Method for 1, 1, 1, 3, 3-pentafluoropropane

Details Method for 1, 1, 1, 3, 3-pentafluoropropane Method for 1, 1, 1, 3, 3-pentafluoropropane

1998-12-22

2001-02-20

Siegel, Alan (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Halogen containing

Reexamination Certificate

active

06191328

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process of purification of 1,1,1,3,3-pentafluoropropane (hereinafter, also referred to as HFC-245fa) which is useful as an alternative fluorocarbons for use in foaming agents.
BACKGROUND OF THE INVENTION
As a process of producing of HFC-245fa, a process is known in which 1,1,1,3,3-pentachloropropane is fluorinated with hydrogen fluoride (hereinafter, also referred to as HF) in the presence of several catalysts in either vapor phase or liquid phase.
In such a process to obtain HFC-245fa, it is necessary to recover HFC-245fa by removing HF from the product since unreacted HF generally remains in the reaction product in addition to HFC-245fa. In such case, HF is simultaneously required to be recovered and recycled to the reaction system from the economical viewpoint. However, HFC-245fa is found to form an azeotropic mixture with HF, which was disclosed in, for example, Japanese Patent Application No. 9085/1997 and Japanese Patent Kokai Application No. 156701/1997 both filed by us. We also found that it is difficult to recover HFC-245fa substantially free of HF through a simple distillation since the composition of such azeotropic mixture varies depending on the pressure, for example, the azeotropic mixture contains 55% by mole of HF at a pressure of 5 atm. In addition, it is not commercially easy to recover HFC-245fa solely without recovering such a large amount of HF.
As processes for separating fluorohydrocarbon compounds from HF, several processes, for example, a process to let each component of the mixture separate from each other to form two liquid layers and recover each component by distillation (Japanese Patent Kokai Publication No. 167803/1990); a process to use sulfuric acid as an extraction agent for HF (U.S. Pat. No. 3,873,629) and a process to remove HF through absorption into hydrofluoric acid (also referred to an aqueous HF solution) (Japanese Patent Kokai Publication No. 279277/1993) are known. Further, it is also known to successively distillate the mixture with two distillation columns in which the internal pressures are different each other, using a property that the composition of the azeotropic mixture varies depending on the pressure as disclosed in Japanese Patent Kokai Publication No. 178768/1993.
DISCLOSURE OF THE INVENTION
The process disclosed in the Japanese Patent Kokai Publication No. 167803/1990 can not be applied to any mixture since the process has to utilize a mixture each component of which separates from each other in liquid phase. The separating process using sulfuric acid has a disadvantage that it shows a strong corrosiveness when it is heated to a high temperature during recovery of HF.
In the separation process using aqueous HF solution, it is a severe disadvantage that the hydrofluoric acid has corrosiveness. For example, frequent check and maintenance of the equipment and lines are required, so that personal cost increases, in addition, the cost of installation also increases because the material to be used in such installation should be selected to have an anti-corrosiveness.
Therefore, an object of the present invention is to provide a process to obtain 1,1,1,3,3-pentafluoropropane (HFC-245fa) through effective separation of 1,1,1,3,3-pentafluoropropane from a mixture comprising at least 1,1,1,3,3-pentafluoropropane and hydrogen fluoride.
A major feature of the present invention is that HFC-245fa is effectively separated from a mixture comprising at least 1,1,1,3,3-pentafluoropropane and hydrogen fluoride by utilizing the following organic compounds (a)-(d) having a property that, on the one hand, they have a good compatibility with HFC-245fa, on the other hand, they have a poor compatibility with HF. In other word, the present invention provides a process to separate HFC-245fa from a mixture comprising at least 1,1,1,3,3-pentafluoropropane and hydrogen fluoride by utilizing a principle that, although the mixture of HFC-245fa and HF does not directly separate into the two liquid layers of each compound, HFC-245fa may be extracted into an extraction agent phase by using the extraction agent as mentioned above.
Concretely, the present invention provides a purification process of 1,1,1,3,3-pentafluoropropane characterized by contacting at least one extraction agent selected from the group consisting of
(a) a fluorohydrocarbon compound corresponds to the general formula (I):
C
x
F
y
H
z
  (I)
in which x is an integer from 3 to 10, y is an integer from 2 to 22 and z is an integer from 0 to 6;
(b) an amine compound corresponds to the general formula (II):
R
1
R
2
R
3
N  (II)
in which R
1
, R
2
and R
3
are fluoroalkyl groups each having 1-10 carbon atoms, respectively, and R
1
, R
2
and R
3
may have at most two hydrogen atoms (0, 1 or 2 hydrogen atoms), respectively;
(c) an ether compound corresponds to the general formula (III):
R
4
OR
5
  (III)
in which R
4
and R
5
are alkyl groups each having 1-10 carbon atoms, respectively, and at least one of R
4
and R
5
contains one fluorine atom; and
(d) a chlorohydocarbon compound corresponds to the general formula (IV):
C
l
Cl
m
H
n
  (IV)
in which 1 is an integer from 3 to 10, m is an integer from 2 to 22 and n is an integer from 0 to 6
with a mixture comprising 1,1,1,3,3-pentafluoropropane and hydrogen fluoride so as to form a liquid mixture and separating the liquid mixture into two liquid layers, followed by obtaining an extraction agent layer including 1,1,1,3,3-pentafluoropropane and the extraction agent as main compounds, and separatively recovering 1,1,1,3,3-pentafluoropropane from the extraction agent layer.


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