JP2000065710A - Method and apparatus for measuring dissolved gas concentration in liquid - Google Patents

Abstract

(57) [Summary] [Problem] The concentration of a plurality of types of dissolved gases in a liquid flowing through a flow path can be easily and constantly obtained as a sum of saturation degrees at once, and particularly, the concentration of dissolved gases in water is measured. Provided are a method and an apparatus for measuring the concentration of dissolved gas in a liquid, which are suitable for the following. A liquid phase and a gas phase are separated by a gas permeable membrane,
A method for measuring the concentration of dissolved gas in a liquid, which comprises measuring the degree of vacuum of a gaseous phase in an equilibrium state with a liquid phase, and providing a gas permeable membrane in a closed container, one side of which is a liquid phase chamber. The other side is partitioned into a gas phase chamber, an introduction pipe for introducing the test liquid and a discharge pipe for discharging the test liquid are provided in the liquid phase chamber, and a pressure gauge for measuring the degree of vacuum is provided in the gas phase chamber. Characteristic measuring device for dissolved gas concentration in liquid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the concentration of dissolved gas in a liquid. More specifically, the present invention can easily and constantly determine the concentrations of a plurality of types of dissolved gases in a liquid flowing through a flow path as a sum of saturation degrees at once, and is particularly useful for measuring the concentration of dissolved gases in water. The present invention relates to a method and apparatus for measuring the concentration of dissolved gas in a liquid, which is suitable.

[0002]

2. Description of the Related Art Conventionally, in liquid treatment techniques such as water treatment, it has been important to control the concentration of dissolved gas. For example, ultrapure water used in the wet cleaning process to remove foreign substances from the surface of silicon substrates for semiconductors, glass substrates for liquid crystals, etc. should reduce the amount of dissolved oxygen to a very small amount in order to suppress the natural oxidation of the substrate surface. Is required. Dissolved oxygen can be reduced to the ppb level by vacuum degassing, nitrogen degassing, catalyst degassing, etc., and its concentration can be accurately measured using existing dissolved oxygen meters. In recent years, the innovation of wet cleaning has been advanced, and so-called functional cleaning water in which only a specific gas is dissolved in a predetermined amount has been applied. For example, it is known that cleaning water in which only hydrogen gas is dissolved to near the saturation concentration is extremely effective in removing fine particles on a substrate. In order to efficiently dissolve only such a specific gas in water at a high concentration,
It is desired that the gas originally dissolved is removed in advance by a preliminary degassing treatment. The target of this preliminary degassing treatment is all dissolved gases such as oxygen gas and nitrogen gas,
To accurately determine the degree of processing, use multiple instruments,
It was necessary to measure at least the concentration of both dissolved oxygen gas and dissolved nitrogen gas. When ultrapure water that has not been deoxygenated is used as the raw water for cleaning, if the preliminary deaeration is performed using a method without selectivity depending on the type of gas, the concentration of the dissolved oxygen gas for which the measurement method is established is established. By the measurement, it was possible to roughly estimate the degree of the degassing process for all dissolved gases. However, when deoxidized ultrapure water is used as raw water for functional cleaning water, as used in recent electronics industry factories, the dissolved oxygen gas concentration is originally as low as the ppb level. In addition, it is impossible to estimate the degree of the preliminary degassing from the dissolved oxygen gas concentration, and it has been necessary to rely on an expensive dissolved nitrogen meter which is inferior in performance to the dissolved oxygen meter and expensive.

[0003]

SUMMARY OF THE INVENTION According to the present invention, the concentrations of a plurality of types of dissolved gases in a liquid flowing through a flow path can be simply and always determined as a sum of saturation degrees at once, and particularly, the concentration of dissolved gases in water can be easily determined. An object of the present invention is to provide a method and an apparatus for measuring the concentration of dissolved gas in a liquid, which are suitable for measuring the concentration of gas.

