Ion-exchange-resin pretreatment device and pretreatment method

Abstract

An ion-exchange-resin pretreatment device 1 for eluting and removing moisture contained in an ion exchange resin into a pretreatment solvent comprises: a tank 2 for storing a non-aqueous solvent as the pretreatment solvent; a circulation line L1 for circulating the pretreatment solvent within the tank 2; a container 3 provided to the circulation line L1, the container 3 accommodating the ion exchange resin being pretreated; a moisture removal device 4 provided to the circulation line L1, the moisture removal device 4 removing moisture from the pretreatment solvent circulating in the circulation line L1; and a drainage line L2 connected to the circulation line L1 between the container 3 and the moisture removal device 4, the drainage line L2 discharging the pretreatment solvent to the outside.

Description

Pretreatment device and pretreatment method for ion exchange resin

[0001] The present invention relates to a pretreatment device and a pretreatment method for ion exchange resins.

[0002] Highly purified nonaqueous solvents are used in the manufacturing processes of semiconductor devices and lithium-ion batteries. A known method for purifying nonaqueous solvents involves passing the nonaqueous solvent through an ion exchange resin to remove impurities (ionic components such as metal ions) from the solvent. However, this method can lead to the elution of water from the ion exchange resin into the purified nonaqueous solvent, potentially making it impossible to meet the recent demand for higher purity nonaqueous solvents. Therefore, when purifying nonaqueous solvents using the above-mentioned method, a pretreatment is also performed prior to the purification to remove water from the ion exchange resin. Specifically, a dehydration process is performed in which a nonaqueous solvent for pretreatment (hereinafter referred to as a "pretreatment solvent") is passed through an ion exchange resin to remove the water from the pretreatment solvent.

[0003] In such dehydration treatment of ion exchange resins, it is preferable to use as little pretreatment solvent as possible from the viewpoints of running costs and environmental impact. Patent Document 1, on the other hand, describes a technique in which the pretreatment solvent in a tank is circulated along a circulation path including a column containing ion exchange resin and a moisture removal device having a moisture adsorbent such as zeolite. This makes it possible to reuse the pretreatment solvent used in the dehydration treatment of the ion exchange resin, thereby reducing the moisture content of the ion exchange resin with a smaller amount of pretreatment solvent.

[0004] Japanese Patent Application Laid-Open No. 2020-121261

[0005] The technology described in Patent Document 1 requires replacing the moisture removal device depending on usage conditions (such as the number of uses and duration of use), and as the frequency of replacement increases, the impact on running costs increases. Therefore, there is room for improvement in this technology. Furthermore, when this technology is applied to ion exchange resins with particularly high moisture contents, the load on the moisture removal device increases, which may lead to early breakthrough of the moisture adsorbent. Therefore, it is preferable to dry such ion exchange resins in advance, such as by vacuum drying, but this complicates the entire pretreatment process.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a simple and economical pretreatment device and pretreatment method for ion exchange resins.

[0007] In order to achieve the above-mentioned object, the pretreatment device for ion exchange resin of the present invention removes moisture contained in the ion exchange resin by dissolving it into a pretreatment solvent, and includes a tank for storing a nonaqueous solvent as a pretreatment solvent, a circulation line for circulating the pretreatment solvent in the tank, a container provided in the circulation line for containing the ion exchange resin to be pretreated, a moisture removal device provided in the circulation line for removing moisture from the pretreatment solvent circulating through the circulation line, and a drainage line connected to either the circulation line between the tank and the container, or the container or the circulation line between the container and the moisture removal device, for discharging the pretreatment solvent to the outside.

[0008] In addition, the pretreatment method for ion exchange resin of the present invention uses the above-mentioned pretreatment device to dissolve and remove moisture contained in the ion exchange resin into a pretreatment solvent, and includes the steps of placing the ion exchange resin to be pretreated in a container, supplying the pretreatment solvent in the tank to the container through a circulation line to bring it into contact with the ion exchange resin to be pretreated, discharging the pretreatment solvent that has come into contact with the ion exchange resin to be pretreated to the outside through a drain line without flowing it into a moisture removal device, and circulating the pretreatment solvent in the tank along the circulation line after discharging the pretreatment solvent to the outside.

