WO2024171825A1 - Ion exchange resin column and method for removing boron - Google Patents

Abstract

Disclosed is an ion exchange resin column 1 for boron removal, the ion exchange resin column 1 comprising a column body 2 and an ion exchange resin layer that is disposed within the column body 2, wherein water to be processed flows downward. With respect to this ion exchange resin column 1, the ion exchange resin layer comprises: a mixed bed resin layer M that is arranged as the lower layer; an anion exchange resin layer A that is arranged as the upper layer; and a boron adsorption resin layer B that is arranged between the mixed bed resin layer and the anion exchange resin. Also disclosed is a method for removing boron with use of this ion exchange resin column 1.

Description

Ion exchange resin tower and boron removal method

The present invention relates to an ion exchange resin tower, and more specifically to an ion exchange resin tower having a boron adsorption resin and an ion exchange resin, and having excellent boron removal performance. The present invention relates to an ion exchange resin tower that is particularly suitable for incorporation into the primary pure water system of an ultrapure water production system. The present invention also relates to a method for removing boron using this ion exchange resin tower.

Conventionally, ultrapure water production equipment that produces ultrapure water from raw water such as city water, groundwater, and industrial water basically consists of a pretreatment device, a primary pure water production device, and a secondary pure water production device. Of these, the pretreatment device consists of coagulation, flotation, filtration, and turbidity membrane devices. The primary pure water production device consists of one or more devices from the activated carbon adsorption tower, ultraviolet (UV) oxidation device, chemical oxidation device, degasification device, etc., and a desalination device, of which the desalination device consists of one or more combinations of reverse osmosis (RO) membrane separation devices, electric deionization devices, and ion exchange devices (mixed-bed ion exchange devices or ion exchange pure water devices). In addition, the secondary pure water production device is an appropriate combination of the same equipment units as the primary pure water production device, and generally consists of a low-pressure UV oxidation device, a mixed-bed ion exchange device, and an ultrafiltration (UF) membrane separation device.

In recent years, strict water quality standards have been required for ultrapure water production, such as boron levels of 1 ppt or less.

To remove boron, a boron adsorption resin tower may be installed downstream of the RO membrane separation device.

Patent Document 1 describes a pure water production system equipped with a boron adsorption device, which is filled with a boron-selective adsorption resin, as well as a cation exchange resin and an anion exchange resin.

Patent Document 2 describes how the breakthrough capacity (BTC) of the boron adsorption tower can be increased by appropriately controlling the water flow rate SV to the boron adsorption tower. Patent Document 2 also describes how the boron adsorption tower can be installed at the final stage of the primary pure water system.

JP 2005-828 A JP 2019-141775 A

The objective of the present invention is to provide an ion exchange resin tower that can efficiently adsorb and remove boron over a long period of time, and a method for removing boron using this ion exchange resin tower.

The ion exchange resin tower of the present invention is an ion exchange resin tower for removing boron, which has a tower body and an ion exchange resin layer provided within the tower body, through which the water to be treated flows downward, and which has as the ion exchange resin layer a mixed bed resin layer arranged in the lower layer, an anion exchange resin layer arranged in the upper layer, and a boron adsorption resin layer arranged between the mixed bed resin layer and the anion exchange resin layer.

In one embodiment of the present invention, the ratio of the layer height of the ion exchange resin layer to the total layer height is: anion exchange resin layer: 1-20%, boron adsorption resin layer: 2-30%, mixed bed resin layer: 50-97%.

In the boron removal method of the present invention, boron-containing water to be treated is passed through the ion exchange resin tower of the present invention in a downward flow.

The ion exchange resin tower and boron removal method of the present invention can efficiently adsorb and remove boron over a long period of time. In addition, the present invention can increase the breakthrough capacity (BTC) of the boron adsorbing ion exchange resin tower.

That is, in the present invention, an anion exchange resin layer is provided above the boron adsorption and removal layer, and the water to be treated introduced into the ion exchange resin tower first comes into contact with the anion exchange resin. As a result, carbonate ions and organic acid ions in the water to be treated are adsorbed by the anion exchange resin, and the pH of the water flowing from the anion exchange resin layer to the boron adsorption resin layer increases. At a pH of 7 or higher, boron in the water exists in the form of B(OH) ₄ ^- , and is therefore efficiently adsorbed by the boron adsorption resin.