[0004]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, in a system in which a liquid phase and a gas phase coexist, the gas amounts of the liquid phase and the gas phase are balanced. State
It has been found that the concentration of dissolved gas in the liquid phase can be easily obtained by measuring the amount of gas in the gas phase as pressure, and the present invention has been completed based on this finding. That is, the present invention provides (1) a method of measuring the concentration of dissolved gas in a liquid, which comprises separating a liquid phase and a gas phase by a gas permeable membrane and measuring the degree of vacuum of the gas phase in an equilibrium state with the liquid phase. The method, and
(2) A gas permeable membrane is provided in a closed container, one side is partitioned into a liquid phase chamber, and the other side is partitioned into a gas phase chamber, and an inlet pipe for introducing a test liquid into the liquid phase chamber and a discharge pipe for discharging. And a pressure gauge for measuring the degree of vacuum in the gas phase chamber is provided.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The method of measuring the concentration of dissolved gas in a liquid according to the present invention comprises separating a liquid phase and a gas phase by a gas permeable membrane,
By measuring the degree of vacuum of the gas phase in an equilibrium state with the liquid phase, the dissolved gas concentration in the liquid is determined. In a system in which the liquid phase and the gas phase coexist, the gas in the liquid phase and the gas in the gas phase are in an equilibrium state, and the concentration of the dissolved gas in the liquid phase is proportional to the amount of the gas in the gas phase, that is, the partial pressure of the gas. The value obtained by dividing the concentration of the gas dissolved in water by the solubility of the gas at a pressure of 0.1 MPa and a temperature of 25 ° C. is defined as the gas saturation. Pressure 0.1MPa,
At a temperature of 25 ° C., water in equilibrium with air is 8.1 mg / liter of oxygen gas and 13.8 mg of nitrogen gas.
/ Liter dissolved. Pressure 0.1MPa, temperature 25 ℃
In the above, the solubility of oxygen gas in water is 40.4 mg / l and the solubility of nitrogen gas is 17.6 mg / l, so that the saturation of oxygen gas in water in equilibrium with air is 0. That is, the saturation of the nitrogen gas becomes 0.8 times, and the sum of the saturation of the oxygen gas and the saturation of the nitrogen gas becomes 1.0 times. If this water is degassed and the concentration of oxygen gas is set to 0.8 mg / l and the concentration of nitrogen gas is set to 1.4 mg / l, the sum of the saturation of oxygen gas and the saturation of nitrogen gas is 0.1 times. The pressure of the gas phase in equilibrium with water is 0.01 MPa, that is, the degree of vacuum is -0.09 MPa.
Therefore, by measuring the degree of vacuum of the gas phase in equilibrium with water, if the degree of vacuum is -0.09 MPa, the saturation of the water gas is 0.1 times and the degree of vacuum is -0. .07MP
In the case of a, assuming that the saturation of the water gas is 0.3 times, the dissolved gas concentration can be collectively obtained in the unit of the saturation.

In the method of the present invention, the liquid phase and the gas phase are separated via a gas permeable membrane, so that the gas-liquid interface increases,
Due to the formation of turbulence and the like, the movement of gas molecules between the gas and liquid phases is likely to occur, and the equilibrium state is reached in a short time. The method of the present invention comprises:
For a test liquid in which the gas concentration in the test liquid fluctuates constantly, the equilibrium state between the gas and liquid phases is difficult to stabilize, making measurement difficult. Like the measurement of the concentration, it can be suitably applied to the measurement of a test liquid in which a gas is dissolved at a substantially constant concentration. In the deaeration of ultrapure water, the operation of the deaerator is usually performed stably,
Fluctuation of dissolved gas concentration is small. For such degassed water, when the degree of vacuum of the gas phase in equilibrium with the liquid phase is constantly measured, the degree of vacuum is almost a stable value, so the dissolved gas concentration can be calculated from the measured value of the degree of vacuum. It can be easily obtained. FIG. 1 is an explanatory diagram of one embodiment of the measuring device of the present invention. The measuring apparatus of this embodiment is provided with a gas permeable membrane 2 in a closed container 1, one side of a liquid phase chamber 3, and the other side of a gas phase chamber 4.
And an inlet pipe 5 for introducing the test liquid into the liquid phase chamber and an outlet pipe 6 for discharging the same, and a pressure gauge 7 for measuring the degree of vacuum of the gas phase in the gas phase chamber.

