JP7593435B2 - Method for separating anion exchange resin and cation exchange resin in mixed ion exchange resin - Google Patents

Description

The present invention relates to a method for separating and regenerating anion exchange resin and cation exchange resin used in non-regenerative ion exchange devices and mixed-bed ion exchange devices used in pure water production systems, etc.

In pure water production systems, impurities in raw water are removed to improve the purity of the water. In order to remove ionic impurities, i.e., anionic and cationic impurities, a mixed-bed ion exchange system filled with mixed ion exchange resins, which are a mixture of anion exchange resin and cation exchange resin, is widely used. In this mixed-bed ion exchange system, when the ion exchange resin exchanges an amount of ions equivalent to the ion exchange capacity, it cannot remove any more ionic impurities and breaks through. Therefore, after a certain amount of treated water has been treated, the ion exchange resins are recovered from the mixed-bed ion exchange system and regenerated with hydrochloric acid or caustic soda in a cation exchange resin regeneration tower and an anion exchange resin regeneration tower, respectively, for reuse. In this case, the anion exchange resin and the cation exchange resin are generally separated by passing the water in an upward flow and taking advantage of the difference in sedimentation speed due to the difference in specific gravity between the anion exchange resin and the cation exchange resin.

An example of this mixed ion exchange resin separation tower is shown in FIG. 4. In FIG. 4, the mixed ion exchange resin separation tower 21 has a cylindrical separation tower body 21A with an inlet/outlet 22 at the bottom, a water supply pipe 23 with multiple discharge nozzles 23A as a water discharge section, and a drain port 24 at the top. A water collection plate 25 is arranged below the discharge nozzles 23A of the separation tower body 21A. An anion exchange resin discharge pipe 26 as an anion exchange resin discharge section is provided near the middle of the separation tower 21 in the vertical direction, and a cation exchange resin discharge pipe 27 is provided below the anion exchange resin discharge pipe 26 and slightly above the water supply pipe 23. In addition, a peep hole 28 is formed on the side of the separation tower 21. 29 is an inlet for used mixed ion exchange resin provided on the upper side of the side of the separation tower 21.

In such a mixed ion exchange resin separation tower 21, used mixed ion exchange resin is put into the separation tower 21, followed by passing a NaOH solution of about 4% by weight through it, and after leaving it for a predetermined time, pure water is poured in through the inlet/outlet 22 and the NaOH solution in the separation tower is pushed out through the outlet 24 for cleaning. Then, the separation tower 21 is filled with a predetermined amount of separation water (pure water). At this time, the water level of the separation water is set to be higher than the top surface of the mixed ion exchange resin, for example, about 500 mm or less higher.

Next, air is injected into the separation tower 21 through the inlet/outlet 22 to bubble the mixed ion exchange resin, loosening the resin particles that have become entangled in a colloidal state. After that, the bubbling is stopped and the mixed ion exchange resin is allowed to settle on the water collection plate 25. At this time, the cation exchange resin, which has a high specific gravity, settles first, and the anion exchange resin, which has a low specific gravity, settles later. Next, in preparation for backwashing, pure water (water for separation) is introduced through the inlet/outlet 22 so that the separation tower 21 is filled with water.

In this full-water state, pure water is discharged from the discharge nozzle 23A and passed through in an upward flow, and adjustments are made while visually checking through the observation window 28 so that the separation interface is at the lower end of the suction port of the anion exchange resin extraction pipe 26. Then, the anion exchange resin is sucked through the anion exchange resin extraction pipe 26 and discharged as an anion exchange resin/water mixed phase flow, which is then removed. After draining, this anion exchange resin/water mixed phase flow is transferred to the anion exchange resin regeneration tower for anion exchange resin regeneration treatment.

After the anion exchange resin has been extracted in this manner, pure water is continuously discharged from the discharge nozzle 23A while being sucked through the cation exchange resin extraction pipe 27, and is discharged and extracted as a cation exchange resin/water mixed phase flow. This cation exchange resin/water mixed phase flow is drained and then transferred to a cation exchange resin regeneration tower for cation exchange resin regeneration treatment. At this time, the cation exchange resin is not completely removed, but a certain amount is left to prevent contamination with anion exchange resin.

