JP7243039B2 - Urea monitoring device and pure water production device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a urea monitoring device capable of easily detecting urea in test water, and to a pure water production apparatus equipped with this urea monitoring device.

Conventionally, the ultrapure water used for semiconductor cleaning is an ultrapure water production system consisting of a pretreatment system, a primary pure water system, and a subsystem (secondary pure water system). It is manufactured by treating water, well water, used ultrapure water discharged from semiconductor factories (hereinafter referred to as “recovered water”), and the like.

Suspended solids and colloidal substances in the raw water are removed in a pretreatment system consisting of flocculation, pressure flotation (sedimentation), and filtration (membrane filtration) devices. In this process, it is also possible to remove polymeric organic substances, hydrophobic organic substances, and the like.

A primary pure water system equipped with a reverse osmosis membrane separation device, a degassing device and an ion exchange device (mixed bed type, 4-bed 5-tower type, etc.) removes ions and organic components from raw water. In addition, the reverse osmosis membrane separator removes salts as well as ionic and colloidal TOC. The ion exchange device removes salts and TOC components adsorbed or ion-exchanged by the ion exchange resin. The deaerator removes inorganic carbon (IC) and dissolved oxygen (DO).

In a sub-system comprising a low-pressure ultraviolet oxidation device, an ion-exchange water purification device, and an ultrafiltration membrane separation device, the purity of the pure water obtained in the primary pure water system is further increased to produce ultrapure water. In the low-pressure ultraviolet oxidizer, TOC is decomposed into organic acids and CO ₂ by ultraviolet rays with a wavelength of 185 nm emitted from a low-pressure ultraviolet lamp. Organic matter and CO ₂ generated by decomposition are removed in the subsequent ion exchange pure water apparatus. The ultrafiltration membrane separation device removes fine particles and also removes particles effluent from the ion exchange pure water device.

However, total organic carbon (TOC) is about 2 to 5 μg/L in the ultrapure water produced by the conventional general ultrapure water production apparatus. TOC in this ultrapure water is present in raw water (city water, industrial water, etc.) on the order of several tens to several hundred μg/L, and urea (NH ₂ CONH ₂ ) is known to be due to
Therefore, it is important to reduce the urea in the raw water and monitor the urea concentration in the raw water and the water in the system in order to obtain ultrapure water with a reduced TOC.

Patent Document 1 proposes an ultrapure water production apparatus provided with urea decomposition means and a urea monitoring device for continuously detecting the urea concentration in the water to be treated at a position upstream of the urea decomposition means. there is The urea monitoring device described in Patent Document 1 includes ion removing means for removing ions contained in the water to be treated, and TOC measuring means for measuring total organic carbon (TOC) contained in the water to be treated after ion removal. Prepare. That is, the ultraviolet TOC measurement means used in Patent Document 1 detects urea from the change in the electrical conductivity of water due to CO ₂ or NO ₃ generated by the decomposition of urea, so that ions are concentrated at a high concentration. Since it cannot be applied to test water containing components, it is necessary to remove ions in the water to be treated by the ion removal means and then perform measurement by the TOC measurement means. Patent Document 1 describes the use of a mixed-bed ion-exchange resin column as the ion removing means because it hardly removes urea.

JP-A-9-94585

In the urea monitoring device of Patent Document 1 using a mixed-bed ion-exchange resin tower as an ion removing means, the ion-exchange resin in the mixed-bed ion-exchange resin tower or the mixed-bed ion-exchange resin tower itself is periodically replaced or Treatment for regeneration of the ion exchange resin is required, and urea cannot be detected without maintenance for a long period of time.

The present invention solves this problem of the urea monitoring device described in Patent Document 1, and provides a urea monitoring device that can be used maintenance-free for a long period of time and that can easily detect urea in test water. An object of the present invention is to provide a pure water production system with a urea monitor.

The present inventors have found that the above problems can be solved by using a combination of a reverse osmosis membrane separation device and an electrodeionization device as ion removing means.
That is, the gist of the present invention is as follows.

[1] A urea monitoring device having an ion removing means for removing ions in test water and a TOC measuring means for measuring the total organic carbon (TOC) concentration of the test water from which the ions have been removed by the ion removing means. A urea monitoring device, wherein said ion removal means includes a reverse osmosis membrane separator and an electrodeionization device.

