U.S. patent application number 10/527649 was filed with the patent office on 2006-02-16 for proton-conducting membrane and use thereof verwendung.
This patent application is currently assigned to PEMEAS GMBH. Invention is credited to Jochen Baurmeister, Brian Benicewicz, Gordon Calundann.
Application Number | 20060035095 10/527649 |
Document ID | / |
Family ID | 32038157 |
Filed Date | 2006-02-16 |
United States Patent
Application |
20060035095 |
Kind Code |
A1 |
Calundann; Gordon ; et
al. |
February 16, 2006 |
Proton-conducting membrane and use thereof verwendung
Abstract
The present invention relates to novel polyazoles, a
proton-conducting polymer membrane based on these polyazoles and
its use as polymer electrolyte membrane (PEM) for producing
membrane-electrode units for PEM-fuel cells, and also other shaped
bodies comprising such polyazoles.
Inventors: |
Calundann; Gordon; (North
Plainfield, NJ) ; Benicewicz; Brian; (Londonville,
NY) ; Baurmeister; Jochen; (Eppstein, DE) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ, LLP
P O BOX 2207
WILMINGTON
DE
19899
US
|
Assignee: |
PEMEAS GMBH
FRANKFURT
DE
|
Family ID: |
32038157 |
Appl. No.: |
10/527649 |
Filed: |
August 20, 2003 |
PCT Filed: |
August 20, 2003 |
PCT NO: |
PCT/EP03/09198 |
371 Date: |
October 20, 2005 |
Current U.S.
Class: |
428/473.5 ;
204/280; 428/474.4; 429/209; 429/413 |
Current CPC
Class: |
C08G 73/08 20130101;
C08G 73/0616 20130101; Y10T 428/31721 20150401; C08J 5/2256
20130101; Y10T 428/31725 20150401; Y02P 70/50 20151101; C08G
73/0633 20130101; H05K 1/0346 20130101; B01D 71/62 20130101; C08G
61/122 20130101; C08J 2479/06 20130101; H01M 8/103 20130101; C08G
61/124 20130101; C08G 73/0694 20130101; H01M 4/8605 20130101; C08G
73/22 20130101; H01M 8/1004 20130101; H01M 8/1018 20130101; H01M
8/1048 20130101; C08G 73/18 20130101; H01M 8/1027 20130101; Y02E
60/50 20130101 |
Class at
Publication: |
428/473.5 ;
429/012; 429/209; 204/280; 428/474.4 |
International
Class: |
H01M 8/00 20060101
H01M008/00; C25C 7/02 20060101 C25C007/02; H01M 4/02 20060101
H01M004/02; B32B 27/34 20060101 B32B027/34; B32B 27/00 20060101
B32B027/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 13, 2002 |
DE |
102 42 708.9 |
Claims
1. A proton-conducting polymer membrane which is based on
polyazoles and is obtainable by a process comprising the steps A)
mixing of one or more aromatic tetramino compounds with one or more
aromatic carboxylic acids or esters thereof which contain at least
two acid groups per carboxylic acid monomer, or mixing of one or
more aromatic and/or heteroaromatic diaminocarboxylic acids, in
phosphoric acid to form a solution and/or dispersion, B) heating of
the solution and/or dispersion obtained in step A) to temperatures
of up to 350.degree. C. to form the polyazole polymer, C)
application of a layer using the mixture from step B) to a support,
D) treatment of the membrane formed in step C).
2. The membrane as claimed in claim 1, characterized in that
3,3',4,4'-tetraaminobiphenyl, 2,3,5,6-tetraminopyridine,
1,2,4,5-tetraminobenzene, bis(3,4-diaminophenyl)sulfone,
bis(3,4-diaminophenyl) ether, 3,3',4,4'-tetraminobenzophenone,
3,3',4,4'-tetraminodiphenylmethane and
3,3',4,4'-tetraminodiphenyldimethylmethane are used as aromatic
tetramino compounds.
3. The membrane as claimed in claim 1, characterized in that
isophthalic acid, terephthalic acid, phthalic acid,
5-hydroxyisophthalic acid, 4-hydroxyisophthalic acid,
2-hydroxyterephthalic acid, 5-aminoisophthalic acid,
5-N,N-dimethylaminoisophthalic acid, 5-N,N-diethylaminoisophthalic
acid, 2,5-dihydroxyterephthalic acid, 2,5-dihydroxyisophthalic
acid, 2,3-dihydroxyisophthalic acid, 2,3-dihydroxyphthalic acid,
2,4-dihydroxyphthalic acid, 3,4-dihydroxyphthalic acid,
3-fluorophthalic acid, 5-fluoroisophthalic acid,
2-fluoroterephthalic acid, tetrafluorophthalic acid,
tetrafluoroisophthalic acid, tetrafluoroterephthalic acid,
1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid,
2,6-naphthalenedicarboxylic acid, 2,7-naphthalene-dicarboxylic
acid, diphenic acid, 1,8-dihydroxynaphthalene-3,6-dicarboxylic
acid, bis(4-carboxyphenyl) ether, benzophenone-4,4'-dicarboxylic
acid, bis(4-dicarboxyphenyl) sulfone, biphenyl-4,4'-dicarboxylic
acid, 4-trifluoromethylphthalic acid,
2,2-bis(4-carboxyphenyl)hexafluoropropane,
4,4'-stilbenedicarboxylic acid, 4-carboxycinnamic acid, or their
C1-C20-alkyl esters or C5-C12-aryl esters, or their acid anhydrides
or acid chlorides are used as aromatic dicarboxylic acids.
4. The membrane as claimed in claim 1, characterized in that
tricarboxylic acids, tetracarboxylic acids or their C1-C20-alkyl
esters or C5-C12-aryl esters or their acid anhydrides or their acid
chlorides.
5. The membrane as claimed in claim 1, characterized in that
tetracarboxylic acids, their C1-C20-alkyl esters or C5-C12-aryl
esters or their acid anhydrides or their acid chlorides, are used
as aromatic carboxylic acids.
6. The membrane as claimed in claim 4, characterized in that the
content of tricarboxylic acids and tetracarboxylic acids (based on
dicarboxylic acid used) is from 0.5 to 20 mol %.
7. The membrane as claimed in claim 1, characterized in that
heteroaromatic dicarboxylic acids and tricarboxylic acids and
tetracarboxylic acids containing at least one nitrogen, oxygen,
sulfur or phosphorus atom in the aromatic, are used as
heteroaromatic carboxylic acids.
8. The membrane as claimed in claim 1, characterized in that a
polyazole-based polymer comprising recurring azole units of the
general formula (I)-(XXII) or a mixture thereof, ##STR7## ##STR8##
##STR9## where the radicals Ar are identical or different and are
each a tetravalent aromatic or heteroaromatic group which can be
monocyclic or polycyclic, the radicals Ar.sup.1 are identical or
different and are each a divalent aromatic or heteroaromatic group
which can be monocyclic or polycyclic, the radicals Ar.sup.2 are
identical or different and are each a divalent or trivalent
aromatic or heteroaromatic group which can be monocyclic or
polycyclic, the radicals Ar.sup.3 are identical or different and
are each a trivalent aromatic or heteroaromatic group which can be
monocyclic or polycyclic, the radicals Ar.sup.4 are identical or
different and are each a trivalent aromatic or heteroaromatic group
which can be monocyclic or polycyclic, the radicals Ar.sup.5 are
identical or different and are each a tetravalent aromatic or
heteroaromatic group which can be monocyclic or polycyclic, the
radicals Ar.sup.6 are identical or different and are each a
divalent aromatic or heteroaromatic group which can be monocyclic
or polycyclic, the radicals Ar.sup.7 are identical or different and
are each a divalent aromatic or heteroaromatic group which can be
monocyclic or polycyclic, the radicals Ar.sup.8 are identical or
different and are each a trivalent aromatic or heteroaromatic group
which can be monocyclic or polycyclic, the radicals Ar.sup.9 are
identical or different and are each a divalent or trivalent or
tetravalent aromatic or heteroaromatic group which can be
monocyclic or polycyclic, the radicals Ar.sup.10 are identical or
different and are each a divalent or trivalent aromatic or
heteroaromatic group which can be monocyclic or polycyclic, the
radicals Ar.sup.11 are identical or different and are each a
divalent aromatic or heteroaromatic group which can be monocyclic
or polycyclic, the radicals X are identical or different and are
each oxygen, sulfur or an amino group which bears a hydrogen atom,
a group having 1-20 carbon atoms, preferably a branched or
unbranched alkyl or alkoxy group, or an aryl group as further
radical, the radicals R are identical or different and are each
hydrogen, an alkyl group or an aromatic group and n, m are each an
integer greater than or equal to 10, is formed in step B).