[0009] As described above, according to the present invention, a simple and economical pretreatment device and pretreatment method for ion exchange resins can be provided.

[0010] Fig. 1 is a schematic configuration diagram of a pre-treatment device according to a first embodiment of the present invention; Fig. 2 is a schematic configuration diagram showing a modified example of the pre-treatment device according to the first embodiment of the present invention; Fig. 3 is a schematic configuration diagram of a pre-treatment device according to a second embodiment of the present invention; Fig. 4 is a schematic configuration diagram showing a modified example of the pre-treatment device according to the second embodiment of the present invention.

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0012] 1 is a schematic diagram of a pretreatment device according to a first embodiment of the present invention. Note that the configuration of the pretreatment device shown in the figure is merely an example, and it goes without saying that it can be modified as needed, for example, by adding valves or measuring instruments.

[0013] Pretreatment device 1 performs dehydration treatment as a pretreatment for ion exchange resin. Specifically, a nonaqueous solvent for pretreatment (hereinafter referred to as "pretreatment solvent") is passed through the ion exchange resin to remove the water content by dissolving it into the pretreatment solvent. Pretreatment device 1 includes a tank 2 for storing the pretreatment solvent, a column 3, and a water removal device 4. A circulation line L1 for circulating the pretreatment solvent in tank 2 is connected to tank 2, and column 3 and water removal device 4 are provided on circulation line L1. In addition, circulation line L1 is provided with a liquid feed pump 5 for circulating the pretreatment solvent in tank 2 through circulation line L1.

[0014] The pretreatment solvent stored in tank 2 is not particularly limited, but if the ion exchange resin pretreated in pretreatment device 1 is used to purify a nonaqueous solvent, it is preferable that the pretreatment solvent be the same type of nonaqueous solvent as that nonaqueous solvent. Examples of such non-aqueous solvents include alcohol-based solvents such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, tert-butyl alcohol, ethylene glycol, diethylene glycol, propylene glycol monomethyl ether, butyl carbitol, and glycerin; amide-based solvents such as N-methyl-2-pyrrolidone; sulfur-containing solvents such as dimethyl sulfoxide and sulfolane; ester-based solvents such as propylene glycol monomethyl ether acetate, methyl lactate, ethyl lactate, ethyl acetate, butyl acetate, isoamyl acetate, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and γ-butyrolactone; amine-based solvents such as monoethanolamine; ketone-based solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; hydrocarbon-based solvents such as toluene, xylene, and cyclohexane; ether-based solvents such as 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, and ethoxymethoxyethane; and mixtures thereof.

[0015] Column 3 is a container made of, for example, resin, for containing the ion exchange resin to be pretreated. The ion exchange resin to be pretreated is not particularly limited and may be either a cation exchange resin or an anion exchange resin. Examples of cation exchange resins include strongly acidic cation exchange resins and weakly acidic cation exchange resins, while examples of anion exchange resins include strongly basic anion exchange resins and weakly basic anion exchange resins. The ion exchange resin to be pretreated may also be a chelate resin. For details of these ion exchange resins, see Patent Document 1. Column 3 is arranged so that the inlet and outlet for the pretreatment solvent are located at the bottom and top of column 3, respectively, allowing the pretreatment solvent to flow upward through column 3 (i.e., the ion exchange resin to be pretreated). The form in which the ion exchange resin is contained in column 3 is not particularly limited as long as it allows contact with the pretreatment solvent supplied to column 3.

[0016] The moisture remover 4 has the function of removing moisture from the pretreatment solvent circulating through the circulation line L1. The moisture remover 4 is not particularly limited, but a device having a moisture adsorbent made of zeolite is preferably used because it can remove moisture efficiently in a short period of time. That is, the moisture remover 4 preferably has, for example, a resin column and zeolite packed in the column as a moisture adsorbent. Examples of zeolites include crystalline zeolites such as A-type zeolite, X-type zeolite, Y-type zeolite, chabazite, ferrierite, ZSM-5, and clinoptilolite, and these can be used alone or in combination. The moisture remover 4 is arranged so that the inlet and outlet for the pretreatment solvent are located at the bottom and top of the moisture remover 4, respectively, thereby allowing the pretreatment solvent to flow upward through the moisture remover 4 (i.e., the zeolite).

