Purification method for ion-exchange resin, ion-exchange device, water treatment system, and anion-exchange resin

Abstract

The present invention performs: a step in which an anion-exchange resin before being packed into an ion-exchange device is brought into contact with an aqueous mineral-acid solution; and a step in which the anion-exchange resin that has been in contact with the aqueous mineral-acid solution is brought into contact with an alkali metal hydroxide solution having a metal concentration not higher than a given threshold.

Description

Ion exchange resin purification method, ion exchange device, water treatment system, and anion exchange resin

[0001] The present invention relates to a method for purifying an ion exchange resin, an ion exchange apparatus, a water treatment system, and an anion exchange resin.

[0002] A method for regenerating anion exchange resins, which involves contacting anion exchange resins used in demineralization equipment with an aqueous mineral acid solution to remove contaminants adhering to the surface of the anion exchange resins, and then regenerating the resins using an aqueous sodium hydroxide solution, has been disclosed (see, for example, Patent Document 1). Also, a method for reducing the amount of metal impurities contained in a cation exchange resin by contacting the resin with a mineral acid solution has been disclosed (see, for example, Patent Document 2).

[0003] Japanese Patent Publication No. 2002-159867

[0004] The technology described in Patent Document 1 is a method for regenerating used anion exchange resins to reduce the frequency of anion exchange resin replacement. Therefore, it does not address the issue of improving the quality of treated water when anion exchange resins are used before being loaded into an ion exchange device. In other words, the purpose of the technology described in Patent Document 1 is to restore used anion exchange resins to their pre-replacement state, restore the performance of the anion exchange resins, and remove contaminants adhering to the anion exchange resins loaded into an ion exchange device, but not to remove impurities or leachables from the anion exchange resins before being loaded into an ion exchange device. Furthermore, even when the amount of metal impurities contained in the cation exchange resins was reduced using the method described in Patent Document 2, it was discovered that metal leaching still occurred from CP (cartridge polisher) resins, which are mixtures of anion exchange resins and cation exchange resins. In other words, to further increase the purity of ultrapure water, it is necessary to devise not only cation exchange resin purification techniques but also anion resin purification techniques.

[0005] An object of the present invention is to provide a method for purifying an ion exchange resin, an ion exchange apparatus, a water treatment system, and an anion exchange resin that can improve the quality of treated water when an anion exchange resin is used.

[0006] The method for purifying an ion exchange resin of the present invention includes the steps of: bringing an aqueous mineral acid solution into contact with an anion exchange resin before the resin is packed into an ion exchange device; and bringing the anion exchange resin that has been contacted with the aqueous mineral acid solution into contact with an alkali metal hydroxide solution having a metal concentration equal to or lower than a predetermined threshold value.

[0007] The ion exchange device of the present invention is filled with an anion exchange resin purified using a purification method for an ion exchange resin, which includes the steps of contacting an aqueous mineral acid solution with the anion exchange resin before it is filled in the ion exchange device, and contacting the anion exchange resin that has been contacted with the aqueous mineral acid solution with an alkali metal hydroxide solution having a metal concentration equal to or lower than a predetermined threshold value.

[0008] The water treatment system of the present invention further comprises an ion exchange device filled with an anion exchange resin purified using a method for purifying anion exchange resin, the method comprising the steps of contacting an aqueous mineral acid solution with an anion exchange resin before the resin is filled in the ion exchange device, and contacting the anion exchange resin that has been contacted with the aqueous mineral acid solution with an alkali metal hydroxide solution having a metal concentration equal to or less than a predetermined threshold value. The method is provided in the secondary pure water production system or downstream of the secondary pure water production system.

[0009] The anion exchange resin of the present invention is purified using a method for purifying an ion exchange resin, which includes the steps of contacting an aqueous mineral acid solution with the anion exchange resin before it is packed into an ion exchange device, and contacting the anion exchange resin that has been contacted with the aqueous mineral acid solution with an alkali metal hydroxide solution having a metal concentration equal to or lower than a predetermined threshold value.