However, the above-mentioned backwash separation method for anion exchange resin and cation exchange resin has a problem in that the separation between the two is insufficient. In particular, the cation exchange resin can be separated well by leaving the interface portion in the separation tower 21, but there is a problem in that the cation exchange resin is likely to be mixed with the anion exchange resin that is extracted first.

Therefore, a method called the Seplex method is used, which uses a highly concentrated NaOH solution to separate the anion exchange resin and the cation exchange resin. The Seplex method is carried out using the process shown in Figure 5.

That is, using the separation tower 21 shown in FIG. 4 described above, after the anion exchange resin is extracted in the backwash separation process in FIG. 5, it is transferred to an advanced separation tower (Seplex tower) dedicated to the separation of cation exchange resin mixed with a small amount of anion exchange resin together with the ultrapure water used for separation. A NaOH solution having a specific gravity intermediate between the specific gravity of the wet anion exchange resin and the specific gravity of the wet cation exchange resin is injected into this Sepplex tower. For example, as shown in FIG. 6, when the specific gravity of the porous anion exchange resin when wet is 1.05 g/mL and the specific gravity of the porous cation exchange resin when wet is 1.28 g/mL, a 16% NaOH solution (specific gravity 1.18 g/mL) having a specific gravity intermediate between the two is injected. As a result, the anion exchange resin floats and the cation exchange resin precipitates, so the cation exchange resin is extracted and removed from the bottom of the Sepplex tower. Then, pure water is supplied into the tower to extrude and wash the NaOH solution, and the remaining anion exchange resin is extracted (advanced separation process). The extracted anion exchange resin is transferred to an anion exchange resin regeneration tower, where the anion exchange resin is regenerated and washed by a standard method. Meanwhile, the cation exchange resin separated in the separation tower during the separation process is transferred to a cation exchange resin regeneration tower, where the cation exchange resin is regenerated and washed by a standard method.

The Seplex method described above makes it possible to separate trace amounts of cation exchange resin mixed into the anion exchange resin. However, in order to produce ultrapure water of even higher purity, it is necessary to separate the anion exchange resin and the cation exchange resin to a higher degree. However, in the Seplex method described above, if there is a large amount of crushed cation exchange resin mixed into the anion exchange resin, the cation exchange resin does not settle but remains in the anion exchange resin, so there is still room for improvement in the separation performance between the anion exchange resin and the cation exchange resin.

The present invention has been made in consideration of the above problems, and aims to provide a method for separating anion exchange resin and cation exchange resin in a mixed ion exchange resin, which is capable of excluding crushed resin when separating anion exchange resin and cation exchange resin with high accuracy using the Seplex method.

In view of the above object, the present invention is a method for separating anion exchange resin and cation exchange resin in a mixed ion exchange resin of anion exchange resin and cation exchange resin, comprising a separation step in which the mixed ion exchange resin is charged into a separation tower, and air and separation water are passed through the separation tower in an upward flow to separate the mixed ion exchange resin into anion exchange resin and cation exchange resin by utilizing the difference in specific gravity; an anion exchange resin transfer step in which the anion exchange resin above the separation interface between the anion exchange resin and the cation exchange resin in the separation tower is extracted from the anion exchange resin extraction section and transferred to an advanced separation tower; and an anion exchange resin advanced separation step in which the cation exchange resin mixed in the anion exchange resin transferred to the advanced separation tower is separated with a solution having an intermediate specific gravity between the anion exchange resin and the cation exchange resin. The method includes a step of extracting the anion exchange resin from the bottom of the high-speed separation tower, a step of extracting the cation exchange resin from the bottom of the high-speed separation tower, and a step of extracting the anion exchange resin thereafter. In the high-speed separation step, the anion exchange resin transferred to the high-speed separation tower is immersed in a solution having an intermediate specific gravity between the anion exchange resin and the cation exchange resin, and is bubbled from the bottom of the high-speed separation tower at LV = 0.5 m / min or more. Then, by stopping the bubbling and leaving it to stand, the mixed cation exchange resin is allowed to settle and is extracted from the bottom of the high-speed separation tower. When extracting the anion exchange resin, 95 volume % or less of the anion exchange resin layer is extracted from the lower layer, and 5 volume % or more of the upper layer is discarded or separated again in a separation step. (Invention 1)

According to this invention (Invention 1), when the anion exchange resin, which has been subjected to primary separation into anion exchange resin and cation exchange resin by backwash separation, is separated in a high-speed separation tower with a solution having an intermediate specific gravity between the anion exchange resin and the cation exchange resin, if bubbling is performed at an LV (linear velocity) of at least a certain flow rate, the crushed ion exchange resin (anion exchange resin and cation exchange resin) will be located above the anion exchange resin layer. Therefore, when the last anion exchange resin is extracted from the high-speed separation tower, 95% or less by volume of the bottom of the entire layer is extracted, which prevents the crushed resin from being mixed in and enables the anion exchange resin to be separated to a high degree.

