JPH03216543A - Apparatus for measuring concentration of hydrogen peroxide - Google Patents

Abstract

PURPOSE:To prevent the lowering of the measuring accuracy of H2O2 by arranging a stirring rod in the vicinity of the center axis of a reaction tank and arranging an ORP electrode at a position separated from the dripping position of KMnO4 along the liquid flow direction due to stirring. CONSTITUTION:A stirring rod 14 is arranged in the vicinity of the center axis of a reaction tank 1 and the ORP electrode 13 is arranged at a position separated from the dripping position of KMnO4 along a liquid flow direction due to stirring. By arranging the electrode 13 at a position separated from the dripping position of KMnO4 as mentioned above, possibility where unreacted KMnO4 directly comes into contact with the electrode 13 is eliminated and, therefore, the lowering of the measuring accuracy of H2O2 can be prevented. Further, by setting the liquid amount in the reaction tank 1 to 5.0 - 150ml, titration speed to 5 - 20ml/min and the supply amount of an aqueous solution to be measured to 5 - 20ml, analytical accuracy can be set in the range of + or -5% and, by forming the stirring part 16 of the stirring rod 14 into a flat plate-shape or columnar shape, air bubbles are made hard to generate.

Description

Detailed Description of the Invention [Industrial Application Field 1] The present invention involves titrating an aqueous solution containing hydrogen peroxide H20 with potassium permanganate K M n O <, and dipping an ORP electrode in the aqueous solution to determine the ORP value. A hydrogen peroxide concentration measuring device that detects the end point of the oxygen reduction reaction between peroxide and potassium permanganate from the change in , and measures the concentration of the aqueous solution from the amount of potassium permanganate consumed until reaching the end point. Regarding.

[Prior Art] Hydrogen peroxide is used in various ways, such as as a bleaching agent or as an enoting agent for copper, etc., and whether it is used as a bleaching agent or an etching agent, hydrogen peroxide is used in aqueous solutions containing hydrogen peroxide. It is necessary to keep the hydrogen peroxide concentration constant.

Therefore, the hydrogen peroxide concentration in the aqueous solution is measured, and when the concentration becomes lower than a preset reference value, a pure solution of hydrogen peroxide is added to the aqueous solution to maintain the concentration.

By the way, capacitive analysis, colorimetric analysis, constant potential electrolysis, and the like are known as methods for measuring hydrogen peroxide concentration.

[Problems to be Solved by the Invention] However, both the volumetric analysis method and the colorimetric analysis method involve manual analysis, and it is difficult to perform continuous analysis during work.

If this is automated, the device becomes complicated, and if high precision is required, a high-performance syringe or plunger pump must be used, resulting in high costs. In addition, in the constant potential electrolysis method, the current value that should change depending on the H20 concentration also changes depending on the temperature, so it is necessary to control the temperature, and if a substance that is easily oxidized is present in the liquid to be measured, the H20. There is a problem in that the oxidative decomposition occurs along with the oxidation, increasing measurement errors.

The present invention was made to solve these problems, and it is possible to make the inside of the reaction tank uniform by limiting the electrode, KMnO, dropping position, sampling amount, reaction tank capacity, titration rate, and stirring speed. The aim is to enable normal analysis and highly accurate measurements without the use of syringes or granger pumps.

[Configuration 1 of the Invention] The present invention firstly arranges a stirring rod for stirring the aqueous solution to be measured near the central axis of the reaction tank, and
Potassium permanganate is dropped at a location away from the RP electrode.

The second aspect of the present invention is to reduce the amount of liquid in the reaction tank by 50 to 150 milliliters/ml.
The titration rate was 5 to 20 ml/min, and the amount of aqueous solution to be measured was 5 to 20 ml/min.

Thirdly, in the present invention, the stirring part at the lower end of the stirring rod is formed into a flat plate or cylindrical shape, and the length of the stirring part is 1/2 to 1/5 of the inner diameter of the reaction tank. The thickness or diameter is 1/2 to 1/20 of the liquid height during titration.

Fourthly, the number of revolutions of the stirring bar should be set to 500 to 200.
The rpm is very low.

A fifth aspect of the present invention is that check means are provided at the lower ends of the tube into which the aqueous solution to be measured is dropped and the tube into which potassium permanganate is dropped.

] Effect j According to the first non-invention, the ORP electrode was placed far from the potassium permanganate dropping position along the stirring direction, so unreacted potassium permanganate was directly applied to the ORP electrode. There is no danger of it being touched. Therefore, unreacted potassium permanganate comes into contact with the ORP electrode, making the ORP detection value unstable, and the end point is detected before reaching the end point, resulting in a low hydrogen peroxide concentration. There is no need to worry. Therefore, the measurement accuracy of hydrogen peroxide is increased.

