U.S. patent application number 12/248294 was filed with the patent office on 2009-11-19 for polyamic acids dope composition, preparation method of hollow fiber using the same and hollow fiber prepared therefrom.
This patent application is currently assigned to Industry-University Cooperation Foundation, HANYANG UNIVERSITY. Invention is credited to Sang-Hoon Han, Chul-Ho Jung, Young-Moo LEE, Ho-Bum Park.
Application Number | 20090286904 12/248294 |
Document ID | / |
Family ID | 41316752 |
Filed Date | 2009-11-19 |
United States Patent
Application |
20090286904 |
Kind Code |
A1 |
LEE; Young-Moo ; et
al. |
November 19, 2009 |
POLYAMIC ACIDS DOPE COMPOSITION, PREPARATION METHOD OF HOLLOW FIBER
USING THE SAME AND HOLLOW FIBER PREPARED THEREFROM
Abstract
Disclosed herein are a polyamic acid dope solution composition,
a method for preparing a hollow fiber using the composition and a
hollow fiber prepared by the method. More specifically, disclosed
are a method for preparing a hollow fiber, comprising preparing a
polyamic acid dope solution composition comprising polyhydroxyamic
acid, polythiolamic acid or polyaminoamic acid, spinning the
composition to prepare a hollow fiber, and imidizing and thermally
rearranging the hollow fiber, and the hollow fiber prepared by the
method. In accordance with the method, a hollow fiber made of a
high free volume polymer membrane can be prepared by spinning the
dope solution composition to prepare a hollow fiber and thermally
rearranging the hollow fiber via thermal treatment. The hollow
fiber thus prepared exhibits excellent gas permeability and
selectivity, thus being suitable for use as a gas separation
membrane.
Inventors: |
LEE; Young-Moo; (Seoul,
KR) ; Han; Sang-Hoon; (Seoul, KR) ; Jung;
Chul-Ho; (Gwangju, KR) ; Park; Ho-Bum; (Ulsan,
KR) |
Correspondence
Address: |
LEXYOUME IP GROUP, LLC
5180 PARKSTONE DRIVE, SUITE 175
CHANTILLY
VA
20151
US
|
Assignee: |
Industry-University Cooperation
Foundation, HANYANG UNIVERSITY
Seoul
KR
|
Family ID: |
41316752 |
Appl. No.: |
12/248294 |
Filed: |
October 9, 2008 |
Current U.S.
Class: |
524/27 ;
264/209.6; 524/379; 524/401; 524/436; 524/54; 524/607; 524/608;
528/170; 528/228; 528/367; 528/423 |
Current CPC
Class: |
Y02C 20/20 20130101;
C08L 79/04 20130101; C08G 73/22 20130101; C08L 81/00 20130101; B01D
2257/102 20130101; Y10T 428/2938 20150115; Y10T 428/2969 20150115;
C08G 75/32 20130101; D01F 6/74 20130101; B01D 2256/12 20130101;
B01D 71/64 20130101; C08G 73/105 20130101; C08G 73/1071 20130101;
B01D 2256/22 20130101; C08G 73/1042 20130101; B01D 69/087 20130101;
C08L 2205/05 20130101; C08G 73/1046 20130101; B01D 2257/702
20130101; C08G 73/1067 20130101; C08L 79/08 20130101; B01D 63/021
20130101; Y10T 428/2975 20150115; C08G 73/1039 20130101; B01D
2256/18 20130101; D01D 10/02 20130101; D01D 5/24 20130101; B01D
2256/16 20130101; D01D 5/06 20130101; B01D 69/08 20130101; B01D
2325/02 20130101; C08G 73/1053 20130101; B01D 53/22 20130101 |
Class at
Publication: |
524/27 ; 524/607;
524/608; 524/379; 524/54; 524/401; 524/436; 528/367; 528/423;
528/170; 528/228; 264/209.6 |
International
Class: |
C08L 5/08 20060101
C08L005/08; C08G 63/685 20060101 C08G063/685; C08L 5/02 20060101
C08L005/02; C08G 73/10 20060101 C08G073/10; C08G 16/00 20060101
C08G016/00; C08K 3/00 20060101 C08K003/00; C08K 5/05 20060101
C08K005/05 |
Foreign Application Data
Date |
Code |
Application Number |
May 19, 2008 |
KR |
10-2008-0046115 |
Claims
1. A dope solution composition comprising: (a) a polymer for
forming a hollow fiber, including one selected from the group
consisting of polyamic acids represented by the following Formulae
1 to 4, polyamic acid copolymers represented by Formulae 5 to 8,
copolymers thereof and blends thereof; (b) an organic solvent; and
(c) an additive. ##STR00058## In Formulae 1 to 8, Ar.sub.1 is a
tetravalent C.sub.5-C.sub.24 arylene group or a tetravalent
C.sub.5-C.sub.24 heterocyclic ring, which is substituted or
unsubstituted with at least one substituent selected from the group
consisting of C.sub.1-C.sub.10 alkyl, C.sub.1-C.sub.10 alkoxy,
C.sub.1-C.sub.10 haloalkyl and C.sub.1-C.sub.10 haloalkoxy, or two
or more of which are fused together to form a condensation ring or
covalently bonded to each other via a functional group selected
from the group consisting of O, S, C(.dbd.O), CH(OH),
S(.dbd.O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2 and
C(.dbd.O)NH; Ar.sub.2 is a bivalent C.sub.5-C.sub.24 arylene group
or a bivalent C.sub.5-C.sub.24 heterocyclic ring, which is
substituted or unsubstituted with at least one substituent selected
from the group consisting of C.sub.1-C.sub.10 alkyl,
C.sub.1-C.sub.10 alkoxy, C.sub.1-C.sub.10 haloalkyl and
C.sub.1-C.sub.10 haloalkoxy, or two or more of which are fused
together to form a condensation ring or covalently bonded to each
other via a functional group selected from the group consisting of
O, S, C(.dbd.O), CH(OH), S(.dbd.O).sub.2, Si(CH.sub.3).sub.2,
(CH.sub.2).sub.p (in which 1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q
(in which 1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2,
C(CF.sub.3).sub.2 and C(.dbd.O)NH; Q is O, S, C(.dbd.O), CH(OH),
S(.dbd.O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2,
C(.dbd.O)NH, C(CH.sub.3)(CF.sub.3), C.sub.1-C.sub.6
alkyl-substituted phenyl or C.sub.1-C.sub.6 haloalkyl-substituted
phenyl in which Q is linked to opposite both phenyl rings in the
position of m-m, m-p, p-m or p-p; Y is --OH, --SH or --NH.sub.2; n
is an integer from 20 to 200; m is an integer from 10 to 400; and l
is an integer from 10 to 400.
2. The dope solution composition according to claim 1, wherein
Ar.sub.1 is selected from the following compounds: ##STR00059##
wherein X is O, S, C(.dbd.O), CH(OH), S(.dbd.O).sub.2,
Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, or
C(.dbd.O)NH; W is O, S or C(.dbd.O); and Z.sub.1, Z.sub.2 and
Z.sub.3 are identical to or different from each other and are O, N
or S.
3. The dope solution composition according to claim 1, wherein
Ar.sub.1 is selected from the following compounds: ##STR00060##
##STR00061## ##STR00062## ##STR00063## ##STR00064## ##STR00065##
##STR00066## ##STR00067##
4. The dope solution composition according to claim 1, wherein
Ar.sub.2 is selected from the following compounds: ##STR00068##
wherein X is O, S, C(.dbd.O), CH(OH), S(.dbd.O).sub.2,
Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, or
C(.dbd.O)NH; W is O, S or C(.dbd.O); and Z.sub.1, Z.sub.2 and
Z.sub.3 are identical to or different from each other and are O, N
or S.
5. The dope solution composition according to claim 1, wherein
Ar.sub.2 is selected from the following compounds: ##STR00069##
##STR00070## ##STR00071## ##STR00072## ##STR00073## ##STR00074##
##STR00075##
6. The dope solution composition according to claim 1, wherein Q is
selected from the group consisting of CH.sub.2, C(CH.sub.3).sub.2,
C(CF.sub.3).sub.2, O, S, S(.dbd.O).sub.2 and C(.dbd.O).
7. The dope solution composition according to claim 1, wherein
##STR00076## and Q is C(CF.sub.3).sub.2.
8. The dope solution composition according to claim 1, wherein the
copolymerization ratio (m:l) of the copolymers of Formulae 5 to 8
is from 0.1:9.9 to 9.9:0.1.
9. The dope solution composition according to claim 1, wherein the
copolymers of polyamic acids represented by Formulae 1 to 4 are
selected from those represented by Formulae 9 to 18 below:
##STR00077## ##STR00078## In Formulae 9 to 18, Ar.sub.1, Q, Y, m
and l are defined as above; and Y' is different from Y and is --OH,
--SH or --NH.sub.2.
10. The dope solution composition according to claim 9, wherein the
copolymerization ratio (m:l) of the copolymers of Formulae 9 to 18
is from 0.1:9.9 to 9.9:0.1.
11. The dope solution composition according to claim 1, wherein the
dope solution composition comprises 5 to 45% by weight of the
polymer for forming a hollow fiber, 25 to 94% by weight of the
organic solvent and 0.5 to 40% by weight of the additive.
12. The dope solution composition according to claim 1, wherein the
organic solvent is selected from the group consisting of: alcohols
including methanol, ethanol, 2-methyl-1-butanol and
2-methyl-2-butanol; ketones including .gamma.-butyrolactone,
cyclohexanone, 3-hexanone, 3-heptanone, 3-octanone, acetone and
methyl ethyl ketone; tetrahydrofurane; dichloroethane; dimethyl
sulfoxide; N-methyl-2-pyrrolidone; N,N-dimethylformamide;
N,N-dimethylacetamide; and mixtures thereof.
