JP7528671B2 - Dissolved gas concentration measuring device and measuring method - Google Patents

Description

The present invention relates to a liquid flow type dissolved gas concentration measuring device and measuring method that can easily and accurately measure the concentration of a gas dissolved in a liquid. The dissolved gas concentration measuring device and measuring method of the present invention are useful for water quality control of ultrapure water and cleaning water used in the cleaning process of precision machined parts such as semiconductor silicon wafers.

Ultrasonic cleaning is widely used in precision cleaning processes for electronic components and the like. In ultrasonic cleaning, the dissolved gas concentration in the cleaning water used affects the cleaning effect. In other words, it is desirable for the dissolved gas concentration of the cleaning water used in ultrasonic cleaning to be close to the saturation concentration, both in terms of high cleaning effect and minimizing damage to the object being cleaned. For this reason, it is necessary to measure the dissolved gas concentration of the cleaning water and rinsing water used in ultrasonic cleaning and control it to the desired concentration.

A variety of devices have been used to measure the concentration of dissolved gases in liquids, but none have been available that meet all the required characteristics in terms of accuracy when measuring dissolved gas concentration, especially concentrations near saturation, versatility to be applicable to many types of gases, cost, etc.

To solve this problem, Patent Document 1 proposes an apparatus for measuring the dissolved gas concentration in a test liquid by providing a gas-permeable membrane in a sealed container, dividing one side into a liquid phase chamber and the other side into a gas phase chamber, flowing the test liquid into the liquid phase chamber of the gas-permeable membrane module, providing a pressure gauge in the gas phase chamber to measure the degree of vacuum within the chamber, and measuring the degree of vacuum in the gas phase, which is in equilibrium with the liquid phase.

Figure 3 is a system diagram showing the dissolved gas concentration measuring device of Patent Document 1, in which 10 is a main pipe through which the test liquid, the object of which is to measure the dissolved gas concentration, flows, and has a flow rate control valve 10V. 1 is a gas permeable membrane module. In this gas permeable membrane module 1, the inside of a sealed container 2 is divided into a liquid phase chamber 4 and a gas phase chamber 5 by a gas permeable membrane 3. Connected to the liquid phase chamber 4 are a water sampling pipe 11 that separates a portion of the test liquid from the main pipe 10 as sample water and introduces it into the liquid phase chamber 4, and a discharge pipe 12 that discharges water from the liquid phase chamber 4. These pipes 11, 12 are provided with opening and closing valves 11V, 12V, respectively.

On the other hand, a gas pressure gauge 6 for measuring the gas pressure in the gas phase chamber 5 is provided in the gas phase chamber 5 via a gas pipe 13 having an opening/closing valve 13V.

The principle of measurement of dissolved gas concentration by such a dissolved gas concentration measuring device is as follows.

In other words, if the test liquid is completely degassed water, when it is passed through the liquid phase chamber 4, the gas in the gas phase chamber 5 inside the sealed container 2 is sucked into the degassed water through the gas permeable membrane 3, and the pressure inside the gas phase chamber 5 (hereinafter sometimes referred to as "gas phase pressure") approaches vacuum (gauge pressure -101.3 kPa). Conversely, if the test liquid contains dissolved gas equivalent to the saturation concentration under atmospheric pressure, when it is passed through the liquid phase chamber 4, the pressure inside the gas phase chamber 5 stabilizes near atmospheric pressure (gauge pressure ±0 kPa).

Since a gas phase pressure of -101.3 to 0 kPa corresponds to a dissolved gas concentration of 0 to saturated dissolved gas concentration in the test liquid, i.e., a saturation level of 0 to 100%, the saturation level of the dissolved gas in the test liquid can be calculated proportionally from the measured gas phase pressure, and if there is essentially one type of dissolved gas, the dissolved gas concentration in the test liquid can be calculated by multiplying the calculated saturation level (%) by the saturation concentration of the dissolved gas in the test liquid at atmospheric pressure.

The measuring device in Patent Document 1 is a simple and inexpensive device that can accurately measure the dissolved gas concentrations of many types of gases. However, when measurements are taken continuously over a long period of time, errors occur in the measured values, and there are still issues with the stability of the measurement accuracy.