[2] The ion removing means has means for introducing the permeated water of the reverse osmosis membrane separation device into the electrodeionization device, and the TOC concentration of the treated water of the electrodeionization device is measured by the TOC measurement means. The urea monitoring device according to [1], characterized in that

[3] The urea monitoring device according to [1] or [2], further comprising computing means for correcting the measured value of the TOC measuring means based on the pre-measured urea removal rate by the ion removing means.

[4] A pure water production apparatus comprising the urea monitoring device according to any one of [1] to [3].

In the urea monitoring device of the present invention, the reverse osmosis membrane separation device and the electrodeionization device used as ion removal means do not require regeneration or replacement unlike ion exchange resins, and can be used maintenance-free for a long period of time. can. Therefore, according to the urea monitoring device of the present invention, urea in test water can be easily detected without maintenance for a long period of time.
Further, according to the pure water production apparatus of the present invention equipped with such a urea monitoring device of the present invention, the urea concentration of raw water or water in the system is rapidly detected, and by reflecting this in the treatment operation, High-quality pure water or ultrapure water with a reduced TOC concentration can be produced.

4 is a graph showing changes over time in urea analysis values in Example 1. FIG.

Embodiments of the present invention will be described in detail below.

[Urea monitor]
The urea monitoring device of the present invention comprises ion removal means for removing ions in test water, and TOC measurement means for measuring the total organic carbon (TOC) concentration of the test water from which the ions have been removed by the ion removal means. wherein the ion removal means includes a reverse osmosis membrane separator and an electrodeionization device.

<Ion removal means>
The ion removal means of the urea monitoring device of the present invention includes an RO membrane separator and an electrodeionization device, the permeated water of the RO membrane separation device is treated by the electrodeionization device, and the treated water of the electrodeionization device is subjected to TOC measurement. It feeds the means.

The RO membrane separation device is not particularly limited, and any RO membrane separation device generally used for pure water production can be suitably used.

As an electrodeionization apparatus, a plurality of cation-exchange membranes and anion-exchange membranes are alternately arranged between a cathode and an anode to alternately form concentration compartments and deionization compartments. A general electrodeionization apparatus in which a salt compartment and a concentration compartment are filled with an ion exchanger such as an ion exchange resin can be used.

When only the RO membrane separator is used as the ion removal means, ions in the test water cannot be removed to a high degree. Silica scale is generated and operation becomes impossible. On the other hand, by using an RO membrane separation device and an electrodeionization device and further treating the permeated water of the RO membrane separation device with the electrodeionization device, the ions in the test water are highly removed and the The water quality is suitable for the water supply of the installed TOC meter.

As will be shown in the examples below, urea is not removed by the electrodeionization apparatus, but is removed by 30 to 40% by the RO membrane separation apparatus. Therefore, as will be described later, it is preferable to perform arithmetic processing for correcting the amount of urea removed by the RO membrane separation device.

<TOC measurement means>
The TOC measuring means used in the present invention comprises a UV irradiation device for irradiating the test water from which ions have been removed by the ion removal means with ultraviolet rays (UV), a carbon dioxide permeable membrane, and an electrical conductivity meter. The UV irradiator is usually provided with a UV lamp around the water passage for the water to be tested, and the water to be tested flowing through the water passage is irradiated with UV. When the test water is irradiated with UV, urea in the test water is decomposed to generate _CO2 . The CO ₂ produced by the decomposition of urea is separated from the test water by a carbon dioxide permeable membrane into the pure water line in the electrical conductivity meter, and the separated CO ₂ (carbonate) is measured by electrical conductivity. .
That is, CO ₂ produced by decomposition of urea is selectively separated by a permeable membrane, and the amount of the separated CO ₂ is measured as electrical conductivity. Therefore, it becomes possible to accurately measure the TOC of urea by excluding other ions. Therefore, the urea concentration of the test water can be determined by applying the measurement results to a calibration curve showing the relationship between the urea concentration and the electrical conductivity, which is prepared in advance using sample water with a known urea concentration.

Such a TOC measuring means can be continuously measured by continuous water flow of the test water, and has a simple structure and space saving, so it is easy to apply as a TOC measuring means of a urea monitoring device. .

