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

Abstract

To measure the concentration of moisture in a non-aqueous solvent with high accuracy in real time.SOLUTION: A method of measuring moisture in a non-aqueous solvent includes the steps of: acquiring in advance a relationship between the number of particles and concentration of moisture in the non-aqueous solvent; and measuring, using a particle counter, the number of particles in the non-aqueous solvent, and calculating the concentration of moisture in the non-aqueous solvent, using the previously acquired relationship on the basis of the measured number of particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and an apparatus for measuring water content in a non-aqueous solvent. [Background technology]

[0002] Highly purified nonaqueous solvents are used in the manufacturing processes of 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 has 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 treatment is also performed in which the nonaqueous solvent to be dehydrated (liquid to be dehydrated) is passed through an ion exchange resin to dissolve and remove the water contained in the nonaqueous solvent into the liquid to be dehydrated (see, for example, Patent Document 2).

[0003] Thus, in highly purified non-aqueous solvents, not only ionic components but also water become impurities. Therefore, in the purification process of non-aqueous solvents, it is necessary to appropriately control the water concentration in the non-aqueous solvent at various stages, and for this purpose, it is important to accurately grasp the water concentration in the non-aqueous solvent. The Karl Fischer (KF) method has traditionally been widely used as a method for measuring the water concentration in non-aqueous solvents, as it is highly reliable and enables highly accurate quantitative analysis of water. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2015-521101 [Patent Document 2] Patent Publication No. 2021-109833 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the KF method for measuring water concentration has the disadvantage that the water concentration cannot be determined in real time because the sample liquid to be measured is sampled and its water concentration is measured offline. 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), the measurement accuracy may be significantly reduced.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a moisture measurement method and moisture measurement device that are capable of measuring the moisture concentration in a non-aqueous solvent in real time with high accuracy. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the method for measuring water content in a non-aqueous solvent of the present invention includes a step of previously obtaining the relationship between the number of particles in the non-aqueous solvent and the water concentration, and a step of measuring the number of particles in the non-aqueous solvent using a particle counter, and calculating the water concentration in the non-aqueous solvent from the measured number of particles using the previously obtained relationship.

[0008] The apparatus for measuring water 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 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.

[0009] According to this method and device for measuring water content in a non-aqueous solvent, by focusing 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 water concentration, the water concentration in the non-aqueous solvent can be measured in real time with high accuracy. [Effects of the Invention]

[0010] As described above, according to the present invention, the water concentration in a non-aqueous solvent can be measured in real time with high accuracy. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic configuration diagram of a liquid purification device according to a first embodiment of the present invention. [Figure 2] 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. [Figure 3] FIG. 4 is a schematic configuration diagram of a liquid purification device according to a second embodiment of the present invention. [Figure 4] FIG. 10 is a schematic configuration diagram of a liquid purification device according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Components common to the following embodiments will be designated by the same reference numerals in the drawings, and redundant explanations will be omitted where appropriate. Note that, although the present specification will be described using an ion exchanger as an example of a means for purifying a non-aqueous solvent, the present invention is not limited to this, and other purification means such as various filters and activated carbon may also be used.

[0013] (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.

[0014] Liquid purification apparatus 10 purifies a nonaqueous solvent by removing impurities (ionic components such as metal ions) from the nonaqueous solvent and supplies the purified nonaqueous solvent to a point of use. The nonaqueous solvent to be purified is not particularly limited, and 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.

[0015] The liquid purification apparatus 10 has a packed tower 11 packed with an ion exchanger that functions as a purification means for the nonaqueous solvent. The inlet and outlet of the packed tower 11 are connected to a solvent supply line L1, through which the nonaqueous solvent to be purified (liquid to be purified) flows, and a solvent delivery line L2, through which the purified nonaqueous solvent (liquid to be purified) flows, respectively. 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 provided with an on-off valve V1, which is used in the pretreatment step and the moisture measurement preparation step, which will be described later, and the solvent delivery line L2 is also provided with an on-off valve V2, which is also used in the pretreatment step and the moisture measurement preparation step.

[0016] Examples of the ion exchanger packed in 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. 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 incorporated 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 they allow for device miniaturization. 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.

[0017] During the flow of the purified liquid, fine particles may be generated from the ion exchanger, such as the ion exchange resin or the monolithic organic porous ion exchanger. Therefore, in order to remove such fine particles derived from the ion exchanger, a porous membrane, such as a microfiltration membrane (MF membrane), may be installed in the packed tower 11 downstream of the ion exchanger.

