JP7813685B2 - Method and apparatus for measuring water content in non-aqueous solvents - Google Patents

Description

The present invention relates to a method and device for measuring moisture in a non-aqueous solvent.

Highly purified nonaqueous solvents are used in the manufacturing processes for semiconductor devices and lithium-ion batteries. A known method for purifying nonaqueous solvents involves passing the nonaqueous solvent (liquid to be purified) through an ion exchange resin to remove impurities (ionic components such as metal ions) in the liquid to be purified (see, for example, Patent Document 1). However, this method carries the risk of water eluting from the ion exchange resin into the liquid to be purified, which could make it impossible to meet the recent demand for higher purity nonaqueous solvents. Therefore, prior to purifying nonaqueous solvents using the above-mentioned method, a dehydration process is also performed in which the nonaqueous solvent to be dehydrated (dehydration treatment liquid) is passed through an ion exchange resin to dissolve and remove the water contained in the dehydration treatment liquid (see, for example, Patent Document 2).

As such, in highly purified non-aqueous solvents, not only ionic components but also water become impurities. Therefore, the non-aqueous solvent purification process requires appropriate management of the water concentration in the non-aqueous solvent at various stages, and to do so, it is important to accurately understand the water concentration in the non-aqueous solvent. The Karl Fischer (KF) method has traditionally been widely used to measure the water concentration in non-aqueous solvents, as it is highly reliable and enables highly accurate quantitative analysis of water.

Special table 2015-521101 publication Japanese Patent Application Laid-Open No. 2021-109833

However, measuring water concentration using the KF method involves sampling the sample liquid to be measured and measuring its water concentration offline, which has the disadvantage of not being able to determine the water concentration in real time. Furthermore, if contamination occurs during sampling or if the sample liquid contains chemicals that interfere with the KF reaction (a quantitative reaction between water and iodine), there is a risk that measurement accuracy will be significantly reduced.

The object of the present invention is to provide a moisture measurement method and moisture measurement device that can measure the moisture concentration in a non-aqueous solvent in real time with high accuracy.

To achieve the above-mentioned objective, the method for measuring moisture in a non-aqueous solvent of the present invention includes the steps of: obtaining in advance the relationship between the number of microparticles in the non-aqueous solvent and the moisture concentration; measuring the number of microparticles in the non-aqueous solvent using a particle counter; and calculating the moisture concentration in the non-aqueous solvent from the measured number of microparticles using the previously obtained relationship.

The apparatus for measuring moisture content in a non-aqueous solvent of the present invention also includes a particle counter that measures the number of particles in the non-aqueous solvent, and a calculation means that calculates the moisture concentration in the non-aqueous solvent from the number of particles measured by the particle counter using a previously obtained relationship between the number of particles and the moisture concentration in the non-aqueous solvent.

This method and device for measuring moisture in a non-aqueous solvent focuses on the number of particles in the non-aqueous solvent, which can be measured online, and by obtaining in advance the correlation between this and the moisture concentration, it is possible to measure the moisture concentration in the non-aqueous solvent in real time with high accuracy.

As described above, the present invention makes it possible to measure the water concentration in a non-aqueous solvent in real time with high accuracy.

1 is a schematic configuration diagram of a liquid purification device according to a first embodiment of the present invention. 10 is a graph showing the results of an experiment conducted to verify the correlation between the number of fine particles and the water concentration in a dehydration treatment liquid. FIG. 4 is a schematic configuration diagram of a liquid purification device according to a second embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a liquid purification device according to a third embodiment of the present invention.

Embodiments of the present invention will be described below with reference to the drawings. Components common to the following embodiments will be designated by the same reference numerals in the drawings, and duplicate descriptions will be omitted where appropriate. Note that, although this specification uses an ion exchanger as an example of a means for purifying non-aqueous solvents, the present invention is not limited to this, and other purification means such as various filters and activated carbon may also be used.

(First embodiment)
1 is a schematic diagram of a liquid purification apparatus according to a first embodiment of the present invention. Note that the configuration of the liquid purification apparatus shown in the figure is merely an example, and it goes without saying that it can be modified as needed, for example, by adding valves or measuring instruments.

The liquid purification device 10 purifies the non-aqueous solvent by removing impurities (ionic components such as metal ions) from the non-aqueous solvent and supplies the purified non-aqueous solvent to a point-of-use. The non-aqueous solvent to be purified is not particularly limited, but examples include various organic solvents such as alcohols (isopropyl alcohol, methanol, ethanol, etc.), ketones (cyclohexanone, methyl isobutyl ketone, acetone, methyl ethyl ketone, etc.), alkenes (2,4-diphenyl-4-methyl-1-pentene, 2-phenyl-1-propene, etc.), esters (propylene glycol monomethyl ether acetate, isopropyl acetate, etc.), aromatics, and amines (N-methylpyrrolidone, etc.), as well as mixtures thereof.

The liquid purification system 10 has a packed tower 11 filled with an ion exchanger that functions as a means for purifying the nonaqueous solvent. The inlet and outlet of the packed tower 11 are connected to a solvent supply line L1, which carries the nonaqueous solvent to be purified (the liquid to be purified), and a solvent delivery line L2, which carries the purified nonaqueous solvent (the purified liquid). The liquid to be purified is supplied to the packed tower 11 through the solvent supply line L1, and after ionic components are removed by the ion exchanger in the packed tower 11, the purified liquid is delivered to the point of use through the solvent delivery line L2. The solvent supply line L1 is equipped with an on-off valve V1, which is used in the pretreatment process and moisture measurement preparation process described below, and the solvent delivery line L2 is equipped with an on-off valve V2, which is also used in the pretreatment process and moisture measurement preparation process.