9. The membrane as claimed in claim 1, characterized in that a
polymer selected from the group consisting of polybenzimidazole,
poly(pyridines), poly(pyrimidines), polyimidazoles,
polybenzothiazoles, polybenzoxazoles, polyoxadiazoles,
polyquinoxalines, polythiadiazoles and poly(tetrazapyrenes) is
formed in step B).
10. The membrane as claimed in claim 1, characterized in that a
polymer comprising recurring benzimidazole units of the formula
##STR10## ##STR11## ##STR12## where n and m are each an integer
greater than or equal to 10, preferably greater than or equal to
100, is formed in step B).
11. The membrane as claimed in claim 1, characterized in that the
viscosity is adjusted by addition of phosphoric acid after step B)
and before step C).
12. The membrane as claimed in claim 1, characterized in that a
layer having a thickness of from 20 to 4000 .mu.m, preferably from
30 to 3500 .mu.m, in particular from 50 to 3000 .mu.m, is produced
in step C).
13. The membrane as claimed in claim 1, characterized in that the
membrane produced in step C) is treated in step D) until the
membrane is self-supporting and can be detached from the support
without damage.
14. The membrane as claimed in claim 1, characterized in that the
membrane produced in step C) is treated in step D) by the action of
heat in the presence of atmospheric oxygen.
15. The membrane as claimed in claim 1, characterized in that the
membrane produced in step C) still contains tricarboxylic or
tetracarboxylic acids which are crosslinked in step D).
16. The membrane as claimed in claim 1, characterized in that the
membrane produced in step C) is crosslinked by treatment with
sulfuric acid in step D).
17. The membrane as claimed in claim 1, characterized in that the
membrane produced in step C) is crosslinked by action of IR or NIR
light or by irradiation with .beta.-rays in step D).
18. The membrane as claimed in claim 1, characterized in that it
has a layer comprising a catalytically active component.
19. The membrane as claimed in claim 1, characterized in that the
formation of the membrane according to steps A) to D) is carried
out on a support or a support film on which the catalyst is
present, and the catalyst is located on the membrane according to
the invention after removal of the support or the support film.
20. The membrane as claimed in claim 1, characterized in that the
formation of the membrane according to steps A) to D) is carried
out on an electrode as support.
21. An electrode provided with a proton-conducting polymer coating
which is based on polyazoles and is obtainable by a process
comprising the steps A) mixing of one or more aromatic tetramino
compounds with one or more aromatic carboxylic acids or esters
thereof which contain at least two acid groups per carboxylic acid
monomer, or mixing of one or more aromatic and/or heteroaromatic
diaminocarboxylic acids, in phosphoric acid to form a solution
and/or dispersion, B) heating of the solution and/or dispersion
obtained in step A) to temperatures of up to 350.degree. C. to form
the polyazole polymer, C) application of a layer using the mixture
from step B) to an electrode, D) optionally treatment of the
membrane formed in step C).
22. The electrode as claimed in claim 21, wherein the coating has a
thickness in the range from 2 to 3000 .mu.m.
23. A membrane-electrode unit comprising at least one electrode and
at least one membrane as claimed in claim 1.
24. A membrane-electrode unit comprising at least one electrode as
claimed in claim 1.
25. A fuel cell comprising one or more membrane-electrode units as
claimed in claim 22.
26. A polymer film which is based on polyazoles and is obtainable
by a process comprising the steps A) mixing of one or more aromatic
tetramino compounds with one or more aromatic carboxylic acids or
esters thereof which contain at least two acid groups per
carboxylic acid monomer, or mixing of one or more aromatic and/or
heteroaromatic diaminocarboxylic acids, in phosphoric acid to form
a solution and/or dispersion, B) heating of the solution and/or
dispersion obtained in step A) to temperatures of up to 350.degree.
C. to form the polyazole polymer, C) application of a layer using
the mixture from step B) to a support, D) treatment of the membrane
formed in step C) until it is self-supporting, E) detachment of the
membrane formed in step C) from the support, F) removal of the
phosphoric acid present and drying.
27. The polymer film as claimed in claim 25, characterized in that
the removal of the phosphoric acid in step F) is carried out by
means of a treatment liquid.
28. (canceled)
29. A polymer which is based on polyazoles defined in claim 8,
whose molecular weight expressed as intrinsic viscosity is at least
1.4 dl/g and which is obtainable by a process comprising the steps
A) mixing of one or more aromatic tetramino compounds with one or
more aromatic carboxylic acids or esters thereof which contain at
least two acid groups per carboxylic acid monomer, or mixing of one
or more aromatic and/or heteroaromatic diaminocarboxylic acids, in
phosphoric acid to form a solution and/or dispersion, B) heating of
the mixture obtainable according to step A) under inert gas to
temperatures of up to 350.degree. C. to form the polyazole polymer,
C) precipitation of the polymer formed in step B) and isolation and
drying of the polymer powder obtained.
30. A molding comprising polymers as claimed in claim 18.
31. A polymer fiber which is based on polyazoles, whose molecular
weight expressed as intrinsic viscosity is at least 1.4 dl/g and
which is obtainable by a process comprising the steps A) mixing of
one or more aromatic tetramino compounds with one or more aromatic
carboxylic acids or esters thereof which contain at least two acid
groups per carboxylic acid monomer, or mixing of one or more
aromatic and/or heteroaromatic diaminocarboxylic acids, in
polyphosphoric acid to form a solution and/or dispersion, B)
heating of the mixture obtained in step A) to temperatures of up to
350.degree. C. to form the polyazole polymer, C) extrusion of the
polyazole polymer formed in step B) to form fibers, D) introduction
of the fibers formed in step C) into a liquid bath, E) isolation
and drying of the fibers obtained.
32. The polymer fiber as claimed in claim 30, characterized in that
the fibers formed in step C) are introduced into a precipitation
bath.
33. A process for the filtration and/or separation of gases and/or
liquids or in reverse osmosis which comprises using the polymer
film as claimed in claim 25.
Description
[0001] The present invention relates to a novel proton-conducting
polymer membrane based on polyazoles, which can, owing to its
excellent chemical and thermal properties, be used for a variety of
purposes and is particularly suitable as polymer electrolyte
membrane (PEM) in PEM fuel cells.
[0002] Polyazoles such as polybenzimidazoles (.RTM.Celazole) have
been known for a long time. Such polybenzimidazoles (PBIs) are
usually prepared by reacting 3,3',4,4'-tetraminobiphenyl with
isophthalic acid or diphenylisophthalic acid or esters thereof in
the melt. The resulting prepolymer solidifies in the reactor and is
subsequently comminuted mechanically. The pulverulent prepolymer is
subsequently fully polymerized in a solid-state polymerization at
temperatures of up to 400.degree. C. and the desired
polybenzimidazole is obtained.
[0003] To produce polymer films, the PBI is, in a further step,
dissolved in polar, aprotic solvents such as dimethylacetamide
(DMAc) and a film is produced by classical methods.