[0018] On the other hand, when the liquid to be purified is passed through packed tower 11, moisture contained in ion exchangers, such as ion exchange resins and monolithic organic porous ion exchangers, may leach into the liquid to be purified, which may result in failure to obtain a highly pure purified liquid. Therefore, in liquid purification apparatus 10, a dehydration treatment (pretreatment) is performed to remove moisture contained in the ion exchangers beforehand during start-up prior to the purification (normal operation) of the liquid to be purified, such as when installing a new apparatus or replacing the ion exchangers. Specifically, a nonaqueous solvent for the dehydration treatment (dehydration treatment liquid) is passed through packed tower 11, and the moisture contained in the ion exchangers in packed tower 11 is eluted into the dehydration treatment liquid and removed.

[0019] As a configuration for performing such a dehydration treatment (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 an 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 an on-off valve V4. Note that, instead of the on-off valves V1 and V3, a three-way valve may be provided at the junction 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 junction of the solvent delivery line L2 and the drainage line L4.

[0020] Furthermore, in the liquid purification apparatus 10, it is preferable to manage the concentration of water contained in the purified liquid during normal operation from the above-mentioned viewpoint. To achieve this, the liquid purification apparatus 10 includes a water content measuring device 20, which is composed of a liquid particle counter (LPC) 21 and a calculation means 22. The LPC 21 is provided on the drain line L4, which functions as a sampling line for collecting the purified liquid during normal operation of the liquid purification apparatus 10. As will be described in detail later, the LPC 21 is used to measure the number of particles, including microbubbles, present in the purified liquid. The calculation means 22 has a function of pre-storing 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 calculating the water concentration in the purified liquid using the information 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 treatment of the ion exchanger. Hereinafter, unless otherwise specified, microbubbles and other microparticles (e.g., metal microparticles) will be collectively referred to as "microparticles," and microparticles other than microbubbles will also be referred to as "other microparticles." Therefore, the "number of particles" means the total number of microbubbles and other particles.

[0021] Since the LPC 21 provided on the drain line L4 is set to a flow rate (rated flow rate) for proper operation, it is preferable that the flow rate of the non-aqueous solvent supplied to the LPC 21 be adjusted to such a flow rate. Therefore, in order to adjust the flow rate of the non-aqueous solvent supplied to the LPC 21, a flow rate 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.

[0022] Furthermore, in order to perform the water measurement preparation step for obtaining the above-mentioned relationship, liquid purification apparatus 10 is configured to be able to add water to the nonaqueous solvent flowing through drain line L4 and to measure the number of particles in the nonaqueous solvent while gradually changing the amount of water added. That is, in addition to the above-mentioned LPC 21, liquid purification apparatus 10 has a water addition line L11, a solvent flow meter 12 provided in drain line L4, a flow control valve V5 provided in water addition line L11, and an ultrapure water flow meter 13. Liquid purification apparatus 10 also has a stirring means 14 provided in drain line L4.

[0023] 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 nonaqueous 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 thus adjusts the amount of water added to the nonaqueous solvent flowing through the drain line L4. The solvent flow meter 12 and the ultrapure water flow meter 13 are used to calculate the amount of water added and measure the flow rates of the nonaqueous solvent flowing through the drain line L4 and the ultrapure water flowing through the water addition line L11, respectively. The stirring means 14 has the function of uniformly dispersing the added ultrapure water in the nonaqueous solvent. The stirring means 14 is not particularly limited, and a known means such as an in-line mixer can be used.

[0024] Here, we will explain the method of operating liquid purification system 10. In particular, we will explain two processes that are performed prior to normal operation, namely, a pretreatment process and a moisture measurement preparation process, and a purification process that is performed during normal operation.

[0025] [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.

[0026] When the pretreatment step is started, 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. As a result, the dehydration treatment liquid is supplied to the packed tower 11 through the dehydration treatment liquid line L3, and the water contained in the ion exchanger in the packed tower 11 is replaced with the dehydration treatment liquid. In this way, the ion exchanger is dehydrated, and the water contained in the ion exchanger is eluted 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.

