Process for the preparation of pentafluoroethane

Details Process for the preparation of pentafluoroethane Process for the preparation of pentafluoroethane

1999-11-22

2001-01-16

Siegel, Alan (Department: 1621)

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

Organic compounds

Halogen containing

C570S180000, C203S057000, C203S098000

Reexamination Certificate

active

06175045

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a process of producing pentafluoroethane characterized in that pentafluoroethane is separated from a mixture comprising at least pentafluoroethane (hereinafter, also referred to as “HFC-125”) and chloropentafluoroethane (hereinafter, also referred to as “CFC-115”), for example a reaction product from a production process for pentafluoroethane through fluorination of tetrachloroethylene, through extractive distillation process using a particular compound as an extracting agent (solvent).
BACKGROUND ART
HFC-125 is a useful compound as an alternative chlorofluorocarbon (or flon) compound free of chlorine and is used as a cooling medium, a blowing agent, an injecting propellant and so on. HFC-125 is conventionally produced through a fluorination process of tetrachloroethylene. In such a production process, dichlorotetrafluoroethane, dichlorotrifluoroethane, hexafluoroethane, CFC-115 and so on are produced as by-products.
Among those by-products, CFC-115 has a boiling point of −38.7° C. which is close to a boiling point of HFC-125 of −48.5° C. Further, a value of the relative volatility between these two compounds is close to 1. Particularly, when a mixture contains HC-125 at a concentration of not less than 95 mole % (that is, the concentration of CFC-115 is not more than 5 mole %), the relative volatility value is about 1.04. Accordingly, when the above mixture is distilled to separate HFC-125 at a high concentration through a conventional distillation treatment, a distillation apparatus having much plate numbers is required, which generally means that the separation using distillation is extremely difficult.
In the present specification, when a solution essentially comprising of at least a remarked component A and a remarked component B (a boiling point of component A<a boiling point of component B) is in a vapor-liquid equilibrium state with the vapor thereof, the term “relative volatility (&agr;)” is defined as follows:
&agr;=(Y
A
/X
A
)/(Y
B
/X
B
)
wherein, X
A
is a molar fraction of the lower boiling component A in the liquid phase, X
B
is a molar fraction of the higher boiling component B in the liquid phase, Y
A
is a molar fraction of the lower boiling component A in the vapor phase which is in equilibrium with its liquid phase, and Y
B
is a molar fraction of the higher boiling component B in such vapor phase.
DISCLOSURE OF INVENTION
In order to recover one component from a mixture of a system having a relative volatility value of around 1, an extractive distillation process is adopted. As an example of the extractive distillation process to separate a mixture comprising HFC-125 and CFC-115, U.S. Pat. No. 5,087,329 discloses an extractive distillation process using fluorocarbon compound having 1 to 4 carbon atoms as an extractant.
In the process disclosed in U.S. Pat. No. 5,087,329, a value of the relative volatility between HFC-125 and CFC-115 is almost 1.2 based on a calculation using figures shown in Example 1 thereof. Thus, when the concentration of HFC-125 is intended to increase to a ratio of HFC-125/CFC-115=99.7 mole %/0.3 mole % from a mixture having a ratio of HFC-125/CFC-115=7 mole %/93 mole %, a theoretical plate number amounting almost to 40 plates is required in that system. This theoretical plate number was obtained according to after-mentioned calculation method.
As a result of extensive studies on a process to separate HFC-125 from a mixture comprising HFC-125 and CFC-115 through an extractive distillation process with high efficiency, the present inventors found the matters as follows:
When a mixture comprising at least HFC-125 and CFC-115 is subjected to an extractive distillation process, HFC-125 may be separated from the above mixture, for example, using a distillation column having a very small theoretical plate number using, as an extractant (or a solvent), at least one compound (thus, a single compound or a mixture of two or more compounds) selected from ethyleneglycol-based compounds having a general formula:
R
1
O(CH
2
CH
2
O)
n
R
2
wherein R
1
and R
2
may be the same or different and are each independently selected from the group consisting of hydrogen and an alkyl group having 1 to 4 carbon atoms, and n is an integer with a value from 1 to 3.
Accordingly, the present invention provides a process of separating HFC-125 from a mixture comprising at least HFC-125 and CFC-115 through an extractive distillation process, characterized in that at least one ethyleneglycol-based compounds aforementioned is used as an extractant to obtain HFC-125 in which a concentration of CFC-115 is relatively reduced, and preferably highly concentrated HFC-125 which is free of CFC-115.
That is, the present invention provides a process of producing pentafluoroethane in which a mixture comprising at least pentafluoroethane and chloropentafluoroethane as a main component thereof is subjected to an extractive distillation to obtain another mixture which contains pentafluoroethane as a main component thereof and does not substantially contain chloropentafluoroethane, characterized in that at least one ethyleneglycol-based compounds is used as an extractant to obtain a mixture comprising pentafluoroethane and the extractant as a bottom product of the extractive distillation step.


REFERENCES:
patent: 3689374 (1972-09-01), Hanson
patent: 5087329 (1992-02-01), Felix
patent: 5919340 (1999-07-01), Kohno et al.
patent: 07133240 (1995-05-01), None
patent: 08003082 (1996-01-01), None
patent: WO9606063 (1996-02-01), None

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