Compositions – Fire-extinguishing
Reexamination Certificate
1998-08-20
2001-05-01
Warden, Jill (Department: 1743)
Compositions
Fire-extinguishing
C203S050000, C203S063000, C203S067000
Reexamination Certificate
active
06224781
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to azeotropic compositions of hydrogen fluoride with halogenated hydrocarbons, their production and their use in manufacturing processes for producing halogenated hydrocarbon mixtures.
BACKGROUND
Hydrofluorocarbons (HFCs), compounds containing only carbon, hydrogen and fluorine, because of their zero ozone depletion potential, are of interest as environmentally attractive alternatives for chlorofluorocarbons (i.e., CFCs) in such established uses as refrigerants, heat transfer media, foam expansion agents, aerosol propellants, solvents, fire extinguishants and power cycle working fluids, among other applications.
Hydrofluorocarbons can be obtained by reacting chlorohalocarbons with HF using various catalysts. For example CHF
2
CHF
2
(i.e., 1,1,2,2-tetrafluoroethane or HFC-134) can be prepared by reacting 1,1,2,2-tetrachloroethane with HF over a fluorination catalyst/agent in the liquid or vapor phase (see Int. Publ. No. WO 93/25506). Normally, excess HF is used to achieve relatively favorable reactor rates. HF may be removed from the halogenated hydrocarbon components of the product mixture using conventional aqueous solution scrubbing techniques. However, the production of substantial amounts of scrubbing discharge can create aqueous waste disposal concerns.
There remains a need for processes utilizing HF in such product mixtures as well as an interest in developing more efficient processes for the manufacture of hydrofluorocarbons.
SUMMARY OF THE INVENTION
This invention provides a process for producing compositions comprising (a) a compound selected from the group consisting of CHF
2
CF
3
, CHF
2
CHF
2
, CH
2
FCF
3
, CH
3
CF
3
, CH
3
CHF
2
, CH
2
FCF
2
CHF
2
and CHF
2
CF
2
CF
2
CHF
2
and (b) at least one saturated compound selected from halogenated hydrocarbons and ethers having the formula:
C
n
H
2n+2−a−b
Cl
a
F
b
O
c
wherein n is an integer from 1 to 4, a is an integer from 0 to 2n+1, b is an integer from 1 to 2n+2−a, and c is 0 or 1, provided that when c is 1 then n is an integer from 2 to 4, and provided that component (b) does not include the selected component (a) compound, wherein the molar ratio of component (b) to component (a) is between about 1:99 and a molar ratio of HF to component (a) in an azeotrope or azeotrope-like composition of component (a) with HF. This process comprises (A) combining (i) said azeotrope or azeotrope-like composition with (ii) at least one fluorination precursor compound wherein the precursor component (ii) is the fluorination precursor to component (b); and (B) reacting a sufficient amount of the HF from the azeotrope or azeotrope-like composition (i) with precursor component (ii) to provide a composition containing components (a) and (b) in said ratio.
In addition, compositions are provided comprising (a) a compound selected from the group consisting of CHF
2
CF
3
, CHF
2
CHF
2
, CH
2
FCF
3
, CH
3
CF
3
, CH
3
CHF
2
, CH
2
FCF
2
CHF
2
and CHF
2
CF
2
CF
2
CHF
2
(e.g., CHF
2
CHF
2
), and (b) at least two saturated compounds selected from halogenated hydrocarbons and ethers having the formula:
C
n
H
2n+2−a−b
Cl
a
F
b
O
c
wherein n is an integer from 1 to 4, a is an integer from 0 to 2n+1, b is an integer from 1 to 2n+2−a, and c is 0 or 1, provided that when c is 1 then n is an integer from 2 to 4, provided that component (b) does not include the selected component (a) compound, and provided that c is 1 for at least one of the component (b) compounds, wherein the molar ratio of component (b) to component (a) is between about 1:99 and a molar ratio of HF to component (a) in an azeotrope or azeotrope-like composition of component (a) with HF.
The present invention further provides a process for recovering HF from a product mixture comprising HF and CHF
2
CHF
2
. The process comprises (1) distilling the product mixture to remove all products which have a lower boiling point than the lowest boiling azeotrope containing HF and CHF
2
CHF
2
; and (2) distilling said azeotrope to recover HF as an azeotropic composition containing HF and CHF
2
CHF
2
.
Also provided are compositions which consist essentially of hydrogen fluoride in combination with an effective amount of CHF
2
CHF
2
to form an azeotrope or azeotrope-like composition with hydrogen fluoride, said composition containing from about 70.5 to 75.5 mole percent CHF
2
CHF
2
.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides compositions which consist essentially of hydrogen fluoride and an effective amount of CHF
2
CHF
2
to form an azeotropic combination with hydrogen fluoride. By effective amount is meant an amount which, when combined with HF, results in the formation of an azeotrope or azeotrope-like mixture. As recognized in the art, an azeotrope or an azeotrope-like composition is an admixture of two or more different components which, when in liquid form under given pressure, will boil at a substantially constant temperature, which temperature may be higher or lower than the boiling temperatures of the individual components, and which will provide a vapor composition essentially identical to the liquid composition undergoing boiling.
An azeotrope is a liquid mixture that exhibits a maximum or minimum boiling point relative to the boiling points of surrounding mixture compositions. An azeotrope is homogeneous if only one liquid phase is present. An azeotrope is heterogeneous if more than one liquid phase is present. Regardless, a characteristic of minimum boiling azeotropes is that the bulk liquid composition is then identical to the vapor composition in equilibrium therewith, and distillation is ineffective as a separation technique. For the purpose of this discussion, azeotrope-like composition means a composition which behaves like an azeotrope (i.e., has constant-boiling characteristics or a tendency not to fractionate upon boiling or evaporation). Thus, the composition of the vapor formed during boiling or evaporation of such compositions is the same as or substantially the same as the original liquid composition. Hence, during boiling or evaporation, the liquid composition, if it changes at all, changes only to a minimal or negligible extent. This is to be contrasted with non-azeotrope-like compositions in which during boiling or evaporation, the liquid composition changes to a substantial degree.
Accordingly, the essential features of an azeotrope or an azeotrope-like composition are that at a given pressure, the boiling point of the liquid composition is fixed and that the composition of the vapor above the boiling composition is essentially that of the boiling liquid composition (i.e., no fractionation of the components of the liquid composition takes place). It is also recognized in the art that both the boiling point and the weight percentages of each component of the azeotropic composition may change when the azeotrope or azeotrope-like liquid composition is subjected to boiling at different pressures. Thus an azeotrope or an azeotrope-like composition may be defined in terms of the unique relationship that exists among components or in terms of the compositional ranges of the components or in terms of exact weight percentages of each component of the composition characterized by a fixed boiling point at a specified pressure. It is also recognized in the art that various azeotropic compositions (including their boiling points at particular pressures) may be calculated (see, e.g., W. Schotte, Ind. Eng. Chem. Process Des. Dev. 1980, 19, pp 432-439). Experimental identification of azeotropic compositions involving the same components may be used to confirm the accuracy of such calculations and/or to modify the calculations for azeotropic compositions at the same or other temperatures and pressures.
A composition may be formed which consists essentially of azeotropic combinations of hydrogen fluoride and CHF
2
CHF
2
. This includes a composition consisting essentially of from about 24.5 to about 29.5 mole percent HF and from about 75.5 to abou
Mahler Barry A.
Rao V. N. Mallikarjuna
Sievert Allen Capron
Subramanian Munirpallam A.
Warwas Edwin James
Cross LaToya
E. I. Du Pont de Nemours and Company
Warden Jill
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