DESC:Field of the Invention
The present invention relates to a process for preparation of olefins containing fluorine using two reactor system.
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°C to –30°C. Such composition upon distillation forms azeotropic composition and the azeotrope like composition of 2, 3, 3, 3-tetrafluoropropene and the methyl chloride.
Summary of the Invention
The present invention provides a process for the preparation of 2,3,3,3-tetrafluoropropene comprising;
a) providing a mixture of methyl chloride to 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 comprises 2,3,3,3-tetrafluoropropene, methyl chloride and the fluorinated compounds having a boiling point of – 14 °C 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 methane, tetrafluoroethyelene, vinylidene fluoride and difluoromethane and a fourth mixture mainly comprising of 2,3,3,3-tetrafluoropropene, methyl chloride, octafluorocyclobutane, chlorotrifluoroethyelene and tetrafluoro chloroethane;
e) contacting the anhydrous third mixture of step d) with a molecular sieve of size 3 Å to 5 Å to obtain a fifth mixture, which is free of difluoromethane;
f) providing the fifth mixture and steam into a second reactor to obtain a sixth mixture;
g) drying the sixth mixture to obtain an anhydrous sixth mixture, alone or in combination with step c);
h) subjecting the anhydrous sixth mixture of step g) to distillation to obtain an anhydrous seventh mixture mainly comprises methane, tetrafluoroethyelene, vinylidene fluoride and difluoromethane and an eighth mixture mainly comprises of 2,3,3,3-tetrafluoropropene, methyl chloride, octafluorocyclobutane, chlorotrifluoroethyelene and tetrafluoro chloroethane, alone or in combination with step d);
i) subjecting the anhydrous fourth mixture of step d) and the seventh mixture of step h) to distillation to obtain an anhydrous ninth mixture mainly comprising of 2,3,3,3-tetrafluoropropene and methyl chloride, and a tenth mixture mainly comprising of methyl chloride , octafluorocyclobutane, chlorotetrafluoroethane and tetrafluoroethane;
j) contacting the anhydrous ninth mixture of step i) with a molecular sieve of size 3 Å to 5 Å to obtain an eleventh mixture, which is free of methyl chloride , and
k) isolating 2,3,3,3-tetrafluoropropene from the eleventh mixture of step j).

