Field of the Invention
The present invention relates to a process for the preparation of olefins containing fluorine.
Background of the Invention
In recent years, 2,3,3,3-tetrafluoropropene (HFO-1234yf) has attracted attention as a new refrigerant to replace 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.
The U.S Patent No. 2,931,840 describes a process for the preparation of HFO-1234yf by heating and decomposing a mixture of methyl chloride and chlorodifluoromethane or tetrafluoroethylene at a temperature of from 700 to 950°C by a common heating means such as an electric heater in a reactor.
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.
PCT Publication No. 2015/053339 describes a process for purification of 2,3,3,3-tetrafluoropropene by distillation of composition 2,3,3,3-tetrafluoropropene and the methyl chloride and the fluorinated compounds having a boiling point of – 14 to – 30 oC. Such composition upon distillation forms azeotropic composition and the azeotrope like composition of 2, 3, 3, 3-tetrafluoropropene and the methyl chloride to obtain a purified fraction of the 2, 3, 3, 3- tetra fluoro propene from the fraction described above, in which the concentration of the 2, 3, 3, 3- tetra fluoro propene is higher than the fraction described previously.

Summary of the Invention
The present invention provides a process for the preparation of 2,3,3,3-tetrafluoropropene comprising;
a) contacting an anhydrous second mixture with a solvent to obtain an anhydrous third mixture in gas phase and a fourth mixture in liquid phase,
wherein the anhydrous third mixture comprises of methane, tetrafluoroethyelene, trifluoromethane, vinylidene fluoride, difluoromethane, chlorotrifluoroethene, hexafluoropropene, chlorodifluoromethane, 2,3,3,3-tetrafluoropropene, octafluorocyclobutane and methyl chloride; and
wherein the fourth mixture comprises of solvent and methyl chloride; and
b) isolating 2,3,3,3-tetrafluoropropene from the anhydrous third mixture.

Detailed Description of the Invention
The present invention provides a process for the preparation of 2,3,3,3-tetrafluoropropene comprising;
a) contacting the anhydrous second mixture with a solvent to obtain an anhydrous third mixture in gas phase and a fourth mixture in liquid phase,
wherein the anhydrous third mixture comprises of methane, tetrafluoroethyelene, trifluoromethane, vinylidene fluoride, difluoromethane, chlorotrifluoroethene, hexafluoropropene, chlorodifluoromethane, 2,3,3,3-tetrafluoropropene, octafluorocyclobutane and methyl chloride;
wherein the fourth mixture comprises of solvent and methyl chloride; and
b) isolating 2,3,3,3-tetrafluoropropene from the anhydrous third mixture.
The fourth mixture obtained in the step a) is distilled to obtain a seventh mixture comprising methyl chloride which is recycled and eight mixture comprising a solvent, which is recycled.
A process to obtain an anhydrous second mixture comprising the following steps:
a) providing a mixture of methyl chloride and chlorodifluoromethane in a first reactor, wherein said mixture is either premixed or mixed separately;
b) providing and contacting the 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 – 14oC to – 90oC;
c) drying the second mixture of step b) to obtain an anhydrous second mixture.
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 3.2 to 5 mol to 1 mol of the R22. 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 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 the second mixture.
The anhydrous second mixture is dried by treating second mixture with drying agent.
The drying agent may be selected from sulphuric scrubber, alumina balls or calcium chloride.
The solvent used for contacting anhydrous second mixture is selected from the group consisting of chloroform, methylene chloride, trichloroethylene, methanol or mixture thereof.
The isolation of 2,3,3,3-tetrafluoropropene from anhydrous third mixture comprising the following steps:
a) contacting the anhydrous third mixture with 4Å molecular sieves to obtain a fifth mixture and a sixth mixture, wherein the fifth mixture is free of methyl chloride and difluoromethane and the sixth mixture comprises of methyl chloride and difluoromethane;
b) subjecting the fifth mixture of step a) to distillation to obtain a ninth mixture comprising methane, tetrafluoroethyelene, trifluoromethane, vinylidene fluoride, hexafluoropropene and chlorodifluoromethane and a tenth mixture comprising chlorotrifluoroethyelene, 2,3,3,3-tetrafluoropropene, octafluorocyclobutane, tetrafluorochloroethane, tetrafluoroethane;
c) recycling the ninth mixture of step b);
d) subjecting the tenth mixture of step b) to distillation column to obtain an eleventh mixture comprising of 2,3,3,3-tetrafluoropropene and chlorotrifluoro ethyelene and a twelfth mixture comprising octafluorocyclobutane, chlorotetrafluoroethanes, tetrafluoroethane and heavies;
e) isolating 2,3,3,3-tetrafluoropropene from the eleventh mixture.
Isolation of 2,3,3,3-tetrafluoropropene from the eleventh mixture may be carried by any method selected from distillation, extraction, adsorption, absorption and hydrogenation 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.
The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention.
Example(s)
Process for the preparation of 2,3,3,3-tetrafluoropropene
A mixture of chlorodifluoromethane and methyl chloride in the mole ratio of 1:3.5 respectively is preheated and the then superheated till 400 0C and then mixed with 800 0C steam (50 % by weight of total feed) in the reactor .The reactor temperature is maintained at 793 0C by electrical furnace. The residence time in the reactor is kept around 0.5 seconds. The reactor outlet compositions in mol % after removing steam and acids are as follows:
The analysis of reactor outlet is given below after eliminating water and acids.
Methane 0.61 %
Tetrafluoroethyelene 3.39 %
Trifluoromethane 0.11 %
Vinylidene fluoride 9.91 %
Trifluoroethene 0.05 %
difluoromethane 0.26 %
pentafluoroethane 0.01 %
chlorotrifluoroethene 0.10 %
hexafluoropropene 0.20 %
chlorodifluoromethane 1.43 %
2,3,3,3-tetrafluoropropene 3.51 %
octafluorocyclobutane 0.08 %
methyl chloride 78.98 %
tetrafluoroethane 0.35 %
Chlorotetrafluoroethane
(R-124a) 0.02 %
Chlorotetrafluoroethane
(R-124) 0.04 %
Heavies 0.917 %