In other words, when measurements are performed continuously over a long period of time with the measuring device of Patent Document 1, water vapor that moves from the liquid phase chamber through the membrane to the gas phase chamber condenses and accumulates in the gas phase chamber. At the same time, the hydrophobicity of the membrane surface is lost. These factors impede the movement of gas through the membrane, hindering accurate concentration measurement.

In order to solve these problems, Patent Document 2 proposes providing a condensate discharge pipe for discharging condensate into the gas phase chamber in a method and device for measuring dissolved gas concentration, in which the liquid and gas phases are separated by a gas-permeable membrane, the test liquid is passed through the liquid phase chamber, and the condensate in the gas phase chamber is discharged while measuring the degree of vacuum of the gas phase in equilibrium with the liquid phase.

JP 2000-65710 A JP 2006-71340 A

The present invention solves the problems of the conventional technology described above, and aims to provide a device and method for measuring the dissolved gas concentration of a test liquid by dividing the inside of a sealed container into a liquid phase chamber and a gas phase chamber with a gas-permeable membrane, flowing the test liquid into the liquid phase chamber, and measuring the pressure in the gas phase chamber, which prevents an increase in water in the gas phase chamber and hydrophilization of the membrane, and can always accurately measure the dissolved gas concentration even when used continuously for long periods of time, while providing a dissolved gas concentration measuring device and method with excellent measurement responsiveness.

The gist of the present invention is as follows:

[1] A dissolved gas concentration measuring device that has a gas-permeable membrane module in which a sealed container is divided into a liquid phase chamber and a gas phase chamber by a gas-permeable membrane, a liquid inlet pipe for introducing a test liquid into the liquid phase chamber, a liquid outlet pipe for discharging the test liquid from the liquid phase chamber, and a pressure gauge for measuring the pressure in the gas phase chamber, and that determines the dissolved gas concentration of the test liquid from the measured pressure in the gas phase chamber when the test liquid is passed through the liquid phase chamber, characterized in that the liquid phase chamber and the gas phase chamber have a volume of 30 mL or less, and are provided with a gas inlet pipe for introducing a drying gas into the gas phase chamber and a gas outlet pipe for discharging the drying gas from the gas phase chamber.

[2] The dissolved gas concentration measuring device according to [1], characterized in that the volume of the gas phase chamber is 0.5 to 30 mL, and the volume of the liquid phase chamber is 1 to 30 mL.

[3] The dissolved gas concentration measuring device according to [1] or [2], wherein a ratio _YG / _YL of a volume _YG of the gas phase chamber to a volume _YL of the liquid phase chamber is 0.3 to 2.5.

[4] In any one of [1] to [3], a dissolved gas concentration measuring device is provided that is characterized by having a switching means for switching between passing the test liquid through the liquid phase chamber, not passing the test liquid through the liquid phase chamber, and passing a drying gas through the gas phase chamber.

[5] A method for measuring dissolved gas concentration in a test liquid, using any one of the dissolved gas concentration measuring devices [1] to [4], by measuring the pressure in the gas phase chamber when the test liquid is passed through the liquid phase chamber, and determining the dissolved gas concentration in the test liquid, characterized in that the method for measuring dissolved gas concentration alternates between a measurement step of passing the test liquid through the liquid phase chamber and a regeneration step of stopping the passage of the test liquid through the liquid phase chamber and passing a drying gas through the gas phase chamber.

[6] The method for measuring a dissolved gas concentration according to [5], characterized in that in the measurement step, the test liquid is passed through the liquid phase chamber at a flow rate SV of 5 to 50 (h ^-1 ) per unit time, and in the regeneration step, the gas phase chamber is passed through at a flow rate SV of 10 to 200 (h ^-1 ) per unit time.

[7] The method for measuring a dissolved gas concentration according to [5] or [6], characterized in that the ratio of the time of the measurement process to the time of the regeneration process is 1:0.1 to 1.

According to the present invention, in an apparatus for measuring the dissolved gas concentration of a test liquid by dividing the inside of a sealed container into a liquid phase chamber and a gas phase chamber with a gas permeable membrane, passing the test liquid through the liquid phase chamber, and measuring the pressure in the gas phase chamber, the apparatus alternates between a measurement process in which the test liquid is passed through the liquid phase chamber to measure the dissolved gas concentration, and a regeneration process in which the passage of the test liquid is stopped and a drying gas is passed through the gas phase chamber, thereby preventing an increase in water in the gas phase chamber and hydrophilization of the gas permeable membrane, and making it possible to constantly and accurately measure the dissolved gas concentration of the test liquid, even during long-term continuous use.

