JPH0532699B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is a liquid-phase oxidation method for organic carbon in water (TOC).
This invention relates to a measuring device. [Prior art] When measuring organic carbon in water (referring to carbon in organic matter present in water), the general principle is to oxidize the organic matter to carbon dioxide and quantitatively detect the concentration of this carbon dioxide. has been adopted. Methods for oxidizing organic substances are broadly classified into dry oxidation methods and wet oxidation methods. Dry oxidation involves combustion and catalytic oxidation at temperatures above 500°C, typically in which a small amount of sample is passed along with oxygen (or air from which carbon dioxide has been removed) through a tube filled with a high-temperature oxidation catalyst for measuring total carbon. There is a combustion method (JIS K0102), and there is also a method in which inorganic carbon is removed from sample water in advance and then a certain amount is weighed on a magnetic combustion boat, as disclosed in JP-A No. 52-36090. , this boat 950
Inserted into a magnetic combustion tube heated to ~1300℃,
A method has been proposed in which organic carbon contained in sample water is combusted while flowing air or oxygen gas from which carbon dioxide has been removed as a carrier gas. A typical wet oxidation method involves adding an oxidizing agent to the sample water. For example, a mixed solution of sample water and a reaction reagent (oxidizing agent) is irradiated with ultraviolet rays to advance the oxidation reaction (UV oxidation). There is also a method (JIS K0102) in which sample water and reaction reagent are placed in an ampoule and the ampoule is heated to oxidize the sample water with the reaction reagent. Extraction of carbon dioxide is carried out by introducing a carrier gas such as nitrogen or helium into the test water to aerate it. In this case, the latter ampule method is performed by breaking the ampule in a heating device after the oxidation process and passing carrier gas through it, which makes the extraction of carbon dioxide complicated and is not used very often. . In addition, in order to quantify the extracted carbon dioxide, carbon dioxide produced by high-temperature oxidation (combustion) of organic matter was detected using an infrared analysis method (Beckman
(Sumitomo Chemical Co., Ltd.), which converts carbon dioxide to methane and detects it using a gas chromatograph with flame ionization detection (Sumitomo Chemical Co., Ltd.), and detects carbon dioxide obtained by UV oxidation using infrared analysis. There is one that measures conductivity by absorbing carbon dioxide into a solution (Dohrman Astro), and another that measures conductivity by absorbing carbon dioxide into a solution (Barnstead). [Problem to be solved by the invention] Of the conventional techniques mentioned above, the lower limit of quantification in the dry oxidation method is at best about 500 ppb, while a highly sensitive TOC analyzer with a quantitative sensitivity of 10 ppb has been developed in the wet oxidation method. ing. The reason why the dry oxidation method has lower quantitative sensitivity than the wet oxidation method is because, for example, in the oxidation catalyst method, a small amount (about 20μ) of the sample is injected into a tube filled with an oxidation catalyst, which has a much larger capacity than the oxidation catalyst method. Examples include the fact that the sample gasified in the filling tube diffuses and becomes diluted, and it is susceptible to external contamination. This means that even if oxidation is carried out by inserting a boat containing a sample into a combustion tube, the combustion tube into which the boat is inserted will be large, so the volume of the combustion tube will be much larger than the sample. Therefore, the same thing can be said. In addition, in the above-mentioned oxidation catalyst method, even if it was attempted to increase the sample supply amount in order to increase the quantitative sensitivity for low-concentration organic carbon, it was difficult to achieve this because the function of the oxidation catalyst deteriorated due to the heat of vaporization. . By the way, the quality of high-purity water used in LSI manufacturing processes, nuclear power plants, etc. is becoming stricter over the years, and along with this, a quantitative sensitivity of around single digit ppb is required. ,
Even with TOC measurement devices using conventional wet oxidation methods, it has been difficult to fully satisfy these demands. The reason for this is that in the conventional wet oxidation method, a carrier gas is introduced into the liquid phase (a mixture of sample water and oxidizing agent) to extract the generated carbon dioxide, so a large amount of carrier gas is required. and the concentration of carbon dioxide extracted into the carrier gas will be lower. In other words, the amount of carbon dioxide dissolved in water is
It is proportional to the partial pressure of carbon dioxide in the gas phase, so when a carrier gas with a low carbon dioxide concentration is bubbled in water, carbon dioxide in the water moves into the carrier gas, but the lower the concentration of carbon dioxide in water, the more Carbon is less likely to be extracted into the carrier gas, and therefore more carrier gas is required to increase the extraction rate of carbon dioxide, resulting in a lower concentration of carbon dioxide in the carrier gas. The present invention has been made in view of the above points, and its purpose is to simplify the operation and reduce the concentration of water at low concentrations (extremely small amounts) in water.