In order to prepare a water containing a specific gas by dissolving a specific gas in water, the water which has been subjected to preliminary degassing treatment is transferred to a dissolving membrane module having a gas permeable membrane for dissolving the specific gas. When water is passed, dissolution proceeds easily without injecting a specific gas. This is a phenomenon in which water that has undergone preliminary degassing is equilibrated with the gas phase according to Henry's law. Here, if gas is not injected into the dissolved film module, the gas remaining in the gas phase in the module proceeds to transfer to the aqueous phase, and the gas phase is reduced in pressure. This degree of pressure reduction correctly reflects the degree of deaeration of the pre-degassed water, that is, the dissolved gas concentration. Therefore, the gas composition of the gas phase chamber of the measuring device at the start of measurement does not particularly affect the degree of vacuum of the gas phase chamber in the gas-liquid equilibrium state. Alternatively, when the test liquid is passed through the liquid phase chamber and the liquid phase and the gas phase are in an equilibrium state, the same degree of vacuum is reached. In order to measure the concentration of dissolved gas in a liquid using the apparatus of the present invention, the test liquid is continuously introduced into the liquid phase chamber, and the degree of vacuum when the degree of vacuum in the gas phase chamber becomes a substantially constant value is measured. Is the desired degree of vacuum. Since the ratio between the pressure of the gas phase chamber and the atmospheric pressure at this time corresponds to the ratio of the concentration of the gas dissolved in the test solution to the saturated dissolved concentration of the gas when exposed to the atmospheric pressure, The gas concentration can be determined. The device of the present invention can be particularly suitably used for measuring the dissolved gas concentration of water which has been pre-degassed in order to prepare water containing specific gas.

In the measuring method of the present invention, a closed container having the same function as the dissolved membrane module is provided separately from the dissolved membrane module, and the whole or a part of the test liquid is passed to reach a gas-liquid equilibrium state. By measuring the degree of vacuum of the gas phase at the time of the above, the dissolved gas concentration of the test solution can be obtained. As the closed container, it is preferable to use the same module as the dissolved membrane module or a small module having the same configuration. Examples of the gas permeable membrane to be used include a polydimethylsiloxane membrane, a polydimethylphenylene oxide membrane,
Cellulose acetate membrane, polypropylene membrane, poly (4
-Methylpentene-1) film and the like.
The gas permeable membrane is preferably a membrane having no gas permeation selectivity or a small membrane. Examples of the membrane having a small gas permeation selectivity include a microporous membrane. Preliminary degassed water having a degassing degree of 1/10, that is, water degassed to a saturation degree of 10% when the equilibrium state with the atmosphere is set to 100%, is measured by passing the water through the measuring apparatus of the present invention. The gas present in the gas phase chamber of the device gradually dissolves into the preliminary deaerated water through the gas permeable membrane, the degree of vacuum in the gas phase chamber increases, and the gas movement through the membrane eventually disappears And the degree of vacuum stabilizes. This degree of vacuum matches the dissolved gas concentration itself of the preliminary degassed water. That is, in the case of the example shown above, the gauge pressure of the gas phase chamber of the dissolved gas concentration measuring device is
Shows -0.09 MPa (-0.9 atm) and stabilizes. This is because the sum of the saturation degrees of the dissolved gas of the preliminary degassed water is 1
This corresponds to 0%. The degree of vacuum does not directly indicate the dissolved oxygen gas concentration or the dissolved nitrogen gas concentration, but is a useful value indicating the total dissolved gas concentration in units of saturation. This example shows that when a specific gas is injected and dissolved in the preliminary degassed water, the gas up to 90% of the saturation is easily dissolved.

FIG. 2 is a process flow chart showing one embodiment of the measuring method of the present invention. The gas phase chamber of the degassing membrane module 8 is kept at a reduced pressure, and ultrapure water is introduced into the liquid phase chamber. In the ultrapure water, the dissolved gas moves to the gas phase chamber via the gas permeable membrane, and becomes preliminarily degassed water. The preliminary degassed water is introduced into the dissolved gas concentration measuring device 9 of the present invention, and the liquid phase and the gaseous phase reach an equilibrium state. Can be determined as the degree of saturation. The preliminary degassed water discharged from the measuring device is then introduced into the dissolved membrane module 10 and dissolves a specific gas supplied to the gas phase chamber of the dissolved membrane module to become specific gas-containing water. The amount of the specific gas corresponding to a value obtained by subtracting the saturation of the preliminary degassed water from the saturation of the preliminary degassed water, that is, the saturation degree of 100%, is easily dissolved in the preliminary degassed water in the dissolved membrane module. In this embodiment, the measuring device has the same structure as the degassing membrane module or the dissolved membrane module, and the preliminary degassed water is introduced into the total amount measuring device.