Purification Experiment:
Experiment No.1: Purification with methanol
For checking the effect of solvent scrubbing, the reactor was operated at 7500C and the molar ratio of water: chlorodifluoromethane :methyl chloride was maintained at 80%:10%:10% with a residence time of 0.5 seconds. The reactor feed consists of 403 g/hour of steam, 242 g/hour of R-22 and 141 g/hour of chloromethane. The reactor outlet stream was passed through water scrubber to remove the acids and then passed through drying agent. The methanol scrubber consists of a 4 liters. Jacketed Vessel over which 3m packed height column was placed. 2.5 kg of methanol was taken in a scrubber and circulated from 1.5 m packed height @ 7LPH. The temperature of the jacketed vessel was maintained between -150C to -200C by passing chilled brine in the jacket. The reactor outlet stream free of acids is passed near the bottom of the packed column. The analysis results before and after passing through methanol scrubber is given below.
Before Methanol Scrubber After Methanol Scrubber
Time of scrubbing 40 minutes 90 minutes
Methane 2.3668% 1.9106% 3.8551% 2.5168%
tetrafluoroethyelene 26.9654% 26.6275% 71.1367% 59.5873%
trifluoromethane 0.3413% 0.3255% 0.5120% 0.5678%
vinylidene fluoride 3.0579% 2.9936% 6.3302% 5.9810%
trifluoroethene 0.1308% 0.1136% 0.1169% 0.1921%
difluoromethane 0.4932% 0.4545% 0.3822% 0.4986%
pentafluroethane 0.0000% 0.0169% 0.0000% 0.0278%
chlorotrifluoroethene 0.1513% 0.1711% 0.3255% 0.3335%
hexafluoropropene 0.1335% 0.1319% 0.1561% 0.2109%
chlorodifluoromethane 10.3373% 9.8081% 2.6778% 5.0420%
2,3,3,3-tetrafluoropropene 1.9401% 1.9312% 2.3089% 3.0510%
octafluorocyclobutane 0.2621% 0.2007% 0.0625% 0.2085%
chloromethane 53.2398% 54.8120% 12.0373% 21.6338%
chlorotetrafluoroethane (R-124a) 0.0763% 0.0333% 0.0000% 0.0000%
chlorotetrafluoroethane (R-124) 0.0536% 0.0452% 0.0000% 0.0000%