Examples of ion exchangers packed into the packed column 11 include ion exchange resins and monolithic organic porous ion exchangers. Depending on the type of ion component to be removed, at least one of cation exchange resins and anion exchange resins can be used as the ion exchange resin. Examples of cation exchange resins include weakly acidic cation exchange resins and strongly acidic cation exchange resins, while examples of anion exchange resins include weakly acidic anion exchange resins and strongly acidic anion exchange resins. Monolithic organic porous ion exchangers have ion exchange groups introduced into the skeleton of a monolithic organic porous material. Compared to typical granular ion exchange resins, they have sufficient ion removal performance even at high treatment flow rates, which is advantageous in that it allows for the miniaturization of the equipment. Depending on the type of ion component to be removed, at least one of monolithic organic porous cation exchangers and monolithic organic porous anion exchangers can be used as the monolithic organic porous ion exchanger.

Note that, during the flow of the purified liquid, fine particles may be generated from ion exchangers such as ion exchange resins and monolithic organic porous ion exchangers. Therefore, to remove such fine particles from the ion exchangers, a porous membrane such as a microfiltration membrane (MF membrane) may be installed downstream of the ion exchanger in the packed tower 11.

However, when the liquid to be purified is passed through the packed tower 11, moisture contained in the ion exchangers, such as ion exchange resins and monolithic organic porous ion exchangers, may leach into the liquid to be purified, potentially preventing the production of a highly pure purified liquid. Therefore, in the liquid purification system 10, a dehydration process (pretreatment) is performed to remove moisture from the ion exchangers beforehand during start-up prior to the purification of the liquid to be purified (normal operation), such as when installing a new system or replacing the ion exchangers. Specifically, a nonaqueous solvent for the dehydration process (dehydration treatment liquid) is passed through the packed tower 11, and the moisture contained in the ion exchangers in the packed tower 11 is eluted into the dehydration treatment liquid and removed.

As a configuration for performing this dehydration process (i.e., a means for passing the dehydration treatment liquid), the liquid purification apparatus 10 has a dehydration treatment liquid line L3 that supplies the dehydration treatment liquid to the packed tower 11, and a drainage line L4 that discharges the dehydration treatment liquid that has flowed out of the packed tower 11 to the outside. The dehydration treatment liquid line L3 joins the solvent supply line L1 (specifically, downstream of the on-off valve V1) via the on-off valve V3, and the drainage line L4 branches off from the solvent delivery line L2 (specifically, upstream of the on-off valve V2) via the on-off valve V4. Note that instead of the on-off valves V1 and V3, a three-way valve may be provided at the confluence of the solvent supply line L1 and the dehydration treatment liquid line L3, and instead of the on-off valves V2 and V4, a three-way valve may be provided at the branch point of the solvent delivery line L2 and the drainage line L4.

In addition, for the above reasons, it is preferable for the liquid purification system 10 to manage the water concentration in the purified liquid during normal operation. To achieve this, the liquid purification system 10 includes a water content measuring device 20, which is comprised of a liquid particle counter (LPC) 21 and a calculation means 22. The LPC 21 is installed on the drain line L4, which functions as a sampling line for collecting the purified liquid during normal operation of the liquid purification system 10. As described in detail below, the LPC 21 is used to measure the number of particles, including microbubbles, present in the purified liquid. The calculation means 22 pre-stores information (e.g., a table or function) indicating the relationship between the number of particles and the water concentration in the nonaqueous solvent to be purified, and calculates the water concentration in the purified liquid using this information based on the number of particles measured by the LPC 21. In addition to the above-mentioned uses, the LPC 21 is also used to determine the timing to terminate the dehydration process of the ion exchanger. Hereinafter, unless otherwise specified, microbubbles and other particles (e.g., metal particles) are collectively referred to as "microparticles," and microparticles other than microbubbles are also referred to as "other microparticles." Therefore, "number of particles" means the total number of microbubbles and other particles.

The LPC21 provided on the drain line L4 is set to a flow rate (rated flow rate) that allows it to operate properly, and it is therefore preferable that the flow rate of the non-aqueous solvent supplied to the LPC21 be adjusted to that flow rate. Therefore, to adjust the flow rate of the non-aqueous solvent supplied to the LPC21, a flow adjustment valve may be provided on the drain line L4, or the solvent flow meter 12 described below may have such a flow rate adjustment function.

Furthermore, in order to perform the moisture measurement preparation process for obtaining the above-mentioned relationship, the liquid purification apparatus 10 is configured to be able to add moisture to the non-aqueous solvent flowing through the drain line L4 and measure the number of particles in the non-aqueous solvent while gradually changing the amount of moisture added. That is, in addition to the above-mentioned LPC 21, the liquid purification apparatus 10 has a moisture addition line L11, a solvent flow meter 12 provided in the drain line L4, a flow control valve V5 and an ultrapure water flow meter 13 provided in the moisture addition line L11. The liquid purification apparatus 10 also has a stirring means 14 provided in the drain line L4.

