Total organic carbon measuring apparatus

Abstract

To provide a total organic carbon measuring device capable of performing measurement in water having high conductivity, and changing sensitivity without using highly sensitive NDIR.SOLUTION: An oxidation device that oxidizes an organic substance in sample water to generate CO2, a CO2 permeation cell into which the sample water containing the CO2 generated in the oxidation device is introduced, a gas supplying unit for supplying a gas other than CO2 to the CO2 permeation cell, and a CO2 concentration measuring unit that measures a CO2 concentration in a mixed gas of the gas supplied from the gas supplying unit and the CO2 gas that has permeated through the CO2 permeation cell, the CO2 permeation cell has a water inlet at one end and a water outlet at the other end, and a coil tube formed by winding a permeable single tube made of a material permeable to CO2 gas is disposed in a cell vessel, and the gas supplier includes a flow controller that controls a flow of gas other than CO2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a method for measuring carbon dioxide (hereinafter referred to as CO2) contained in an aqueous solution, and in particular to CO2 detection in a total organic carbon meter (hereinafter referred to as TOC meter). [Background technology]

[0002] A widely known conventional method for determining the carbon dioxide content in an aqueous solution is to separate the CO2 contained in the test water or a solution containing gasified gas using an aeration method or the like, and then measure the CO2 using a non-diffusive infrared analyzer (hereinafter referred to as NDIR). However, NDIR requires the elimination of corrosive gases and high humidity conditions, and requires expensive equipment such as devices for this purpose.

[0003] The most common type of conventional TOC analyzer is the wet oxidation (UV oxidation) TOC analyzer. The measurement principle of wet oxidation (UV oxidation) is to oxidize organic matter dissolved in water with UV light, converting it to CO2 in the water, and then determine the total organic carbon from the amount of CO2 produced. There are two main methods known for measuring CO2:

[0004] (1) Conductivity detection method One method for detecting the amount of CO2 generated is the "conductivity detection method," which measures the amount of CO2 generated by UV rays, which proportionally increases the conductivity of water in accordance with the amount of CO2. This measurement determines the TOC from the difference between the conductivity before CO2 generation and the conductivity caused by the CO2 generated by UV oxidation. A schematic diagram of this measurement is shown in Figure 9. TOC in this method is determined from the difference in conductivity between conductivity meter A and conductivity meter B in Figure 9.

[0005] However, this method of TOC has the problem that there is an upper limit to the CO2 concentration that can be measured. This is because when CO2 generated by UV oxidation dissolves in pure water, the increase in CO2 causes a decrease in pH, which in turn reduces the dissolved CO2 concentration that can be detected by conductivity.

[0006] Furthermore, the conductivity method can only be used with pure water or water of higher purity. This is because low-purity water (high-conductivity water) may contain substances that inhibit changes in conductivity due to CO2 or that make the conductivity after oxidation lower than the conductivity before oxidation, and to avoid this, this method requires the use of ultrapure water or water of higher purity (low conductivity) than pure water.

[0007] One way to overcome these water quality limitations is to separate only the CO2 produced by UV oxidation (Figure 10) using a membrane, dissolve it in standard pure water, and measure its conductivity to determine the TOC. In this method, acid is added to the water to be UV oxidized in advance to lower the pH to below 2, causing oxidation, and all of the CO2 generated is converted into a dissolved gas that is then allowed to permeate the membrane. The permeated CO2 then dissolves in the circulating standard pure water, and the change in conductivity according to the amount of CO2 is measured to determine the TOC. After measurement, the water is purified in a pure water device and circulated.

[0008] (2) Detection by NDIR The above-mentioned conductivity detection method is dependent on the conductivity of water, and to overcome this limitation, a complex mechanism such as that shown in FIG. 8 must be used. On the other hand, the NDIR method measures the CO2 generated by UV oxidation as a gas, which means that it is not affected by the conductivity of the water in which the CO2 is dissolved, and has the advantage of being usable with water of higher conductivity. There are also wet oxidation methods that do not use UV but use high temperature and high pressure, but the UV oxidation NDIR method is widely used because it is easy to handle and highly economical.