[0004] Proton-conducting, i.e. acid-doped, polyazole membranes for
use in PEM fuel cells are already known. The basic polyazole films
are doped with concentrated phosphoric acid or sulfuric acid and
then act as proton conductors and separators in polymer electrolyte
membrane fuel cells (PEM fuel cells).
[0005] Due to the excellent properties of the polyazole polymer,
such polymer electrolyte membranes can, when processed to produce
membrane-electrode units (MEUs), be used in fuel cells at long-term
operating temperatures above 100.degree. C., in particular above
120.degree. C. This high long-term operating temperature allows the
activity of the catalysts based on noble metals which are present
in the membrane-electrode unit (MEU) to be increased. Particularly
when using reformates of hydrocarbons, significant amounts of
carbon monoxide are present in the reformer gas and these usually
have to be removed by means of a costly gas work-up or gas
purification. This ability to increase the operating temperature
enables significantly higher concentrations of CO impurities to be
tolerated over the long term.
[0006] The use of polymer electrolyte membranes based on polyazole
polymers allows, firstly, the costly gas work-up or gas
purification to be omitted in some cases and, secondly, the
catalyst loading in the membrane-electrode unit to be reduced. Both
are indispensable prerequisites for large-scale use of PEM fuel
cells, since otherwise the costs of a PEM fuel cell system are too
high.
[0007] The previously known acid-doped polymer membranes based on
polyazoles display a favorable property profile. However, owing to
the applications desired for PEM fuel cells, in particular in the
automobile sector and in decentralized power and heat generation
(stationary sector), these need to be improved overall.
Furthermore, the previously known polymer membranes have a high
content of dimethylacetamide (DMAC) which cannot be removed
completely by means of known drying methods. The German patent
application No.10109829.4 describes a polymer membrane which is
based on polyazoles and in which the DMAc contamination has been
eliminated. Although such polymer membranes display improved
mechanical properties, specific conductivities do not exceed 0.1
S/cm (at 140.degree. C.).
[0008] It is an object of the present invention to provide
acid-containing polymer membranes based on polyazoles, which
firstly have the use advantages of the polymer membrane based on
polyazoles and, secondly, have an increased specific conductivity,
in particular at operating temperatures above 100.degree. C., and
make do without additional moistening of the fuel gas.
[0009] We have now found that a proton-conducting membrane based on
polyazoles can be obtained when the parent monomers are suspended
or dissolved in phosphoric acid, spread as a thin layer by means of
a doctor blade and polymerized in the phosphoric acid.
[0010] In the case of this novel membrane, the specific
after-treatment described in the German patent application No.
10109829.4, an additional preparation of a polymer solution and the
subsequent doping of the film can be dispensed with. The doped
polymer membranes display a significantly improved proton
conductivity.
[0011] The present invention provides a proton-conducting polymer
membrane which is based on polyazoles and is obtainable by a
process comprising the steps [0012] A) mixing of one or more
aromatic tetramino compounds with one or more aromatic carboxylic
acids or esters thereof which contain at least two acid groups per
carboxylic acid monomer, or mixing of one or more aromatic and/or
heteroaromatic diaminocarboxylic acids, in phosphoric acid to form
a solution and/or dispersion, [0013] B) heating of the solution
and/or dispersion obtained in step A) to temperatures of up to
350.degree. C., preferably up to 280.degree. C., to form the
polyazole polymer, [0014] C) application of a layer using the
mixture from step B) to a support or an electrode, [0015] D)
treatment of the membrane formed in step C) (until it is
self-supporting).
[0016] The aromatic and heteroaromatic tetramino compounds used
according to the invention are preferably
3,3',4,4'-tetraminobiphenyl, 2,3,5,6-tetraminopyridine,
1,2,4,5-tetraminobenzene, bis(3,4-diaminophenyl)sulfone,
bis(3,4-diaminophenyl) ether, 3,3',4,4'-tetraminobenzophenone,
3,3',4,4'-tetraminodiphenylmethane and
3,3',4,4'-tetraminodiphenyldimethylmethane and their salts, in
particular their monohydrochloride, dihydrochloride,
trihydrochloride and tetrahydrochloride derivatives.
[0017] The aromatic carboxylic acids used according to the
invention are dicarboxylic acids, tricarboxylic acids and
tetracarboxylic acids or their esters or their anhydrides or their
acid chlorides. The term aromatic carboxylic acids likewise
encompasses heteroaromatic carboxylic acids. The aromatic
dicarboxylic acids are preferably isophthalic acid, terephthalic
acid, phthalic acid, 5-hydroxyisophthalic acid,
4-hydroxyisophthalic acid, 2-hydroxyterephthalic acid,
5-aminoisophthalic acid, 5-N,N-dimethylaminoisophthalic acid,
5-N,N-diethylaminoisophthalic acid, 2,5-dihydroxyterephthalic acid,
2,6-dihydroxyisophthalic acid, 4,6-dihydroxyisophthalic acid,
2,3-dihydroxyphthalic acid, 2,4-dihydroxyphthalic acid,
3,4-dihydroxyphthalic acid, 3-fluorophthalic acid,
5-fluoroisophthalic acid, 2-fluoroterephthalic acid,
tetrafluorophthalic acid, tetrafluoroisophthalic acid,
tetrafluoroterephthalic acid, 1,4-naphthalenedicarboxylic acid,
1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid,
2,7-naphthalenedicarboxylic acid, diphenic acid,
1,8-dihydroxynaphthalene-3,6-dicarboxylic acid,
bis(4-carboxyphenyl) ether, benzophenone-4,4'-dicarboxylic acid,
bis(4-dicarboxyphenyl) sulfone, biphenyl-4,4'-dicarboxylic acid,
4-trifluoromethylphthalic acid,
2,2-bis(4-carboxyphenyl)hexafluoropropane,
4,4'-stilbenedicarboxylic acid, 4-carboxycinnamic acid, or their
C1-C20-alkyl esters or C5-C12-aryl esters, or their acid anhydrides
or acid chlorides. The aromatic tricarboxylic acids,
tetracarboxylic acids or their C1-C20-alkyl esters or C5-C12-aryl
esters or their acid anhydrides or their acid chlorides are
preferably 1,3,5-benzenetricarboxylic acid (trimesic acid),
1,2,4-benzenetricarboxylic acid (trimellitic acid),
(2-carboxyphenyl)iminodiacetic acid, 3,5,3'-biphenyltricarboxylic
acid, 3,5,4'-biphenyltricarboxylic acid. The aromatic
tetracarboxylic acids or their C1-C20-alkyl esters, C5-C12-aryl
esters or their acid anhydrides or their acid chlorides are
preferably 3,5,3',5'-biphenyltetracarboxylic acid,
1,2,4,5-benzenetetracarboxylic acid, benzophenonetetracarboxylic
acid, 3,3',4,4'-biphenyltetracarboxylic acid,
2,2',3,3'-biphenyltetracarboxylic acid,
1,2,5,6-naphthalenetetracarboxylic acid,
1,4,5,8-naphthalenetetracarboxylic acid.
[0018] The heteroaromatic carboxylic acids used according to the
invention are heteroaromatic dicarboxylic acids and tricarboxylic
acids and tetracarboxylic acids or their esters or their
anhydrides. For the purposes of the present invention,
heteroaromatic carboxylic acids are aromatic systems in which at
least one nitrogen, oxygen, sulfur or phosphorus atom is present in
the aromatic. Preference is given to pyridine-2,5-dicarboxylic
acid, pyridine-3,5-dicarboxylic acid, pyridine-2,6-dicarboxylic
acid, pyridine-2,4-dicarboxylic acid,
4-phenyl-2,5-pyridinedicarboxylic acid, 3,5-pyrazoledicarboxylic
acid, 2,6-pyrimidinedicarboxylic acid, 2,5-pyrazinedicarboxylic
acid, 2,4,6-pyridinetricarboxylic acid,
benzimidazole-5,6-dicarboxylic acid, and also their C1-C20-alkyl
esters or C5-C12-aryl esters, or their acid anhydrides or their
acid chlorides.