In addition, in general, in an ion exchange resin tower, the downward flow velocity is greater toward the center of the tower (the center in the horizontal cross section; the same applies below). If an anion exchange resin layer is present above a boron adsorption resin layer, the treated water introduced into the ion exchange resin tower and flowing downward is subjected to a rectifying effect in the anion exchange resin layer (the effect of making the downward flow velocity distribution approximately equal in the horizontal cross section). As a result, the downward flow velocity distribution in the boron adsorption resin layer becomes smaller. As a result, the time difference until breakthrough between the center and peripheral sides of the boron adsorption removal layer becomes smaller, and the amount of boron adsorbed until breakthrough in the entire boron adsorption resin layer increases.

FIG. 2 is a schematic vertical cross-sectional view of an ion-exchange resin tower according to an embodiment. FIG. 1 is an explanatory diagram of an experimental apparatus. 1 is a graph showing the results of an example.

The following describes the embodiment with reference to the drawings.

As shown in Figure 1, the ion exchange resin tower 1 has a tower body 2 and a mixed bed resin layer M, a boron adsorption and removal layer B, and an anion exchange resin layer A, which are arranged in this tower body 2 from the bottom up. An inlet for the water to be treated is provided at the top of the tower body 2, and an outlet for the treated water is provided at the bottom. The water to be treated flows downward through this ion exchange resin tower 1.

The mixed bed resin layer M is a mixed layer of anion exchange resin and cation exchange resin. The mixing ratio of anion exchange resin to cation exchange resin is preferably 50:50 (weight ratio when dried, the same applies below), but it may be within the range of 50:50 to 90:10.

As a boron adsorption resin, one that adsorbs boron by ion exchange or chelating action is suitable, and commercially available products (e.g., Diaion CRB manufactured by Mitsubishi Chemical Corporation, Chelesto Fiber GRY manufactured by Chelesto Co., Ltd., etc.) can be used.

The height of the resin-filled layer (total layer height) in the tower body 2 is preferably 500 to 3500 mm, and more preferably 500 to 1000 mm.

The layer height of the anion exchange resin layer A in the total layer height is preferably 1 to 50%, particularly preferably 10 to 25%, and even more preferably 10 to 20%. The layer height of the boron adsorption resin layer B is preferably 2 to 30%, particularly preferably 15 to 25%, and the layer height of the mixed bed resin layer M is preferably 30 to 97%, particularly preferably 50 to 95%, and even more preferably 50 to 70%.

The water flow rate SV of the ion-exchange resin tower 1 is preferably about 20 to 200 hr ⁻¹ , particularly about 20 to 100 hr ⁻¹ .

In this ion exchange resin tower 1, an anion exchange resin layer A is provided above a boron adsorption removal layer B, and the water to be treated introduced into the ion exchange resin tower 1 first comes into contact with the anion exchange resin A. As a result, carbonate ions and organic acid ions in the water to be treated are adsorbed by the anion exchange resin A, increasing the pH of the water flowing from the anion exchange resin layer A to the boron adsorption resin layer B. At a pH of 7 or higher, boron in the water exists in the form of B(OH) ₄ ^- and is therefore efficiently adsorbed by the boron adsorption resin.

In addition, in this ion exchange resin tower 1, the anion exchange resin layer A is present above the boron adsorption resin layer B, so that the water to be treated that is introduced into the ion exchange resin tower 1 and flows downward is subjected to a rectifying effect in the anion exchange resin layer A (the effect of making the downward flow velocity distribution approximately equal in horizontal cross section). As a result, the downward flow velocity distribution in the boron adsorption resin layer B is smaller than when the anion exchange resin layer A is not provided. As a result, the time difference until breakthrough between the center and peripheral sides of the boron adsorption removal layer B is reduced, and the amount of boron adsorbed until breakthrough in the entire boron adsorption resin layer B is increased.

This ion exchange resin tower 1 is preferably installed at the most downstream part of the primary pure water system. In this case, the boron concentration in the water to be treated is preferably 5 to 1000 ng/L, and more preferably 50 to 800 ng/L. In addition, the resistivity of the water to be treated is preferably ≧10 MΩ·cm, and more preferably ≧15 MΩ·cm.

[Experimental Example 1]
As shown in FIG. 2, ion exchange columns (1) to (4) were constructed by packing ion exchange resins in cylindrical columns having an inner diameter of 20 mm.

In column (1), a boron adsorption and removal layer B was installed in the top layer, and a mixed bed resin layer M was installed below that. No anion exchange resin layer was installed.

In columns (2) to (4), an anion exchange resin layer A is provided in the top layer, a boron adsorption and removal layer B is provided below that (middle), and a mixed bed resin layer M is provided below that (bottom layer).