FIG. 3 is a process flow chart showing another embodiment of the measuring method of the present invention. The gas phase chamber of the degassing membrane module 8 is kept at a reduced pressure, and ultrapure water is introduced into the liquid phase chamber. In ultrapure water, the dissolved gas moves to the gas phase chamber through the gas permeable membrane,
It becomes preliminary deaerated water. Part of the preliminary degassed water is
From the measuring device 9 of the present invention, and discharged from the measuring device. The discharged water may be returned to the main pipe again, or may be discharged outside the system. In the measuring device, the liquid phase and the gaseous phase reach an equilibrium state, the pressure gauge 7 shows a constant degree of vacuum, and the sum of the dissolved gas concentrations in the preliminary degassed water can be obtained as the saturation degree from the value. . The preliminary deaerated water is introduced into the dissolved membrane module 10,
The specific gas supplied to the gas phase chamber of the dissolving film module is dissolved to form water containing the specific gas. The amount of the specific gas corresponding to a value obtained by subtracting the saturation of the preliminary degassed water from the saturation of the preliminary degassed water, that is, the saturation degree of 100%, is easily dissolved in the preliminary degassed water in the dissolved membrane module. In this aspect, the measuring device can be smaller than the degassing membrane module or the dissolving membrane module. In this embodiment, the preliminary degassed water can be always passed through the measuring device, or can be passed only for a required time at the time of measurement, and can be measured in a state where the degree of vacuum is constant. The equilibrium state of the gas concentration in the liquid phase and the gas phase is achieved in a shorter time as the capacity of the liquid phase chamber is larger and the area of the gas permeable membrane is larger than the capacity of the gas phase chamber. It is preferable to form a measuring device satisfying the following. By applying the method and apparatus for measuring the concentration of dissolved gas in a liquid according to the present invention, the total dissolved gas concentration in ultrapure water, which has recently attracted attention, can be collectively and extremely easily measured. So you can
Its management becomes easy. The value obtained by using the method and the apparatus of the present invention is not the absolute concentration of each gas component, but the sum of the degrees of saturation. It is a numerical value that reflects directly and is extremely useful information.

[0011]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. Example 1 (Evaluation of Deaeration of Preliminarily Degassed Water) Ultrapure water having a dissolved oxygen gas concentration of 8.0 mg / liter, which has not been degassed, was treated with a degassing membrane module [4-inch module, trade name : Liquicel, manufactured by Hoechst Celanese Co., Ltd.] at a flow rate of 16.7 L / min, and the membrane was deaerated using a vacuum pump. A part of the preliminary deaerated water, 1.67 liter / min, is passed through a 2.5 inch module having the same configuration as the above deaerated membrane module,
The gas phase was sealed and the degree of vacuum was measured. Separately, the dissolved oxygen gas concentration of the preliminary degassed water was measured using a diaphragm type dissolved oxygen meter. As a result, the degree of vacuum was stabilized at -0.09 MPa, and the dissolved oxygen gas concentration was 0.8 mg / liter.
The value of the dissolved oxygen gas concentration indicates that the dissolved oxygen gas has decreased to 1/10 of that before degassing, and the value of the degree of vacuum indicates that the total dissolved gas concentration is 1 / 10, which was well in agreement. Example 2 (Evaluation of Deaeration of Preliminarily Degassed Water) Using ultrapure water that has been subjected to nitrogen degassing, has a dissolved oxygen gas concentration of 5 μg / liter, and is in a saturated state with dissolved nitrogen gas,
The same operation as in Example 1 was performed. The dissolved oxygen gas concentration of the preliminary degassed water was difficult to measure exactly, but the gas phase vacuum of the 2.5-inch module was −
0.09MPa was shown. From this result, it was found that the total dissolved gas concentration was reduced to 1/10 of that before degassing. When the dissolved nitrogen gas concentration before and after degassing was measured using a dissolved nitrogen meter, the concentration was 18.6 mg / l before degassing, and 1.9 mg / l after degassing.
It was in good agreement with the change in dissolved gas concentration determined by the degree of vacuum.