[0027] From the viewpoint of minimizing the amount of dehydration treatment liquid used, it is preferable to terminate the pretreatment step promptly when the water content of the ion exchanger in the packed tower 11 has been sufficiently reduced. As the water content of the ion exchanger decreases with the flow of the dehydration treatment liquid, 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 discharged from the packed tower 11 has been sufficiently reduced. While the Karl Fischer (KF) method can 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, a time lag occurs between the actual reduction in the water content of the ion exchanger and the confirmation of this reduction, resulting in wasteful disposal of the dehydration treatment liquid during that time.

[0028] Therefore, in this embodiment, when determining the end time of the pretreatment step, attention is focused on the number of particles in the non-aqueous solvent, which can be measured online. The reason for this is the following finding made by the present inventors. This finding is that, as water is mixed into a non-aqueous solvent, the solubility of gas (air) in the non-aqueous solvent decreases, and the dissolved gas in the non-aqueous solvent is known to generate fine bubbles. The number of particles containing such fine bubbles 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 finding are described below.

[0029] The inventors conducted a liquid-passage test simulating the pretreatment process of this embodiment to examine the relationship between the number of particles and the water concentration in the dehydration treatment liquid after the liquid-passage. Since LPC measurement of the number of particles cannot distinguish between microbubbles derived from water in the dehydration treatment liquid and other particles, it is preferable that the dehydration treatment liquid after the liquid-passage does not contain other particles in order to accurately determine whether or not the desired correlation exists. Therefore, the liquid-passage test was conducted using a particle removal filter instead of an ion exchanger, which may generate other particles, to examine the relationship between the number of particles and the water concentration in the dehydration treatment liquid after the liquid-passage.

[0030] 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. IPA, from which other particulates had been removed and the moisture concentration adjusted to 25 ppm or less, was used as the dehydrated liquid. The particulate removal filter used was an ultra-high molecular weight polyethylene (UPE) filter manufactured by Entegris (product name: Optimizer® D filter) with a particle removal diameter of 20 nm. The flow rate of IPA was set to 10 mL / min when passing through the particulate removal filter.

[0031] The particle count was measured using a liquid particle counter (product name: KS-18F) manufactured by Rion Co., Ltd., and the total number of particles (particles / mL) for each particle size range was used as the measured value. The moisture concentration was measured using a trace moisture analyzer (product name: AQ-2200F) manufactured by Hiranuma Sangyo Co., Ltd. In practice, before 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 blank measurement was then performed simultaneously to confirm that the measurement value using the liquid particle counter had reached a steady state of 1 particle / mL or less, i.e., that the background noise was negligibly small, before the above measurements were performed.

[0032] Figure 2 is a graph showing the measurement results, showing the change in particle count and water concentration in the dehydration treatment liquid versus the total amount of liquid passing through. Figure 2 shows that there is a correlation between the particle count and water concentration in the dehydration treatment liquid, and that the water 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 water concentration range of the dehydration treatment liquid, exceeding 10,000 ppm, the particle count deviates significantly from this correlation. This is thought to be because when the water 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 the water concentration from the particle count.

[0033] Therefore, in this embodiment, during the execution of the pretreatment step (while the dehydration treatment liquid is being passed through), the LPC 21 provided on the drain line L4 measures the number of particles in the dehydration treatment liquid flowing out from the packed tower 11. Then, based on the measured number of particles, it is determined whether or not to terminate the pretreatment step (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 an LPC provided on the dehydration treatment liquid line L3). Then, when 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 step should be terminated. Alternatively, it may be determined whether or not 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.

[0034] In this way, by focusing on the number of 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, and it can be quickly determined 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 step (the start-up time until the ion exchanger in the packed tower 11 reaches a state where it can purify the nonaqueous solvent) can be shortened as much as possible, and the amount of dehydration treatment liquid used can be reduced as much as possible.

[0035] It is preferable that the LPC 21 measure the number of particles continuously, which allows for stable measurement results. Furthermore, since the measured values ​​of the LPC 21 may become unstable for a certain period after the start of measurement, it is preferable that the LPC 21 not be used to determine the end of the pretreatment process. When dehydrating (pretreatment) an ion exchanger stored in a wet state, a large amount of water dissolves in the dehydration treatment solution at the beginning of the pretreatment process, and therefore the number of particles in the dehydration treatment solution is also very large. Therefore, the LPC 21 may be contaminated by such a large amount of particles (microbubbles), or some of these particles may remain in the drainage line L4, which may prevent stable measurement of the number of particles by the LPC 21. For this reason, it is preferable not to pass the dehydration treatment solution through the LPC 21 at the beginning of the pretreatment process. To achieve this, it is preferable to provide a bypass line bypassing the LPC 21 in the drainage line L4, or to provide a separate drainage line connected to the solvent supply line L2.