The object of the present invention is to provide an extremely high-precision measuring device for organic carbon in water by improving the quantitative sensitivity for organic carbon in water. [Means to solve the problem] In order to increase the quantitative sensitivity of organic carbon in water,
Measures need to be taken to increase the amount of carbon dioxide produced by increasing the amount of sample water processed, to prevent contamination during analysis operations, and to improve the extraction rate of produced carbon dioxide. In order to solve such problems, the present invention has the following features:
Basically, we propose the following TOC measuring device. That is, it has a tube for feeding a reaction liquid consisting of sample water and an oxidizing agent, and this liquid feeding tube has a tube that removes inorganic carbonic acid dissolved in the sample water in the process of feeding a mixture of sample water and reaction liquid. A deaerator is installed downstream of the deaerator, a liquid feeding/pressurizing pump, a reaction tube with a heater, and a constriction section on the outlet side of the reaction tube are installed. Then, the reaction tube forms a part of the liquid sending pipe, and the mixed liquid is heated to a high temperature while flowing therethrough, and is pressurized to a level higher than the vapor pressure by cooperation of the liquid sending and pressurizing pump and the throttle part. The organic matter contained in the sample water of the mixed solution is set to be oxidized in liquid phase by the reaction solution under pressure. Further, a gasification pipe for steaming or atomizing the liquid mixture is extended downstream of the throttle part, and for extracting carbon dioxide generated by liquid phase oxidation of the organic matter into this gasification pipe. A carrier gas feeding means, a gas-liquid separator for separating the carrier gas from the vaporized or atomized water, and a carbon dioxide detection means for detecting carbon dioxide in the carrier gas after separating and removing the water. Become. [Operation] The sample water and the reaction solution are mixed in a liquid sending pipe and then transferred to a deaerator, where inorganic carbonic acid dissolved in the sample water is removed. In other words, dissolved carbonic acid is mixed in high-purity water that is in contact with air. In order to distinguish this from carbon dioxide produced by oxidation of organic matter, it is removed in advance using a deaerator during the liquid feeding process. The mixed liquid that has passed through the deaerator is transferred to the reaction tube via a liquid sending pipe and a liquid sending and pressurizing pump. Since the reaction tube is heated by a heater, the mixed liquid passing through it is heated to a high temperature, and the high temperature mixed liquid inside the reaction tube is is pressurized above vapor pressure. As a result, the mixed solution is kept in a liquid phase, and the organic matter in the sample water is oxidized in the liquid phase (wet oxidation) by the reaction solution at a high temperature. That is, when the temperature of the mixed liquid is raised, the oxidation reaction of the organic matter in the sample water by the reaction liquid progresses, and carbon dioxide is generated from the organic matter contained in the sample water. In this case, the liquid phase oxidation step is carried out continuously (continuous flow method) because the liquid mixture is caused to flow through the reaction tube by driving the liquid feeding/pressurizing pump.
Therefore, the amount of sample water to be processed is increased to increase the ability to generate carbon dioxide (corresponding to the above-mentioned factors).
Furthermore, since it is a liquid phase oxidation, there is no possibility of the gasified sample being diffused in the reaction tube as in dry oxidation by combustion. After passing through the reaction tube, the mixed liquid flows through the gasification pipe and becomes steamed or atomized after exiting the constriction section, and a carrier gas is introduced into this steamed or atomized atmosphere, and the aforementioned liquid is The carbon dioxide produced during the phase oxidation process is extracted into the carrier gas. When extracting carbon dioxide with a carrier gas, in order to increase the extraction rate, an atmosphere containing carbon dioxide (in the conventional wet oxidation method, this corresponds to water,
In the present invention, this can be achieved by speeding up the diffusion of the carrier gas into the vaporized or atomized gaseous atmosphere described above, and the diffusion of carbon dioxide into the carrier gas. Diffusion coefficient (cm ² /
s), but the diffusion coefficient is larger at high temperatures than at low temperatures, and the diffusion coefficient of gas for liquid is 10 ^-5
On the other hand, the diffusion coefficient for gases is on the order of 0.1, which is 10 ⁴ times larger (edited by Saburo Kamei, Basic Chemical Engineering, Izumi Shobo). Therefore,
After oxidizing the organic matter in water, the sample water is vaporized or atomized, and a carrier gas is mixed with this, making it possible to effectively extract low concentrations of carbon dioxide with a small amount of carrier gas. confirmed this experimentally (corresponding to the factors mentioned above). In addition, in the present invention, since the gasification pipe line for water vaporization or atomization is carried out by extending the liquid sending pipe, a thin pipe with a small volume (for example, an inner diameter of 0.5 to 1 mm) is used.