[0017] The Si / Al molar ratio of the zeolite used in the moisture removal device 4 is preferably 1 to 5. This stabilizes the zeolite structure and ensures an appropriate cation content, allowing for good adsorption of moisture in the pretreatment solvent. The cations in the zeolite may or may not be ion-exchanged with lithium ions or calcium ions. From the viewpoint of moisture adsorption, the zeolite pore diameter is preferably 0.3 to 1 nm, more preferably 0.3 to 0.6 nm, and even more preferably 0.3 to 0.5 nm. The pore diameter here is a theoretical value estimated from the zeolite's crystal structure and the cation species retained. The zeolite is preferably spherical or cylindrical in shape, and its diameter is preferably 0.5 to 5 mm, allowing for good impregnation of the pretreatment solvent without compromising ease of handling.

[0018] An on-off valve V1 is provided in the circulation line L1 near the outlet of the column 3 (i.e., between the column 3 and the water removal device 4), and a drain line L2 is connected upstream of the on-off valve V1 via an on-off valve V2. As will be described in detail later, the drain line L2 is provided to discharge the pretreatment solvent that has flowed out of the column 3 to the outside. Note that, instead of the two on-off valves V1 and V2, a single three-way valve may be provided at the connection between the circulation line L1 and the drain line L2. Furthermore, a filtration device such as a filter may be provided in the circulation line L1 downstream of the water removal device 4 to capture and remove powdered zeolite produced from the water removal device 4.

[0019] In the above-described pretreatment device 1, the ion exchange resin to be pretreated is packed (stored) in the column 3, and then a draining step and a circulation treatment step are performed in this order to dehydrate the ion exchange resin. These two steps are described below. The following steps may be performed by an operator or automatically by a control device such as a controller.

[0020] The draining process is a process in which the pretreatment solvent in the tank 2 is passed only through the column 3 and discharged directly to the outside. When the draining process is initiated, the feed pump 5 is operated, and simultaneously, the on-off valve V1 in the circulation line L1 is closed and the on-off valve V2 in the draining line L2 is opened. As a result, the pretreatment solvent in the tank 2 is supplied to the column 3 through the circulation line L1 and comes into contact with the ion exchange resin in the column 3, thereby replacing the moisture contained in the ion exchange resin with the pretreatment solvent. As a result, the ion exchange resin is dehydrated in the column 3, and the moisture contained in the ion exchange resin is eluted and removed into the pretreatment solvent. The pretreatment solvent that has absorbed moisture in this way is discharged to the outside through the draining line L2 without being supplied (flowing into) the moisture removal device 4. The draining process is continued until a predetermined amount of pretreatment solvent is discharged. The discharged amount can be confirmed, for example, by an integrating flow meter (not shown) provided in the draining line L2.

[0021] The circulation process is a process in which the pretreatment solvent in the tank 2 is passed through the column 3 and the water removal device 4 and the pretreatment solvent is returned to the tank 2. This process is performed following the drainage process. That is, once it is confirmed that a predetermined amount of the pretreatment solvent has been discharged in the drainage process, the on-off valve V1 in the circulation line L1 is opened and the on-off valve V2 in the drainage line L2 is closed, thereby ending the drainage process and simultaneously starting the circulation process. Thus, in the circulation process, the ion exchange resin is dehydrated in the column 3, as in the drainage process, but the pretreatment solvent that absorbed water there is supplied to the water removal device 4 through the circulation line L1. The pretreatment solvent supplied to the water removal device 4 then has water removed by contact with a water adsorbent made of zeolite, after which it is returned to the tank 2 through the circulation line L1 and stored there. Thus, by circulating the pretreatment solvent in the tank 2 along the circulation line L1, the pretreatment solvent used in the dehydration process of the ion exchange resin in the column 3 is reused after water is removed by the water removal device 4.

[0022] The circulation treatment step is performed until it is confirmed that the water content of the ion exchange resin in the column 3 has been sufficiently reduced so that almost no water is eluted from the ion exchange resin into the pretreatment solvent. Whether or not water is eluting from the ion exchange resin can be confirmed, for example, by checking whether the measured water concentration of the pretreatment solvent sampled near the outlet of the column 3 is equal to or less than a predetermined value (e.g., 10 mg / L). The Karl Fischer (KF) method is preferably used to measure the water concentration in the pretreatment solvent, as this method is highly reliable and enables highly accurate quantitative analysis of water.