The total layer height is 1000 mm, and the layer height of each layer is as follows:
Column (1): B = 200 mm, M = 800 mm
Column (2): A = 100 mm, B = 200 mm, M = 700 mm
Column (3): A = 200 mm, B = 200 mm, M = 600 mm
Column (4): A = 500 mm, B = 200 mm, M = 300 mm

The ion exchange resins used are as follows:
Anion exchange resin: Commercially available product (manufactured by Mitsubishi Chemical Corporation)
Boron adsorption resin: Commercially available product (manufactured by Mitsubishi Chemical Corporation)
Cation exchange resin: Commercially available product (manufactured by Mitsubishi Chemical Corporation)

In all columns (1) to (4), the mixing ratio of anion exchange resin and cation exchange resin in the mixed bed resin layer M was 50:50 (weight ratio).

The treated water was ultrapure water containing boron, with 600 ng/L of B(OH) ₃ added as boron. The water was passed through the top of the column at 12.6 L/h (SV of boron adsorption resin layer = 200 hr ^-1 , SV of ion exchange resin tower (all layers) = 40 hr ^-1 ), and the boron concentration of the treated water flowing out from the bottom of the column was measured by ICP-MS. The change in the boron concentration of the treated water over time is shown in Figure 3.

<Considerations>
As shown in FIG. 3, columns (2) to (4) enable the boron concentration in the treated water to be maintained low for a long period of time.

Comparing the boron loading (mg-B/L-R) required to maintain the treated water boron concentration at 1 ng/L or less, columns (2) and (4) were approximately 1.5 times higher than column (1), and column (3) was approximately 1.7 times higher.

These results also confirmed that the ratio of the anion exchange resin A placed above the boron adsorption and removal layer B to the total layer height is preferably 10 to 50%, and more preferably 15 to 30%.

[Experimental Example 2]
In Experimental Example 1, the height of the boron adsorption/removal layer B was set to 300 mm, and the heights of the layers were as follows: Column (1): B = 300 mm, M = 700 mm
Column (2): A = 100 mm, B = 300 mm, M = 600 mm
Column (3): A = 200 mm, B = 300 mm, M = 500 mm
Column (4): A = 500 mm, B = 300 mm, M = 200 mm
The test was carried out under the same conditions as in Experimental Example 1, except for the above.

As a result, when comparing the time during which the treated water boron concentration can be maintained at 1 ng/L or less,
Column (1) is 80 mg-B/L-R,
Column (2) was 120 mg-B/L-R (1.5 times that of column (1)),
Column (3) was 135 mg-B/L-R (1.7 times that of column (1)),
Column (4) is 120 mg-B/L-R (1.5 times that of column (1))
The same tendency as in Experimental Example 1 was observed.

Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications are possible within the scope of the invention.
This application is based on Japanese Patent Application No. 2023-023544, filed on February 17, 2023, the entirety of which is incorporated by reference.

1 ion exchange resin tower 2 tower body

Claims (8)

An ion exchange resin tower for removing boron, comprising a tower body and an ion exchange resin layer provided in the tower body, through which water to be treated flows downward,
The ion exchange resin layer may include
A mixed bed resin layer disposed in the lower layer;
An anion exchange resin layer disposed in an upper layer;
The ion exchange resin tower has a boron-adsorbing resin layer disposed between the mixed bed resin layer and the anion exchange resin layer. The ratio of the layer height to the total layer height of the ion exchange resin layer is
Anion exchange resin layer: 1 to 50%,
Boron-adsorbed resin layer: 2 to 30%,
Mixed bed resin layer: 30-97%
The ion exchange resin tower according to claim 1, The ratio of the layer height to the total layer height of the ion exchange resin layer is
Anion exchange resin layer: 10 to 25%,
Boron adsorption resin layer: 15 to 25%,
Mixed bed resin layer: 50-70%
The ion exchange resin tower according to claim 1, The ion exchange resin tower of claim 2, wherein the total layer height is 500 to 3500 mm. The ion exchange resin tower of claim 1, wherein the boron adsorption resin adsorbs boron by ion exchange or chelating action. A method for removing boron, in which boron-containing water to be treated is passed downward through an ion exchange resin tower according to any one of claims 1 to 4. The boron removal method of claim 6, wherein the boron concentration in the treated water is 5 to 1000 ng/L. The method for removing boron according to claim 6, wherein the water flow rate SV of the ion exchange resin tower is 20 to 200 hr ⁻¹ .

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