Method and apparatus for producing deionized water

Details Method and apparatus for producing deionized water Method and apparatus for producing deionized water

1999-06-23

2001-05-08

Phasge, Arun S. (Department: 1741)

Chemistry: electrical and wave energy

Apparatus

Electrophoretic or electro-osmotic apparatus

C204S524000

Reexamination Certificate

active

06228240

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a method and an apparatus for producing deionized water, which are useful for producing pure water or ultrapure water useful for the production of pharmaceuticals or semiconductors or water for boilers for power generation.
BACKGROUND ART
As a method for producing deionized water, it is common to employ a method of obtaining deionized water by passing water to be treated through a packed bed of ion exchange resins so that impurity ions are removed as adsorbed on the ion exchange resin. Here, it is common to employ a method of regenerating the ion exchange resin having its adsorbing ability lowered, by means of an acid or alkali. However, such a method has a problem that a waste liquid of the acid or alkali used for the regeneration, is discharged. Therefore, a method for producing deionized water which requires no such regeneration is desired. From such a viewpoint, an attention has been drawn in recent years to a self-regenerating type electrodialytic deionized water producing method wherein ion exchange resins are used in combination with ion exchange membranes. This method is a method wherein a mixture of an anion exchange resin and a cation exchange resin is packed in demineralizing compartments of an electrodialyzer having anion exchange membranes and cation exchange membranes alternately arranged, and while supplying water to be treated to the demineralizing compartments, a voltage is applied to carry out electrodialysis to produce deionized water. In this method, it is common that the ion exchange resins in a wet condition are accommodated in the demineralizing compartments, whereby there have been drawbacks that the contact among the ion exchange resins to one another or between the ion exchange resins and the ion exchange membranes, is inadequate, and if it is attempted to increase the thickness of the mineralizing compartments to reduce the effective membrane area, electrical resistance tends to increase.
As a method for overcoming these drawbacks, it has been proposed to prevent the increase of the resistance by adjusting the width of each demineralizing compartment to a level of from about 0.762 to 10.16 cm (from about 0.3 to 4 inches) and the thickness to a level of from about 0.127 to 0.635 cm (from about 0.05 to 0.25 inch) in JP-B-4-72567 and JP-B-6-20513. However, this method has had drawbacks that since the thickness of the demineralizing compartment is thin, it is difficult to pack the ion exchanger into the demineralizing compartment, and the amount of water produced per unit area is small.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a novel apparatus for producing deionized water whereby, in a self-regenerating type electrodialytic deionized water producing apparatus wherein ion exchangers and ion exchange membranes are used in combination, the increase of electrical resistance is small even if the thickness of a demineralizing compartment is made thick, and pure water can be constantly obtained over a long period of time without the above-mentioned drawbacks of the prior art, and to provide a method for producing deionized water by using such an apparatus.
The present invention provides an apparatus for producing deionized water comprising an electrodialyzer having cation exchange membranes and anion exchange membranes alternately arranged between a cathode and an anode to form demineralizing compartments and concentrating compartments, and ion exchangers accommodated in the demineralizing compartments, wherein a pressure of from 0.1 to 20 kg/cm
2
is exerted between the ion exchangers accommodated in the demineralizing compartments and the cation exchange membranes and anion exchange membranes defining the demineralizing compartments.


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