<Correction of measured value>
As described above, in the RO membrane separator used as the ion removing means in the present invention, not only ions but also urea in the test water are partially removed. Therefore, it is preferable to obtain the urea removal rate of the RO membrane separator in advance, and correct the measured value of the TOC measuring means with this urea removal rate.
Further, as shown in the examples below, when an activated carbon tower is provided in the preceding stage of the RO membrane separation device, urea in the test water is also removed in the activated carbon tower. It is preferable to obtain the urea removal rate by the method and correct the measured value of the TOC measuring means with the urea removal rate by the activated carbon tower and the urea removal rate by the RO membrane separator.

Correction of this measured value can be automatically carried out by means of computing means to which the urea removal rate of the RO membrane separator or the activated carbon tower is input.

[Pure water production equipment]
The pure water production apparatus of the present invention includes the urea monitoring device of the present invention as described above. water, city water, well water, recovered water, etc.), those having a means for removing fine particles, ions, organic substances, bacteria, gas, etc. contained in these raw waters in stages.

For example, as described above, a pretreatment system consisting of flocculation, pressure flotation (sedimentation), filtration (membrane filtration) equipment, etc., reverse osmosis membrane separation equipment, degassing equipment and ion exchange equipment (mixed bed type or 4 beds 5 tower type, etc.), and a sub-system comprising a low-pressure ultraviolet oxidation device, an ion-exchange water purification device, and an ultrafiltration membrane separation device. may be omitted.

The urea monitoring device of the present invention continuously or intermittently detects urea in raw water or treated water (produced pure water or water in the system) in such a pure water production device. provided to monitor the For example, a portion of the raw water or treated water is sampled and the urea concentration in the raw water or treated water is continuously or intermittently measured by the urea monitoring device of the present invention.

In the pure water production system of the present invention, it is preferable to further provide a urea removing device as necessary and perform the following control based on the urea concentration in the raw water or treated water measured by the urea monitoring device.

Continuously or intermittently measure the urea concentration of raw water or treated water with a urea monitoring device, operate the urea removal device when the urea concentration of raw water or treated water exceeds the standard value, is below the reference value, the operation of the urea remover is stopped. Alternatively, a urea removal device is provided branching from the pure water production device, and when the urea concentration in the raw water or the treated water exceeds the standard value, some or all of the raw water is treated by the pure water production device and then purified water is produced. When the urea concentration in the raw water or treated water falls below the reference value, the raw water is fed directly to the water purifying device or the amount of raw water to be treated by the urea removing device is reduced.

The operation and stop of the urea removal device can be automatically performed by inputting the measurement result of the urea monitoring device and providing control means for controlling the operation of the urea removal device based on the input value. .
Also, regarding the control of the amount of raw water flowing into the urea removal device, the measurement result of the urea monitoring device is input, and based on this input value, the flow control valve that controls the amount of raw water flowing into the urea removal device is opened. This can be done automatically by adjusting the temperature or by providing control means for operating a switching valve for changing the supply destination of the raw water.

If a urea removal device is not installed in the pure water production system, the urea concentration in raw water or treated water is measured continuously or intermittently with a urea monitoring device, and when the urea concentration in raw water or treated water exceeds the standard value, The supply of raw water to the water purifier is stopped, and the water purifier is supplied with spare raw water that has been separately stored, or the water purifier is temporarily stopped. Also, when the urea concentration in the raw water or treated water falls below the reference value, the supply of raw water is resumed.
The above-mentioned control of the supply of raw water can also be automatically carried out by providing control means for controlling the supply of raw water or treated water to be stopped or restarted based on the input values of the measurement results of the urea monitoring device. be able to.

The above-mentioned "reference value of urea concentration in raw water or treated water" is appropriately determined according to the use of treated water obtained from the water purifying apparatus (permissible value of urea concentration).

When a urea removal device is provided in the pure water production apparatus, the urea removal device is not particularly limited. A substance that decomposes urea in water can be used.
(1) Hypobromite (2) Alkaline bromide and sodium hypochlorite (3) Alkali bromide and ozone Further, an enzymatic decomposition apparatus in which urease, which is a urease, is supported on an appropriate carrier is used. can also

EXAMPLES The present invention will be described more specifically with reference to examples below.