[0009] However, the NDIR method also has the following issues. First, when measuring TOC at extremely low ppb levels, the amount of CO2 generated by oxidation is extremely small. As a result, the amount of CO2 that becomes gaseous is also very small. The disadvantage is that increasing the volume of the aeration tank, the amount of recovered gas, and the aeration time are all fixed, so it is not easy to change these. For this reason, in many cases, the solution is to increase the sensitivity of the NDIR, but since such high-sensitivity NDIRs are very expensive, the ability to measure low concentrations also becomes very expensive.

[0010] Another problem is that the gas used in the gas-liquid separator always contains moisture. This moisture has the drawback of affecting NDIR measurements when measuring low concentrations such as 0.1 ppmC. To correct this drawback, a dehumidifying device with high gas drying performance, as shown in Figure 11, is required, which has the added drawback of making the measuring instrument more expensive. Summary of the Invention [Problem to be solved by the invention]

[0011] Under these circumstances, the inventors conducted extensive research and discovered that it was possible to provide a total organic carbon measuring device that includes a "CO2 permeation cell" based on the conventional wet UV oxidation NDIR method, which would enable measurement in water with high conductivity, which is an issue, and would also enable sensitivity changes without using a highly sensitive NDIR, thereby improving the CO2 separation method and dehumidification process, which are the cause of the device's high cost, and thus completed the present invention. [Means for solving the problem]

[0012] A first aspect of the total organic carbon measuring device of the present invention includes an oxidation device that oxidizes organic matter in sample water to generate CO2, a CO2 permeation cell into which sample water containing CO2 generated by the oxidation device is introduced, a gas supply unit that supplies gases other than CO2 to the CO2 permeation cell, and a CO2 concentration measurement unit that measures the CO2 concentration in a mixed gas of the gas supplied from the gas supply unit and the CO2 gas that has permeated the CO2 permeation cell, wherein the CO2 permeation cell has a water inlet at one end and a water outlet at the other end, and a coiled tube formed by wrapping a single permeable tube made of a material that allows CO2 gas to permeate, and is placed in a cell container, and the gas supply unit includes a flow rate control unit that controls the flow rate of gases other than CO2.

[0013] A second aspect of the total organic carbon measuring device of the present invention is the invention described in the first aspect, characterized in that the coil tube is a flat coil tube formed by spirally winding a permeable single tube made of a material that is permeable to CO2 gas, and is installed inside the cell container.

[0014] A third aspect of the total organic carbon measuring device of the present invention is characterized in that, in the invention described in the first aspect, the coil tube is a three-dimensional coil tube formed by winding a permeable single tube made of a material that is permeable to CO2 gas into a three-dimensional spiral shape, and is installed in the core part of the cell container.

[0015] A fourth aspect of the total organic carbon measuring device of the present invention is the invention described in the first aspect, characterized in that there is a gap between adjacent single tubes of the coil tube.

[0016] A fifth aspect of the total organic carbon measuring device of the present invention is characterized in that, in the invention described in the first aspect, the coil tube is installed in the cell container so that the flow of liquid in the coil tube is from the center to the periphery.

[0017] A sixth aspect of the total organic carbon measuring device of the present invention is the invention described in the first aspect, characterized in that the gas supply unit can control the flow rate so that the CO2 gas that has permeated the CO2 permeation cell can be diluted by the supplied gas by 100 times or more.

[0018] A seventh aspect of the total organic carbon measuring device of the present invention is characterized in that, in the invention described in the first aspect, the CO2 concentration in the mixed gas of the gas supplied by the gas supply unit and the CO2 gas that has permeated the CO2 permeation cell is adjusted to 1000 ppm or less.

[0019] An eighth aspect of the total organic carbon measuring device of the present invention is characterized in that, in the invention described in the first aspect, it includes a dehumidification unit for dehumidifying the CO2 gas that has permeated the CO2 permeation cell and the gas supplied from the gas supply unit.

[0020] A ninth aspect of the present invention is the total organic carbon measuring device according to the first aspect, further comprising a pretreatment device that pretreats the sample water before the sample water is supplied to the oxidation device, The pretreatment device is characterized by including an acid adding device that adds an acid to the water sample, and a mixing section that mixes the water sample with the acid.

[0021] A tenth aspect of the total organic carbon measuring device of the present invention is characterized in that, in the invention described in the ninth aspect, the pretreatment device includes a heating device for heating the mixture of the sample water and the acid.