In the present invention, the volume of the gas phase chamber is reduced, improving the responsiveness with which the pressure in the gas phase chamber reaches a pressure corresponding to the dissolved gas saturation. In addition, the volume of the gas phase chamber is small, so the consumption of drying gas is reduced. In the present invention, the volume of the liquid phase chamber is reduced, so the amount of drainage is reduced.

1 is a system diagram showing an example of an embodiment of a dissolved gas concentration measuring device of the present invention, illustrating the opening and closing of valves in a measurement process. 1 is a system diagram showing an example of an embodiment of a dissolved gas concentration measuring device of the present invention, illustrating the opening and closing of a valve in a regeneration process. FIG. 2 is a system diagram showing another embodiment of the dissolved gas concentration measuring device of the present invention, showing the opening and closing of the valves in the measurement process of the first gas permeation membrane module and the pause process of the second gas permeation membrane module. FIG. 2 is a system diagram showing another embodiment of the dissolved gas concentration measuring device of the present invention, showing the opening and closing of valves in the regeneration process of the first gas permeation membrane module and the measurement process of the second gas permeation membrane module. FIG. 2 is a system diagram showing another embodiment of the dissolved gas concentration measuring device of the present invention, showing the opening and closing of the valves in the resting process of the first gas permeation membrane module and the measuring process of the second gas permeation membrane module. FIG. 2 is a system diagram showing another embodiment of the dissolved gas concentration measuring device of the present invention, showing the opening and closing of valves in the measurement process of the first gas permeation membrane module and the regeneration process of the second gas permeation membrane module. FIG. 1 is a system diagram showing a conventional dissolved gas concentration measuring device.

The following describes in detail an embodiment of the dissolved gas concentration measuring device and measuring method of the present invention.

In the present invention, a measurement process in which the test liquid is passed through a liquid phase chamber with a volume of 30 mL or less and the gas pressure in a gas phase chamber with a volume of 30 mL or less is measured, and a regeneration process in which the passing of the test liquid through the liquid phase chamber is stopped and a drying gas is passed through the gas phase chamber are alternately repeated. The timing of the switching can be controlled by a simple timer, or by switching when water accumulating in the gas phase chamber is detected.

Various factors are involved in the hydrophilization of the gas-permeable membrane and the condensation of water vapor that has migrated to the gas phase chamber.

The main factors are the characteristics of the gas-permeable membrane itself, the temperature of the measurement environment, and the dissolved gas concentration in the test liquid. For example, the following may be considered:

As a gas-permeable membrane that does not allow water to pass through but allows gas to pass through, a porous membrane made of a hydrophobic polymer material such as polypropylene is preferable, and those generally used for degassing purposes are suitable. When the surface of such a gas-permeable membrane is oxidized (deteriorated) due to long-term water passage or contact with oxidizing fluids, the original hydrophobicity decreases. In a gas-permeable membrane with reduced hydrophobicity, water is likely to move from the liquid phase chamber to the gas phase chamber.

In addition, if the measurement environment temperature is low, the water vapor in the gas phase chamber is more likely to condense.

When the dissolved gas concentration in the test liquid is low, the gas in the gas phase chamber is sucked into the liquid phase chamber through the gas permeable membrane, lowering the air pressure in the gas phase chamber. As a result, the amount of water vapor moving from the liquid phase chamber to the gas phase chamber increases.

The combination of these conditions causes the membrane to become hydrophilic and increases the amount of condensation water on the gas phase side.

To efficiently handle any conditions, it would be possible to use some means to detect when a certain amount of condensation water has accumulated on the gas phase chamber side and switch to the regeneration process in which drying gas is introduced. However, if the water flow conditions do not change frequently, the purpose can be achieved sufficiently with simple timer control that identifies the tendency for fluctuations in the measurement values and the tendency for condensation water to increase under those conditions, and switches to the regeneration process before this affects accurate measurements.

According to the present invention, condensation water on the gas phase chamber side is discharged to the outside of the gas phase chamber by passing drying gas through the gas phase chamber, and in addition, the hydrophobicity of the gas permeable membrane can be restored by sufficiently drying the gas phase chamber side surface of the gas permeable membrane. Therefore, by inserting a regeneration process by passing drying gas through, the surface of the gas permeable membrane is not hydrophilized, so that it is maintained in a state close to that of a new membrane, and accurate measurement values can be easily obtained.