In the above invention (Invention 1), it is preferable that the solution with an intermediate specific gravity between the anion exchange and cation exchange resins is a NaOH solution (Invention 2).

According to this invention (Invention 2), the NaOH solution can have a specific gravity between the specific gravity of the anion exchange resin when wet and the specific gravity of the cation exchange resin when wet, so the anion exchange resin can be suspended and the cation exchange resin mixed in the anion exchange resin can be suitably separated.

In the above invention (Invention 1 or 2), it is preferable that both the anion exchange resin and the cation exchange resin are porous ion exchange resins (Invention 3).

According to this invention (Invention 3), the specific gravity of the NaOH aqueous solution can be set to be intermediate between the specific gravity of the porous anion exchange resin when wet and the specific gravity of the porous ion exchange resin when wet, and is 5% by weight to 30% by weight. By using such an NaOH aqueous solution, the cation exchange resin mixed in the anion exchange resin can be suitably separated.

According to the method of separating anion exchange resin and cation exchange resin in a mixed ion exchange resin of the present invention, when the anion exchange resin that has been subjected to primary separation into anion exchange resin and cation exchange resin by backwash separation is separated in a high-speed separation tower with a solution having an intermediate specific gravity between the anion exchange resin and the cation exchange resin, bubbling is performed at a LV (linear velocity) of at least a certain flow rate, and then at the time of the final anion exchange resin withdrawal, 95% or less by volume of the lower part of the entire layer is withdrawn, so that it is possible to prevent the inclusion of crushed ion exchange resin and to separate the anion exchange resin to a high degree.

FIG. 2 is a process diagram showing a method for separating anion exchange resin and cation exchange resin in a mixed ion exchange resin according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing a separation state after bubbling of a cation exchange resin mixed in an anion exchange resin in the advanced separation step of the embodiment. FIG. 2 is a schematic diagram showing a state after separation of the cation exchange resin mixed in the cation exchange resin in the advanced separation step of the embodiment. FIG. 2 is a schematic diagram showing an example of a separation column for anion exchange resin and cation exchange resin in a mixed ion exchange resin. FIG. 1 is a process diagram showing a method for separating anion exchange resin and cation exchange resin in a conventional mixed ion exchange resin by the Seplex method. FIG. 1 is a schematic diagram showing the principle of the Sepplex method.

The method for separating the anion exchange resin and the cation exchange resin in the mixed ion exchange resin of the present invention will be described in detail below with reference to the attached drawings.

[Configuration of mixed ion exchange resin separation system]
The method for separating the anion exchange resin and the cation exchange resin in the mixed ion exchange resin of this embodiment can be carried out, for example, by using a configuration consisting of a separation tower, a cation exchange resin regeneration tower, and a Seplex tower (anion exchange resin high-speed separation tower) as shown in FIG.

[Mixed ion exchange resins]
The mixed ion exchange resin to be separated in this embodiment is a mixed resin of anion exchange resin and cation exchange resin. The ratio (volume ratio) of anion exchange resin to cation exchange resin in this mixed ion exchange resin is not particularly limited, but is about 30:70 to 70:30.

The anion exchange resin and the cation exchange resin are both preferably porous ion exchange resins. The porous anion exchange resin has a specific gravity (when wet) of, for example, about 1.03 to 1.09 g/mL, and the porous cation exchange resin has a specific gravity (when wet) of, for example, about 1.22 to 1.30 g/mL.

[Method for separating anion exchange resin and cation exchange resin in mixed ion exchange resin]
Next, the method for separating the mixed ion exchange resin of this embodiment using the above-mentioned apparatus configuration will be described with reference to the flow chart shown in FIG.

