Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Ion-exchange polymer or process of preparing
Reexamination Certificate
2001-07-23
2003-10-14
Zitomer, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Ion-exchange polymer or process of preparing
C521S028000, C521S032000, C525S233000, C525S240000
Reexamination Certificate
active
06632848
ABSTRACT:
The present invention relates to a heterogeneous anion exchanger.
Anion exchange membranes are reported in many literatures and patents. However, the most practical and useful one may be an anion exchange membrane having anion exchange groups introduced into a styrene/divinylbenzene copolymer having chloromethyl groups on its aromatic rings, or an anion exchange membrane made from a vinylpyridine/divinylbenzene copolymer. In addition to its chemical resistance and thermal resistance, such a membrane has a feature that the ion exchange characteristics or the selective permeability can be controlled by changing the content of the divinylbenzene as a crosslinking agent. Accordingly, various types have been synthesized and developed for various applications. Especially in the field of electrodialytic concentration of sea water for salt production, a membrane has been developed which has a low electric resistance and a high transport number and which has a high level of function to selectively permeate monovalent ions.
However, such an ion exchange membrane made of a styrene/divinylbenzene copolymer requires a cumbersome and sensitive process of polymerization and reaction, which is costly, and it is difficult to control the heat generation or dimensional change which takes place during the process, whereby the yield tends to be poor. Further, it is constituted by a styrene type resin which is relatively brittle, whereby during a high temperature use or depending upon the components in the water to be treated, the membrane is likely to excessively swell, thus leading to a problem of deterioration of the membrane strength or the selective ion permeability.
As a means to solve such problems, a heterogeneous ion exchange membrane prepared by mixing a pulverized ion exchange resin and a binder polymer, followed by heat extrusion or casting by means of a solvent to form a membrane, has been extensively studied since about 1950.
For example, U.S. Pat. No. 3,627,703 and JP-B-47-24262 disclose a case wherein polypropylene is used as a binder polymer; U.S. Pat. No. 4,167,551, JP-B-52-3912, JP-B-53-18472 and JP-B-51-12313 disclose a case wherein a polyolefin such as polyethylene or polypropylene is employed; U.S. Pat. Nos. 2,681,319 and 2,681,320 disclose a case wherein polyethylene, polyisobutylene, natural rubber, butyl rubber, polyisoprene, polychloroprene, a styrene/butadiene rubber, nitrile rubber or vinyl chloride/fatty acid vinyl ester copolymer is employed; and U.S. Pat. No. 5,346,924 and WO94-06850 disclose a case wherein a linear low density polyethylene or a high molecular weight high density polyethylene is used. Further, JP-A-9-132654 discloses use of a. styrene type thermoplastic elastomer, and JP-A-10-36530 discloses a case wherein a mixture comprising a low density polyethylene and an ethylene/propylene rubber or an ethylene/propylene/diene rubber, is employed.
However, heterogeneous ion exchangers employing such binders had a problem of high costs, or a problem that the durability in an alkaline solution, although improved to some extent, was not necessarily sufficient. On the other hand, with respect to anion exchange resins having good durability, many proposals have been made including JP-A-5-15789 which proposes an anion exchange resin having certain specific anion exchange groups. However, no ion exchange membranes made of such anion exchange resins, are known.
It is an object of the present invention to provide a heterogeneous anion exchanger which is inexpensive, as it is a heterogeneous anion exchanger, and which has durability and dimensional stability at the same time and to provide a novel water treating method employing a membrane made of such an ion exchanger.
The present invention provides a heterogeneous anion exchanger comprising from 35 to 85 mass % of an anion exchange resin and from 15 to 65 mass % of a binder polymer, wherein the anion exchange resin. is made of a polymer having repeating units represented by the following formula (1):
wherein R is a C
3-8
alkylene group or an alkyleneoxyalkyl group having a total carbon number of from 4 to 9, R
1
is a C
1-4
alkyl group which may be substituted by a hydroxyl group, each of R
2
and R
3
is a C
1-4
alkyl group, and X
−
is an anion, and wherein any hydrogen atom bonded to the benzene ring may be substituted by an alkyl group or a halogen atom.
Now, the present invention will be described in detail with reference to the preferred embodiments.
In the repeating units represented by the formula (1), R is a C
3-8
alkylene group or an alkyrleneoxyalkyl group (an alkylene group containing an oxygen atom of an ether bond) having a total carbon number of from 4 to 9. Specifically, R may, for example, be —(CH
2
)
n
—, wherein n is an integer of from 1 to 6, a tetramethyleneoxymethyl group (—(CH
2
)
4
—O—CH
2
—, one having the tetramethylene group side bonded to nitrogen) or a pentamethyleneoxymethyl group (—(CH
2
)
5
—O—CH
2
—, one having the pentamethylene group side bonded to nitrogen).
R
1
is a C
1-4
alkyl group which may be substituted by a hydroxyl group, and each of R
2
and R
3
is a C
1-4
alkyl group. They may be the same or different from one another. Such an alkyl group may, for example, be a methyl group, an ethyl group, a propyl group or a butyl group. Particularly preferred is a case where R
1
is a methyl group or a hydroxyethyl group, and each of R
2
and R
3
is a methyl group.
X
−
is a monovalent anion which is a counter ion coordinated with the cation exchange group which is the quaternary ammonium group. Specifically, it may, for example, be a halogen ion such as Cl
−
, Br
−
or I
−
, NO
3
−
, OH
−
or a p-toluene sulfonic ion. Otherwise, X
1
may be a polyvalent anion such as SO
4
2−
. In such a case, a polyvalent anion is coordinated so that the electrical equivalence balances between the polyvalent anion and the cation of the ion exchange group, and X
−
represents a polyvalent anion corresponding to monovalent.
Any hydrogen atom on the benzene ring in the formula (1) may be substituted by an alkyl group or a halogen atom. As the substituent on the benzene ring, an alkyl group such as an ethyl group, or a halogen atom such as a chlorine atom or a bromine atom, may be mentioned.
The anion exchange resin having repeating units represented by the formula (1), may contain, in addition to the repeating units represented by the formula (1), other repeating units to control ion selectivity or mechanical strength. As such other repeating units, repeating units derived from a crosslinkable monomer made of a hydrocarbon compound having an unsaturated bond, are preferred. The crosslinkable monomer is not particularly limited, and it may, for example, be divinylbenzene, trivinylbenzene, divinyltoluene, divinylnaphthalene or ethylene glycol dimethacrylate. Further, the anion exchange resin may contain, as repeating units which do not contribute to crosslinking or ion exchange, repeating units derived from a monomer such as styrene, vinyltoluene or acrylonitrile.
The ion exchange groups may include ion exchange groups other than those contained in the repeating units represented by the formula (1). In such a case, in order to maintain the heat resistance or durability, it is preferred that at least 90 mol % of the total ion exchange group capacity is the ion exchange capacity of the ion exchange groups contained in the repeating units represented by the formula (1). The monomer from which repeating units other than the repeating units represented by the formula (1) are derived, may, for example, be vinylpyridine or chloromethylstyrene.
The ion exchange capacity of the ion exchange resin in the present invention is preferably from 1.0 to 5.0 meq/g dry resin. If the ion exchange capacity is smaller than this, the electrical resistance of the heterogeneous anion exchanger thereby obtainable, tends, to be high, and if it is larger than this, the mechanical strength of the heterogeneous anion exchanger tends to be low, such being undesirable.
The pa
Asahi Glass Company Limited
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Zitomer Fred
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