According to the second aspect of the invention, the liquid volume in the reaction tank is 50 to 1
Since the volume is 50 ml, a moderate stirring efficiency can be obtained. That is, if the liquid volume in the reaction tank is less than 50 ml, the effect of potassium permanganate on the ORP electrode will be large, and the measurement accuracy will be poor. Moreover, if it exceeds 150 ml, the stirring effect will be insufficient, and it will become difficult to equalize the concentration throughout the reaction tank, thus reducing measurement accuracy. Therefore, high measurement accuracy can be obtained with 50 to 150 milliliters.

Furthermore, since the titration rate is 5 to 20 milliliters/min, measurement accuracy can be increased. That is, if the titration rate is less than 5 milliliter/minute, the response of the ORP electrode will be delayed. Therefore, end point detection is delayed and the measured concentration is higher than the actual concentration. Moreover, if it exceeds 20 milliliters/min, the influence of unreacted potassium permanganate on the ORP electrode is too strong, and the end point is detected too early, resulting in a low hydrogen peroxide concentration. However, the difference in setting the titration rate from 5 to 20 ml/min should be considered in terms of concentration or accurate measurement.

Furthermore, since the sampling amount of the aqueous solution containing hydrogen peroxide is set to 5 to 20 milliliters, the accuracy of analysis can be increased. That is, if the sampling amount is less than 5 milliliters, it is too small and the sampling error becomes large, resulting in low analysis accuracy. On the other hand, if the sampling amount is 20 milliliters or more, it will be too large and the sampled aqueous solution will react violently with potassium permanganate, generating a large amount of scum, causing liquid to scatter, and reducing analysis accuracy. . Also,
Excessive sampling amount leads to increased consumption of potassium permanganate and increases measurement cost. However, if the sampling amount is between 5 and 20 milliliters, the accuracy of analysis can be increased, and the consumption of potassium permanganate will not be too large.

According to the experiments of the present inventor, the second aspect of the present invention makes it possible to reduce the analytical accuracy to within ±5%.

According to the third aspect of the present invention, since the stirring part is not a propeller but a flat plate or a cylinder, bubbles are less likely to be generated. Then, the length of the stirring part or the inner diameter of the reaction tank is 1/2 to 1/5
Since the thickness or diameter is 1/2 to 1/20 of the liquid height during titration, a sufficient stirring effect can be obtained without producing bubbles.

According to the fourth aspect of the present invention, the number of revolutions of the stirring bar is set to 500.
By setting the stirring speed to ~1.200 rpm, it is possible to obtain a suitable stirring efficiency, and to avoid the possibility that a large amount of bubbles will be generated and the sensitivity of the ORP electrode will be reduced. That is, if the rotation speed is less than 500 rpm, the stirring efficiency will be low, the uniform dispersion of the sampled aqueous solution and potassium permanganate will be poor, and the ORP value will be large near the ORP electrode and at the potassium permanganate dropping position. Differences occur and analysis errors become larger. Also, the rotation speed is 1200 rpm
If it is more than that, a large amount of bubbles will be generated, and the bubbles will adhere to the ORP electrode, reducing the accuracy of ORP detection. However, 500-1
If the speed is 20 O rpm, it is possible to obtain sufficient uniform dispersion while preventing the generation of bubbles, and by extension, the measurement accuracy can be increased.

According to the fifth aspect of the present invention, check means are provided at the ends of the tube into which the aqueous solution for sampling is dropped and the tube into which potassium permanganate is dropped, so that when the analysis is stopped, residual liquid remains from the tip of the tube. It is possible to prevent the solution from flowing back and changing the concentration of the solution supplied into the reaction tank during the next measurement, thereby reducing analytical accuracy.

[Example: 1 Hereinafter, the present invention will be explained according to illustrated embodiments.

The drawings are for explaining one embodiment of the present invention,
FIG. 1 is a block diagram showing the overall structure of the apparatus.

In the drawing, 2 is a funnel-shaped reaction tank, 2 is a tank for storing water for washing, and 3 is a pump. The pump 3 supplies water to the reaction tank 1 for washing. 4 is a tank for storing potassium permanganate; 5 is a pump that supplies potassium permanganate from the tank 4 to the reaction tank 1; 6
7 is a tank for storing a sampling liquid, 7 is a tank for storing pure hydrogen peroxide liquid for replenishment, 8 is a pump for supplying the hydrogen peroxide in the tank 7 to the tank 6, and 9 is a tank for transferring the sampling liquid in the tank 6 to the reaction tank 1 10 is a tank for storing sulfuric acid H2SO4, which is a diluent for the redox reaction, and 11 is a pump for supplying sulfuric acid in tank 10 to reaction tank 1.
This is a pump that supplies water to the inside.

