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

Abstract

To enable accurate, real-time measurement of water content of non-aqueous solvents.SOLUTION: A method of measuring water content of a non-aqueous solvent is provided, the method comprising preparing a calibration curve representing a relationship between resistivity or conductivity of the non-aqueous solvent and water content in advance, and measuring resistivity or conductivity of the non-aqueous solvent to derive water content of the non-aqueous solvent from the measured resistivity or conductivity using the calibration curve prepared in advance.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for measuring moisture in a non-aqueous solvent and a moisture measuring device.

Background Art

[0002] In the manufacturing processes of semiconductor devices and lithium-ion batteries, highly purified non-aqueous solvents are used. As a method for purifying a non-aqueous solvent, a method is known in which a non-aqueous solvent to be purified (a liquid to be purified) is passed through an ion exchange resin, and impurities (ionic components such as metal ions) in the liquid to be purified are removed by the ion exchange resin (see, for example, Patent Document 1). However, in this method, there is a risk that moisture contained in the ion exchange resin elutes into the liquid to be purified, which may prevent meeting the recent requirements for high purity of non-aqueous solvents. Therefore, in the purification of non-aqueous solvents using the above-described method, prior to that, a dehydration treatment is also performed in which a non-aqueous solvent for dehydration treatment (dehydration treatment liquid) is passed through an ion exchange resin, and the contained moisture is eluted into the dehydration treatment liquid and removed (see, for example, Patent Document 2).

[0003] As described above, in a highly purified non-aqueous solvent, not only ionic components but also moisture becomes an impurity. Therefore, in the process of purifying a non-aqueous solvent, it is required to appropriately control the moisture concentration in the non-aqueous solvent in various situations, and for that purpose, it is important to accurately grasp the moisture concentration in the non-aqueous solvent. As a method for measuring the moisture concentration in a non-aqueous solvent, the Karl Fischer (KF) method, which has high reliability and enables quantitative analysis of moisture with high accuracy, has been widely used.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

[0005] However, the KF method for measuring water concentration has the disadvantage of not being able to determine the water concentration in real time, as it involves sampling the sample solution and measuring its water concentration offline. Furthermore, if contamination occurs during sampling, or if the sample solution contains chemicals that interfere with the KF reaction (a quantitative reaction between water and iodine), the measurement accuracy may be significantly reduced.

[0006] Therefore, the object of the present invention is to provide a moisture measurement method and a moisture measurement device that can measure the moisture concentration in a non-aqueous solvent in real time with high accuracy. [Means for solving the problem]

[0007] To achieve the above-mentioned objective, the present invention provides a method for measuring moisture content in a non-aqueous solvent, comprising the steps of: creating a calibration curve in advance that represents the relationship between the resistivity or conductivity of the non-aqueous solvent and the moisture content; A step to remove impurities other than water contained in the non-aqueous solvent, and after removing impurities other than water, The method includes the steps of measuring the resistivity or conductivity of a non-aqueous solvent and calculating the water concentration in the non-aqueous solvent using a pre-prepared calibration curve based on the measured resistivity or conductivity.

[0008] Furthermore, the moisture content measuring device in a non-aqueous solvent according to the present invention is A removal means for removing impurities other than water contained in a non-aqueous solvent, and a means from which impurities other than water have been removed. The system includes a measuring means for measuring the resistivity or conductivity of a non-aqueous solvent, and a calculation means for calculating the water concentration in the non-aqueous solvent using a calibration curve that has been prepared in advance and represents the relationship between the resistivity or conductivity of the non-aqueous solvent and the water concentration, based on the resistivity or conductivity measured by the measuring means.

[0009] With this method and apparatus for measuring moisture content in non-aqueous solvents, by focusing on the resistivity or conductivity of the non-aqueous solvent, which can be measured online, and pre-determining the correlation (calibration curve) between it and the moisture content, the moisture content 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 drawing]

[0011] [Figure 1] This is a schematic diagram of a liquid purification apparatus according to the first embodiment of the present invention. [Figure 2] This is a schematic diagram of a liquid purification apparatus according to a second embodiment of the present invention. [Figure 3] This is a schematic diagram of a liquid purification apparatus according to a third embodiment of the present invention. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described below with reference to the drawings. Components common to each of the following embodiments are denoted by the same reference numerals in the drawings, and redundant explanations will be omitted as appropriate.