[0022] An eleventh aspect of the total organic carbon measuring device of the present invention is the invention described in the first aspect, characterized in that the gas supply unit can control the flow rate so that the concentration of CO2 gas that has permeated the CO2 permeation cell can be diluted by 100 times or more with the gas being supplied. [Effects of the Invention]

[0023] According to the present invention, CO2 that has passed through the CO2 permeation cell is mixed with gas supplied by a gas supply unit at a controlled flow rate to dilute the CO2 before measuring the CO2 concentration, making it easy to detect changes in CO2 concentration. This makes it possible to realize a total organic carbon measurement device that can easily detect changes in total organic carbon. According to the present invention, gas permeation technology is used for inorganic carbon removal (aeration treatment), so it is possible to carry out the process without using CO2-free gas or high-purity nitrogen gas for aeration. Furthermore, because the sample water (measurement solution) is aerated using gas permeation technology, TOC measurement is possible without being affected by the conductivity of the sample water (measurement solution). Furthermore, the measurement sensitivity can be changed by increasing or decreasing the flow rate of the collected gas; when measuring trace amounts of CO2 (TOC), the flow rate can be reduced, and when measuring high concentrations, the flow rate can be increased. This means that it is possible to use an inexpensive NDIR instead of the conventional expensive analytical NDIR. Furthermore, since the amount of moisture generated from the permeation tube is small, expensive dehumidifiers and halogen removal devices are not required, which has the advantage of significantly reducing the cost of the entire measurement system. Furthermore, in the case of dissolved CO2, it is possible to measure the sample water as is without using inorganic carbon treatment or UV oxidation equipment, and in this case, it is possible to measure dissolved CO2 in water inexpensively using this method instead of an expensive dissolved carbon dioxide meter. Furthermore, stable measurements are possible even in gas-liquid mixed states such as water with many bubbles. [Brief explanation of the drawings]

[0024] [Figure 1] 1A and 1B are schematic diagrams of a "CO2 permeation cell" according to one embodiment of the present invention, in which (a) is an external perspective view and (b) is a plan view with the lid 10a removed. [Figure 2] 1A and 1B are schematic diagrams of a "spiral-type CO2 permeation cell" according to another embodiment of the present invention, in which (a) is an external perspective view and (b) is a longitudinal cross-sectional view. [Figure 3] 1 is a structural schematic diagram of a single-tube CO2 permeable membrane 4 according to the present invention. [Figure 4] It is a diagram of an experimental apparatus used in an embodiment according to the present invention, showing the measurement equipment and measurement flow. [Figure 5] It is a graph showing the relationship between the TOC concentration and the NDIR output in Example 1 of the present invention. [Figure 6] It is a graph showing the TOC concentration measurement results by the CO2 permeation cell of the present invention. [Figure 7] It is a schematic diagram of the structure of a conventional flat permeation membrane. (a) is an assembly configuration diagram, and (b) is a schematic diagram of the structure of the flat permeation membrane. [Figure 8] It is a structural diagram of a conventional collective CO2 permeation tube. (a) is an external perspective view, and (b) is an explanatory diagram of the bubble behavior of sample water (UV-oxidized water). [Figure 9] It is a schematic diagram of a measurement system in a conventional conductivity detection method. [Figure 10] It is a measurement schematic diagram of a conductivity detection method with improved constraints on the quality of sample water. [Figure 11] It is a schematic diagram of a measurement system with improved dehumidification of the NDIR detection method. [Figure 12] It is a diagram for explaining the principle of CO2 concentration measurement showing an example when a pretreatment device including a mixing device (mixer) and a heating device is provided. [Figure 13] It is a diagram showing an example of a total organic carbon measurement device using a gas supply device including a gas flow control unit. [Figure 14] It is a diagram showing the image of the CO2 permeation cell of FIG. 4, where (a) shows the case of a permeation membrane and (b) shows the case of a coiled tube.

Mode for Carrying Out the Invention

[0025] <Basic Principle of CO2 Permeation Cell> The basic principle of the "CO2 permeation cell" according to the present invention is to use a membrane that permeates CO2 to separate CO2 from water (sample water). The separated CO2 is introduced into the NDIR together with the recovered gas (carrier gas), and the concentration measurement is carried out to measure the CO2 concentration.

[0026] The challenges with this type of membrane separation are the effects on measurement caused by minute amounts of UV-oxidized water and the actual membrane shape and placement.

[0027] The present invention will be described in detail below with reference to the drawings.

