Process for purification of perfluorovinyl ethers

Details Process for purification of perfluorovinyl ethers Process for purification of perfluorovinyl ethers

1999-05-21

2001-11-13

Manoharan, Virginia (Department: 1764)

Distillation: processes, separatory

Adding material to distilland except water or steam per se

Organic compound

C203S062000, C203S063000, C203S098000, C203S058000, C568S683000, C568S682000, C568S615000, C568S677000

Reexamination Certificate

active

06315869

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method for the purification of a perfluorovinyl ether. In particular, the present invention relates to a method for the purification of a perfluorovinyl ether by effectively separating the hydrogen fluoride adduct of a perfluorovinyl ether (hereinafter referred to as “HF adduct”) or hydrogen-containing analogous compounds, which are difficult to separate from the perfluorovinyl ether by conventional methods.
Perfluorovinyl ethers are useful as the constituent monomers of tetrafluoroethylene-perfluorovinyl ether copolymers (PFA), or as the raw materials of perfluororubbers (see U.S. Pat. No. 3,132,123).
PRIOR ART
The synthesis of perfluorovinyl ethers is disclosed in U.S. Pat. No. 3,114,778, etc., and in general, perfluorovinyl ethers are prepared by pyrolyzing corresponding acid fluorides as raw materials in a gas or liquid phase. However, the HF adducts of perfluorovinyl ethers tend to be incidentally produced due to the presence of a slight amount of water in perfluorovinyl ethers prepared by the pyrolysis. In particular, in the synthesis of perfluorovinyl ethers having a high molecular weight, it is difficult to remove water by simply heating or reducing pressure, if formed salts are viscous solids. Furthermore, the reaction mixture cannot be effectively agitated, since the viscous solids adhere to agitating blades. Since the sufficient removal of water is difficult for such reasons, a large amount of HF adducts are often incidentally produced. The formation of HF adducts decreases the yield of perfluorovinyl ethers, and influences the polymerization reactions of perfluorovinyl ethers, or the physical properties of obtained polymers. Thus, the formation of HF adducts should be suppressed as much as possible in the synthesis of perfluorovinyl ethers.
Although various measures are applied, perfluorovinyl ethers, which are formed in the early stage of a reaction, often contain a relatively large amount of HF adducts due to a slight amount of water present in the reaction system.
When perfluorovinyl ethers are polymerized, HF adducts are concentrated in the unreacted perfluorovinyl ethers, which are recovered after the polymerization reaction. Thus, such recovered perfluorovinyl ethers are hardly be reused.
Among perfluorovinyl ethers, CF
3
OCF═CF
2
, C
3
F
7
OCF═CF
2
, etc. can be purified by conventional rectification. However, HF adducts may not be effectively removed from C
3
F
7
O(C
3
F
6
O)
m
CF═CF
2
in which m is 1, 2 or 3 by conventional rectification methods.
SUMMARY OF THE INVENTION
The present invention intends to provide a method for the purification of a perfluorovinyl ether by effectively separating the HF adduct of a perfluorovinyl ether or hydrogen-containing analogous compounds, which are difficult to separate from the perfluorovinyl ether by conventional methods.
Thus, the present invention provides a method for the purification of a perfluorovinyl ether of the formula:
 RfO(CF
2
O)
x
(CF
2
CF
2
O)
y
(CF
2
CF
2
CF
2
O)
z
[CF(CF
3
)CF
2
O]
n
CF═CF
2
  (I)
wherein Rf is a perfluoroalkyl group having 1 to 8 carbon atoms, x, y, z and n are each a number of 0 to 20, provided that the sum of x, y, z and n is a number of 1 to 20, preferably a number of 1 to 5,
comprising the step of removing a HF adduct of said perfluorovinyl ether (I) represented by the formula:
RfO(CF
2
O)
x
(CF
2
CF
2
O)
y
(CF
2
CF
2
CF
2
O)
z
[CF(CF
3
)CF
2
O]
n
CFHCF
3
  (II)
in which Rf, x, y, z and n are the same as defined above, and optionally an analogous compound of said perfluorovinyl ether represented by the formula (I) in which at least one fluorine atom is replaced with a hydrogen atom, as impurities, wherein said perfluorovinyl ether (I) is distilled in the presence of at least one solvent selected from the group consisting of ketones and ethers having a lower boiling point than that of said perfluorovinyl ether (I) while refluxing said solvent.


REFERENCES:
patent: 3985810 (1976-10-01), von Halasz et al.
patent: 4209635 (1980-06-01), Munekata et al.
patent: 47 34214 (1972-11-01), None
patent: 3294242 (1991-12-01), None
patent: 6 25054 (1994-02-01), None
patent: 6 72938 (1994-03-01), None

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