[0013] (First Embodiment) Figure 1 is a schematic diagram of a liquid purification apparatus according to the first embodiment of the present invention. It goes without saying that the configuration of the liquid purification apparatus shown is merely an example, and can be modified as needed, for example, by adding valves or measuring instruments.

[0014] The liquid purification apparatus 10 purifies a non-aqueous solvent by removing impurities (ionic components such as metal ions) and supplies the purified non-aqueous solvent to the 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.

[0015] The liquid purification apparatus 10 has a packed column 11 filled with an ion exchanger that functions as a means of purifying a non-aqueous solvent. The inlet and outlet of the packed column 11 are connected to a solvent supply line L1 through which the non-aqueous solvent to be purified (liquid to be purified) flows, and to a solvent delivery line L2 through which the purified non-aqueous solvent (purified liquid) flows, respectively. Thus, the liquid to be purified is supplied to the packed column 11 through the solvent supply line L1, and after ionic components are removed by the ion exchanger in the packed column 11, it is sent as a purified liquid through the solvent delivery line L2 to the point of use. The solvent supply line L1 is provided with an on / off valve V1 used in the pretreatment process and moisture measurement preparation process described later, and the solvent delivery line L2 is also provided with an on / off valve V2 used in the pretreatment process and moisture measurement preparation process.

[0016] Examples of ion exchange materials packed into the packed column 11 include ion exchange resins and monolithic organic porous ion exchange materials. As for the ion exchange resin, at least one of cation exchange resins and anion exchange resins can be used depending on the type of ionic component to be removed. 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 exchange materials have ion exchange groups introduced into the framework of a monolithic organic porous material. Compared to general granular ion exchange resins, they have sufficient ion removal performance even at high processing flow rates, which is advantageous as it allows for miniaturization of the equipment. As for the monolithic organic porous ion exchange material, at least one of a monolithic organic porous cation exchange material and a monolithic organic porous anion material can be used depending on the type of ionic component to be removed.

[0017] During the passage of the liquid to be purified, fine particles may be generated from ion exchangers such as ion exchange resins and monolithic organic porous ion exchangers. Therefore, in order to remove such fine particles derived from the ion exchanger, a filtration membrane such as a microfiltration membrane (MF membrane) may be accommodated on the downstream side of the ion exchanger in the packed tower 11.

[0018] On the other hand, during the passage of the liquid to be purified through the packed tower 11, the moisture contained in the ion exchanger such as an ion exchange resin or a monolithic organic porous ion exchanger may elute into the liquid to be purified, thereby possibly preventing the obtainment of a highly pure purified liquid. Therefore, in the liquid purification apparatus 10, at the start-up before the purification (normal operation) of the liquid to be purified, such as when the apparatus is newly installed or when the ion exchanger is replaced, a dehydration treatment (pretreatment) for preliminarily removing the moisture contained in the ion exchanger is performed. Specifically, a non-aqueous solvent (dehydration treatment liquid) for dehydration treatment is passed through the packed tower 11, and a dehydration treatment is performed to elute the moisture contained in the ion exchanger in the packed tower 11 into the dehydration treatment liquid and remove it.

[0019] As a configuration for performing such a dehydration treatment (that is, a means for passing the dehydration treatment liquid), the liquid purification apparatus 10 has a dehydration treatment liquid line L3 for supplying the dehydration treatment liquid to the packed tower 11 and a drainage line L4 for discharging the dehydration treatment liquid flowing out from the packed tower 11 to the outside. The dehydration treatment liquid line L3 merges with the solvent supply line L1 (specifically, the downstream side of the on-off valve V1) via the on-off valve V3, and the drainage line L4 branches from the solvent feed line L2 (specifically, the upstream side of the on-off valve V2) via the on-off valve V4. Instead of the on-off valves V1 and V3, a three-way valve may be provided at the confluence point 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 branching point of the solvent feed line L2 and the drainage line L4.

