Field of the Invention
The present invention relates to a process for 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 chloromethane 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 chloromethane 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.
The U.S Patent No. 9,206,096 describes a process for the production of 2,3,3,3-tetrafluoropropene (HFO-1234yf) from chlorodifluoromethane (R22) and chloromethane (R40), such amounts that the R40 would be in a ratio of from 0.01 to 3 mol to 1 mol of the R22. One of the byproduct formed in the reaction is chloro trifluoroethylene (CTFE). The boiling point of CTFE is -28oC which is very close to the boiling point (-29oC) of 2,3,3,3-tetrafluoropropene and thus, it becomes a challenge to separate or purify 2,3,3,3-tetrafluoropropene by routine separation and/or purification techniques, such as distillation.
In the present invention, by using a higher molar ratio, we have found that CTFE formed in comparision to 2,3,3,3-tetrafluoropropene can be substantially reduced and it is possible to obtain 2,3,3,3-tetrafluoropropene having a higher purity.
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.
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US 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.
Summary of the Invention
The present inventors have surprisingly observed upon treatment of an anhydrous mixture comprising 2,3,3,3-tetrafluoropropene and methyl chloride, with molecular sieves of size 3 Å to 5 Å resulted in the selective adsorption of methyl chloride. Thus, aiding in the purification of 2,3,3,3-tetrafluoropropene.
The present invention provides a process for the preparation of 2,3,3,3-tetrafluoropropene comprising;
a) providing a mixture of chloromethane to chlorodifluoromethane, in a molar ratio of 3.2 to 4.7 in a reactor,
b) providing and contacting a heat medium with step a) mixture to form an anhydrous second mixture comprising 2,3,3,3-tetrafluoropropene and methyl chloride,
c) contacting the anhydrous second mixture of step b) with a molecular sieve of size 3 Å to 5 Å to obtain a third mixture free of methyl chloride, and
d) isolating 2,3,3,3-tetrafluoropropene from the third mixture of step c).
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 chloromethane to chlorodifluoromethane, in a molar ratio of 3.2 to 4.7 in a reactor,
b) providing and contacting a heat medium with step a) mixture to form an anhydrous second mixture comprising 2,3,3,3-tetrafluoropropene and methyl chloride,
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c) contacting the anhydrous second mixture comprising 2,3,3,3-tetrafluoropropene and methyl chloride of step b) with a molecular sieve of size 3 Å to 5 Å to obtain a third mixture free methyl chloride, and
d) isolating 2,3,3,3-tetrafluoropropene from the third mixture of step c).
The mixture of chloromethane to chlorodifluoromethane, in a molar ratio of 3.2 to 4.7, is provided in a reactor. The chloromethane and chlorodifluoromethane may be preliminarily mixed and provided in a reactor or chloromethane 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 chloromethane and 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 comprising 2,3,3,3-tetrafluoropropene and methyl chloride is contacted with molecular sieve of size 3 Å to 5 Å to obtain third mixture which is free of methyl chloride.
The isolation of 2,3,3,3-tetrafluoropropene from third mixture is carried out by any method known in the art, for example, by series of distillations.
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
Water @380 g/hour was passed through steam jacketed preheater, where the temperature was raised to 160oC followed by electrical super heater where the temperature of steam was raised to
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800oC. This superheated steam goes 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 were passed through their respective preheaters at the rate of 105 g/hour and 250 g/hour
respectively and then mixed in organic super heater where the temperature was maintained at
600oC followed by reactor which was maintained at 775oC. The residence time in the reaction
system was maintained at around 0.5 seconds.
The analysis of Reactor outlet was given below after eliminating water and acids. The reactor
outlet stream was recycled back into the reactor and reaction was made continuous in nature.Purification:
The reactor outlet stream was then passed through a quencher, where the temperature of
the reaction mass was cooled below 100 oC and then it was passed through a serious of caustic
scrubber and sulfuric acid scrubber followed by alumina ball dryer to remove acidity and
moisture. The 2.4 kg of 4 Å molecular sieves was taken and the reactor outlet stream was passed
through this molecular sieves bed, to give following results.

We claim:
1. A process for the preparation of 2,3,3,3-tetrafluoropropene comprising;
a) providing a mixture of chloromethane to chlorodifluoromethane, in a molar ratio of 3.2 to 4.7 in a reactor,
b) providing and contacting a heat medium with step a) mixture to form an anhydrous second mixture comprising 2,3,3,3-tetrafluoropropene and methyl chloride,
c) contacting the anhydrous second mixture comprising 2,3,3,3-tetrafluoropropene and methyl chloride of step b) with a molecular sieve of size 3 Å to 5 Å to obtain a third mixture free methyl chloride, and
d) isolating 2,3,3,3-tetrafluoropropene from the third mixture of step c).
2. The process as claimed in claim 1, wherein 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 chloromethane to chlorodifluoromethane.
3. The process as claimed in claim 1, wherein the anhydrous second mixture is obtained by treating second mixture with drying agent.
4. The process as claimed in claim 3, wherein the drying agent is selected from alumina balls and calcium chloride.
5. The process as claimed in claim 4, wherein the step d) is carried out by series of distillations.