The water addition line L11 connects the ultrapure water line L5, which carries ultrapure water, to the drain line L4, and is provided to add ultrapure water (water) to the non-aqueous solvent flowing through the drain line L4. The flow control valve V5 adjusts the flow rate of ultrapure water flowing through the water addition line L11 and the amount of water added to the non-aqueous solvent flowing through the drain line L4. The solvent flow meter 12 and ultrapure water flow meter 13 are used to calculate the amount of water added, and measure the flow rate of the non-aqueous solvent flowing through the drain line L4 and the flow rate of ultrapure water flowing through the water addition line L11, respectively. The stirring means 14 functions to uniformly disperse the added ultrapure water in the non-aqueous solvent. There are no particular limitations on the stirring means 14, and a known means such as an in-line mixer can be used.

Here, we will explain the operating method of the liquid purification system 10. In particular, we will explain two processes that are performed prior to normal operation, namely the pretreatment process and the moisture measurement preparation process, and the purification process that is performed during normal operation.

[Pretreatment process]
As described above, the pretreatment process is a process carried out as part of the start-up operation of the liquid purification system 10, such as when installing a new system or replacing the ion exchanger, and is a process for removing water contained in unused or regenerated ion exchangers in advance.

When the pretreatment process begins, the on-off valves V3 and V4 on the dehydration treatment liquid line L3 and the drainage liquid line L4 are opened, and the on-off valves V1 and V2 on the solvent supply line L1 and the solvent delivery line L2 are closed. This supplies the dehydration treatment liquid to the packed tower 11 through the dehydration treatment liquid line L3, and within the packed tower 11, the water contained in the ion exchanger is replaced with the dehydration treatment liquid. In this way, the ion exchanger is dehydrated, and the water contained in the ion exchanger is dissolved into the dehydration treatment liquid and removed. The dehydration treatment liquid that has absorbed the water is discharged from the packed tower 11 to the outside through the drainage liquid line L4.

From the perspective of minimizing the amount of dehydration treatment liquid used, it is preferable to quickly terminate the pretreatment process once the water content of the ion exchanger in the packed tower 11 has been sufficiently reduced. When the water content of the ion exchanger is reduced as the dehydration treatment liquid is passed through, the amount of water eluted into the dehydration treatment liquid also decreases. Therefore, whether the water content of the ion exchanger has been sufficiently reduced can be confirmed by whether the water concentration in the dehydration treatment liquid flowing out from the packed tower 11 has been sufficiently reduced. While the Karl Fischer (KF) method can also be used to measure the water concentration in the dehydration treatment liquid, this method only allows offline measurements and therefore does not allow for real-time monitoring of the water concentration in the dehydration treatment liquid. Therefore, there is a time lag between when the water content of the ion exchanger is actually reduced and when this is confirmed, resulting in unnecessary disposal of the dehydration treatment liquid during that time.

Therefore, in this embodiment, when determining when to end the pretreatment process, attention is focused on the number of microparticles in the non-aqueous solvent, which can be measured online. This is because the inventors discovered the following: When water is mixed into a non-aqueous solvent, the solubility of gas (air) in the non-aqueous solvent decreases, and it is known that the dissolved gas in the non-aqueous solvent is generated as microbubbles. The number of microparticles containing such microbubbles is strongly correlated with the mixing ratio of the non-aqueous solvent to water, i.e., the water concentration. The experimental results that led to this discovery are described below.

The inventors conducted a liquid flow test simulating the pretreatment process of this embodiment and examined the relationship between the number of particles and the moisture concentration in the dehydrated liquid after the liquid flow. It should be noted that measuring the number of particles using LPC does not allow for distinction between microbubbles derived from moisture in the dehydrated liquid and other particles. Therefore, in order to accurately determine whether or not the desired correlation exists, it is preferable that the dehydrated liquid after the liquid flow does not contain other particles. Therefore, instead of an ion exchanger, which may generate other particles, the liquid flow test was conducted using a particle removal filter, and the relationship between the number of particles and the moisture concentration in the dehydrated liquid after the liquid flow was examined.

Specifically, a dehydrated liquid was passed through an unused particulate removal filter that had been stored in a wet state, and the number of particulates in the dehydrated liquid after passing through was continuously measured online using an LPC installed downstream of the particulate removal filter. Simultaneously, the dehydrated liquid flowing out of the particulate removal filter was sampled over time, and the moisture concentration of the sampled dehydrated liquid was measured offline using a KF moisture meter. The dehydrated liquid used was IPA, from which other particulates had been removed in advance and whose moisture concentration had been adjusted to 25 ppm or less. The particulate removal filter used was an ultra-high molecular weight polyethylene (UPE) particulate removal filter with a particle size of 20 nm manufactured by Entegris (product name: Optimizer® D filter). The flow rate of IPA when passing through the particulate removal filter was 10 mL/min.

To measure the number of particles, a liquid-borne particle counter (product name: KS-18F) manufactured by Rion Co., Ltd. was used, and the total number of particles (particles/mL) for each particle size category was used as the measured value. To measure the moisture concentration, a trace moisture analyzer (product name: AQ-2200F) manufactured by Hiranuma Sangyo Co., Ltd. was used. Note that, prior to installing the particle removal filter, the test system was cleaned by passing a dehydration treatment liquid through it to remove particles from the test system and reduce background noise. A simultaneous blank measurement was then performed to confirm that the measurement value from the liquid-borne particle counter had reached a steady state of 1 particle/mL or less, i.e., that the background noise was small enough to be ignored, before the above measurements were conducted.