Each of the pumps 3, 5, 8, 9, and 11 uses a diaphragm. In other words, in tube pumps that are often used in conventional automatic analyzers, contact with rollers causes the tube to deteriorate, making the flow rate unstable, and it is necessary to constantly change the contact surface to improve the stability of the flow rate. There is a problem that it is not desirable for work. In addition, plunger bongs have traditionally been often used, and although plunger bongs have a high flow rate stability, they are very expensive. However, the flow stability of diaphragm pumps is much better than that of tube pumps, and only slightly worse than that of plunger pumps. Therefore, sufficient analytical precision can be obtained and the price is low. Therefore, a diaphragm pump was adopted.

12, 12, 12 are pumps 5, 9, 1l to reaction tank 1
This is a check valve installed at the end of the hose that leads the liquid to the tank. These check valves 12, 12, and 12 are for preventing liquid from flowing backward when analysis is stopped, and can prevent the accuracy of the next measurement from being lowered due to liquid backflow.・13 is O
The RP electrode uses a less sensitive type of electrode for fermentation in order to obtain a smooth titration curve. Specifically, platinum is used as an electrode. Using a low-sensitivity one is
This is because if a highly sensitive one is used, it will be susceptible to the influence of potassium permancanate and the analysis values will vary widely, making it impossible to accurately detect the end point.

14 is a stirring rod, which is rotated by a motor I5. FIGS. 2(A) and 2(B) are perspective views showing different examples of the stirring rod 14. The stirring rod 14 is provided with a stirring part 16 at the lower end, and it is preferable that the stirring part 16 be made into a flat plate shape as shown in the figure (A), or a cylindrical shape as shown in the figure (B). . Conventionally, propellers were used for stirring, but
When a propeller was used, there was a problem in that a large amount of bubbles were generated. If the stirring part I6 is flat, plate-shaped, or cylindrical, the amount of such bubbles generated will be significantly reduced. 17 is a controller for keeping the hydrogen peroxide concentration constant.

Fig. 3 is a plan view showing the planar positional relationships among the stirring rod, the ORP electrode, the dropping position of potassium permanganate, the dropping position of washing water, the dropping position of sulfuric acid as a diluent, and the dropping position of the sampling aqueous solution; The figure is a sectional view showing seven stirring bars of the ORP electrode.

ORP electrode J3 is placed along the stirring direction around the reaction tank 1,
The dropping position of potassium permanganate, the dropping position of cleaning water, the dropping position of H, So4, and the dropping position of the sampling aqueous solution are arranged, and the ORP electrode is placed at the farthest point along the stirring direction from the dropping position of potassium permanganate. are doing.

This is because the unreacted potassium permanganate is directly dissolved into the ORP electrode and the ORP occurs at the end point or at an earlier timing than originally intended.
This is to avoid the hydrogen peroxide concentration being detected by the electrode and being measured as low.

By the way, the liquid volume in the reaction tank 1 is 50 to 150 mm, and the titration rate is 5 to 20 mm.
per minute, and the sampling amount is 5 to 20 milliliters. The reason for setting the liquid volume in reaction tank 1 to 50 to 150 milliliters is because if the liquid volume is at or below the level, potassium permanganate is
It directly affects the P electrode and reduces analysis accuracy, and if the liquid volume exceeds the above range, that is, 150ml or more, the stirring efficiency will be low and the dispersion will be insufficiently uniform, which will also affect analysis accuracy. This is because it becomes too low and undesirable. In addition, the reason for setting the titration rate to 5 to 20 ml/min is that if the titration rate is less than 5 ml/min, the response of the ORP electrode will be delayed and the concentration will be higher than the actual concentration, and if it is more than 20 ml/min, there will be no reaction. This is because the potassium permanganate in the sample has too strong an effect on the ORP electrode, resulting in a lower concentration than the actual concentration.

In addition, the reason why the sampling amount should be 5 to 20 ml is that if it is less than that, the sampling error will be large and will affect the analysis accuracy, and the analysis accuracy will decrease.On the other hand, if the sampling amount is more than that, the redox reaction will be too intense. This is because a large amount of gas is generated, and furthermore, this causes the inconvenience of liquid scattering.

The length of the stirring part I6 is half the inner diameter of the reaction tank 1.
The thickness or diameter of the stirring part 16 is 1/2 to 1/20 of the liquid height during titration, or under such conditions, the thickness or diameter of the stirring part 16 is sufficient without generating bubbles. Therefore, it is possible to obtain a high stirring efficiency. The rotation speed of the stirring rod 14 by the motor 15 is 500 to l20.
This is because, by setting the stirring speed to 0 rpm, a sufficient stirring effect can be obtained to improve uniform dispersion of the aqueous sampling solution and potassium permanganate while preventing the generation of bubbles. Among them, 800 rpm
degree or optimum.

Next, the operation of the device will be explained.