As mentioned above, the purpose of the regeneration process is to drain the condensation water and make the gas-permeable membrane hydrophobic, but the conditions can be determined in general as long as the drying gas aeration process can achieve this. If the measurement process in which the test liquid is passed is long and the regeneration process is started after a certain amount of condensation water has accumulated, it is desirable to make the conditions of the regeneration process stronger. In other words, the flow rate of the drying gas should be increased and the aeration time should be longer.

Conversely, if you move to the regeneration process when the amount of condensation is still minor and not enough to affect the measurement, you can achieve the desired objective with lighter conditions for the regeneration process (i.e., a lower flow rate of drying gas and a shorter ventilation time).

For these reasons, the respective times for the measurement process and regeneration process in the present invention vary depending on the water quality of the test liquid, the characteristics of the gas-permeable membrane, the measurement environment temperature, and other surrounding environmental conditions, and cannot be generally specified, but it is preferable that the ratio of the measurement process time to the regeneration process time is 1:0.1 to 1. One example is a time schedule in which a regeneration process of 0.2 to 6 hours is performed for every measurement process of 2 to 20 hours.

The drying gas used in the present invention is not particularly limited as long as it can exhaust the condensed water on the gas phase chamber side to the outside of the gas phase chamber and can sufficiently dry the gas phase chamber side surface of the gas permeable membrane, but dry gases such as nitrogen gas and clean dry air are preferred. In addition, if dry gas cannot be used, normal air can be used, although it has a lower regeneration effect (particularly the effect of drying the gas phase chamber side surface of the gas permeable membrane) than dry gas.

As described above, in the present invention, by alternating between the measurement process and the regeneration process, it is possible to stably obtain accurate measurement values over a long period of time.

In the present invention, the volume of the gas phase chamber is reduced, improving the responsiveness with which the pressure in the gas phase chamber reaches a pressure corresponding to the dissolved gas saturation. In addition, the small volume of the gas phase chamber reduces the consumption of drying gas. In addition, by reducing the volume of the gas phase chamber, the volume inside the connecting pipe becomes relatively large. Therefore, in order to reduce this effect, it is desirable to make the connecting pipe as short as possible.

In the present invention, the volume of the liquid phase chamber is reduced, which reduces the amount of water discharged.

If there is only one gas permeable membrane module, the measurement will be stopped during the regeneration process, resulting in intermittent measurement. However, by arranging two gas permeable membrane modules in parallel and using them alternately, or by arranging three or more gas permeable membrane modules in parallel and rotating them in a merry-go-round fashion, the measurement process and regeneration process can be carried out simultaneously for the entire device, making it possible to perform continuous measurement without interrupting the measurement.

When multiple gas-permeable membrane modules are arranged in parallel, it is not necessary to switch between aeration (regeneration) through the water-passing gas-permeable membrane module and water passage (measurement) through the regenerated gas-permeable membrane module at the same time. Instead, an overlap period is provided during which the same sample water is passed through two or more gas-permeable membrane modules at the same time prior to the switch from aeration to water passage, and once the gas-phase pressure of the module through which water is passed later becomes equivalent to that of the preceding module, the water passage through the preceding water-passing gas-permeable membrane module is switched to aeration, thereby avoiding fluctuations in gas-phase pressure during switching and enabling stable continuous measurement.

The principle of measuring the dissolved gas concentration using the gas permeable membrane module used in the present invention is as described above, but in precision cleaning processes for electronic components and the like, gas-dissolved water in which a single gas is dissolved in thoroughly degassed ultrapure water is widely used. In this way, when there is essentially only one type of dissolved gas in the test liquid, the dissolved gas concentration can be calculated by multiplying the saturation concentration of that gas at room temperature and atmospheric pressure (hydrogen is about 1.6 mg/L, oxygen is about 40 mg/L, nitrogen is about 18 mg/L) by the degree of saturation (%).

In addition, by creating a calibration curve in advance between the gas phase pressure measured by the dissolved gas concentration measuring device of the present invention and the dissolved gas saturation of the test liquid or the dissolved gas concentration calculated from this dissolved gas saturation, the dissolved gas concentration of the test liquid can be easily determined from the measured gas phase pressure.

