Separating 1,1,1,3,3-pentafluoropropane from hydrogen fluoride

Details Separating 1,1,1,3,3-pentafluoropropane from hydrogen fluoride Separating 1,1,1,3,3-pentafluoropropane from hydrogen fluoride

2000-03-31

2001-10-16

Siegel, Alan (Department: 1621)

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

Organic compounds

Halogen containing

C570S180000

Reexamination Certificate

active

06303838

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to processes for separating 1,1,1,3,3-pentafluoropropane (HFC-245fa) from hydrogen fluoride (HF) by distillation, wherein hydrocarbons, chlorofluorocarbons, hydrochlorofluorocarbons and fluorocarbons are used as entraining agents.
BACKGROUND OF THE INVENTION
New regulations have been established to protect the stratospheric ozone layer from possible damage by chlorofluorocarbons (CFCs). 1,1,1,3,3-Pentafluoropropane (CF
3
CH
2
CHF
2
, HFC-245fa ) is a hydrofluorocarbon (HFC) which may be used either alone or in blends with other materials as a non-ozone depleting replacement for CFCs. HFC-245fa may be prepared by fluorinating appropriate halopropanes or propenes with hydrogen fluoride (HF). For example, HFC-245fa may be prepared by fluorinating 1-chloro-3,3,3-trifluoropropene in the presence of antimony pentachloride catalyst as is described in U.S. Pat. No. 5,616,819. The HFC-245fa product may contain a variety of impurities such as by-product hydrogen chloride (HCl) and fluorocarbon by-products, as well as unreacted chlorinated precursors and hydrogen fluoride (HF). The presence of HF in HFC-245fa product is objectionable for most uses of HFC-245fa. While most of these impurities can be removed from HFC-245fa by conventional distillation, HF is difficult to remove by conventional distillation because HF and HFC-245fa form an azeotrope. This azeotrope is disclosed in World Intellectual Property Organization publication WO 97/5,089. Due to the formation of the HF/HFC-245fa azeotrope, it is difficult, if not impossible, to completely separate HFC-245fa and HF by conventional distillation to produce streams of HFC-245fa or HF that are substantially-free of the other compound.
The use of conventional methods for removing the HF, such as scrubbing the HFC-245fa with water or in water/caustic solutions, causes loss of the utility of the HF for further reaction and incurs significant product loss due to the high solubility of HFC-245fa in water.
Where many organic compounds form an azeotrope with HF, it is sometimes possible to effect a phase separation by condensing and cooling the mixture, wherein the mixture separates into two liquid phases, one comprising increased HF concentration and the other comprising increased organic concentration relative to the HF and organic concentrations in the azeotrope. Such methods typically do not produce substantially-pure fractions of either HF or organic. Further, mixtures of HF and HFC-245fa do not exhibit such phase separation even when cooled below −25° C.
World Intellectual Property Organization publication WO 97/05089 discloses azeotropic distillation processes for separating HFC-245fa and HF. To obtain high purities and high-recovery-efficiencies of HFC-245fa and HF, these methods require distillating the HFC-245fa and HF-containing streams successively at divergent pressures, which is extremely expensive in practice. It is difficult to obtain HFC-245fa and/or HF substantially-free of the other component by such a method.
SUMMARY OF THE INVENTION
The present invention comprises processes for separating 1,1,1,3,3-pentafluoropropane (HFC-245fa) from hydrogen fluoride (HF), comprising:
contacting a first mixture comprising 1,1,1,3,3-pentafluoropropane (HFC-245fa) and hydrogen fluoride (HF) with an entraining agent to form a second mixture,
distilling the second mixture and thereby separating the 1,1,1,3,3-pentafluoropropane (HFC-245fa) from hydrogen fluoride (HF) and entraining agent, and
recovering 1,1,1,3,3-pentafluoropropane (HFC-245fa).


REFERENCES:
patent: 95/27689 (1995-10-01), None
patent: 97/03936 (1997-02-01), None
patent: 97/05089 (1997-02-01), None

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