Embodiment 3 (Evaluation of Ultrapure Water) In recent years, ultrapure water used in electronic industry factories is often subjected to a nitrogen purge in a tank in order to prevent a decrease in water quality. Even though the dissolved oxygen gas concentration of ultrapure water is strictly controlled,
In most cases, the dissolved nitrogen gas concentration is left to run. When the produced ultrapure water is used promptly, the dissolution of nitrogen gas is small, but when the time of holding in the tank is increased, the dissolution amount of nitrogen gas increases. At the electronics industry factory, the ultrapure water degassed by the membrane is stored in a tank purged with nitrogen, and the ultrapure water is used in the ultrapure water system as in Example 1.
A 5-inch module was provided to measure the degree of vacuum in the gas phase in equilibrium with ultrapure water, and the dissolved nitrogen gas concentration was measured using a dissolved nitrogen meter. Initially, the degree of vacuum is -0.0
9 MPa, the dissolved nitrogen gas concentration was 1.9 mg / liter. The degree of vacuum in the gas phase gradually decreases to -0.08 MPa,-
0.07MPa, -0.06MPa, -0.05MPa, -0.04M
When the pressure reaches Pa, the dissolved nitrogen gas concentration is 3.7 mg each.
/ Liter, 5.6mg / liter, 7.4mg / liter,
9.3 mg / l and 11.2 mg / l, indicating a good correspondence between the degree of vacuum in the gas phase and the concentration of dissolved nitrogen gas. Example 4 (Application to Hydrogen Water Production) Hydrogen water was produced using the apparatus shown in FIG. Degassed ultrapure water having a dissolved oxygen gas concentration of 8.0 mg / L and not subjected to degassing treatment is used as a degassing membrane module [4-inch module, trade name: Liquicel, manufactured by Hoechst Celanese Corporation]
The membrane was deaerated by adjusting the degree of vacuum of the membrane deaerator in five stages using a vacuum pump. A part of the preliminary deaerated water, 1.67 liter / min,
Water was passed through a 2.5-inch module having the same configuration as the above-mentioned degassing membrane module, the gas phase was sealed, the degree of vacuum was measured, and the passed water was returned to the main pipe. Preliminarily degassed water is passed through a gas dissolving module, hydrogen gas is continuously injected into the gas phase at a flow rate of 270 Nml / min, and the dissolved hydrogen gas concentration of the resulting hydrogen water is measured using a diaphragm type dissolved hydrogen meter. It was measured.
When the membrane deaerator is not evacuated, the gas phase vacuum of the 2.5-inch module is 0 MPa, the degree of deaeration of the preliminary deaerated water is 0%, and the dissolved hydrogen gas concentration of the hydrogen water is 0.41 mg / The dissolution efficiency of 1 liter and hydrogen gas was 28%. The vacuum degree of the membrane deaerator is sequentially increased, and the vacuum degree of the gas phase of the 2.5-inch module is -0.03 MPa, -0.07 MPa, -0.09 M
Pa, -0.10MPa, Deaeration degree of preliminary deaerated water is 30%, 70
%, 90%, and 99%, the dissolved hydrogen gas concentrations of the obtained hydrogen water are 0.75 mg / liter and 1.2, respectively.
4 mg / liter, 1.40 mg / liter, 1.44 mg / liter, the dissolution efficiency of hydrogen gas was 52%,
86%, 97% and 100%. Table 1 shows the relationship between the degree of vacuum in the gas phase, the degree of deaeration of the pre-deaerated water, the concentration of the dissolved hydrogen gas obtained, and the efficiency of dissolving the hydrogen gas.