In this case, the degree of saturation of the dissolved gas can be determined more accurately by subtracting the water vapor pressure corresponding to the temperature of the sample water from the gas phase pressure. When calculating the dissolved concentration from the degree of saturation of a specific gas, accurate calculations can be achieved by taking into account the temperature dependence of the saturation concentration.

There are no particular limitations on the dissolved gases that can be measured by the dissolved gas concentration measuring device and method of the present invention, and examples include nitrogen, oxygen, hydrogen, argon, mixed gases of these, and air. The present invention is useful for measuring the dissolved gas concentration in gas-dissolved water used in the cleaning process of electronic materials such as semiconductors and electronic displays (liquid crystal displays, plasma displays, organic electroluminescence, etc.).

Below, an embodiment of the dissolved gas concentration measuring device of the present invention will be described in more detail with reference to the drawings.

Figures 1A and 1B are system diagrams showing an example of an embodiment of the dissolved gas concentration measuring device of the present invention, and Figures 2A, 2B, 2C, and 2D are system diagrams showing other examples. In these figures, members that perform the same functions as the members shown in Figure 3 are given the same reference numerals.

Note that 10V indicates a flow control valve, and 11V, 12V, 13V, 14V, 15V, 11aV, 11bV, 12aV, 12bV, 13aV, 13bV, 14aV, 14bV, 15aV, and 15bV indicate opening and closing valves, with the open valves indicating valves that are "open" and the filled-in valves indicating valves that are "closed." Additionally, the piping indicated by solid lines indicates liquid flow paths, and the piping indicated by dotted lines indicates gas flow paths.

In Figures 1A and 1B, a single gas-permeable membrane module 20 alternates between a measurement process in which the test liquid is passed through the liquid phase chamber 4 and a regeneration process in which the passage of the test liquid through the liquid phase chamber 4 is stopped and a drying gas is passed through the gas phase chamber 5, thereby discharging water that has accumulated in the gas phase chamber 5 during the measurement process from the gas phase chamber 5 and drying the gas-permeable membrane 3 to restore hydrophobicity. The gas phase chamber 5 of the gas-permeable membrane module 20 is provided with a gas inlet pipe 14 for introducing a drying gas and a gas outlet pipe 15 for discharging the introduced drying gas from the gas phase chamber 5. 14V and 15V are on-off valves provided on the respective pipes 14 and 15.

The volume of the liquid phase chamber 4 is 30 mL or less, preferably 1 to 30 mL, and particularly preferably 1 to 25 mL. The volume of the gas phase chamber 5 is 30 mL or less, preferably 0.5 to 30 mL.

The ratio _YG / _YL of the volume _YG of the gas phase chamber 5 to the volume _YL of the liquid phase chamber 4 is preferably 0.3 to 2.5, particularly preferably 0.5 to 1.6.

To measure the dissolved gas concentration of the test liquid using the gas permeable membrane module 20 configured in this manner, first, as shown in FIG. 1A, open the on-off valves 11V, 12V, and 13V and close the on-off valves 14V and 15V, pass the sample water collected in the pipe 11 through the liquid phase chamber 4, and measure the pressure in the gas phase chamber 5 at this time with the gas pressure gauge 6. The dissolved gas concentration of the sample water is calculated from the measured gas phase pressure using the above-mentioned principle.

The sample water from pipe 12 may be discharged outside the system, or it may be returned to the main pipe 10 for the test liquid via the return pipe shown by the dashed dotted line.

The amount of water passing through the liquid phase chamber 4 per unit time SV is preferably 5 to 50 (h ⁻¹ ), and more preferably 10 to 35 (h ⁻¹ ).

After a specified period of measurement has been performed, or when it is detected that the measurement error has increased, the regeneration process is performed by switching the on-off valve as shown in Figure 1B.

That is, by opening the on-off valves 14V and 15V and closing the on-off valves 11V, 12V, and 13V, the sampling of sample water is stopped and the flow of water to the liquid phase chamber 4 is stopped, and instead, drying gas is passed from the gas inlet pipe 14 into the gas phase chamber 5 and discharged from the gas exhaust pipe 15, thereby discharging the water from the gas phase chamber 5 and drying the gas phase chamber side of the gas permeable membrane 3 to make the gas permeable membrane 3 hydrophobic. Note that although the on-off valve 12V is closed in this embodiment, it may be left open. In some cases, both on-off valves 11V and 12V may be opened to continue passing water while regenerating the gas phase chamber side.

