U.S. patent application number 13/163790 was filed with the patent office on 2012-06-28 for process for the separation of fluorocarbons using ionic liquids.
This patent application is currently assigned to E. I. DU PONT DE NEMOURS AND COMPANY. Invention is credited to JEFFREY P. KNAPP, MARK BRANDON SHIFLETT, AKIMICHI YOKOZEKI.
Application Number | 20120165579 13/163790 |
Document ID | / |
Family ID | 39926484 |
Filed Date | 2012-06-28 |
United States Patent
Application |
20120165579 |
Kind Code |
A1 |
SHIFLETT; MARK BRANDON ; et
al. |
June 28, 2012 |
PROCESS FOR THE SEPARATION OF FLUOROCARBONS USING IONIC LIQUIDS
Abstract
This invention relates to a process for separating
1,1,2,2-tetrafluoroethane or 1,1,1,2-tetrafluoroethane from a
mixture comprising both 1,1,1,2-tetrafluoroethane and
1,1,2,2-tetrafluoroethane wherein at least one ionic liquid is used
to enhance the efficiency of the separation.
Inventors: |
SHIFLETT; MARK BRANDON;
(WILMINGTON, DE) ; YOKOZEKI; AKIMICHI;
(WILMINGTON, DE) ; KNAPP; JEFFREY P.; (WILMINGTON,
DE) |
Assignee: |
E. I. DU PONT DE NEMOURS AND
COMPANY
Wilmington
DE
|
Family ID: |
39926484 |
Appl. No.: |
13/163790 |
Filed: |
June 20, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12124441 |
May 21, 2008 |
7964760 |
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13163790 |
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60940292 |
May 25, 2007 |
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Current U.S.
Class: |
570/180 |
Current CPC
Class: |
C07C 17/386 20130101;
C07C 17/386 20130101; C07C 19/08 20130101 |
Class at
Publication: |
570/180 |
International
Class: |
C07C 17/38 20060101
C07C017/38 |
Claims
1. A process for separating 1,1,2,2-tetrafluoroethane or
1,1,1,2-tetrafluoroethane from a mixture comprising
1,1,2,2-tetrafluoroethane and 1,1,1,2-tetrafluoroethane, comprising
(a) contacting the mixture with at least one ionic liquid in which
1,1,1,2-tetrafluoroethane is soluble to a greater extent than
1,1,2,2-tetrafluoroethane and separating 1,1,2,2-tetrafluoroethane
from the mixture; or (b) contacting the mixture with at least one
ionic liquid in which 1,1,2,2-tetrafluoroethane is soluble to a
greater extent than 1,1,1,2-tetrafluoroethane and separating
1,1,1,2-tetrafluoroethane from the mixture; wherein an ionic liquid
comprises a fluorinated cation, or a fluorinated anion, or both a
fluorinated cation and a fluorinated anion.
2. A process according to claim 1 wherein 1,1,1,2-tetrafluoroethane
is soluble in an ionic liquid to a greater extent than
1,1,2,2-tetrafluoroethane.
3. A process according to claim 1 wherein 1,1,2,2-tetrafluoroethane
is soluble in an ionic liquid to a greater extent than
1,1,1,2-tetrafluoroethane.
4. A process according to claim 1 wherein an ionic liquid comprises
a cation selected from the group consisting of the following eleven
cations: ##STR00002## wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4,
R.sup.5 and R.sup.6 are independently selected from the group
consisting of: (i) H; (ii) halogen; (iii) --CH.sub.3,
--C.sub.2H.sub.5, or C.sub.3 to C.sub.25 straight-chain, branched
or cyclic alkane or alkene, optionally substituted with at least
one member selected from the group consisting of Cl, Br, F, I, OH,
NH.sub.2 and SH; (iv) --CH.sub.3, --C.sub.2H.sub.5, or C.sub.3 to
C.sub.25 straight-chain, branched or cyclic alkane or alkene
comprising one to three heteroatoms selected from the group
consisting of O, N, Si and S, and optionally substituted with at
least one member selected from the group consisting of Cl, Br, F,
I, OH, NH.sub.2 and SH; (v) C.sub.6 to C.sub.20 unsubstituted aryl,
or C.sub.3 to C.sub.25 unsubstituted heteroaryl having one to three
heteroatoms independently selected from the group consisting of O,
N, Si and S; and (vi) C.sub.6 to C.sub.25 substituted aryl, or
C.sub.3 to C.sub.25 substituted heteroaryl having one to three
heteroatoms independently selected from the group consisting of O,
N, Si and S; and wherein said substituted aryl or substituted
heteroaryl has one to three substituents independently selected
from the group consisting of: (1) --CH.sub.3, --C.sub.2H.sub.5, or
C.sub.3 to C.sub.25 straight-chain, branched or cyclic alkane or
alkene, optionally substituted with at least one member selected
from the group consisting of Cl, Br, F I, OH, NH.sub.2 and SH, (2)
OH, (3) NH.sub.2, and (4) SH; R.sup.7, R.sup.8, R.sup.9 and
R.sup.10 are independently selected from the group consisting of:
(vii) --CH.sub.3, --C.sub.2H.sub.5, or C.sub.3 to C.sub.25
straight-chain, branched or cyclic alkane or alkene, optionally
substituted with at least one member selected from the group
consisting of Cl, Br, F, I, OH, NH.sub.2 and SH; (viii) --CH.sub.3,
--C.sub.2H.sub.5, or C.sub.3 to C.sub.25 straight-chain, branched
or cyclic alkane or alkene comprising one to three heteroatoms
selected from the group consisting of O, N, Si and S, and
optionally substituted with at least one member selected from the
group consisting of Cl, Br, F, I, OH, NH.sub.2 and SH; (ix) C.sub.6
to C.sub.25 unsubstituted aryl, or C.sub.3 to C.sub.25
unsubstituted heteroaryl having one to three heteroatoms
independently selected from the group consisting of O, N, Si and S;
and (x) C.sub.6 to C.sub.25 substituted aryl, or C.sub.3 to
C.sub.25 substituted heteroaryl having one to three heteroatoms
independently selected from the group consisting of O, N, Si and S;
and wherein said substituted aryl or substituted heteroaryl has one
to three substituents independently selected from the group
consisting of: (1) --CH.sub.3, --C.sub.2H.sub.5, or C.sub.3 to
C.sub.25 straight-chain, branched or cyclic alkane or alkene,
optionally substituted with at least one member selected from the
group consisting of Cl, Br, F, I, OH, NH.sub.2 and SH, (2) OH, (3)
NH.sub.2, and (4) SH; and wherein, optionally, at least two of
R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7,
R.sup.8, R.sup.9 and R.sup.10 together form a cyclic or bicyclic
alkanyl or alkenyl group.
5. A process according to claim 4 wherein at least one of R.sup.1,
R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8,
R.sup.9, and R.sup.10 comprises F--.
6. A process according to claim 1 wherein an ionic liquid comprises
an anion selected from the group consisting of
[CH.sub.3CO.sub.2].sup.-, [HSO.sub.4].sup.-,
[CH.sub.3OSO.sub.3].sup.-, [C.sub.2H.sub.5OSO.sub.3].sup.-,
[AlCl.sub.4].sup.-, [CO.sub.3].sup.2-, [HCO.sub.3].sup.-,
[NO.sub.2].sup.-, [NO.sub.3].sup.-, [SO.sub.4].sup.2-,
[PO.sub.4].sup.3-, [HPO.sub.4].sup.2-, [H.sub.2PO.sub.4].sup.-,
[HSO.sub.3].sup.-, [CuCl.sub.2].sup.-, Cl.sup.-, Br.sup.-, I.sup.-,
SCN.sup.-, and any fluorinated anion.
7. A process according to claim 1 wherein an ionic liquid comprises
an anion selected from the group consisting of [BF.sub.4].sup.-,
[BF.sub.3CF.sub.3].sup.-, [BF.sub.3C.sub.2F.sub.5].sup.-,
[PF.sub.6].sup.-, [PF.sub.3(C.sub.2F.sub.5).sub.3].sup.-,
[SbF.sub.6].sup.-, [CF.sub.3SO.sub.3].sup.-,
[HCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3HFCCF.sub.2SO.sub.3].sup.-, [HCClFCF.sub.2SO.sub.3].sup.-,
[(CF.sub.3SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3SO.sub.2).sub.3C].sup.-, [CF.sub.3CO.sub.2].sup.-,
[CF.sub.3OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CFHOCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2HCF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2ICF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[(CF.sub.2HCF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CFHCF.sub.2SO.sub.2).sub.2N].sup.-, and F.sup.-.
8. A process according to claim 1 wherein an ionic liquid comprises
a cation selected from the group consisting of imidazolium and
pyridinium ions, and an anion selected from the group consisting of
[BF.sub.4].sup.-, [BF.sub.3CF.sub.3].sup.-,
[BF.sub.3C.sub.2F.sub.5].sup.-, [PF.sub.6].sup.-,
[PF.sub.3(C.sub.2F.sub.5).sub.3].sup.-, [SbF.sub.6].sup.-,
[CF.sub.3SO.sub.3].sup.-, [HCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3HFCCF.sub.2SO.sub.3].sup.-, [HCClFCF.sub.2SO.sub.3].sup.-,
[(CF.sub.3SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3SO.sub.2).sub.3C].sup.-, [CF.sub.3CO.sub.2].sup.-,
[CF.sub.3OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CFHOCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2HCF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2ICF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[(CF.sub.2HCF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CFHCF.sub.2SO.sub.2).sub.2N].sup.- and
[CH.sub.3OSO.sub.3].sup.-.
9. A process according to claim 1 wherein an ionic liquid comprises
a 1-butyl-3-methylimidazolium cation, and an anion selected from
the group consisting of [BF.sub.4].sup.-, [BF.sub.3CF.sub.3].sup.-,
[BF.sub.3C.sub.2F.sub.5].sup.-, [PF.sub.6].sup.-,
[PF.sub.3(C.sub.2F.sub.5).sub.3].sup.-, [SbF.sub.6].sup.-,
[CF.sub.3SO.sub.3].sup.-, [HCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3HFCCF.sub.2SO.sub.3].sup.-, [HCClFCF.sub.2SO.sub.3].sup.-,
[(CF.sub.3SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3SO.sub.2).sub.3C].sup.-, [CF.sub.3CO.sub.2].sup.-,
[CF.sub.3OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CFHOCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2HCF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2ICF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[(CF.sub.2HCF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CFHCF.sub.2SO.sub.2).sub.2N].sup.-.
10. A process according to claim 1 wherein an ionic liquid
comprises a 1-ethyl-3-methylimidazolium cation, and an anion
selected from the group consisting of [BF.sub.4].sup.-,
[BF.sub.3CF.sub.3].sup.-, [BF.sub.3C.sub.2F.sub.5].sup.-,
[PF.sub.6].sup.-, [PF.sub.3(C.sub.2F.sub.5).sub.3].sup.-,
[SbF.sub.6].sup.-, [CF.sub.3SO.sub.3].sup.-,
[HCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3HFCCF.sub.2SO.sub.3].sup.-, [HCClFCF.sub.2SO.sub.3].sup.-,
[(CF.sub.3SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3SO.sub.2).sub.3C].sup.-, and [CF.sub.3CO.sub.2].sup.-,
[CF.sub.3OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CFHOCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2HCF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2ICF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[(CF.sub.2HCF.sub.2SO.sub.2).sub.2N].sup.-, and
[(CF.sub.3CFHCF.sub.2SO.sub.2).sub.2N].sup.-.
11. A process according to claim 1 wherein an ionic liquid
comprises a 1-ethyl-3-methylimidazolium cation, and an anion
selected from the group consisting of
[(CF.sub.3CF.sub.2SO.sub.2).sub.2N].sup.-, [PF.sub.6].sup.-, and
[HCF.sub.2CF.sub.2SO.sub.3].sup.-.
12. A process according to claim 1 wherein an ionic liquid
comprises a 1,3-dimethylimidazolium cation, and an anion selected
from the group consisting of [BF.sub.4].sup.-,
[BF.sub.3CF.sub.3].sup.-, [BF.sub.3C.sub.2F.sub.5].sup.-,
[PF.sub.6].sup.-, [PF.sub.3(C.sub.2F.sub.5).sub.3].sup.-,
[SbF.sub.6].sup.-, [CF.sub.3SO.sub.3].sup.-,
[HCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3HFCCF.sub.2SO.sub.3].sup.-, [HCClFCF.sub.2SO.sub.3].sup.-,
[(CF.sub.3SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3SO.sub.2).sub.3C].sup.-, and [CF.sub.3CO.sub.2].sup.-,
[CF.sub.3OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CFHOCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2HCF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2ICF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[(CF.sub.2HCF.sub.2SO.sub.2).sub.2N].sup.-, and
[(CF.sub.3CFHCF.sub.2SO.sub.2).sub.2N].sup.-.
13. A process according to claim 1 wherein an ionic liquid
comprises a 3-methyl-1propylpyridinium cation, and a
[(CF.sub.3SO.sub.2).sub.2N].sup.- anion.
14. A process according to claim 1 wherein an ionic liquid
comprises a 1-hexyl-3-methylimidazolium cation, and a
[PF.sub.3(C.sub.2F.sub.5).sub.3].sup.- anion.
15. A process according to claim 1 which is performed in a
distillation column.
16. A process according to claim 15 wherein an ionic liquid is fed
to the column as an extractant and contacts the mixture in the
column.
17. A process according to claim 15 wherein
1,1,2,2-tetrafluoroethane exits the top of the column as a
vapor.