(Backwash separation process)
The backwashing separation step is the same as the backwashing separation step in FIG. 5 described above, and therefore a detailed description thereof will be omitted.

(Anion exchange resin advanced separation process)
The anion exchange resin taken out in the separation process contains a small amount of cation exchange resin mixed in. Therefore, the following operation is carried out in the Seplex column as an advanced separation column.

First, the anion exchange resin separated in the backwash separation process described above is loaded into the Seplex tower, and then an aqueous NaOH solution is injected. This NaOH solution is set to a concentration of 5-30% by weight so that it has a specific gravity intermediate between that of the anion exchange resin and cation exchange resin when wet. For example, if the anion exchange resin and cation exchange resin are porous, the NaOH solution should have a concentration of 9-25% by weight. This NaOH solution has a specific gravity of approximately 1.10-1.27 g/mL.

Next, air is injected into the Seplex tower from the inlet and outlet, and the anion exchange resin is bubbled for a predetermined time. At this time, the flow rate of the bubbling is set to LV = 0.5 m / min or more, especially 1 m / min or more. This causes the crushed cation exchange resin and the crushed anion exchange resin to float. Then, by leaving it to stand, as shown in Figure 2, in the Seplex tower 1, the uncrushed cation exchange resin 3, which has a larger specific gravity than the NaOH solution 4, settles, and the anion exchange resin 2 and the crushed ion exchange resin (anion exchange resin + cation exchange resin) 5, which have a smaller specific gravity than this, float. Therefore, the cation exchange resin 3 is sucked from the cation exchange resin extraction pipe (not shown) installed at the bottom of the Seplex tower 1 and discharged as a cation exchange resin / water mixed phase flow and extracted. After draining the water, this cation exchange resin / water mixed phase flow can be introduced together with the next separation and regeneration of the mixed ion exchange resin. It is preferable that such bubbling time is 2 minutes or more, especially 5 minutes or more. If the bubbling time is less than 2 minutes, the effect of floating the crushed cation exchange resin is insufficient. There is no particular upper limit on the bubbling time, but since the effect of floating the cation exchange resin is poor even if it exceeds 10 minutes, it is sufficient to set it to about 10 minutes. In the figure, the symbol 6 is a transfer pipe for the anion exchange resin (which contains a small amount of cation exchange resin) separated in the backwash separation process.

After that, when the inside of the Seplex tower 1 is replaced with water and the state shown in Figure 3 is reached, 95% or less by volume is extracted from the lower layer of the anion exchange resin layer, which is regenerated, washed, and reused. If more than 95% by volume is extracted at this time, there is a high risk of the crushed cation exchange resin layer being mixed in. On the other hand, 5% or more by volume of the remaining upper layer can be discarded or separated again in the separation process.

(Cation exchange resin regeneration process)
In the cation exchange resin regeneration tower, the same operation as in the conventional method is carried out. First, the cation exchange resin is charged into the cation exchange resin regeneration tower, and then an HCl solution as an inorganic acid is injected to regenerate the cation exchange resin.

Next, pure water is supplied into the cation exchange resin regeneration tower to push out and discharge the HCl solution from the tower, and the cation exchange resin is washed. In this way, the cation exchange resin can be regenerated. After regeneration, the cation exchange resin can be removed from the cation exchange resin regeneration tower and reused.

In the present embodiment described above, the anion exchange resin transferred to the Seplex tower is immersed in a solution with an intermediate specific gravity between the anion exchange resin and the cation exchange resin, and then bubbled from the bottom of the advanced separation tower at LV = 0.5 m / min or more. Therefore, the crushed ion exchange resin (anion exchange resin and cation exchange resin) is located above the anion exchange resin layer. After the mixed cation exchange resin is allowed to settle and extracted from the bottom of the advanced separation tower, 95 volume % or less of the anion exchange resin layer is extracted from the lower layer when extracting the anion exchange resin, thereby enabling the anion exchange resin to be separated to a high degree in the advanced separation tower.

