Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
2002-03-13
2004-10-26
Phasge, Arun S. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S524000, C204S536000, C204S632000, C204S633000, C210S659000, C210S900000
Reexamination Certificate
active
06808608
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to method and apparatus for purifying water, particularly in a current efficient manner.
Purified deionized (DI) water is used in a number of analytical applications such as in chromatography and in ion chromatography for making online or offline eluents, in sample preparation applications using auto samplers and in a variety of day to day laboratory uses. Many electrodialytic methods have been used to produce purify DI water.
Electrodialysis as described in the literature is a term used when a cation exchange membrane and an anion exchange membrane are used in conjunction with an electric field for purification of tap water, salt water or brackish water. “Electrodeionization” is the term used to describe the use of ion exchange materials in the above approach. A number of patents discuss the above approaches with various ion exchange materials and configurations.
An early apparatus and method for treating liquids by electrodialysis was shown by Kollsman in U.S. Pat. No. 2,689,826. This device contained anion and cation exchange diaphragms that are arranged in series with electrodes flanking the end of the device. One volume of liquid to be treated is placed in a depletion (purifying) chamber and the ions migrate over time from this volume into a second volume of liquid in the concentration chamber. Thus, the treated liquid is depleted of ions and the liquid in the concentration chamber is enriched with the transferred ions. U.S. Pat. No. 2,794,777 disclosed devices of similar construction with acid and base solutions flowing in the chamber adjacent to the anion and cation diaphragm, respectively. The function of the acid and base solution was to provide a conductive pathway and, thus, lower resistance. The anion and cation exchange diaphragms were walls made with cloth and packed with the respective resin materials. Partial ionization was accomplished with this device in combination with other packed bed columns.
U.S. Pat. No. 2,815,320 disclosed devices that use macroporous ion exchange beads as a filler between permselective anion and cation exchange membranes to lower the resistance and maintain a conductive pathway. There is a suggestion that electrolytes could be circulated in the electrode chambers. According to this patent, the electrolyte in the electrode chambers, and the conductive filler in the intermediate chambers provided a conductive path for current transport. U.S. Pat. No. 2,923,674 disclosed similar electrodialysis devices with multiple anion and cation exchange treatment chambers that facilitate removal of ions and hence purification of a water stream. The above devices also used acid electrolytes in certain chambers.
U.S. Pat. No. 3,149,061 disclosed devices that were useful for removal of both strongly and weakly ionized species from aqueous solutions. The dilution (purifying) chambers in the above devices were either filled with a mixture of cation and anion exchange resins or anion exchange resin by itself. U.S. Pat. No. 3,341,441 disclosed an electrodialytic process where the applied polarity was reversed periodically to minimize scale buildup in the electrode chambers.
U.S. Pat. No. 3,869,376 disclosed devices that were useful for demineralizing soft water. The treatment chamber in these devices were packed with ion exchange resins.
U.S. Pat. No. 4,148,708 disclosed electrodialytic cells that were packed with mixed anion and cation exchange resin in the feed compartment while packing the anode and the cathode compartments with anion exchange and cation exchange resin, respectively. This cell was useful for generating acid, a base and purifier water from the three chambers.
U.S. Pat. No. 4,632,745 disclosed an electrodeionization apparatus with depleting chambers packed with mixed anion and cation exchange resins while the concentration chamber was free of ion exchange resins. Similarly, U.S. Pat. No. 4,925,541 disclosed electrodeionization apparatus with the depletion chambers filled with anion and cation exchange resin beads while the concentration compartments are free of ion exchange beads. The beads in the depleting compartments were housed within subcompartments of controlled width and thickness and were retained therein by ion permeable membranes, which were secured to the wall of the subcompartments. Another version of the above device was shown in U.S. Pat. No. 4,931,160 in which the liquid to be purified was passed through at least two ion depletion compartments filled with anion and cation exchange resin beads. U.S. Pat. No. 4,956,071 disclosed electrodeionization devices that have both the depletion chambers and the concentration chambers filled with ion exchange resin beads. This patent discloses means for reversing the applied polarity and means of recovering a purified product continuously. U.S. Pat. No. 5,154,809 disclosed electrodeionization devices with depletion chambers and possibly concentration chambers filled with mixed ion exchange beads of uniform size.
U.S. Pat. No. 5,308,466 disclosed devices with at least one section of the device having ion exchange membranes/resins of lower crosslinking and lower selectivity, thus reducing the electrical resistance and facilitating removal of large, heavily hydrated, highly or weakly charged molecules (such as silica) from the feed water. U.S. Pat. No. 5,308,467 disclosed electrodeionizers with a radiation grated polymer with mixed ion exchange moieties (anion and cation exchange) as a packing in the demineralizing or dilution compartment.
U.S. Pat. No. 5,736,023 disclosed an electrodeionization apparatus having ion exchange resins in both the depletion and concentration chambers. The apparatus has a polarity reversal means and a means of substituting the fluid in the ion-concentrating compartment with a fluid of lower ionic concentration while maintaining flow in the ion-depleting compartment. U.S. Pat. No. 5,868,915 disclosed electrodeionization apparatus with electroactive media in the depletion and concentration compartments. There are several other patents that disclose improvements to the electrodeionization apparatus and process, such as U.S. Pat. Nos. 6,117,927, 6,126,805, 6,254,753, 6,241,866, 6,241,867 and 6,312,577.
All of the above-disclosed devices are current inefficient devices that require an excess current than predicted from theory for the deionization process. Devices with mixed ion exchange packing materials in the depletion chamber split water and hence are current inefficient.
U.S. Pat. Nos. 6,077,434 and 6,328,885 disclosed means of improving current efficiency for suppressor and suppressor like devices in ion chromatography. The devices disclosed for anion analysis remove cations and convert the matrix ions to a nonconductive form while converting all anion species to conductive acids.
In ion chromatography, the presence of ionic impurities in the water can affect peak response and sensitivity, linearity of response, background stability and baseline noise. The life time of consumables, such as columns and suppressors may also suffer due to the presence of contaminants.
Some of the issues with contaminants in the eluents or reagents may be addressed by using ultra high purity reagents with certified level of contaminants. Analytical laboratories have point of use polisher systems that are intended to lower the level of ionic contaminants in the DI water. With these systems, however, replacing the polisher is not mandated. The detection of water quality on most systems is also not reliable. Use of certified bottled water for eluent or reagent preparation is another approach. This approach, however, suffers from the limitation of contamination from the environment, handling issues, shelf life and added costs. Additionally, it is difficult to eliminate certain contaminants such as carbon dioxide and ammonia, during the reagent preparation process.
The net effect of the above-discussed factors is variability in the water quality from one laboratory to another laboratory. Therefore, it is desirable to have a way to purif
Avdalovic Nebojsa
Srinivasan Kannan
Brezner David J.
Dionex Corporation
Phasge Arun S,.
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