JPH07962A - Production of pure water - Google Patents

Abstract

PURPOSE:To provide a method for effectively removing gaseous CO2 passed through a membrane in a pure water producing system mainly using a reverse osmosis device. CONSTITUTION:Carbonate components in liquid to be treated and to be passed through a reverse osmosis device 8 are all made in the form of gaseous CO2 and passed through the reverse osmosis device 8, and gaseous CO2 existing in permeated water is removed from the water by liquid-gas separation action of a membrane deaeration device 9 located in the poststage. Ions increased by injecting a pH controlling chemical are removed by a reverse osmosis device 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pure water production system, and more particularly to a method for producing pure water having a reverse osmosis device and a dissolved oxygen removing device.

[0002]

2. Description of the Related Art Generally, in the production of pure water, well water or tap water is subjected to coagulation sedimentation or a sand filter, and activated carbon is adsorbed to pretreat impurities contained in water. It is manufactured by the pure water manufacturing system. That is, in this pure water production system, a system in which cations in water are removed by a cation exchange resin device, carbonate ions in water by a decarboxylation device, and anions in water by an anion exchange resin device is the mainstream. In recent years, with the progress of semiconductor manufacturing technology, the concentration of impurities in the cleaning water and pure water used in semiconductors and ultrapure water has been decreasing. Devices for removing oxygen are often added.

However, in the above-mentioned cation exchange resin device, anion exchange resin device, and mixed bed type ion exchange resin device in which both ion exchange resins are mixed, it is necessary to periodically regenerate the resin by using a chemical agent. In addition, since it is necessary to also perform wastewater treatment of the chemicals used for regeneration, the pure water production system that does not use the regenerated ion exchange resin device is often applied to small to medium-sized pure water production equipment. .

In a pure water production system that does not use such a regenerative ion exchange resin device, for example, as shown in FIG.
As shown in (A), the effluent from the pretreatment device is passed through a reverse osmosis device and then through a non-regenerative ion exchange resin device to produce pure water. As shown, a method of passing water through a non-regeneration type ion exchange resin device after applying it to a two-stage reverse osmosis device is adopted.

However, in such a system configuration, the carbon dioxide gas dissolved in water passes through the separation membrane in the reverse osmosis device, and becomes a load of the non-regenerated ion exchange resin in the subsequent stage as bicarbonate ions to cause non-regeneration. There is a drawback that the period of use of the ion-exchange resin is significantly shortened. Also, in order to remove carbon dioxide gas in water with a reverse osmosis device, for example, as shown in FIG.
A method of injecting an alkaline agent such as caustic soda into the middle of the two-stage reverse osmosis device as shown in (C) and separating and removing carbon dioxide gas as bicarbonate ions by the reverse osmosis device is also effective,
There is a risk that metal scale will be generated on the reverse osmosis membrane where the metal hydroxide was formed by the injection of the alkaline agent, resulting in clogging of the membrane.

As described above, in a pure water production system that makes full use of the reverse osmosis device, carbon dioxide gas that has passed through the membrane is caught by the non-regeneration type ion exchange resin device in the subsequent stage and the life of the resin is shortened. There is a need for an efficient method of removing components.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a pure water production system centered on the above reverse osmosis device,
It is to provide an efficient method of removing carbon dioxide gas that has passed through a membrane.

[0008]

The present invention utilizes the fact that the form of carbonic acid component in water is present as carbon dioxide gas in the acidic region of pH 5 or less.
A mineral acid such as hydrochloric acid is used as the pH adjusting agent.
In the present invention, all the carbonic acid components in the liquid to be treated passing through the reverse osmosis device are made into carbon dioxide gas, and are intentionally passed through the reverse osmosis device, and the permeated water is separated by the liquid / gas separation action of the membrane degassing device located at the subsequent stage. The carbon dioxide gas existing in
Ions (for example, H
In the case of C〓, the point is to remove C〓 ions by the reverse osmosis device.

[0009]

EXAMPLES Next, the present invention will be specifically described with reference to the drawings. FIG. 2 is a block diagram of a pure water production system showing an embodiment of the method of the present invention. The main equipment configuration is a pretreatment system 1 for coagulating sedimentation, sand filtration, and activated carbon treatment of well water or tap water, and a pH adjusting device 6 for adjusting the pH of the water to be treated flowing out of the pretreatment system, and a predetermined pH, PH of
Injecting device 7 for pH-adjusting chemicals held at 1, first-stage reverse osmosis device 8 for removing impurity ions in the water to be treated that has been adjusted to a predetermined pH, and further into effluent water from the first-stage reverse osmosis device Membrane degassing device 9 for removing contained carbonic acid components and dissolved oxygen, second-stage reverse osmosis device 10 for removing trace amounts of ionic components, and a mixed bed type in which cation exchange resin and anion exchange resin are mixed. It is composed of an ion exchange resin device 11.

The water to be treated flowing out of the pretreatment system 1 contains 20 to 100 ppm of carbonic acid component, depending on the properties of the raw water supplied such as well water or tap water. There are two types of carbonic acid components, one that exists as carbon dioxide gas in water and one that exists as bicarbonate ions.
Contains 30-60% carbon dioxide. Most of carbonic acid in water exists as carbon dioxide at pH 5. That is, in the present invention, the pH adjusting tank 6 has a function of making the carbonic acid component in the water to be treated into a gas state. Here, when hydrochloric acid is used as a pH adjusting agent, a reaction in which bicarbonate ions existing in water are changed to carbonic acid occurs. Since the reverse osmosis membrane has a property of passing a gaseous component as it is, carbon dioxide gas cannot be removed by the first-stage reverse osmosis device and remains in the permeated water. The carbon dioxide gas contained in the water leaks into the water to be treated in this manner, but most of the anion component increased by the addition of the pH adjusting agent is removed by the first-stage reverse osmosis device.