[0020] Also, in the liquid purification apparatus 10, from the above viewpoints, it is preferable to control the concentration of moisture contained in the purified liquid during normal operation. As a configuration for this purpose, the liquid purification apparatus 10 includes a moisture measurement device 20 composed of a specific resistance meter 21 and an arithmetic unit 22. The specific resistance meter 21 is provided in a drain line L4 that functions as a sampling line for collecting the purified liquid during normal operation of the liquid purification apparatus 10, and functions as a measuring unit for measuring the specific resistance of the purified liquid. The arithmetic unit 22 stores a calibration curve (a relational expression or table representing the relationship between the specific resistance of the non-aqueous solvent and the moisture concentration) created in advance for the non-aqueous solvent to be purified, and has a function of calculating the moisture concentration in the purified liquid from the specific resistance measured by the specific resistance meter 21 using the calibration curve. In addition to the above-described uses, the specific resistance meter 21 is also used to determine the timing for ending the dehydration treatment of the ion exchanger.

[0021] In addition, since a flow rate range for the proper operation of the specific resistance meter 21 provided in the drain line L4 is set, the flow rate of the non-aqueous solvent supplied to the specific resistance meter 21 is preferably adjusted to such a flow rate range. Therefore, a flow rate adjustment valve for adjusting the flow rate of the non-aqueous solvent supplied to the specific resistance meter 21 may be provided in the drain line L4, or the solvent flow meter 12 described later may have such a flow rate adjustment function.

[0022] Furthermore, the liquid purification apparatus 10 has a configuration that can add moisture to the non-aqueous solvent flowing through the drain line L4 and measure the specific resistance of the non-aqueous solvent while changing the addition amount step by step in order to perform a moisture measurement preparation process for creating the above-described calibration curve. That is, the liquid purification apparatus 10 includes, in addition to the above-described specific resistance meter 21, a moisture addition line L11, a solvent flow meter 12 provided in the drain line L4, and a flow rate adjustment valve V5 and an ultrapure water flow meter 13 provided in the moisture addition line L11. The liquid purification apparatus 10 further includes stirring means 14 provided in the drain line L4.

[0023] The water addition line L11 connects the ultrapure water line L5, which carries ultrapure water, and 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 rate control valve V5 has the function of adjusting the flow rate of ultrapure water flowing through the water addition line L11 and adjusting the amount of water added to the non-aqueous 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 have the function of measuring 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 has the function of uniformly dispersing the added ultrapure water in the non-aqueous solvent. The stirring means 14 is not particularly limited, and known types such as in-line mixers can be used.

[0024] Here, we will describe the operation method of the liquid purification apparatus 10. In particular, we will describe two steps performed prior to normal operation, namely the pretreatment step and the moisture content measurement preparation step, and the purification step performed during normal operation.

[0025] [Pre-treatment process] As described above, the pretreatment process is performed as part of the startup operation of the liquid purification apparatus 10, such as when the apparatus is newly installed or when the ion exchanger is replaced, and is a process to remove water contained in unused or regenerated ion exchangers in advance.

[0026] When the pretreatment process begins, the on-off valves V3 and V4 of the dehydration liquid line L3 and the drainage line L4 are opened, while the on-off valves V1 and V2 of the solvent supply line L1 and the solvent delivery line L2 are closed. As a result, the dehydration liquid is supplied to the packed column 11 through the dehydration liquid line L3, and the water contained in the ion exchanger is replaced by the dehydration liquid inside the packed column 11. In this way, the ion exchanger is dehydrated, and the water contained in the ion exchanger is dissolved into the dehydration liquid and removed. The dehydration liquid, which has absorbed the water, is discharged from the packed column 11 to the outside through the drainage line L4.

[0027] From the viewpoint of minimizing the amount of dehydration solution used, the pretreatment process is preferably terminated quickly when the water content of the ion exchanger in the packed column 11 has been sufficiently reduced. As the water content of the ion exchanger is reduced by the passage of the dehydration solution, the amount of water eluted into the dehydration solution is also reduced. Therefore, whether or not the water content of the ion exchanger has been sufficiently reduced can be confirmed by whether or not the water concentration in the dehydration solution flowing out of the packed column 11 has been sufficiently reduced. Although the Karl Fischer (KF) method could be used to measure the water concentration in the dehydration solution, this method can only be measured offline, so it is not possible to grasp the water concentration in the dehydration solution in real time. Therefore, a time lag occurs between the actual reduction of the water content of the ion exchanger and its confirmation, resulting in the unnecessary disposal of the dehydration solution during that time. Therefore, in this embodiment, when determining the timing of the termination of the pretreatment process, we focus on resistivity, a physical quantity that has a strong correlation with the water concentration of the non-aqueous solvent and can be measured online.