[0019] The content of tricarboxylic acids or tetracarboxylic acids
(based on dicarboxylic acid used) is in the range from 0 to 30 mol
%, preferably from 0.5 to 20 mol %, in particular from 1 to 20 mol
%.
[0020] The aromatic and heteroaromatic diaminocarboxylic acids used
according to the invention are preferably diaminobenzoic acid and
its monohydrochloride and dihydrochloride derivatives.
[0021] Mixtures of at least 2 different aromatic carboxylic acids
are preferably used in step A). Particular preference is given to
using mixtures comprising not only aromatic carboxylic acids but
also heteroaromatic carboxylic acids. The mixing ratio of aromatic
carboxylic acids to heteroaromatic carboxylic acids is from 1:99 to
99:1, preferably from 1:50 to 50:1.
[0022] These mixtures are, in particular, mixtures of
N-heteroaromatic dicarboxylic acids and aromatic dicarboxylic
acids. Nonlimiting examples are isophthalic acid, terephthalic
acid, phthalic acid, 2,5-dihydroxyterephthalic acid,
2,6-dihydroxyisophthalic acid, 4,6-dihydroxyisophthalic acid,
2,3-dihydroxyphthalic acid, 2,4-dihydroxyphthalic acid,
3,4-dihydroxyphthalic acid, 1,4-naphthalenedicarboxylic acid,
1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid,
2,7-naphthalenedicarboxylic acid, diphenic acid,
1,8-dihydroxynaphthalene-3,6-dicarboxylic acid,
bis(4-carboxyphenyl) ether, benzophenone-4,4'-dicarboxylic acid,
bis(4-carboxyphenyl) sulfone, biphenyl-4,4'-dicarboxylic acid,
4-trifluoromethylphthalic acid, pyridine-2,5-dicarboxylic acid,
pyridine-3,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid,
pyridine-2,4-dicarboxylic acid, 4-phenyl-2,5-pyridinedicarboxylic
acid, 3,5-pyrazoledicarboxylic acid, 2,6-pyrimidinedicarboxylic
acid, 2,5-pyrazinedicarboxylic acid.
[0023] The phosphoric acid used in step A) is a commercial
phosphoric acid as can be obtained, for example, from Riedel-de
Haen.
[0024] It is preferably a concentrated phosphoric acid
H.sub.3PO.sub.4 which usually has a concentration of 85%. More
highly concentrated phosphoric acids are also possible, but these
contain no polyphosphoric acids H.sub.n+2P.sub.nO.sub.3n+1
(n.gtoreq.2).
[0025] The mixture produced in step A) has a weight ratio of
phosphoric acid to the sum of all monomers of from 1:10 000 to 10
000:1, preferably from 1:1000 to 1000:1, in particular from 1:100
to 100:1.
[0026] The polymerization of the mixture from step A) is carried
out in step B). For this purpose, the mixture is heated to a
temperature of up to 350.degree. C., preferably up to 280.degree.
C., in particular up to 250.degree. C. The mixture is preferably
heated in a closed reactor, so that the phosphoric acid is not
converted into diphosphoric acid (H.sub.4P.sub.2O.sub.7), i.e. the
simplest form of the polyphosphoric acids
H.sub.n+2P.sub.nO.sub.3n+1 (n=2), by elimination of water at above
200.degree. C. The polymerization thus takes place under the
partial pressure of water vapor prevailing at the particular
temperature. In one variant, the water formed by the
polycondensation can be completely or partly removed. This can be
effected by separating off the water or by use of anhydrides.
[0027] The polyazole-based polymer formed in step B) comprises
recurring azole units of the general formula (I) and/or (II) and/or
(III) and/or (IV) and/or (V) and/or (VI) and/or (VII) and/or (VIII)
and/or (IX) and/or (X) and/or (XI) and/or (XII) and/or (XIII)
and/or (XIV) and/or (XV) and/or (XVI) and/or (XVII) and/or (XVIII)
and/or (XIX) and/or (XX) and/or (XXI) and/or (XXII) ##STR1##
##STR2## ##STR3## where [0028] the radicals Ar are identical or
different and are each a tetravalent aromatic or heteroaromatic
group which can be monocyclic or polycyclic, [0029] the radicals
Ar.sup.1 are identical or different and are each a divalent
aromatic or heteroaromatic group which can be monocyclic or
polycyclic, [0030] the radicals Ar.sup.2 are identical or different
and are each a divalent or trivalent aromatic or heteroaromatic
group which can be monocyclic or polycyclic, [0031] the radicals
Ar.sup.3 are identical or different and are each a trivalent
aromatic or heteroaromatic group which can be monocyclic or
polycyclic, [0032] the radicals Ar.sup.4 are identical or different
and are each a trivalent aromatic or heteroaromatic group which can
be monocyclic or polycyclic, [0033] the radicals Ar.sup.5 are
identical or different and are each a tetravalent aromatic or
heteroaromatic group which can be monocyclic or polycyclic, [0034]
the radicals Ar.sup.6 are identical or different and are each a
divalent aromatic or heteroaromatic group which can be monocyclic
or polycyclic, [0035] the radicals Ar.sup.7 are identical or
different and are each a divalent aromatic or heteroaromatic group
which can be monocyclic or polycyclic, [0036] the radicals Ar.sup.8
are identical or different and are each a trivalent aromatic or
heteroaromatic group which can be monocyclic or polycyclic, [0037]
the radicals Ar.sup.9 are identical or different and are each a
divalent or trivalent or tetravalent aromatic or heteroaromatic
group which can be monocyclic or polycyclic, [0038] the radicals
Ar.sup.10 are identical or different and are each a divalent or
trivalent aromatic or heteroaromatic group which can be monocyclic
or polycyclic, [0039] the radicals Ar.sup.11 are identical or
different and are each a divalent aromatic or heteroaromatic group
which can be monocyclic or polycyclic, [0040] the radicals X are
identical or different and are each oxygen, sulfur or an amino
group which bears a hydrogen atom, a group having 1-20 carbon
atoms, preferably a branched or unbranched alkyl or alkoxy group,
or an aryl group as further radical, [0041] the radicals R are
identical or different and are each hydrogen, an alkyl group or an
aromatic group and [0042] n, m are each an integer greater than or
equal to 10, preferably greater than or equal to 100.
[0043] Preferred aromatic or heteroaromatic groups are derived from
benzene, naphthalene, biphenyl, diphenyl ether, diphenylmethane,
diphenyldimethylmethane, bisphenone, diphenyl sulfone, quinoline,
pyridine, bipyridine, pyridazine, pyrimidine, pyrazine, triazine,
tetrazine, pyrrole, pyrazole, anthracene, benzopyrrole,
benzotriazole, benzoxathiadiazole, benzoxadiazole, benzopyridine,
benzopyrazine, benzopyrazidine, benzopyrimidine, benzopyrazine,
benzotriazine, indolizine, quinolizine, pyridopyridine,
imidazopyrimidine, pyrazinopyrimidine, carbazole, acridine,
phenazine, benzoquinoline, phenoxazine, phentothiazine, acridizine,
benzopteridine, phenanthroline and phenanthrene, which may also be
substituted. [0044] Ar.sup.1, Ar.sup.4, Ar.sup.6, Ar.sup.7,
Ar.sup.8, Ar.sup.9, Ar.sup.10, Ar.sup.11 can have any substitution
pattern; in the case of phenylene, Ar.sup.1, Ar.sup.4, Ar.sup.6,
Ar.sup.7, Ar.sup.8, Ar.sup.9, Ar.sup.10, Ar.sup.11 can be, for
example, ortho-, meta- or para-phenylene. Particularly preferred
groups are derived from benzene and biphenylene, which may also be
substituted.
[0045] Preferred alkyl groups are short-chain alkyl groups having
from 1 to 4 carbon atoms, e.g. methyl, ethyl, n- or i-propyl and
t-butyl groups.
