Chemistry: electrical and wave energy – Apparatus – Electrophoretic or electro-osmotic apparatus
Reexamination Certificate
1999-02-23
2001-06-19
Phasge, Arun S. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrophoretic or electro-osmotic apparatus
C204S524000
Reexamination Certificate
active
06248226
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for producing, by electrodeionization, deionized water which can be used in a variety of industrial or reseach facilities, etc. in the semiconductor manufacturing industry, the pharmaceutical industry, the food industry, etc., and more particularly to a deionized water production process excellent in removal of silica.
BACKGROUND ART
A method wherein feed water is passed through ion exchange resins to effect deionization thereof has hitherto been known as a deionized water production process. In this method, however, the ion exchange resins, when exhausted with ions, must be regenerated with respective aqueous solutions of an acid and an alkali. In an effort to eliminate such a disadvantage involved in the foregoing treatment operation, an electrodeionization deionized water production process entirely without need of such regeneration with any chemicals has recently been established and put into practical use.
For this electrodeionization process, an ion exchange material(s) such as an ion exchange resin(s) or an ion exchange fiber(s) is filled between cation exchange membranes and anion exchange membranes to form ion depletion compartments, concentration compartments are provided on both outer sides of the ion depletion compartments, and the ion depletion compartments and the concentration compartments are disposed between an anode and a cathode. While applying a voltage, feed water is flowed into the ion depletion compartments and concentrating water is flowed into the concentration compartments. Impurity ions in the feed water are removed in the ion depletion compartments while electrically transferring the impurity ions to the concentration compartments to produce deionized water. Since the ion exchange material(s) is never saturated with ions according to this process, regeneration thereof with any chemicals is advantageously unnecessary.
However, the deionized water production process according to electrodeionization involves a problem of a low removal rate of silica in feed water. In order to solve this problem, the instant applicant has previously proposed electrodeionized water production equipment wherein ion exchange material layers through which feed water is first to be passed are anion exchange material layers (Japanese Patent Laid-Open No. 71,624/1992).
Although the silica removal rate can be improved using this equipment, the inventors of the present invention have made intensive investigations with a view to establishing a process for further increasing the silica removal rate. As a result, they have found out that the silica removal rate can be remarkably improved when the current direction of feed water being fed into ion depiction compartments is set opposite to the current direction of concentrating water being fed into concentration compartments while at the same time feed water flowed into the ion depletion compartments is first passed through respective anion exchange material layers. The present invention has been completed based on this finding.
An object of the present invention is to provide a process for producing deionized water by electrodeionization, wherein silica as an impurity in feed water can be removed at a very high removal rate.
DISCLOSURE OF THE INVENTION
In carrying out an electrodeionization deionized water production process wherein an anion exchange material and a cation exchange material are filled between cation exchange membranes and anion exchange membranes to form ion depletion compartments, concentration compartments are provided on both sides of the ion depletion compartments with the cation exchange membranes or the anion exchange membranes therebetween, and the ion depletion compartments and the concentration compartments are disposed between an anode and a cathode, and wherein feed water is flowed into the ion depletion compartments with application of a voltage while flowing concentrating water into the concentration compartments to remove impurity ions in feed water for production of deionized water; the present invention is characterized in that feed water and concentrating water are flowed into the ion depletion compartments and the concentration compartments, respectively, in such a way that the current direction of feed water being fed into the ion depletion compartments is opposite to the current direction of concentrating water being fed into the concentration compartments, while feed water flowed into the ion depletion compartments is first passed through respective anion exchange material layers.
In producing deionized water by electrodeionization wherein feed water is fed into the ion depletion compartments and concentrating water is fed into the concentration compartments, feed water and concentrating water are fed in mutually opposite current directions according to the present invention. More specifically, when feed water is passed through the ion depletion compartments in the downward current direction, concentrating water is passed through the concentration compartments in the upward current direction. On the other hand, when feed water is passed through the ion depletion compartments in the upward current direction, concentrating water is passed through the concentration compartments in the downward current direction.
Further, in the present invention, feed water flowed into the ion depletion compartments is first passed through the anion exchange material layers. More specifically, although there are various methods of how to arrange layers of such ion exchange materials as an anion exchange material and a cation exchange material to be filled in each ion depletion compartment, the layer arrangement in the present invention is determined in such a way that an ion exchange material layer through which feed water is first to be passed is an anion exchange material layer.
Accordingly, when the mode of feed water passage is downward current water passage, the anion exchange material layer is disposed in an upper portion of each ion depletion compartment with other ion exchange material layer(s) disposed thereunder. On the other hand, when that mode is upward current water passage, the anion exchange material layer is disposed in a lower portion of each ion depletion compartment with other ion exchange material layer(s) disposed thereon.
In the present invention, a partition wall may be either existent or nonexistent between the anion exchange material layer and other ion exchange material layer adjacent to the former layer. Thus, the two layers may be either in or out of contact with each other.
According to the present invention, since feed water and concentrating water are flowed into the ion depletion compartments and the concentration compartments, respectively, in such a way that the current direction of feed water being fed into the ion depletion compartments is opposite to the current direction of concentrating water being fed into the concentration compartments, while feed water flowed into the ion depletion compartments is first passed through the anion exchange material layers, the electric current density in the portions of the anion exchange material layers through which feed water is first passed is increased to promote the migration of anions into the concentration compartments, whereby the alkalinity of feed water in the portions of the anion exchange material layers becomes so strong that the dissociation of silica proceeds, with the result that the silica removal rate can be greatly improved as compared with those in conventional processes.
REFERENCES:
patent: 5308466 (1994-05-01), Ganzi et al.
patent: 5316637 (1994-05-01), Ganzi et al.
patent: 52-047580 (1977-04-01), None
patent: 4071624 (1992-03-01), None
patent: 7265865 (1995-10-01), None
patent: 8150326 (1996-06-01), None
Kakuda Minoru
Shinmei Yasutaka
Organo Corporation
Phasge Arun S,.
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