18. A process according to claim 15 wherein
1,1,1,2-tetrafluoroethane exits the top of the column as a
vapor.
19. A process according to claim 15 wherein the ratio of the moles
of ionic liquid fed to the column to the moles of mixture to be
separated fed to the column is in the range of from about 0.1 to
about 25.
20. A process according to claim 15 wherein an ionic liquid is
recovered from the column bottoms and is recycled to the column.
Description
[0001] This application is a continuation of and claims the benefit
of U.S. application Ser. No. 12/124,441, filed 21 May 2008, which
claimed the benefit of U.S. Provisional Application No. 60/940,292,
filed 25 May 2007, each of which is by this reference incorporated
in its entirety as a part hereof for all purposes.
TECHNICAL FIELD
[0002] This invention relates to a process for separating various
isomers of a compound that are contained together in the same
mixture. In particular, this invention relates to a process for
separating 1,1,2,2-tetrafluoroethane or 1,1,1,2-tetrafluoroethane
from a mixture containing both 1,1,1,2-tetrafluoroethane and
1,1,2,2-tetrafluoroethane wherein at least one ionic liquid is used
to enhance the efficiency of the separation.
BACKGROUND
[0003] 1,1,1,2-Tetrafluoroethane, CF.sub.3CH.sub.2F (also known as
HFC-134a, F-134a, or R-134a), can be used as a refrigerant, an
aerosol propellant, a heat transfer medium, a gaseous dielectric, a
fire extingushing agent, an expansion agent for polyolefins and
polyurethanes, a fluid for absorption cooling systems, and a power
cycle working fluid. R-134a is nonflammable, has no ozone depletion
potential, and has low global warming potential. It is therefore
suited as a replacement for chlorine-containing gases, such as
chlorofluorocarbons and hydrochlorofluorocarbons, that are believed
to be involved in ozone depletion.
[0004] Depending on the operating conditions under which R-134a is
made, 1,1,2,2-tetrafluoroethane, CHF.sub.2CHF.sub.2 (also known as
HFC-134, F-134, or R-134), can also be made as a product of the
synthesis. R-134 and R-134a may be obtained from a variety of
different manufacturing processes or sources. For example, a
mixture containing R-134 and R-134a can be produced by reacting a
mixture containing CF.sub.3CCl.sub.3 (R-113a) and
CCl.sub.2FCClF.sub.2 (R-113) with hydrogen fluoride to produce a
mixture containing CCl.sub.2FCF.sub.3 (R-114a) and
CClF.sub.2CClF.sub.2 (R-114). The mixture containing R-114a and
R-114 is then hydrogenated under appropriate conditions to produce
a mixture of R-134a and R-134. This mixture containing R-134a and
R-134 can also contain impurities, such as CClHFCF.sub.3 (R-124),
CHF.sub.2CClF.sub.2 (R-124a) and unreacted R-114 and R-114a.
[0005] R-134 is also useful as a refrigerant, and for other
applications as described above for R-134a. R-134 and R-134a are,
however, difficult to separate because they have similar boiling
points--the normal boiling point of R-134 being -19.6.degree. C.
and the normal boiling point of R-134a being -26.1.degree. C. These
close boiling points make efficient separation of R-134 and R-134
by conventional distillation extremely difficult because of the
tendency of those components to form an azeotrope, azeotropic
composition or an azeotrope-like composition in a mixture. In order
to achieve separation by conventional distillation, impracticably
tall columns would have to be operated at high reflux ratios, which
would likely result in high capital and operating costs, and
possibly also in substantial yield loss of the product.
[0006] U.S. Pat. No. 5,470,442 discloses a method for separating
R-134 and R-134a from each other, and/or from fluorocarbon
impurities, by extractive distillation where an alcohol is used as
the extractive agent. U.S. application Ser. No. 11/525,466, which
by this reference is incorporated in its entirety as a part hereof
for all purposes, describes the use of ionic liquids in separation
processes to separate components of mixtures. Despite these
existing separation processes, a need still remains for a
separation process better suited to the objective of separating
R-134 and R-134a from each other.
SUMMARY
[0007] In one embodiment, this invention relates to a process for
separating 1,1,2,2-tetrafluoroethane from a mixture that contains
both 1,1,2,2-tetrafluoroethane and 1,1,1,2-tetrafluoroethane, by
contacting the mixture with at least one ionic liquid in which
1,1,1,2-tetrafluoroethane is soluble to a greater extent than
1,1,2,2-tetrafluoroethane and separating 1,1,2,2-tetrafluoroethane
from the mixture.
[0008] In another embodiment, this invention relates to a process
for separating 1,1,1,2-tetrafluoroethane from a mixture that
contains both 1,1,2,2-tetrafluoroethane and
1,1,1,2-tetrafluoroethane, by contacting the mixture with at least
one ionic liquid in which 1,1,2,2-tetrafluoroethane is soluble to a
greater extent than 1,1,1,2-tetrafluoroethane and separating
1,1,1,2-tetrafluoroethane from the mixture.
[0009] In a further embodiment, the processes of this invention may
be conveniently performed by contacting the mixture of
1,1,2,2-tetrafluoroethane and 1,1,1,2-tetrafluoroethane with an
ionic liquid in a distillation column.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 shows a process schematic of an extractive
distillation process.
[0011] FIG. 2 shows a process schematic of an extractive
distillation process.
DETAILED DESCRIPTION
[0012] This invention relates to a process for separating either
1,1,2,2-tetrafluoroethane (R-134) or 1,1,1,2-tetrafluoroethane
(R-134a) from a mixture that contains both isomers of the compound,
wherein at least one ionic liquid is used to increase the
efficiency of the separation. An ionic liquid is well suited for
use for this purpose since it exhibits negliglible volatility and
is not flammable. If R-134 is to be separated from the mixture, the
mixture of R-134 and R-134a is contacted with at least one ionic
liquid in which R-134a is soluble to a greater extent than R-134,
and R-134 is then separated from the mixture. Conversely, if R-134a
is to be separated from the mixture, the mixture of R-134 and
R-134a is contacted with at least one ionic liquid in which R-134
is soluble to a greater extent than R-134a, and R-134a is then
separated from the mixture.
[0013] In the description of this invention, the following
definitional structure is provided for certain terminology as
employed variously in the specification:
[0014] An "alkane" or "alkane compound" is a saturated hydrocarbon
compound that has the general formula C.sub.nH.sub.2n+2, and that
may be a straight-chain, branched or cyclic compound.
[0015] An "alkene" or "alkene compound" is an unsaturated
hydrocarbon compound that contains one or more carbon-carbon double
bonds, and that may be a straight-chain, branched or cyclic
compound. An alkene requires a minimum of two carbons. A cyclic
compound requires a minimum of three carbons.
[0016] An "aromatic" or "aromatic compound" includes benzene and
compounds that resemble benzene in chemical behavior.
[0017] An "azeotrope" or "azeotropic composition" is a
constant-boiling mixture of two or more substances that behaves as
a single substance with respect to the fact that the vapor produced
by partial evaporation or distillation of the liquid of the
azeotrope has the same composition as the liquid from which it is
evaporated or distilled, i.e. the mixture distills/refluxes without
compositional change. Constant-boiling compositions are
characterized as azeotropic because they exhibit either a maximum
or minimum boiling point as compared with that of the
non-azeotropic mixture of the same components. Azeotropic
compositions are also characterized by a minimum or a maximum in
the vapor pressure relative to the vapor pressure as a function of
composition at a constant temperature.
[0018] An "azeotrope-like composition" is a composition that has a
constant-boiling characteristic, or a tendency not to fractionate
upon boiling or evaporation. Therefore, the composition of the
vapor formed is the same as, or substantially the same as, the
original liquid composition. During boiling or evaporation, the
liquid composition, if it changes at all, changes to only a minimal
or negligible extent. An azeotrope-like composition can also be
characterized by the area that is adjacent to the maximum or
minimum vapor pressure in a plot of composition vapor pressure at a
given temperature as a function of mole fraction of components in
the composition. A composition is azeotrope-like if, after about 50
weight percent of an original composition is evaporated or boiled
off to produce a remaining composition, the change between the
original composition and the remaining composition is no more than
about 6 weight %, and often is no more than about 3 weight %,
relative to the original composition.
[0019] An azeptrope, azeotropic composition or azeotrope-like
composition may also be characterized as a close-boiling,
substantially constant-boiling or constant-boiling mixture that may
appear under many guises, depending upon the existing conditions,
as illustrated by the manner in which the following factors may
apply: [0020] 1) At different pressures, the compositional content
of these kinds of mixture will vary to at least some degree, as
will the boiling point temperature. Thus, such a mixture represents
a unique type of relationship between the components thereof, but
will typically have variable compositional content, which depends
on temperature and/or pressure. Therefore, ranges of compositional
content, rather than a fixed compositional content, are often used
to define such a mixture. [0021] 2) These kinds of mixtures can be
characterized by a boiling point at a given pressure rather than by
a specific compositional content, the determination of which is
limited by, and is only accurate as, the analytical equipment
available to make the determination. [0022] 3) Both the boiling
point and the weight (or mole) percent content of each component in
these kinds of mixtures may change when the mixture is allowed to
boil at different pressures. Thus, such a mixture may be defined in
terms of the unique relationship that exists among the components
thereof, or in terms of the exact weight (or mole) percentages of
each component therein in terms of a fixed boiling point at a
specific pressure.
[0023] An "extractant" is a compound such as a solvent that, when
added to a mixture, interacts with the components of that mixture
in a way that changes the relative volatilities of at least two of
the components such that those components may then be more easily
separated from each other. An extractant, when used herein, is used
in an "effective amount", which is an amount that, when added to a
mixture of components, causes the volatility of one component to
increase relative to the volatility of the other component to allow
the separation of the more volatile component from the mixture.
[0024] "Extractive distillation" is a process in which an
extractant is added to the components of a mixture, such as an
azeptrope, azeotropic composition or azeotrope-like composition, to
facilitate the separation of the components thereof. The extractant
interacts selectively with (but does not react with) one or more
components within the mixture, and is typically introduced at an
upper feed point of a distillation column, while the mixture
requiring separation is introduced at the same, or preferably a
relatively lower, feed point of the column than the extractant. The
extractant passes downwardly through trays or packing located in
the column and exits the column bottoms with one or more components
of the mixture to be separated. While in the presence of the
extractant, at least one of the components to be separated becomes
relatively more volatile compared to the other components of the
mixture, and the more volatile component of the initial mixture
exits the column overhead.
[0025] A "fluorinated ionic liquid" is an ionic liquid having at
least one fluorine on either the cation or the anion. A
"fluorinated cation" or "fluorinated anion" is a cation or anion,
respectively, comprising at least one fluorine.
[0026] A "fluorocarbon" or "fluorocarbon compound" is a compound
comprising fluorine and carbon. A fluorocarbon or fluorocarbon
compound may contain other atoms, such as chlorine or hydrogen.
[0027] A "high-boiling azeotrope" is an azeotrope, azeotropic
composition or azeotrope-like composition that boils at a higher
temperature at any given pressure than any one of the components
therein would boil separately at that pressure. A high-boiling
azeotrope may also be any azeotrope, azeotropic composition or
azeotrope-like composition that has a lower vapor pressure at any
given temperature than any one of the components therein would have
separately at that temperature.
[0028] A "hydrofluorocarbon" or "hydrofluorocarbon compound" is a
compound comprising fluorine, carbon, and at least one hydrogen
atom.
[0029] A "halogen" is bromine, iodine, chlorine or fluorine
atom.
[0030] A "heteroaryl" group is an aromatic group having a
heteroatom.
[0031] A "heteroatom" is an atom other than carbon in the structure
of an alkanyl, alkenyl or aromatic compound.
[0032] An "impurity" is a compound other than R-134 or R-134a in a
mixture that contains R-134 and R-134a.
[0033] A "low-boiling-azeotrope" is an azeotrope, azeotropic
composition or azeotrope-like composition that boils at a lower
temperature at any given pressure than any one of the components
therein would boil separately at that pressure. A low-boiling
azeotrope may also be any azeotrope, azeotropic composition or
azeotrope-like composition that has a higher vapor pressure at any
given temperature than the vapor pressure of any one of the
components therein would have separately at that temperature.
[0034] "Optionally substituted with at least one member selected
from the group consisting of", when referring to an alkane, alkene,
alkoxy, fluoroalkoxy, perfluoroalkoxy, fluoroalkyl, perfluoroalkyl,
aromatic or heteroaryl radical or moiety, means that one or more
hydrogens on a carbon chain of the radical or moiety may be
independently substituted with one or more of the members of a
recited group of substituents. For example, a substituted
--C.sub.2H.sub.5 radical or moiety may, without limitation, be
--CF.sub.2CF.sub.3, --CH.sub.2CH.sub.2OH or --CF.sub.2CF.sub.2I
where the group or substituents consist of F, I and OH.
[0035] "Selectivity", .varies..sub.ij, with respect to components i
and j in a mixture, is the ratio of the infinite dilution activity
coefficient of component i to the infinite dilution activity
coefficient of component j, component i and j being present at an
infinite degree of dilution in the mixture as subjected to a
separation process.
[0036] "Separating" or "to separate" refers to the removal of one
or more components from a mixture. In various embodiments,
separating or to separate may refer to the partial or complete
removal of one or more components from a mixture. If purification
is required, a series of separation steps may be required to
achieve complete removal of a component. Subsequent separation
steps, like initial separation steps, may be performed, for
example, by processes such as distillation, gas stripping,
chromatography and/or evaporation.