Figure 2 is a graph showing the measurement results, illustrating the change in particle count and moisture concentration in the dehydration treatment liquid versus the total liquid flow rate. Figure 2 shows that there is a correlation between the particle count and moisture concentration in the dehydration treatment liquid, and that moisture concentration can be estimated by measuring the particle count in the dehydration treatment liquid. However, as indicated by the dashed ellipse in the graph, in the high moisture concentration range of the dehydration treatment liquid, where the moisture concentration exceeds 10,000 ppm, the particle count deviates significantly from this correlation. This is thought to be because when the moisture concentration in the dehydration treatment liquid is too high, some of the particles (microbubbles) generated in large quantities accordingly become trapped in the flow path, causing a time delay before they are measured by the LPC. Therefore, care must be taken when estimating moisture concentration from the particle count.

Therefore, in this embodiment, during the pretreatment process (while the dehydration treatment liquid is being passed through), the LPC 21 installed on the drain line L4 measures the number of particles in the dehydration treatment liquid flowing out of the packed tower 11. Then, based on the measured number of particles, it is determined whether to terminate the pretreatment process (passing the dehydration treatment liquid). Specifically, the measured value at that time is compared with the number of particles in the dehydration treatment liquid supplied to the packed tower 11, which is measured in advance or online (for example, by the LPC installed on the dehydration treatment liquid line L3). If the two values match within a predetermined error range, it is determined that the water content of the ion exchanger in the packed tower 11 has been sufficiently reduced, and it is determined that the pretreatment process should be terminated. Alternatively, it may be determined whether the water content of the ion exchanger in the packed tower 11 has been sufficiently reduced based on whether the number of particles in the dehydration treatment liquid after passing through the packed tower 11 has sufficiently decreased and reached a steady state. Whether the number of particles in the dehydrated liquid after passing through the packed tower 11 has reached a steady state can be determined, for example, by comparing two consecutive pieces of time-series data on the number of particles and determining whether they match within a specified error range.

In this way, by focusing on the number of fine particles in the dehydration treatment liquid, the amount of water eluted from the ion exchanger in the packed tower 11 into the dehydration treatment liquid can be indirectly measured in real time, making it possible to quickly determine whether the water content of the ion exchanger in the packed tower 11 has been sufficiently reduced. As a result, the time required for the pretreatment process (the start-up time until the ion exchanger in the packed tower 11 reaches a state where it can purify the non-aqueous solvent) can be minimized, and the amount of dehydration treatment liquid used can be minimized.

It is preferable to measure the number of particles using the LPC21 continuously, which allows for stable measurement results. Furthermore, since the LPC21 measurement values may become unstable for a certain period after measurement begins, it is preferable not to use it to determine the end of the pretreatment process. When dehydrating (pretreatment) an ion exchanger that has been stored in a wet state, a very large amount of water dissolves in the dehydration treatment liquid at the beginning of the pretreatment process, resulting in a very large number of particles in the dehydration treatment liquid. Therefore, the LPC21 may be contaminated by such a large amount of particles (microbubbles), or some of these particles may remain in the drainage line L4, preventing stable measurement of the number of particles using the LPC21. For this reason, it is preferable not to pass the dehydration treatment liquid through the LPC21 at the beginning of the pretreatment process. To achieve this, it is preferable to provide a bypass line in the drainage line L4 that bypasses the LPC21, or to provide a separate drainage line connected to the solvent supply line L2.

The dehydration treatment liquid used in the pretreatment step may be a nonaqueous solvent of a different type from the liquid to be purified. In this case, however, before the purification step, the liquid to be purified must be passed through the packed tower 11 to replace the dehydration treatment liquid in the packed tower 11 with the liquid to be purified. Therefore, it is preferable to use the same type of nonaqueous solvent as the liquid to be purified as the dehydration treatment liquid. That is, for example, when purifying isopropyl alcohol (IPA) as the liquid to be purified, it is preferable to use IPA as the dehydration treatment liquid.

It is also preferable that the nonaqueous solvent used as the dehydration treatment liquid be as pure as possible. That is, the water concentration in the dehydration treatment liquid is preferably as low as possible, for example, preferably equal to or less than the water concentration required for the purified liquid. This allows for a reduction in the amount of dehydration treatment liquid required for dehydrating the ion exchanger. It is also preferable that the concentrations of each ion in the dehydration treatment liquid are as low as possible, for example, preferably equal to or less than the concentrations required for the purified liquid. This prevents the ion exchange capacity of the ion exchanger from being consumed more than necessary in the pretreatment process, preventing a shortened lifespan for the ion exchanger.

In this embodiment, the dehydration treatment liquid is used as the standard liquid for acquiring (creating) concentration-relationship information in the water measurement preparation process described below. Therefore, the dehydration treatment liquid is a high-purity non-aqueous solvent of the same type as the liquid to be purified, from which both water and ionic components have been removed. "Removed" here refers not only to a state in which the water and ionic components have been completely removed, but also to a state in which the water and ionic components have been substantially removed. It also means that trace amounts of water and ionic components may be present, as long as they do not significantly affect the creation of concentration-relationship information.