13. The dope solution composition according to claim 1, wherein the
additive is selected from the group consisting of: water; alcohols
including glycerol, ethylene glycol, propylene glycol and
diethylene glycol; polymers including polyvinylalcohol, polyacrylic
acid, polyacrylamide, polyethylene glycol, polypropylene glycol,
chitosan, chitin, dextran and polyvinylpyrrolidone; and salts
including lithium chloride, sodium chloride, calcium chloride,
lithium acetate, sodium sulfate and sodium hydroxide and mixtures
thereof.
14. A method for preparing a hollow fiber comprising: (S1) spinning
the dope solution composition according to claim 1 to prepare a
polyamic acid hollow fiber; (S2) imidizing the polyamic acid hollow
fiber to obtain a polyimide hollow fiber; and (S3) thermal-treating
the polyimide hollow fiber to induce intramolecular and
intermolecular rearrangement and obtain a hollow fiber comprising
one selected from polymers represented by the following Formulae 19
to 32 and copolymers thereof. ##STR00079## ##STR00080## In Formulae
19 to 32, Ar.sub.1 is a tetravalent C.sub.5-C.sub.24 arylene group
or a tetravalent C.sub.5-C.sub.24 heterocyclic ring, which is
substituted or unsubstituted with at least one substituent selected
from the group consisting of C.sub.1-C.sub.10 alkyl,
C.sub.1-C.sub.10 alkoxy, C.sub.1-C.sub.10 haloalkyl and
C.sub.1-C.sub.10 haloalkoxy, or two or more of which are fused
together to form a condensation ring or covalently bonded to each
other via a functional group selected from the group consisting of
O, S, C(.dbd.O), CH(OH), S(.dbd.O).sub.2, Si(CH.sub.3).sub.2,
(CH.sub.2).sub.p (in which 1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q
(in which 1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2,
C(CF.sub.3).sub.2 and C(.dbd.O)NH; Ar.sub.1' and Ar.sub.2 are
identical to or different from each other and are each
independently a bivalent C.sub.5-C.sub.24 arylene group or a
bivalent C.sub.5-C.sub.24 heterocyclic ring, which is substituted
or unsubstituted with at least one substituent selected from the
group consisting of C.sub.1-C.sub.10 alkyl, C.sub.1-C.sub.10
alkoxy, C.sub.1-C.sub.10 haloalkyl and C.sub.1-C.sub.10 haloalkoxy,
or two or more of which are fused together to form a condensation
ring or covalently bonded to each other via a functional group
selected from the group consisting of O, S, C(.dbd.O), CH(OH),
S(.dbd.O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2 and
C(.dbd.O)NH; Q is O, S, C(.dbd.O), CH(OH), S(.dbd.O).sub.2,
Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2,
C(.dbd.O)NH, C(CH.sub.3)(CF.sub.3), C.sub.1-C.sub.6
alkyl-substituted phenyl or C.sub.1-C.sub.6 haloalkyl-substituted
phenyl in which Q is linked to opposite both phenyl rings in the
position of m-m, m-p, p-m or p-p; Y'' is --O or S; n is an integer
from 20 to 200; m is an integer from 10 to 400; and l is an integer
from 10 to 400.
15. The method according to claim 14, wherein in the step S1, the
spinning is dry-jet-wet spinning or wet-spinning.
16. The method according to claim 14, wherein in the step S2, the
imidization is carried out under an inert atmosphere at 150 to
300.degree. C. for 1 minute to 12 hours.
17. The method according to claim 14, wherein the polyimide hollow
fiber includes polyimides represented by Formulae 33 to 40 below:
##STR00081## In Formulae 33 to 40, Ar.sub.1, Ar.sub.2, Q, Y, n, m,
and l are defined as above.
18. The method according to claim 14, wherein in the step S3, the
thermal treatment is carried out under an inert atmosphere at 350
to 500.degree. C. for 1 minute to 12 hours.
19. The method according to claim 14, wherein in the step S3, the
thermal treatment is carried out under an inert atmosphere at 400
to 450.degree. C. for 10 minutes to 2 hours.
20. The method according to claim 14, wherein the method comprises:
a1) preparing a polyamic acid dope solution composition according
to claim 1; a2) bringing the dope solution composition into contact
with an internal coagulant and spinning the composition in air,
while coagulating an insidie of a hollow fiber, to form a polyamic
acid hollow fiber; a3) coagulating the hollow fiber in a
coagulation bath; a4) washing the hollow fiber with a cleaning
solution, followed by drying; a5) imidizing the hollow fiber to
obtain a polyimide hollow fiber; and a6) thermally treating the
polyimide hollow fiber.
21. The method according to claim 20, wherein the spinning is
carried out at a spinning temperature of 5 to 120.degree. C. and a
spinning rate of 5 to 100 m/min.
22. The method according to claim 20, wherein the coagulation bath
has a temperature of 0 to 50.degree. C.
23. The method according to claim 20, wherein the internal
coagulant has a flow rate of 1 to 10 ml/min.
24. A hollow fiber comprising one selected from polymers
represented by Formulae 19 to 32 and copolymers thereof:
##STR00082## ##STR00083## In Formulae 19 to 32, Ar.sub.1 is a
tetravalent C.sub.5-C.sub.24 arylene group or a tetravalent
C.sub.5-C.sub.24 heterocyclic ring, which is substituted or
unsubstituted with at least one substituent selected from the group
consisting of C.sub.1-C.sub.10 alkyl, C.sub.1-C.sub.10 alkoxy,
C.sub.1-C.sub.10 haloalkyl and C.sub.1-C.sub.10 haloalkoxy, or two
or more of which are fused together to form a condensation ring or
covalently bonded to each other via a functional group selected
from the group consisting of O, S, C(.dbd.O), CH(OH),
S(.dbd.O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2 and
C(.dbd.O)NH; Ar.sub.1' and Ar.sub.2 are identical to or different
from each other and are each independently a bivalent
C.sub.5-C.sub.24 arylene group or a bivalent C.sub.5-C.sub.24
heterocyclic ring, which is substituted or unsubstituted with at
least one substituent selected from the group consisting of
C.sub.1-C.sub.10 alkyl, C.sub.1-C.sub.10 alkoxy, C.sub.1-C.sub.10
haloalkyl and C.sub.1-C.sub.10 haloalkoxy, or two or more of which
are fused together to form a condensation ring or covalently bonded
to each other via a functional group selected from the group
consisting of O, S, C(.dbd.O), CH(OH), S(.dbd.O).sub.2,
Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2 and
C(.dbd.O)NH; Q is O, S, C(.dbd.O), CH(OH), S(.dbd.O).sub.2,
Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2,
C(.dbd.O)NH, C(CH.sub.3)(CF.sub.3), C.sub.1-C.sub.6
alkyl-substituted phenyl or C.sub.1-C.sub.6 haloalkyl-substituted
phenyl in which Q is linked to opposite both phenyl rings in the
position of m-m, m-p, p-m or p-p; Y'' is --O or S; n is an integer
from 20 to 200; m is an integer from 10 to 400; and l is an integer
from 10 to 400.
25. The hollow fiber according to claim 24, wherein Ar.sub.1 is
selected from the following compounds: ##STR00084## wherein X is O,
S, C(.dbd.O), CH(OH), S(.dbd.O).sub.2, Si(CH.sub.3).sub.2,
(CH.sub.2).sub.p (in which 1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q
(in which 1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2,
C(CF.sub.3).sub.2, or C(.dbd.O)NH; W is O, S or C(.dbd.O); and
Z.sub.1, Z.sub.2 and Z.sub.3 are identical to or different from
each other and are O, N or S.
26. The hollow fiber according to claim 24, wherein Ar.sub.1 is
selected from the following compounds: ##STR00085## ##STR00086##
##STR00087## ##STR00088## ##STR00089## ##STR00090## ##STR00091##
##STR00092##
27. The hollow fiber according to claim 24, wherein Ar.sub.1' and
Ar.sub.2 are selected from the following compounds: ##STR00093##
wherein X is O, S, C(.dbd.O), CH(OH), S(.dbd.O).sub.2,
Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, or
C(.dbd.O)NH; W is O, S or C(.dbd.O); and Z.sub.1, Z.sub.2 and
Z.sub.3 are identical to or different from each other and are O, N
or S.
28. The hollow fiber according to claim 24, wherein Ar.sub.1' and
Ar.sub.2 are selected from the following compounds: ##STR00094##
##STR00095## ##STR00096## ##STR00097## ##STR00098## ##STR00099##
##STR00100##
29. The hollow fiber according to claim 24, wherein Q is selected
from the group consisting of CH.sub.2, C(CH.sub.3).sub.2,
C(CF.sub.3).sub.2, O, S, S(.dbd.O).sub.2 and C(.dbd.O).
30. The hollow fiber according to claim 24, wherein ##STR00101##
and Q is C(CF.sub.3).sub.2.
31. The hollow fiber according to claim 24, wherein the hollow
fiber is used as a gas separation membrane for separation of mixed
gas pair of H.sub.2/N.sub.2, H.sub.2/CH.sub.4, H.sub.2/O.sub.2,
H.sub.2/CO.sub.2, O.sub.2/CO.sub.2, N.sub.2/CH.sub.4,
O.sub.2/N.sub.2, CO.sub.2/CH.sub.4 and CO.sub.2/N.sub.2.
32. The hollow fiber according to claim 24, wherein the hollow
fiber has O.sub.2/N.sub.2 selectivity of 3 or higher and
CO.sub.2/CH.sub.4 selectivity of 20 or higher.
33. The hollow fiber according to claim 24, wherein the hollow
fiber has O.sub.2/N.sub.2 selectivity of 3 to 30 and
CO.sub.2/CH.sub.4 selectivity of 20 to 100.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to and the benefit of
Korean Patent Application No. 10-2008-0046115 filed in the Korean
Intellectual Property Office on May 19, 2008, the entire contents
of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] (a) Field of the Invention
[0003] The present invention relates to a polyamic acid dope
solution composition, a method for preparing a hollow fiber using
the same and a hollow fiber prepared by the method. More
specifically, the present invention relates to a dope solution
composition to prepare hollow fibers that have well-connected
microcavities and are thus applicable to gas separation membranes
for separating various types of gases via thermal rearrangement, a
method for preparing hollow fibers from the composition and hollow
fibers prepared by the method.