[0028] In other words, in this embodiment, during the execution of the pretreatment process (while the dewatering liquid is flowing), the change in resistivity of the dewatering liquid flowing out of the packed column 11 is measured over time by a resistivity meter 21 installed in the drain line L4. Based on the measured change over time, it is determined whether or not to terminate the pretreatment process (flow of the dewatering liquid). Specifically, it is determined whether or not the resistivity has risen and reached a steady state, and if it has reached a steady state, it is determined that the water content of the ion exchanger in the packed column 11 has been sufficiently reduced, and it is determined to terminate the pretreatment process. Whether or not the resistivity of the dewatering liquid flowing out of the packed column 11 has reached a steady state can be determined, for example, by comparing two time-consecutive data points from the time-series resistivity data and determining whether or not they match within a predetermined error range. In other words, if the two data points match within a predetermined error range, it can be determined that the resistivity of the dewatering liquid flowing out of the packed column 11 has reached a steady state.

[0029] By focusing on the resistivity of the dehydration solution, the amount of water eluted from the ion exchanger in the packed column 11 into the dehydration solution can be measured indirectly in real time, allowing for a quick determination of whether the water content of the ion exchanger in the packed column 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 column 11 is ready for purification of the non-aqueous solvent) can be minimized, and the amount of dehydration solution used can be minimized.

[0030] While a different type of non-aqueous solvent may be used as the dehydrating solution in the pretreatment step, in that case, it is necessary to pass the liquid to be purified through the packed column 11 before the purification step to replace the dehydrating solution in the packed column 11 with the liquid to be purified. Therefore, it is preferable to use the same type of non-aqueous solvent as the liquid to be purified as the dehydrating solution. That is, for example, when purifying isopropyl alcohol (IPA) as the liquid to be purified, it is preferable to use IPA as the dehydrating solution.

[0031] Furthermore, the non-aqueous solvent used as the dehydration solution is preferably of the highest possible purity. That is, the water concentration in the dehydration solution is preferably as low as possible, for example, preferably equal to or lower than the water concentration required for the purification solution. This reduces the amount of dehydration solution required for the dehydration of the ion exchanger. The concentrations of each ion in the dehydration solution are also preferably as low as possible, for example, preferably equal to or lower than the concentrations of each ion required for the purification solution. This prevents the ion exchange capacity of the ion exchanger from being consumed unnecessarily in the pretreatment step, thereby suppressing a shortened lifespan of the ion exchanger.

[0032] In this embodiment, since the dehydrated solution is used as a standard solution for creating a calibration curve in the moisture content measurement preparation step described later, a high-purity non-aqueous solvent of the same type as the solution to be purified, from which both water and ionic components have been removed, is used as the dehydrated solution. Here, "removal" includes not only a state of complete removal but also a state of substantially removal, and it means that a small amount of water and ionic components may be present as long as it does not significantly affect the creation of the calibration curve.

[0033] Incidentally, if a high-purity non-aqueous solvent is passed through an ion exchanger whose water content has been sufficiently reduced, there will be almost no exchange of water between the non-aqueous solvent and the ion exchanger, so the resistivity of the non-aqueous solvent before and after passing through should be substantially the same. Therefore, as mentioned above, when a high-purity non-aqueous solvent is used as the dehydration solution, whether or not the water content of the ion exchanger in the packed column 11 has been sufficiently reduced can also be confirmed by comparing the resistivity of the dehydration solution before and after passing through the packed column 11.

[0034] In other words, in this embodiment, during the execution of the pretreatment process, in addition to the resistivity of the dewatering liquid discharged from the packed column 11, the resistivity of the dewatering liquid flowing into the packed column 11 may be measured, for example, by a resistivity meter installed in the dewatering liquid line L3. Based on these measurement results, it may be determined whether or not to terminate the pretreatment process. Specifically, if the resistivity of the dewatering liquid discharged from the packed column 11 matches the resistivity of the dewatering liquid flowing into the packed column 11 within a predetermined error range, it may be determined that the water content of the ion exchanger in the packed column 11 has been sufficiently reduced, and the pretreatment process may be terminated.