As mentioned above, the particle counting by the LPC21 cannot distinguish between microbubbles and other particles. Therefore, to accurately measure the microbubbles resulting from the water content in the dehydration treatment liquid, it is preferable that the dehydration treatment liquid supplied to the LPC21 does not contain other particles. Therefore, it is preferable that the dehydration treatment liquid used in the pretreatment process not only has a low water concentration and ion concentration, but also a low particle count. To remove other particles that may be generated from the ion exchanger in the packed tower 11, a porous membrane such as an MF membrane may be installed in the packed tower 11 as described above, or may be provided as a particle removal filter in the drain line L4 upstream of the LPC21. In this case, the pore size of the porous membrane is preferably equal to or smaller than the minimum measurable particle size of the LPC21 so as not to allow the passage of particles that can be measured by the LPC21. The installation of such a particle removal filter is also effective in the water content measurement preparation process and purification process described below, in order to obtain desired measurement values by removing other particles from the nonaqueous solvent supplied to the LPC21.

The location of the particulate removal filter is not particularly limited as long as it is located upstream of the LPC 21, but is preferably located downstream of the agitator 14. The number of filters may be one, or multiple filters may be used so as to sequentially remove other particulates from the dehydration treatment liquid. In this case, the downstream filter preferably has a smaller pore size than the upstream filter, and is more preferably made of a different material. The pore size of each filter is not particularly limited, but it is preferable that at least one filter has a pore size equal to or smaller than the minimum measurable particle size of the LPC 21, as described above. The material of each filter is not particularly limited, and examples include polyethylene (PE), polytetrafluoroethylene (PTFE), and polyamide (PA) such as nylon.

[Moisture measurement preparation process]
The moisture measurement preparation step is performed after the pretreatment step is completed and before the purification step is started, in preparation for measuring the moisture concentration in the purified liquid, to obtain concentration relationship information indicating the relationship between the number of particles in the nonaqueous solvent to be purified and the moisture concentration. However, if such concentration relationship information is separately obtained and pre-stored in the calculation means 22 of the moisture measurement device 20, the moisture measurement preparation step does not need to be performed. Furthermore, the liquid purification device 10 does not need to be provided with a configuration for this purpose (such as the moisture addition line L11). Furthermore, since it is sufficient to obtain the concentration relationship information once for the nonaqueous solvent to be purified, the moisture measurement preparation step does not necessarily need to be performed after the pretreatment step, unless the type of nonaqueous solvent to be purified is changed.

As described above, once it is confirmed in the pretreatment process that the water content of the ion exchanger in the packed tower 11 has been sufficiently reduced, the moisture measurement preparation process begins. In this moisture measurement preparation process, the dehydrated liquid flowing through the drain line L4 (in this embodiment, a high-purity nonaqueous solvent of the same type as the liquid to be purified, from which both water and ionic components have been removed) is used as the standard liquid for acquiring (creating) concentration-related information. After other particulates are removed as needed, moisture is gradually added to this standard liquid. Specifically, the pressure in the drain line L4 is adjusted as needed by adjusting the opening of the on-off valve V4, while the flow control valve V5 of the moisture addition line L11 is gradually opened, gradually adding ultrapure water (moisture) to the standard liquid flowing through the drain line L4. At each step, i.e., each time the amount of water added to the standard liquid increases, the LPC 21 counts the number of particles in the standard liquid, and the measured data (preferably its moving average value) along with the amount of water added at that time is acquired by the calculation means 22. Based on the data thus acquired, the calculation means 22 then creates concentration relationship information (such as a table or function) that shows the relationship between the number of particles in the standard solution and the water concentration.

The amount of water to be added to the standard solution is calculated from the measurement value (preferably its moving average value) of the solvent flow meter 12 and the measurement value (preferably its moving average value) of the ultrapure water flow meter 13. Alternatively, if the pressure in the drain line L4 and the water addition line L11 is constant and the pressure difference between the ultrapure water line L5 and the drain line L4 and the viscosity of the standard solution are known, the amount of water to be added to the standard solution may be calculated from the opening of the flow control valve V5. In this case, the flow meters 12 and 13 may be omitted.

To obtain reliable concentration-related information, the LPC21 must provide stable measurement results. To achieve this, it is preferable to maintain a constant flow rate and pressure of the standard solution supplied to the LPC21. Therefore, when water is added to the standard solution through the water-addition line L11, it is preferable to adjust the pressure in the drain line L4 to a predetermined set pressure, for example, by adjusting the opening of the on-off valve V4. From this perspective, it is preferable that the supply of the dehydrated solution and the purified solution to the LPC21 in the pretreatment process described above and the purification process described below be performed under the same conditions as in the water content measurement preparation process. Furthermore, because the LPC21 is susceptible to environmental influences, it is preferable to use it in an environment within a preset operating temperature and humidity range. For example, the ambient temperature is preferably 5 to 50°C, and the ambient humidity is preferably 85% or less relative humidity without condensation. Furthermore, because vibrations in the device can generate bubbles or change the flow of generated bubbles, it is preferable to install the entire device in an environment free of external disturbances such as vibrations, and it may be installed in a clean room with controlled temperature and humidity.

Furthermore, as described in relation to Figure 2, in high-concentration regions where the water concentration in the standard solution exceeds 10,000 ppm, there is a possibility that a correlation with the number of microparticles does not exist. Therefore, it is preferable to acquire the concentration relationship information described above when the water concentration in the standard solution is in the range of 0 to 10,000 ppm. Therefore, when calculating the water concentration in a non-aqueous solvent using the concentration relationship information acquired in this way, it is also preferable that the calculation range be 0 to 10,000 ppm.

