PROCESS FOR THE PREPARATION OF OLEFINS CONTAINING FLUORINE

Field of the Invention
The present invention relates to a process for preparation of olefins containing fluorine.

Background of the Invention
Olefins containing fluorine compounds play an important role as refrigerant. In recent years, one of olefin containing compound namely 2,3,3,3-tetrafluoropropene (HFO-1234yf) has attracted attention as a new refrigerant to replace another fluorinated refrigerant namely 1,1,1,2-tetrafluoroethane (HFC-134a) which is a greenhouse gas.
The JP Application No. 40-2132 describes a process for the preparation of olefins containing fluorine by heating a mixture of methyl chloride and chlorodifluoromethane in the mol ratio of 5:1 at the temperature range of 600°C to 1000oC in the presence of steam.
US Patent No. 8,252,964 describes a process for purification of 2,3,3,3-tetrafluoropropene containing saturated halogenated impurities using molecular sieves of size 5 Å to 11 Å. The saturated halogenated impurities mentioned are 236ea, 245eb, R254. Such impurities are bulky in nature and therefore requires molecular sieves of size greater than 7.5 Å.
US Application No. 12/308,327 describes a process of drying a fluid comprising a 2,3,3,3-tetrafluoropropene and water using molecular sieve of size 3 Å to 5 Å.
U.S Patent Publication No. 2015/0291490 describes a process for separation of 2,3,3,3-tetrafluoropropene and methyl chloride from azeotrope or azeotrope-like composition of 2,3,3,3-tetrafluoropropene and methyl chloride by contacting such composition with specific extraction solvent. An azeotrope composition of 2,3,3,3-tetrafluoropropene and methyl chloride is defined as a composition wherein the content ratio of 2,3,3,3-tetrafluoropropene and methyl chloride is mol % ratio of 63 mol % and 37 mol % respectively. An azeotrope-like composition is a composition wherein the content ratio of 2,3,3,3-tetrafluoropropene is 58 to 78 mol % and content ratio of methyl chloride is 22 to 42 mol %.

Summary of the Invention
The present invention provides a process for the preparation of 2,3,3,3-tetrafluoropropene comprising;
a) process to prepare a non-azeotropic composition which includes mainly 2,3,3,3-tetrafluoropropene and methyl chloride,
b) process to supply the step a) non-azeotropic composition for solvent scrubbing by contacting the step a) non-azeotropic composition with a solvent in a solvent scrubber to separate the step a) non-azeotropic composition into a first fraction in which the content ratio of methyl chloride in the total amount of 2,3,3,3-tetrafluoropropene and the methyl chloride is lower than the content of methyl chloride in total amount of the step a) non-azeotropic composition, and a second fraction in which the content ratio of methyl chloride in the total amount of 2,3,3,3-tetrafluoropropene and the methyl chloride is higher than the content ratio of methyl chloride in the step a) non-azeotropic composition, and
c) obtaining 2,3,3,3-tetrafluoropropene from the first fraction.

The present invention provides a process for the preparation of 2,3,3,3-tetrafluoropropene comprising;
a) providing a mixture of methyl chloride and chlorodifluoromethane in a reaction vessel, said mixture is either permixed or added separately,
b) providing and contacting a heat medium with step a) mixture to form a second mixture comprising 2,3,3,3-tetrafluoropropene, methyl chloride and the fluorinated compounds having a boiling point of –14 to –90 °C,
c) drying the second mixture of step b) to obtain an anhydrous second mixture,
d) subjecting the anhydrous second mixture of step c) to distillation to obtain an anhydrous third mixture mainly comprises trifluoromethane, tetrafluoroethyelene, vinylidene fluoride, difluoromethane and an anhydrous fourth mixture mainly comprising of 2,3,3,3-tetrafluoropropene, methyl chloride, octafluorocyclobutane, chlorotrifluoroethyelene and tetrafluorochloroethane,
e) Subjecting the anhydrous fourth mixture of step d) to distillation to obtain an anhydrous fifth mixture comprises mainly of a non-azeotropic composition comprises 2,3,3,3-tetrafluoropropene and methyl chloride,
f) contacting the step e) anhydrous fifth mixture for solvent scrubbing by contacting the step e) anhydrous fifth mixture with solvent in a solvent scrubber to separate the step e) anhydrous fifth mixture into a first fraction in which the content ratio of methyl chloride in the total amount of 2,3,3,3-tetrafluoropropene and the methyl chloride is lower than the content of methyl chloride in total amount of the step e) anhydrous fifth mixture, and a second fraction in which the content ratio of methyl chloride in the total amount of 2,3,3,3-tetrafluoropropene and the methyl chloride is higher than the content ratio of methyl chloride in the step e) anhydrous fifth mixture,
g) obtaining a sixth mixture mainly comprises 2,3,3,3-tetrafluoropropene which is free of methyl chloride from the first fraction by contacting the first fraction with 4Å molecular sieves, and
h) isolating 2,3,3,3-tetrafluoropropene from the sixth mixture.