The membrane deaerator 9 is separated into water to be treated and a vacuum exhaust unit by a gas separation membrane, and carbon dioxide gas contained in the water to be treated moves to the vacuum exhaust unit through the gas separation membrane. To do. By this action, carbon dioxide gas in the water to be treated is removed from the water. The water to be treated flowing out from the membrane degassing device 9 is further sent to the second-stage reverse osmosis device, where the impurity ion components remaining without being removed by the first-stage reverse osmosis device. Are removed.

Therefore, according to the present invention, a mineral acid such as hydrochloric acid is added before the reverse osmosis device to bring the pH of the water to be treated into an acidic region so that the carbonic acid component in the water becomes gaseous and the reverse osmosis device By removing the carbonic acid component by applying it to the membrane deaerator installed at the latter stage (the above is the middle of the second stage reverse osmosis device), the impurity ion derived from hydrochloric acid used for this pH adjustment is the reverse of the first and second stages. High-purity pure water can be produced by removing it with a permeation device.

FIG. 2 shows an embodiment of the present invention. Hydrochloric acid was injected into the treated water that had been subjected to coagulation sedimentation, sand filtration, and activated carbon treatment using well water as raw water, and p
After setting H to 6.0, water was passed through a two-stage reverse osmosis device with a membrane degassing device loaded in the middle. FIG. 3 shows the results of continuous measurement of the specific resistance value of the water to be treated after being subjected to these series of treatment devices. In addition, Table 1 shows the water quality of the water to be treated after pretreatment such as coagulation sedimentation. Further, in order to compare the performance of the method of the present invention with that of the conventional method, the results of passing water only through the two-stage reverse osmosis device without pH adjustment are also shown in FIG.

As is clear from the results shown in FIG. 3, the specific resistance value of the treated water flowing out from the conventional two-stage reverse osmosis device is
0.3 to 0.5 MΩcm, while 2 to 3 M when the membrane degassing apparatus of the method of the present invention is added in the middle of the two-stage reverse osmosis apparatus
A very good specific resistance value of Ωcm was obtained. In addition, the results of measuring the carbonic acid component and the amount of dissolved oxygen remaining in this treated water showed that carbon dioxide was 1500 ppb and dissolved oxygen was 2800 pp in the case of the conventional method.
In contrast to the remaining b, in the method of the present invention, carbonic acid was less than 50 ppb and the dissolved oxygen was less than 10 ppb, which were good results for both the carbonic acid component and the dissolved oxygen.

Furthermore, FIG. 4 shows that treated water obtained by the conventional method and the method of the present invention are passed through an ion exchange resin device of the same volume,
It is a result of comparing the break times of the ion exchange resins. As described above, the difference in the specific resistance value of the water to be treated has a great influence on the break times of the ion exchange resins. It was found that the life of the ion exchange resin can be extended by at least 4 times.

[0016]

INDUSTRIAL APPLICABILITY As described above, by adopting the method of the present invention, it becomes possible to efficiently remove carbonic acid components contained in water, and it is possible to use a cation exchange resin that is usually used on a large scale. It was found that pure water having the same purity as that of the decarboxylation device and the anion exchange resin can be produced by the system using the reverse osmosis device. Although the pure water production system according to the method of the present invention has been evaluated by the two-stage reverse osmosis method as described above, it goes without saying that the present invention is also effective for a single-stage reverse osmosis apparatus. In this case, the specific resistance of the treated water is about 1 MΩcm, which is somewhat insufficient, but it can be used as washing water depending on the application.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a conventional pure water production system.

FIG. 2 is a schematic configuration diagram showing an embodiment of the method of the present invention.

FIG. 3 is a manufacturing comparison diagram of the method of the present invention and the conventional method.

FIG. 4 is a performance comparison diagram of the method of the present invention and a conventional method using ion-exchange resin using treated water.

[Explanation of symbols]

 1 Pretreatment system 2 1st-stage reverse osmosis device 3 2nd-stage reverse osmosis device 4 Mixed bed type ion exchange resin device 5 Alkali injection device 6 pH adjustment device 7 pH adjustment chemical injection device 8 First step of the method of the present invention Reverse osmosis device 9 Membrane degassing device 10 Second stage reverse osmosis device of the method of the present invention 11 Non-regenerated ion exchange resin device

Claims (3)

[Claims] 1. In a system for producing pure water by passing well water or tap water through a pure water production system including a reverse osmosis device, a pH adjusting tank is provided in advance of the reverse osmosis device to adjust the pH of raw water raw water. A so-called membrane deaerator in which the liquid layer portion and the gas layer portion are separated by a gas permeable membrane for the treated water flowing through the reverse osmosis device after being adjusted to 4 to 6 and further flowing out from the reverse osmosis device. A method for producing pure water, characterized in that the dissolved carbonic acid and the dissolved oxygen contained in the treated water of the reverse osmosis device are removed at the same time by passing water through the water. 2. The reverse osmosis device in the pure water production system has a single-stage or two-stage configuration, and a hollow fiber-shaped gas permeable membrane or a membrane degassing device is provided at the subsequent stage of the single-stage or first-stage reverse osmosis device. The method for producing pure water according to claim 1, wherein a spiral gas-permeable film is incorporated. 3. The agent used for pH adjustment is hydrochloric acid, sulfuric acid,
A mineral acid such as nitric acid, before flowing into the reverse osmosis device,
The method for producing pure water according to claim 1, characterized in that means for adjusting the pH to a predetermined value by using these chemicals is added.