Water can be vaporized or atomized in a continuous flow due to the liquid feeding action of a pressure pump that also serves as a liquid feeder. is forced to be transferred one after another to the carrier gas confluence part without much time for it to accumulate and diffuse in the pipe (in other words, when the mixed liquid enters the gasification pipe through the constriction part of the reaction pipe, the inflow volume (The vaporized or atomized mixed liquid is forcibly pushed out to the gas-liquid separator side.) As a result, the steamed or atomized sample is always mixed with the carrier gas at a substantially constant ratio, while the degree of dilution of the carbon dioxide with respect to the carrier gas is greatly reduced (this effect further enhances the aforementioned factors). . The carrier gas from which carbon dioxide has been extracted is separated (dehumidified) from water vaporized or atomized in a gas-liquid separator, and then the carbon dioxide in the carrier gas is detected (measured) as a quantitative concentration. Note that the distance between the reaction tube with a heater and the condenser does not require the heating temperature of the reaction tube to be higher than in the dry oxidation method (combustion method), so the thermal influence of the reaction tube on the condenser can be reduced. Therefore, the length between the reaction tube and the condenser (gasification pipe length) can be shortened (e.g., about 50 cm), and this, together with the small diameter of this pipe, reduces the pipe volume. to suppress the diffusion of water vapor or atomized gaseous sample within the pipe (this action also promotes the above-mentioned factors). Further, the above carbon dioxide measurement can be performed without being exposed to external contamination by passing the liquid pipe and gasification pipe in series (corresponding to the above-mentioned factors). [Example] FIG. 1 is a block diagram showing an example of an apparatus for measuring organic carbon in water according to the present invention. In FIG. 1, 1 is a sample water, and 2 is a carrier liquid for sending the sample water 1 to a reaction tube 10 (described later). 3 is a reaction liquid for oxidizing organic matter in sample water 1, in which potassium persulfate (potassium peroxonisulfate), which functions as an oxidizing agent, and generated carbon dioxide are mixed in water. sulfuric acid to reduce its solubility. The sample water 1 is sent by a pump 5a, and the carrier liquid 2 is sent by a pump 5b to a six-way valve 6 provided in a common liquid sending pipe 5 at different times. In this case, a certain amount of sample water 1 is sent in advance to the measuring coil 7 in the state of the six-way valve shown in FIG.
Switch the carrier liquid 2 side, the measuring coil 7, and the liquid sending pipe 5 to connect the sample water 1 in the measuring coil 7.
is pushed out toward the liquid sending pipe 5 by the force of the flow of the carrier liquid 2 on the upstream side. Due to this liquid feeding, the sample water 1 flows through the liquid feeding pipe 5, and along the way, the reaction liquid 3 sent by the pump 5c joins at a predetermined ratio, and the mixed liquid is transferred to the deaerator 8. The deaerator 8 has a tank shape, and helium 4 is bubbled through the mixed liquid as a carrier gas to remove inorganic carbonic acid contained in the mixed liquid, and the helium 4 is released into the atmosphere as exhaust gas 18. Ru. For example, when sample water 1 is high purity water, the dissolved carbonic acid therein is carbon dioxide (CO ₂ ),
Bicarbonate ion (HCO ₃ ^- ), carbonate ion (CO ₃ ^2- )
However, the proportion of these substances differs depending on the pH. In order to efficiently remove dissolved carbonic acid by the aeration method, it is necessary to make it exist as carbonic acid.
The pH at which more than 99% of carbonic acid can exist is 4.
It is as follows. Therefore, the acid concentration of sample water 1 during aeration is set to 1 mmol/sulfuric acid. The liquid feeding pipe 5 has an inner diameter of approximately φ0.5 to 1 mm.