Detailed Description of the Invention
The present invention provides a process for the preparation of 2,3,3,3-tetrafluoropropene comprising;
a) process to prepare a non-azeotropic composition which includes mainly 2,3,3,3-tetrafluoropropene and methyl chloride,
b) process to supply the step a) non-azeotropic composition for solvent scrubbing by contacting the step a) non-azeotropic composition with solvent in a solvent scrubber to separate the step a) non-azeotropic composition into a first fraction in which the content ratio of methyl chloride in the total amount of 2,3,3,3-tetrafluoropropene and the methyl chloride is lower than the content of methyl chloride in total amount of the step a) non-azeotropic composition, and a second fraction in which the content ratio of methyl chloride in the total amount of 2,3,3,3-tetrafluoropropene and the methyl chloride is higher than the content ratio of methyl chloride in the step a) non-azeotropic composition, and
c) obtaining 2,3,3,3-tetrafluoropropene from the first fraction.

The present invention provides a process for the preparation of 2,3,3,3-tetrafluoropropene comprising;
a) providing a mixture of methyl chloride and chlorodifluoromethane in a reaction vessel, said mixture is either permixed or added separately,
b) providing and contacting the heat medium with step a) mixture to form second mixture comprises 2,3,3,3-tetrafluoropropene, methyl chloride and the fluorinated compounds having a boiling point of –14 to – 90 °C,
c) drying the second mixture of step b) to obtain an anhydrous second mixture,
d) subjecting the anhydrous second mixture of step c) to distillation to obtain an anhydrous third mixture mainly comprises trifluoromethane, tetrafluoroethyelene, vinylidene fluoride, difluoromethane and a fourth mixture mainly comprises 2,3,3,3-tetrafluoropropene, methyl chloride, octafluorocyclobutane, chlorotrifluoro ethyelene and tetrafluorochloroethane,
e) subjecting the anhydrous fourth mixture of step d) to distillation to obtain an anhydrous fifth mixture comprises mainly of a non-azeotropic composition comprises 2,3,3,3-tetrafluoropropene and methyl chloride,
f) contacting the step e) anhydrous fifth mixture for solvent scrubbing by contacting the step e) anhydrous fifth mixture with solvent in a solvent scrubber to separate the step e) anhydrous fifth mixture into a first fraction in which the content ratio of methyl chloride in the total amount of 2,3,3,3-tetrafluoropropene and the methyl chloride is lower than the content of methyl chloride in total amount of the step e) anhydrous fifth mixture, and a second fraction in which the content ratio of methyl chloride in the total amount of 2,3,3,3-tetrafluoropropene and the methyl chloride is higher than the content ratio of methyl chloride in the step e) anhydrous fifth mixture,
g) obtaining a sixth mixture mainly comprises 2, 3, 3, 3- tetra fluoro propene which is free of methyl chloride from the first fraction by contacting the first fraction with 4Å molecular sieves, and
h) isolating 2,3,3,3-tetrafluoropropene from the sixth mixture.