[0035] [Moisture measurement preparation process] The moisture measurement preparation step is performed after the pretreatment step and before proceeding to the purification step, in order to prepare for measuring the moisture concentration in the purified solution. This step is performed to create a calibration curve that shows the relationship between the resistivity of the non-aqueous solvent to be purified and its moisture concentration. However, if such a calibration curve is prepared separately and stored in advance in the calculation means 22 of the moisture measuring device 20, the moisture measurement preparation step does not need to be performed. Furthermore, the liquid purification device 10 does not need to be equipped with a configuration for this purpose (such as a moisture addition line L11). Also, since the creation of the calibration curve only needs to be done once for the non-aqueous solvent to be purified, the moisture measurement preparation step does not necessarily need to be performed after the pretreatment step unless the type of non-aqueous solvent to be purified is changed.

[0036] As described above, once it is confirmed that the water content of the ion exchanger in the packed column 11 has been sufficiently reduced in the pretreatment step, the moisture measurement preparation step is started. In the moisture measurement preparation step, a dewatered liquid (in this embodiment, 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) flowing through the drain line L4 is used as a standard solution for creating a calibration curve, and water is added to this standard solution in stages. Specifically, while the pressure in the drain line L4 is adjusted as needed by adjusting the opening of the on / off valve V4, the flow rate 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 this time, the resistivity of the standard solution is measured by the resistivity meter 21 at each stage, that is, each time the amount of water added to the standard solution increases in stages, and the measured data (preferably its moving average value) is acquired by the calculation means 22 along with the amount of water added at that time. Then, based on the data thus acquired, the calculation means 22 creates a calibration curve representing the relationship between the resistivity and water concentration of the standard solution, for example, using the least squares method.

[0037] The amount of water added to the standard solution is calculated from the measured value of the solvent flow meter 12 (preferably its moving average) and the measured value of the ultrapure water flow meter 13 (preferably its moving average). 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, as well as the viscosity of the standard solution, are known, the amount of water added to the standard solution may be calculated from the opening degree of the flow control valve V5. In that case, the flow meters 12 and 13 may be omitted.

[0038] Furthermore, in this process, the stirring means 14 can uniformly disperse water in the standard solution, thereby stabilizing the measurement value of the resistivity meter 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 resistivity meter 21 is long, or if the flow of the standard solution in the drain line L4 is turbulent, the stirring means 14 can be omitted. In addition, the solvent flow meter 12 may be provided upstream of the resistivity meter 21, but considering the possibility that eluted substances from the solvent flow meter 12 may affect the measurement value of the resistivity meter 21, it is preferable to provide it downstream of the resistivity meter 21 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 its position be downstream of the resistivity meter 21.

[0039] [Refining process] The purification process involves passing the liquid to be purified through the packed column 10 and removing ionic components contained as impurities in the liquid using an ion exchanger in the packed column 11, thereby purifying the liquid. This process is carried out during the normal operation of the liquid purification apparatus 10.

[0040] Once the calibration curve is created, the on-off valve V3 of the dehydration liquid line L3 and the flow control valve V5 of the water addition line L11 are closed. This stops the supply of the standard solution (dehydration liquid) from the dehydration liquid line L3 to the drain line L4 through the packed column 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 solvent delivery line L2 are opened, allowing the liquid to be purified to flow into the packed column 11, and the purification process begins. In the purification process, the liquid to be purified is supplied to the packed column 11 through the solvent supply line L1, and ionic components in the liquid are removed by the ion exchanger in the packed column 11. The purified liquid thus obtained is sent to the point of use through the solvent delivery line L2.

[0041] Furthermore, in this process, as part of operational management to ensure a stable supply of high-purity purified liquid to the point of use, the moisture content of the purified liquid is continuously measured by the moisture measuring device 20. Specifically, a portion of the purified liquid flowing through the solvent delivery line L2 is collected as a sample liquid through the sampling line (drainage line) L4, and the resistivity of the collected sample liquid is measured by the resistivity meter 21. Then, the moisture content of the sample liquid is calculated from the measured resistivity using a calibration curve stored in the calculation means 22. In this way, the moisture content of the purified liquid purified by the liquid purification device 10 is measured in real time with high accuracy.

[0042] Furthermore, the resistivity of a non-aqueous solvent is strongly correlated not only with the water content in the solvent but also with the concentration of other impurities (ionic components such as metal ions and fine particles). Therefore, if the performance of the ion exchanger in the packed column 11 deteriorates, ionic components contained in the liquid being purified will leak into the purified liquid without being removed, and this will be reflected in the measurement results of the resistivity meter 21. For this reason, the measurement results of the resistivity meter 21 in the purification process can also be used to determine whether the performance of the ion exchanger in the packed column 11 has deteriorated, that is, whether or not the ion exchanger needs to be replaced.