For example, open the drain 18 for about 30 seconds, then turn on the sampling pump 9 for about 600 seconds to replace the water, and then open the water washing pump 3 for about 30 seconds to drain the reaction tank 1.
Rinse with water and open train 18 again for 30 seconds. How many times should you repeat this washing process? This is to prevent the previous measurement from affecting the current measurement.

Next, the sulfuric acid pump 11 is turned on, for example, for 108 seconds, and then the sampling pump 9 is turned on for 60 seconds. Thereafter, the potassium permanganate pump 5 is turned on to perform titration. ．． Then, wait for about 20 seconds, and then select the ORP value or the predetermined value (8
Measure the time (X) required to reach 0 mV). Next, the hydrogen peroxide concentration is calculated from this measurement result (X), and if the concentration is lower than the reference value, the time (Y) for which the hydrogen peroxide pump 8 should be turned on is calculated.

Then, the pump 8 is turned on for a time Y to replenish the insufficient hydrogen peroxide in the tank 6. Thereby, the hydrogen peroxide concentration of the main solution in the tank 6 can be maintained at a predetermined reference value.

Thereafter, the reaction tank 1 is washed with water.

This series of operations is repeated for 1800 seconds as one cycle.

[Effects of the Invention] As is clear from the above description, the following effects can be obtained according to the present invention.

First, since the ORP electrode was placed far from the potassium permanganate dropping position along the stirring direction, the ORP electrode
There is no risk of unreacted potassium permanganate coming into direct contact with the P electrode. Therefore, it is possible to prevent the measurement accuracy of hydrogen peroxide from decreasing.

Second, by setting the liquid volume in the reaction tank to 50 to 150 ml, the titration rate to 5 to 20 ml/min, and the sampling amount to 5 to 20 ml, the analytical accuracy can be increased to ±
It was decided to keep it within 5%, and the necessary analytical accuracy was obtained.

Thirdly, since the stirring part is not a propeller but a flat plate or columnar shape, air bubbles are less likely to be generated. By setting the length of the stirring part to 1/2 to 1/5 of the inner diameter of the reaction tank and the thickness or diameter to 1/2 to 1/20 of the liquid height during titration, air bubbles can be created. It was possible to obtain a sufficient stirring effect without producing any.

Fourthly, since the rotation speed of the stirring rod was set to 500 to 120 rpm, sufficient stirring efficiency could be obtained without generating a large amount of bubbles.

Fifth, we installed check means at the ends of the tube for dropping the aqueous solution for sampling and the tube for dropping potassium permanganate, so that when the analysis is stopped, the residual solution flows backwards from the tip of the tube and is used for the next step. It is possible to prevent a change in the concentration of the solution supplied into the reaction tank during measurement and a decrease in analysis accuracy.

[Brief explanation of drawings]

The figures also show one embodiment of the present invention; FIG. 1 is an overall configuration diagram, FIGS. 2(A) and (B) are perspective views showing different examples of stirring rods, and FIG. 3 is a diagram showing one embodiment of the present invention. is a plan view of the reaction tank, and FIG. 4 is a longitudinal sectional view of the reaction tank. - Reaction tank - Check means - ORP electrode - Stirring rod - Stirring section (A) (B) 2 Figure 13 3 Figure 4

Claims (5)

[Claims] (1) Drop an aqueous solution to be measured containing hydrogen peroxide into a reaction tank, drop potassium permanganate to titrate the aqueous solution to be measured into the reaction tank, and apply an ORP electrode to the aqueous solution to be measured in the reaction tank. This is a hydrogen peroxide concentration measuring device for measuring the concentration of hydrogen peroxide by soaking water in the aqueous solution. A hydrogen peroxide concentration measuring device, characterized in that it is placed at a location apart from the dripping position of potassium permanganate along the flow direction. (2) The amount of liquid in the reaction tank is 5.0 to 150 ml,
2. The hydrogen peroxide concentration measuring device according to claim 1, wherein the titration rate is 5 to 20 ml/min and the amount of the aqueous solution to be measured is 5 to 20 ml. (3) The stirring part provided at the lower end of the stirring rod is formed into a flat plate or columnar shape, and the length of the stirring part is 1/2 to 5 times the inner diameter of the reaction tank.
The method according to claim 1 or 2, characterized in that the thickness or diameter of the stirring part is 1/2 to 1/20 of the liquid height during titration. Hydrogen oxide concentration measuring device. (4) The hydrogen peroxide concentration measuring device according to claim 1, (2) or (3), characterized in that the rotation speed of the stirring rod is 500 to 1200 rpm. (5) A hydrogen peroxide concentration measuring device characterized in that a check means is provided at the lower ends of the tube into which the aqueous solution to be measured is dropped and the tube into which potassium permanganate is dropped.