[0037] A "vacuum" is a pressure less than 1 bar but greater than
10.sup.-4 bar for practical use in extractive distillation
equipment.
[0038] Because of their tendency to form an azeotrope, azeotropic
composition or an azeotrope-like composition, R-134 and R-134a are
extremely difficult to separate. An ionic liquid is therefore used
to increase the efficiency of the separation of thosc components
from a mixture thereof. An ionic liquid suitable for use herein to
increase the efficiency of the separation of a mixture containing
both R-134 and R-134a can in principle be any ionic liquid in which
R-134 is more soluble than R-134a, or in which R-134a is more
soluble than R-134. Preferably, to maximize separation efficiency,
the ionic liquid should have high solubility for one of these two
mixture components, thereby allowing for high-efficiency separation
of the two components.
[0039] An ionic liquid, or a mixture of two or more thereof, may be
used in a process hereof to facilitate the separation of R-134 and
R-134a in a mixture thereof. Ionic liquids are organic compounds
that are liquid at room temperature (approximately 25.degree. C.).
They differ from most salts in that they have very low melting
points, and they generally tend to be liquid over a wide
temperature range. They also generally tend to not be soluble in
non-polar hydrocarbons; to be immiscible with water (depending on
the anion); and to be highly ionizing (but have a low dielectric
strength). Ionic liquids have essentially no vapor pressure, most
are air and water stable, and they can either be neutral, acidic or
basic.
[0040] A cation or anion of an ionic liquid useful herein can in
principle be any cation or anion such that the cation and anion
together form an organic salt that is liquid at or below about
100.degree. C. The properties of an ionic liquid can, however, be
tailored by varying the identity of the cation and/or anion. For
example, the acidity of an ionic liquid can be adjusted by varying
the molar equivalents and type and combinations of Lewis acids
used.
[0041] Many ionic liquids are formed by reacting a
nitrogen-containing heterocyclic ring, preferably a heteroaromatic
ring, with an alkylating agent (for example, an alkyl halide) to
form a quaternary ammonium salt, and performing ion exchange or
other suitable reactions with various Lewis acids or their
conjugate bases to form the ionic liquid. Examples of suitable
heteroaromatic rings include substituted pyridines, imidazole,
substituted imidazole, pyrrole and substituted pyrroles. These
rings can be alkylated with virtually any straight, branched or
cyclic C.sub.1-20 alkyl group, but preferably, the alkyl groups are
C.sub.1-16 groups, since groups larger than this may produce low
melting solids rather than ionic liquids. Various
triarylphosphines, thioethers and cyclic and non-cyclic quaternary
ammonium salts may also been used for this purpose. Counterions
that may be used include chloroaluminate, bromoaluminate, gallium
chloride, tetrafluoroborate, tetrachloroborate,
hexafluorophosphate, nitrate, trifluoromethane sulfonate,
methylsulfonate, p-toluenesulfonate, hexafluoroantimonate,
hexafluoroarsenate, tetrachloroaluminate, tetrabromoaluminate,
perchlorate, hydroxide anion, copper dichloride anion, iron
trichloride anion, zinc trichloride anion, as well as various
lanthanum, potassium, lithium, nickel, cobalt, manganese, and other
metal-containing anions.
[0042] Ionic liquids may also be synthesized by salt metathesis, by
an acid-base neutralization reaction or by quaternizing a selected
nitrogen-containing compound; or they may be obtained commercially
from several companies such as Merck (Darmstadt, Germany) or BASF
(Mount Olive, N.J.).
[0043] Representative examples of useful ionic liquids are
described in sources such as J. Chem. Tech. Biotechnol., 68:351-356
(1997); Chem. Ind., 68:249-263 (1996); J. Phys. Condensed Matter,
5: (supp 34B):B99-B106 (1993); Chemical and Engineering News, Mar.
30, 1998, 32-37; J. Mater. Chem., 8:2627-2636 (1998); Chem. Rev.,
99:2071-2084 (1999); and US 2004/0133058 (which is incorporated as
a part hereof). In one embodiment hereof, a library, i.e. a
combinatorial library, of ionic liquids may be prepared, for
example, by preparing various alkyl derivatives of a particular
cation (such as the quaternary ammonium cation), and varying the
associated anions.
[0044] In various different embodiments of this invention, an ionic
liquid suitable for use may have a cation selected from those shown
in the following formulae:
##STR00001##
wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are
independently selected from the group consisting of: [0045] (i) H;
[0046] (ii) halogen; [0047] (iii) --CH.sub.3, --C.sub.2H.sub.5, or
C.sub.3 to C.sub.25 straight-chain, branched or cyclic alkane or
alkene, optionally substituted with at least one member selected
from the group consisting of Cl, Br, F, I, OH, NH.sub.2 and SH;
[0048] (iv) --CH.sub.3, --C.sub.2H.sub.5, or C.sub.3 to C.sub.25
straight-chain, branched or cyclic alkane or alkene comprising one
to three heteroatoms selected from the group consisting of O, N, Si
and S, and optionally substituted with at least one member selected
from the group consisting of Cl, Br, F, I, OH, NH.sub.2 and SH;
[0049] (v) C.sub.6 to C.sub.20 unsubstituted aryl, or C.sub.3 to
C.sub.25 unsubstituted heteroaryl having one to three heteroatoms
independently selected from the group consisting of O, N, Si and S;
and [0050] (vi) C.sub.6 to C.sub.25 substituted aryl, or C.sub.3 to
C.sub.25 substituted heteroaryl having one to three heteroatoms
independently selected from the group consisting of O, N, Si and S;
and wherein said substituted aryl or substituted heteroaryl has one
to three substituents independently selected from the group
consisting of: [0051] (1) --CH.sub.3, --C.sub.2H.sub.5, or C.sub.3
to C.sub.25 straight-chain, branched or cyclic alkane or alkene,
optionally substituted with at least one member selected from the
group consisting of Cl, Br, F I, OH, NH.sub.2 and SH, [0052] (2)
OH, [0053] (3) NH.sub.2, and [0054] (4) SH; R.sup.7, R.sup.8,
R.sup.9 and R.sup.10 are independently selected from the group
consisting of: [0055] (vii) --CH.sub.3, --C.sub.2H.sub.5, or
C.sub.3 to C.sub.25 straight-chain, branched or cyclic alkane or
alkene, optionally substituted with at least one member selected
from the group consisting of Cl, Br, F, I, OH, NH.sub.2 and SH;
[0056] (viii) --CH.sub.3, --C.sub.2H.sub.5, or C.sub.3 to C.sub.25
straight-chain, branched or cyclic alkane or alkene comprising one
to three heteroatoms selected from the group consisting of O, N, Si
and S, and optionally substituted with at least one member selected
from the group consisting of Cl, Br, F, I, OH, NH.sub.2 and SH;
[0057] (ix) C.sub.6 to C.sub.25 unsubstituted aryl, or C.sub.3 to
C.sub.25 unsubstituted heteroaryl having one to three heteroatoms
independently selected from the group consisting of O, N, Si and S;
and [0058] (x) C.sub.6 to C.sub.25 substituted aryl, or C.sub.3 to
C.sub.25 substituted heteroaryl having one to three heteroatoms
independently selected from the group consisting of O, N, Si and S;
and wherein said substituted aryl or substituted heteroaryl has one
to three substituents independently selected from the group
consisting of: [0059] (1) --CH.sub.3, --C.sub.2H.sub.5, or C.sub.3
to C.sub.25 straight-chain, branched or cyclic alkane or alkene,
optionally substituted with at least one member selected from the
group consisting of Cl, Br, F, I, OH, NH.sub.2 and SH, [0060] (2)
OH, [0061] (3) NH.sub.2, and [0062] (4) SH; and wherein,
optionally, at least two of R.sup.1, R.sup.2, R.sup.3, R.sup.4,
R.sup.5, R.sup.6, R.sup.7, R.sup.8, R.sup.9 and R.sup.10 together
form a cyclic or bicyclic alkanyl or alkenyl group.
[0063] In another embodiment, ionic liquids useful for this
invention include fluorinated cations wherein at least one member
selected from R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6,
R.sup.7, R.sup.8, R.sup.9 and R.sup.10 comprises F.sup.-.
[0064] In another embodiment, ionic liquids have anions selected
from the group consisting of [CH.sub.3CO.sub.2].sup.-,
[HSO.sub.4].sup.-, [CH.sub.3OSO.sub.3].sup.-,
[C.sub.2H.sub.5OSO.sub.3].sup.-, [AlCl.sub.4].sup.-,
[CO.sub.3].sup.2-, [HCO.sub.3].sup.-, [NO.sub.2].sup.-,
[NO.sub.3].sup.-, [SO.sub.4].sup.2-, [PO.sub.4].sup.3-,
[HPO.sub.4].sup.2-, [H.sub.2PO.sub.4].sup.-, [HSO.sub.3].sup.-,
[CuCl.sub.2].sup.-, Cl.sup.-, Br.sup.-, I.sup.-, SCN.sup.-; and
preferably any fluorinated anion. Fluorinated anions of the
invention include [BF.sub.4].sup.-, [BF.sub.3CF.sub.3].sup.-,
[BF.sub.3C.sub.2F.sub.5].sup.-, [PF.sub.6].sup.-,
[PF.sub.3(C.sub.2F.sub.5).sub.3].sup.-, [SbF.sub.6].sup.-,
[CF.sub.3SO.sub.3].sup.-, [HCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3HFCCF.sub.2SO.sub.3].sup.-, [HCClFCF.sub.2SO.sub.3].sup.-,
[(CF.sub.3SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3SO.sub.2).sub.3C].sup.-, [CF.sub.3CO.sub.2].sup.-,
[CF.sub.3OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CFHOCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2HCF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2ICF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[(CF.sub.2HCF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CFHCF.sub.2SO.sub.2).sub.2N].sup.-; and F.sup.-. In
another embodiment, ionic liquids comprise a cation selected from
the group consisting of pyridinium, pyridazinium, pyrimidinium,
pyrazinium, imidazolium, pyrazolium, thiazolium, oxazolium,
triazolium, phosphonium, and ammonium as defined above; and an
anion selected from the group consisting of
[CH.sub.3CO.sub.2].sup.-, [HSO.sub.4].sup.-,
[CH.sub.3OSO.sub.3].sup.-, [C.sub.2H.sub.5OSO.sub.3].sup.-,
[AlCl.sub.4].sup.-, [CO.sub.3].sup.2-, [HCO.sub.3].sup.-,
[NO.sub.2].sup.-, [NO.sub.3].sup.-, [SO.sub.4].sup.2-,
[PO.sub.4].sup.3-, [HPO.sub.4].sup.2-, [H.sub.2PO.sub.4].sup.-,
[HSO.sub.3].sup.-, [CuCl.sub.2].sup.-, Cl.sup.-, Br.sup.-, I.sup.-,
SCN.sup.-; and any fluorinated anion. In yet another embodiment,
ionic liquids comprise a cation selected from the group consisting
of pyridinium, pyridazinium, pyrimidinium, pyrazinium, imidazolium,
pyrazolium, thiazolium, oxazolium, triazolium, phosphonium, and
ammonium as defined above; and an anion selected from the group
consisting of [BF.sub.4].sup.-, [BF.sub.3CF.sub.3].sup.-,
[BF.sub.3C.sub.2F.sub.5].sup.-, [PF.sub.6].sup.-,
[PF.sub.3(C.sub.2F.sub.5).sub.3].sup.-, [SbF.sub.6].sup.-,
[CF.sub.3SO.sub.3].sup.-, [HCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3HFCCF.sub.2SO.sub.3].sup.-, [HCClFCF.sub.2SO.sub.3].sup.-,
[(CF.sub.3SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3SO.sub.2).sub.3C].sup.-, [CF.sub.3CO.sub.2].sup.-,
[CF.sub.3 OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CFHOCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2HCF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2ICF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[(CF.sub.2HCF.sub.2SO.sub.2).sub.2N].sub.-,
[(CF.sub.3CFHCF.sub.2SO.sub.2).sub.2N].sup.-,
[PF.sub.3(C.sub.2H.sub.5).sub.3].sup.- and F.sup.-.
[0065] In still another embodiment, ionic liquids comprise a cation
selected from the group consisting of pyridinium, pyridazinium,
pyrimidinium, pyrazinium, imidazolium, pyrazolium, thiazolium,
oxazolium, triazolium, phosphonium, and ammonium as defined above,
wherein at least one member selected from R.sup.1, R.sup.2,
R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8, R.sup.9, and
R.sup.10 comprises F.sup.-; and an anion selected from the group
consisting of [CH.sub.3CO.sub.2].sup.-, [HSO.sub.4].sup.-,
[CH.sub.3OSO.sub.3].sup.-, [C.sub.2H.sub.5OSO.sub.3].sup.-,
[AlCl.sub.4].sup.-, [CO.sub.3].sup.2-, [HCO.sub.3].sup.-,
[NO.sub.2].sup.-, [NO.sub.3].sup.-, [SO.sub.4].sup.2-,
[PO.sub.4].sup.3-, [HPO.sub.4].sup.2-, [H.sub.2PO.sub.4].sup.-,
[HSO.sub.3].sup.-, [CuCl.sub.2].sup.-, Cl.sup.-, Br.sup.-, I.sup.-,
SCN.sup.-; and any fluorinated anion. In still another embodiment,
ionic liquids comprise a cation selected from the group consisting
of pyridinium, pyridazinium, pyrimidinium, pyrazinium, imidazolium,
pyrazolium, thiazolium, oxazolium, triazolium, phosphonium, and
ammonium as defined above, wherein at least one member selected
from R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7,
R.sup.8, R.sup.9, and R.sup.10 comprises F.sup.-; and an anion
selected from the group consisting of [BF.sub.4].sup.-,
[BF.sub.3CF.sub.3].sup.-, [BF.sub.3C.sub.2F.sub.5].sup.-,
[PF.sub.6].sup.-, [PF.sub.3(C.sub.2F.sub.5).sub.3].sup.-,
[SbF.sub.6].sup.-, [CF.sub.3 SO.sub.3].sup.-,
[HCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3HFCCF.sub.2SO.sub.3].sup.-, [HCClFCF.sub.2SO.sub.3].sup.-,
[(CF.sub.3SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3SO.sub.2).sub.3C].sup.-, [CF.sub.3CO.sub.2].sup.-,
[CF.sub.3 OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CFHOCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2HCF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2ICF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[(CF.sub.2HCF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CFHCF.sub.2SO.sub.2).sub.2N].sup.-, and F.sup.-.