In this process, the agitation means 14 can uniformly disperse water, i.e., fine bubbles, in the standard solution, thereby stabilizing the measurement value of the LPC21. However, if the piping distance from the water addition point (the connection point between the drain line L4 and the water addition line L11) to the LPC21 is long or if the flow of standard solution in the drain line L4 becomes turbulent, the agitation means 14 can be omitted. Furthermore, while the solvent flow meter 12 may be located upstream of the LPC21, considering the possibility that elution from the solvent flow meter 12 may affect the measurement value of the LPC21, it is preferable to locate it downstream of the LPC21 as shown in the figure. Furthermore, as mentioned above, even if a flow control valve is provided in the drain line L4, it is preferable that it be located downstream of the LPC21.

[Purification process]
The purification process is a process in which the liquid to be purified is passed through the packed tower 10 and ion components contained as impurities in the liquid to be purified are removed using an ion exchanger in the packed tower 11, thereby purifying the liquid to be purified. This process is carried out during normal operation of the liquid purification device 10.

Once concentration relationship information indicating the relationship between the number of particles and the water concentration in the standard solution is created and acquired, the on-off valve V3 on the dehydrated solution line L3 and the flow control valve V5 on the water addition line L11 are closed. This stops the supply of the standard solution (dehydrated solution) from the dehydrated solution line L3 to the drain line L4 via the packed tower 11, and also stops the injection of ultrapure water into the drain line L4. The on-off valves V1 and V2 on the solvent supply line L1 and solvent delivery line L2 are then opened, starting the flow of the purified solution into the packed tower 11 and initiating the purification process. In the purification process, the purified solution is supplied to the packed tower 11 via the solvent supply line L1, and ionic components in the purified solution are removed by the ion exchanger in the packed tower 11. The purified solution obtained in this manner is sent to the point of use via the solvent delivery line L2.

In addition, during this process, the moisture concentration of the purified liquid is continuously measured by the moisture measuring device 20 as part of operational management to ensure a stable supply of high-purity purified liquid to points of use. That is, a portion of the purified liquid flowing through the solvent delivery line L2 is collected as a sample liquid via the sampling line (discharge line) L4, and the number of particles in the collected sample liquid is measured by the LPC 21, preferably continuously. At this time, other particles in the sample liquid are removed as necessary before the particle count is measured. The moisture concentration in the sample liquid is then calculated from the measured particle count using the concentration-related information stored in the calculation means 22. In this way, the moisture concentration of the purified liquid purified by the liquid purification device 10 is measured in real time with high accuracy.

Unlike the pretreatment process and the moisture measurement preparation process, the sample liquid flowing through the sampling line L4 in the purification process is a high-purity nonaqueous solvent, just like the purified liquid flowing through the solvent delivery line L2. Therefore, it does not necessarily need to be discharged to the outside. For example, to reduce the amount of nonaqueous solvent wasted, the sample liquid flowing through the sampling line L4 may be returned to the solvent delivery line L2. However, due to pressure loss in the LPC 21 and solvent flow meter 12, simply connecting the downstream side of the sampling line L4 to the solvent delivery line L2 does not allow the sample liquid flowing through the sampling line L4 to be returned to the solvent delivery line L2. Therefore, while it is possible to install a pump downstream of the sampling line L4, considering the impact of eluates from the pump, it is preferable to provide a pressure reduction means, such as an orifice, in the solvent delivery line L2 and connect the sampling line L4 downstream of that. Alternatively, if the pressure in the solvent delivery line L2 can be adjusted using the on-off valve V2, the sampling line L4 may be directly connected to the solvent delivery line L2.

In each of the above-described processes, the opening and closing of the on-off valves V1 to V4 and the adjustment of the opening degree of the flow rate control valve V5 may be performed automatically by a separately provided control means. That is, the liquid purification apparatus 10 may have a control means such as a controller that controls the operation of the liquid purification apparatus 10, and the on-off valves V1 to V4 and the flow rate control valve V5 may be automatic valves that can be controlled by that control means. Furthermore, the control means may, for example, determine whether or not to terminate the pretreatment process, and may also function as the calculation means 22 of the moisture measuring apparatus 20.

Second Embodiment
3 is a schematic diagram of a liquid purification system according to a second embodiment of the present invention. This embodiment differs from the first embodiment in the piping configuration for circulating the dehydrated treatment liquid. The following description will focus on these differences.

In this embodiment, the dehydration treatment liquid line L3 is provided in parallel with the solvent supply line L1 and the solvent delivery line L2. Accordingly, the drainage line L4 of the first embodiment is omitted, and the agitation means 14, moisture measuring device 20, and solvent flow meter 12 are provided in the dehydration treatment liquid line L3 rather than in the drainage line L4. The dehydration treatment liquid line L3 is connected to the solvent supply line L1 (specifically, downstream of the on-off valve V1) via a junction line L12, and the on-off valve V3 is provided in the junction line L12 rather than in the dehydration treatment liquid line L3. Furthermore, the dehydration treatment liquid line L3 is connected to the solvent delivery line L2 (specifically, upstream of the on-off valve V2) via a branch line L13, and the on-off valve V4 is provided in the branch line L13 rather than in the drainage line L4. The agitation means 14 is provided downstream of the connection between the dehydration treatment liquid line L3 and the branch line L13. In addition, the dehydrated liquid line L3 is equipped with an on-off valve V6 downstream of its connection with the junction line L12 and upstream of its connection with the water addition line L11. Note that the on-off valve V6 may be an automatic valve, similar to the on-off valves V1 to V4 and the flow rate adjustment valve V5.

