Polymer separation membrane

Details Polymer separation membrane Polymer separation membrane

2002-08-22

2003-12-02

Spitzer, Robert H. (Department: 1724)

Gas separation: apparatus

Apparatus for selective diffusion of gases

C095S050000, C095S051000, C096S014000

Reexamination Certificate

active

06656252

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a gas separation membrane used for separating a gas from a mixture of various gases. Particularly, the gas separation membrane of the present invention is excellent in permeation of especially a carbon dioxide gas and various hydrocarbon gases. Therefore, the gas separation membrane of the present invention is suitable as a gas separation membrane which separates a carbon dioxide gas from a carbon dioxide-containing gas mixture comprising the carbon dioxide gas and other gases (for example, a nitrogen gas and/or air and/or a hydrogen gas), or as a gas separation membrane which separates a hydrocarbon gas from a hydrocarbon-containing gas mixture comprising the hydrocarbon gas and other gases (for example, a nitrogen gas and/or air and/or a hydrogen gas).
RELATED ARTS
Hitherto, gas separation membranes comprising various polymeric materials such as cellulose acetate, silicone rubber, polysulfone and polyamide are well-known. These well-known gas separation membranes are practically used in various fields. However, these gas separation membranes are not practical membranes, because a separation coefficient of carbon dioxide to nitrogen is low, at most 10 as a separation membrane for carbon dioxide which is deemed to be responsible for global warming, and the membrane is plasticized with carbon dioxide to decrease the separation coefficient. A gas separation membrane comprising an aromatic polyimide is also known (JP-A-60-150806; JP-A-61-133106; JP-A-63-123420; and JP-A-8-332362). Although the separation coefficient of carbon dioxide to nitrogen in these polyimide gas separation membranes is relatively high, from 20 to 40, these membranes do not have sufficiently high efficiency. In addition, since these membranes are made from the aromatic polyimide, the cost also is problematic.
Apart from the above, a gas separation membrane, in which a porous membrane is impregnated with polyethylene glycol or a polymer is blended or copolymerized with another polymer, is proposed (Bulletin of Chemical Society of Japan, pages 847-853, 1983; JP-A-6-71148; and JP-A-8-24602). Although these separation membranes exhibit a high separation coefficient of 50 to 100, these separation membrane can not be practically used because of a low permeation coefficient, poor membrane productivity, and poor membrane stability giving gradual membrane property deterioration. A silicone rubber is proposed as a membrane for separating carbon dioxide from a mixture of carbon dioxide and hydrogen, but this membrane has a separation coefficient of about 5 so that the separation efficiency is low. Conventional polymer membranes as the membrane for separating hydrocarbon gas have problems of chemical instability due to plasticization.
A separation membrane comprising polyepichlorohydrin is also proposed (Progress in Polymer Science, 13, 339-401 (1988)). However, disadvantageously, polyepichlorohydrin has high crystallinity and has a low permeation coefficient of the separation membrane.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a separation membrane having a high permeation coefficient of gases, and a high separation coefficient.
The present inventors intensively studied, discovered that a polyether polymer obtained from an oxirane compound is useful for a gas separation membrane, and completed the present invention. The gas separation membrane of the present invention is suitable for separating one gas from a gas mixture comprising at least two gases. The polymer gas separation membrane of the present invention can be a gas separation membrane having high selectivity, particularly high selective permeability of a CO
2
gas and a hydrocarbon gas, and stability for long term.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a separation membrane comprising a polyether polymer having a weight-average molecular weight of 10
4
to 10
7
and obtained by polymerizing an oxirane compound of the formula (a):
wherein R is a hydrogen atom;
an alkyl group, an alkyl group having an halogen atom, or
—CH
2
O(CH
2
CH
2
O)
k
—R′ (R′ is a group selected from an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, a cycloalkyl group having 3 to 8 carbon atoms, an aryl group having 6 to 14 carbon atoms and an aralkyl group having 7 to 12 carbon atoms; k is from 0 to 12); or
an ethylenically unsaturated group, a reactive silicon-containing group or a methylepoxy-containing group.
The present invention provides a separation membrane comprising a polyether polymer having a weight-average molecular weight of 10
4
to 10
7
and obtained by polymerizing an oxirane compound of the formula (a):
wherein R is a hydrogen atom;
an alkyl group, an alkyl group having an halogen atom, or
—CH
2
O(CH
2
CH
2
O)
k
—R′ (R′ is a group selected from an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, a cycloalkyl group having 3 to 8 carbon atoms, an aryl group having 6 to 14 carbon atoms and an aralkyl group having 7 to 12 carbon atoms; k is from 0 to 12); or
an ethylenically unsaturated group, a reactive silicon-containing group or a methylepoxy-containing group, and
a branched-chain ether compound exhibiting liquid properties at normal temperature and selected from the group consisting of the formulas (i), (ii) and (iii):
wherein R
11
, R
12
and R
13
are a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms; l, m and n are from 0 to 12 (provided that all of l, m and n are not simultaneously 0),
wherein R
14
, R
15
, R
16
and R
17
are a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms; o, p, q and r are from 0 to 12 (provided that all of o, p, q and r are not simultaneously 0),
wherein R
18
, R
19
, R
20
and R
21
are a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms; s, t, u and v are from 0 to 12 (provided that s, t, u and v are not simultaneously 0); R
22
is a methylene group or —(OCH
2
CH
2
)
x
— (x is from 0 to 12); and w is 0 or 1.
The separation membrane of the present invention may be made of a copolymer comprising at least two oxirane compounds (a)
Particularly, the oxirane compound (a) can be classified into the following monomer (1), monomer (2) and monomer (3).
In the above formula (2), R
1
is an alkyl group, an alkyl group containing a halogen atom, or —CH
2
O(CH
2
CH
2
O)
k
—R′. The number of carbon atoms in the alkyl group and the alkyl group containing the halogen atom is preferably from 1 to 12, for example, from 1 to 8, particularly from 1 to 3. R′ is a group selected from an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, a cycloalkyl group having 3 to 8 carbon atoms, an aryl group having 6 to 14 carbon atoms and an aralkyl group having 7 to 12 carbon atoms. k is from 0 to 12, for example, from 0 to 6.
In the formula (3), R
2
is an ethylenically unsaturated group, a reactive silicon-containing group, a methylepoxy-containing group or an alkyl group containing a halogen atom.
In the copolymer comprising both of monomer (2) and monomer (3), the monomer (2) and the monomer (3) are not the same compound.
Preferably, the monomers constituting the copolyether polymer are:
(i) a combination of the monomers (1) and (2),
(ii) a combination of the monomers (1) and (3),
(iii) a combination of the monomers (1), (2) and (3), or
(iv) a combination of the monomers (2) and (3).
The polyether polymer may be constituted by the following repeat units of the formulas (4), (5) and (6) derived from each of the monomers (1), (2) and (3).
It is known that a polyether copolymer of ethylene oxide of the formula (1) and an oxirane compound comprising the oligooxyethylene group of the formula (2) (JP-A-9-324114) and a crosslinked material of a polyether copolymer of oxirane compounds comprising said copolymerizable monomers and a crosslinkable o

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