[0004] (b) Description of the Related Art
[0005] Separation membranes must satisfy the requirements of
superior thermal, chemical and mechanical stability, high
permeability and high selectivity so that they can be
commercialized and then applied to a variety of industries. The
term "permeability" used herein is defined as a rate at which a
substance permeates through a separation membrane. The term
"selectivity" used herein is defined as a permeation ratio between
two different gas components.
[0006] Based on the separation performance, separation membranes
may be classified into reverse osmosis membranes, ultrafiltration
membranes, microfiltration membranes, gas separation membranes,
etc. Based on the shape, separation membranes may be largely
classified into flat sheet membranes spiral-wound membranes,
composite membranes and hollow fiber membranes. Of these,
asymmetric hollow fiber membranes have the largest membrane areas
per unit volume and are thus generally used as gas separation
membranes.
[0007] A process for separating a specific gas component from
various ingredients constituting a gas mixture is greatly
important. This gas separation process generally employs a membrane
process, a pressure swing adsorption process, a cryogenic process
and the like. Of these, the pressure swing adsorption process and
the cryogenic process are generalized techniques, design and
operations methods of which have already been developed, and are
now in widespread use. On the other hand, gas separation using the
membrane process has a relatively short history.
[0008] The gas separation membrane for membrane process application
is used to separate and concentrate various gases, e.g., hydrogen
(H.sub.2), helium (He), nitrogen (N.sub.2), oxygen (O.sub.2),
carbon monoxide (CO), carbon dioxide (CO.sub.2), water vapor
(H.sub.2O), ammonia (NH.sub.3), sulfur compounds (SO.sub.x) and
light hydrocarbon gases such as methane (CH.sub.4), ethane
(C.sub.2H.sub.6), ethylene (C.sub.2H.sub.4), propane
(C.sub.3H.sub.8), propylene (C.sub.3H.sub.6), butane
(C.sub.4H.sub.10), butylene (C.sub.4H.sub.8). Gas separation may be
used in the fields including separation of oxygen or nitrogen
present in air, removal of moisture present in compressed air and
the like.
[0009] The principle for the gas separation using membranes is
based on the difference in permeability between respective
components constituting a mixture of two or more gases. The gas
separation involves a solution-diffusion process, in which a gas
mixture comes in contact with a surface of a membrane and at least
one component thereof is selectively dissolved. Inside the
membrane, selective diffusion occurs. The gas component which
permeates the membrane is more rapid than at least one of other
components.
[0010] Gas components having a relatively low permeability pass
through the membrane at a speed lower than at least one component.
Based upon such a principle, the gas mixture is divided into two
flows, i.e., a selectively permeated gas-containing flow and a
non-permeated gas-containing flow. Accordingly, in order to
suitably separate gas mixtures, there is a demand for techniques to
select a membrane-forming material having high perm-selectivity to
a specific gas ingredient and to control the material to have a
structure capable of exhibiting sufficient permeability.
[0011] In order to selectively separate gases and concentrate the
same through the membrane separation method, the separation
membrane must generally have an asymmetric structure comprising a
dense selective-separation layer arranged on the surface of the
membrane and a porous supporter with a minimum permeation
resistance arranged on the bottom of the membrane. One membrane
property, i.e., selectivity, is determined depending upon the
structure of the selective-separation layer. Another membrane
property, i.e., permeability, depends on the thickness of the
selective-separation layer and the porosity level of the lower
structure, i.e., the porous supporter of the asymmetric membrane.
Furthermore, to selectively separate a mixture of gases, the
separation layer must be free from surface defects and have a pore
size not more than 5 .ANG..
[0012] Since a system using a gas separation membrane module was
developed in 1977 by the Monsanto Company under the trade name
"Prism", gas separation processes using polymer membranes has been
first available commercially. The gas separation process has shown
a gradual increase in annual gas separation market share due to low
energy consumption and low installation cost, as compared to
conventional methods.
[0013] Since a cellulose acetate semi-permeation membrane having an
asymmetric structure as disclosed in U.S. Pat. No. 3,133,132 was
developed, a great deal of research has been conducted on polymeric
membranes and various polymers are being prepared into hollow
fibers using phase inversion methods.
[0014] General methods for preparing asymmetric hollow fiber
membranes using phase-inversion are wet-spinning and dry-jet-wet
spinning. A representative hollow fiber preparation process using
dry-jet-wet spinning comprises the following four steps, (1)
spinning hollow fibers with a polymeric dope solution, (2) bringing
the hollow fibers into contact with air to evaporate volatile
ingredients therefrom, (3) precipitating the resulting fibers in a
coagulation bath, and (4) subjecting the fibers to post-treatment
including washing, drying and the like.
[0015] Organic polymers such as polysulfones, polycarbonates,
polypyrrolones, polyarylates, cellulose acetates and polyimides are
widely used as hollow fiber membrane materials for gas separation.
Various attempts have been made to impart permeability and
selectivity for a specific gas to polyimide membranes having
superior chemical and thermal stability among these polymer
materials for gas separation. However, in general polymeric
membrane, permeability and selectivity are inversely
proportional.
[0016] For example, U.S. Pat. No. 4,880,442 discloses polyimide
membranes wherein a large free volume is imparted to polymeric
chains and permeability is improved using non-rigid anhydrides.
Furthermore, U.S. Pat. No. 4,717,393 discloses crosslinked
polyimide membranes exhibiting high gas selectivity and superior
stability, as compared to conventional polyimide gas separation
membranes. In addition, U.S. Pat. Nos. 4,851,505 and 4,912,197
disclose polyimide gas separation membranes capable of reducing the
difficulty of polymer processing due to superior solubility in
generally-used solvents. In addition, PCT Publication No. WO
2005/007277 discloses defect-free asymmetric membranes comprising
polyimide and another polymer selected from the group consisting of
polyvinylpyrrolidones, sulfonated polyetheretherketones and
mixtures thereof.
[0017] However, polymeric materials having membrane performance
available commercially for use in gas separation (in the case of
air separation, oxygen permeability is 1 Barrer or higher, and
oxygen/nitrogen selectivity is 6.0 or higher) are limited to only a
few types. This is because there is considerable limitation in
improving polymeric structures, and great compatibility between
permeability and selectivity makes it difficult to obtain
separation and permeation capabilities beyond a predetermined upper
limit.
[0018] Furthermore, conventional polymeric membrane materials have
a limitation of permeation and separation properties and
disadvantages in that they undergo decomposition and aging upon a
long-term exposure to high pressure and high temperature processes
or to gas mixtures containing hydrocarbon, aromatic and polar
solvents, thus causing a considerable decrease in inherent membrane
performance. Due to these problems, in spite of their high economic
value, gas separation processes are utilized in considerably
limited applications to date.
[0019] Accordingly, there is an increasing demand for development
of polymeric materials capable of achieving both high permeability
and superior selectivity, and novel gas separation membranes using
the same.
[0020] In accordance with such demand, a great deal of research has
been conducted to modify polymers into ideal structures that
exhibit superior gas permeability and selectivity, and have a
desired pore size. As a result of this research, polymeric
membranes having superior gas separation performance have
remarkably developed.
[0021] For example, nanocomposites, hydride materials and composite
polymers have been designed, taking into the consideration the fact
that the high free volumes of polymers should be imparted to these
materials.
[0022] In addition, a method for obtaining medium and small pore
size distribution has been recently reported [H. B. Park, C. H.
Jung, Y. M. Lee, A. J. Hill, S. J. Pas, S. T. Mudie, E. Van Wagner,
B. D. Freeman, D. J. Cookson, Polymers with cavities tuned for fast
selective transport of small molecules and ions, Science 2007, 318,
254.38].
[0023] The inventors of the present invention suggested that
completely aromatic, insoluble, infusible polybenzoxazole
(TR-.alpha.-PBO) membranes can be prepared by thermally modifying
ortho-hydroxyl group-containing polyimide aromatic polymers through
thermal rearrangement to molecular rearrangement at 350 to
450.degree. C. [H. B. Park, C. H. Jung, Y. M. Lee, A. J. Hill, S.
J. Pas, S. T. Mudie, E. Van Wagner, B. D. Freeman, D. J. Cookson,
Polymers with cavities tuned for fast selective transport of small
molecules and ions, Science 2007, 318, 254. 38].
[0024] TR-.alpha.-PBO membranes have advantages of excellent gas
separation performance and superior chemical stability and
mechanical properties from intramolecular and intermolecular
thermal rearrangement, surpassing the limitations of typical
polymeric membranes (i.e., the Robeson's upper bound). [L. M.
Robeson, Correlation of separation factor versus permeability for
polymeric membrane, J. Membr. Sci., 1991, 62, 165, L. M. Robeson,
The upper bound revisited, J. Membr. Sci., 2008, 320, 390].
[0025] Furthermore, through research on methods for improving gas
permeability, the present inventors have disclosed polymer
structures acting as permeable sites and suggested
polyimide-polybenzoxazole copolymers in which these polymer
structures are incorporated in polyimide backbones
(PCT/KR2008/001282).
[0026] As a result of subsequent diverse research on methods for
preparing hollow fibers for gas separation from these polymers, the
present inventors have established a novel process. Based on the
process, the present invention was completed.
SUMMARY OF THE INVENTION
[0027] Therefore, it is one object of the present invention to
provide a dope solution composition suitable for use in preparing
hollow fibers made of high free volume polymers by imidizing
polyamic acid hollow fibers to obtain polyimide hollow fibers and
subjecting the polyimide hollow fibers to thermal rearrangement via
thermal treatment.
[0028] It is another object of the present invention to provide a
method for preparing hollow fibers with superior gas permeability
and selectivity, by preparing polyimide hollow fibers from the dope
solution composition, followed by thermal treatment.