Due to these configuration changes, the steps of the operating method of the liquid purification system 10 in this embodiment differ from those in the first embodiment in the following ways:

That is, in the pretreatment step, the on-off valves V3 and V4 on the junction line L12 and branch line L13 are opened, and the on-off valves V1 and V2 on the solvent supply line L1 and solvent delivery line L2, as well as the on-off valve V6 on the dehydration treatment liquid line L3, are closed. As a result, dehydration treatment liquid is supplied from the dehydration treatment liquid line L3 through the junction line L12 to the packed tower 11, and the dehydration treatment liquid flowing out of the packed tower 11 is discharged to the outside via the branch line L13 and the dehydration treatment liquid line L3.

Furthermore, during the moisture measurement preparation process, the on-off valves V3 and V4 on the junction line L12 and branch line L13 are closed, and the on-off valve V6 on the dehydration treatment liquid line L3 is opened. This causes the dehydration treatment liquid to be supplied to the dehydration treatment liquid line L3 as a standard liquid for acquiring (creating) concentration-relationship information, and the creation of concentration-relationship information begins.

Furthermore, during the purification process, the flow control valve V5 of the water addition line L11 and the on-off valve V6 of the dehydration treatment liquid line L3 are closed, and the on-off valves V1 and V2 of the solvent supply line L1 and the solvent delivery line L2 are opened. In this manner, the flow of the liquid to be purified into the packed tower 11 begins. In this embodiment, by opening the on-off valves V1 and V2 of the solvent supply line L1 and the solvent delivery line L2 after the pretreatment process is completed, the flow of the liquid to be purified into the packed tower 11 may begin simultaneously with the start of the water measurement preparation process.

As in the first embodiment, at least one particle removal filter may be provided in the dehydration treatment liquid line L3 upstream of the LPC21, preferably between the agitator 14 and the LPC21, to remove other particle particles in the nonaqueous solvent supplied to the LPC21 in each of the above-described steps. The pore size and material of this particle removal filter are as described in the first embodiment.

(Third embodiment)
4 is a schematic diagram of a liquid purification apparatus according to a third embodiment of the present invention. In the above-described embodiment, a high-purity nonaqueous solvent is used as the dehydration treatment liquid, but there are cases where such a high-purity nonaqueous solvent cannot be prepared. This embodiment is a modified example applicable to such cases, and differs from the above-described embodiment in that a liquid to be purified is used as the dehydration treatment liquid. The following description will focus on the differences from the first embodiment in this regard.

In this embodiment, the dehydration treatment liquid line L3 of the first embodiment is omitted, and the drainage line L4 branches off from the solvent supply line L1 (specifically, downstream of the on-off valve V1) rather than from the solvent delivery line L2. Accordingly, the on-off valve V3 is provided in the drainage line L4 rather than the dehydration treatment liquid line L3. Furthermore, the drainage line L4 is connected to the solvent delivery line L2 (specifically, the on-off valve V2) via a branch line L13, and the on-off valve V4 is provided in the branch line L13 rather than the drainage line L4. The stirring means 14 is provided downstream of the connection between the drainage line L4 and the branch line L13. Additionally, a moisture removal means 15 and an ion removal means 16 are provided in the drainage line L4 upstream of the point where water is added via the moisture addition line L11.

The moisture removal means 15 and ion removal means 16 are used in the moisture measurement preparation process, respectively, and function to remove moisture and ionic components from the purified liquid. The moisture removal means 15 is not particularly limited, and known materials such as zeolite can be used. The ion removal means 16 can be a dehydrated ion exchanger (such as an ion exchange resin or a monolithic organic porous ion exchanger) similar to the material packed in the packed tower 11. When using such an ion exchanger, it is preferable to provide a particle removal means downstream of the ion removal means 16, preferably between the agitation means 14 and the LPC 21, to remove other particulates generated therefrom. This particle removal means includes at least one porous membrane, such as an MF membrane, and has the same configuration and function as the particulate removal filter of the first embodiment.

Due to these configuration changes, the steps of the operating method of the liquid purification system 10 in this embodiment differ from those in the first embodiment in the following ways:

That is, in the pretreatment step, the on-off valves V1 and V4 on the solvent supply line L1 and branch line L13 are opened, and the on-off valves V2 and V3 on the solvent delivery line L2 and drain line L4 are closed. As a result, the liquid to be purified is supplied to the packed tower 11 from the solvent supply line L1 as the dehydration treatment liquid, and the dehydration treatment liquid flowing out of the packed tower 11 is discharged to the outside via branch line L13 and drain line L4. Note that in this embodiment, to determine the end of the pretreatment step, the number of particles in the dehydration treatment liquid after passing the liquid is compared with the number of particles corresponding to the required specifications for the water concentration in the purified liquid. However, apart from this point, the method for determining the end of the pretreatment step is the same as in the first embodiment.