[0043] Unlike the pretreatment and moisture content preparation steps, the sample liquid flowing through the sampling line L4 in the purification step is the same high-purity non-aqueous solvent as the purified liquid flowing through the solvent delivery line L2, and therefore does not necessarily need to be discharged to the outside. For example, from the viewpoint of reducing the amount of non-aqueous solvent waste, the sample liquid flowing through the sampling line L4 may be recirculated into the solvent delivery line L2. However, due to the pressure loss of the resistivity meter 21 and the solvent flow meter 12, simply connecting the downstream side of the sampling line L4 to the solvent delivery line L2 will not allow the sample liquid flowing through the sampling line L4 to be recirculated into the solvent delivery line L2. Therefore, it is conceivable to install a pump downstream of the sampling line L4, but considering the influence of elutions 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 it. Alternatively, if the pressure in the solvent delivery line L2 can be adjusted by the on-off valve V2, the sampling line L4 may be connected directly to the solvent delivery line L2.

[0044] In each of the processes described above, the opening and closing of the on-off valves V1 to V4 and the adjustment of the opening degree of the flow 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 control valve V5 may be automatic valves that can be controlled by that control means. Furthermore, that control means may, for example, determine whether or not to terminate the pretreatment process, and may also perform the function of the calculation means 22 of the moisture content measuring device 20.

[0045] (Second embodiment) Figure 2 is a schematic diagram of a liquid purification apparatus according to a second embodiment of the present invention. This embodiment differs from the first embodiment in the piping configuration for circulating the dewatered liquid. The following will focus on these differences.

[0046] In this embodiment, the dewatering liquid line L3 is provided in parallel with the solvent supply line L1 and the solvent delivery line L2. Accordingly, the drain line L4 of the first embodiment is omitted, and the stirring means 14, moisture measuring device 20, and solvent flow meter 12 that were provided in the drain line L4 are provided in the dewatering liquid line L3. The dewatering liquid line L3 is connected to the solvent supply line L1 (specifically, the downstream side of the on-off valve V1) via the confluence line L12, and the on-off valve V3 that was provided in the dewatering liquid line L3 is provided in the confluence line L12. Furthermore, the dewatering liquid line L3 is connected to the solvent delivery line L2 (specifically, the upstream side of the on-off valve V2) via the branch line L13, and the on-off valve V4 that was provided in the drain line L4 is provided in the branch line L13. The stirring means 14 is provided upstream of the connection point between the dewatering liquid line L3 and the branch line L13. In addition, the dewatering liquid line L3 is equipped with an on-off valve V6 downstream of the connection point with the merging line L12 and downstream of the connection point 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 control valve V5.

[0047] Due to these configuration changes, each step of the operating method of the liquid purification apparatus 10 in this embodiment differs from that of the first embodiment in the following respects.

[0048] In other words, during the pretreatment process, the on-off valves V3 and V4 of the confluence line L12 and branch line L13 are opened, while the on-off valves V1 and V2 of the solvent supply line L1 and solvent delivery line L2, as well as the on-off valve V6 of the dewatering liquid line L3, are closed. As a result, the dewatering liquid is supplied from the dewatering liquid line L3 to the packed tower 11 through the confluence line L12, and the dewatering liquid that flows out of the packed tower 11 is discharged to the outside through the dewatering liquid line L3 via the branch line L13.

[0049] Furthermore, during the moisture measurement preparation process, the on-off valves V3 and V4 of the confluence line L12 and branch line L13 are closed, while the on-off valve V6 of the dewatering liquid line L3 is opened. As a result, the dewatering liquid is supplied to the dewatering liquid line L3 as a standard solution for creating the calibration curve, and the creation of the calibration curve begins.

[0050] 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 liquid line L3 are closed, while the on-off valves V1 and V2 of the solvent supply line L1 and solvent delivery line L2 are opened. In this way, the flow of the liquid to be purified into the packed column 11 begins. In this embodiment, however, by opening the on-off valves V1 and V2 of the solvent supply line L1 and solvent delivery line L2 after the completion of the pretreatment process, the flow of the liquid to be purified into the packed column 11 may begin simultaneously with the start of the moisture measurement preparation process.

