Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Ion-exchange polymer or process of preparing
Reexamination Certificate
2002-07-30
2004-08-24
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Ion-exchange polymer or process of preparing
C521S030000, C525S534000
Reexamination Certificate
active
06780893
ABSTRACT:
The present invention relates to a process for producing an anion exchange membrane, particularly to a process for producing an anion exchange membrane which is useful for diffusion dialysis, electrodialysis or electrolysis and which can be used as a diaphragm for batteries. Further, the present invention relates to an anion exchanger constituting such an ion exchange membrane.
As a practical useful anion exchanger, an anion exchanger obtained by amination of a copolymer of chloromethylated styrene with divinyl benzene, or an anion exchanger obtained by quaternary pyridinium-modification of a copolymer of vinyl pyridine with divinyl benzene, is available. Such an anion exchanger is excellent in the chemical resistance, heat resistance and ion exchange performance, and the ion exchange characteristics or selective permeability can be controlled by changing the content of divinyl benzene serving as a cross-linking agent. Accordingly, it has been used for various applications, and various products have been synthesized.
In new applications including e.g. efficient recovery of an acid having a high oxidation ability such as hydrofluoric acid or nitric acid, recovery of an acid containing an oxidative metal, recovery of phosphoric acid from an etching waste liquid in aluminum industry, concentration of sea water to produce inexpensive sodium chloride comparable to industrial salt, and electrolysis of an aqueous solution containing electrolytes or organic substances, ion exchange membranes are required to have low electric resistance, low permeability of water and corrosion resistance.
However, conventional ion exchange membranes made of divinyl benzene type copolymers, have had a problem that they cannot satisfy the above requirements. Namely, in order to lower the electric resistance, it is necessary to increase the ion exchange capacity and to increase the water content, but if the content of chloromethylated styrene or divinyl benzene is increased, and the content of divinyl benzene serving as a cross-linking agent, is reduced, for that purpose, not only the mechanical strength of the resulting ion exchange membrane decreases, but also the selective permeability and corrosion resistance will decrease, and permeability of water will increase. As another method for reducing the electric resistance, a method of reducing the membrane thickness is conceivable. However, with an ion exchange membrane made of a styrene/divinyl benzene copolymer, it is difficult to reduce the thickness to a level of not more than 100 &mgr;m, in view of its mechanical strength, particularly in view of its brittleness.
On the other hand, for separation membranes such as ultrafiltration membranes, reverse osmosis membranes or gas separation membranes, materials of engineering plastic type excellent in mechanical strength and processability are used. Particularly for a membrane made of a polysulfone type polymer excellent in chemical resistance, one having ion exchange groups introduced, is used for improving the permeability of ultrafiltration membranes or reverse osmosis membranes, and one having ion selective permeability imparted has been studied for application to ion exchange membranes. For example, an anion exchange membrane synthesized from a chloromethylated product of a polysulfone having a repeating unit of the formula (a), is disclosed in J. Membrane Science, 22 (1985), 325-332. However, the ion exchange membrane made of such a polysulfone type polymer has had a problem such that if the ion exchange capacity is increased to lower the electric resistance, the ion selective permeability, the mechanical strength and the durability tend to deteriorate.
Further, an anion exchange membrane prepared from a mixture of a polysulfone having a repeating unit of the formula (a) and its bromomethylated product, is disclosed in “Fibers and Industry” vol. 44, No. 1, p. 11 (1988). This membrane was effective to control the ion exchange capacity at a constant level, but, from the practical viewpoint, it was not qualified as a substitute for a conventional anion exchange membrane made of a styrene/divinyl benzene type copolymer.
As a method to solve the above problems, it has been proposed to use a block copolymer of a polysulfone type and to introduce ion exchange groups thereto in a block structure to obtain an ion exchanger (JP-A-2-211257), and a practical anion exchange membrane employing such an anion exchanger has been proposed (JP-A-2-265929, JP-A-2-269745). Further, an anion exchanger having a crosslinked structure obtained by reacting a chloromethylated product of a polysulfone type polymer with a polyamine, has been proposed (JP-A-2-68146), and an anion exchange membrane having such a crosslinked structure and being excellent in the corrosion resistance has been proposed (JP-A-6-80799, JP-A-6-172559, JP-A-6-271688).
These anion exchange membranes have excellent ion selective permeability and chemical resistance, and they are now useful for applications in which conventional anion exchange membranes made of styrene/divinyl benzene copolymer could not be used. However, their durability is still not adequate in applications to recover acids or alkalis from solutions containing highly oxidative acids such as permanganic acid, peroxyvanadic acid, etc., or highly concentrated alkalis. Accordingly, an anion exchange membrane having higher durability, has been desired. Further, since specific copolymers having ion exchange groups and crosslinked structures introduced in block structures, there has been a problem that their production costs are high, and they cannot be provided as inexpensive products.
It is an object of the present invention to provide a process for producing an anion exchange membrane which has a high ion selective permeability and is excellent in durability in a highly oxidative aqueous solution, and which can be produced at low costs.
In a first aspect, the present invention provides a process for producing an anion exchange membrane, which comprises mixing from 25 to 95 mass % of a polymer having anion exchange groups or active groups convertible to anion exchange groups (hereinafter referred to as polymer 1), and from 5 to 75 mass % of a polymer having no anion exchange groups or no active groups convertible to anion exchange groups (hereinafter referred to as polymer 2), and forming the obtained composition into a membrane, said process including a step of cross-linking an aromatic ring of a repeating unit constituting polymer 1 with an aromatic ring of another repeating unit constituting polymer 1 or with a cross-linkable site of polymer 2, and in a case where polymer 1 is a polymer having active groups convertible to anion exchange groups, a step of converting the active groups to anion exchange groups.
The anion exchange membrane obtained by the process of the present invention is made of a mixture comprising polymer 1 which selectively permeate ions, and polymer 2 which does not permeate ions. It is believed that polymers 1 and 2 are uniformly mixed, and an aromatic ring of a repeating unit constituting polymer 1 is crosslinked with an aromatic ring of another repeating unit constituting polymer 1, or with a cross-linkable site of polymer 2, whereby a uniform mixed state can be maintained stably, and high ion selective permeability and high durability will be developed. Here, if polymer 2 is an aromatic hydrocarbon compound, the aromatic ring will be a cross-linkable site (i.e. hydrogen bonded to the aromatic ring will be substituted).
Further, the anion exchange membrane obtained by the present invention is one having polymers 1 and 2 mixed. Accordingly, as compared with conventional membranes made of copolymers, types of polymers to be employed, are many, and it can be produced at a low costs.
Further, in a second aspect, the present invention provides an anion exchanger made of a polymer having haloalkyl groups in an aromatic polysulfone polymer having a repeating unit represented by the formula 4, reacted with an amine:
where in the formula 4, Q
1
, Q
2
, a and b are as defined
Kawazoe Hisao
Sugaya Yoshio
Asahi Glass Engineering Co., Ltd.
Teskin Fred
LandOfFree
Anion exchanger and process for producing anion exchange... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Anion exchanger and process for producing anion exchange..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Anion exchanger and process for producing anion exchange... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3308540