[0066] In a more specific embodiment, ionic liquids useful for the
invention comprise:
[0067] a) imidazolium or pyridinium as the cation, and an anion
selected from the group consisting of [BF.sub.4].sup.-,
[BF.sub.3CF.sub.3].sup.-, [BF.sub.3C.sub.2F.sub.5].sup.-,
[PF.sub.6].sup.-, [PF.sub.3(C.sub.2F.sub.5).sub.3].sup.-,
[SbF.sub.6].sup.-, [CF.sub.3SO.sub.3].sup.-,
[HCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3HFCCF.sub.2SO.sub.3].sup.-, [HCClFCF.sub.2SO.sub.3].sup.-,
[(CF.sub.3SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3SO.sub.2).sub.3C].sup.-, [CF.sub.3CO.sub.2].sup.-,
[CF.sub.3OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CFHOCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2HCF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2ICF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[(CF.sub.2HCF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CFHCF.sub.2SO.sub.2).sub.2N].sup.-, [CH.sub.3
OSO.sub.3].sup.-;
[0068] b) 1-butyl-3-methylimidazolium as the cation, and an anion
selected from the group consisting of [BF.sub.4].sup.-,
[BF.sub.3CF.sub.3].sup.-, [BF.sub.3C.sub.2F.sub.5].sup.-,
[PF.sub.6].sup.-, [PF.sub.3(C.sub.2F.sub.5).sub.3].sup.-,
[SbF.sub.6].sup.-, [CF.sub.3SO.sub.3].sup.-,
[HCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3HFCCF.sub.2SO.sub.3].sup.-, [HCClFCF.sub.2SO.sub.3].sup.-,
[(CF.sub.3SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3SO.sub.2).sub.3C].sup.-, [CF.sub.3CO.sub.2].sup.-,
[CF.sub.3 OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CFHOCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2HCF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2ICF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[(CF.sub.2HCF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CFHCF.sub.2SO.sub.2).sub.2N].sup.-;
[0069] c) 1-ethyl-3-methylimidazolium as the cation, and an anion
selected from the group consisting of [BF.sub.4].sup.-,
[BF.sub.3CF.sub.3].sup.-, [BF.sub.3C.sub.2F.sub.5].sup.-,
[PF.sub.6].sup.-, [PF.sub.3(C.sub.2F.sub.5).sub.3].sup.-,
[SbF.sub.6].sup.-, [CF.sub.3SO.sub.3].sup.-,
[HCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3HFCCF.sub.2SO.sub.3].sup.-, [HCClFCF.sub.2SO.sub.3].sup.-,
[(CF.sub.3SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3SO.sub.2).sub.3C].sup.-, and [CF.sub.3CO.sub.2].sup.-,
[CF.sub.3OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CFHOCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2HCF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2ICF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[(CF.sub.2HCF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CFHCF.sub.2SO.sub.2).sub.2N].sup.-;
[0070] d) 1-ethyl-3-methylimidazolium as the cation, and
[(CF.sub.3CF.sub.2SO.sub.2).sub.2N].sup.-, [PF.sub.6].sup.-, and
[HCF.sub.2CF.sub.2SO.sub.3].sup.-as the anion;
[0071] e) 1,3-dimethylimidazolium as the cation, and an anion
selected from the group consisting of [BF.sub.4].sup.-,
[BF.sub.3CF.sub.3].sup.-, [BF.sub.3C.sub.2F.sub.5].sup.-,
[PF.sub.6].sup.-, [PF.sub.3(C.sub.2F.sub.5).sub.3].sup.-,
[SbF.sub.6].sup.-, [CF.sub.3SO.sub.3].sup.-,
[HCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3HFCCF.sub.2SO.sub.3].sup.-, [HCClFCF.sub.2SO.sub.3].sup.-,
[(CF.sub.3SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3SO.sub.2).sub.3C].sup.-, and [CF.sub.3CO.sub.2].sup.-,
[CF.sub.3OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCFHCF.sub.2SO.sub.3].sup.-,
[CF.sub.3CFHOCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2HCF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.2ICF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[CF.sub.3CF.sub.2OCF.sub.2CF.sub.2SO.sub.3].sup.-,
[(CF.sub.2HCF.sub.2SO.sub.2).sub.2N].sup.-,
[(CF.sub.3CFHCF.sub.2SO.sub.2).sub.2N].sup.-;
[0072] (f) 3-methyl-1propylpyridinium as the cation and
[(CF.sub.3SO.sub.2).sub.2N].sup.- as the anion; and
[0073] (g) 1-hexyl-3-methylimidazolium as the cation and
[PF.sub.3(C.sub.2F.sub.5).sub.3].sup.- as the anion.
[0074] In various other embodiments of this invention, an ionic
liquid formed by selecting any of the individual cations described
or disclosed herein, and by selecting any of the individual anions
described or disclosed herein, may be used for the purpose of
effecting the separation of either R-134 or R-134a as a component
from a mixture in which it is contained. Correspondingly, in yet
other embodiments, a subgroup of ionic liquids formed by selecting
(i) a subgroup of any size of cations, taken from the total group
of cations described and disclosed herein in all the various
different combinations of the individual members of that total
group, and (ii) a subgroup of any size of anions, taken from the
total group of anions described and disclosed herein in all the
various different combinations of the individual members of that
total group, may be used for the purpose of effecting the
separation of either R-134 or R-134a as a component from a mixture
in which it is contained. In forming an ionic liquid, or a subgroup
of ionic liquids, by making selections as aforesaid, the ionic
liquid or subgroup will be used in the absence of the members of
the group of cations and/or anions that are omitted from the total
group thereof to make the selection, and, if desirable, the
selection may thus be made in terms of the members of the total
group that are omitted from use rather than the members of the
group that are included for use.
[0075] Systems of particular interest in this invention are those
in which either R-134 or R-134a is separated as a component from a
mixture in which it is contained with the other isomer by the
addition to the mixture of at least one fluorinated ionic liquid,
such as an ionic liquid that has a fluorinated anion, a fluorinated
cation or both, in view of what may be useful interactions between
and/or among the various fluorinated species that may increase the
solubility of either R-134 or R-134a in an ionic liquid.
[0076] R-134 and R-134a, in their separated and pure states, have
normal boiling points of -19.59.degree. C. (R-134) and
-26.11.degree. C. (R-134a), respectively. These close boiling
points make efficient separation of R-134 and R-134a by
conventional processes extremely difficult because of the tendency
of those components to form an azeotrope, azeotropic composition or
an azeotrope-like composition in a mixture. The processes of this
invention are consequently needed to improve the efficiency of
efforts made to separate the two isomers, and do so by contacting
the mixture with at least one ionic liquid. This is advantageous
because at least one of the isomeric components of the mixture will
be less soluble in the ionic liquid than the other component(s),
and preferably much less soluble. This difference in solubility
facilitates the separation of the lower-solubility component from
the mixture because when that component is removed, such as by
volatilization, the more-soluble component will be removed to a
more limited extent, and will preferably not be removed at all,
because to the extent that it is soluble in the ionic liquid, it
will tend to remain in, and not be removed from, the mixture.
[0077] The separation processes of this invention may be performed,
for example, by a technique such as extractive distillation. In
extractive distillation, as in conventional distillation, the use
of temperature and pressure control enables the volatilization of
at least one individual component in a mixture, and the volatilized
component(s) is captured in a separate stream in which it is
condensed apart from, and is thus removed from, the mixture. In
extractive distillation, however, there is added to the mixture a
miscible, high boiling, relatively nonvolatile component, the
extractant, that has low latent heat of vaporization, does not form
an azeotrope with any of the components in the mixture, and does
not chemically react with any of the components in the mixture. The
extractant is specially chosen to interact differently with the
various components of the mixture, thereby altering their relative
volatilities and "breaking" any azeotrope, azeotropic composition
or azeotrope-like composition in which they would otherwise exist.
The extractant is chosen to be a substance in which one or more of
the components of the mixture is more soluble, and preferably much
more soluble, than at least one other component of the mixture. A
component that is less soluble in the extractant may, as a result,
be more easily volatilized and separated from the mixture than a
component that is more soluble in the extractant. The tendency that
the components of an azeotrope, azeotropic composition or
azeotrope-like composition would ordinarily have to volatilize in
the essentially the same compositional ratio as they possess in
liquid from is thus altered by the presence in the mixture of the
extractant, which, by solubilizing at least one component of the
mixture to a greater extent than at least one other component,
causes a corresponding change in the compositional content of the
stream of volatiles liberated from the mixture at a selected
temperature and pressure. The component(s) that are caused to be
more volatile than others by the presence of the extractant in the
mixture are then removed from the mixture as vapor in much higher
concentration than the other components at the selected temperature
and pressure. The more soluble, less volatile component(s) remain
in the mixture with the extractant, and another criterion for
selection of the extractant is that it be a substance that is
easily separated from the remaining high-solubility, low-volatility
component(s) of the mixture.
[0078] In various embodiments, it may be desirable to evaluate as
the extractant a substance that causes the lower-boiling of two
components in a mixture to become the more volatile of the two
components as well. For example, a substance having greater
chemical similarity to the higher-boiling of two components than to
the lower-boiling may be evaluated for use as the extractant in
such an embodiment. In various other embodiments, criteria that may
be considered in evaluating a substance for selection as an
extractant is whether the substance causes a positive deviation
from Raoult's law with the lower-boiling of two components, or
causes a negative deviation from Raoult's law with the
higher-boiling of the two components.
[0079] When the separation process of this invention is performed
by extractive distillation, an ionic liquid is used as an
extractant. Mixtures of extractants, and thus mixtures of ionic
liquids as extractants, may also be useful for achieving a desired
extent of separation. In one embodiment, a mixture of extractants
may be selected wherein one extractant has a high selectivity for
the higher-volatility of the two components, and the other
extractant has a high capacity to solubilize that component. In
another embodiment, a mixture of ionic liquids may be used to
separate the components of a mixture comprising at least two
hydrofluorocarbon compounds by using multiple, discrete separation
steps.
[0080] When the separation process of this invention is performed
by extractive distillation, it may be advantageously performed in a
distillation column such as is shown in the schematic diagram of
FIG. 1. In the column of FIG. 1, separator elements 1 are used for
the separation from the extractant of the top product, which is the
mixture component that is made more volatile (less soluble) by the
presence of the extractant in the mixture. Use of an ionic liquid
as the extractant has the advantage of essentially eliminating the
presence of the extractant in the overhead product 7 because of
what is typically the negligible volatility of an ionic liquid. The
overhead or distillate stream exiting the column may be condensed
using reflux condensers. At least a portion of this condensed
stream can be returned to the top of the column as reflux, and the
remainder recovered as product or for optional processing. The
ratio of the condensed material that is returned to the top of the
column as reflux to the material removed as distillate is commonly
referred to as the reflux ratio. In extractive distillation, the
extractant exits from the bottom of the column along with at least
one mixture component that is more soluble in the ionic liquid.
These may be sent to a second separation step where the extractant
and a more soluble component are separated and recovered. The
extractant may be recycled to the extractive distillation column
for reuse.
[0081] The flow of the extractant enters at inlet 2, which is
preferably located in the enriching section close to the top of the
column below the condenser, or at the bottom of the rectifying
section, wherein any amount of the extractant that has unexpectedly
volatilized is separated from the higher-volatility, less-soluble
component of the mixture. The ionic liquid as extractant then
proceeds in a countercurrent flow direction downward in the column
relative to the upward flow of the higher-volatility component, and
perhaps other components of the mixture to be separated. The
mixture enters at inlet 4, above the stripping section, where any
of the higher-volatility component that is still admixed with the
extractant is finally vaporized. The inlet feed of the mixture to
be separated may be in liquid or gaseous form, and, if the mixture
is in liquid form when fed into the column, the higher-volatility
component(s) thereof will be volatilzed by the temperature and
pressure conditions of the column, which will have been selected
for that purpose. The vapors rising in the column are continuously
enriched in content of the higher-volatility, less-soluble
component of the mixture, and the liquid moving downward in the
column is continuously depleted in content of that
higher-volatility component.
[0082] Separator elements 3 and 5 contain a useful number of stages
along the height of the column at which there is thorough
gas-liquid contacting, which is desirable for the purpose of
obtaining extensive separation of a higher-volatility, less-soluble
component, which exits the column as the overhead product 7, from a
lower-volatility, more-soluble component, which exits the column
together with the extractant as the bottom product 6. Separator
elements can be either plates, or ordered or disordered packings.