For example, if the pipe line 5 is made to have a diameter of 1 mm and a length of about 1.2 m,
The volume of liquid in it is 1 ml. In this liquid sending pipe 5,
A liquid feeding/pressurizing pump 5d, a coiled reaction tube 10, and a pressure regulating valve 12 serving as a constriction portion on the outlet side of the reaction tube are arranged downstream of the deaerator 8. The reaction tube 10 is equipped with a constant temperature bath 11 serving as a heater, and the constant temperature bath 11 has a temperature of 200
The mixed liquid that is heated to a high temperature of about °C and flows through it is kept at a constant pressure (approximately 10 Kgf/cm ² higher than the vapor pressure of water at the above set temperature) by the cooperation of the pump 5d and the pressure regulating valve 12. The pressure is applied to the Specifically, for example, 200℃, 20-30Kg
It is in a high temperature and pressurized state of f/cm ² . 9 is a pressure gauge. The sample water 1 continuously flows through this high temperature, pressurized reaction tube 10 at a flow rate of 10 ml/min, and during this flow process, the temperature is raised and the organic matter in the sample water 1 is oxidized by the reaction liquid 3. (liquid phase oxidation). Organic matter (C _x H _y N _z ) in high purity water is oxidized by potassium persulfate (K ₂ S ₂ O ₈ ) as shown in equations (1) and (2) to generate carbon dioxide. K ₂ S ₂ O ₈ +H ₂ OK ₂ SO ₄ +H ₂ SO ₄ +(O) ...(1) C _x H _y N _z (O)+nxCO ₂ +y/2H ₂ O+zNO ₃ ^- ...(2) Equation ( Reaction 1) does not proceed unless the temperature is high. In this example, in order to improve the automation and processing capacity of the apparatus, the sample water 1 and the reaction liquid 3 are passed through the reaction tube 10 kept at high temperature, and the organic matter is poured into carbon dioxide in a continuous flow. is being converted to . Downstream of the pressure control valve 12 of the reaction tube 10, a water vapor generation tube (gasification tube) is provided by extending the liquid sending tube 5.
A carrier gas mixing valve 14 is added in the middle of the steam generation pipe 13 to feed helium 4 through a flow rate control valve 17, a moisture separator (condenser) 15 is downstream of the carrier gas mixing valve 14, and a carbon dioxide gas is further downstream of the carrier gas mixing valve 14. An infrared analyzer for carbon detection is installed. The steam generating tube 13 also has an inner diameter of about 0.5 to 1 mm. The mixed liquid that has passed through the reaction tube 10 and has been subjected to the liquid phase oxidation process is reduced in pressure after passing through the pressure control valve 12 and is vaporized in the steam generation tube 13, where it merges with helium 4 and is oxidized by organic matter. The carbon dioxide thus produced is extracted with helium-4. The helium 4 from which carbon dioxide has been extracted is led to the gas-liquid separator 15 together with water vapor, where the water vapor is separated and removed as condensed water 19, and the dehumidified helium 4 is sent to the infrared analyzer 16, where the carbon dioxide contained in the helium 4 is The concentration of carbon is quantitatively measured, and from this measurement value sample water 1
The organic carbon inside is measured. According to the present embodiment described above, first, while the sample water 1 is flowing into the reaction tube 10, organic substances in the sample water are oxidized. If such a flow system is adopted, the amount of sample water to be processed can be increased, which increases the amount of carbon dioxide produced in the sample water and increases the detection sensitivity. In addition, during the analysis operation, the liquid sending pipe 5 and the water vapor pipe 13 are
Since the sample is analyzed through the sensor, external contamination can be effectively prevented. In addition, after the organic matter in the sample is oxidized in a liquid phase at high temperature and pressure in the reaction tube 10, it is turned into steam and a carrier gas for carbon dioxide extraction is introduced into this steam atmosphere. A lower concentration of carbon dioxide can be effectively extracted using a smaller amount of carrier gas than when carbon dioxide is extracted by feeding the carrier gas (for the reason, please refer to the section on the operation of the invention). Furthermore, the steam pipe 13 has an inner diameter of approximately φ0.5 to 1 mm and a length of approximately 50 cm, and its volume is extremely small.Moreover, the sample steamed in the steam pipe 13 is forced to flow through the force of the pump 5d. Therefore, the carbon dioxide in the carrier gas 4 is diluted because it joins with the carrier gas 4 almost before being diffused in the steam pipe 13 and is immediately sent to the infrared analyzer 16 via the gas-liquid separator 15. detected by the infrared analyzer 16. Therefore, the above-mentioned effects have improved the sensitivity of quantitative determination of carbon dioxide in water, making it possible to quantify organic carbon at extremely low concentrations of around 1 ppb. The proof of this specific effect will be explained with reference to FIG. FIG. 3 shows data obtained by creating a calibration curve using the apparatus of this example. To create a calibration curve,
It is necessary to prepare the standard solution with water that does not contain organic substances. Even if it is low in ordinary high purity water
Contains around 20ppb of organic carbon. For this reason, it is necessary to use purified water that substantially does not contain organic substances as the water that serves as the base of the standard solution. Then, the drain from the gas-liquid separator 19 is used for water that does not substantially contain organic matter, and a certain amount of potassium hydrogen phthalate, which is commonly used as a standard substance for organic carbon, is added to the water to reduce the organic carbon concentration to 5. ~
A standard solution with a concentration of 100 ppb was prepared and analyzed.