The solvent used for scrubbing is selected from the group consisting of chlorinated hydrocarbon, fluorinated hydrochlorocarbon, alcohol, an ether, a nitrile, a ketone, a carbonate, an amine, an ester, dimethylformamide. The solvent used for scrubbing is preferably selected from the group consisting of chloroform, methylene chloride, trichloroethylene and methanol or mixture thereof.

The mixture of methyl chloride (R40) to chlorodifluoromethane (R22) is provided in a reactor. The mixture may be such that the R40 would be in a ratio of from 0.01 to 5 mol to 1 mol of the R22. The mixture of methyl chloride (R40) and chlorodifluoromethane (R22) preferably in a molar ratio of 3.2 to 4.7.
The methyl chloride and chlorodifluoromethane may be preliminarily mixed and provided in a reactor or methyl chloride and chlorodifluoromethane may be separately added into the reactor to form a mixture.
The heat medium of step b) is reactor heated to the temperature range of 550oC to 900oC or providing a steam medium, to the mixture of methyl chloride to chlorodifluoromethane to obtain the temperature range of 550oC to 900oC in the reactor, or both to obtain second mixture.
The anhydrous second mixture may be obtained by treating second mixture with drying agent. The drying agent may be selected from alumina balls and calcium chloride.
The anhydrous second mixture is subjected to distillation to obtain anhydrous third mixture mainly comprises trifluoromethane, tetrafluoroethyelene, vinylidene fluoride, difluoromethane, hexafluoropropene and a fourth mixture mainly comprises 2,3,3,3-tetrafluoropropene, methyl chloride, chlorotrifluoroethyelene, octafluorocyclobutane, tetrafluorochloroethane and tetrafluoroethane.
The fourth mixture thus obtained is subjected to another distillation to obtain anhydrous fifth mixture mainly comprising of a non-azeotropic composition comprises 2,3,3,3-tetrafluoropropene and methyl chloride. The anhydrous fifth mixture is taken for solvent scrubbing by contacting the anhydrous fifth mixture with solvent in a solvent scrubber to separate the anhydrous fifth mixture into a first fraction in which the content ratio of methyl chloride in the total amount of 2,3,3,3-tetrafluoropropene and the methyl chloride is lower than the content of methyl chloride in total amount of the anhydrous fifth mixture, and a second fraction in which the content ratio of methyl chloride in the total amount of 2,3,3,3-tetrafluoropropene and the methyl chloride is higher than the content ratio of methyl chloride in the anhydrous fifth mixture. The first fraction is contacted with 4Å molecular sieves to obtain a sixth mixture mainly comprising of 2,3,3,3-tetrafluoropropene free of methyl chloride. The sixth mixture may contain minor quantity of other chlorofluoroolefins such as chlorotrifluoroethylene.
The 2,3,3,3-tetrafluoropropene is isolated from sixth mixture by methods known in the art, for example, azeotropic distillation, extractive distillation, absorption and adsorption or mixture thereof.
While 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.

Example(s)
Experiment No. 1:
Process for the preparation of 2,3,3,3-tetrafluoropropene
Water (403 g/hour) is passed through steam jacketed SS preheater, where the temperature is raised to 160 oC followed by electrical inconel super heater where the temperature of steam is raised to 800 oC. This superheated steam goes to the inconel reactor whose temperature is maintained at 7400 C by superheated steam and electrical heaters. After adjusting the water flow rate, chlorodifluoromethane and methyl chloride are passed through their respective preheaters at the rate of 242 g/hour and 141 g/hour respectively and then mixed in organic super heater where the temperature is maintained at 400 oC followed by reactor where it mixes with steam .The residence time in the reactor is maintained at 0.5 seconds. The reactor outlet stream is made free of acids and moisture by quenching in water, followed by caustic wash, sulphuric wash and then passing the outlet stream through alumina balls. This anhydrous stream was then passed through solvent scrubber and the sample were analysed before and after the scrubber. The results are given below in G.C area %.