Detailed Description of the Invention
The present invention provides a process for the preparation of 2,3,3,3-tetrafluoropropene comprising;
a) providing a mixture of methyl chloride to 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 second mixture comprises 2,3,3,3-tetrafluoropropene, methyl chloride and the fluorinated compounds having a boiling point of – 14 °C 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 methane, tetrafluoroethyelene, vinylidene fluoride and difluoromethane and a fourth mixture mainly comprises of 2,3,3,3-tetrafluoropropene, methyl chloride, octafluorocyclobutane, chlorotrifluoroethyelene and tetrafluoro chloroethane;
e) contacting the anhydrous third mixture of step d) with a molecular sieve of size 3 Å to 5 Å to obtain a fifth mixture, which is free of difluoromethane;
f) providing the fifth mixture and steam into a second reactor to obtain a sixth mixture,
g) drying the sixth mixture to obtain an anhydrous sixth mixture, alone or in combination with step c);
h) subjecting the anhydrous sixth mixture of step g) to distillation to obtain an anhydrous seventh mixture mainly comprising of methane, tetrafluoroethyelene, vinylidene fluoride and difluoromethane and an eighth mixture mainly comprises 2,3,3,3-tetrafluoropropene, methyl chloride, octafluorocyclobutane, chlorotrifluoroethyelene and tetrafluoro chloroethane, alone or in combination with step d);
i) subjecting the anhydrous fourth mixture of step d) and the seventh mixture of step h) to distillation to obtain an anhydrous ninth mixture mainly comprises 2,3,3,3-tetrafluoropropene and methyl chloride, and a tenth mixture mainly comprises methyl chloride, octafluorocyclobutane, chlorotetrafluoroethane and tetrafluoroethane;
j) contacting the anhydrous ninth mixture of step i) with a molecular sieve of size 3 Å to 5 Å to obtain an eleventh mixture, which is free of methyl chloride and
k) isolating 2,3,3,3-tetrafluoropropene from the eleventh mixture of step j).
The mixture of methyl chloride (R40) to chlorodifluoromethane (R22) may be in ratio of from 0.01 to 5 mol of R40 to 1 mol of the R22. The methyl chloride and chlorodifluoromethane may be preliminarily mixed and provided in first reactor or methyl chloride and chlorodifluoromethane may be separately added into the first 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 is obtained by passing the second mixture and, optionally, the seventh mixture through a water quencher, caustic scrubber, sulphuric scrubber and alumina balls.
The anhydrous second mixture is subjected to distillation, to obtain anhydrous third mixture mainly comprising of methane, tetrafluoroethyelene, vinylidenefluoride, trifluoromethane and difluoromethane and a fourth mixture mainly comprising of 2,3,3,3-tetrafluoropropene, methyl chloride, chlorotrifluoroethyelene, octafluorocyclobutane and tetrafluoroethane.
The third mixture thus obtained is contacted with molecular sieve of size 3 Å to 5 Å in molecular sieves bed to obtain a fifth mixture, which is free of difluoromethane. The fifth mixture is send into a second reactor and providing steam in it to obtain a sixth mixture. The sixth mixture is dried to obtain anhydrous sixth mixture alone or in combination with step c). The anhydrous sixth mixture is distilled to obtain anhydrous seventh mixture mainly comprising of methane, tetrafluoroethyelene, vinylidene fluoride and difluoromethane and an eighth mixture mainly comprises 2,3,3,3-tetrafluoropropene, methyl chloride, octafluorocyclobutane, chlorotrifluoroethyelene and tetrafluoro chloroethane, alone or in combination with step d.
The fourth mixture thus obtained is subjected to another distillation to obtain anhydrous ninth mixture mainly comprising of 2,3,3,3-tetrafluoropropene and methylchloride and a tenth mixture comprising mainly of methylchloride, octafluorocyclobutane, tetrafluorochloroethane, tetrafluoroethane. Such distillation does not involve the formation of azeotrope and azeotrope like compositions of 2, 3, 3, 3-tetrafluoropropene and the methyl chloride.
The reactor is heated by superheated steam or electrical heaters or combination of both.
The anhydrous ninth mixture mainly comprising 2,3,3,3-tetrafluoropropene and methyl chloride is contacted with molecular sieve of size 3 Å to 5 Å to obtain eleventh mixture, which is free of methyl chloride.
The isolation of 2,3,3,3-tetrafluoropropene from eleventh mixture is carried out by any method known in the art, for example, distillation, adsorption, absorption and mixture thereof.
The tenth mixture thus obtained is subjected to another distillation, to obtain twelfth mixture comprising mainly of octafluorocyclobutane, tetrafluorochloroethane, tetrafluoroethane which is recycled back into first reactor and thirteenth mixture which constitutes heavies which is sent for incineration.
The present inventors have surprisingly observed that an industrially feasible process for the preparation of 2,3,3,3-tetrafluoropropene by dividing the reaction into two steps. In the first step chlorodifluoromethane and methyl chloride is reacted to get mainly 2,3,3,3-tetrafluoropropene, tetrafluoroethyelene, vinylidenefluoride, methane, hexafluoro propene. In the second step, the reaction takes place with the intermediate from the first step mainly methane, tetrafluoroethyelene, vinylidenefluoride, hexafluoropropene, unreacted chlorodifluoromethane to give 2,3,3,3-tetrafluoropropene. The second reactor can be operated at same temperature or higher temperature than the first reactor. The resulted anhydrous composition comprising of 2,3,3,3-tetrafluoropropene, methyl chloride and the fluorinated compounds having a boiling point of – 14 °C to – 90 °C was subjected to distillation . Such a distillation did not involve the formation of azeotrope and azeotrope like compositions of 2, 3, 3, 3-tetrafluoropropene and the methyl chloride. Such distillation resulted in the formation of second composition mainly comprising of 2,3,3,3-tetrafluoropropene and methyl chloride. This second composition is contacted with molecular sieves of size 3 Å to 5 Å, thus, resulting in the selective adsorption of methyl chloride to obtain 2,3,3,3-tetrafluoropropene.

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
Process for the preparation of 2,3,3,3-tetrafluoropropene
Water (@380 gm/hour) was passed through steam jacketed preheater, where the temperature is raised to 160oC followed by electrical super heater where the temperature of steam was raised to 800oC. This superheated steam went to the reactor whose temperature was maintained at 775oC either by superheated steam or by electrical heaters. After adjusting the water flow rate, R-22 and R-40 are passed through their respective preheaters at the rate of 139gm/hour and 245 gm/hour respectively and then mixed in organic super heater where the temperature is maintained at 600oC followed by reactor which was maintained at 775oC. The residence time in the reaction system is maintained at around 0.5 seconds.
The analysis of First Reactor outlet was given below after eliminating water and acids.