[0046] Preferred aromatic groups are phenyl or naphthyl groups. The
alkyl groups and the aromatic groups may be substituted.
[0047] Preferred substituents are halogen atoms such as fluorine,
amino groups, hydroxy groups or short-chain alkyl groups such as
methyl or ethyl groups.
[0048] Preference is given to polyazoles having recurring units of
the formula (I) in which the radicals X within one recurring unit
are identical.
[0049] The polyazoles can in principle also have different
recurring units which differ, for example, in their radical X.
However, preference is given to only identical radicals X being
present in a recurring unit.
[0050] Further, preferred polyazole polymers are polyimidazoles,
polybenzothiazoles, polybenzoxazoles, polyoxadiazoles,
polyquinoxalines, polythiadiazoles, poly(pyridines),
poly(pyrimidines) and poly(tetrazapyrenes).
[0051] In a further embodiment of the present invention, the
polymer comprising recurring azole units is a copolymer or a blend
comprising at least two units of the formulae (I) to (XXII) which
differ from one another. The polymers can be in the form of block
copolymers (diblock, triblock), random copolymers, periodic
copolymers and/or alternating polymers.
[0052] In a particularly preferred embodiment of the present
invention, the polymer comprising recurring azole units is a
polyazole comprising only units of the formula (I) and/or (II).
[0053] The number of recurring azole units in the polymer is
preferably greater than or equal to 10. Particularly preferred
polymers contain at least 100 recurring azole units.
[0054] For the purposes of the present invention, polymers
comprising recurring benzimidazole units are preferred. Some
examples of extremely advantageous polymers comprising recurring
benzimidazole units are represented by the following formulae:
##STR4## ##STR5## ##STR6## where n and m are each an integer
greater than or equal to 10, preferably greater than or equal to
100.
[0055] The polyazoles obtainable by means of the process described,
but in particular the polybenzimidazoles, have a high molecular
weight. Measured as intrinsic viscosity, it is at least 1.4 dl/g
and is thus significantly above that of commercial
polybenzimidazole (IV<1.1 dl/g).
[0056] If tricarboxylic acids and/or tetracarboxylic acids capable
of crosslinking are also present in the mixture obtained in step
A), they effect branching/crosslinking of the polymer formed. This
contributes to an improvement in the mechanical properties of the
membrane formed. In particular, the membrane becomes
self-supporting more quickly as a result of the crosslinking by
means of any tricarboxylic acids or tetracarboxylic acids present,
so that the treatment in step D) may be able to be shortened. If a
very high content of tricarboxylic acids or tetracarboxylic acids
capable of crosslinking is present, the after-treatment may be able
to be omitted entirely.
[0057] Furthermore, it has been found that when using aromatic
dicarboxylic acids (or heteroaromatic dicarboxylic acids) such as
isophthalic acid, terephthalic acid, 2,5-dihydroxyterephthalic
acid, 4,6-dihydroxyisophthalic acid, 2,6-dihydroxyisophthalic acid,
diphenic acid, 1,8-dihydroxynaphthalene-3,6-dicarboxylic acid,
bis(4-carboxyphenyl) ether, benzophenone-4,4'-dicarboxylic acid,
bis(4-carboxyphenyl) sulfone, biphenyl-4,4'-dicarboxylic acid,
4-trifluoromethylphthalic acid, pyridine-2,5-dicarboxylic acid,
pyridine-3,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid,
pyridine-2,4-dicarboxylic acid, 4-phenyl-2,5-pyridinedicarboxylic
acid, 3,5-pyrazoledicarboxylic acid, 2,6-pyrimidinedicarboxylic
acid, 2,5-pyrazinedicarboxylic acid, the temperature in step B) is
advantageously in the range up to 300.degree. C., preferably from
100.degree. C. to 250.degree. C.
[0058] The layer formation in step C) is carried out by means of
measures known per se from the prior art for polymer film
production (casting, spraying, spreading by doctor blade).
[0059] Possible supports are, in particular, supports which are
inert under the conditions selected. However, apart from these
inert supports, supports composed of polymer films which are not
inert can also be used. Among this group, polymer films based on
polyazoles are particularly preferred.
[0060] To adjust the viscosity, the solution can, if appropriate,
be admixed with phosphoric acid (concentrated phosphoric acid,
85%). In this way, the viscosity can be set to the desired value
and the formation of the membrane can be made easier.
[0061] The layer produced in step C) has a thickness of from 20 to
4000 .mu.m, preferably from 30 to 3500 .mu.m, in particular from 50
to 3000 .mu.m.
[0062] The intramolecular and intermolecular structures present in
step C) lead to ordered membrane formation which is responsible for
the particular properties of the membrane formed.
[0063] The treatment of the membrane in step D) makes it
self-supporting.
[0064] For the purposes of the present invention, "self-supporting"
means that the membrane formed can be detached from the support
without damage and can, if desired, subsequently be directly
processed further.
[0065] The after-treatment in step D) is carried out by action of
heat in the presence of atmospheric oxygen. This leads to
crosslinking, so that the membrane becomes self-supporting.
[0066] The after-treatment in step D) can also be carried out
exclusively by the action of heat. This variant is selected when
the temperature chosen in step B) has not crosslinked tricarboxylic
or tetracarboxylic acids present or has not crosslinked them
completely. The temperature is selected in the range from
220.degree. C. to 400.degree. C., preferably from 250.degree. C. to
380.degree. C. The treatment time is from 5 seconds to 10
hours.
[0067] In another form of the after-treatment in step D), the
treatment can be carried out using sulfuric acid, in particular
dilute sulfuric acid. This treatment is known for the production of
polybenzimidazole fibers for protective clothing. For this purpose,
the surface to be treated is wetted with sulfuric acid or dilute
sulfuric acid and is subsequently heated briefly to temperatures of
up to 550.degree. C. This ensures crosslinking of the membrane so
that it becomes self-supporting. The treatment time is from 0.5
seconds to 10 minutes. This treatment is usually carried out by
bringing the membrane into contact with a heated surface.
[0068] The after-treatment or crosslinking can also be effected by
action of IR or NIR (IR=infrared, i.e. light having a wavelength of
more than 700 nm; NIR=near IR, i.e. light having a wavelength in
the range from about 700 to 2000 nm or an energy in the range from
about 0.6 to 1.75 eV). A further method is irradiation with
.beta.-rays. The radiation dose is in the range from 5 to 200
kGy.
[0069] According to the invention, the concentration of the
phosphoric acid is reported as mole of acid per mole of repeating
unit of the polymer. For the purposes of the present invention, a
concentration (mole of phosphoric acid per mole of repeating units
of the formula (III), i.e. polybenzimidazole) of from 10 to 50, in
particular from 12 to 40, is preferred. Such high degrees of doping
(concentrations) can be obtained only with difficulty, if at all,
by doping of previously produced polyazole films with commercially
available ortho-phosphoric acid, since a decrease in the mechanical
integrity is observed.
[0070] The polymer membrane of the invention displays improved
materials properties compared to the previously known doped polymer
membranes. In particular, it displays improved power compared to
known doped polymer membranes. This is due, in particular, to an
improved proton conductivity. At temperatures of 120.degree. C.,
this is at least 0.1 S/cm, preferably at least 0.11 S/cm, in
particular at least 0.12 S/cm.
[0071] To achieve a further improvement in the use properties,
fillers, in particular proton-conducting fillers, and additional
acids can also be added to the membrane. The addition can be
carried out either in step A) or in step B) or after the
polymerization in step B).