Experiment No. 2 : Purification with trichloroethyelene (TCE)
The procedure followed is same as given in example 1, here the solvent has been changed to trichloroethyelene. 4 kg of trichloroethyelene was taken for scrubbing. The analysis results before and after passing through Trichloroethyelene is given below.
Before TCE Scrubber After TCE Scrubber
Methane 0.5492% 1.0334% 0.6427% 0.5312%
tetrafluoroethyelene 21.0258% 58.1862% 47.0447% 38.4720%
trifluoromethane 0.1854% 0.2654% 0.4253% 0.3509%
vinylidene fluoride 1.6590% 7.1405% 6.2605% 5.6319%
trifluoroethene 0.0484% 0.1138% 0.1317% 0.1175%
difluoromethane 0.1686% 0.2625% 0.3377% 0.2960%
pentafluroethane 0.0000% 0.0616% 0.0759% 0.0456%
chlorotrifluoroethene 0.1098% 0.2380% 0.3149% 0.2940%
hexafluoropropene 0.1046% 0.0528% 0.1390% 0.1658%
chlorodifluoromethane 27.7009% 10.4771% 14.8363% 16.0611%
2,3,3,3-tetrafluoro propene 1.1494% 2.7354% 3.2141% 3.5169%
octafluorocyclobutane 0.1037% 0.1922% 0.1860% 0.2095%
chloromethane 46.7794% 13.3714% 21.3325% 29.4327%
chlorotetrafluoroethane (R-124a) 0.0539% 0.0385% 0.0240% 0.0398%
chlorotetrafluoroethane (R-124) 0.0713% 0.0000% 0.0606% 0.0773%

Experiment No. 3 : Purification with chloroform (C3)
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 C3 Scrubber After C3 Scrubber
Methane 0.1922% 0.6033% 0.4514% 0.2954%
tetrafluoroethyelene 23.9417% 48.3656% 56.7726% 38.7284%
trifluoromethane 0.1010% 0.3540% 0.5103% 0.4225%
vinylidene fluoride 1.1235% 3.1519% 7.4865% 8.0002%
trifluoroethene 0.0370% 0.0672% 0.1116% 0.1171%
difluoromethane 0.0446% 0.0336% 0.1614% 0.2117%
pentafluroethane 0.0000% 0.0000% 0.0376% 0.0564%
chlorotrifluoroethene 0.0966% 0.1487% 0.4312% 0.4439%
hexafluoropropene 0.0454% 0.0000% 0.0000% 0.1581%
chlorodifluoromethane 29.8098% 0.1139% 4.0906% 16.6569%
2,3,3,3-tetrafluoropropene 0.8911% 0.3750% 2.1269% 4.7536%
octafluorocyclobutane 0.0465% 0.0000% 0.0609% 0.1661%
chloromethane 42.0800% 0.1579% 3.4045% 10.8744%
chlorotetrafluoroethane (R-124a) 0.0356% 0.0000% 0.0000% 0.0438%
chlorotetrafluoroethane (R-124) 0.0375% 0.0000% 0.0000% 0.0467%

The analysis result of solvent chloroform after scrubbing is given below:
Hexafluoropropene 0.008%
octafluorocyclobutane 0.008%
2,3,3,3-tetrafluoropropene 0.240%
chlorodifluoromethane 0.147%
chloromethane 19.163%
chloroform 80.431%

Experiment No. 4: Purification with methylene chloride (C2)
The procedure followed is same as given in example 1, here 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 C2 Scrubber After C2 Scrubber
Methane 0.1638% 0.3703% 0.1404%
tetrafluoroethyelene 22.3233% 40.7030% 21.2515%
trifluoromethane 0.2112% 0.3343% 0.1751%
vinylidene fluoride 5.2918% 5.9353% 4.9834%
trifluoroethene 0.0709% 0.0129% 0.0642%
difluoromethane 0.1436% 0.0000% 0.1287%
pentafluroethane 0.0190% 0.0231% 0.0165%
chlorotrifluoroethene 0.2417% 0.2393% 0.2284%
hexafluoropropene 0.2101% 0.0000% 0.2020%
chlorodifluoromethane 5.5228% 0.0319% 5.1449%
2,3,3,3-tetrafluoropropene 3.6240% 0.4812% 3.5295%
octafluorocyclobutane 0.1130% 0.0000% 0.1186%
chloromethane 61.3566% 0.1915% 34.3825%
chlorotetrafluoroethane
(R-124a) 0.0249% 0.0000% 0.0261%
chlorotetrafluoroethane
(R-124) 0.1056% 0.0000% 0.0842%