[0029] It is another object of the present invention to provide
hollow fibers that have microcavities, increased polymer backbone
strength and high fractional free volumes, thus exhibiting superior
gas permeability and selectivity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The above and other objects, features and other advantages
of the present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0031] FIG. 1 is a cross-section scanning electron microscope (SEM)
image of a finger-type hollow fiber prepared in Example 1 of the
present invention at 100.times. magnification;
[0032] FIG. 2 is a cross-section scanning electron microscope (SEM)
image of a finger-type hollow fiber prepared in Example 1 of the
present invention at 500.times. magnification;
[0033] FIG. 3 is a cross-section scanning electron microscope (SEM)
image of a finger-type hollow fiber prepared in Example 1 of the
present invention at 5,000.times. magnification;
[0034] FIG. 4 is a cross-section scanning electron microscope (SEM)
image of a sponge-type hollow fiber prepared in Example 14 of the
present invention at 100.times. magnification;
[0035] FIG. 5 is a cross-section scanning electron microscope (SEM)
image of a sponge-type hollow fiber prepared in Example 14 of the
present invention at 1,000.times. magnification;
[0036] FIG. 6 is a cross-section scanning electron microscope (SEM)
image of a sponge-type hollow fiber prepared in Example 14 of the
present invention at 10,000.times. magnification;
[0037] FIG. 7 is a graph comparing oxygen permeability (GPU) and
oxygen/nitrogen selectivity for hollow fibers prepared in Examples
1 to 17 of the present invention and Comparative Examples 1 to 3
(the numbers 1' to 3' indicate Comparative Examples 1 to 3,
respectively; and the numbers 1 to 17 indicate Examples 1 to 17,
respectively); and
[0038] FIG. 8 is a graph comparing carbon dioxide permeability
(GPU) and carbon dioxide/methane selectivity for hollow fibers
prepared in Examples 1 to 17 of the present invention and
Comparative Examples 1 to 3 (the numbers 1' to 3' indicate
Comparative Examples 1 to 3, respectively; and the numbers 1 to 17
indicate Examples 1 to 17, respectively).
DETAILED DESCRIPTION OF THE INVENTION
[0039] Hereinafter, the present invention will be illustrated in
more detail.
[0040] In one aspect, the present invention is directed to a dope
solution composition comprising: (a) a polymer for forming a hollow
fiber, including one selected from the group consisting of polyamic
acids represented by the following Formulae 1 to 4, polyamic acid
copolymers represented by Formulae 5 to 8, copolymers thereof and
blends thereof; (b) an organic solvent; and (c) an additive.
##STR00001##
[0041] In Formulae 1 to 8,
[0042] Ar.sub.1 is a tetravalent C.sub.5-C.sub.24 arylene group or
a tetravalent C.sub.5-C.sub.24 heterocyclic ring, which is
substituted or unsubstituted with at least one substituent selected
from the group consisting of C.sub.1-C.sub.10 alkyl,
C.sub.1-C.sub.10 alkoxy, C.sub.1-C.sub.10 haloalkyl and
C.sub.1-C.sub.10 haloalkoxy, or two or more of which are fused
together to form a condensation ring or covalently bonded to each
other via a functional group selected from the group consisting of
O, S, C(.dbd.O), CH(OH), S(.dbd.O).sub.2, Si(CH.sub.3).sub.2,
(CH.sub.2).sub.p (in which 1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q
(in which 1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2,
C(CF.sub.3).sub.2 and C(.dbd.O)NH;
[0043] Ar.sub.2 is a bivalent C.sub.5-C.sub.24 arylene group or a
bivalent C.sub.5-C.sub.24 heterocyclic ring, which is substituted
or unsubstituted with at least one substituent selected from the
group consisting of C.sub.1-C.sub.10 alkyl, C.sub.1-C.sub.10
alkoxy, C.sub.1-C.sub.10 haloalkyl and C.sub.1-C.sub.10 haloalkoxy,
or two or more of which are fused together to form a condensation
ring or covalently bonded to each other via a functional group
selected from the group consisting of O, S, C(.dbd.O), CH(OH),
S(.dbd.O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2 and
C(.dbd.O)NH;
[0044] Q is O, S, C(.dbd.O), CH(OH), S(.dbd.O).sub.2,
Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2,
C(.dbd.O)NH, C(CH.sub.3)(CF.sub.3), C.sub.1-C.sub.6
alkyl-substituted phenyl or C.sub.1-C.sub.6 haloalkyl-substituted
phenyl in which Q is linked to opposite both phenyl rings in the
position of m-m, m-p, p-m or p-p;
[0045] Y is --OH, --SH or --NH.sub.2;
[0046] n is an integer from 20 to 200;
[0047] m is an integer from 10 to 400; and
[0048] l is an integer from 10 to 400.
[0049] Ar.sub.1 and Ar.sub.2 may be the same arylene or
heterocyclic ring.
[0050] Preferably, Ar.sub.1 is selected from the following
compounds and the linkage position thereof includes all of o-, m-
and p-positions.
##STR00002##
[0051] wherein X is O, S, C(.dbd.O), CH(OH), S(.dbd.O).sub.2,
Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, or
C(.dbd.O)NH; W is O, S or C(.dbd.O); and Z.sub.1, Z.sub.2 and
Z.sub.3 are identical to or different from each other and are O, N
or S.
[0052] More preferably, Ar.sub.1 is selected from the following
compounds:
##STR00003## ##STR00004## ##STR00005## ##STR00006## ##STR00007##
##STR00008## ##STR00009## ##STR00010##
[0053] Preferably, Ar.sub.2 is selected from the following
compounds and the linkage position thereof includes all of o-, m-
and p-positions.
##STR00011##
[0054] wherein X is O, S, C(.dbd.O), CH(OH), S(.dbd.O).sub.2,
Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, or
C(.dbd.O)NH; W is O, S or C(.dbd.O); and Z.sub.1, Z.sub.2 and
Z.sub.3 are identical to or different from each other and are O, N
or S.
[0055] More preferably, Ar.sub.2 is selected from the following
compounds:
##STR00012## ##STR00013## ##STR00014## ##STR00015## ##STR00016##
##STR00017##
[0056] Preferably, Q is CH.sub.2, C(CH.sub.3).sub.2,
C(CF.sub.3).sub.2, O, S, S(.dbd.O).sub.2 or C(.dbd.O).
[0057] More preferably,
##STR00018##
and Q is C(CF.sub.3).sub.2.
[0058] The polyamic acids of Formulae 1 to 4 can be prepared in
accordance with methods well known in the art. For example, the
polyamic acids may be prepared by reacting tetracarboxylic acid
anhydrides as monomers with aromatic diamines containing --OH, --SH
or --NH.sub.2.
[0059] The polyamic acids represented by Formulae 1 to 4 are
thermally rearranged through a preparation process which will be
mentioned later, to form polybenzoxazole, polybenzothiazole and
polybenzopyrrolone hollow fibers, each having a high fractional
free volume. At this time, the polybenzoxazole hollow fiber is
prepared from polyhydroxyamic acid in which Y is --OH, the
polybenzothiazole hollow fiber is prepared from polythiolamic acid
in which Y is --SH, and the polybenzopyrrolone hollow fiber is
prepared from polyaminoamic acid in which Y is --NH.sub.2.
[0060] The dope solution composition of the present invention
comprises copolymers of polyamic acids represented by Formulae 1 to
4, which are selected from those represented by Formulae 9 to 18
below.
##STR00019## ##STR00020##
[0061] In Formulae 9 to 18,
[0062] Ar.sub.1, Q, Y, m and l are defined as above; and
[0063] Y' is different from Y and is --OH, --SH or --NH.sub.2.
[0064] The polyamic acid copolymers represented by Formulae 9 to 18
are subjected to imidization and thermal rearrangement, to form
hollow fibers made of copolymers of polybenzoxazole,
polybenzothiazole and polybenzopyrrolone, each having a high free
volume. The physical properties of hollow fibers thus prepared from
intramolecular and intermolecular rearrangement can be controlled
by controlling the copolymerization ratio between blocks which are
thermally rearranged into polybenzoxazole, polybenzothiazole and
polybenzopyrrolone.
[0065] In addition, polyamic acid copolymers represented by
Formulae 5 to 8 are imidized and thermally rearranged to form
hollow fibers made of benzoxazole-imide copolymer,
benzothiazole-imide copolymer or benzopyrrolone-imide copolymers
which have a high fractional free volume. At this time, it is
possible to control physical properties of the prepared hollow
fibers by controlling the copolymerization ratio between blocks
which will be thermally rearranged into polybenzoxazole,
polybenzothiazole and polybenzopyrrolone, and blocks which will be
thermally rearranged into polyimides.
[0066] Preferably, the copolymerization ratio between the blocks,
m:l, is from 0.1:9.9 to 9.9:0.1, more preferably 2:8 to 8:2, most
preferably 5:5. The copolymerization ratio affects the morphology
of the hollow fibers thus prepared. Since such morphologic change
is associated with gas permeability and selectivity, it is
considerably important to control the copolymerization ratio.
[0067] The polymer for forming hollow fiber including one selected
from the group consisting of polyamic acids represented by Formulae
1 to 4, polyamic acid copolymers represented by Formulae 5 to 8,
copolymers thereof and blends thereof is present in an amount of 5
to 45% by weight, based on the total weight of the dope solution
composition. When the polymer content is less than the level as
defined above, the strength of hollow fibers is decreased. On the
other hand, when the polymer content exceeds this range,
disadvantageously, gas permeability is difficult to be kept
high.
[0068] In addition to the polymer for forming hollow fiber, the
dope solution composition of the present invention comprises a
solvent to dissolve the polymer and an additive to control
phase-inversion temperature and viscosity.
