Process for preparing pentafluoroethane

Details Process for preparing pentafluoroethane Process for preparing pentafluoroethane

2000-03-20

2003-03-04

Manoharan, Virginia (Department: 1764)

Distillation: processes, separatory

Adding material to distilland except water or steam per se

Organic compound

C203S078000, C570S178000

Reexamination Certificate

active

06527917

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a process of separating pentafluoroethane through extractive distillation process using a particular compound as an extractant (or solvent) 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.
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. and HFC-125 which is the desired product has a boiling point of −48.5° C. However, 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 comprising 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 1,1,1,2-tetrafluoro-2,2-dichloroethane or 1,1,1-trifluoro-2,2-dichloroethane 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 a 15 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 according to a theoretical calculation. In this process, a mixture comprising extractant and CFC-115 and HFC-125 is obtained as a bottom product from the extractive distillation step. Thus, it is necessary to sufficiently remove CFC-115 from the bottom product in order to re-use the extractant.
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-125and CFC-115 is subjected to an extractive distillation process, HFC-125 may be efficiently separated from the above mixture by using, for example, as an extractant (or a solvent), at least one compound (thus, a single compound or a mixture of two or more compounds) selected from the group of hydrofluorocarbon compounds having two carbon atoms.
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 compound (thus, a single compound or a mixture of two or more compounds) selected from the group of hydrofluorocarbon compounds having two carbon atoms at least one compound selected from the group of hydrofluorocarbon compounds having two carbon atoms is used as an extractant to obtain HFC-125 in which a concentration of CFC-115is 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 compound selected from the group of hydrofluorocarbon compounds having two carbon atoms is used as an extractant to obtain a mixture comprising pentafluoroethane and the extractant as a main component thereof as a bottom product of the extractive distillation step.
In the present specification, the term “main component” means that the content of the other components is relatively smaller than the content of the main component in the mixture. Concretely, it is sufficient that an amount of the main component is not less than 50%, more concretely not less than 60%, for example not less than 80% (these amount may be on a molar or weight basis). Additionally, in the present specification, the phrase “pentafluoroethane substantially free of chloropentafluoroethane” means that the finally obtainable product is a mixture including pentafluoroethane as its main component, wherein for example, such a mixture may have a concentration of pentafluoroethane not less than 90 weight %, preferably not less than 99.9 weight %, and more preferably not less than 99.99 weight %.
According to the present process when at least one compound selected from the group of hydrofluorocarbon compounds having two carbon atoms is used as an extractant, a mixture may be obtained as a bottom product, which contains pentafluoroethane and the extractant as the main component thereof, preferably a mixture containing chloropentafluoroethane at a concentration not more than 0.1 weight %, and more preferably not more than 0.01 weight %. In this case, the composition and the amount of the distillate product from the extractive distillation is not particularly limited, provided that a ratio of chloropentafluoroethane to pentafluoroethane in the bottom product is reduced by somewhat an extent than an original ratio thereof, preferably the ratio is reduced to not more than 1/10 of the original ratio, and more preferably reduced to not more than 1/100 of the original ratio. In addition, the distillate product may contain, as a main component thereof, chloropentafluoroethane or pentafluoroethane or a mixture of chloropentafluoroethane and pentafluoroethane.


REFERENCES:
patent: 5087329 (1992-02-01), Felix
patent: 5211867 (1993-05-01), Shankland et al.
patent: 5421964 (1995-06-01), Mahler et al.
patent: 6039845 (2000-03-01), Bartocchio et al.
patent: 6156161 (2000-12-01), Miller
patent: 8143486 (1996-06-01), None
patent: 8143486 (1996-06-01), None
patent: 9255597 (1997-09-01), None
patent: 9508626 (1997-09-01), None
patent: 9508626 (1997-09-01), None
patent: 9512793 (1997-12-01), None
patent: 9512793 (1997-12-01), None
patent: WO9220640 (1992-11-01), None
patent: WO9521147 (1995-08-01), None
patent: WO9527689 (1995-10-01), None
patent: WO9606063 (1996-02-01), None
Schweitzer, “Handbook of Separation Techniques for Chemical Engineers”, PP1-136 -1-138.

Affiliated with

Also associated with

Rating

Process for preparing pentafluoroethane does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Process for preparing pentafluoroethane, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for preparing pentafluoroethane will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3043513