[0036] 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 packed tower 11 to replace the dehydration treatment liquid in 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. 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.

[0037] Furthermore, it is preferable that the nonaqueous solvent used as the dehydration treatment liquid is as pure as possible. That is, it is preferable that the water concentration in the dehydration treatment liquid is 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 the dehydration treatment of the ion exchanger. It is also preferable that the ion concentrations in the dehydration treatment liquid are as low as possible, for example, preferably equal to or less than the ion 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 step, thereby preventing a shortened lifespan of the ion exchanger.

[0038] In this embodiment, the dehydration treatment liquid is used as a standard liquid for acquiring (creating) concentration-relationship information in the water measurement preparation step described below, and therefore, 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 dehydration treatment liquid. The term "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, and means that traces of water and ionic components may be present as long as they do not significantly affect the creation of concentration-relationship information.

[0039] As described above, the LPC21 cannot distinguish between microbubbles and other microparticles when counting microparticles. Therefore, to accurately measure the microbubbles resulting from water in the dehydrated solution, it is preferable that the dehydrated solution supplied to the LPC21 does not contain other microparticles. Therefore, it is preferable that the dehydrated solution used in the pretreatment process not only has a low water concentration and ion concentration, but also a low microparticle count. To remove other microparticles that may be generated from the ion exchanger in the packed tower 11, a porous membrane such as an MF membrane may be housed in the packed tower 11 as described above, or may be provided as a microparticle 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 microparticles that can be measured by the LPC21. The installation of such a microparticle removal filter is also effective in the water measurement preparation process and purification process described below, in order to obtain desirable measurement values ​​by removing other microparticles from the nonaqueous solvent supplied to the LPC21.

[0040] 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 more preferably is made of a different material. The pore size of each filter is not particularly limited, but at least one filter preferably 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.

[0041] [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 order to prepare for measuring the moisture concentration in the purified liquid by acquiring 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 acquired separately and stored in advance in the calculation means 22 of the moisture measuring device 20, the moisture measurement preparation step does not have to be performed. Furthermore, a configuration for this purpose (such as the moisture addition line L11) does not have to be provided in the liquid purification device 10. Furthermore, since it is sufficient to acquire the concentration-relationship information once for the nonaqueous solvent to be purified, the moisture measurement preparation step does not necessarily have to be performed after the pretreatment step is completed, unless the type of nonaqueous solvent to be purified is changed.

[0042] As described above, once it is confirmed in the pretreatment step that the water content of the ion exchanger in the packed tower 11 has been sufficiently reduced, the water content measurement preparation step is initiated. In the water content measurement preparation step, the dehydrated solution flowing through the drain line L4 (in this embodiment, a high-purity nonaqueous solvent of the same type as the purified solution, from which both water and ionic components have been removed) is used as a standard solution for acquiring (creating) concentration-relationship information. After other particles are removed as necessary, water is added to this standard solution in stages. Specifically, while the pressure in the drain line L4 is adjusted as necessary by adjusting the opening of the on-off valve V4, the flow control valve V5 of the water addition line L11 is opened in stages, and ultrapure water (water) is added in stages to the standard solution flowing through the drain line L4. At each stage, i.e., each time the amount of water added to the standard solution increases in stages, the LPC 21 counts the number of particles in the standard solution, and the measured data (preferably its moving average value) together with the amount of water added at that time are acquired by the calculation means 22. Then, based on the data thus acquired, the calculation means 22 creates concentration relationship information (table, function, etc.) that indicates the relationship between the number of particles and the water concentration in the standard solution.

[0043] 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 pressures in the drain line L4 and the water addition line L11 are 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 rate adjustment valve V5. In this case, the flow meters 12 and 13 may be omitted.

[0044] 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 dehydration treatment solution and the purified solution be supplied to the LPC21 in the pretreatment process described above and the purification process described below be supplied 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 predetermined 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 applied to 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. It may also be installed in a clean room with controlled temperature and humidity.