[0051] (Third embodiment) Figure 3 is a schematic diagram of a liquid purification apparatus according to a third embodiment of the present invention. In the embodiments described above, a high-purity non-aqueous solvent is used as the dehydration liquid, but there are cases where such a high-purity non-aqueous solvent cannot be prepared. This embodiment is a modified version that can be applied in such cases and differs from the embodiments described above in that the liquid to be purified is used as the dehydration liquid. The following will explain this point in detail, focusing on the differences from the first embodiment.

[0052] In this embodiment, the dehydration liquid line L3 of the first embodiment is omitted, and the drainage line L4, which branched from the solvent delivery line L2, is branched from the solvent supply line L1 (specifically, downstream of the on-off valve V1). Accordingly, the on-off valve V3 that was provided in the dehydration liquid line L3 is now provided in the drainage line L4. Furthermore, the drainage line L4 is connected to the solvent delivery line L2 (specifically, the on-off valve V2) via the branch line L13, and the on-off valve V4 that was provided in the drainage line L4 is now provided in the branch line L13. The stirring means 14 is provided upstream of the connection point between the drainage line L4 and the branch line L13. In addition, a water removal means 15 and an ion removal means 16 are provided upstream of the water addition point by the water addition line L11 in the drainage line L4.

[0053] The water removal means 15 and the ion removal means 16 are used in the water content measurement preparation step, and each has the function of removing water and ionic components from the liquid to be purified. The water removal means 15 is not particularly limited, and known materials such as zeolites can be used. As the ion removal means 16, an ion exchange material (such as an ion exchange resin or a monolithic organic porous ion exchange material) that has been dehydrated, similar to those packed in the packed column 11, can be used. Furthermore, when using such an ion exchange material, it is preferable to provide a filtration means including a filtration membrane such as an MF membrane downstream of the ion removal means 16 in order to remove fine particles generated therefrom.

[0054] Due to these configuration changes, each step of the operating method of the liquid purification apparatus 10 in this embodiment differs from that of the first embodiment in the following respects.

[0055] In other words, during the pretreatment process, the on-off valves V1 and V4 of the solvent supply line L1 and branch line L13 are opened, while the on-off valves V2 and V3 of the solvent delivery line L2 and drain line L4 are closed. As a result, the liquid to be purified is supplied to the packed column 11 from the solvent supply line L1 as the dewatering liquid, and the dewatering liquid that flows out of the packed column 11 is discharged to the outside through the drain line L4 via the branch line L13. Even when the liquid to be purified is used as the dewatering liquid, once the water content of the ion exchanger in the packed column 11 is sufficiently reduced, the resistivity of the dewatering liquid flowing out of the packed column 11 reaches a steady state, so the method for determining the end of the pretreatment process is the same as in the first embodiment.

[0056] Furthermore, in the moisture measurement preparation step, the on-off valve V3 of the drainage 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 liquid to be purified is supplied from the solvent supply line L1 to the drainage line L4. Then, the water is removed from the liquid to be purified by the water removal means 15, and the ionic components in the liquid to be purified are removed by the ion removal means, thereby preparing a standard solution, which is a high-purity non-aqueous solvent. Ultrapure water (water) is added to the standard solution obtained in this way through the water addition line L11, and the resistivity of the standard solution is measured by the resistivity meter 21 while gradually changing the amount of water added, thereby creating a calibration curve. At this time, in order to accurately measure the resistivity of the standard solution, it is preferable that the flow rate of the standard solution supplied to the resistivity meter 21 is sufficiently secured. For this reason, it is preferable to use a monolithic organic porous ion exchanger that can obtain a large space velocity as the ion removal means 16.

[0057] Furthermore, during the purification process, the on-off valve V3 of the drainage line L4 and the flow rate 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 initiating the flow of the liquid to be purified into the packed column 11. In this embodiment, however, the on-off valve V2 of the solvent delivery line L2 may be left open after the completion of the pretreatment process, thereby initiating the flow of the liquid to be purified into the packed column 11 simultaneously with the start of the moisture measurement preparation process.

[0058] In the embodiments described above, a method for measuring moisture content focusing on the resistivity of a non-aqueous solvent was illustrated by applying it to a non-aqueous solvent purified by a liquid purification apparatus. However, it is also applicable to general non-aqueous solvents that have not been purified. However, before performing such moisture measurement, it is preferable to remove impurities other than moisture contained in the non-aqueous solvent to be measured, specifically impurities whose concentration has a strong correlation with the resistivity of the non-aqueous solvent. That is, it is preferable to remove ionic components and fine particles from the non-aqueous solvent to be measured using, for example, an ion exchanger such as an ion exchange resin or a monolithic organic porous ion exchanger, or a filtration membrane such as an MF membrane.