In either event, the purpose is to provide a downward cascade of
the liquid extractant to contact the rising stream of vaporized
high-volatility component. If plates are used, the liquid may flow
over the edge of one plate onto another, or the liquid may flow
through the same holes in the plates through which the volatilized
component rises. In either case, the objective is to achieve
maximum residence time of gas-liquid contact consistent with
providing a rate of upward vapor flow that is high enough to
prevent the column from being flooded by the downcoming liquid, but
is not so high that the vapor is pushed out of the column without
sufficient time to contact the liquid.
[0083] There is, in terms of the amount of the mixture to be
separated, a minimum amount of the extractant that is needed to
"break" any azeotrope, azeotropic composition or azeotrope-like
composition that may exist, and enable the separation of at least
one of the components from the mixture from the others in a yield
and at a rate that is commercially feasible. In a ratio of the
amount of extractant to the amount of feed, where the amount of
extractant used in the ratio is the minimum amount described above,
the value of the ratio may be set, for example, in the range of
about 2 to about 4. Although feed ratios above 5 are sometimes
found to offer no particular advantage in terms of being able to
reduce the number of stages in a column, higher or lower feed
ratios may be used herein as circumstances dictate such as a molar
ratio of extractant to feed in the range of about 0.1 to about
25.
[0084] The extractant is then removed from the mixture together
with the lower-volatility, more-soluble component in a separate
step, and is recycled to the column for re-entry into the column at
inlet 2. The extractant may be separated from the bottom product 6
using various separating operations including regeneration by
simple evaporation. Thin film evaporators, such as falling-film or
rotary evaporators, are commonly used for continuous evaporation.
In discontinuous concentration processes, two evaporator stages are
run alternately so that regenerated ionic liquid, as extractant,
can be returned continuously to the distillation column. The
extractant can also be regenerated by means of a stripping column
since the vapor pressure of the ionic liquid is essentially zero.
An alternative means of recovering an ionic liquid as extractant
takes advantage of the fact that many ionic liquids can solidify
below 0.degree. C. In these cases, low cost separation of the ionic
liquid can be achieved by cooling to form a solid phase. The bottom
product can also be precipitated using techniques such as cooling,
evaporative, or vacuum crystallization.
[0085] These and other aspects of extractive distillation are
further discussed in well-known sources such as Perry's Chemical
Engineers' Handbook, 7.sup.th Ed. (Section 13, "Distillation",
McGraw-Hill, 1997).
[0086] When the separation process of this invention is performed
by extractive distillation, more than one distillation column may
be required in systems in which a mixture contains multiple
components to be separated. For example, non-close-boiling
components may be separated and removed from the mixture using a
first distillation column, and an azeotrope, azeotropic composition
or azeotrope-like composition can then be separated using a second
distillation column. An ionic liquid may be used as an extractant
for one or both of the distillation columns. For example, where it
is desirable to separate either R-134 or R-134a using one ionic
liquid, one of the components may be recovered from the top of the
column whereas the second component and ionic liquid can be
recovered from the bottom of the column. The mixture comprising the
second component and the ionic liquid can then be separated using a
second distillation column (or flash tank); the second component
can be recovered from the top of the second column (or flash tank),
and the ionic liquid can be recovered from the bottom of the column
(or flash tank) and recycled back to the first distillation
column.
[0087] When the separation process of this invention is performed
by extractive distillation, the individual components of the
mixture to be separated may have respective concentrations ranging
from about 0.05 to about 99.95 mole percent relative to the total
weight of all components in the mixture plus the extractant
depending on their location at any particular time in the column,
at which location and time they may be subjected to a temperature
in the range of from the reboiler temperature to the condenser
temperature, and a pressure in the range of from vacuum to the
critical pressure.
[0088] Extractive distillation processes operate at varying feed,
reboiler, and condenser temperatures depending on the appropriate
conditions for optimum separation. A typical extractive
distillation process might operate with a condenser and/or feed
composition chilled by water to a temperature of 5 to 10.degree.
C., or chilled by brine or ethylene glycol to even lower
temperatures of 0 to -40.degree. C. In some cases, if the
extractive distillation column operates at close to the normal
boiling point of a compound at about 1 atmosphere pressure, the
feed and/or the condenser may cool the gas to even lower
temperatures of -40 to -80.degree. C. The reboiler can operate over
a wide temperature range depending on the operating pressure of the
column and the identity of the compound(s) being separated, which
in the case of a fluorinated compound could be a temperature range
of from about -80 to about 240.degree. C. The operating pressure of
the distillation system may range from about -100 kPa to about 3.45
MPa, and is typically about 101.3 kPa to about 2.76 MPa. Typically,
an increase in the extractant feed rate relative to the feed rate
of the mixture to be separated causes an increase in the purity of
the product to be recovered with regard to those compound(s) being
removed. The molar ratio of the extractant feed rate relative to
the feed rate of the mixture to be separated may range from about
0.1 to about 25, and typically ranges from about 1 to about 10.
Normally, increasing the reflux ratio results in increased
distillate stream purity. Generally, the reflux ratio ranges
between 1/2 to 200/1. The temperature of the condenser, if present,
which is located adjacent to the top of the column, is normally
either sufficient to substantially fully condense the distillate
that is exiting from the top of the column, or is that temperature
required to achieve the desired reflux ratio by partial
condensation.
[0089] Referring now to FIG. 2, there is shown a process flow
diagram of an extractive distillation system for separating R-134a
from a mixture comprising both R-134 and R-134a wherein the
extractant is at least one ionic liquid in which R-134 is more
soluble than R-134a, such as 1-ethyl-3-methylimidazolium
bis(trifluoromethylsulfonyl)imide ([emim][Tf.sub.2N]. Use of an
ionic liquid as the extractant has the advantage of having
essentially no extractant loss in the overhead product due to its
negligble volatility; therefore it may not be necessary to have any
separation stages above the extractant feed point. The feed mixture
comprising R-134 and R-134a is supplied via conduit 100 typically
to an intermediate location in extractive distillation column 101.
The extractant comprising at least one ionic liquid is supplied via
conduit 102 to the extractive distillation column 101 at a feed
point (i.e., separation stage) higher in the column than the feed
point of the 134/134a mixture. The overhead distillate 103 from
column 101 contains concentrated R-134a, reduced in R-134 relative
to the feed mixture, and essentially free of the extractant
(<0.1%). A stream comprising the extractant and R-134, reduced
in R-134a relative to the feed mixture, is removed from the bottom
of column 101 via conduit 104 and transported to optional equipment
105 capable of heating or cooling and/or increasing or reducing the
stream pressure.
[0090] Optional equipment 105 may be a heat exchanger, a pump, a
valve, and/or any other devices for accomplishing the temperature,
pressure, and/or phase change of a material stream. From optional
equipment 105, the material stream comprising the extractant and
R-134 substantially free of R-134a is transported via conduit 106
to extractant recovery unit 107. Extractant recovery unit 107
separates the stream comprising the ionic liquid extractant and
R-134 into an R-134 stream essentially free of the extractant,
which is removed via conduit 108, and an extractant stream
substantially free of R-134 and R-134a that is removed via conduit
109 and transported to optional equipment 110 and from there
optionally returned via conduit 102 to extractive distillation
column 101 as the extractant stream. Extractant recovery unit 107
can consist of any separation method capable of separating a
low-boiling compound from an extractant comprising an essentially
nonvolatile ionic liquid. Such separation methods include
stripping, especially stripping in the presence of a gas (e.g. air
or nitrogen) or a condensable vapor (e.g. steam), provided that the
gas or vapor does not adversely interact with the low-boiling
compound or ionic liquid, flashing at elevated temperature and/or
reduced pressure, evaporation, especially falling-film or
wiped-film evaporation.
[0091] An alternative means of recovering the ionic liquid takes
advantage of the fact that many ionic liquids solidify below
0.degree. C. In these cases, separation of the ionic liquid can be
achieved by cooling to form a solid phase. The ionic liquid is
obtained in solid form leaving behind the purified R-134. Optional
equipment 110 may be a heat exchanger, pump, valve, and/or any
other devices for accomplishing the temperature, pressure, and/or
phase change of a material stream. The R-134 stream essentially
free of the extractant, which is removed via conduit 108.
[0092] Impurities present in the feed mixture or in the separated
R-134 or R-134a streams (i.e., stream 108 and stream 103,
respectively) can be separated using one or more additional
separation steps (not shown). The one or more additional separation
steps can be placed prior to the extractive distillation column
wherein R-134 or R-134a is separated from the mixture, or can be
placed after said extractive distillation column as appropriate.
Whether or not any impurities present in these streams will need to
be separated will depend on the use of the product to be obtained
by this process.
[0093] A process similar to that described as above and in FIG. 2
can also be used to separate R-134 from a mixture comprising both
R-134 and R-134a by selecting an ionic liquid for carrying out an
extractive distillation using the techniques as described above.
Separated R-134 and/or R-134a streams can be partially or
completely recovered as a liquid or as a vapor by conventional
means.
[0094] For example, in one embodiment of a process as provided
herein, (a) a mixture of R-134 and R-134a may be contacted with an
ionic liquid to form a second mixture, (b) the second mixture may
be processed by distillation, (c) R-134 may be recovered as a
distillation-column overhead stream, and (d) R-134a and an ionic
liquid may be recovered as a distillation-column bottom stream.
Conversely, in another embodiment, (a) a mixture of R-134 and
R-134a may be contacted with an ionic liquid to form a second
mixture, (b) the second mixture may be processed by distillation,
(c) R-134a may be recovered as a distillation-column overhead
stream, and (d) R-134 and an ionic liquid may be recovered as a
distillation-column bottom stream.
[0095] The ease of separation for a binary mixture of two
components i and j by distillation can be determined by their
relative volatility. The larger the relative volatility difference,
the easier the separation. For mixtures with a small relative
volatility, extractive distillation may be used to make the
separation easier. In extractive distillation, the extractant
influences the separation by selectively interacting with one or
more of the components in the mixture. The selectivity for a binary
mixture composed of i and j is defined as the ratio of the infinite
dilution activity coefficient of compound i to the infinite
dilution activity coefficient of compound j, where compounds i and
j are present at an infinite degree of dilution in the extractant.
The further the selectivity is from the value of one, the easier it
is for the compounds of the mixture to be separated by extractive
distillation. In general, the selectivity can be greater than or
less than 1.0 depending on whether the more volatile or less
volatile compound is in the numerator and depending on how the
extractant modifies the volatility of the two compounds. Normally
the more volatile compound is placed in the numerator and the
selectivity has a value greater than 1.0, although in some cases
the value can be less than 1.0. The selectivity ratio for
components in a mixture is further discussed in sources such as
Kirk-Othmer Encyclopedia of Chemical Technology, 5.sup.th Edition,
Volume 13, pages 242-281 (2005) John Wiley & Sons, Inc.,
Hoboken, N.J. In order to achieve any practical amount of
separation, a selectivity of greater than or less than 1.0 is
required. In one embodiment of the processes of this invention, the
selectivity is greater than about 1.9 to about 2.3.
[0096] The following examples are presented to illustrate the
advantages of this invention and to assist one of ordinary skill in
making and using the same. These examples are not intended in any
way to limit the scope of the invention. The operation of the
invention is illustrated by data related to the solubility of R-134
and R-134a in various ionic liquids. In this work, selectivities
such as are described in Example 1 were used to determine the
extent to which R-134 and R-134a could be separated. Example 2 uses
a process simulation program (Aspen Plus.TM.; Aspen Technology,
Inc., Version 13.2, Cambridge, Mass.) to model the separation of
R-134a and R-134 by extractive distillation using
1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide
([emim][Tf.sub.2N]) as the extractant.
General Methods and Materials
[0097] The following nomenclature and abbreviations are used:
C=concentration (molm.sup.-3) C.sub.b=buoyancy force (N)
C.sub.f=correction factor (kg) C.sub.0=initial concentration
(molm.sup.-3) C.sub.s=saturation concentration (molm.sup.-3)
<C>=space-averaged concentration (molm.sup.-3) D=diffusion
constant (m.sup.2s.sup.-1) g=gravitational acceleration (9.80665
ms.sup.-2) L=length (m) m.sub.a=mass absorbed (kg)= m.sub.i=mass of
i-th species on sample side of balance (kg) m.sub.j=mass of j-th
species on counterweight side of balance (kg)= m.sub.IL=mass of
ionic liquid sample (kg) MW.sub.i=molecular weight of i-th species
(kgmol.sup.-1) N=n-th number component P=pressure (MPa)
P.sub.0=initial pressure (MPa) t=time (s) T.sub.ci=critical
temperature of i-th species (K) T.sub.i=temperature of i-th species
(K) T.sub.j=temperature of j-th species (K) T.sub.s=temperature of
sample (K) V.sub.i=volume of i-th species (m.sup.3) V.sub.IL=volume
of ionic liquid (m.sup.3) V.sub.m=liquid sample volume (m.sup.3)
{tilde over (V)}.sub.g=molar volume of gas (m.sup.3mol.sup.-1)
{tilde over (V)}.sub.i=molar volume of i-th species
(m.sup.3mol.sup.-1) {tilde over (V)}.sub.IL=molar volume of ionic
liquid (m.sup.3mol.sup.-1) {tilde over (V)}.sub.m=molar volume of
mixture (m.sup.3mol.sup.-1) {tilde over (V)}.sub.0=initial molar
volume (m.sup.3mol.sup.-1) .DELTA.{tilde over (V)}=change in molar
volume (m.sup.3mol.sup.-1) x.sub.i=mole fraction of i-th species
z=depth (m)= .lamda..sub.n=eigenvalue (m.sup.-1)
.rho..sub.g=density of gas (kgm.sup.-3) .rho..sub.i=density of i-th
component on sample side of balance (kgm.sup.-3)
.rho..sub.j=density of j-th component on counter weight side of
balance (kgm.sup.-3) .rho..sub.air=density of air (kgm.sup.-3)
.rho..sub.s=density of sample (kgm.sup.-3)
Units
Pa.ident.Pascal
MPa.ident.Mega Pascal
[0098] kPa.ident.kilopascal mol.ident.mole m.ident.meter
cm.ident.centimeter
K.ident.Kelvin
N.ident.Newton
J.ident.Joule
[0099] kJ.ident.kilojoule kg.ident.kilogram g.ident.gram
mg.ident.milligram .mu.g.ident.microgram T.ident.temperature
P.ident.pressure mbar.ident.millibar h or hr.ident.hour
min.ident.minute .degree. C..ident.degrees Centigrade
sec.ident.second kW.ident.kilowatt kg/s.ident.kilogram per second
kg/hr.ident.kilogram per hour
[0100] 1-Butyl-3-methylimidazolium hexafluorophosphate
([bmim][PF.sub.6], 1-ethyl-3-methylimidazolium
bis(trifluoromethylsulfonyl)imide ([emim][Tf.sub.2N] and
3-methyl-1-propylpyridinium bis(trifluoromethylsulfonyl)imide
([pmpy][Tf.sub.2N] were obtained from Fluka Chemika (may be
obtained from Sigma-Aldrich, St. Louis, Mo.) with a purity of
>97%. 1-Hexyl-3-methylimidazolium
tris(pentafluoroethyl)trifluorophosphate
[hmim][PF.sub.3(C.sub.2F.sub.5).sub.3] was obtained from Merck
& Co. (Gibbstown, N.J.).