[0069] Solvents that can be used in the present invention are not
particularly limited. Any solvent may be used without particular
limitation so long as it can homogeneously dissolve the polymer and
additive. For example, the solvent may be selected from the group
consisting of: alcohols including methanol, ethanol,
2-methyl-1-butanol and 2-methyl-2-butanol; ketones including
.gamma.-butyrolactone, cyclohexanone, 3-hexanone, 3-heptanone,
3-octanone, acetone and methyl ethyl ketone; tetrahydrofurane;
dichloroethane; dimethyl sulfoxide; N-methyl-2-pyrrolidone;
N,N-dimethylformamide; N,N-dimethylacetamide and mixtures
thereof.
[0070] The content of the solvent is 25 to 94% by weight, based on
the total weight of the dope solution composition. When the content
of the solvent is below 25%, the viscosity of the dope solution is
excessively high, thus disadvantageously making it difficult to
prepare hollow fibers and causing a decrease in permeability of the
prepared hollow fibers. Conversely, when the solvent content
exceeds 94%, the viscosity of the dope solution is low, thus
disadvantageously making it difficult to prepare continuous hollow
fibers.
[0071] The present invention is not particularly limited in terms
of the additive. Any additive may be used so long as it is used in
the art. Representative examples of useful pore controllers include
polymers selected from the group consisting of polyvinylalcohol,
polyacrylic acid, polyacrylamide, polyethylene glycol,
polypropylene glycol, chitosan, chitin, dextran and
polyvinylpyrrolidone. Examples of pore formers include salts
selected from the group consisting of lithium chloride, sodium
chloride, calcium chloride, lithium acetate, sodium sulfate and
sodium hydroxide. Other useful additives are water; alcohols
selected from the group consisting of glycerol, ethylene glycol,
propylene glycol and diethylene glycol and mixtures thereof.
[0072] At this time, the content of the additive is 0.5 to 40% by
weight, based on the total weight of the dope solution composition.
When the content of the additive is less than 0.5%, surface pores
of the hollow fibers are excessively large, thus making it
difficult to form dense surface layers. Conversely, when the
content of the additive exceeds 40%, the viscosity of the dope
solution is excessively high, thus making it difficult to prepare
hollow fibers.
[0073] In addition, the hollow fiber of the present invention is
prepared by (S1) spinning the dope solution composition to prepare
a polyamic acid hollow fiber, (S2) imidizing the hollow fiber to
obtain a polyimide hollow fiber, and (S3) thermally treating the
polyimide hollow fiber to induce intramolecular and intermolecular
rearrangement and obtain a hollow fiber comprising one selected
from polymers represented by the following Formulae 19 to 32 and
copolymers thereof.
##STR00021## ##STR00022##
[0074] In Formulae 19 to 32,
[0075] Ar.sub.1, Ar.sub.2, Q, n, m and l are defined as above;
[0076] Ar.sub.1' is the same as defined in Ar.sub.2 and is
identical to or different from Ar.sub.2; and
[0077] Y'' is O or S.
[0078] First, in the step S1, the dope solution composition is spun
and then undergoes phase-inversion to prepare a hollow fiber.
[0079] At this time, the spinning may be carried out in accordance
with a method well-known in the art and is not particularly
limited. In the present invention, dry or dry-jet-wet spinning is
used for the preparation of hollow fibers. A solvent-exchange
method using solution-spinning is generally used as the hollow
fiber preparation method. In accordance with the solvent exchange
method, after polymers are dissolved along with an additive in a
solvent and spun using a dry or dry-jet-wet spinning method, the
solvent and the non-solvent are exchanged in the presence of the
non-solvent to form microcavities. In the process in which the
solvent is diffused into a coagulation bath as the non-solvent, an
asymmetric membrane or a symmetric membrane in which the interior
is identical to the exterior was formed.
[0080] For example, in a case where dry-jet-wet spinning is used
for the preparation of hollow fibers, the dry-jet-wet spinning is
achieved through the steps of: a1) preparing a polyamic acid dope
solution composition; a2) bringing the dope solution composition
into contact with an internal coagulant, and spinning the
composition in air, while coagulating an inside of a hollow fiber
to form a polyamic acid hollow fiber; a3) coagulating the hollow
fiber in a coagulation bath; a4) washing the hollow fiber with a
cleaning solution, followed by drying; a5) imidizing the hollow
fiber to obtain a polyimide hollow fiber; and a6) thermally
treating the polyimide hollow fiber.
[0081] At this time, a flow rate of internal coagulant discharged
through an inner nozzle is preferably 1 to 10 ml/min, more
preferably 1 to 3 ml/min. In addition, a double nozzle preferably
has an outer diameter of 0.1 to 2.5 mm. The flow rate of the
internal coagulant, and the outer diameter of the double nozzle can
be controlled within the range according to the use and conditions
of hollow fibers. In addition, the air gap between the nozzle and
the coagulation bath is preferably 0.1 to 200 cm, more preferably 5
to 50 cm.
[0082] The phase-inversion is induced in a coagulation bath by
passing the hollow fiber through a high-temperature spinning
nozzle, while maintaining a spinning temperature of 5 to
120.degree. C. and a spinning rate of 5 to 100 m/min. The spinning
temperature and spinning rate may be varied within the range
depending upon the use and operation conditions of hollow
fibers.
[0083] At this time, when the spinning temperature is below the
above range, the viscosity of the dope solution is increased, thus
making it difficult to perform rapid spinning, and on the other
hand, when the spinning temperature exceeds the above range,
solvent evaporation and the viscosity of the dope solution are
decreased, thus disadvantageously making it impossible to
continuously prepare hollow fibers. In addition, when the spinning
rate is below the above range, the surface layer is thickened and a
flow rate is then decreased, and on the other hand, when the
spinning rate exceeds the above range, the mechanical properties of
hollow fibers thus produced are deteriorated, thus
disadvantageously making it impossible to smoothly perform hollow
fiber spinning. Accordingly, it is preferable that the spinning
rate be maintained within the range.
[0084] At this time, the temperature of the coagulation bath is
preferably 0 to 50.degree. C. When the coagulation bath temperature
is below this range, phase-inversion is delayed, thus making it
difficult to form surface layers, and on the other hand, when the
temperature exceeds this range, the solvent present in the
coagulation bath evaporates, thus disadvantageously making it
impossible to smoothly prepare hollow fibers.
[0085] As the external coagulant present in the coagulation bath,
any type may be used so long as it does not dissolve polymeric
materials and is compatible with the solvent and additive.
Representative examples of useful external coagulants include
water, glycerine, propylene glycol and mixtures thereof. Water is
preferred.
[0086] To remove the solvent, additive, and the coagulated solution
that remain inside the coagulated hollow fibers and on the surface
thereof, washing and drying processes may be performed. Water or
hot-water may be used as the cleaning solution. The washing time is
not particularly limited. Preferably, the washing is carried out
for 1 to 24 hours.
[0087] After the washing, the drying is performed at a temperature
ranging from 20 to 100.degree. C. for 3 to 72 hours.
[0088] Subsequently, in the step S2), the hollow fiber thus
prepared is imidized.
[0089] The imidization may be carried out in accordance with a
method well-known in the art. For example, the hollow fiber made of
polyamic acid is thermally imidized to obtain a hollow fiber made
of polyimide. Preferably, the thermal imidization is carried out
under an inert atmosphere at 150 to 300.degree. C. for 1 minute to
12 hours.
[0090] When the imidization temperature is below this range,
polyamic acid as a precursor is only slightly imidized, and on the
other hand, when the imidization temperature exceeds this range,
significant effects cannot be obtained and economic efficiency is
thus very low. The imidization conditions may be suitably
controlled within the range according to the functional groups,
Ar.sub.1, Ar.sub.2, Q and Y.
[0091] Subsequently, in the step S3), the polyimide hollow fiber is
thermally treated to obtain hollow fibers including polymers
represented by Formulae 19 to 32 or copolymers thereof.
[0092] Through the thermal-rearrangement using thermal treatment,
it is possible to obtain hollow fibers including polymers
represented by Formulae 19 to 32 or copolymers thereof that have a
decreased density, an increased fractional free volume (FFV) and an
increased d-spacing due to an increased microcavity size, and thus
exhibit improved gas permeability, as compared to polyimide hollow
fibers.
[0093] The thermal treatment is carried out under an inert
atmosphere at 350 to 500.degree. C., preferably 400 to 450.degree.
C., for 1 minute to 12 hours, preferably 10 minutes to 2 hours at a
heating rate of 1 to 20.degree. C./min. When the temperature is
below this range, the thermal rearrangement is not completed and
the polyimide precursor remains unreacted, causing deterioration in
purity. On the other hand, when the temperature exceeds this range,
polyimide is disadvantageously converted into a carbon substance as
an inorganic due to polymer carbonization. Accordingly, it is
preferable that the thermal treatment be suitably performed within
this temperature range.
[0094] The imidization of step S2) and the thermal treatment of
step S3) will be illustrated in detail with reference to Reaction
Schemes 1 and 2 below:
##STR00023## ##STR00024##
##STR00025## ##STR00026##
[0095] In Reaction Schemes 1 and 2, Ar.sub.1, Ar.sub.1', Ar.sub.2,
Q, Y, Y'', n, m, and l are defined as above.
[0096] As can be seen from Reaction Scheme 1, hollow fibers made of
polyamic acid represented by Formula 1, Formula 2, Formula 3 and
Formula 4 are imidized as mentioned above and are then prepared
into hollow fibers made of polyimides represented by Formula 33,
Formula 34, Formula 35 and Formula 36, respectively.
[0097] Subsequently, through the afore-mentioned thermal treatment,
the polyimide hollow fibers of Formulae 33, 34, 35 and 36 are
converted into polybenzoxazole, polybenzothiazole and
polybenzopyrrolone polymers of Formulae 19 to 25. The conversion of
polyimide hollow fibers into the polymers is carried out through
the removal reaction of CO.sub.2 present in the polymers of
Formulae 33 to 36.