The ventilation volume per unit time SV of the drying gas is preferably 10 to 200 (h ⁻¹ ), particularly preferably 20 to 100 (h ⁻¹ ).

After this regeneration process, the process switches back to the water flow process as shown in Figure 1A, and the regeneration process and the water flow process are repeated alternately thereafter.

The opening and closing of these valves 11V to 15V can be done automatically using timer control.

In contrast to the dissolved gas concentration measurement device shown in Figures 1A and 1B, a dissolved gas concentration measurement device equipped with two gas permeable membrane modules 20A and 20B as shown in Figures 2A to 2D can perform continuous measurements by alternately switching between the gas permeable membrane module performing measurement and the gas permeable membrane module performing regeneration.

In Figures 2A to 2D, 20A is a first gas-permeable membrane module, in which the inside of a sealed container 2a is divided into a liquid phase chamber 4a and a gas phase chamber 5a by a gas-permeable membrane 3a, and the liquid phase chamber 4a is provided with a pipe 11a branching off from a sample collection pipe 11 for the test liquid and a discharge pipe 12a, which is connected to a pipe 12. A gas pressure gauge 6a is provided in the gas phase chamber 5a via a pipe 13a, and a pipe 14a branching off from a drying gas introduction pipe 14 and a discharge pipe 15a are provided.

20B is a second gas-permeable membrane module, in which the inside of the sealed container 2b is divided into a liquid phase chamber 4b and a gas phase chamber 5b by a gas-permeable membrane 3b, and the liquid phase chamber 4b is provided with a pipe 11b branched off from the sample liquid sampling pipe 11 and a discharge pipe 12b, which is connected to the pipe 12. A gas pressure gauge 6b is provided in the gas phase chamber 5b via a pipe 13b, and a pipe 14b branched off from the drying gas introduction pipe 14 and a discharge pipe 15b are provided.

To perform continuous measurement of the test liquid using this dissolved gas concentration measuring device, first, as shown in FIG. 2A, open the on-off valves 11aV, 12aV, and 13aV and close the other on-off valves, pass the sample water collected in the pipe 11 through the liquid phase chamber 4a via the pipe 11a, and measure the pressure in the gas phase chamber 5a at this time with the gas pressure gauge 6a (measurement process of the first gas permeable membrane module 20A, rest process of the second gas permeable membrane module 20B).

After the measurement process in the first gas permeable membrane module 20A has been performed for a predetermined time, as shown in FIG. 2B, the on-off valves 11bV, 12bV, 13bV and on-off valves 14aV, 15aV are opened, and the other on-off valves are closed, switching the destination of the sample water to the second gas permeable membrane module 20B, and similar measurements are performed in the second gas permeable membrane module 20B, while in the first gas permeable membrane module 20A, drying gas is passed through the gas phase chamber 5a to discharge water and dry the gas permeable membrane 3a (regeneration process of the first gas permeable membrane module 20A, measurement process of the second gas permeable membrane module 20B).

After the regeneration process of the first gas permeable membrane module 20A has been performed for a predetermined time, as shown in FIG. 2C, the opening and closing valves 14aV and 15aV are closed, and only the opening and closing valves 11bV, 12bV, and 13bV are opened, and the measurement using the second gas permeable membrane module 20B is continued. In addition, all water and air flows are stopped for the first gas permeable membrane module 20A (resting process for the first gas permeable membrane module 20A, measuring process for the second gas permeable membrane module 20B).

After the measurement process in the second gas permeable membrane module 20B has been performed for a predetermined time, as shown in FIG. 2D, opening/closing valves 11aV, 12aV, 13aV and opening/closing valves 14bV, 15bV are opened, and the other opening/closing valves are closed, the destination of the sample water is switched to the first gas permeable membrane module 20A, and measurement in the first gas permeable membrane module 20A is resumed, while the regeneration process of the second gas permeable membrane module 20B is performed (measurement process of the first gas permeable membrane module 20A, regeneration process of the second gas permeable membrane module 20B).

Then, steps 2A to 2D are performed in sequence in the same manner. As a result, while measurements are being performed with the first gas permeable membrane module 20A, regeneration is being performed with the second gas permeable membrane module 20B, and while the first gas permeable membrane module 20A is being regenerated, measurements are being performed with the second gas permeable membrane module 20B, making it possible to continuously measure the dissolved gas concentration of the test liquid.