The result is shown by solid line B in FIG. 3, and the calculated value when potassium hydrogen phthalate is completely oxidized is also shown by broken line A. The calibration curve shows a straight line up to 100 ppb. Furthermore, if the ratio of the experimental value to the calculated value is taken as the recovery rate, the value is approximately 95%. Approximately 5 ppb of organic carbon was detected even in the drain of the gas-liquid separator, which was thought to contain no organic matter. Possible causes of this include the method of cleaning the container in which the drain was collected and external contamination during standard solution preparation, but the details are not clear. The repeat accuracy at this time is the standard deviation.
It was 0.19 ppb. The lower limit of quantification is 0.9 ppb when five times the standard deviation is taken, and from the above it can be seen that it is possible to quantify organic carbon at extremely low concentrations of around 1 ppb. The coefficient of variation at this time is 20%, assuming it is the same as the standard deviation at 5 ppb. Table 1 shows the results of analyzing various types of high-purity water using the apparatus according to this example. The analytical values of various types of high-purity water vary considerably, from 3 to 108 ppb. In addition, No.1
The sample was made by passing water vapor through a platinum catalyst layer at 900°C in an oxygen atmosphere, burning organic matter, and then condensing it.

【table】

〔Effect of the invention〕

As described above, according to the present invention, the above-mentioned ~
By satisfying all of the quantitative sensitivity improvement factors mentioned above, it is possible to measure organic carbon in water at extremely low concentrations (concentrations around 1 ppb), and it also becomes possible to measure organic carbon in ultrapure water, which has been difficult to achieve until now. It has excellent effects. In addition, organic carbon in the water is automatically measured by driving the pump during the process of flowing the liquid through the liquid sending pipe and the gas lower pipe extending therefrom, so that analysis operations can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
The figure is a block diagram showing an application example of the present invention, and FIG. 3 is a diagram showing a calibration curve created using the apparatus of the above embodiment. 1... Sample water, 2... Carrier liquid, 3... Reaction liquid (oxidizing agent), 4... Helium (carrier gas),
5...Liquid feeding pipe, 5a to 5c...Liquid feeding pump, 5d
...Liquid feeding and pressurizing pump, 6...Six-way valve, 7...Measuring coil, 8...Deaerator, 9...Pressure gauge, 10...
...Reaction tube, 11... Constant temperature bath (heater), 12...
Pressure control valve (throttling part), 13... Steam generation pipe (gasification pipe), 14... Carrier gas mixing valve (carrier gas feeding means), 15... Gas-liquid separator, 1
6...Infrared analyzer (carbon dioxide detection means).

Claims (1)

[Scope of Claims] 1. It has a tube for conveying a reaction liquid consisting of sample water and an oxidizing agent, and this liquid conveyance tube contains a liquid that is added to the sample water during the process of conveying the mixed liquid of the sample water and reaction liquid. A deaerator for removing dissolved inorganic carbon dioxide, a liquid feeding/pressurizing pump downstream of the deaerator, a reaction tube with a heater, and a constriction part on the outlet side of the reaction tube are provided, and the reaction tube is connected to the feeder. The mixed liquid is heated to a high temperature while flowing through a part of the liquid pipe, and is pressurized to a level higher than the vapor pressure by the cooperation of the liquid feeding/pressurizing pump and the throttle section, and under this high temperature and pressure, a sample of the mixed liquid is heated. The organic matter contained in the water is set to be oxidized in the liquid phase by the reaction liquid, and a gasification pipe for vaporizing or atomizing the mixed liquid is extended downstream of the throttle part, and the gasification pipe is a carrier gas feeding means for extracting the carbon dioxide produced by the liquid phase oxidation of the organic matter, a gas-liquid separator for separating the carrier gas and the vaporized or atomized moisture, and a gas-liquid separator for separating and removing the moisture; An apparatus for measuring organic carbon in water, comprising a carbon dioxide detection means for detecting carbon dioxide in the carrier gas. 2. The apparatus for measuring organic carbon in water according to claim 1, wherein the throttle section is constituted by a pressure regulating valve. 3 In claim 1 or 2,
An apparatus for measuring organic carbon in water, wherein the carrier gas feeding means is connected near an inlet of the gas-liquid separator.