[0098] At this time, polyhydroxyamic acids of Formulae 1 to 4 in
which Y is --OH, or polythiolamic acids of Formulae 1 to 4 in which
Y is --SH are thermally rearranged into polybenzoxazoles (Y''=O) or
polybenzothiazoles (Y''=S) of Formula 19, Formula 21, Formula 23
and Formula 24. In addition, polyaminoamic acids of Formulae 1 to 4
in which Y is --NH.sub.2 are thermally rearranged into
polybenzopyrrolones of Formulae 20, 22 and 25.
[0099] As can be seen from Reaction Scheme 2, hollow fibers made of
polyamic acid copolymers represented by the Formula 5, Formula 6,
Formula 7 and Formula 8 are converted through imidization into
hollow fibers made of polyimides represented by Formula 37, Formula
38, Formula 39 and Formula 40, respectively.
[0100] Subsequently, through the afore-mentioned thermal treatment,
hollow fibers made of polyimides of Formula 37, Formula 38, Formula
39 and Formula 40 are converted through the removal reaction of
CO.sub.2 present in the polyimides into polymers of Formulae 26 to
32.
[0101] At this time, polyhydroxyamic acids of Formulae 5 to 8 in
which Y is --OH, or polythiolamic acids of Formulae 5 to 8 in which
Y is --SH are thermally rearranged into benzoxazole(Y''=O)-imide
copolymers or benzothiazole(Y''=S)-imide copolymers of Formulae 26,
28, 30 and 31. In addition, polyaminoamic acids of Formulae 5 to 8
in which Y is --NH.sub.2 are thermally rearranged into
benzopyrrolone-imide copolymers of Formulae 27, 29 and 32.
[0102] The blocks constituting the hollow fibers made of polyamic
acid copolymers represented by Formulae 9 to 18 are imidized and
then converted into polyimide hollow fibers composed of different
imide blocks. Subsequently, through thermal treatment, the
respective imide blocks are thermally rearranged into
polybenzoxazole, polybenzothiazole and polybenzopyrrolone,
depending upon the type of Y to form hollow fibers made of
copolymers thereof, i.e., copolymers of polymers represented by
Formulae 19 to 25.
[0103] At this time, by controlling the preparation process, the
hollow fibers are prepared in the form of a macropore-formed finger
or a sponge that has a macropore-free selective layer and thus
exhibits stable membrane performance. Alternatively, the hollow
fibers may be prepared in a symmetric or asymmetric form by
controlling the preparation process. Furthermore, by controlling
polymer design while taking into consideration the characteristics
of Ar.sub.1, Ar.sub.1' Ar.sub.2 and Q present in the chemical
structure, permeability and selectivity for various gas types can
be controlled.
[0104] The hollow fibers thus prepared comprise polymers
represented by Formula 19 to Formula 32 or copolymers thereof.
##STR00027## ##STR00028##
[0105] In Formulae 19 to 32, Ar.sub.1, Ar.sub.1', Ar.sub.2, Q, Y'',
n, m and l are defined as above.
[0106] At this time, Ar.sub.1, Ar.sub.1' and Ar.sub.2 may be the
same arylene or heterocyclic ring.
[0107] Preferably, Ar.sub.1 is selected from the following
compounds and the linkage position thereof includes all of o-, m-
and p-positions.
##STR00029##
[0108] wherein X is O, S, C(.dbd.O), CH(OH), S(.dbd.O).sub.2,
Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, or
C(.dbd.O)NH; W is O, S or C(.dbd.O); and Z.sub.1, Z.sub.2 and
Z.sub.3 are identical to or different from each other and are O, N
or S.
[0109] More preferably, Ar.sub.1 is selected from the following
compounds:
##STR00030## ##STR00031## ##STR00032## ##STR00033## ##STR00034##
##STR00035## ##STR00036## ##STR00037##
[0110] In addition, preferably, Ar.sub.1' and Ar.sub.2 are selected
from the following compounds and the linkage position thereof
includes all of o-, m- and p-positions.
##STR00038##
[0111] wherein X is O, S, C(.dbd.O), CH(OH), S(.dbd.O).sub.2,
Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (in which
1.ltoreq.p.ltoreq.10), (CF.sub.2).sub.q (in which
1.ltoreq.q.ltoreq.10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, or
C(.dbd.O)NH; W is O, S or C(.dbd.O); and Z.sub.1, Z.sub.2 and
Z.sub.3 are identical to or different from each other and are O, N
or S.
[0112] More preferably, Ar.sub.1' and Ar.sub.2 are selected from
the following compounds:
##STR00039## ##STR00040## ##STR00041## ##STR00042## ##STR00043##
##STR00044##
[0113] Preferably, Q is CH.sub.2, C(CH.sub.3).sub.2,
C(CF.sub.3).sub.2, O, S, S(.dbd.O).sub.2 or C(.dbd.O).
[0114] More preferably,
##STR00045##
and Q is C(CF.sub.3).sub.2.
[0115] The hollow fibers of the present invention can endure not
only mild conditions, but also harsh conditions such as long
operation time, acidic conditions and high humidity, due to rigid
backbones present in the polymers.
[0116] The polymers represented by Formulae 19 to 32 or copolymers
thereof are designed to have a desired molecular weight,
preferably, a weight average molecular weight of 10,000 to 200,000
Da. When the molecular weight is less than 10,000 Da, the physical
properties of the polymers are poor, and when the molecular weight
exceeds 200,000 Da, the viscosity of the dope solution is greatly
increased, thus making it difficult to spin the dope solution using
a pump.
[0117] In addition, the hollow fibers of the present invention have
well-connected microcavities and a high free volume, thus
exhibiting superior permeability for CO.sub.2 and O.sub.2 and
superior selectivity for mixed gas pair of H.sub.2/N.sub.2,
H.sub.2/CH.sub.4, H.sub.2/O.sub.2, H.sub.2/CO.sub.2,
O.sub.2/CO.sub.2, N.sub.2/CH.sub.4, O.sub.2/N.sub.2,
CO.sub.2/CH.sub.4 and CO.sub.2/N.sub.2. At this time, the hollow
fibers of the present invention exhibit O.sub.2/N.sub.2 selectivity
of 3 or higher and CO.sub.2/CH.sub.4 selectivity of 20 or higher at
25.degree. C., preferably, O.sub.2/N.sub.2 selectivity of 3 to 30
and CO.sub.2/CH.sub.4 selectivity of 20 to 100 at 25.degree. C.
[0118] In accordance with the method of the present invention, a
hollow fiber with superior polymeric backbone strength and improved
free volume is prepared by imidizing a polyamic acid hollow fiber
to obtain a polyimide hollow fiber and subjecting the polyimide
hollow fiber to intramolecular and intermolecular rearrangement via
thermal treatment.
[0119] The hollow fiber thus prepared exhibits superior gas
permeability and selectivity, thus being suitable for use in gas
separation membranes. Furthermore, the hollow fiber can endure
harsh conditions such as long operation time, acidic conditions and
high humidity, due to rigid backbones present in the polymers
constituting the hollow fiber.
EXAMPLES
[0120] Hereinafter, preferred examples will be provided for a
further understanding of the invention. These examples are for
illustrative purposes only and are not intended to limit the scope
of the present invention.
Example 1
[0121] As depicted in Reaction Scheme 3 below, a hollow fiber
comprising polybenzoxazole represented by Formula 41 are prepared
from the polyhydroxyamic acid-containing dope solution.
##STR00046##
[0122] (1) Preparation of Polyhydroxyamic Acid
[0123] 36.6 g (0.1 mol) of
2,2'-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and 44.4 g (0.1
mol) of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride were
added to 189 g (70 wt %) of N-methylpyrrolidone (NMP) and were
allowed to react at 15.degree. C. for 4 hours to prepare a pale
yellow viscous polyamic acid.
[0124] (2) Preparation of Dope Solution
[0125] Without removing the solvent, 5% by weight of
tetrahydrofurane as an additive was added to the NMP containing
polyamic acid and then mixed to prepare a homogeneous dope
solution.
[0126] (3) Preparation of Hollow Fiber
[0127] The dope solution thus prepared was defoamed at ambient
temperature under reduced pressure for 24 hours, and foreign
materials were removed using a glass filter (pore diameter: 60
.mu.m). Subsequently, the resulting solution was allowed to stand
at 25.degree. C. and was then spun through a double-ring nozzle. At
this time, distilled water was used as an internal coagulating
solution and an air gap was set at 50 cm. The spun hollow fiber was
coagulated in a coagulation bath-containing water at 25.degree. C.
and was then wound at a rate of 30 m/min. The resulting hollow
fiber was washed, air-dried at ambient temperature for 3 days,
imidized under an inert atmosphere in a heating furnace at
300.degree. C. for one hour and then thermally treated under an
inert atmosphere at 450.degree. C. for one hour to prepare a hollow
fiber thermally rearranged into polybenzoxazole represented by
Formula 41.
[0128] The hollow fiber thus prepared had a weight average
molecular weight of 22,000 Da. As a result of FT-IR analysis,
characteristic bands of polybenzoxazole at 1,553 cm.sup.-1, 1,480
cm.sup.-1 (C.dbd.N) and 1,058 cm.sup.-1 (C--O) which were not
detected in polyimide were confirmed.
Example 2
[0129] A hollow fiber comprising polybenzothiazole represented by
the following Formula 42 was prepared from the polythiolamic
acid-containing dope solution through the following reactions.
##STR00047##
[0130] A hollow fiber thermally rearranged into polybenzothiazole
represented by Formula 42 was prepared in the same manner as in
Example 1, except that 20.8 g (0.1 mol) of
2,5-diamino-1,4-benzenedithiol dihydrochloride and 44.4 g (0.1 mol)
of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride as starting
materials were reacted to prepare thiol group (--SH)-containing
polyamic acid.
[0131] The hollow fiber thus prepared had a weight average
molecular weight of 14,500 Da. As a result of FT-IR analysis,
characteristic bands of polybenzothiazole at 1,484 cm.sup.-1 (C--S)
and 1,404 cm.sup.-1 (C--S) which were not detected in polyimide
were confirmed.