[0045] 2, in a high concentration range where the water concentration in the standard solution exceeds 10,000 ppm, there is a possibility that a correlation between the water concentration and the number of particles does not exist. Therefore, it is preferable that the above-mentioned concentration relationship information is acquired 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 the nonaqueous solvent using the concentration relationship information acquired in this way, the calculation range is also preferably 0 to 10,000 ppm.

[0046] In this step, the stirring means 14 can uniformly disperse water, i.e., fine bubbles, in the standard solution, thereby stabilizing the measurement value of the LPC 21. 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 LPC 21 is long or if the flow of the standard solution in the drain line L4 becomes turbulent, the stirring means 14 can be omitted. Furthermore, although the solvent flow meter 12 may be provided upstream of the LPC 21, it is preferable to provide it downstream of the LPC 21 as shown in the figure, considering the possibility that elution from the solvent flow meter 12 may affect the measurement value of the LPC 21. Furthermore, as described above, even if a flow control valve is provided in the drain line L4, it is also preferable that it be located downstream of the LPC 21.

[0047] [Refining 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.

[0048] 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 of the dehydrated solution line L3 and the flow control valve V5 of 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 through the packed tower 11, and also stops the injection of ultrapure water into the drain line L4. Then, the on-off valves V1 and V2 of the solvent supply line L1 and the solvent delivery line L2 are 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 through 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 through the solvent delivery line L2.

[0049] Furthermore, in this process, the moisture concentration of the purified liquid is continuously measured by the moisture measuring device 20 as part of operational management for ensuring 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 through the sampling line (drain line) L4, and the number of particles in the collected sample liquid is measured by the LPC 21, preferably continuously. At this time, before the number of particles is measured, other particles in the sample liquid are removed as necessary. Then, the moisture concentration of the sample liquid is calculated from the measured number of particles 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.

[0050] Unlike the pretreatment process and the water content 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, 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 due to pressure loss in the LPC 21 and the solvent flow meter 12. Therefore, while it is possible to install a pump downstream of the sampling line L4, considering the influence 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.

[0051] In each of the above-described steps, 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 the control means. Furthermore, the control means may, for example, determine whether or not to terminate the pretreatment step, and may also function as the calculation means 22 of the moisture measuring apparatus 20.

[0052] (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.

[0053] In this embodiment, a 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, the moisture measuring device 20, and the 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 provided with an on-off valve V6 downstream of the connection with the junction line L12 and upstream of the 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.

[0054] Due to such changes in configuration, the steps of the method of operating liquid purification system 10 in this embodiment differ from those in the first embodiment in the following respects.

[0055] That is, in the pretreatment step, the on-off valves V3 and V4 of the confluence line L12 and the branch line L13 are opened, and the on-off valves V1 and V2 of the solvent supply line L1 and the solvent delivery line L2, as well as the on-off valve V6 of the dehydrated solution line L3, are closed. As a result, the dehydrated solution is supplied from the dehydrated solution line L3 through the confluence line L12 to the packed tower 11, and the dehydrated solution flowing out of the packed tower 11 is discharged to the outside through the branch line L13 and the dehydrated solution line L3.

[0056] In the moisture measurement preparation step, the on-off valves V3 and V4 of the junction line L12 and the branch line L13 are closed, and the on-off valve V6 of the dehydration treatment liquid line L3 is opened. As a result, the dehydration treatment liquid is supplied to the dehydration treatment liquid line L3 as a standard liquid for acquiring (creating) the concentration-relationship information, and creation of the concentration-relationship information is initiated.

[0057] Furthermore, in the purification step, 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 liquid to be purified begins to be passed through the packed tower 11. In this embodiment, the on-off valves V1 and V2 of the solvent supply line L1 and the solvent delivery line L2 may be opened after the pretreatment step is completed, thereby starting the passage of the liquid to be purified through the packed tower 11 simultaneously with the start of the water content measurement preparation step.

[0058] As in the first embodiment, in order to remove other fine particles in the nonaqueous solvent supplied to the LPC 21 in each of the above-mentioned steps, at least one fine particle removal filter may be provided in the dehydration treatment liquid line L3 upstream of the LPC 21, preferably between the stirring means 14 and the LPC 21. The pore size and material of this fine particle removal filter are as described in the first embodiment.

[0059] (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. In this regard, the following description will focus on the differences from the first embodiment.