[0023] The flow rate of the pretreatment solvent in each step is not particularly limited for the column 3 as long as it is within a range that can reduce the water content of the ion exchange resin, and is not particularly limited for the water removal device 4 as long as it is within a range that can reduce the water concentration in the pretreatment solvent. The direction of flow of the pretreatment solvent for the column 3 may be either upward or downward, and the direction of flow of the pretreatment solvent for the water removal device 4 may also be either upward or downward. However, in order to facilitate the discharge to the outside of air bubbles that may be generated or mixed in during the flow, an upward flow is preferred in both cases, as shown in the figure.

[0024] As described above, according to this embodiment, the drain line L2 is connected to the downstream side of the column 3 in the circulation line L1, allowing the pretreatment solvent that flows out of the column 3 immediately after the start of flowing the liquid through the column 3 to be directly discharged to the outside. This prevents pretreatment solvent containing a large amount of water from being supplied to the water removal device 4, thereby reducing the load on the water removal device 4. As a result, the life of the water adsorbent (zeolite) is extended, thereby reducing the frequency of replacement of the water removal device 4 and suppressing increases in running costs. Furthermore, since prior drying such as vacuum drying is not required for ion exchange resins with particularly high water contents, further pretreatment is not required. The amount of pretreatment solvent discharged is not particularly limited, but is preferably at least 0.1 times the volume of the ion exchange resin to be pretreated, as shown in the examples described below.

[0025] 2(a) and 2(b) are schematic diagrams showing modified examples of the pretreatment device of this embodiment.

[0026] The position of the drain line L2 relative to the column 3 is not limited to the position shown in the figure, as long as the pretreatment solvent that has come into contact with the ion exchange resin in the column 3 can be discharged to the outside without flowing into the water removal device 4. For example, as shown in FIG. 2( a), the drain line L2 may be directly connected to the column 3 (specifically, to its upper side). In this case, both the draining step and the circulation treatment step are performed in the same manner as described above. Alternatively, as shown in FIG. 2( b), the drain line L2 may be connected to the circulation line L1 near the inlet of the column 3 (in other words, between the tank 2 and the column 3). In this case, the circulation treatment step is performed in the same manner as described above, while the draining step is performed in a different manner.

[0027] That is, in the modified example shown in FIG. 2( b), when the draining step is started, the on-off valves V1 and V2 of the circulation line L1 and the drain line L2 are both closed, and an air vent valve (not shown) provided at the top of the column 3 is opened. At the same time, the feed pump 5 is operated, and the pretreatment solvent in the tank 2 is supplied to the column 3 through the circulation line L1 and accumulated in the column 3. Then, when the ion exchange resin in the column 3 is immersed in the pretreatment solvent, the feed pump 5 is stopped, and the supply of the pretreatment solvent to the column 3 is stopped. Thus, in the column 3, the ion exchange resin is immersed in and comes into contact with the pretreatment solvent, thereby dehydrating the ion exchange resin. Then, the on-off valve V2 of the drain line L2 is opened, and the pretreatment solvent accumulated in the column 3 is discharged to the outside through the drain line L2. Then, when draining of the pretreatment solvent is completed, the on-off valve V2 of the drain line L2 and the above-mentioned air vent valve are closed, and the on-off valve V1 of the circulation line L1 is opened. At the same time, the liquid feed pump 5 is operated again to start circulating the pretreatment solvent through the circulation line L1, thereby starting the circulation treatment process.

[0028] 2(b), the on-off valve V1 may be a three-way valve. In this case, the air in the column 3 can be purged by switching the three-way valve, thereby allowing the column 3 to be filled with the pretreatment solvent in the draining step, and therefore the above-mentioned air purging valve does not need to be provided. Furthermore, the on-off valve V2 may also be a three-way valve provided at the connection between the circulation line L1 and the draining line L2.

[0029] Second Embodiment Fig. 3 is a schematic diagram of a pretreatment device according to a second embodiment of the present invention. Hereinafter, the same components as those in the first embodiment will be denoted by the same reference numerals in the drawing and their description will be omitted, and only the components different from those in the first embodiment will be described.