[0010] In the present invention, the quality of treated water can be further improved when an anion exchange resin is used.

[0011] 1 is a flowchart illustrating an example of a method for purifying an ion exchange resin according to the present invention. 2 is a flowchart illustrating an example of a method for purifying a CP resin using a cation exchange resin as an intermediate raw material and an anion exchange resin as an intermediate raw material purified in the process described using the flowchart shown in Figure 1. 3 is a graph showing an example of the relationship between the metal concentration of an alkali metal hydroxide solution used in a regeneration process and the amount of metal eluted from the CP resin. 4 is a diagram showing an example of a water treatment system to which a CP resin purified in the process described using the flowchart shown in Figure 2 is applied.

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0013] 1 is a flowchart illustrating an example of the method for purifying an ion exchange resin of the present invention. A raw material resin for an anion exchange resin and a pre-purification (unpurified) anion exchange resin are prepared. This anion exchange resin is a resin before being packed into an ion exchange device. Examples of resin before being packed into an ion exchange device include unused resin that has never been packed into an ion exchange device installed in a primary or secondary pure water production system (subsystem), and resin that has been packed into an ion exchange device installed in a primary or secondary pure water production system and used, then removed from the ion exchange device and regenerated, and yet to be repacked into the ion exchange device.

[0014] First, in the first step, a mineral acid aqueous solution is brought into contact with a prepared unpurified (unpurified) anion exchange resin (step S1). Step S1 is a cleaning step using an acid (chemical). For example, a predetermined anion exchange resin purification column may be filled with unpurified anion exchange resin, and the mineral acid aqueous solution may be supplied through a first pipe connected to the anion exchange resin purification column. In this case, an on-off valve may be provided in the first pipe, and the supply of the mineral acid aqueous solution may be controlled by controlling the opening and closing of the on-off valve. Examples of the mineral acid aqueous solution used in step S1 include hydrochloric acid (HCl), sulfuric acid (HSO), and nitric acid (HNO).

[0015] Subsequently, in the second step, the anion exchange resin washed in step S1 is contacted with an alkali metal hydroxide solution (step S2). Step S2 is a regeneration step using alkali. When the acid (chemical) washing step in step S1 is performed, the ion exchange groups of the anion exchange resin are converted to a salt form. Therefore, the regeneration step in step S2 is performed to return the ion exchange groups of the salt-form anion exchange resin to their usable form. Alternatively, for example, the alkali metal hydroxide solution may be supplied through a second pipe connected to an anion exchange resin purification column packed with the anion exchange resin contacted with the mineral acid aqueous solution in step S1. In this case, an on-off valve may be provided on this second pipe, and the supply of the alkali metal hydroxide solution may be controlled by controlling the opening and closing of this on-off valve. The alkali metal hydroxide solution used here is an aqueous solution maintained at 25 wt%. This 25 wt% alkali metal hydroxide solution is diluted to a predetermined concentration (e.g., 4 wt%) and contacted with the anion exchange resin. The metal concentration of the alkali metal hydroxide solution used here is below a predetermined threshold. The metal concentration of this alkali metal hydroxide solution is preferably 200 μg / L or less when the iron concentration in the alkali metal hydroxide solution is 25 wt %. Alternatively, the metal concentration of the alkali metal hydroxide solution is preferably 100 μg / L or less when the aluminum concentration in the alkali metal hydroxide solution is 25 wt %. By using such a quality-controlled alkali metal hydroxide solution in the anion exchange resin regeneration process, the water quality of the treated water treated using the anion exchange resin can be controlled to a desired value. Iron and aluminum exist in anionic form at pH 13 or higher. Therefore, iron and aluminum can adhere to the anion exchange resin during the alkali-based regeneration process in step S2. Therefore, it is desirable to consider the concentration of the alkali metal hydroxide solution used in step S2.