The present invention has been described above based on the above embodiment, but in the advanced separation step, the anion exchange resin transferred to the advanced separation tower is immersed in a solution with an intermediate specific gravity between the anion exchange resin and the cation exchange resin, bubbled from the bottom of the advanced separation tower at LV = 0.5 m / min or more, and then left to stand, the mixed cation exchange resin is allowed to settle and extracted from the lower part of the advanced separation tower, and when extracting the anion exchange resin, it is possible to implement various modifications as long as 95 volume % or less of the anion exchange resin layer is extracted from the lower layer. For example, in an advanced separation tower (Seplex tower), the anion exchange resin and the cation exchange resin are highly separated, the upper crushed resin is removed, and the remaining anion exchange resin is regenerated in the Sepplex tower.

The present invention will be described in more detail with reference to the following specific examples.

[Comparative Example 1]
In the separation method shown in FIG. 5, a mixed resin of a porous anion exchange resin (specific gravity 1.05 g/mL when wet) and a porous cation exchange resin (specific gravity 1.28 g/mL when wet) was backwashed and separated in a separation tower. Only the anion exchange resin after separation was transferred to a Seplex tower, and 16 wt % NaOH solution (specific gravity 1.28 g/mL) was injected and immersed in this solution, and bubbling was performed for 10 minutes at LV = 0.15 m / min. After that, it was left to stand for 30 minutes, and the sunk cation exchange resin was extracted. Next, the inside of the Seplex tower was replaced with water, and 90 volume % of the lower layer of the anion exchange resin layer was extracted and regenerated and washed. The regenerated anion exchange resin and cation exchange resin were mixed in a volume ratio of 3:1, and ultrapure water was passed through this mixed ion exchange resin, and the Na concentration of the obtained treated water was measured and found to be 2 ng / L.

[Comparative Example 2]
In the separation method shown in FIG. 5, a mixed resin of a porous anion exchange resin (specific gravity when wet: 1.05 g/mL) and a porous cation exchange resin (specific gravity when wet: 1.28 g/mL) was backwashed and separated in a separation tower. Only the anion exchange resin after separation was transferred to a Seplex tower, and 16 wt % NaOH solution (specific gravity: 1.28 g/mL) was injected and immersed in this solution, and bubbling was performed for 1 minute at LV = 0.15 m/min. After that, it was left to stand for 30 minutes, and the sunk cation exchange resin was extracted. Next, the inside of the Seplex tower was replaced with water, and 95 volume % of the lower layer of the anion exchange resin layer was extracted and regenerated and washed. The regenerated anion exchange resin and cation exchange resin were mixed in a volume ratio of 3:1, and ultrapure water was passed through this mixed ion exchange resin, and the Na concentration of the obtained treated water was measured and found to be 4 ng/L.

[Example 1]
In the separation method shown in FIG. 1, a mixed resin of a porous anion exchange resin (specific gravity when wet: 1.05 g/mL) and a porous cation exchange resin (specific gravity when wet: 1.28 g/mL) was backwashed and separated in a separation tower. Only the anion exchange resin after separation was transferred to a Seplex tower, and 16 wt % NaOH solution (specific gravity: 1.28 g/mL) was injected and immersed in this solution, and bubbling was performed for 10 minutes at LV = 0.5 m / min. After that, it was left to stand for 30 minutes, and the sunk cation exchange resin was extracted. Next, the inside of the Seplex tower was replaced with water, and 95 volume % of the lower layer of the anion exchange resin layer was extracted and regenerated and washed. The regenerated anion exchange resin and cation exchange resin were mixed in a volume ratio of 3:1, and ultrapure water was passed through this mixed ion exchange resin, and the Na concentration of the obtained treated water was measured and found to be 0.5 ng / L.

[Example 2]
In the separation method shown in FIG. 1, a mixed resin of a porous anion exchange resin (specific gravity when wet: 1.05 g/mL) and a porous cation exchange resin (specific gravity when wet: 1.28 g/mL) was backwashed and separated in a separation tower. Only the anion exchange resin after separation was transferred to a Seplex tower, and 16 wt % NaOH solution (specific gravity: 1.28 g/mL) was injected and immersed in this solution, and bubbling was performed for 10 minutes at LV = 1.0 m/min. After that, it was left to stand for 30 minutes, and the sunk cation exchange resin was extracted. Next, the inside of the Seplex tower was replaced with water, and 95 volume % of the lower layer of the anion exchange resin layer was extracted and regenerated and washed. The regenerated anion exchange resin and cation exchange resin were mixed in a volume ratio of 3:1, and ultrapure water was passed through this mixed ion exchange resin. The Na concentration of the obtained treated water was measured and found to be 0.2 ng/L.