[0030] In the first embodiment, the water removal device 4 is provided downstream of the column 3 in the circulation line L1, but from the viewpoint of reusing the pretreatment solvent, the positions of the two may be reversed, as shown in Fig. 3. That is, in the present embodiment, the column 3 is provided downstream of the water removal device 4. Accordingly, the drainage line L2 including the on-off valve V1 and the on-off valve V2 is provided in the circulation line L1 near the outlet of the column 3 (i.e., between the column 3 and the tank 2). As a result, this embodiment differs from the first embodiment in that the pretreatment solvent is passed through not only the column 3 but also the water removal device 4 in the drainage step, but the effects obtained are similar to those of the first embodiment.

[0031] In this embodiment, the position of the drain line L2 relative to the column 3 is not limited to the position shown in the figure and may be changed, for example, as in the first embodiment. That is, the drain line L2 may be directly connected to the column 3 (specifically, to the upper side surface thereof) as shown in Fig. 4(a), or may be connected to the circulation line L1 near the inlet of the column 3 (in other words, between the water removal device 4 and the column 3) as shown in Fig. 4(b).

[0032] Next, the effects of the present invention will be described with reference to specific examples.

[0033] Example 1 In this example, the dehydration treatment of an ion exchange resin was repeatedly performed using the pretreatment device shown in FIG. 1 to verify how many dehydration treatments could be performed before the water removal device needed to be replaced. Specifically, a column was first filled with unused ion exchange resin, and a predetermined amount of pretreatment solvent was discharged in the draining step. A circulating treatment step was then performed for 17 hours. The water concentration in the pretreatment solvent sampled from the outlet of the column after the circulating treatment step was measured by the KF method. The dehydration treatment of the ion exchange resin was considered complete when the measured value was below 10 mg / L. This dehydration treatment was repeated, and the number of dehydration treatments performed up to the point at which the water concentration in the pretreatment solvent no longer fell below the threshold after the circulating treatment step, i.e., the point at which the water removal device had broken through, was determined.

[0034] A fluororesin column with an inner diameter of 16 mm and a height of 200 mm was used, packed with 20 mL of an ion exchange resin with a water content of 8 wt%. A weakly basic anion exchange resin, specifically a styrene-based MP (macroporous) weakly basic anion exchange resin with dimethylamine groups as anion exchange groups, was used as the ion exchange resin packed in the column (i.e., the target of pretreatment). A fluororesin column with an inner diameter of 16 mm and a height of 200 mm packed with 20 mL of zeolite with a pore size of 0.5 nm was used as the water removal device. An ethylene carbonate / dimethyl carbonate mixed solvent (volume ratio 1:1) with a water concentration of less than 10 mg / L was used as the pretreatment solvent, and 1 BV of this solvent was discharged in the drainage process. The space velocity of the pretreatment solvent was 10 h for both the column and the water removal device throughout the drainage and circulation processes. －１ It should be noted that BV is a unit that indicates how many times the volume of the ion exchange resin in the column it corresponds to.

[0035] (Example 2) An ion exchange resin having a water content of 61% by weight was prepared as the ion exchange resin to be pretreated, and verification was carried out under the same conditions as in Example 1, except that 4 BV of the pretreatment solvent was discharged in the draining step.

[0036] Comparative Example 1 Verification was carried out under the same conditions as in Example 1, except that the draining step was not carried out before the circulation treatment step.

[0037] Comparative Example 2 Verification was carried out under the same conditions as in Example 2, except that the draining step was not carried out before the circulation treatment step.

[0038] Example 3 In this example, a different method from Example 1 was used to verify how many dehydration treatments could be performed before the water removal device needed to be replaced. Specifically, an unused ion exchange resin with a water content of 0.5 wt% was prepared as the ion exchange resin to be pretreated. Then, while a pretreatment solvent was passed through a column packed with the resin, the water concentration in the pretreatment solvent collected from the column outlet was measured over time using the KF method. The pretreatment solvent was passed through until the measured value fell below 10 mg / L, and the total amount of water eluted from the ion exchange resin up to that point was calculated based on the change in the measured water concentration over time. From the calculated total amount of water, the number of dehydration treatments that could be performed until the water adsorption capacity of the zeolite reached its saturated adsorption capacity was calculated, assuming that the ion exchange resin was repeatedly dehydrated under the same conditions as Example 1. Other conditions were the same as Example 1.