[0028] FIG. 1 is a schematic diagram of a CO2 permeation cell 1A according to the present invention, where (a) is an external perspective view and (b) is a plan view with the lid 10a removed. FIG. 2 is a schematic diagram of another CO2 permeation cell 1B according to the present invention, where (a) is an external perspective view and (b) is a longitudinal cross-sectional view. The CO2 permeation cell of the present invention employs a single tubular CO2 permeable membrane 4, which has a sample water inlet 2 at one end and a sample water outlet 3 at the other end and which functions to allow CO2 gas to pass through, as shown in Figures 1 and 2. The membrane is wound in a spiral shape in the form of a flat coil tube (see Figure 1) or a three-dimensional coil tube (see Figure 2).

[0029] The CO2 permeation cell in Figure 1 is a "single-tube CO2 permeation cell (symbol 1A)" with a single tubular CO2 permeation membrane 4 housed in a container 10 (also called a cell, which in Figure 1(a) is composed of a lid 10a and a separation chamber 10b). The cell is wound so that the sample water flows from the outside to the inside. Note that there is no difference in performance even if the sample water flows in the opposite direction. Furthermore, the collected CO2 gas is discharged to the outside by a recovery gas (introduced through a recovery gas inlet 5a and discharged together with CO2 gas through a recovery gas outlet 5b) that is a recovery carrier introduced into the cell 10. The CO2 permeation cell can be configured to convert organic matter into CO2 using a UV oxidation device, for example, and then recover this CO2.

[0030] On the other hand, the CO2 permeation cell 1B in Fig. 2 employs a structure in which the CO2 permeation tube 4 is wound spirally around the cell core 10c (see Fig. 2(b)). Because of this configuration, when a 500 mm tube is used, the dimensions are approximately 40 mm square, which allows for a smaller installation area than the permeation cell in Fig. 1. In this permeation cell 1B, the CO2 permeation tube is wound in a spiral, so the captured gas comes into contact with the spiral shape, and there are fewer areas where the gas stagnates, which has the advantage of allowing for rapid capture in response to changes in CO2 concentration.

[0031] The single-tube CO2 permeable membrane 4 (see FIGS. 1 and 2) according to the present invention expels air bubbles present in the sample water as shown in FIG. FIG. 3 is a structural schematic diagram of the single-tube CO2 permeable membrane 4 according to the present invention, and shows the "UV oxidized water W" containing bubbles Bu, which is the sample water. UV The sample water W enters the CO2 permeation cell 10 incorporating the single-tube CO2 permeable membrane 4 in the order of the positions of the bubbles, together with the bubbles Bu present, and is discharged from the cell 10 in the same order. UV moves at a constant flow rate through one flow path, so bubbles Bu move through the sample water W UV It moves with the material and is not affected by adhesion or retention. In addition, since the length of the pipe is longer than that of the collecting pipe type, the time for the CO2 in the bubbles to permeate can be extended, and the CO2 gas that has permeated outside the permeable membrane is collected as gas C that flows on the surface of the permeable membrane. G (flowing in the direction of the black arrow) and discharged. As a result, stable TOC measurement becomes possible.

[0032] <Installation of pretreatment equipment when introducing sample water> The pretreatment device will be explained with reference to Figure 12. The measurement method in a TOC analyzer involves converting organic matter in sample water into water and CO2 through oxidative combustion, and the amount of CO2 generated is proportional to the organic matter, so the amount of CO2 is converted into a TOC (total organic carbon) value. However, since the original sample water often contains CO2 from the beginning, it is preferable to remove this CO2. In other words, the result will be TC (total carbon) rather than TOC, which can result in a large error, so it is preferable to always remove CO2 first at the sample water inlet.

[0033] First, sulfuric acid or phosphoric acid is added to the sample water to lower the pH to below 2, which converts all carbonate ionized CO2 into inorganic carbon (CO2) and then removes it.

[0034] As shown in Figure 4, CO2 can be removed by adding phosphoric acid and then aerating with nitrogen gas or other gases to expel CO2 from the sample water. The aeration method is expected to convert carbonate ions into inorganic carbon through the aeration action of the added acid, and to shorten the reaction time. Coiled tubes (spiral tubes) like those used in this device and similar structures have limited agitation capabilities, and it is thought that conversion to inorganic carbon by adding acid requires at least two minutes. Therefore, placing the sample water into the coiled tube (spiral tube) immediately after adding the acid will require time for the chemical reaction within the coiled tube (spiral tube), inhibiting CO2 removal by the membrane, making complete CO2 removal difficult.