Methane 0.34%
TFE 6.79%
R23 0.13%
VdF 6.28%
Trifluoroethene 0.06%
R-32 0.23%
CTFE 0.15%
HFP 0.16%
R22 2.19%
R-1234yf 3.67%
OFCB 0.13%
C-1 77.47%
R-134 0.20%
R-124 0.06%

This stream was made acid free and anhydrous by passing these stream through quencher, caustic scrubber, sulphuric scrubber and alumina balls. This anhydrous stream was distilled and then passed through 4Å molecular sieves bed to obtain a mixture of composition given below:
Methane : 2.15 %
TFE : 43.03 %
VdF : 39.92 %
R-23 : 0.82 %
TriFEthene : 0.38 %
R-22: 13.88 %
HFP : 1.01 %
In this stream, CH2 group of R-1234yf comes from methane and VdF while CF2 group of R-1234yf comes from TFE, VdF, R-23, R-22 and HFP. This stream was passed to second reactor to obtain the following composition :
Methane : 0.54 %
TFE : 37.68%
VdF : 29.52 %
CTFE : 0.0027 %
R-22 : 0.176 %
R-1234yf : 24.09 %

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/ R40
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) providing a mixture of methyl chloride to 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 comprises 2,3,3,3-tetrafluoropropene, methyl chloride and the fluorinated compounds having a boiling point in the range of – 14°C 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 methane, tetrafluoroethyelene, vinylidene fluoride and difluoromethane and a fourth mixture comprises 2,3,3,3-tetrafluoropropene, methyl chloride, octafluorocyclobutane, chlorotrifluoro ethyelene and tetrafluorochloroethane;
e) contacting the anhydrous third mixture of step d) with a molecular sieve of size 3 Å to 5 Å to obtain a fifth mixture, said mixture is free of difluoromethane;
f) providing the fifth mixture and steam into a second reactor to obtain a sixth mixture,
g) drying the sixth mixture to obtain anhydrous sixth mixture, alone or in combination with step c);
h) subjecting the anhydrous sixth mixture of step g) to distillation to obtain an anhydrous seventh mixture comprises of methane, tetrafluoroethyelene, vinylidene fluoride and difluoromethane and an eighth mixture comprises 2,3,3,3-tetrafluoropropene, methyl chloride, octafluorocyclobutane, chlorotrifluoroethyelene and tetrafluorochloroethane, alone or in combination with step d);
i) subjecting the anhydrous fourth mixture of step d) and the seventh mixture of step h) to distillation to obtain an anhydrous ninth mixture comprises 2,3,3,3-tetrafluoropropene and methyl chloride, and a tenth mixture comprises methyl chloride, octafluorocyclobutane, chlorotetrafluoroethane and tetrafluoroethane;
j) contacting the anhydrous ninth mixture of step i) with a molecular sieve of size 3 Å to 5 Å to obtain an eleventh mixture, said mixture is free of methyl chloride , and
k) isolating 2,3,3,3-tetrafluoropropene from the eleventh mixture of step j).
2. The process as claimed in claim 1, wherein the reactor is heated at a temperature in range of 550oC to 900oC or by providing a steam medium to the mixture of methyl chloride to chlorodifluoromethane to obtain the temperature range of 550oC to 900oC or both to obtain the step b) second mixture.
3. The process as claimed in claim 1, wherein the mixture of methyl chloride to chlorodifluoromethane is added in ratio of from 0.01 to 5 mol of methyl chloride to 1 mol of the chlorodifluoromethane.
4. The process as claimed in claim 1, wherein the step c) anhydrous second mixture is obtained by passing the second mixture through water quencher, caustic scrubber, sulphuric scrubber and alumina balls.
5. The process as claimed in claim 1, wherein in step i) tenth mixture is subjected to distillation to obtain twelfth mixture comprises octafluorocyclobutane, tetrafluorochloroethane, tetrafluoroethane, said mixture is recycled into first reactor.
6. The process as claimed in claim 1, wherein distillation is not involve the formation of azeotrope and azeotrope like compositions of 2, 3, 3, 3-tetrafluoropropene and the methyl chloride.
7. The process as claimed in claim 1, wherein the second reactor is operated at the same temperature or higher temperature than the first reactor.