[Example 1]
Nogi town water is used as test water, and after it is processed by sequentially passing it through the activated carbon tower, intermediate tank, RO membrane separator, and electrodeionization device, the TOC concentration is measured with a TOC meter. The change in urea concentration over time was analyzed using a prepared calibration curve showing the relationship between TOC concentration and urea concentration.
The activated carbon tower was used for the purpose of removing chlorine contained in Nogi Town water.
As the activated carbon tower, RO membrane separation device, electrodeionization device, and TOC meter, the following were used.
Activated carbon tower: Carboner "C-07" manufactured by Kurita Water Industries Ltd.
RO membrane: "DOW FILMTECTM TW30-1812-75" manufactured by Dow Chemical Co.
Electrodeionization device: "IONPURE (registered trademark) MX30" manufactured by Evoqua Water Technologies
Ultraviolet TOC meter: SUEZ Sievers (registered trademark) online TOC meter 500RLe type

For the test water, activated carbon tower outlet water, RO membrane separator outlet water (permeated water), and electrodeionization apparatus outlet water (treated water), a liquid chromatograph mass spectrometer manufactured by Shimadzu Corporation with the following specifications "LC (Nexera X2)- Table 2 below shows the results of analyzing the urea concentration by MS (LCMS8040). Table 2 also shows the results of calculating the urea removal rate from the urea concentration of each outlet water relative to the urea concentration of the test water.

<LC-MS specifications>
Column: SeQuant ZIC-HILIC 2.1×100 mm 3.5 μm manufactured by Merck Millipore
Mobile phase: 5 mM ammonium acetate (pH 6.8)/acetonitrile Flow rate: 0.2 mL/min
Injection volume: 40 μL
Gradient conditions: Table 1 below

オーブン温度：４０℃
測定ｍ／ｚ：６１．００＞－４４．０５
測定モード：ＭＲＭ
ＤＬ温度：１８０℃
ヒートブロック温度：４８０℃
ＣＩＤガス：アルゴン
ネブライザーガス：３Ｌ／分
ドライングガス：１５Ｌ／分
イオン化：ＥＳＩ Ｐｏｓｉｔｉｖｅ

Oven temperature: 40°C
Measurement m/z: 61.00>-44.05
Measurement mode: MRM
DL temperature: 180°C
Heat block temperature: 480°C
CID gas: Argon Nebulizer gas: 3 L/min Drying gas: 15 L/min Ionization: ESI Positive

From Table 2, a small amount of urea in the test water is removed by the activated carbon tower, but most of it is removed by the RO membrane separator, and urea is not removed by the electrodeionization equipment. 45% of the urea in the sample water is removed by treatment with the electrodeionization device, and 32.5% is removed by treatment with only the RO membrane separation device. It can be seen that it corresponds to 55% of the urea concentration in the test water.

Based on the above results, urea analysis with the above TOC meter was performed over time, and the urea concentration measurement result based on the TOC meter was corrected with the urea removal rate by the activated carbon tower, RO membrane separation device and electrodeionization device. as the urea analysis value of the test water (specifically, the urea concentration measurement result based on the TOC meter was divided by 0.55 to obtain the urea concentration of the test water.), and the results are shown in FIG. .
FIG. 1 also shows urea analysis values obtained by intermittently analyzing the test water with the aforementioned LC (Nexera X2)-MS (LCMS8040) manufactured by Shimadzu Corporation.
As can be seen from FIG. 1, the urea analysis values according to the present invention and the LC-MS analysis values match, and it can be seen that the urea concentration of the test water can be accurately measured by the urea monitoring device of the present invention.

Claims (4)

A urea monitoring device provided in a water purifier for monitoring urea in raw water or treated water of the water purifier,
An ion removing means for removing ions in test water, and a TOC measuring means for measuring a total organic carbon (TOC) concentration of the test water from which the ions have been removed by the ion removing means , the TOC measuring means. is a means for measuring the CO 2 generated by the decomposition of urea as an electrical conductivity, and the measurement result of the TOC measurement means is a relationship between the urea concentration and the electrical conductivity prepared in advance using a sample water with a known _urea concentration A urea monitoring device for determining the urea concentration of the test water by applying a calibration curve showing Equipment (excluding those constructed equivalently to the pure water production equipment mentioned above). The ion removing means has means for introducing permeated water from the reverse osmosis membrane separation device into the electrodeionization device, and the TOC concentration of the treated water of the electrodeionization device is measured by the TOC measurement means. The urea monitor of claim 1, characterized by: 3. The urea monitoring apparatus according to claim 1, further comprising computing means for correcting the measured value of said TOC measuring means based on the urea removal rate by said ion removing means measured in advance. A pure water production apparatus comprising the urea monitoring device according to any one of claims 1 to 3.

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