[0035] Therefore, when using a coiled tube (spiral tube), adding a mixer (mixer) and a heating mechanism (heating device) to mix the sample water with the acid injected as a pretreatment before the sample water is placed in the coiled tube (spiral tube) will promote inorganic carbonization and stabilize the temperature in each operation after the coiled tube, preventing errors due to the temperature of the measured water in summer and winter, and further increasing the temperature will promote chemical reactions.

[0036] Specifically, the inventors of the present invention have confirmed that, taking into consideration the differences between summer and winter, heating to approximately 40°C provides favorable results for the equipment.

[0037] <Concept of total organic carbon measuring device> An example of a total organic carbon measurement device will be described with reference to Figure 13. After passing through the pretreatment device, sample water is passed through an inorganic carbon removal coil tube to remove CO2, and then through a UV oxidation device, where the organic matter in the sample water is oxidized to produce water and CO2. This CO2-containing sample water is passed through a CO2 permeation cell, where the CO2 migrates from the coiled tube into a sealed space. While CO2 removal, like with the inorganic carbon removal coil tube, would be discarded (exhausted), the purpose of this device is to measure the concentration of the migrated CO2. Instead of discarding the CO2, the gas is mixed with gas supplied from a gas supply unit (corresponding to the gas flow control in Figure 13) and introduced into the NDIR, where the CO2 concentration is measured. The gas from the gas supply unit can be any gas that does not contain CO2 and does not react with CO2, such as nitrogen gas.

[0038] If necessary, a dehumidifying section may be included between the permeation cell and the NDIR to dehumidify the gas flowing from the permeation cell to the NDIR. Gas-permeable membranes and tubes allow gases other than CO2 to pass through due to their molecular structure, and also allow water vapor to pass through. Since this device has a high dilution rate, reliability can be improved by using a simple dehumidifying tube, even though condensation in the NDIR is low.

[0039] The inventors of this application discovered that when gas is not supplied from the gas supply unit, even when measured using NDIR, the concentration of the transmitted CO2 gas is nearly 100% (strictly speaking, it contains trace amounts of N2 gas and O2 gas), so the NDIR display value remains at a high concentration and does not change regardless of the TOC concentration.

[0040] This device sends a CO2-free gas or nitrogen gas, etc., as a flow-controlled gas (gas from the gas supply unit) into the CO2 permeation cell, and mixes the permeated CO2 with this gas. This allows the NDIR to measure the mass of CO2 gas contained in the sample water, even at high concentrations. This mixed gas can be used at a dilution rate of approximately 1000 times, depending on the TOC concentration of the sample water and the gas flow rate. The dilution rate of this CO2 gas can be, for example, 100 times or more, and the effects of this embodiment can be further enhanced by diluting it at a rate of, for example, 500 times or more. This means that TOC concentrations as low as 1 ppm can be easily measured, and by adjusting the dilution ratio, even inexpensive NDIRs can measure concentrations in the 100 ppb range. While the suction pump uses a very small negative pressure, by considering the pressure balance of the device, the pump can be eliminated by applying very small pressure at the flow control section. Regarding dilution with CO2-free gas (gas not containing CO2) in the CO2 permeation cell, more specifically, when the CO2-free gas flow rate is 5 cc / min and the sample water flow rate is 5 cc / min, we confirmed that TOC values ​​below 100 ppb can be measured with an inexpensive NDIR, as shown in Figure 6. Since CO2-free gas requires only a residual CO2 concentration of 10 ppm or less, a simple method of passing air through soda lime granules can also be applied.

[0041] The present embodiment is significant in that it is possible to measure the amount of change in CO2 concentration in real time. [Example]

