Azeotropic mixture of 1,1-difluoroethane and hydrogen fluoride a

Details Azeotropic mixture of 1,1-difluoroethane and hydrogen fluoride a Azeotropic mixture of 1,1-difluoroethane and hydrogen fluoride a

1995-09-29

1998-12-08

Manoharan, Virginia

Distillation: processes, separatory

Adding material to distilland except water or steam per se

Organic compound

203 91, 252 67, 252DIG9, 423488, 570178, B01D 336, C07C 17383

Patent

active

058463887

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to an azeotropic mixture of 1,1-difluoroethane (which is, hereinafter, also referred to as "HFC152a") and hydrogen fluoride (which is, hereinafter, also referred to as "HF") and a production process of HFC152a comprising a step of recovering, from a mixture comprising HFC152a and HF, one component of HFC152a and HF which is substantially free from the other component of HFC152a and HF.


BACKGROUND OF THE INVENTION

HFC152a has been noteworthy as a substitute for 1-chloro-1,1-difluoromethane and it is useful as, for example, a foaming agent.
HFC152a is generally produced by reacting a chlorinated carbon such as vinyl chloride with HF in the presence of a catalyst in a vapor or liquid phase. During this reaction process, HF which has not been reacted remains in a reaction product.
As a manner to separate HF from the reaction product, a process has been hitherto used in which a mixture comprising a reaction product such as HFC152a and unreacted feed materials such as HF is washed with an aqueous phase to remove HF. However, such process requires a large amount of an alkali which is to be used for neutralization of the washing aqueous phase, and a waste from the neutralization has to be treated. Thus, such a process is not so useful.
It is, therefore, desirable to provide a production process of HFC152a comprising a step wherein HF which does not contain HFC152a or HFC152a which does not contain HF is more effectively recovered from a mixture comprising HF and HFC152a.


BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a flow sheet of one embodiment of a process for the production of 1,1-difluorochloroethane in which the process according to the present invention is adopted.


DETAILED DESCRIPTION OF THE INVENTION

The inventors have made extensive studies on a separation process of HF from a mixture comprising at least HF and HFC152a and found that HFC152a and HF forms a minimum azeotropic mixture and that the above problem is solved by utilizing the azeotropic mixture.
In the first aspect, the present invention, therefore, provides an azeotropic mixture consisting essentially of HFC152a and HF. This azeotropic mixture can be used as a reflux stream for a distillation operation which separates HF or HFC152a from a mixture comprising HFC152a and HF. That is, by subjecting the mixture comprising HFC152a and HF to the distillation operation, distilling off such an azeotropic mixture from a top of a distillation column as a distillate and returning a portion of the distillate to the distillation column, HF or HFC152a is effectively separated and removed from the mixture so that HFC152a which does not contain HF or HF which does not contain HFC152a can be recovered as a bottom product.
As described above, there is formed a (minimum) azeotropic mixture in a two component system of HFC152a and HF. Such an azeotropic mixture has been firstly found by the present inventors.
The above finding is based on observations that when a mixture of HFC152a and HF is subjected to a distillation operation under, for example, an atmospheric pressure, HFC152a cannot be further concentrated above an HFC152a/HF molar ratio of about 88/12. In other words, a composition of a liquid phase in such a state is the same as that of a vapor phase which is equilibrium with the liquid phase.
This azeotropic mixture has a boiling point of -45.degree. C. at a pressure of 0.5 kg/cm.sup.2 -abs. and a composition of the mixture is about 15 mol % of HF and about 85 mol % of HFC152a. The azeotropic mixture has an azeotropic boiling point of -28.degree. C. at an atmospheric pressure and an azeotropic composition of the mixture is about 12 mol % of HF and about 88 mol % of HFC152a. The azeotropic mixture has an azeotropic boiling point of about 45.degree. C. at a pressure of 10 kg/cm.sup.2 -abs. and an azeotropic composition of the mixture is about 10 mol % of HF and about 90 mol % of HFC152a. The azeotropic mixture has an azeotropic boiling point of about 90.degree. C. at a pressure of 30 kg/cm.sup.2

REFERENCES:
patent: 4818513 (1989-04-01), Trager et al.
patent: 4944846 (1990-07-01), Manzer et al.
patent: 5196616 (1993-03-01), Lee et al.
patent: 5211817 (1993-05-01), Adams et al.
patent: 5523015 (1996-06-01), Tsuda et al.
patent: 5560899 (1996-10-01), Solinas et al.
patent: 5626725 (1997-05-01), Balthasart et al.

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