering hydrogen fluoride.
2. The process as claimed in claim 1 wherein, the metal salt is a metal fluoride selected from a group consisting of sodium fluoride and potassium fluoride or an inorganic sulphate selected from a group consisting of potassium sulphate and potassium bisulphate.
3. The process as claimed in claim 1, wherein the gas stream containing 1234yf and hydrogen fluoride is sequentially contacted with one metal salt followed by another metal salt.
4. The process as claimed in claim 1, wherein the gas stream containing 1234yf and hydrogen fluoride is first contacted with a metal fluoride followed by an inorganic sulphate.
5. The process as claimed in claim 1, wherein the gas stream containing 1234yf and hydrogen fluoride is first contacted with an inorganic sulphate followed by a metal fluoride.
6. The process as claimed in claim 1, wherein the gas stream is further contacted with an absorbent selected from a group consisting of alumina, carbon and molecular sieves.
7. The process as claimed in claim 1 wherein, the hydrogen fluoride is recovered by heating metal salt-hydrogen fluoride complex formed by the contact of metal salt and hydrogen fluoride at a temperature of 60-300°C.
8. The process as claimed in claim 1, wherein the gas stream contains hydrogen fluoride in the range of 0.1-99%.
9. The process as claimed in claim 1, wherein the isolated 2,3,3,3-tetrafluoropropene contains hydrogen fluoride in the range of 0.001 to 2%.
10. The process as claimed in claim 1, wherein 1234yf is obtained with a purity of 99 to 99.9%.

Dated this 23rd July 2020.