[0101] R-134 (CHF.sub.2CHF.sub.3, molecular weight 102 g
mol.sup.-1, normal boiling point -19.6.degree. C.), R-134a
(CH.sub.2FCF.sub.3, molecular weight 102 g mol.sup.-1, normal
boiling point -26.1.degree. C.), R-114 (CClF.sub.2CClF.sub.2,
molecular weight 170.9 g mol.sup.-1, normal boiling point
3.6.degree. C.), R-114a (CCl.sub.2FCF.sub.3 molecular weight 170.9
g mol.sup.-1, normal boiling point 3.0.degree. C.), R-124
(CClHFCF.sub.3, molecular weight 136.5 g mol.sup.-1, normal boiling
point -12.0.degree. C.), and R-124a (CHF.sub.2CClF.sub.2 molecular
weight 136.5 g mol.sup.-1, normal boiling point -10.2.degree. C.)
were obtained from DuPont Fluorochemicals (Wilmington, Del.), with
a minimum purity of 99%.
[0102] The R-134, R-134a, R-114, R-114a, R-124, and R-124a
solubility measurements were made using a gravimetric microbalance
(IGA 003, Hiden Isochema Ltd., Warrington, UK). The microbalance
consists of an electrobalance with sample and counterweight
components inside a stainless steel pressure-vessel. The balance
has a weigh range of 0-100 mg with a resolution of 0.1 .mu.g. An
enhanced pressure stainless steel (SS316LN) reactor capable of
operation to 2.0 MPa and 100.degree. C. was installed.
Approximately 60 mg of ionic liquid sample was added to the sample
container and the reactor was sealed. The sample was dried and
degassed by first pulling a coarse vacuum on the sample with a
diaphragm pump (Pfeiffer, model MVP055-3, Asslar, Germany) and then
fully evacuating the reactor to 10.sup.-9 MPa with a turbopump
(Pfeiffer, model TSH-071). While under deep vacuum, the sample was
heated to 75.degree. C. for 10 h with an external water jacket
connected to a remote-controlled constant-temperature bath (Huber
Ministat, model cc-S3, Offenburg, Germany). A 30 percent ethylene
glycol and 70 percent water mixture by volume was used as the
recirculating fluid with a temperature range of 5 to 90.degree. C.
The sample mass slowly decreased as residual water and gases were
removed. Once the mass had stabilized for at least 60 min, the
sample dry mass was recorded.
[0103] The IGA003 can operate in both dynamic and static mode.
Dynamic mode operation provides a continuous flow of gas (maximum
500 cm.sup.3 min.sup.-1) past the sample, and the exhaust valve
controls the set-point pressure. Static mode operation introduces
gas into the top of the balance away from the sample and both the
admittance and exhaust valves control the set-point pressure. All
absorption measurements were performed in static mode.
[0104] The sample temperature was measured with a type K
thermocouple with an accuracy of .+-.0.1.degree. C. The
thermocouple was located inside the reactor next to the sample
container. The water jacket maintained the set-point temperature
automatically to within a typical regulation accuracy of
.+-.0.1.degree. C. Four isotherms (at 10, 25, 50, and 75.degree.
C.) were measured beginning with 10.degree. C.
[0105] Once the desired temperature was achieved and stable, the
admittance and exhaust valves opened and closed as necessary to
adjust the pressure to the first set-point. Pressures from
10.sup.-10 to 10.sup.-2 MPa were measured using a capacitance
manometer (Pfeiffer, model PKR251), and pressures from 10.sup.-2 to
2.0 MPa were measured using a piezo-resistive strain gauge (Druck,
model PDCR4010, New Fairfield, Conn.). Regulation maintained the
reactor pressure set-point to within .+-.4 to 8 kPa. The pressure
ramp rate was set at 200 kPa min.sup.-1 and the temperature ramp
rate was set at 1.degree. C. min.sup.-1. The upper pressure limit
of the stainless steel reactor was 2.0 MPa, and several isobars
(i.e. 0.1, 0.5, 1, 2, 3 MPa) were measured. To ensure sufficient
time for gas-liquid equilibrium, the ionic liquid samples were
maintained at set-point for a minimum of 3 h with a maximum
time-out of 12 h. Additional details of the experimental equipment
and procedures have been published (M. B. Shiflett and A. Yokozeki,
Ind. Eng. Chem. Res. (2005) 44(12), 4453-4464).
Example 1
Separation of 1,1,2,2-tetrafluoroethane (R-134) and
1,1,1,2-tetrafluoroethane (R-134a)
[0106] This example focuses on the thermodynamic properties at the
infinite dilution state. Activity coefficients at infinite dilution
.gamma..sup..infin. were analyzed for R-134 and R-134a in
[bmim][PF.sub.6] and [emim][Tf.sub.2N].
[0107] Experimental solubility (PTx) data for R-134 and R-134a in
[bmim][PF.sub.6] and [emim][Tf.sub.2N] are summarized in Examples 3
and 4 for [bmim][PF.sub.6] and Examples 5 and 10 for
[emim][Tf.sub.2N]. Data have been correlated with the
Non-Random-Two-Liquid (NRTL) solution model. The NRTL (S. I.,
Sandler, Chemical and Engineering Thermodynamics, 3.sup.rd Edition
(1999) John Wiley and Sons, Inc., New York, Chapter 7) activity
coefficient (.gamma..sub.i) model for a binary system is given
by:
ln .gamma. 1 = x 2 2 [ .tau. 21 ( G 21 x 1 + x 2 G 21 ) 2 + .tau.
12 G 12 ( x 2 + x 1 G 12 ) 2 ] , ( 1 ) ln .gamma. 2 = x 1 2 [ .tau.
12 ( G 12 x 2 + x 1 G 12 ) 2 + .tau. 21 G 21 ( x 1 + x 2 G 21 ) 2 ]
, ( 2 ) ##EQU00001##
[0108] where
G.sub.12.ident.exp(-.alpha..tau..sub.12), and
G.sub.21.ident.exp(-.alpha..tau..sub.21), (3)
.tau..sub.12 and .tau..sub.21: adjustable binary interaction
parameters. (4)
[0109] .alpha.=0.2 (assumed to be a constant of 0.2 in this work).
The temperature-dependent binary interaction parameter
(.tau..sub.ij) is modeled by:
.tau..sub.ij=.tau..sub.ij.sup.(0)+.tau..sub.ij.sup.(1)/T. (5)
[0110] Vapor liquid equilibria (VLE) are obtained by solving the
following equations:
y.sub.iP.PHI..sub.i=x.sub.i.gamma..sub.iP.sub.i.sup.S, (i=1 for
R-134 or R-134a and i=2 for ionic liquid) (6)
In the present system, it was assumed that P.sub.2.sup.S.apprxeq.0
and y.sub.2.apprxeq.0 (or y.sub.1.apprxeq.1). Thus, eq 6 becomes
only one equation with i=1, and the correction factor for
vapor-phase non-ideality, .PHI..sub.1, can be written as:
.PHI. 1 = exp [ ( B 11 - V _ 1 ) ( P - P 1 s ) RT ] . ( 7 )
##EQU00002##
The second virial coefficient, B.sub.11(T), of pure species 1 can
be calculated with proper equation-of-state models, and the
saturated molar liquid volume, V.sub.1(T), is calculated using the
method described in Shiflett, M. B. and Yokozeki, A. (Solubility
and Diffusivity of Hydrofluorocarbons in Room-Temperature Ionic
Liquids. AIChE J. (2006), 52, 1205). The vapor pressure of pure
species 1 is modeled by:
log 10 P 1 s = A 1 - B 1 T + C 1 . ( 8 ) ##EQU00003##
The coefficients in eq 8 for R-134 are (A.sub.1=7.810141,
B.sub.1=2306.21, C.sub.1=-25.3612) and R-134a are (A.sub.1=8.10384,
B.sub.1=2432.86, C.sub.1=-12.3310), and it was assumed that eq 8
holds even above VLE (vapor liquid equilibrium) critical
temperature T.sub.c as an extrapolated hypothetical vapor
pressure.
[0111] The present solubility model contains a maximum of four
adjustable parameters: .tau..sub.12.sup.(0), .tau..sub.12.sup.(1),
.tau..sub.21.sup.(0), and .tau..sub.21.sup.(1). These parameters
have been determined using non-linear least-squares analysis with
an objective function of:
.SIGMA..sub.i=1.sup.N(1-P.sub.obs(i)/P.sub.calc(i)).sup.2 for N
data points. Optimal values for these parameters for R-134 in
[bmim][PF.sub.6] are .tau..sub.12.sup.(0)=8.63198,
.tau..sub.12.sup.(1)=-2228.072 K, .tau..sub.21.sup.(0))=-2.89313,
and .tau..sub.21.sup.(1)=551.474 K. Optimal values for these
parameters for R-134a in [bmim][PF.sub.6] are
.tau..sub.12.sup.(0)=2.92373, .tau.=192.105 K,
.tau..sub.21.sup.(0)=-0.50499, and .tau..sub.21.sup.(1)=-251.738 K.
Optimal values for these parameters for R-134 in [emim][Tf.sub.2N]
are .tau..sub.12.sup.(0)=3.23841, .tau..sub.12.sup.(1)=-1641.731 K,
.tau..sub.21.sup.(0)=-5.24746, and .tau..sub.21.sup.(1)=2460.150 K.
Optimal values for these parameters for R-134a in [emim][Tf.sub.2N]
are .tau..sub.12.sup.(0)=-1.41623, .tau..sub.12.sup.(1)=1466.520 K,
.tau..sub.21.sup.(0)=1.20533, and .tau..sub.21.sup.(1)=-838.522
K.
[0112] Although the infinite dilution state is only a limited (or
extrapolated) state of actual solutions, the thermodynamic
properties at such a state provide important physiochemical
understandings about solute and solvent interactions. Activity
coefficients at infinite dilution, .gamma..sub.1.sup..infin., of
R-134 and R-134a in [bmim][PF.sub.6] can be derived from eq 1 by
setting x.sub.1=0 and x.sub.2=1.
ln .gamma..sub.1.sup.28=.tau..sub.21+.tau..sub.12G.sub.12. (9)
Table 1 provides the temperature (T), the saturated vapor pressure
(P.sub.i.sup.S), the 2.sup.nd virial coefficient (B.sub.11), and
the activity coefficient at infinite dilution
(.gamma..sub.1.sup..infin.) for R-134 and R-134a in
[bmim][PF.sub.6].
TABLE-US-00001 TABLE 1 T P.sub.i.sup.S B.sub.11 Gas Ionic Liquid
(C.) (MPa) (cm.sup.3 mol.sup.-1) .gamma..sub.1.sup..infin. R-134a
[bmim][PF.sub.6] 10 0.415 -566.51 1.431 R-134a [bmim][PF.sub.6] 25
0.665 -493.66 1.490 R-134a [bmim][PF.sub.6] 50 1.317 -398.96 1.579
R-134a [bmim][PF.sub.6] 75 2.363 -328.12 1.659 R-134
[bmim][PF.sub.6] 10 0.322 -478.80 0.748 R-134 [bmim][PF.sub.6] 25
0.525 -433.71 0.883 R-134 [bmim][PF.sub.6] 50 1.062 -369.23 1.042
R-134 [bmim][PF.sub.6] 75 1.933 -315.40 1.127 R-134a
[emim][Tf.sub.2N] 10 0.415 -566.51 1.017 R-134a [emim][Tf.sub.2N]
25 0.665 -493.66 1.140 R-134a [emim][Tf.sub.2N] 50 1.317 -398.96
1.326 R-134a [emim][Tf.sub.2N] 75 2.363 -328.12 1.485 R-134
[emim][Tf.sub.2N] 10 0.322 -478.80 0.436 R-134 [emim][Tf.sub.2N] 25
0.525 -433.71 0.568 R-134 [emim][Tf.sub.2N] 50 1.062 -369.23 0.743
R-134 [emim][Tf.sub.2N] 75 1.933 -315.40 0.847
[0113] These activity coefficients at infinite dilution
.gamma..sub.1.sup..infin. were used to calculate the selectivity
(.alpha..sub.ij):
.alpha. ij = .gamma. i .infin. .gamma. j .infin. ##EQU00004##
where components i and j are present at an infinite degree of
dilution in the extractant [bmim][PF.sub.6] or [emim][Tf.sub.2N],
and i represents R-134a, and j represents R-134. In order to
achieve separation, a selectivity of greater than or less than 1.0
is required. The selectivities (.alpha..sub.ij) in Tables 2a and 2b
show that the use of [bmim][PF.sub.6] as an extractant will
separate R-134a and R-134 with a selectivity of greater than 1.5 to
1.9 over a temperature range from 10 to 75.degree. C. The
selectivities (.alpha..sub.ij) in Table 2 show that the use of
[emim][Tf.sub.2N] as an extractant will separate R-134a and R-134
with a selectivity of greater than 1.7 to 2.3 over a temperature
range from 10 to 75.degree. C.