During the moisture measurement preparation process, the on-off valve V3 on the drain line L4 is opened, and the on-off valves V2 and V4 on the solvent supply line L2 and branch line L13 are closed, allowing the purified liquid to be supplied from the solvent supply line L1 to the drain line L4. The moisture removal means 15 removes moisture from the purified liquid, and the ion removal means removes ionic components from the purified liquid, preparing a high-purity nonaqueous solvent standard solution. Ultrapure water (moisture) is added to the standard solution obtained in this manner through the moisture addition line L11, and the number of particles in the standard solution is measured by the LPC 21 while the amount of water added is gradually changed. This creates and acquires concentration-related information. To accurately measure the number of particles in the standard solution, it is preferable to ensure a sufficient flow rate of the standard solution supplied to the LPC 21. To this end, it is preferable to use a monolithic organic porous ion exchanger, which can achieve a high space velocity, as the ion removal means 16.

Furthermore, during the purification process, the on-off valve V3 on the drain line L4 and the flow control valve V5 on the water addition line L11 are closed, and the on-off valve V2 on the solvent delivery line L2 is opened, thereby starting the flow of the liquid to be purified into the packed tower 11. In this embodiment, by leaving the on-off valve V2 on the solvent delivery line L2 open rather than closing it after the pretreatment process is completed, the flow of the liquid to be purified into the packed tower 11 can be started simultaneously with the start of the water measurement preparation process.

In the above-described embodiment, the moisture measurement method focusing on the number of microparticles in a non-aqueous solvent was illustrated as being applied to a non-aqueous solvent purified using a liquid purification device, but it can also be applied to general non-purified non-aqueous solvents. However, before performing such moisture measurement, it is preferable to remove impurities other than moisture contained in the non-aqueous solvent to be measured, in particular other microparticles that cannot be distinguished from microbubbles in LPC measurements. In other words, it is preferable to remove other microparticles from the non-aqueous solvent to be measured using a microparticle removal filter made of a porous membrane such as an MF membrane.

In addition, in the above-described embodiment, another method focusing on the number of particles in a non-aqueous solvent, i.e., a method for determining the end of a pretreatment process, was illustrated as being applied to the dehydration process of an ion exchanger. However, this method can also be applied to pretreatment of other purification means other than ion exchangers. That is, while the above-described embodiment illustrates an ion exchanger as a purification means for a non-aqueous solvent, the liquid purification device may be provided with other purification means, such as various filters or activated carbon. Some of these other purification means are stored in a wet state before use, and some require pretreatment by passing a non-aqueous solvent (pretreatment liquid) through the purification means to replace the moisture contained in the purification means with non-aqueous solvent. For such purification means, the method for determining the end of a pretreatment process based on the number of particles in the non-aqueous solvent, as illustrated in the above-described embodiment, can be applied.

REFERENCE SIGNS LIST 10 Liquid purification apparatus 11 Packed column 12 Solvent flow meter 13 Ultrapure water flow meter 14 Stirring means 15 Water removal means 16 Ion removal means 20 Water content measuring device 21 Liquid particle counter (LPC)
22 Calculation means L1 Solvent supply line L2 Solvent delivery line L3 Dehydration treatment liquid line L4 Drainage line L5 Ultrapure water line L11 Water addition line L12 Confluence line L13 Branch line V1 to V4, V6 Open/close valve V5 Flow rate adjustment valve

Claims (9)

A method for measuring water content in a non-aqueous solvent, comprising:
a step of previously obtaining a relationship between the number of microparticles in the non-aqueous solvent and the water concentration;
using a particle counter to measure the number of particles in the non-aqueous solvent, and calculating the water concentration in the non-aqueous solvent from the measured number of particles using the previously obtained relationship. The moisture measurement method according to claim 1, further comprising a step of removing particles other than microbubbles contained in the non-aqueous solvent before measuring the number of particles in the non-aqueous solvent. The moisture measurement method of claim 2, wherein the step of removing particles other than microbubbles includes removing the particles other than microbubbles using a porous membrane having a pore size equal to or smaller than the minimum measurable particle size of the particle counter. The moisture measurement method according to any one of claims 1 to 3, wherein the moisture concentration in the non-aqueous solvent is measured in the range of 0 to 10,000 ppm. The step of acquiring the relationship in advance includes:
preparing the non-aqueous solvent from which water has been removed as a standard solution, and adding water to the standard solution;
The moisture measurement method according to claim 1 , further comprising the step of measuring the number of particles in the standard solution while gradually changing the amount of water added to the standard solution, and creating the relationship. The moisture measurement method of claim 5, wherein the step of acquiring the relationship in advance further includes a step of removing particles other than microbubbles contained in the standard solution before measuring the number of particles in the standard solution. The moisture measurement method of claim 6, wherein the step of removing particles other than microbubbles includes removing the particles other than microbubbles using a porous membrane having a pore size equal to or smaller than the minimum measurable particle size of the particle counter. The moisture measurement method of claim 5, wherein the relationship is created for a moisture concentration in the nonaqueous solvent in the range of 0 to 10,000 ppm. An apparatus for measuring water content in a non-aqueous solvent,
a particle counter that measures the number of fine particles in the non-aqueous solvent;
and a calculation means for calculating the water concentration in the non-aqueous solvent from the number of particles measured by the particle counter using a previously obtained relationship between the number of particles in the non-aqueous solvent and the water concentration.