[0013]

[Table 1]

It has been confirmed that the concentration of dissolved hydrogen gas in hydrogen water and the efficiency of dissolving hydrogen gas can be improved by increasing the degree of deaeration of ultrapure water. Example 5 (Degassing Test) Combination of a degassing membrane module [4-inch module, trade name: Liquicel, manufactured by Hoechst Celanese Co., Ltd.] and a 2.5-inch module having the same configuration for measuring the degree of vacuum in the gas phase. A degassing test was performed. Ultrapure water in equilibrium with the atmosphere is passed through the degassing membrane module at a rate of 20 liters / min, and 1.5 liters / min of degassed water is passed through a 2.5-inch module. Was measured. The degree of vacuum in the gas phase reaches -0.085 MPa 60 minutes after the start of operation,
Thereafter, the pressure stabilized. After 120 minutes from the start of operation, the vacuum pump was stopped to return the gas phase of the membrane degassing module to normal pressure. When the gas phase of the 2.5-inch module was reduced in vacuum, the pressure returned to normal pressure 60 minutes later. . Example 6 (Deaeration test) The amount of preliminary deaerated water passed through a 2.5-inch module was set to 2.0.
The same operation as in Example 5 was repeated except that the liter / min was increased. The degree of vacuum in the gas phase of the 2.5-inch module reached -0.085 MPa 40 minutes after the start of operation, and was stabilized at this pressure thereafter. After 120 minutes from the start of operation, the vacuum pump was stopped and the gas phase of the membrane degassing module was returned to normal pressure.
Forty minutes later, the pressure returned to normal pressure. Example 7 (Deaeration test) The amount of preliminary deaerated water passed through a 2.5-inch module was set to 4.0.
The same operation as in Example 5 was repeated except that the liter / min was increased. The degree of vacuum in the gas phase of the 2.5-inch module reached -0.085 MPa 25 minutes after the start of operation, and was stabilized at this pressure thereafter. After 120 minutes from the start of operation, the vacuum pump was stopped and the gas phase of the membrane degassing module was returned to normal pressure.
25 minutes later, the pressure returned to normal pressure. The results of Example 5, Example 6, and Example 7 are shown in FIG. From this result, it can be seen that, even with preliminary degassed water having the same degassing degree, the response to the degree of vacuum in the gas phase becomes faster as the flow rate increases.

[0015]

By applying the method and apparatus of the present invention, the total dissolved gas concentration in ultrapure water, which has recently attracted attention, can be measured very easily and collectively. Its management becomes easy. The value obtained by using the method and the apparatus of the present invention is not the absolute concentration of each gas component, but the sum of the degrees of saturation. It is a numerical value that reflects directly and is extremely useful information.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of one embodiment of a measuring device of the present invention.

FIG. 2 is a process flow chart showing one embodiment of the measuring method of the present invention.

FIG. 3 is a process flow chart showing another embodiment of the measurement method of the present invention.

FIG. 4 is a graph showing the relationship between the elapsed time and the degree of vacuum in Examples 5 to 7.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Closed container 2 Gas permeable membrane 3 Liquid phase chamber 4 Gas phase chamber 5 Inlet pipe 6 Discharge pipe 7 Pressure gauge 8 Degassing membrane module 9 Dissolved gas concentration measuring device 10 Dissolution membrane module 11 Main piping

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Osamu Ota 3-4-7 Nishi-Shinjuku, Shinjuku-ku, Tokyo Inside Kurita Industry Co., Ltd. (72) Inventor Junichi Ida 3-4-2 Nishishinjuku, Shinjuku-ku, Tokyo Kurita Industry Co., Ltd.

Claims (2)

[Claims] 1. A liquid and a gas phase are separated by a gas permeable membrane,
A method for measuring the concentration of dissolved gas in a liquid, comprising measuring the degree of vacuum of a gas phase in an equilibrium state with a liquid phase. 2. A gas permeable membrane is provided in a closed vessel, one side of which is partitioned into a liquid phase chamber and the other side is partitioned into a gas phase chamber, and an introduction pipe for introducing a test liquid into the liquid phase chamber and discharge. An apparatus for measuring the concentration of dissolved gas in a liquid, comprising: a discharge pipe; and a pressure gauge for measuring a degree of vacuum in a gas phase chamber.