[0072] Nonlimiting examples of proton-conducting fillers are [0073]
sulfates such as CsHSO.sub.4, Fe(SO.sub.4).sub.2,
(NH.sub.4).sub.3H(SO.sub.4).sub.2, LiHSO.sub.4, NaHSO.sub.4,
KHSO.sub.4, RbSO.sub.4, LiN.sub.2H.sub.5SO.sub.4,
NH.sub.4HSO.sub.4, [0074] phosphates such as
Zr.sub.3(PO.sub.4).sub.4, Zr(HPO.sub.4).sub.2,
HZr.sub.2(PO.sub.4).sub.3, U0.sub.2PO.sub.4.3H.sub.2O,
H.sub.8UO.sub.2PO.sub.4, Ce(HPO.sub.4).sub.2, Ti(HPO.sub.4).sub.2,
KH.sub.2PO.sub.4, NaH.sub.2PO.sub.4, LiH.sub.2PO.sub.4,
NH.sub.4H.sub.2PO.sub.4, CsH.sub.2PO.sub.4, CaHPO.sub.4,
MgHPO.sub.4, HSbP.sub.2O.sub.8, HSb.sub.3P.sub.2O.sub.14,
H.sub.5Sb.sub.5P.sub.2O.sub.20, [0075] polyacids such as
H.sub.3PW.sub.12O.sub.40.nH.sub.2O (n=21-29),
H.sub.3SiW.sub.12O.sub.40.nH.sub.2O (n=21-29), H.sub.xWO.sub.3,
HSbWO.sub.6, H.sub.3PMo.sub.12O.sub.40, H.sub.2Sb.sub.4O.sub.11,
HTaWO.sub.6, HNbO.sub.3, HTiNbO.sub.5, HTiTaO.sub.5, HSbTeO.sub.6,
H.sub.5Ti.sub.4O.sub.9, HSbO.sub.3, H.sub.2MoO.sub.4, [0076]
selenites and arsenides such as (NH.sub.4).sub.3H(SeO.sub.4).sub.2,
UO.sub.2AsO.sub.4, (NH.sub.4).sub.3H(SeO.sub.4).sub.2,
KH.sub.2AsO.sub.4, Cs.sub.3H(SeO.sub.4).sub.2,
Rb.sub.3H(SeO.sub.4).sub.2, [0077] oxides such as Al.sub.2O.sub.3,
Sb.sub.2O.sub.5, ThO.sub.2, SnO.sub.2, ZrO.sub.2, MoO.sub.3, [0078]
silicates such as zeolites, zeolites(NH.sub.4+), sheet silicates,
framework silicates, H-natrolites, H-mordenites,
NH.sub.4-analcines, NH.sub.4-sodalites, NH.sub.4-gallates,
H-montmorillonites, [0079] acids such as HClO.sub.4, SbF.sub.5,
[0080] fillers such as carbides, in particular SiC,
Si.sub.3N.sub.4, fibers, in particular glass fibers, glass powders
and/or polymer fibers, preferably ones based on polyazoles.
[0081] In addition, this membrane can further comprise
perfluorinated sulfonic acid additives (0.1-20% by weight,
preferably 0.2-15% by weight, very particularly preferably 0.2-10%
by weight). These additives lead to an increase in power, in the
vicinity of the cathode to an increase in the oxygen solubility and
oxygen diffusion and to a reduction in the adsorption of phosphoric
acid and phosphate onto platinum. (Electrolyte additives for
phosphoric acid fuel cells. Gang, Xiao; Hjuler, H. A.; Olsen, C.;
Berg, R. W.; Bjerrum, N.J. Chem. Dep. A, Tech. Univ. Denmark,
Lyngby, Den. J. Electrochem. Soc. (1993), 140(4), 896-902 and
Perfluorosulfonimide as an additive in phosphoric acid fuel cell.
Razaq, M.; Razaq, A.; Yeager, E.; DesMarteau, Darryl, D.; Singh, S.
Case Cent. Electrochem. Sci., Case West, Reserve Univ., Cleveland,
Ohio, USA. J. Electrochem. Soc. (1989),136(2), 385-90.)
[0082] Nonlimiting examples of perflourated additives are:
trifluoromethanesulfonic acid, potassium trifluoromethanesulfonate,
sodium trifluoromethanesulfonate, lithium
trifluoromethanesulfontate, ammonium trifluoromethanesulfonate,
potassium perfluorohexanesulfonate, sodium
perfluorohexanesulfonate, lithium perfluorohexanesulfonate,
ammonium perfluorohexanesulfonate, perfluorohexanesulfonic acid,
potassium nonafluorobutanesulfonate, sodium
nonafluorobutanesulfonate, lithium nonafluorobutanesulfonate,
ammonium nonafluorobutanesulfonate, cesium
nonafluorobutanesulfonate, triethylammonium
perfluorohexanesulfonate, perfluorosulfonimides and Nafion.
[0083] Furthermore, the membrane can further comprise additives
which scavenge (primary antioxidants) or destroy (secondary
antioxidants) the free peroxide radicals produced in the reduction
of oxygen during operation and thereby improve the life and
stability of the membrane and membrane-electrode unit as described
in JP2001118591 A2. The mode of action and molecular structures of
such additives are described in F. Gugumus in Plastics Additives,
Hanser Verlag, 1990; N. S. Allen, M. Edge Fundamentals of Polymer
Degradation and Stability, Elsevier, 1992; or H. Zweifel,
Stabilization of Polymeric Materials, Springer, 1998.
[0084] Nonlimiting examples of such additives are:
bis(trifluoromethyl) nitroxide, 2,2,-diphenyl-1-picrinylhydrazyl,
phenols, alkylphenols, sterically hindered alkylphenols such as
Irganox, aromatic amines, sterically hindered amines such as
Chimassorb; sterically hindered hydroxylamines, sterically hindered
alkylamines, sterically hindered hydroxylamines, sterically
hindered hydroxylamine ethers, phosphites such as Irgafos,
nitrosobenzene, methyl-2-nitrosopropane, benzophenone, benzaldehyde
tert-butyl nitron, cysteamine, melanines, lead oxides, manganese
oxides, nickel oxides, cobalt oxides.
[0085] Possible fields of use of the doped polymer membranes of the
invention include, inter alia, use in fuel cells, in electrolysis,
in capacitors and in battery systems. Owing to their property
profile, the doped polymer membranes are preferably used in fuel
cells.
[0086] The present invention also provides a membrane-electrode
unit comprising at least one polymer membrane according to the
invention. For further information on membrane-electrode units,
reference may be made to the specialist literature, in particular
the patents U.S. Pat. No. 4,191,618, U.S. Pat. No. 4,212,714 and
U.S. Pat. No. 4,333,805. The disclosure of the abovementioned
references [U.S. Pat. No. 4,191,618, U.S. Pat. No. 4,212,714 and
U.S. Pat. No. 4,333,805] in respect of the structure and the
production of membrane-electrode units and also the electrodes, gas
diffusion layers and catalysts to be selected is incorporated by
reference into the present description.
[0087] In one variant of the present invention, the membrane
formation in step C) can be carried out directly on the electrode
rather than on a support. The treatment according to step D) can in
this way be correspondingly shortened, since it is no longer
necessary for the membrane to be self-supporting. Such a membrane
is also provided by the present invention.
[0088] The present invention further provides an electrode provided
with a proton-conducting polymer coating which is based on
polyazoles and is obtainable by a process comprising the steps
[0089] A) mixing of one or more aromatic tetramino compounds with
one or more aromatic carboxylic acids or esters thereof which
contain at least two acid groups per carboxylic acid monomer, or
mixing of one or more aromatic and/or heteroaromatic
diaminocarboxylic acids, in phosphoric acid to form a solution
and/or dispersion, [0090] B) heating of the solution and/or
dispersion obtained in step A) to temperatures of up to 350.degree.
C., preferably up to 280.degree. C., to form the polyazole polymer,
[0091] C) application of a layer using the mixture from step B) to
an electrode, [0092] D) if appropriate, treatment of the membrane
formed in step C).
[0093] The above-described variants and preferred embodiments also
apply to this subject matter, so that they will not be repeated at
this point.