Example 3
[0132] A hollow fiber comprising polybenzopyrrolone represented by
Formula 43 was prepared from the polyaminoamic acid-containing dope
solution through the following reactions.
##STR00048##
[0133] A hollow fiber thermally rearranged into polybenzopyrrolone
represented by Formula 43 was prepared in the same manner as in
Example 1, except that 21.4 g (0.1 mol) of 3,3'-diaminobenzidine as
a starting material was reacted with 44.4 g (0.1 mol) of
4,4'-(hexafluoroisopropylidene)diphthalic anhydride to prepare an
amine group (--NH.sub.2)-containing polyamic acid.
[0134] The prepared hollow fiber had a weight average molecular
weight of 18,000 Da. As a result of FT-IR analysis, characteristic
bands of polybenzopyrrolone at 1,758 cm.sup.-1 (C.dbd.O) and 1,625
cm.sup.-1 (C.dbd.N) which were not detected in polyimide were
confirmed.
Example 4
[0135] A hollow fiber comprising polybenzoxazole represented by
Formula 44 was prepared from the polyhydroxyamic acid-containing
dope solution through the following reactions.
##STR00049##
[0136] A hollow fiber thermally rearranged into polybenzoxazole
represented by Formula 44 was prepared in the same manner as in
Example 1, except that 21.6 g (0.1 mol) of 3,3'-dihydroxybenzidine
and 44.4 g (0.1 mol) of 4,4'-(hexafluoroisopropylidene)diphthalic
anhydride as starting materials were added to 264 g (80 wt %) of
N-methylpyrrolidone (NMP) and then allowed to react for about 4
hours to prepare a pale yellow viscous polyamic acid.
[0137] The hollow fiber thus prepared had a weight average
molecular weight of 19,000 Da. As a result of FT-IR analysis,
characteristic bands of polybenzoxazole at 1,553 cm.sup.-1, 1,480
cm.sup.-1 (C.dbd.N) and 1,052 cm.sup.-1 (C--O) which were not
detected in polyimide were confirmed.
Example 5
[0138] A hollow fiber comprising polybenzopyrrolone represented by
Formula 45 was prepared from the polyaminoamic acid-containing dope
solution through the following reactions.
##STR00050##
[0139] A hollow fiber thermally rearranged into polybenzopyrrolone
represented by Formula 45 was prepared in the same manner as in
Example 1, except that 28.4 g (0.1 mol) of
benzene-1,2,4,5-tetramine tetrahydrochloride and 31.0 g (0.1 mol)
of 4,4'-oxydiphthalic anhydride as starting materials were added to
139 g (70 wt %) of N-methylpyrrolidone (NMP) and allowed to react
for about 4 hours to prepare a pale yellow viscous polyaminoamic
acid.
[0140] The hollow fiber thus prepared had a weight average
molecular weight of 12,460 Da. As a result of FT-IR analysis,
characteristic bands of polybenzopyrrolone at 1,758 cm.sup.-1
(C.dbd.O) and 1,625 cm.sup.-1 (C.dbd.N), which were not detected in
polyimide were confirmed.
Example 6
[0141] A hollow fiber comprising a benzoxazole copolymer
represented by Formula 46 was prepared through the following
reactions.
##STR00051##
[0142] A hollow fiber thermally rearranged into a benzoxazole
copolymer (molar ratio of benzoxazole:benzoxazole=5:5) represented
by Formula 46 was prepared in the same manner as in Example 1,
except that 36.6 g (0.1 mol) of
2,2'-bis(3-amino-4-hydroxy-phenyl)hexafluoropropane and 21.6 g (0.1
mol) of 3,3'-dihydroxybenzidine as starting materials were
thoroughly dissolved in 272 g (70 wt %) of N-methylpyrrolidone
(NMP) as a solvent and 58.8 g (0.2 mol) of 4,4'-biphthalic
anhydride was slowly added thereto to prepare a polyhydroxyamic
acid-polyhydroxyamic acid copolymer.
[0143] The hollow fiber thus prepared had a weight average
molecular weight of 18,290 Da. As a result of FT-IR analysis,
characteristic bands of polybenzoxazole at 1,553 cm.sup.-1, 1,480
cm.sup.-1 (C.dbd.N) and 1,058 cm.sup.-1 (C--O) which were not
detected in polyimide were confirmed.
Example 7
[0144] A hollow fiber comprising a benzoxazole-imide copolymer
represented by Formula 47 was prepared through the following
reactions.
##STR00052##
[0145] A hollow fiber thermally rearranged into a benzoxazole-imide
copolymer (molar ratio of benzoxazole:imide=8:2) represented by
Formula 47 was prepared in the same manner as in Example 1, except
that 58.60 g (0.16 mol) of
2,2'-bis(3-amino-4-hydroxy-phenyl)hexafluoropropane and 8.01 g
(0.04 mol) of 4,4'-diaminodiphenylether as starting materials were
thoroughly dissolved in 393 g (70 wt %) of N-methylpyrrolidone
(NMP) as a solvent, and 64.45 g (20 mol) of
3,3',4,4'-benzophenonetetracarboxylic dianhydride was slowly added
thereto to prepare a polyhydroxyamic acid copolymer.
[0146] The hollow fiber thus prepared had a weight average
molecular weight of 24,210 Da. As a result of FT-IR analysis,
characteristic bands of polybenzoxazole at 1,553 cm.sup.-1, 1,480
cm.sup.-1 (C.dbd.N) and 1,058 cm.sup.-1 (C--O), and characteristic
bands of polyimide at 1,720 cm.sup.-1 (C.dbd.O) and 1,580 cm.sup.-1
(C.dbd.O).
Example 8
[0147] A hollow fiber comprising a benzopyrrolone-imide copolymer
represented by Formula 48 was prepared through the following
reactions.
##STR00053##
[0148] A hollow fiber thermally rearranged into a
benzopyrrolone-imide copolymer (molar ratio of
benzopyrrolone:imide=8:2) represented by Formula 48 was prepared in
the same manner as in Example 1, except that 17.1 g (0.08 mol) of
3,3'-diaminobenzidine and 4.0 g (0.02 mol) of
4,4'-diaminodiphenylether as starting materials were thoroughly
dissolved in 196.5 g (75 wt %) of N-methylpyrrolidone (NMP) as a
solvent and 44.4 g (0.1 mol) of
4,4'-(hexafluoroisopropylidene)diphthalic anhydride was slowly
added thereto to prepare a polyaminoamic acid copolymer.
[0149] The hollow fiber thus prepared had a weight average
molecular weight of 19,140 Da. As a result of FT-IR analysis,
characteristic bands of polypyrrolone at 1,758 cm.sup.-1 (C.dbd.O)
and 1,625 cm.sup.-1 (C.dbd.N) and characteristic bands of polyimide
at 1,720 cm.sup.-1 (C.dbd.O) and 1,580 cm.sup.-1 (C.dbd.O).
Example 9
[0150] A hollow fiber comprising a benzothiazole-imide copolymer
represented by Formula 49 was prepared through the following
reactions.
##STR00054##
[0151] A hollow fiber thermally rearranged into a
benzothiazole-imide copolymer (molar ratio of
benzothiazole:imide=8:2) represented by Formula 49 was prepared in
the same manner as in Example 1, except that 33.30 g (0.16 mol) of
2,5-diamino-1,4-benzenedithiol dihydrochloride and 8.0 g (0.04 mol)
of 4,4'-diaminodiphenylether as starting materials were dissolved
in 390.3 g (75 wt %) of N-methylpyrrolidone (NMP) as a solvent, and
88.8 g (0.1 mol) of 4,4'-(hexafluoroisopropylidene)diphthalic
anhydride was slowly added thereto to prepare a polyaminoamic acid
copolymer.
[0152] The hollow fiber thus prepared had a weight average
molecular weight of 22,360 Da. As a result of FT-IR analysis,
characteristic bands of polybenzothiazole at 1,484 cm.sup.-1 (C--S)
and 1,404 cm.sup.-1 (C--S) and characteristic bands of polyimide at
1,720 cm.sup.-1 (C.dbd.O) and 1,580 cm.sup.-1 (C.dbd.O).
Example 10
[0153] A hollow fiber comprising a benzoxazole-benzothiazole
copolymer represented by Formula 50 was prepared through the
following reactions.
##STR00055##
[0154] A hollow fiber thermally rearranged into a
benzoxazole-benzothiazole copolymer (molar ratio of
benzoxazole:benzothiazole=5:5) represented by Formula 50 was
prepared in the same manner as in Example 1, except that 10.8 g
(0.05 mol) of 3,3'-dihydroxybenzidine and 10.9 g (0.05 mol) of
2,5-diamino-1,4-benzenedithiol dihydrochloride as starting
materials were added to 198.3 g (75 wt %) of N-methylpyrrolidone
(NMP) as a solvent and thoroughly dissolved in the solvent, and
29.4 g (0.1 mol) of 4,4'-biphthalic anhydride was slowly added
thereto to prepare a hydroxyamic acid-thiolamic acid copolymer.
[0155] The hollow fiber thus prepared had a weight average
molecular weight of 26,850 Da. As a result of FT-IR analysis,
characteristic bands of polybenzoxazole at 1,553 cm.sup.-1, 1,480
cm.sup.-1 (C.dbd.N) and 1,052 cm.sup.-1 (C--O), and characteristic
bands of polybenzothiazole at 1,484 cm.sup.-1 (C--S) and 1,404
cm.sup.-1 (C--S) which were not detected in polyimide were
confirmed.
Example 11
[0156] A hollow fiber comprising a benzopyrrolone copolymer
represented by Formula 51 was prepared through the following
reactions.
