Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
2002-06-28
2004-12-14
Bell, Bruce F. (Department: 1746)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S531000, C204S522000, C204S296000, C205S697000, C205S703000
Reexamination Certificate
active
06830671
ABSTRACT:
FIELD OF APPLICATION IN INDUSTRIES
This invention relates to a novel ion-exchange membrane and a method for removing low molecular weight electrolytes from an aqueous solution of said low molecular weight electrolytes containing high-molecular organic components by electrodialysis using said ion-exchange membrane.
PRIOR ART
In general, in case an aqueous solution of salts containing organic substances, particularly macromolecules, which become to have electric charge through ionization or intramolecular polarization (hereinafter referred to also as organic macroions etc.), is desalinated by ion-exchange membrane electrodialysis, there comes up a problem of so-called organic fouling of membrane, that organic macroions etc. in the solution to be treated stick to the ion-exchange membrane and deteriorate the performance of the membrane. When the organic fouling comes up, the electric resistance of the membrane increases, the current efficiency decreases, pH of the solution changes and so forth and thus the electrodialytic performance deteriorates.
Up to now, there have been proposed as an ion-exchange membrane, which inhibits organic fouling, an ion-exchange membrane that easily transmits organic macroions etc., or an ion-exchange membrane that prevents organic macroions etc. from penetration into the membrane at a surface layer part of the membrane. As a method to facilitate the transmission of organic macroions etc. through the membrane, a method to loosen the membrane structure is known (Desalination, 13, 105 (1973)). But, when the membrane structure is loosened, the ion selectivity decreases inevitably and consequently no efficient desalination can be conducted. On the other hand, as an ion-exchange membrane that prevents organic macroions etc. from penetrating into the membrane there is one to which a thin layer, that is neutral, amphoteric, or oppositely charged to the ion-exchange group, is formed on the surface of the membrane. The more dense the membrane structure is, or the higher the molecular weight of organic macroions etc. is, the more remarkable is the effect. There is reported, for example, an anion-exchange membrane that prevents organic anions from penetrating into the membrane through introduction of oppositely charged sulfonic acid group to the surface layer part of the resin membrane having anion-exchange group (Japanese Patent Publication No. 40556/1976), etc.
Problems the Invention is Going to Solve
Although the ion-exchange membrane disclosed in the above-mentioned publication has a resistance against organic fouling to some extent, it has a disadvantage that the electric resistance of the ion-exchange membrane (hereinafter referred to as membrane resistance) increases remarkably by the aforementioned oppositely charged layer put on the surface layer part of the resin membrane. The purpose of the present invention is, therefore, to provide an ion-exchange membrane having excellent resistance against organic fouling and showing low electric resistance.
Means of Solving the Problems
The present inventors have been intensively continuing research aiming at improvement of the resistance against organic fouling of the conventional ion-exchange membrane. As a result, they have found that the resistance against organic fouling can be given to an ion-exchange membrane with almost no increase in membrane resistance of the ion-exchange membrane by fixing a hydrophilic polyether compound to the ion-exchange membrane, and completed the present invention.
Thus, according to the present invention, there is provided an ion-exchange membrane characterized by that a polyether compound having polyalkylene glycol chain is fixed on the surface of the membrane and/or inside of the membrane.
According to the present invention, there is also provided a method for manufacturing an aqueous solution, whose concentration of low molecular weight electrolytes is reduced, characterized by removing the low molecular weight electrolytes by electrodialysis using the above-mentioned ion-exchange membrane from an aqueous solution containing low molecular weight electrolytes, as the electrolytes to be removed, comprising organic acids or inorganic acids with molecular weight of 1,000 or less or organic salts or inorganic salts with molecular weight of 1,000 or less, and high molecular weight organic compounds or organic ions with higher molecular weight than said low molecular weight electrolytes.
The ion-exchange membrane of the present invention is one in which a polyether compound having polyalkylene glycol chain (hereinafter simply referred to as polyether compound) is fixed on the surface of the membrane and/or inside of the membrane. In this case an ion-exchange membrane means a resin membrane of hydrocarbon type or fluorine type having cation-exchange ability or anion-exchange ability. Cation-exchange ability and anion-exchange ability are expressed by the existence of a cation-exchange group and an anion-exchange group, respectively. As such an ion-exchange group there is no strict limitation, if it is a functional group capable of being negatively or positively charged in an aqueous solution. Specifically there are mentioned, as cation-exchange groups, sulfonic acid group, carboxylic acid group, phosphonic acid group, etc. and generally sulfonic acid group, a strongly acid group, is preferably used. As anion-exchange groups there are mentioned primary to tertiary amino groups, quaternary ammonium groups, pyridyl groups, imidazole groups, quaternary pyridinium groups, etc. and generally quaternary ammonium groups and quaternary pyridinium groups, which are strongly basic groups, are preferably used.
The ion-exchange membrane may be of any kind, irrespective of polymerization type, condensation type, homogeneous type, heterogeneous type, etc., with or without reinforcing core materials, or kind or form of ion-exchange membrane depending upon the materials or manufacturing methods. Many of organic macroions, however, are anions and therefore anion-exchange membranes often suffer organic fouling and their performance is deteriorated. Therefore, the ion-exchange membrane in the present invention is preferably an anion-exchange membrane, because the effect of the present invention to inhibit the deterioration of dialytic performance of electrodialysis is remarkable.
The ion-exchange membrane of the present invention has the biggest characteristic in the fixation of a polyether compound on the surface and/or inside of the membrane having the above-mentioned ion-exchange group. It is thought that the existence of a polyether compound on the surface and/or inside of the ion-exchange membrane prevents the ion-exchange groups from the direct contact of organic macroions etc., inhibits the adsorption of organic macroions etc. to the ion-exchange membrane, and consequently improves the resistance against organic fouling. Moreover, the polyether compound can inhibit the increase of the electric resistance of the ion-exchange membrane to a great extent due to the hydrophilic property originated from the alkylene glycol chain. Further, in the ion-exchange membrane of the present invention, the polyether compound is fixed to the ion-exchange membrane itself, for example, the polyether compound does not dissolve in the solution to be dialyzed, in case the electrodialysis is conducted using said ion-exchange membrane, and the excellent effect of the resistance against organic fouling can be maintained for a long time.
Moreover, in general, in case the electrodialysis is conducted to a solution containing organic substances as the solution to be treated using an ion-exchange membrane, periodical membrane washing is conducted with an alkaline solution etc. for the purpose of removing fouling substances stuck to the ion-exchange membrane in order to maintain a stable operation for a long period. As a polyether compound is stable against an alkaline solution compared with other hydrophilic compounds, for example, compounds having ester bond or amide bond, it is usually possible to conduct an effective me
Aritomi Toshio
Kawashima Minoru
Bell Bruce F.
Tokuyama Corporation
Wenderoth , Lind & Ponack, L.L.P.
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