[0042] Tests were conducted using the CO2 permeation cell 1A or 1B according to the present invention, using the measurement equipment and measurement flow used in the examples shown in the experimental apparatus diagram in Figure 4. The following results, shown in Figures 5 and 6, were obtained. Figures 5 and 6 compare the NDIR signals of this device using TOC values ​​(reagent standard), demonstrating the linearity and ability to measure trace amounts of TOC even within the measurement range of inexpensive NDIR. Figure 4 shows a schematic diagram of the CO2 permeation cell, and Figure 14 shows images of the cell in the case of a permeable membrane and in the case of a coiled tube. The measuring equipment will be briefly explained below. <Description of the measuring equipment> This measuring equipment continuously measures the TOC in the sample water, and the measurement flow is as follows. First, the sample water is continuously introduced into the aeration tank 30 by the sample water pump Ps. Next, in the aeration tank, an acid is added to change the inorganic carbon to carbon dioxide and release it from the liquid into the atmosphere, and the pH is adjusted to below 2. Clean air or high-purity nitrogen gas containing no carbon dioxide is used as the aeration gas. Then, the aerated sample water is continuously sent to the ultraviolet oxidation device by the measurement pump Pm. Furthermore, the organic substances contained in the water are oxidized by this device and changed to carbon dioxide. Furthermore, the sample water coming out of the ultraviolet (UV) oxidation device enters the CO2 permeation cell 1A or 1B, and the water and the carbon dioxide in the water are separated by the carbon dioxide permeation membrane. The gas is scavenged by the recovered gas with a negative pressure by the recovery gas pump Pg. Finally, the recovered gas is sent to the non-dispersive infrared analyzer NDIR, and the carbon dioxide concentration is measured. <Description of the test using the CO2 permeation cell> In the case of the ultraviolet (UV) oxidation method, the low concentration limit is 0.5 ppmC (500 ppbC), and the high concentration side shows linearity up to 2 ppmC (2000 ppbC). When considering measurements on the higher concentration side, it was obtained that measurements up to 50 ppmC are possible by adding an oxidizing agent, using an excimer lamp in the oxidation device, or raising the sample water temperature.

Example

[0043] The application of the CO2 permeation cell according to the present invention to the measurement of characteristics other than TOC measurement enables the continuous measurement of TC, IC, and TC - IC = TOC presented in Table 1 below using the function of the present invention, although in the experimental apparatus diagram described in FIG. 4, a multi-stage aeration tank is used as the inorganic carbon removal device 30 in conventional TOC measuring instruments. The CO2 exhausted for the purpose of removing CO2 in the sample water in the inorganic carbon removal device 30 is discarded.

[0044]

Table 1

[0045] Therefore, it is possible to replace the aeration method in the inorganic carbon removal process with a CO2 permeation cell. However, care must be taken when using a cell containing substances such as surfactants that may affect the permeation tube, as this may shorten the tube's lifespan.

[0046] In measuring physical properties using a TOC analyzer, the inorganic carbon removal process was replaced from the aeration method with a CO2 permeation cell, and the results of continuous measurements of tap water are shown in Table 2 below. The tap water sample was continuously introduced into a TOC analyzer equipped with a CO2 permeation cell according to the present invention. "Zero water" in Table 2 is pure water containing no CO2 for comparison. The measurements were taken from the left data to the right data in Table 2, but the order could be changed.

[0047] [Table 2]

[0048] [result] The difference between TC and IC was 3.7 ppmC, which is higher than the TOC measurement value of approximately 1 ppmC. This is thought to be due to the presence of organic matter (POC) etc. that was released into the atmosphere by aeration.

[0049] (Comparative Example 1) To separate CO2 gas using a flat CO2 permeable membrane, a cell like the one shown in Figure 7(a) was used. In this case, there were the following difficulties in its use.

[0050] Looking at the cross-sectional view of the cell in Figure 7(b), there is a chamber on the left through which the sample water passes and a chamber on the right through which the carrier gas passes, with a permeable membrane separating the chambers. UV oxidation water enters the cell from the bottom and is discharged from the top outlet, while the recovered gas enters from the top inlet and exits from the bottom. The gas contains the permeated CO2 and is sent to the NDIR.

[0051] In reality, UV oxidation water contains bubbles when it enters the cell, as dissolved CO2 appears as bubbles due to oxidation and pH-adjusting acid. Therefore, the effect of these bubbles on TOC measurement is as follows:

[0052] As shown in Figure 7(b), the measurement is affected by the air bubbles being sent into the cell. First, the membrane and the bubbles come into contact irregularly, causing the membrane surface to physically bend, which in turn changes the speed at which the collected gas passes through. Next, air bubbles adhere to the surface of the membrane, which prevents the permeable membrane from contacting the sample water, causing a change in the amount of CO2 permeation. In this way, when air bubbles adhere to the cell wall, the volume of the cell changes, which in turn changes the speed at which the UV oxidized water passes through the cell. Therefore, it is almost impossible to perform stable measurements using this method.