##STR00056##
[0157] A hollow fiber thermally rearranged into a benzopyrrolone
copolymer (molar ratio of benzopyrrolone:benzopyrrolone=8:2)
represented by Formula 51 was prepared in the same manner as in
Example 1, except that 34.2 g (0.16 mol) of 3,3'-diaminobenzidine
and 11.4 g (0.04 mol) of benzene-1,2,4,5-tetramine
tetrahydrochloride as starting materials were added to 403.2 g (75
wt %) of N-methylpyrrolidone (NMP) as a solvent and thoroughly
dissolved in the solvent, and 88.8 g (20 mmol) of
4,4'-(hexafluoroisopropylidene)diphthalic anhydride was added
thereto to prepare a polyaminoamic acid copolymer.
[0158] The hollow fiber thus prepared had a weight average
molecular weight of 13,270 Da. As a result of FT-IR analysis,
characteristic bands of polybenzopyrrolone at 1,758 cm.sup.-1
(C.dbd.O) and 1,625 cm.sup.-1 (C.dbd.N), which were not detected in
polyimide, were confirmed.
Example 12
[0159] A hollow fiber comprising a benzoxazole-benzothiazole
copolymer represented by Formula 52 was prepared through the
following reactions.
##STR00057##
[0160] A hollow fiber thermally rearranged into a
benzoxazole-benzothiazole copolymer (molar ratio of
benzoxazole:benzothiazole=8:2) represented by Formula 52 was
prepared in the same manner as in Example 1, except that 21.8 g
(0.1 mol) of 2,5-diamino-1,4-benzenedithiol dihydrochloride and
36.6 g (0.16 mol) of
2,2'-bis(3-amino-4-hydroxy-phenyl)hexafluoropropane as starting
materials were added to 441.6 g (75 wt %) of N-methylpyrrolidone
(NMP) as a solvent and thoroughly dissolved in the solvent, and
88.8 g (20 mmol) of 4,4'-(hexafluoroisopropylidene)diphthalic
anhydride was slowly added thereto to prepare a thiolamic
acid-aminoamic acid copolymer.
[0161] The hollow fiber thus prepared had a weight average
molecular weight of 16,190 Da. As a result of FT-IR analysis,
characteristic bands of polybenzoxazole at 1,553 cm.sup.-1, 1,480
cm.sup.-1 (C.dbd.N) and 1,058 cm.sup.-1 (C--O), and characteristic
bands of polybenzothiazole at 1,484 cm.sup.-1 (C--S) and 1,404
cm.sup.-1 (C--S) which were not detected in polyimide were
confirmed.
Example 13
[0162] A hollow fiber was prepared in the same manner as in Example
1, except that 5% by weight of tetrahydrofurane and 5% by weight of
polyvinylpyrrolidone as additives were added and then mixed to
prepare a homogeneous solution.
Example 14
[0163] A hollow fiber was prepared in the same manner as in Example
1, except that 5% by weight of tetrahydrofurane and 15% by weight
of propylene glycol as additives were added and then mixed to
prepare a homogeneous solution.
Example 15
[0164] A hollow fiber was prepared in the same manner as in Example
1, except that 15% by weight of polyethylene glycol (Aldrich, pore
controller, molecular weight: 2,000) was added as an additive and
mixed to prepare a homogeneous solution.
Example 16
[0165] A hollow fiber was prepared in the same manner as in Example
1, except that after the imidization at 300.degree. C. for one
hour, thermal treatment was performed at 400.degree. C. for one
hour.
Example 17
[0166] A hollow fiber was prepared in the same manner as in Example
1, except that after the imidization at 300.degree. C. for one
hour, thermal treatment was performed at 350.degree. C. for one
hour.
Comparative Example 1
[0167] As disclosed in Korean Patent Laid-open No. 2002-0015749,
35% by weight of polyether sulfone (Sumitomo, sumikaexcel) was
dissolved in 45% by weight of NMP, 5% by weight of tetrahydrofurane
and 15% by weight of ethanol as additives were added thereto to
prepare a homogeneous solution. Then, the solution was spun through
a double nozzle with a 10 cm air gap. The resulting solution was
washed with flowing water for 2 days and dried under vacuum for 3
hours or more to prepare a hollow fiber.
Comparative Example 2
[0168] A hollow fiber was prepared in the same manner as in Example
1, except that thermal treatment was not performed.
Comparative Example 3
[0169] As disclosed in PCT Patent Publication No. WO2005/007277, a
19% by weight solution of a polyamic acid (PAA) was prepared from
4,4'-diaminodiphenyl ether (ODA) and benzophenone tetracarboxylic
dianhydride (BTDA) in N-methylpyrrolidone (NMP) as a solvent. A
solution containing 50% by weight of polyvinylpyrrolidone (PVP) in
NMP was added to the PAA solution. Then, glycerol and NMP were
added to the solution. The final solution had a composition of
PAA/PVP/GLY/NMP of 13/1/17/69 by wt %. The solution was mixed for a
period of about 12 hours prior to spinning.
[0170] 20.degree. C. water was used as an internal coagulant and
the spinning solution was spun through a spinneret. The flow rate
of the internal coagulant was adjusted to 12 ml/min. The hollow
fiber was spun at a rate of 4 cm/s such that the retention time in
an air cap was adjusted to 6 seconds. At this time, the hollow
fiber membrane was coagulated in 100% water at 30.degree. C.
Subsequently, the membrane was washed with water for 2 to 4 hours
at ambient temperature until the remaining solvent and glycerol
were completely extracted. In addition, the membrane was dried in
air. Then, the membrane was imidized in an oven equipped with a
nitrogen purge. The membrane was heated to 150.degree. C. over a
period of three hours, heated at 150.degree. C. for one hour,
heated to 250.degree. C. over a period of two hours, heated at
250.degree. C. for two hours and slowly cooled to ambient
temperature over a period of 4 hours. The polyimide/PVP membrane
thus prepared had an outer diameter of 2.2 mm and a thickness of
0.3 mm.
Experimental Example 1
Scanning Electron Microscopy
[0171] FIGS. 1, 2 and 3 are cross-section scanning electron
microscope (SEM) images of finger-type hollow fibers prepared in
Example 1 of the present invention at 100.times., 500.times. and
5,000.times. magnifications, respectively.
[0172] FIGS. 4, 5 and 6 are cross-section scanning electron
microscope (SEM) images of sponge-type hollow fibers prepared in
Example 14 of the present invention at 100.times., 1,000.times. and
10,000.times. magnifications, respectively.
[0173] As can be seen from FIGS. 1 to 6, the hollow fibers of the
present invention have surface defect-free separation layers.
Experimental Example 2
Measurement of Permeability and Selectivity
[0174] In order to ascertain gas permeability and selectivity of
the hollow fibers prepared in Examples 1 to 17 and Comparative
Examples 1 to 3, the following processes were performed. The
results are shown in Table 1 and FIGS. 7 and 8.
[0175] The term "gas permeability" is an index indicating a speed
at which a gas permeates through a membrane. A separation membrane
module for gas permeability measurement was prepared from the
prepared hollow fiber and gas permeation flow was calculated using
the following Equation 1. The gas permeation unit used herein was
GPU (Gas Permeation Unit, 1.times.10.sup.-6
cm.sup.3/cm.sup.2seccmHg).
[0176] "Selectivity" was derived from a permeability ratio between
respective gases measured with the same membrane.
P = p t [ VT 0 P 0 TP f A eff ] Equation 1 ##EQU00001##
[0177] wherein P is a gas permeability; dp/dt is a pressure
increase rate in a normal state; V is lower part volume; P.sub.f is
pressure difference between the upper and lower parts; T is
temperature upon measurement; A.sub.eff is an effective area; and
P.sub.0 and T.sub.0 are standard pressure and standard temperature,
respectively.
TABLE-US-00001 TABLE 1 H.sub.2 O.sub.2 CO.sub.2 O.sub.2/N.sub.2
CO.sub.2/CH.sub.4 permeability permeability permeability selec-
selec- (GPU) (GPU) (GPU) tivity tivity Ex. 1 1,417 396 1,821 4.6
39.6 Ex. 2 671 125 314 5.4 17.4 Ex. 3 396 92 378 4.2 36.3 Ex. 4 86
5.2 18.6 6.4 48.9 Ex. 5 149 41 175 6.6 48.6 Ex. 6 417 67 289 6.4
43.1 Ex. 7 512 148 451 4.4 19.3 Ex. 8 200 40 209 5.1 36.7 Ex. 9
1,100 247 462 6.5 21.6 Ex. 10 509 110 364 6.1 33.1 Ex. 11 350 89
451 5.6 41.0 Ex. 12 3,200 790 3,011 4.0 20.5 Ex. 13 640 127 401 4.7
21.0 Ex. 14 2,153 607 2,842 5.0 42.4 Ex. 15 2,957 852 3,651 4.5
29.4 Ex. 16 648 103 476 5.0 52.3 Ex. 17 138 15 60 7.1 49.8 Comp. 65
16 52 5.0 31.1 Ex. 1 Comp. 21.7 1.42 23.6 4.9 20.7 Ex. 2 Comp. 12.1
0.66 2.47 6.0 30.9 Ex. 3
[0178] As can be seen from Table 1, the hollow fiber of the present
invention exhibited superior permeability to gas species such as
H.sub.2, O.sub.2 and CO.sub.2, as compared to the Comparative
Examples.
[0179] FIG. 7 is a graph comparing oxygen permeability (GPU) and
oxygen/nitrogen selectivity for hollow fibers prepared in Examples
1 to 17 of the present invention and Comparative Examples 1 to
3.
[0180] FIG. 8 is a graph comparing carbon dioxide permeability
(GPU) and carbon dioxide/methane selectivity for hollow fibers
prepared in Examples 1 to 17 of the present invention and
Comparative Examples 1 to 3.
[0181] As can be seen from FIGS. 7 and 8, the hollow fibers of the
present invention exhibited similar oxygen/nitrogen selectivity or
carbon dioxide/methane selectivity, but showed superior
permeability, as compared to the Comparative Examples.
* * * * *