[0059] Furthermore, in the embodiments described above, another method focusing on the resistivity of the non-aqueous solvent, namely a method for determining the end time of the pretreatment step, was exemplified when applied to the dehydration treatment of an ion exchanger. However, it is also applicable to the pretreatment of other purification means other than ion exchangers. That is, in the embodiments described above, an ion exchanger was exemplified as a means of purifying a non-aqueous solvent, but the liquid purification apparatus may be equipped with other purification means such as various filters and activated carbon. Some of these other purification means require pretreatment by passing a non-aqueous solvent (pretreatment solution) through them in order to remove impurities contained therein. For such purification means that contain impurities whose concentration is strongly correlated with the resistivity of the non-aqueous solvent, the method of determining the end time of the pretreatment step based on the resistivity of the non-aqueous solvent, as exemplified in the embodiments described above, can be applied.

[0060] In the embodiments described above, the resistivity of the non-aqueous solvent was the focus, but instead, the conductivity, which is a value expressed as the reciprocal of resistivity and can be measured online in the same way as resistivity, may be the focus. That is, a conductivity meter may be installed instead of a resistivity meter, and based on the measurement results, the water concentration in the non-aqueous solvent may be measured or the timing of the end of the pretreatment process may be determined in the same way as in the case of resistivity. [Explanation of Symbols]

[0061] 10 Liquid purification equipment 11 Packed tower 12 Solvent flow meter 13 Ultrapure water flow meter 14. Stirring means 15 Moisture removal means 16 Ion removal means 20 Moisture measuring device 21 Resistivity meter 22 Calculation means L1 Solvent supply line L2 Solvent delivery line L3 Dehydration liquid line L4 Drainage Line L5 Ultrapure Water Line L11 Moisture Addition Line L12 Merging Line L13 Branch Line V1~V4, V6 Shut-off valves V5 Flow Control Valve

Claims

1. A method for measuring moisture content in a non-aqueous solvent, A step of creating a calibration curve in advance that shows the relationship between the resistivity or conductivity of the non-aqueous solvent and the water concentration, A step of removing impurities other than water contained in the non-aqueous solvent, A method for measuring moisture, comprising the steps of: removing impurities other than moisture; measuring the resistivity or conductivity of the non-aqueous solvent; and calculating the moisture concentration in the non-aqueous solvent from the measured resistivity or conductivity using a pre-prepared calibration curve.

2. The method for measuring moisture content according to claim 1, wherein the step of removing impurities other than moisture includes at least one of passing the non-aqueous solvent through an ion exchanger to remove ionic components and filtering the non-aqueous solvent to remove fine particles.

3. The moisture measurement method according to claim 2, wherein the ion exchange material is a monolithic organic porous ion exchange material.

4. The process of creating the calibration curve in advance is, The process involves preparing the non-aqueous solvent from which water has been removed as a standard solution, and adding water to the standard solution. A method for measuring moisture content according to any one of claims 1 to 3, comprising the step of measuring the resistivity or conductivity of the standard solution while gradually changing the amount of water added to the standard solution, and creating the calibration curve.

5. The moisture measurement method according to claim 4, wherein the step of preparing the calibration curve in advance further includes a step of removing impurities other than water contained in the standard solution before adding water to the standard solution.

6. The moisture measurement method according to claim 5, wherein the step of removing impurities other than moisture includes at least one of passing the standard solution through an ion exchanger to remove ionic components and filtering the standard solution to remove fine particles.

7. The moisture measurement method according to claim 6, wherein the ion exchange material is a monolithic organic porous ion exchange material.

8. A device for measuring moisture content in a non-aqueous solvent, A removal means for removing impurities other than water contained in the non-aqueous solvent, A measuring means for measuring the resistivity or conductivity of the non-aqueous solvent from which impurities other than water have been removed, A moisture measuring device comprising: a calculation means for calculating the water concentration in the non-aqueous solvent using a calibration curve that has been prepared in advance and represents the relationship between the resistivity or conductivity of the non-aqueous solvent and the water concentration, based on the resistivity or conductivity measured by the measuring means.

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