Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing nonmetal element
Reexamination Certificate
2000-10-27
2002-07-23
Phasge, Arun S. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing nonmetal element
C205S635000
Reexamination Certificate
active
06423205
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a deionization apparatus, more particularly to an electrical deionization apparatus capable of efficient and consistent deionization of water over a wide range of ion concentrations.
2. Discussion of the Related Art
In the technology of separating aqueous solutions into the solvent and the solute, separating the solute which accounts for only a small portion of the solution is theoretically more energy-saving than separating the major-component solvent, as is obvious to the skilled artisan.
This difference is also-reflected in methods of removing ions that are contained in small amounts in liquids and they can be classified into two groups, the first group being intended to remove the solvent water and comprising distillation and reverse osmosis, and the second group being for removing the solute ions and comprising ion exchange and electrodialysis.
Distillation is a method for causing changes in the phase of water by heating and cooling cycles, and reverse osmosis is a method for pressurizing water with a high-pressure pump so that it passes through a permeable membrane. Both methods are energy-intensive approaches.
Ion exchange is a method using an ion-exchange resin that causes selective exchange and adsorption of ions in liquids. In this method, acids or alkalis are used as a regeneralizer of the ion-exchange resin and must be handled with great care. The corrosion of the equipment and leakage due to the regeneralizer are other necessary considerations. Another requirement is the treatment of the liquid waste resulting from the regeneration step.
Electrodialysis uses an electrodialyzer in which cation-exchange membranes are alternated with anion-exchange membranes to make an alternate arrangement of concentration compartments and deionization compartments between electrodes. With a gradient in electrical potential used as the driving force, the ions in a liquid are separated by selective movement from the deionization compartment through the ion-exchange membranes into the concentration compartments. Although electrodialysis permits continuous operation without using any chemicals, its applicability has been limited for the following reasons: a current must be applied in an amount sufficient to transport the ions of interest; if the percent salt removal is to be increased, hardness components are prone to precipitate at the interface with the ion-exchange membrane, making it impossible to produce deionized water of high specific resistance (i.e., high purity); and if the feed solution has low ion concentration, a higher voltage is required to transport the ions.
Under these circumstances, it has generally been held that solutions of high salt concentrations can advantageously be deionized by reverse osmosis, solutions of lower salt concentrations by electrodialysis, and solutions of even lower salt concentrations by ion exchange.
An electrical regenerable deionization apparatus and method that fills an ion exchanger between ion-exchange membranes in the deionization compartment of an electro-dialyzer and which enables more efficient deionization to yield products of higher purity than achievable by the conventional electrodialysis method was first proposed by Paul Kollsman (Japanese Patent Publication Nos. 1859/1958 and 4681/1959). However, for more than 25 years after his proposal, no reliable apparatus of this model has been offered for operation on a commercial scale.
Nevertheless, primarily being motivated by the improvements in the performance of ion-exchange membranes, the advances in pre-treatment methods, the demand of the industrial sector for a deionization apparatus that does not need complicated regeneralizing facilities, and a global concern for the saving of resources and energy, efforts have been constantly made to develop a practically feasible electrical deionization technology that fills the ion exchanger between ion-exchange membranes and many salient improvements have been proposed in recent years.
Some of these improvements are commercially applicable and include the following: a method in which the deionization compartment is limited in terms of structural parameters such as width and thickness and filled with a mixture of cation- and anion-exchange resins (Japanese Patent Publication No. 72567/1992); a method in which the interior of the deionization compartment is segmented and filled with anion- and cation-exchange membranes alternately (Japanese Patent Public Disclosure No. 71624/1992); a method in which the deionization compartment is filled with a mixture of cation-exchange fiber, anion-exchange fiber and inactive synthetic fiber (Japanese Patent Public Disclosure No. 236889/1995); a method in which the deionization compartment is filled with a mixture of cation/anion-exchange resins and cation/anion-exchange fibers (Japanese Patent Public Disclosure No. 277344/1993); and a method in which a multi-core composite fiber of sea-island pattern having cation-exchange groups introduced therein is mixed with a multi-core composite fiber of the same pattern having anion-exchange groups incorporated therein and the mixture is shaped for filling (Japanese Patent Public Disclosure No. 192163/1996). These methods share the common feature of combining the mixed-bed ion-exchange resin technology (MB method) with electrodialysis.
However, all of these proposals have had difficulty in producing deionized water of high purity consistently over a prolonged time because they have one or more of the following problems: in order to prevent short-circuiting by the feed stream, the deionization compartment must be closely filled with the ion exchangers by a cumbersome procedure; due to the close filling, the pressure of the stream flowing into the deionization compartment must be held high; the variations in the flow of the water being fed into the deionization compartment may potentially disrupt the homogeneity of the mixed ion exchangers; ion-exchange resins of a rigidly cross-linked structure may become disintegrated during service; since the oppositely charged ion exchangers arranged in the direction of ion migration retard the smooth transport of ions, the ion exchangers become gradually “loaded” as the operation proceeds, potentially resulting in incomplete deionization; the ion exchangers must be mixed uniformly by a cumbersome procedure; it is difficult to secure the strength of the shaped ion exchanger; it is cumbersome to control the porosity of the shaped ion exchanger; and it is difficult to clean the ion exchangers sufficiently to prevent the dissolution of organic carbon (TOC).
The structure of the conventional electrodialyzer is characterized in that the spacer secures the necessary passageway for the feed stream, that it can be operated at low in-flow pressure and that no ion exchangers that interfere with the movement of ions are provided in the direction of ion migration. Continued attempts have also been made to design an advanced type electrodialyzers by filling the deionization compartment with an ion-conducting spacer so that power consumption is reduced while retaining the advantageous features of that structure. Although several tens of percent of cut on power consumption has been demonstrated, those attempts could not reach the stage of commercialization because of the following reasons: due to the difficulty in controlling the chemical reaction involved in introducing ion-exchange groups into the spacer material, mass production of the spacer is difficult; it is also difficult to secure the strength of the spacer; difficulty is also encountered in suppressing the dissolution of TOC from the spacer. Particularly in the case where the deionization compartment is filled with the ion-conducting spacer alone in place of ion-exchange resins, the spacer which, as an ion exchanger, has a smaller surface area than the ion-exchange resins makes only insufficient contact with the ions in the deionization compartment and the water to be treated flows as if it “short-circuits
Akahori Masaji
Akiyama Toru
Fujiwara Kunio
Kawamoto Takayoshi
Konishi Satoshi
Ebara Corporation
Parsons Thomas H.
Phasge Arun S,.
LandOfFree
Electric deionization apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electric deionization apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electric deionization apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2865758