Before Methanol Scrubber After Methanol Scrubber
Time of Scrubbing 40 minutes 90 minutes
Methane 2.36% 1.19% 3.85% 2.51%
TFE 26.96% 26.62% 71.13% 59.58%
R-23 0.34% 0.32% 0.51% 0.56%
VdF 3.05% 2.969% 6.33% 5.98%
TriFEthene 0.13% 0.11% 0.11% 0.19%
R-32 0.49% 0.45% 0.38% 0.49%
CTFE 0.15% 0.17% 0.32% 0.33%
HFP 0.13% 0.13% 0.15% 0.21%
R-22 10.33% 9.80% 2.67% 5.04%
R-1234yf 1.94% 1.93% 2.30% 3.05%
OFCB 0.26% 0.20% 0.06% 0.20%
C-1 53.23% 54.81% 12.03% 21.63%
R124a 0.07% 0.03% 0% 0%
R124 0.05% 0.45% 0% 0%

Experiment No. 2:
The procedure followed is same as given in example 1, and the solvent has been changed to trichloroethylene. 4 kg of trichloroethylene was taken for scrubbing. The analysis results before and after passing through trichloroethylene is given below.

Before TCE Scrubber After TCE Scrubber
Time of Scrubbing 20 minutes 40 minutes
Methane 0.54% 1.03% 0.64%
TFE 21.02% 58.18% 47.04%
R-23 0.18% 0.26% 0.42%
VdF 1.65% 7.14% 6.26%
TriFEthene 0.04% 0.11% 0.13%
R-32 0.16% 0.26% 0.33%
CTFE 0.10% 0.23% 0.31%
HFP 0.10% 0.05% 0.13%
R-22 27.70% 10.47% 14.83%
R-1234yf 1.14% 2.73% 3.21%
OFCB 0.10% 0.19% 0.18%
C-1 46.77% 13.37% 21.33%
R124a 0.05% 0.03% 0.02%
R124 0.07% 0% 0.06%

Experiment No. 3: The procedure followed is same as given in example 1, here the solvent has been changed to chloroform. 4 kg of chloroform was taken for scrubbing. The analysis results before and after passing through chloroform is given below.

Before Chloroform Scrubber After Chloroform Scrubber
Time of Scrubbing 23 minutes 46 minutes
Methane 0.19% 0.60% 0.45%
TFE 23.94% 48.36% 56.77%
R-23 0.10% 0.35% 0.51%
VdF 1.12% 3.15% 7.48%
TriFEthene 0.03% 0.06% 0.11%
R-32 0.04% 0.03% 0.16%
CTFE 0.09% 0.14% 0.43%
HFP 0.04% 0% 0%
R-22 29.80% 0.11% 4.09%
R-1234yf 0.89% 0.37% 2.12%
OFCB 0.04% 0% 0.06%
C-1 42.08% 0.15% 3.40%
R124a 0.03% 0% 0%
R124 0.03% 0% 0%

Experiment No. 4: The procedure followed is same as given in example 1, only difference is reactor temperature was raised to 7550C and the solvent has been changed to methylene chloride. 4 kg of methylene chloride was taken for scrubbing. The analysis results before and after passing through methylene chloride is given below.

Before Methyl Chloride Scrubber After Methyl Chloride Scrubber
Time of Scrubbing 15 minutes 30 minutes
Methane 0.16% 0.37% 0.14%
TFE 22.32% 40.70% 21.25%
R-23 0.21% 0.33% 0.17%
VdF 5.29% 5.93% 4.98%
TriFEthene 0.07% 0.01% 0.06%
R-32 0.14% 0% 0.12%
CTFE 0.24% 0.23% 0.22%
HFP 0.21% 0% 0.20%
R-22 5.52% 0.03% 5.14%
R-1234yf 3.62% 0.48% 3.52%
OFCB 0.11% 0% 0.11%
C-1 61.35% 0.19% 34.38%
R124a 0.02% 0% 0.02%
R124 0.10% 0% 0.08%

From the analysis data, it is clear that methyl chloride (C-1) and R-22 gets preferentially absorbed in these solvents. Based on this experimental details, the purification process is given below.