[0039] (Example 4) The same ion exchange resin as in Example 1 was prepared as the ion exchange resin to be pretreated, and verification was carried out under the same conditions as in Example 3, except that it was assumed that 0.5 BV of the pretreatment solvent was discharged in the drainage step.

[0040] Comparative Example 3 A verification was carried out under the same conditions as in Example 3, except that it was assumed that the draining step was not carried out before the circulation treatment step.

[0041] Table 1 shows the verification results of Examples 1 to 4 and Comparative Examples 1 to 3. For reference, Table 1 also shows the water content of the ion exchange resin to be pretreated and the amount of pretreatment solvent discharged in the drainage step.

[0042]

[0043] As shown in Table 1, it was confirmed that in Examples 1 to 4, the number of times the moisture removal device could be used (the number of dehydration treatments that could be performed before the moisture removal device needed to be replaced) was increased compared to the corresponding Comparative Examples (Comparative Examples in which the moisture content of the ion exchange resin to be pretreated was the same). In addition, when Example 1 and Example 4 were compared, better results were obtained in Example 1, which discharged a larger amount of pretreatment solvent. From these results, it is believed that discharging a certain amount of pretreatment solvent immediately after the start of dehydration treatment reduced the load on the moisture removal device, thereby extending the life of the zeolite.

[0044] Furthermore, in Example 2, the water removal device could be used eight times, whereas in Comparative Example 2, the water concentration in the pretreatment solvent did not fall below 10 mg / L after the first circulation treatment step, and the dehydration treatment of the ion exchange resin was not even completed. Therefore, it is clear that, particularly when performing dehydration treatment of ion exchange resins with high water contents, it is very effective to discharge a certain amount of pretreatment solvent immediately after the start of the treatment.

[0045] REFERENCE SIGNS LIST 1 Pretreatment device 2 Tank 3 Column 4 Water removal device 5 Liquid transfer pump L1 Circulation line L2 Drain line V1, V2 Open / close valve

Claims

1. A pretreatment device for ion exchange resins that removes moisture contained in the ion exchange resins by dissolving it into a pretreatment solvent, the pretreatment device comprising: a tank that stores a non-aqueous solvent as the pretreatment solvent; a circulation line that circulates the pretreatment solvent in the tank; a container that is provided in the circulation line and that contains the ion exchange resin to be pretreated; a moisture removal device that is provided in the circulation line and that removes moisture from the pretreatment solvent circulating through the circulation line; and a drainage line that is connected to either the circulation line between the tank and the container, the container, or the circulation line between the container and the moisture removal device, and that discharges the pretreatment solvent to the outside.

2. The pretreatment device according to claim 1, wherein the moisture removal device has a moisture adsorbent made of zeolite.

3. The pretreatment device according to claim 2, wherein the moisture removal device is arranged so that the pretreatment solvent flows upward through the moisture adsorbent.

4. A pretreatment device according to any one of claims 1 to 3, wherein the container is arranged so that the pretreatment solvent flows upward through the ion exchange resin to be pretreated.

5. A pretreatment method for ion exchange resins, using a pretreatment device according to any one of claims 1 to 3, in which moisture contained in the ion exchange resins is removed by dissolving it into a pretreatment solvent, the pretreatment method comprising the steps of: placing the ion exchange resin to be pretreated in the container; supplying the pretreatment solvent in the tank to the container through the circulation line to bring it into contact with the ion exchange resin to be pretreated; discharging the pretreatment solvent that has come into contact with the ion exchange resin to be pretreated to the outside through the drain line without flowing it into the moisture removal device; and, after discharging the pretreatment solvent to the outside, circulating the pretreatment solvent in the tank along the circulation line.

6. The pretreatment method according to claim 5, wherein the ion exchange resin to be pretreated has a water content of 0.1% by weight or more.

7. The pretreatment method according to claim 5, wherein the step of discharging includes discharging the pretreatment solvent to the outside in an amount equal to or greater than 0.1 times the volume of the ion exchange resin to be pretreated.

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