[0094] The coating after step C) has a thickness of from 2 to 3000
.mu.m, preferably from 3 to 2000 .mu.m, in particular from 5 to
1500 .mu.m.
[0095] The after-treatment in step D) is carried out for the
purpose of fully polymerizing any oligomers still present.
[0096] Such a coated electrode can be installed in a
membrane-electrode unit which, if appropriate, has at least one
polar membrane according to the invention.
[0097] In a further variant, a catalytically active layer can be
applied to the membrane according to the invention and this
catalytically active layer can be joined to a gas diffusion layer.
For the purpose, a membrane is formed according to steps A) to D)
and the catalyst is applied. These structures are also provided by
the present invention.
[0098] Furthermore, the formation of the membrane according to
steps A) to D) can also be carried out on a support or a support
film to which the catalyst has previously been applied. After
removal of the support or the support film, the catalyst is present
on the membrane according to the invention. These structures are
also provided by the present invention.
[0099] The present invention provides a polymer film which is based
on polyazoles and is obtainable by a process comprising the steps
[0100] A) mixing of one or more aromatic tetramino compounds with
one or more aromatic carboxylic acids or esters thereof which
contain at least two acid groups per carboxylic acid monomer, or
mixing of one or more aromatic and/or heteroaromatic
diaminocarboxylic acids, in phosphoric acid to form a solution
and/or dispersion, [0101] B) heating of the solution and/or
dispersion obtained in step A) to temperatures of up to 350.degree.
C., preferably up to 280.degree. C., to form the polyazole polymer,
[0102] C) application of a layer using the mixture from step B) a
support, [0103] D) treatment of the membrane formed in step C)
until it is self-supporting, [0104] E) detachment of the membrane
formed in step C) from the support, [0105] F) removal of the
phosphoric acid present and drying.
[0106] Subsequent to step E), the phosphoric acid present in the
polymer film is removed in step F). This is carried out by means of
a treatment liquid in the temperature range from room temperature
(20.degree. C.) to the boiling point of the treatment liquid (at
atmospheric pressure).
[0107] Treatment liquids used for the purposes of the invention and
for the purposes of step F) are solvents which are liquid at room
temperature [i.e. 20.degree. C.] and are selected from the group
consisting of alcohols, ketones, alkanes (aliphatic and
cycloaliphatic), ethers (aliphatic and cycloaliphatic), glycols,
esters, carboxylic acids, with the above members of the group being
able to be halogenated, water and mixtures thereof.
[0108] Preference is given to using C1-C10-alcohols, C2-C5-ketones,
C1-C10-alkanes (aliphatic and cycloaliphatic), C2-C6-ethers
(aliphatic and cycloaliphatic), C2-C5-esters, C1-C3-carboxylic
acids, dichloromethane, water and mixtures thereof.
[0109] The treatment liquid introduced in step F) is subsequently
removed again. This is preferably achieved by drying at a
temperature and pressure chosen as a function of the partial vapor
pressure of the treatment liquid. Drying is usually carried out at
atmospheric pressure and temperatures in the range from 20.degree.
C. to 200.degree. C. More gentle drying can also be carried out
under reduced pressure. In place of drying, the membrane can also
be dabbed off and thus freed of excess treatment liquid. The order
is not critical.
[0110] Subsequent to the treatment according to step F) the polymer
film can be additionally crosslinked on the surface by the action
of heat in the presence of atmospheric oxygen. This hardening of
the film surface achieves an additional improvement in the
properties. This treatment can partly or completely replace the
above drying or can be combined with it.
[0111] Crosslinking can also, as indicated above, be effected by
action of IR or NIR light or by means of .beta.-rays.
[0112] Furthermore, a thermal after-treatment with sulfuric acid as
described above can be carried out subsequent to the treatment
according to step F). This leads to a further improvement in the
use properties of the surface.
[0113] The polymer film of the invention has improved materials
properties compared to the previously known polymer films.
[0114] Furthermore, not only does the polymer film of the invention
display the known advantages of separation membranes based on
polyazoles, e.g. high thermal stability and resistance to
chemicals, but the separation membranes according to the invention
have improved mechanical properties as a result of a higher
molecular weight which lead to increased long-term stability and
life and also an improved separation behavior. A further advantage
is, in particular, that these polymer films do not contain any
impurities which are costly to remove or cannot be removed
completely.
[0115] Such separation membranes can be produced as dense polymer
films, porous hollow fiber membranes or as porous, open-celled
polymer films, if desired with a compact covering layer.
[0116] To produce a porous membrane, the polymer solution from step
A) can additionally contain a pore former such as glycerol. In the
treatment in step F), known porous structures are formed by solvent
replacement. Depending on the chosen composition of the
precipitant, different morphologies of the separation membranes can
be obtained in this way. The following structures are preferred for
separation applications: i) symmetrical, porous structure, ii)
unsymmetrical porous structure having denser polymer close to one
membrane surface. Scanning electron micrographs of such
particularly suitable structures of polybenzimidazole membranes are
disclosed in Journal of Membrane Science, Volume 20,1984, pages
147-66.
[0117] Such phase inversion membranes and structures are known to
those skilled in the art. Membranes having a symmetrical porous
structure are employed as separation or filtration membranes for
filtration of air and gas or for microfiltration or ultrafiltration
of liquids. Membranes having an unsymmetrical, porous structure can
be utilized for reverse osmosis in a variety of applications, in
particular desalination of water, dialysis or processing of
gases.
[0118] A particularly advantageous application is the separation of
hydrogen and carbon dioxide from gas mixtures in combination with a
porous metallic support. Alternative technologies for CO.sub.2
separation require cooling of the gas to 150.degree. C. because of
the low thermal stability of the polymer membrane, resulting in a
reduction in the efficiency. The polyazole-based separation
membranes of the invention can be operated continuously at
temperatures up to 400.degree. C. and thus lead to an increase in
the yield and a reduction in costs.
[0119] For further information on separation membranes based on
polyazoles, reference may be made to the specialist literature, in
particular the patents WO 98/14505; U.S. Pat. No. 4,693,815; U.S.
Pat. No. 4,693,824; U.S. Pat. No. 375,262; U.S. Pat. No. 3,737,042;
U.S. Pat. No. 4,512,894; U.S. Pat. No. 448,687; U.S. Pat. No.
3,841,492. The disclosure of the abovementioned references in
respect of the structure and production of separation membranes is
incorporated by reference into the present description. In
particular, such separation membranes can be produced in the form
of flat films or as hollow fiber membranes.
[0120] To achieve a further improvement in the use properties,
fillers can be additionally added to the polymer films. The
addition can be carried out either in step A and/or B or after the
polymerization (step B).
[0121] Nonlimiting examples of such fillers are [0122] oxides such
as Al.sub.2O.sub.3, Sb.sub.2O.sub.5, ThO.sub.2, SnO.sub.2,
ZrO.sub.2, MoO.sub.3 [0123] silicates such as zeolites,
zeolites(NH.sub.4+), sheet silicates, framework silicates,
H-natrolites, H-mordenites, NH.sub.4-analcines, NH.sub.4-sodalites,
NH.sub.4-gallates, H-montmorillonites [0124] fillers such as
carbides, in particular SiC, Si.sub.3N.sub.4, fibers, in particular
glass fibers, glass powders and/or polymer fibers, preferably ones
based on polyazoles.
[0125] Furthermore, the polymer film can also contain additives
which scavenge or destroy any free radicals produced during use in
gas filtration.
[0126] Nonlimiting examples of such additives are:
bis(trifluoromethyl)nitroxide, 2,2-diphenyl-1-picrylhydrazyl,
phenols, alkylphenols, sterically hindered alkylphenols such as
Irganox, aromatic amines, sterically hindered amines such as
Chimassorb; sterically hindered hydroxylamines, sterically hindered
alkylamines, sterically hindered hydroxylamines, sterically
hindered hydroxylamine ethers, phosphates such as Irgafos,
nitrosobenzene, methyl-2-nitrosopropane, benzophenone, benzaldehyde
tert-butyl nitrone, cysteamine, melanines, lead oxides, manganese
oxides, nickel oxides, cobalt oxides.