TABLE-US-00002 TABLE 2a Selectivity for R-134a (i) and R-134 (j) in
[bmim][PF.sub.6] T (C.) .gamma..sub.i.sup..infin.
.gamma..sub.j.sup..infin. .alpha..sub.ij 10 1.431 0.748 1.91 25
1.490 0.883 1.69 50 1.579 1.042 1.52 75 1.659 1.127 1.47
TABLE-US-00003 TABLE 2b Selectivity for R-134a (i) and R-134 (j) in
[emim][Tf.sub.2N] T (C.) .gamma..sub.i.sup..infin.
.gamma..sub.j.sup..infin. .alpha..sub.ij 10 1.017 0.436 2.33 25
1.140 0.568 2.01 50 1.326 0.743 1.78 75 1.485 0.847 1.75
Example 2
Separation of a mixture comprising 1,1,1,2 tetrafluoroethane and
1,1,2,2 tetrafluoroethane
[0114] The Aspen Plus.TM. (Aspen Technology, Inc., Version 13.2,
Cambridge, Mass.) process simulator was used to model the
separation of a mixture comprising of 1,1,1,2 tetrafluoroethane
(also known as HFC-134a or R-134a) and 1,1,2,2 tetrafluoroethane
(also known as HFC-134 or R-134) by extractive distillation using
[emim][Tf.sub.2N] as the extractant.
[0115] The ionic liquid was treated as non-dissociating liquid with
a very low vapor pressure. The nonrandom two-liquid (NRTL) activity
coefficient model (S. I., Sandler, Chemical and Engineering
Thermodynamics, 3.sup.rd Edition (1999) John Wiley and Sons, Inc.,
New York, Chapter 7) was used to model the liquid phase
interactions between the ionic liquid and the fluorocarbon
compounds and the Peng-Robinson equation of state was used to model
the vapor phase. Binary NRTL interaction parameters for the ionic
liquid with the fluorocarbons R-134, R-134a, R-114, R-114a, R-124,
and R-124a were regressed from (P, T, x) data obtained from
solubility experiments. (See Examples 5 and 10 to 14 for the
solubility data.)
[0116] In this modeled example, 100 lb/hr (45.36 kg/hr) of a
mixture of composition 66.08 wt % R-134a, 31.74 wt % R-134, 0.11 wt
% R-114, 130 ppm R-114a, 1.89 wt % R-124, and 0.17 wt % R-124a is
fed to an extractive distillation column containing 32 theoretical
stages and operating at 54.7 psia (377 kPa) with a reflux ratio of
3.0. This fluorocarbon feed, at a temperature of about 12.degree.
C., is fed on the 13.sup.th stage from the top of the column. The
extractant stream, with a composition of 99.5 wt % of the ionic
liquid [emim][Tf.sub.2N], 0.49 wt % R-134, and 110 ppm of R-124, is
fed at 0.degree. C. to the second stage from the top of the
extractive distillation column. The mass flowrate of the extractant
stream is controlled at approximately 4.0 times the mass flowrate
of the fluorocarbon feed.
[0117] As seen in Table 3 below, at these conditions, 99.7% of the
R-134a in the fluorocarbon feed is recovered in the extractive
distillation column distillate at a purity of 99.0 wt %. In
addition, the distillate also contains 0.61 wt % R-134, all of the
chlorofluorocarbons (R-114 and R-114a) and about 6% of the
hydrochlorofluorocarbons (R-124 and R-124a) present in the original
feed mixture. About 98.8% of the R-134 in the fluorocarbon feed
leaves from the bottom of the extractive distillation column along
with the ionic liquid extractant and the remaining fraction of
R-124 and R-124a. The temperatures at the top and bottom of the
extractive distillation column are 7.2 and 80.7.degree. C.,
respectively.
[0118] The bottoms stream from the extractive distillation column
is reduced in pressure across a valve (labeled 105 in FIG. 1) to
17.7 psia (122 kPa), causing partial vaporization of the stream,
and fed to a wiped-film evaporator (labeled 107 in FIG. 1). Because
the viscosity of [emim][Tf.sub.2N] is not too high, a standard
falling-film evaporator, could have been used instead. The
wiped-film evaporator operates at 17.7 psia (122 kPa) and produces
a vapor stream (labeled as 108 in FIG. 1) containing 98.7% of the
R-134 in the original fluorocarbon feed mixture. This stream has a
composition of 93.66 wt % R-134, 5.29 wt % R-124, 0.59 wt % R-134a,
0.47 wt % R-124a, and nondetectible amounts of the ionic liquid
[emim][Tf.sub.2N]. Essentially all of the ionic liquid
[emim][Tf.sub.2N]leaves as the concentrate from the wiped-film
evaporator. One way to keep the temperature of this stream
reasonable is to allow some amount of fluorocarbon to remain with
the nonvolatile [emim][Tf.sub.2N]. For this example, 0.50 wt %,
essentially all R-134, remains in the recovered [emim][Tf.sub.2N].
The recovered ionic liquid stream is cooled and pumped to higher
pressure (both steps are represented by block 110 in FIG. 1) and
then returned to the extractive distillation column as the
extractant feed stream.
TABLE-US-00004 TABLE 3 Aspen Plus .TM. Simulation Results Stream
Number: 100 102 103 104 106 108 109 Mass Flow Rates: kg/hr R-114
0.0515 0.0000 0.0515 0.0000 0.0000 0.0000 0.0000 R-114a 0.0061
0.0000 0.0061 0.0000 0.0000 0.0000 0.0000 R-124 0.8577 0.0203
0.0554 0.8225 0.8225 0.8022 0.0203 R-124a 0.0758 0.0020 0.0044
0.0733 0.0733 0.0713 0.0020 R-134 14.3954 0.8642 0.1854 15.0743
15.0743 14.2100 0.8642 R-134a 29.9728 0.0016 29.8837 0.0907 0.0907
0.0891 0.0016 [emim][Tf.sub.2N] 0.0000 176.5853 0.0000 176.5853
176.5853 0.0000 176.5853 Mass Fractions R-114 0.0011 0.0000 0.0017
0.0000 0.0000 0.0000 0.0000 R-114a 0.0001 0.0000 0.0002 0.0000
0.0000 0.0000 0.0000 R-124 0.0189 0.0001 0.0018 0.0043 0.0043
0.0529 0.0001 R-124a 0.0017 0.0000 0.0001 0.0004 0.0004 0.0047
0.0000 R-134 0.3174 0.0049 0.0061 0.0782 0.0782 0.9366 0.0049
R-134a 0.6608 0.0000 0.9900 0.0005 0.0005 0.0059 0.0000
[emim][Tf.sub.2N] 0.0000 0.9950 0.0000 0.9166 0.9166 0.0000 0.9950
Total Mass Flows: kg/hr 45.3592 177.4734 30.1865 192.6462 192.6462
15.1727 177.4734
[0119] Examples 3 and 4 provide solubility results for
1,1,2,2-tetrafluoroethane (R-134) and 1,1,1,2-tetrafluoroethane
(R-134a) in [bmim][PF.sub.6].sup.-, respectively. These data are
used for calculating the activity coefficient at infinite dilution
(.gamma..sub.1.sup..infin.) as shown in Example 1.
Example 3
Solubility of 1,1,2,2-tetrafluoroethane (R-134) in
1-butyl-3-methylimidazolium hexafluorophosphate
[bmim][PF.sub.6]
[0120] A solubility study was made at temperatures of about 10 to
75.degree. C. over a pressure range from 0.1 bar (0.01 MPa) to
about 3.5 bar (0.35 MPa) where the solubilities (x) or mole
fractions of R-134 in [bmim][PF.sub.6] were measured using a
gravimetric microbalance. Table 4 provides data for T, P, and x,
respectively.
TABLE-US-00005 TABLE 4 T (.degree. C.) P (bar) R-134 (mole
fraction) 10.01 0.10 0.029 9.97 0.50 0.176 9.99 1.00 0.357 9.99
1.50 0.528 9.97 2.00 0.686 9.98 2.50 0.814 9.96 3.00 0.974 25.02
0.10 0.024 24.93 0.50 0.116 24.89 1.00 0.225 24.93 1.50 0.330 24.92
2.00 0.428 25.00 2.50 0.522 24.90 3.00 0.611 24.94 3.50 0.689 49.97
0.10 0.006 49.97 0.50 0.049 49.99 1.00 0.103 50.01 1.50 0.155 49.98
2.00 0.205 50.00 2.50 0.255 49.97 3.00 0.302 50.01 3.50 0.346 74.93
0.10 0.006 75.01 0.50 0.029 74.99 1.00 0.058 75.01 1.50 0.087 74.99
2.00 0.114 75.01 2.50 0.141 75.00 3.00 0.167 74.99 3.50 0.196
Example 4
Solubility of 1,1,1,2-tetrafluoroethane (R-134a) in
1-butyl-3-methylimidazolium hexafluorophosphate
[bmim][PF.sub.6]
[0121] A solubility study was made at temperatures of about 10 to
75.degree. C. over a pressure range from 0.1 bar (0.01 MPa) to
about 3.5 bar (0.35 MPa) where the solubilities (x) or mole
fractions of R-134a in [bmim][PF.sub.6] were measured using a
gravimetric microbalance. Table 5 provides data for T, P, and x,
respectively.
TABLE-US-00006 TABLE 5 T (.degree. C.) P (bar) R134a (mole
fraction) 9.8 0.100 0.003 10.0 0.498 0.050 9.9 0.999 0.126 9.9
1.498 0.213 9.9 2.002 0.305 9.9 2.491 0.404 9.9 2.997 0.519 9.9
3.490 0.724 25.0 0.100 0.011 24.9 0.498 0.042 25.0 0.997 0.086 25.0
1.499 0.130 25.0 1.993 0.176 24.9 2.500 0.224 25.0 2.995 0.275 24.9
3.500 0.326 49.9 0.099 0.004 50.0 0.498 0.021 49.9 0.997 0.043 49.9
1.499 0.065 50.0 1.990 0.087 50.0 2.490 0.109 50.0 2.990 0.131 50.0
3.493 0.154 75.0 0.097 0.000 74.9 0.498 0.009 74.9 0.993 0.022 74.9
1.501 0.035 75.0 1.998 0.047 75.0 2.501 0.059 75.0 3.002 0.072 75.0
3.490 0.085
[0122] Additional examples 5 to 9 provide solubility results for
1,1,2,2-tetrafluoroethane (R-134) in several other ionic liquids
which all work to varying degrees to separate R-134 from R-134a. A
low viscosity ionic liquid with high solubility for R-134 is
1-ethyl-3-ethylimidazolium bis(trifluoromethylsulfonyl)imide
([emim][Tf.sub.2N] or [emim][BMeI]). Solubility results for R-134
in [emim][Tf.sub.2N] are shown in Example 5. This ionic liquid,
[emim][Tf.sub.2N], was also measured with R-134a (Example 10) and
several of the impurities which can be present in the manufacturing
to produce R-134/R-134a. These data are shown in Examples 11 to 14.
The data in Examples 3, 4, 5, and 10 were used for calculating the
activity coefficients and ideal selectivities in Example 1.
Furthermore the data in Examples 5 and 10, along with the data
found in Examples 11-14 for the solubility of R-114, R-114a, R-124,
and R-124a were used for calculating the physical property
parameters used in the Aspen Plus.TM. modeling in Example 2.
Example 5
Solubility of 1,1,2,2-tetrafluoroethane (R-134) in
1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide
[emim][Tf.sub.2N]
[0123] A solubility study was made at temperatures of about 10 to
75.degree. C. over a pressure range from 0.1 bar (0.01 MPa) to
about 3.5 bar (0.35 MPa) where the solubilities (x) or mole
fractions of R-134 in [emim][Tf.sub.2N] were measured using a
gravimetric microbalance. Table 6 provides data for T, P, and x,
respectively.