In the embodiment shown in Figures 2A to 2D described above, when switching from Figure 2A to Figure 2B and from Figure 2C to Figure 2D, valves 11aV, 12aV, 11bV, and 12bV are all open, and an overlap time is provided in which the same sample water is passed through both modules, enabling more stable continuous measurements.

In addition, in Figures 2A to 2D, as in Figures 1A and 1B, the sample water discharged from the liquid phase chambers 4a and 4b may be discharged outside the system or returned to the main pipe 10 for the test liquid.

To obtain a more accurate saturation degree of the dissolved gas, it is necessary to measure the temperature of the test water and subtract the atmospheric pressure of the saturated vapor pressure of the test water at that water temperature from the pressure in the gas phase chamber. Furthermore, when converting from the saturation degree to the dissolved gas concentration, it is necessary to use the saturated concentration of the gas based on the water temperature value in the calculation (for example, the saturated vapor pressure of water is 2.3 kPa at 20°C and 3.2 kPa at 25°C, and if the dissolved gas is _N2 , the saturated concentration is 18.9 mg/L at 20°C and 17.3 mg/L at 25°C).

The following examples will explain the present invention in more detail.

[Example 1, Comparative Example 1]
In the following examples and comparative examples, the gas-permeable membrane module used was a sealed container with external dimensions of 30 mm x 50 mm x 13 mm, in which a hollow fiber gas-permeable membrane was provided and partitioned into a gas phase chamber (volume _YG = 0.69 mL) and a liquid phase chamber (volume _YL = 1.22 mL). _YG / _YL = 0.57. The gas pressure gauge used was a "GC67 Digital Pressure Gauge" manufactured by Nagano Keiki Co., Ltd.

Degassed water (Example 1-1) and water with 90% gas dissolved in it (Example 1-2) were passed through this gas permeable membrane module. The test liquid was passed through the outside of the hollow fibers, and the gas was allowed to permeate into the hollow fibers.

High-purity _N2 gas with a moisture concentration of 0% was used as the drying gas.

The measurement error for the dissolved gas concentration in the test liquid was calculated using the following formula.

[Example 1-1: Measurement of dissolved gas concentration in deaerated water]
The test liquid was ultrapure water in which the dissolved _N2 gas concentration had been reduced to less than 1 mg/L (measured using an Orbissphere liquid-phase dissolved _N2 concentration meter) through degassing treatment. As shown in Figures 1A to 1D, the dissolved gas concentration was measured by continuously passing the water through a single gas permeable membrane module 20, which alternated between a measurement process and a regeneration process.

The regeneration process in each gas permeable membrane module 20 was carried out for 6 hours after every 18-hour measurement process. The test liquid flow rate in the measurement process was SV24.6 h ^-1 , and the drying gas flow rate in the regeneration process was 43.5 h ^-1 . The measurement error in continuous measurements over 30 days was determined, and the results are shown in Table 1.

[Example 1-2: Measurement of dissolved gas concentration in water with 90% saturation of gas solution]
The measurement error in continuous measurements for 30 days was determined in the same manner as in Example _1-1 , except that the test liquid was ultrapure water in which the dissolved _N2 gas concentration had been reduced to less than 1 mg/L by degassing treatment and _N2 gas had been dissolved to a saturation concentration of 90% (15.8 mg/L: measured value using an Orbissphere liquid-phase N2 meter). The results are shown in Table 1.

[Comparative Example 1-1: Measurement of Dissolved Gas Concentration in Deaerated Water]
Ultrapure water in which the dissolved _N2 gas concentration was reduced to less than 1 mg/L by degassing was used as the test liquid, and the dissolved gas concentration was measured using a conventional dissolved gas concentration measuring device shown in Figure 3. The gas permeable membrane module used here had the same configuration as the gas permeable membrane module used in Example 1-1, except that it did not have a ventilation means for drying gas, and measurements were performed continuously for 30 days without performing a regeneration process. The measurement error at this time was calculated, and the results are shown in Table 1.

[Comparative Example 1-2: Measurement of dissolved gas concentration in water with 90% gas saturation]
The measurement error in continuous measurements for 30 days was determined in the same manner as in Comparative Example 1-1, except that the test liquid was the same 90% saturated _N2 gas dissolved water as in Example 1-2, and the results are shown in Table 1.