The reactor outlet stream passes through a quencher followed by caustic scrubber, sulphuric scrubber and then through alumina balls for making the organic mass anhydrous and acid free. This anhydrous organic mass is compressed and then transferred to distillation column 1, from where methane, tetrafluoroethyelene, vinylidenefluoride, trifluoromethane, trifluoroethene, difluoromethane, hexafluoropropene, dichlorodifluoromethane is taken from the top and can be recycled back. The distillation column bottom which contains octafluorocyclobutane, chlorotrifluoroethyelene, 2,3,3,3-tetrafluoropropene, methyl chloride and tetrafluorochloroethane is sent to distillation column 2. In distillation column 2, the top fraction consists mainly of 2,3,3,3-tetrafluoropropene and methyl chloride in the mole ratio (55 % : 45 % to 1% : 99%) and the rest of the material is recovered from the bottom and is transferred to third distillation column from where methyl chloride, octafluorocyclobutane and tetrafluorochloroethane is taken from the top and recycled back into the reactor and the heavies collected at third distillation column bottom is sent to incineration.

The top product from distillation column 2 consisting mainly of methyl chloride and 2,3,3,3-tetrafluoropropene is passed through solvent scrubber where selective absorption of methyl chloride takes place and 2,3,3,3-tetrafluoropropene containing less amount of methyl chloride is obtained which is passed through 4Å molecular sieves to get mainly 2,3,3,3-tetrafluoropropene free of methyl chloride. The final purification of methyl chloride free 2,3,3,3-tetrafluoropropene can be done by azeotropic distillation, extractive distillation, absorption, adsorption and mixture thereof. The methyl chloride absorbed can be recovered from solvent through normal distillation.
The fraction coming out from the chloroform solvent scrubber was then passed through 4Å molecular sieves bed to make 2,3,3,3-tetrafluoropropene free of methyl chloride.

Before C3 Scrubber After C3 Scrubber After passing through 4Aº molecular sieves
Time of scrubbing 23 minutes 46 minutes
Methane 0.19% 0.60% 0.45% 0.26%
TFE 23.94% 48.36% 56.77% 78.54%
R-23 0.10% 0.35% 0.51% 0%
VdF 1.12% 3.15% 7.48% 18.48%
TriFEthene 0.03% 0.06% 0.11% 0%
R-32 0.04% 0.03% 0.16% 0%
CTFE 0.09% 0.14% 0.43% 0.10%
HFP 0.04% 0% 0% 0%
R-22 29.80% 0.11% 4.09% 0.02%
R-1234yf 0.89% 0.37% 2.12% 2.45%
OFCB 0.04% 0% 0.06% 0%
C-1 42.08% 0.15% 3.40% 0%
R124a 0.03% 0% 0% 0%
R124 0.03% 0% 0% 0%

Abbreviation

Tetrafluoroethyelene : TFE
Trifluoromethane : R-23
Vinylidenefluoride : VdF
1,1,2-Trifluoroethene : TriFEthene
Difluoromethane : R-32
Chlorotrifluoroethyelene : CTFE
Hexafluoropropene : HFP
Chlorodifluoromethane : R-22
2,3,3,3-Tetrafluoropropene : R-1234yf
Octafluorocyclobutane : OFCB
Methyl chloride : C-1
1-Chloro-1,2,2,2-tetrafluoroethane : R-124
1-Chloro-1,1,2,2-tetrafluoroethane : R-124a

CLAIMS:
WE CLAIM:
1. A process for the preparation of 2,3,3,3-tetrafluoropropene comprising;
a) a process to prepare a non-azeotropic composition which comprises 2,3,3,3- tetrafluoropropene and methyl chloride;
b) process to supply the step a) non-azeotropic composition for solvent scrubbing by contacting the step a) non-azeotropic composition with a solvent in a solvent scrubber to separate the step a) non-azeotropic composition into a first fraction in which content ratio of methyl chloride in total amount of 2,3,3,3- tetrafluoropropene and methyl chloride is lower than content of methyl chloride in total amount of the step a) non-azeotropic composition, and a second fraction in which the content ratio of methyl chloride in total amount of 2,3,3,3- tetrafluoropropene and methyl chloride is higher than content ratio of methyl chloride in step a) non-azeotropic composition; and
c) obtaining 2,3,3,3-tetrafluoropropene from the first fraction.