TABLE-US-00007 TABLE 6 T (.degree. C.) P (bar) R-134 (mole
fraction) 9.76 0.10 0.055 10.01 0.50 0.246 9.92 1.00 0.433 10.10
1.50 0.573 9.81 2.00 0.702 9.98 2.50 0.811 10.01 3.00 0.964 25.08
0.10 0.033 25.01 0.50 0.156 25.01 1.00 0.284 24.97 1.50 0.395 25.05
2.00 0.490 24.91 2.50 0.573 24.90 2.99 0.648 25.02 3.50 0.716 49.90
0.10 0.016 49.94 0.50 0.076 50.01 1.00 0.147 49.93 1.51 0.210 49.91
2.00 0.269 49.87 2.49 0.323 49.94 3.00 0.374 49.94 3.50 0.421 74.98
0.10 0.006 74.94 0.50 0.040 74.95 1.01 0.079 74.92 1.50 0.116 74.91
2.00 0.152 74.93 2.50 0.186 74.94 3.00 0.219 74.95 3.50 0.250
Example 6
Solubility of 1,1,2,2-tetrafluoroethane (R-134) in
3-methyl-1-propylpyridinium bis(trifluoromethylsulfonyl)imide
[pmpy][Tf.sub.2N]
[0124] A solubility study was made at temperatures of about 10 to
75.degree. C. over a pressure range from 0.1 bar (0.01 MPa) to
about 3.5 bar (0.35 MPa) where the solubilities (x) or mole
fractions of R-134 in [pmpy][Tf.sub.2N] were measured using a
gravimetric microbalance. Table 7 provides data for T, P, and x,
respectively.
TABLE-US-00008 TABLE 7 T (.degree. C.) P (bar) R-134 (mole
fraction) 9.85 0.10 0.058 9.93 0.50 0.258 9.96 1.00 0.442 9.87 1.50
0.584 10.03 1.99 0.697 9.98 2.50 0.803 9.97 2.99 0.925 24.99 0.10
0.035 24.99 0.50 0.161 24.92 1.00 0.292 24.87 1.50 0.403 24.91 2.00
0.496 25.04 2.49 0.574 25.07 3.00 0.645 25.00 3.49 0.711 50.05 0.10
0.018 49.93 0.50 0.081 49.94 1.00 0.154 49.94 1.50 0.219 49.94 2.00
0.279 49.94 2.50 0.334 49.86 2.99 0.385 49.87 3.50 0.432 74.94 0.10
0.005 74.94 0.50 0.040 74.97 1.00 0.082 74.91 1.50 0.122 74.98 2.00
0.160 74.99 2.50 0.196 74.93 3.00 0.230 74.92 3.50 0.262
Example 7
Solubility of 1,1,2,2-tetrafluoroethane (R-134) in
1-hexyl-3-methylimidazolium
tris(pentafluoroethyl)trifluorophosphate
[hmim][PF.sub.3(C.sub.2F.sub.5).sub.3]
[0125] A solubility study was made at temperatures of about 10 to
75.degree. C. over a pressure range from 0.1 bar (0.01 MPa) to
about 3.5 bar (0.35 MPa) where the solubilities (x) or mole
fractions of R-134 in [hmim][PF.sub.3(C.sub.2F.sub.5).sub.3] were
measured using a gravimetric microbalance. Table 8 provides data
for T, P, and x, respectively.
TABLE-US-00009 TABLE 8 T (.degree. C.) P (bar) R-134 (mole
fraction) 9.93 0.10 0.055 9.92 0.50 0.240 9.98 1.00 0.422 10.02
1.50 0.568 9.95 2.00 0.689 9.97 2.49 0.810 9.98 2.99 0.959 24.98
0.10 0.035 24.93 0.50 0.160 25.05 1.00 0.293 24.87 1.50 0.403 24.96
1.99 0.498 25.02 2.50 0.583 24.99 3.00 0.656 24.91 3.50 0.727 49.97
0.10 0.018 49.94 0.50 0.085 49.95 1.00 0.161 49.95 1.50 0.229 49.94
2.00 0.291 50.04 2.50 0.347 49.98 3.00 0.401 49.94 3.50 0.448 74.92
0.10 0.009 74.91 0.50 0.047 74.99 1.00 0.092 74.98 1.50 0.135
74.968 2.00 0.176 74.96 2.50 0.213 74.99 3.00 0.250 74.98 3.49
0.284
Example 8
Solubility of 1,1,2,2-tetrafluoroethane (R-134) in
1,2-dimethyl-3-propylimidazolium
tris(trifluoromethylsulfonyl)methide [dmpim][TMeM]
[0126] A solubility study was made at temperatures of about 10 to
75.degree. C. over a pressure range from 0.1 bar (0.01 MPa) to
about 3.5 bar (0.35 MPa) where the solubilities (x) or mole
fractions of R-134 in [dmpim][TMeM] were measured using a
gravimetric microbalance. Table 9 provides data for T, P, and x,
respectively.
TABLE-US-00010 TABLE 9 T (.degree. C.) P (bar) R-134 (mole
fraction) 10.11 0.10 0.054 9.97 0.50 0.252 9.88 1.00 0.443 10.01
1.50 0.596 10.01 1.99 0.717 9.99 2.50 0.827 10.05 3.00 0.963 24.90
0.10 0.029 25.07 0.50 0.149 24.86 1.00 0.287 24.93 1.50 0.403 25.01
2.00 0.503 24.85 2.49 0.587 25.04 3.00 0.667 25.03 3.49 0.732 49.96
0.10 0.006 49.98 0.50 0.069 49.98 1.00 0.145 49.96 1.50 0.215 49.95
2.00 0.278 49.91 2.50 0.337 49.92 3.00 0.390 49.96 3.50 0.440 74.94
0.10 0.010 74.95 0.50 0.046 74.99 1.00 0.089 74.93 1.50 0.131 74.98
2.00 0.170 74.93 2.50 0.207 74.97 3.00 0.243 74.98 3.50 0.277
Example 9
Solubility of 1,1,2,2-tetrafluoroethane (R-134) in
1-ethyl-3-methylimidazolium bis(pentafluoroethylsulfonyl)imide
[emim][BEI]
[0127] A solubility study was made at temperatures of about 10 to
75.degree. C. over a pressure range from 0.1 bar (0.01 MPa) to
about 3.5 bar (0.35 MPa) where the solubilities (x) or mole
fractions of R-134 in [emim][BEI] were measured using a gravimetric
microbalance. Table 10 provides data for T, P, and x,
respectively.
TABLE-US-00011 TABLE 10 T (.degree. C.) P (bar) R-134 (mole
fraction) 9.999 0.10 0.039 9.973 0.50 0.236 9.982 1.00 0.430 9.999
1.50 0.584 9.973 2.00 0.708 9.999 2.50 0.823 10.042 3.00 0.980
25.062 0.10 0.038 25.004 0.50 0.169 25.004 1.00 0.305 25.037 1.50
0.417 24.978 2.00 0.518 24.995 2.50 0.606 25.079 3.00 0.677 24.953
3.50 0.735 49.998 0.11 0.019 50.023 0.50 0.086 49.998 1.00 0.162
49.99 1.50 0.232 49.99 2.00 0.295 49.982 2.50 0.355 49.982 3.00
0.407 49.998 3.49 0.460 75.014 0.11 0.010 74.998 0.50 0.048 74.982
1.00 0.094 74.973 1.50 0.136 75.006 2.00 0.176 75.006 2.50 0.215
75.014 3.00 0.293 74.99 3.50 0.371
Example 10
Solubility of 1,1,1,2-tetrafluoroethane (R-134a) in
1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide
[emim][Tf.sub.2N]
[0128] A solubility study was made at temperatures of about 10 to
75.degree. C. over a pressure range from 0.1 bar (0.01 MPa) to
about 3.5 bar (0.35 MPa) where the solubilities (x) or mole
fractions of R-134a in [emim][Tf.sub.2N] were measured using a
gravimetric microbalance. Table 11 provides data for T, P, and x,
respectively.
TABLE-US-00012 TABLE 11 T (.degree. C.) P (bar) R-134a (mole
fraction) 10.529 0.10 0.019 9.585 0.50 0.105 9.968 1.00 0.219
10.061 1.50 0.318 10.036 2.00 0.415 10.036 2.50 0.516 10.07 3.00
0.613 10.036 3.50 0.755 25.057 0.10 0.016 24.923 0.50 0.071 24.964
1.00 0.138 24.964 1.50 0.203 24.931 2.00 0.263 25.073 2.50 0.322
24.914 3.00 0.382 24.931 3.49 0.443 49.935 0.10 0.008 49.96 0.50
0.036 49.968 1.00 0.071 49.96 1.50 0.105 49.935 2.00 0.138 49.885
2.50 0.169 50.025 3.00 0.201 49.984 3.50 0.231 74.952 0.10 0.000
74.927 0.50 0.017 74.968 1.00 0.038 74.96 1.50 0.058 74.935 2.00
0.077 74.935 2.50 0.096 74.935 3.00 0.115 74.968 3.50 0.133
Example 11
Solubility of 1,2-dichloro-1,1,2,2-tetrafluoroethane (R-114) in
1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide
[emim][Tf.sub.2N]
[0129] A solubility study was made at temperatures of about 10 to
75.degree. C. over a pressure range from 0.1 bar (0.01 MPa) to
about 1.5 bar (0.15 MPa) where the solubilities (x) or mole
fractions of R-114 in [emim][Tf.sub.2N] were measured using a
gravimetric microbalance. Table 12 provides data for T, P, and x,
respectively.
TABLE-US-00013 TABLE 12 T (.degree. C.) P (bar) R-114 (mole
fraction) 9.976 0.10 0.012 9.874 0.50 0.060 9.9 0.75 0.092 9.9 1.00
0.126 24.881 0.10 0.006 25.073 0.50 0.034 25.157 0.70 0.050 24.923
1.00 0.073 25.006 1.25 0.093 24.931 1.50 0.113 49.877 0.10 0.004
49.976 0.50 0.018 49.968 0.71 0.026 49.984 1.00 0.036 49.918 1.25
0.045 49.91 1.50 0.055 74.952 0.10 0.000 74.968 0.50 0.009 74.984
0.71 0.013 74.976 1.00 0.019 74.944 1.25 0.024 74.952 1.50
0.030
Example 12
Solubility of 1,1-dichloro-1,2,2,2-tetrafluoroethane (R-114a) in
1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide
[emim][Tf.sub.2N]
[0130] A solubility study was made at temperatures of about 10 to
75.degree. C. over a pressure range from 0.1 bar (0.01 MPa) to
about 1.5 bar (0.15 MPa) where the solubilities (x) or mole
fractions of R-114a in [emim][Tf.sub.2N] were measured using a
gravimetric microbalance. Table 13 provides data for T, P, and x,
respectively.
TABLE-US-00014 TABLE 13 T (.degree. C.) P (bar) R-114a (mole
fraction) 10.053 0.10 0.013 9.968 0.50 0.066 9.951 0.75 0.101 9.951
1.00 0.142 25.132 0.10 0.006 24.931 0.50 0.032 24.998 0.70 0.048
24.998 1.00 0.073 24.839 1.25 0.095 24.897 1.50 0.117 49.951 0.10
0.002 49.943 0.50 0.017 49.91 0.70 0.025 49.951 1.00 0.037 49.968
1.25 0.047 49.96 1.50 0.057 74.968 0.10 0.001 74.968 0.50 0.010
74.96 0.71 0.015 74.96 1.00 0.021 74.984 1.25 0.027 74.992 1.50
0.032
Example 13
Solubility of 1-chloro-1,2,2,2-tetrafluoroethane (R-124) in
1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide
[emim][Tf.sub.2N]
[0131] A solubility study was made at temperatures of about 10 to
75.degree. C. over a pressure range from 0.1 bar (0.01 MPa) to
about 3.0 bar (0.30 MPa) where the solubilities (x) or mole
fractions of R-124 in [emim][Tf.sub.2N] were measured using a
gravimetric microbalance. Table 14 provides data for T, P, and x,
respectively.
TABLE-US-00015 TABLE 14 T (.degree. C.) P (bar) R-124 (mole
fraction) 9.883 0.10 0.050 10.027 0.50 0.224 9.934 1.00 0.422 9.942
1.50 0.591 9.985 2.00 0.757 24.914 0.10 0.028 25.015 0.50 0.134
24.872 1.00 0.259 25.04 1.50 0.369 24.923 2.00 0.473 25.048 2.50
0.568 24.99 3.00 0.665 49.993 0.10 0.010 49.951 0.50 0.058 49.976
1.00 0.115 49.96 1.50 0.169 49.976 2.00 0.221 49.951 2.50 0.272
49.943 3.00 0.322 74.96 0.10 0.001 74.984 0.50 0.026 74.976 1.00
0.057 74.976 1.50 0.088 74.952 2.00 0.118 74.968 2.50 0.145 74.927
3.00 0.171
Example 14
Solubility of 1-chloro-1,1,2,2-tetrafluoroethane (R-124a) in
1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide
[emim][Tf.sub.2N]
[0132] A solubility study was made at temperatures of about 10 to
75.degree. C. over a pressure range from 0.1 bar (0.01 MPa) to
about 3.0 bar (0.30 MPa) where the solubilities (x) or mole
fractions of R-124a in [emim][Tf.sub.2N] were measured using a
gravimetric microbalance. Table 15 provides data for T, P, and x,
respectively.
TABLE-US-00016 TABLE 15 T (.degree. C.) P (bar) R-124a (mole
fraction) 10.044 0.10 0.047 9.968 0.50 0.212 9.934 1.00 0.401 9.959
1.50 0.573 9.985 2.00 0.759 24.964 0.10 0.029 25.065 0.50 0.128
24.964 1.00 0.244 24.973 1.50 0.356 24.822 1.99 0.461 24.998 2.50
0.572 24.948 3.00 0.692 49.894 0.10 0.012 49.894 0.50 0.058 50.034
1.00 0.116 50.025 1.50 0.171 49.935 2.00 0.222 49.935 2.50 0.271
49.96 3.00 0.322 74.927 0.10 0.001 74.919 0.50 0.027 74.935 1.00
0.057 74.968 1.50 0.087 74.895 2.00 0.116 74.927 2.50 0.143 74.952
3.00 0.171
* * * * *