[0060] In this embodiment, the dehydration processing 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 supply line L2. Accordingly, the on-off valve V3 is provided in the drainage line L4 rather than the dehydration processing liquid line L3. The drainage line L4 is connected to the solvent supply 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. In addition, a moisture removal means 15 and an ion removal means 16 are provided in the drainage line L4 upstream of the position where moisture is added by the moisture addition line L11.

[0061] The moisture removal means 15 and the ion removal means 16 are each used in the moisture measurement preparation step and have the function of removing 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 an ion exchanger (such as an ion exchange resin or a monolithic organic porous ion exchanger) that has been subjected to a dehydration treatment, 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 stirring means 14 and the LPC 21, in order to remove other particles 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 particle removal filter of the first embodiment.

[0062] Due to such changes in configuration, the steps of the method of operating liquid purification system 10 in this embodiment differ from those in the first embodiment in the following respects.

[0063] That is, in the pretreatment step, the on-off valves V1 and V4 of the solvent supply line L1 and the branch line L13 are opened, and the on-off valves V2 and V3 of the solvent delivery line L2 and the 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 a dehydration treatment liquid, and the dehydration treatment liquid flowing out of the packed tower 11 is discharged to the outside through the branch line L13 and the drain line L4. In this embodiment, to determine the end of the pretreatment step, the number of particles in the dehydration treatment liquid after passing through the packed tower 11 is compared with the number of particles corresponding to the required specification for the water concentration in the purified liquid. Except for this point, the method for determining the end of the pretreatment step is the same as in the first embodiment.

[0064] In the moisture measurement preparation step, the on-off valve V3 of the drain line L4 is opened, and the on-off valves V2 and V4 of the solvent supply line L2 and branch line L13 are closed, and the purified liquid is 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, thereby 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, thereby creating and acquiring 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. For this purpose, it is preferable to use a monolithic organic porous ion exchanger, which can achieve a high space velocity, as the ion removal means 16.

[0065] Furthermore, in the purification step, the on-off valve V3 of the drain line L4 and the flow control valve V5 of the water addition line L11 are closed, and the on-off valve V2 of 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 of the solvent delivery line L2 open rather than closing it after the pretreatment step is completed, the flow of the liquid to be purified into the packed tower 11 may be started simultaneously with the start of the water content measurement preparation step.

[0066] In the above-described embodiment, the moisture measurement method focusing on the number of particles in a non-aqueous solvent was exemplified as being applied to a non-aqueous solvent purified by 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, especially other particles that cannot be distinguished from microbubbles in measurement by LPC. That is, it is preferable to remove other particles from the non-aqueous solvent to be measured using a particle removal filter made of a porous membrane such as an MF membrane.

[0067] In the above-described embodiment, another method focusing on the number of particles in a nonaqueous solvent, i.e., a method for determining the end of a pretreatment step, was illustrated as being applied to the dehydration treatment of an ion exchanger. However, the method can also be applied to pretreatment of other purification means other than ion exchangers. That is, although the above-described embodiment illustrates an ion exchanger as a nonaqueous solvent purification means, the liquid purification apparatus 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 pretreatment is required to replace the moisture contained in such purification means with a nonaqueous solvent (pretreatment liquid). For such purification means, the method for determining the end of a pretreatment step based on the number of particles in the nonaqueous solvent, as illustrated in the above-described embodiment, can be applied. [Explanation of symbols]

[0068] 10 Liquid purification equipment 11 Packed tower 12 Solvent flow meter 13 Ultrapure water flowmeter 14 Stirring means 15 Moisture removal means 16 Ion removal means 20 Moisture 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 merging line L13 branch line V1~V4, V6 shut-off valves V5 Flow Control Valve

Claims

1. 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.

2. The moisture measurement method according to claim 1 , further comprising the step of removing particles other than microbubbles contained in the non-aqueous solvent before measuring the number of particles in the non-aqueous solvent.

3. 3. The moisture measurement method according to 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.

4. The water content measuring method according to any one of claims 1 to 3, wherein the water content in the non-aqueous solvent is measured in the range of 0 to 10,000 ppm.

5. 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.

6. 6. The moisture measurement method according to claim 5, wherein the step of obtaining the relationship in advance further comprises the step of removing particles other than microbubbles contained in the standard solution before measuring the number of particles in the standard solution.

7. 7. The moisture measurement method according to 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.

8. 6. The moisture measurement method according to claim 5, wherein the relationship is created for a moisture concentration in the non-aqueous solvent in the range of 0 to 10,000 ppm.

9. 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.

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