As is clear from Table 1, in Comparative Example 1-1, which does not perform a regeneration process by passing drying gas through it, continuous measurement results in reduced measurement accuracy and increased measurement error. In particular, when the test liquid is degassed water, as described above, the gas in the gas phase chamber is sucked into the liquid phase chamber through the gas permeable membrane, lowering the air pressure in the gas phase chamber, resulting in an increase in water vapor moving from the liquid phase chamber to the gas phase chamber. Therefore, in Comparative Example 1-1, which does not have a regeneration process, water is likely to accumulate in the gas phase chamber, resulting in increased measurement error.

In contrast, in Example 1-1, in which a means for ventilating the drying gas into the gas phase chamber was provided and the measurement process and the regeneration process were performed alternately, there was no measurement error even after 30 days of continuous measurement, and measurements could be made with high accuracy.

[Example 2, Comparative Example 2]
The sealed container used had an outer dimension of 30 mmΦ×length of 180 mm. 1400 hollow fiber membranes with a length of 140 mm and an inner diameter of 0.4 mm were provided, and a module with a gas phase chamber volume of 25 mL, a liquid phase chamber volume of 16 mL, and Y _G /Y _L = 1.56 was produced. Measurements were performed in the same manner as in Examples 1-1 and 1-2 and Comparative Examples 1-1 and 1-2 with a water flow SV of 31.3 h ^-1 and aeration SV of 20.0 h ^-1 , and it was found that accurate measurements could be made in Example 2.

2, 2a, 2b Airtight container 3, 3a, 3b Gas permeable membrane 4, 4a, 4b Liquid phase chamber
5, 5a, 5b Gas phase chamber 6, 6a, 6b Gas pressure gauge 20, 20A, 20B Gas permeable membrane module

Claims (5)

A method for measuring a dissolved gas concentration in a test liquid using a dissolved gas concentration measuring device, comprising:
The dissolved gas concentration measuring device comprises:
a gas-permeable membrane module in which a sealed container is divided into a liquid phase chamber and a gas phase chamber by a gas-permeable membrane;
a liquid introduction pipe for introducing a test liquid into the liquid phase chamber and a liquid discharge pipe for discharging the test liquid from the liquid phase chamber;
a pressure gauge for measuring the pressure in the gas phase chamber;
A dissolved gas concentration measuring device for determining a dissolved gas concentration of a test liquid from a pressure measurement value in a gas phase chamber when the test liquid is passed through the liquid phase chamber, comprising:
The volume of the liquid phase chamber and the gas phase chamber is 30 mL or less;
a gas inlet pipe for introducing a drying gas into the gas phase chamber and a gas outlet pipe for discharging the drying gas from the gas phase chamber ;
a measuring step of passing a test liquid through the liquid phase chamber, measuring the pressure in the gas phase chamber, and determining the dissolved gas concentration of the test liquid;
a regeneration step of stopping the passage of the test liquid through the liquid phase chamber and passing a drying gas through the gas phase chamber,
Two gas permeable membrane modules were installed.
A method for measuring a dissolved gas concentration, characterized in that a measurement process is carried out in one gas permeable membrane module while a regeneration process is carried out in the other gas permeable membrane module, thereby continuously measuring the dissolved gas concentration in a test liquid . 2. The method for measuring a dissolved gas concentration according to claim 1, wherein the volume of the gas phase chamber is 0.5 to 30 mL, and the volume of the liquid phase chamber is 1 to 30 mL. 3. The method for measuring a concentration of a dissolved gas according to claim 1, wherein a ratio _YG / _YL of a volume _YG of the gas phase chamber to a volume _YL of the liquid phase chamber is 0.3 to 2.5. According to claim 1 or 2 , in the measuring step, the test liquid is passed through the liquid phase chamber at a flow rate per unit time SV=5 to 50 (h ⁻¹ );
The method for measuring a concentration of a dissolved gas, wherein in the regeneration step, aeration is performed through the gas phase chamber at a flow rate per unit time SV=10 to 200 (h ⁻¹ ). 3. The method for measuring a dissolved gas concentration according to claim 1 , wherein the ratio of the time of the measurement step to the time of the regeneration step is 1:0.1 to 1 .

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