2. The process as claimed in claim 1, wherein in step b) the solvent used for scrubbing is selected from the group consisting of chlorinated hydrocarbon, fluorinated hydrochlorocarbon, alcohol, an ether, a nitrile, a ketone, a carbonate, an amine, an ester and dimethylformamide.

3. The process as claimed in claim 1, wherein in step b) the solvent used for scrubbing is selected from the group consisting of chloroform, methylene chloride, trichloroethylene and methanol or mixture thereof.

4. A process for the preparation of 2,3,3,3-tetrafluoropropene comprising;
a) providing a mixture of methyl chloride and chlorodifluoromethane in a reaction vessel, said mixture is either premixed or added separately,
b) providing and contacting a heat medium with step a) mixture to form a second mixture comprises 2,3,3,3-tetrafluoropropene, methyl chloride and fluorinated compounds having a boiling point in the range of –14 to –90 °C,
c) drying the second mixture of step b) to obtain an anhydrous second mixture,
d) subjecting the anhydrous second mixture of step c) to distillation to obtain an anhydrous third mixture comprises trifluoromethane, tetrafluoroethyelene, vinylidene fluoride and difluoromethane and an anhydrous fourth mixture comprises 2,3,3,3-tetrafluoropropene, methyl chloride, octafluorocyclobutane, chlorotrifluoroethyelene and tetrafluorochloroethane,
e) subjecting the anhydrous fourth mixture of step d) to distillation to obtain an anhydrous fifth mixture comprises a non-azeotropic composition comprises 2,3,3,3-tetrafluoropropene and methyl chloride,
f) contacting the step e) anhydrous fifth mixture for solvent scrubbing by contacting the step e) anhydrous fifth mixture with a solvent in a solvent scrubber to separate the step e) anhydrous fifth mixture into a first fraction in which the content ratio of methyl chloride in the total amount of 2,3,3,3-tetrafluoropropene and the methyl chloride is lower than the content of methyl chloride in total amount of the step e) anhydrous fifth mixture, and a second fraction in which the content ratio of methyl chloride in the total amount of 2,3,3,3-tetrafluoropropene and the methyl chloride is higher than the content ratio of methyl chloride in the step e) anhydrous fifth mixture,
g) obtaining a sixth mixture comprises 2,3,3,3-tetrafluoropropene which is free of methyl chloride from the first fraction by contacting the first fraction with 4Å molecular sieves, and
h) isolating 2,3,3,3-tetrafluoropropene from the sixth mixture.

5. The process as claimed in claim 4, wherein in step a) the mixture of methyl chloride and chlorodifluoromethane is in a molar ratio of 3.2 to 4.7.

6. The process as claimed in claim 4, wherein in step b) the heat medium is heating a reactor at the temperature in range of 550oC to 900oC or providing a steam medium, to the mixture of methyl chloride and chlorodifluoromethane to obtain the temperature range of 550oC to 900oC in the reactor, or both to obtain second mixture.

7. The process as claimed in claim 4, wherein in step c) the anhydrous second mixture is obtained by treating the second mixture with drying agent.

8. The process as claimed in claim 4, wherein in step c) the anhydrous second mixture is obtained by treating the second mixture with a drying agent, selected from alumina balls and calcium chloride.

9. The process as claimed in claim 4, wherein in step f) the solvent used for scrubbing is selected from the group consisting of chlorinated hydrocarbon, fluorinated hydrochlorocarbon, alcohol, an ether, a nitrile, a ketone, a carbonate, an amine, an ester and dimethylformamide.

10. The process as claimed in claim 4, wherein in step f) the solvent used for scrubbing is selected from the group consisting of chloroform, methylene chloride, trichloroethylene and methanol or mixture thereof.