The analysis result of solvent methyelene chloride after scrubbing is
Hexafluoropropene 0.007%
octafluorocyclobutane 0.015%
2,3,3,3-tetrafluoropropene 0.078%
chlorodifluoromethane 0.066%
chloromethane 13.310%
methyelene chloride 85.780%

WE CLAIM:
1. A process for the preparation of 2,3,3,3-tetrafluoropropene comprising;
a) contacting an anhydrous second mixture with a solvent to obtain an anhydrous third mixture in gas phase and a fourth mixture in liquid phase,
wherein the anhydrous third mixture comprises of methane, tetrafluoroethyelene, trifluoromethane, vinylidene fluoride, difluoromethane, chlorotrifluoroethene, hexafluoropropene, chlorodifluoromethane, 2,3,3,3-tetrafluoropropene, octafluorocyclobutane and methyl chloride;
and wherein the fourth mixture comprises of solvent and methyl chloride; and
b) isolating 2,3,3,3-tetrafluoropropene from the anhydrous third mixture.
2. The process as claimed in claim 1, wherein the anhydrous second mixture is obtained by
a) providing a mixture of methyl chloride and chlorodifluoromethane in a first reactor, wherein said mixture is either premixed or mixed separately;
b) providing and contacting the 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 – 14oC to – 90oC;
c) drying the second mixture of step b) to obtain an anhydrous second mixture;
3. The process as claimed in claim 1, wherein the solvent used in step a) is selected from chloroform, methylene chloride, trichloroethylene, methanol or mixture thereof.
4. The process as claimed in claim 1, wherein the fourth mixture obtained in the step a) is distilled to obtain a seventh mixture comprising methyl chloride which is recycled back into the first reactor and an eight mixture comprising a solvent which is recycled;
5. The process as claimed in claim 1, wherein 2,3,3,3-tetrafluoropropene is isolated from anhydrous third mixture by
a) contacting the anhydrous third mixture with 4Å molecular sieves to obtain a fifth mixture and a sixth mixture, wherein the fifth mixture is free of methyl chloride and difluoromethane and the sixth mixture comprises of methyl chloride and difluoromethane;
b) subjecting the fifth mixture of step a) to distillation to obtain a ninth mixture comprising methane, tetrafluoroethyelene, trifluoromethane, vinylidene fluoride, hexafluoropropene and chlorodifluoromethane and a tenth mixture comprising chlorotrifluoroethyelene, 2,3,3,3-tetrafluoropropene, octafluorocyclobutane, tetrafluorochloroethane, tetrafluoroethane;
c) recycling the ninth mixture of step b);
d) subjecting the tenth mixture of step b) to distillation column to obtain an eleventh mixture comprising of 2,3,3,3-tetrafluoropropene and chlorotrifluoro ethyelene and a twelfth mixture comprising octafluorocyclobutane, chlorotetrafluoroethanes, tetrafluoroethane and heavies;
e) isolating 2,3,3,3-tetrafluoropropene from the eleventh mixture.
6. The process as claimed in claim 2, wherein in step a) methyl chloride is in a ratio of from 3.2 to 5 mol to 1 mol of chlorodifluoromethane.
7. The process as claimed in claim 2, wherein the reactor is heated at a temperature in range of 550°C to 900°C or providing a steam medium to the mixture of methyl chloride to chlorodifluoromethane to obtain the temperature range of 550°C to 900°C in the reactor or both to obtain the second mixture.
8. The process as claimed in claim 2, wherein step c) anhydrous second mixture is obtained by treating second mixture with drying agent selected from sulphuric scrubber, alumina balls or calcium chloride.