[0053] (Comparative Example 2) When the CO2 permeable membrane uses the CO2 permeable tube assembly shown in Figure 8(a), the effects of air bubbles are as follows.

[0054] As shown in Figure 8(b), the bubbles are sent to the collecting tube along with the sample water, but the UV oxidized water flows unevenly into each tube. Therefore, the effect of these bubbles on TOC measurement is as follows: In other words, UV oxidized water and air bubbles concentrate in the areas of each permeation tube where they flow easily, causing bubbles to adhere and become trapped. This results in some tubes where the water flows easily and others where it does not, and this changes, making the CO2 permeation performance unstable. Next, if there are no bubbles remaining, the bubbles will be discharged from the cell before passing through the membrane due to the short length of the tube, resulting in a low measurement value. The above problems make TOC measurements unstable. Therefore, it is almost impossible to stably measure TOC using this method. [Explanation of symbols]

[0055] 1A CO2 permeation cell (flat coil tube configuration) 1B CO2 permeation cell (3D coil tube configuration) 2. Sample water inlet 3. Sample water outlet 4. Single-tube CO2 permeable membrane (CO2 permeable tube) 5a Recovered gas inlet 5b Recovered gas outlet 10 Container (cell) 10a lid 10b Separation Room 10c Core part of cell container (cell core part) 30 Inorganic carbon removal device (aeration tank) Bu bubbles C G Recovery gas (also called carrier gas) Pg Recovery Gas Pump Pm measuring pump Ps sample water pump W UV UV oxidized water (sample water)

Claims

1. Oxidize organic matter in the sample water to produce CO ２ an oxidation device that generates CO generated in the oxidation device; ２ The sample water containing CO ２ a permeation cell and the CO ２ CO in the permeation cell ２ a gas supply unit for supplying a gas other than CO; ２ CO permeated through the permeation cell ２ CO in the gas mixed with ２ Measure the concentration of CO ２ a concentration measuring unit; The CO ２ The permeation cell has a water inlet at one end and a water outlet at the other end. ２ A coil tube formed by winding a permeable single tube made of a gas-permeable material is placed in a cell container, The gas supply unit is CO ２ A total organic carbon measuring device comprising a flow rate control section for controlling the flow rate of a gas other than the total organic carbon.

2. The coil tube is ２ The total organic carbon measuring device according to claim 1, characterized in that a flat coil tube formed by spirally winding a permeable single tube made of a gas-permeable material is installed inside the cell container.

3. The coil tube is ２ The total organic carbon measuring device described in claim 1 is characterized in that it is a three-dimensional coil tube formed by winding a permeable single tube made of a gas-permeable material into a three-dimensional spiral shape, and is installed in the core part of the cell container.

4. 2. The total organic carbon measuring device according to claim 1, wherein the coiled tube has gaps between adjacent single tubes.

5. 2. The total organic carbon measuring device according to claim 1, wherein the coil tube is installed in the cell container so that the flow of liquid in the coil tube is from the center to the periphery.

6. The gas supply unit supplies gas to ２ CO permeated through the permeation cell ２ 2. The total organic carbon measuring device according to claim 1, wherein the flow rate can be controlled so that the gas can be diluted 100 times or more.

7. The gas supplied by the gas supply unit and the CO ２ CO permeated through the permeation cell ２ In the gas mixture, CO ２ 7. The total organic carbon measuring device according to claim 6, wherein the concentration of is adjusted to 1000 ppm or less.

8. The CO ２ CO permeated through the permeation cell ２ 2. The total organic carbon measuring device according to claim 1, further comprising a dehumidifying unit for dehumidifying the gas and the gas supplied from the gas supply unit.

9. a pretreatment device that pretreats the sample water before the sample water is supplied to the oxidation device; 2. The total organic carbon measuring apparatus according to claim 1, wherein the pretreatment device includes an acid adding device that adds an acid to the sample water, and a mixing unit that mixes the sample water with the acid.

10. 10. The total organic carbon measuring apparatus according to claim 9, wherein the pretreatment device includes a heating device for heating the mixture of the sample water and the acid.

11. The gas supply unit ２ CO permeated through the permeation cell ２ 2. The total organic carbon measuring device according to claim 1, wherein the flow rate of the gas to be supplied can be controlled so that the concentration of the gas can be diluted by 100 times or more.

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