[Examples 3 to 6 and Comparative Examples 3 and 4]
In Example 1, the LV of the bubbling was changed in various ways, and then the mixture was left to stand for 30 minutes, and the sunk cation exchange resin was removed. Next, the inside of the Seplex column was replaced with water, and 95% by volume of the lower layer of the anion exchange resin layer was removed and regenerated and washed. The regenerated anion exchange resin and cation exchange resin were mixed in a volume ratio of 3:1, and ultrapure water was passed through the mixed ion exchange resin. The Na concentration of the resulting treated water was measured, and the results are shown in Table 1.

As is clear from Table 1, by setting the LV to 0.5 m/min or more, the Na concentration of the treated water can be reduced to 1 ng/L or less. This shows that there is very little contamination with cation exchange resin when regenerating the anion exchange resin.

[Example 7]
In Example 1, the bubbling time was changed at LV = 0.5 m/min, and then the mixture was left to stand for 30 minutes, and the sunk cation exchange resin was removed. Next, the inside of the Seplex column was replaced with water, and 95 volume % of the lower layer of the anion exchange resin layer was removed and regenerated and washed. The regenerated anion exchange resin and cation exchange resin were mixed in a volume ratio of 3:1, and ultrapure water was passed through this mixed ion exchange resin. The Na concentration of the resulting treated water was measured, and the results are shown in Table 2.

As is clear from Table 2, by bubbling for 2 minutes or more at LV = 0.5 m/min, the Na concentration of the treated water can be reduced to 1 ng/L or less. This shows that there is very little contamination of the cation exchange resin when regenerating the anion exchange resin.

1 Seplex column 2 Anion exchange resin 3 Cation exchange resin 4 NaOH solution 5 Crushed ion exchange resin (crushed cation exchange resin)
6 Transfer pipe 21 Mixed ion exchange resin separation tower 21A Separation tower body 22 Inlet/outlet port 23 Water supply pipe 23A Discharge nozzle 24 Drain port 25 Water collection plate 26 Anion exchange resin extraction pipe 27 Cation exchange resin extraction pipe 28 Observation window 29 Inlet for used mixed ion exchange resin

Claims (3)

A method for separating an anion exchange resin and a cation exchange resin from a mixed ion exchange resin of an anion exchange resin and a cation exchange resin, comprising the steps of:
a separation step of feeding the mixed ion exchange resin into a separation tower, and passing air and separation water through the separation tower in an upward flow manner to separate the mixed ion exchange resin into anion exchange resin and cation exchange resin by utilizing the difference in specific gravity;
an anion exchange resin transfer step in which the anion exchange resin above the separation interface between the anion exchange resin and the cation exchange resin in the separation tower is extracted from an anion exchange resin extraction section and transferred to a high-speed separation tower;
an anion exchange resin high-speed separation step of separating the cation exchange resin mixed in the anion exchange resin transferred to the high-speed separation tower with a solution having an intermediate specific gravity between the anion exchange resin and the cation exchange resin;
The method includes a cation exchange resin extraction step of extracting the cation exchange resin from the bottom of the high-speed separation tower, and a subsequent anion exchange resin extraction step,
In the high-speed separation step, the anion exchange resin transferred into the high-speed separation tower is immersed in a solution having an intermediate specific gravity between the anion exchange resin and the cation exchange resin, and bubbled from the bottom of the high-speed separation tower at LV = 0.5 m/min or more. Then, the bubbling is stopped and the tower is allowed to stand, whereby the mixed cation exchange resin is allowed to settle and is extracted from the bottom of the high-speed separation tower. When the anion exchange resin is extracted, 95 volume % or less of the anion exchange resin layer is extracted from the lower layer, and 5 volume % or more of the upper layer is discarded or separated again in a separation step. 2. The method for separating anion exchange resin and cation exchange resin from a mixed ion exchange resin according to claim 1, wherein the solution having an intermediate specific gravity between the anion exchange resin and the cation exchange resin is a NaOH solution. A method for separating anion exchange resin and cation exchange resin in a mixed ion exchange resin according to claim 1 or 2, wherein both the anion exchange resin and the cation exchange resin are porous ion exchange resins.

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