[0127] Possible fields of use of the polymer films of the invention
include, inter alia, use as filter medium in gas filtration and
separation or gas purification, and also in reverse osmosis, as
substrates for flexible electric circuits, as battery separators,
as protective film for electric cables, as insulator in electric
components and devices such as capacitors, as protective film for
metal surfaces and other surfaces.
[0128] The present invention therefore also provides a polymer
which is based on polyazoles as per the above features, whose
molecular weight expressed as intrinsic viscosity is at least 1.4
dl/g and which is obtainable by a process comprising the steps
[0129] A) mixing of one or more aromatic tetramino compounds with
one or more aromatic carboxylic acids or esters thereof which
contain at least two acid groups per carboxylic acid monomer, or
mixing of one or more aromatic and/or heteroaromatic
diaminocarboxylic acids, in phosphoric acid to form a solution
and/or dispersion, [0130] B) heating of the mixture obtainable
according to step A) under inert gas to temperatures of up to
350.degree. C., preferably up to 280.degree. C., to form the
polyazole polymer, [0131] C) precipitation of the polymer formed in
step B) and isolation and drying of the polymer powder
obtained.
[0132] The preferred embodiments for the steps A) and B) have been
described above, so that they will not be repeated at this
point.
[0133] The precipitation in step C) can be achieved by introducing
the material from step B) into a precipitation bath. This
introduction is generally carried out in the temperature range from
room temperature (20.degree. C.) to the boiling point of the
precipitation liquid (at atmospheric pressure).
[0134] Precipitation liquids used for the purposes of the invention
and for the purposes of step C) are solvents which are liquid at
room temperature [i.e. 20.degree. C.] and are selected from the
group consisting of alcohols, ketones, alkanes (aliphatic and
cycloaliphatic), ethers (aliphatic and cycloaliphatic), esters,
carboxylic acids, with the above members of the group being able to
be halogenated, water and mixtures thereof.
[0135] Preference is given to using C1-C10-alcohols, C2-C5-ketones,
C1-C10-alkanes (aliphatic and cycloaliphatic), C2-C6-ethers
(aliphatic and cycloaliphatic), C2-C5-esters, C1-C3-carboxylic
acids, dichloromethane, water and mixtures thereof.
[0136] The precipitated polymer is subsequently freed of the
precipitation liquid again. This is preferably achieved by drying
at a temperature and pressure selected as a function of the partial
vapor pressure of the precipitation liquid. Drying is usually
carried out at atmospheric pressure and temperatures in the range
from 20.degree. C. to 200.degree. C. Gentler drying can also be
carried out under reduced pressure. The drying method is not
subject to any restrictions.
[0137] The polyazoles obtainable by means of the process described,
but in particular the polybenzimidazoles, have a high molecular
weight. Measured as intrinsic viscosity, this is at least 1.4 dl/g,
preferably at least 1.5 dl/g, and is thus significantly above that
of commercial polybenzimidazole (IV.<1.1 dl/g).
[0138] The polymer powders obtained in this way are suitable, in
particular, as raw material for producing shaped bodies, in
particular films and fibers.
[0139] The present invention further provides a polymer fiber which
is based on polyazoles, whose molecular weight expressed as
intrinsic viscosity is at least 1.4 dl/g and which is obtainable by
a process comprising the steps [0140] A) mixing of one or more
aromatic tetramino compounds with one or more aromatic carboxylic
acids or esters thereof which contain at least two acid groups per
carboxylic acid monomer, or mixing of one or more aromatic and/or
heteroaromatic diaminocarboxylic acids, in phosphoric acid to form
a solution and/or dispersion, [0141] B) heating of the mixture
obtained in step A) to temperatures of up to 350.degree. C.,
preferably up to 280.degree. C., to form the polyazole polymer,
[0142] C) extrusion of the polyazole polymer formed in step B) to
form fibers, [0143] D) introduction of the fibers formed in step C)
into a liquid bath, [0144] E) isolation and drying of the fibers
obtained.
[0145] The preferred embodiments for the steps A) and B) has been
presented above, so that they will not be repeated at this
point.
[0146] The extrusion in step C) can be carried out by means of all
known fiber formation methods. The fibers formed can be continuous
filaments or, if fiber formation is carried out by a method
analogous to the "melt blow method", have the character of staple
fibers. The thicknesses of the fibers formed are not subject to any
restrictions, so that monofilaments, i.e. wire-like fibers, can
also be produced. Apart from these, hollow fibers can also be
produced. The desired thickness is determined by the envisaged use
of the fiber. The entire handling of the fibers formed can be
carried out by means of known fiber technologies.
[0147] After extrusion in step C), the fibers formed are introduced
into a precipitation bath. This introduction is carried out in the
temperature range from room temperature (20.degree. C.) to the
boiling point of the precipitation liquid (at atmospheric
pressure).
[0148] Precipitation liquids used for the purposes of the invention
and for the purposes of step C) are solvents which are liquid at
room temperature [i.e. 20.degree. C.] and are selected from the
group consisting of alcohols, ketones, alkanes (aliphatic and
cycloaliphatic), ethers (aliphatic and cycloaliphatic), esters,
carboxylic acids, with the above members of the group being able to
be halogenated, water and mixtures thereof. [0149] Preference is
given to using C1-C.sub.10-alcohols, C2-C5-ketones,
C1-C.sub.10-alkanes (aliphatic and cycloaliphatic), C2-C6-ethers
(aliphatic and cycloaliphatic), C2-C5-esters, C1-C3-carboxylic
acids, dichloromethane, water and mixtures thereof.
[0150] The fiber is subsequently freed of the precipitation liquid
again. This is preferably achieved by drying at a temperature and
pressure selected as a function of the partial vapor pressure of
the precipitation liquid. Drying is usually carried out at
atmospheric pressure and temperatures in the range from 20.degree.
C. to 200.degree. C. Gentler drying can also be carried out under
reduced pressure. The drying method is not subject to any
restrictions.
[0151] The treatment in the precipitation bath can lead to
formation of porous structures. Depending on the application, these
may be desirable for the subsequent use.
General Measurement Methods:
Measurement Methods for IEC
[0152] The conductivity of the membrane depends strongly on the
content of acid groups expressed as the ion-exchange capacity
(IEC). To measure the ion-exchange capacity, a specimen having a
diameter of 3 cm is stamped out and placed in a glass beaker
containing 100 ml of water. The acid liberated is titrated with 0.1
M NaOH. The specimen is subsequently taken up, excess water is
dabbed off and the specimen is dried at 160.degree. C. for 4 hours.
The dry weight, m.sub.0, is then determined gravimetrically to a
precision of 0.1 mg. The ion-exchange capacity is then calculated
from the consumption of 0.1 M NaOH to the first titration end
point, V.sub.1 in ml, and the dry weight, m.sub.0 in mg, according
to the following formula: IEC=V.sub.1*1300/m.sub.0 Measurement
Method for Specific Conductivity
[0153] The specific conductivity is measured by means of impedance
spectroscopy in a 4-pole arrangement in the potentiostatic mode
using platinum electrodes (wire, 0.25 mm diameter). The distance
between the current-collecting electrodes is 2 cm. The spectrum
obtained is evaluated using a simple model comprising a parallel
arrangement of an ohmic resistance and a capacitor. The specimen
cross section of the membrane doped with phosphoric acid is
measured immediately before mounting of the specimen. To measure
the temperature dependence, the measurement cell is brought to the
desired temperature in an oven and the temperature is regulated by
means of a Pt-100 resistance thermometer positioned in the
immediate vicinity of the specimen. After the temperature has been
reached, the specimen is maintained at this temperature for 10
minutes before commencement of the measurement.
* * * * *