[0016] Then, in the third step, the anion exchange resin regenerated in step S2 is washed with ultrapure water (step S3). The ultrapure water used for this washing is room temperature ultrapure water. The washed anion exchange resin is used as the purified anion exchange resin to be packed into the CP.

[0017] Note that other steps may be performed between each of steps S1 to S3. Furthermore, each of steps S1 to S3 may be repeated a predetermined number of times. Examples of other steps include a step of passing an alkaline bicarbonate solution through the substrate, a step of passing ultrapure water through the substrate, etc.

[0018] 2 is a flowchart illustrating an example of a method for purifying a CP resin using a cation exchange resin as an intermediate raw material and an anion exchange resin as an intermediate raw material purified by the process described using the flowchart in FIG. 1. The cation exchange resin used here is an intermediate raw material purified by a general purification method. This cation exchange resin intermediate raw material may be an intermediate raw material purified by the method described in the above-mentioned Patent Document 2 (Japanese Patent No. 4,441,472), for example.

[0019] In the fourth step, the intermediate cation exchange resin is mixed with the intermediate anion exchange resin purified in the step described with reference to the flowchart in Figure 1 (step S11). Subsequently, in the fifth step, the mixed resin of the cation exchange resin and the anion exchange resin is washed with ultrapure water at room temperature (step S12). In this way, the CP resin used in water treatment to produce ultrapure water is purified.

[0020] Figure 3 is a graph showing an example of the relationship between the metal concentration of the alkali metal hydroxide solution used in the regeneration process and the amount of metal eluted from the CP resin. The upper graph in Figure 3 shows the relationship between Cases 1 to 3 and the conventional concentration and the ratio of the amount of aluminum and iron eluted from a 25 wt% alkali metal hydroxide solution to the amount of conventional CP resin eluted. The aluminum and iron concentrations of the 25 wt% alkali metal hydroxide solutions in Cases 1 to 3 are shown below. Note that in the regeneration process, the 25 wt% alkali metal hydroxide solution is diluted to a predetermined concentration (e.g., 4 wt%) before use, as described above. Case 1: Iron concentration 200 μg / L or less, aluminum concentration 100 μg / L or less; Case 2: Iron concentration 200 μg / L or less, aluminum concentration 100 μg / L or more; Case 3: Iron concentration 200 μg / L or more, aluminum concentration 100 μg / L or more. The lower graph in Figure 3 shows an example of the relationship between the metal concentration of a 25 wt% alkali metal hydroxide solution and the ratio of the amount of eluted from a conventional CP resin. The relationship shown in FIG. 3 is the result of an experiment.

[0021] As shown in the lower graph of Figure 3, the lower the metal concentration in the 25 wt% alkali metal hydroxide solution used in the regeneration process, the lower the amount of metal elution in the treated water treated with CP resin. Also, as shown in the upper graph of Figure 3, when both the iron concentration and aluminum concentration in the 25 wt% alkali metal hydroxide solution used in the regeneration process are above a predetermined threshold, as in Case 3, both the amount of iron elution and the amount of aluminum elution in the treated water treated with CP resin are greater than conventional. Also, when the iron concentration in the 25 wt% alkali metal hydroxide solution used in the regeneration process is below a predetermined threshold and the aluminum concentration is above a predetermined threshold, as in Case 2, the amount of aluminum elution in the treated water treated with CP resin is greater than conventional. Also, when both the iron concentration and the aluminum concentration in the 25 wt% alkali metal hydroxide solution used in the regeneration process are below a predetermined threshold, as in Case 1, both the amount of iron elution and the amount of aluminum elution in the treated water treated with CP resin are less than conventional. In this way, by lowering the metal concentration contained in the 25 wt% alkali metal hydroxide solution used in the regeneration process and further reducing the individual metal concentrations to below a predetermined threshold, it is possible to achieve even higher purity of the treated water treated with CP resin.

[0022] FIG. 4 is a diagram showing an example of a water treatment system that uses CP resin purified through the process described using the flowchart in FIG. 2 . The water treatment system shown in FIG. 4 includes a pretreatment system 10, a primary pure water production system 20, and a secondary pure water production system 30, which is a so-called subsystem. The pretreatment system 10 may be a system used in a general water treatment system. The pretreatment system 10 is a water treatment facility that removes fine particles from raw water supplied to the system. The primary pure water production system 20 is a water treatment facility that performs a predetermined treatment on the treated water treated in the pretreatment system 10 and supplies the treated water to the secondary pure water production system 30. The secondary pure water production system 30 may be a secondary pure water production system used in a general water treatment system. The secondary pure water production system 30 is a water treatment facility that removes trace amounts of ions and total organic carbon that were not completely removed in the primary pure water production system 20. The treated water treated in the secondary pure water production system 30 is supplied to a point of use, which is the destination of the treated water.

[0023] The secondary pure water production system 30 is provided with a CP100. The CP100 is a water treatment device filled with a mixed bed of anion exchange resin and cation exchange resin purified by the above-mentioned purification method. The CP100 removes ions from the water to be treated supplied from a UV oxidation device installed upstream. The secondary pure water production system 30 is a system that is managed so that the metal concentration in the treated water is 1 ppt or less. The CP100 may be installed in a system downstream of the secondary pure water production system 30.

[0024] In this manner, in this embodiment, the unpurified anion exchange resin is washed with an acid, regenerated with an alkali, and washed with ultrapure water. This reduces the metal components contained in the unpurified anion exchange resin. The anion exchange resin is then used as the resin to be packed in the secondary pure water production system 30 or the CP 100 located downstream thereof. In this case, the anion exchange resin is packed in the CP 100 as a mixed bed with a cation exchange resin. This further improves the quality of the ultrapure water supplied from the secondary pure water production system 30. The anion exchange resin may also be used as a single bed.

[0025] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above-described embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

[0026] This application claims priority based on Japanese Patent Application No. 2024-029832, filed February 29, 2024, the disclosure of which is incorporated herein in its entirety by reference.

[0027] 10 Pretreatment system 20 Primary pure water production system 30 Secondary pure water production system 100 CP

Claims

1. A method for purifying an ion exchange resin, comprising the steps of: bringing an aqueous mineral acid solution into contact with an anion exchange resin before the resin is packed into an ion exchange device; and bringing the anion exchange resin that has been contacted with the aqueous mineral acid solution into contact with an alkali metal hydroxide solution having a metal concentration equal to or lower than a predetermined threshold value.

2. The method for purifying an ion exchange resin according to claim 1, wherein the anion exchange resin before being packed into the ion exchange device is an unused resin that has never been packed into the ion exchange device.

3. A method for purifying an ion exchange resin according to claim 1, wherein the anion exchange resin before being packed into the ion exchange device is packed into the ion exchange device and used, then removed from the ion exchange device and regenerated, and is the anion exchange resin before being repacked into the ion exchange device.

4. A method for purifying an ion exchange resin according to any one of claims 1 to 3, wherein the threshold value is a concentration of iron contained in a 25% by weight solution of the alkali metal hydroxide of 200 μg / L, or a concentration of aluminum contained in a 25% by weight solution of the alkali metal hydroxide of 100 μg / L.

5. An ion exchange device filled with an anion exchange resin purified using the method for purifying an ion exchange resin according to claim 1.

6. The ion exchange apparatus according to claim 5, wherein the anion exchange resin and the cation exchange resin are packed in a mixed bed.

7. A water treatment system in which the ion exchange device according to claim 5 or 6 is provided in a secondary pure water production system or downstream of the secondary pure water production system.

8. A water treatment system according to claim 7, wherein the treated water treated by said secondary pure water production system has a metal concentration of 1 ppt or less.

9. An anion exchange resin purified using the method for purifying an ion exchange resin according to claim 1.

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