JPS6315547B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the concentration of subhalite or hypohalite, and more specifically, the present invention relates to a method for controlling the concentration of subhalite or hypohalite, which contains various malodorous components generated in, for example, human waste, sewage treatment plants, poultry farming, pork frying, various factories, etc. The present invention relates to a method for controlling the concentration of a sub- or hypohalite salt solution used for cleaning when treating malodorous gases.

Conventionally, methods for controlling the concentration of such sub- or hypohalite salts include, for example, near-ultraviolet absorption spectrophotometry and coulometric method. However, near-ultraviolet absorption spectrophotometry has the drawback that the equipment is expensive to begin with and, for example, the absorbance of hypochlorite ion (ClO ^- ) is affected by pH and temperature, so the detection part must be kept in a highly concentrated alkali solution. There is. Therefore, this method requires a highly concentrated alkaline solution, and is disadvantageous in terms of installation of a mixing tank in front of the detection section and ancillary equipment such as pH control. In addition, in the coulometric method, the influence of pH on the detection electrode is significant, and it is necessary to maintain the pH of the detection part at a high level, and there are disadvantages in that scale adhesion to the detection part due to water turbidity, etc., and the influence of liquid temperature are significant. .

Therefore, in order to solve the drawbacks of the conventional method, the present inventor connected an oxidation-reduction potential meter (hereinafter oxidation-reduction potential is abbreviated as ORP) directly to the controlled solution.
A method of controlling the concentration of sub- or hypohalite in the controlled solution (referred to as direct ORP control method)
We considered the following. However, direct ORP
In the control method, there is almost no change in ORP due to a change in the concentration of the halide salt, and therefore it must be controlled by a change in potential of several mV, which is impossible to operate at an industrial level, and therefore it is not possible to use it arbitrarily. It was difficult to control the concentration to .

In view of such problems, the present inventor has continued to conduct intensive research on methods for controlling the concentration of controlled solutions containing sub- or hypohalite salts, and has
We conducted various studies on a concentration control method using the ORP measurement method, that is, a concentration control method in which a part of the solution to be controlled is taken out, a redox reaction reagent is mixed therein, and the ORP is measured. As a result, such indirect
Among the various redox reaction reagents that can be used in the ORP control method, Na ₂ SO ₃ , Na ₂ S ₂ O ₃ , H ₂ O _2, etc., in particular, have no problems such as scale formation or toxicity due to hydroxides. Useful, but with Na ₂ SO ₃
It is unsuitable as a reagent for continuous control where the Na ₂ SO ₃ concentration changes significantly over time, and Na ₂ S ₂ O ₃ also shows little change over time, but the reaction ratio with, for example, ClO ^- differs depending on the liquid pH. It has been found that there is a problem when using it as a control reagent as it is necessary to keep the pH strictly constant.On the other hand, when using H ₂ O ₂ ,
The pH of the H ₂ O ₂ solution becomes a problem; if the pH becomes too high, HO ₂ ^- is produced due to the dissociation equilibrium of H ₂ O ₂ , which prevents the reaction from proceeding, and if the pH is low, the reaction rate slows down and cannot be completed in a short time. It was found that the reaction could no longer be expected, and the equivalence point fluctuated significantly depending on the pH of the solution to be controlled, making control difficult because the ORP control set point could not be determined. However, further research revealed that by adding a buffer to the H ₂ O ₂ solution as a redox reaction reagent, the equivalence point variation due to the pH of the controlled solution was significantly suppressed, and at the same time, the addition of the buffer also suppressed the change in the equivalence point due to the _pH of the controlled solution. We have found that control errors can be significantly reduced by keeping the PH of the O ₂ solution within a specific range. The present invention has been completed based on this new knowledge.

That is, the present invention takes out a part of the solution to be controlled in which the concentration of subhalite or hypohalite is to be controlled,
By mixing this with a hydrogen peroxide solution whose pH has been adjusted to 6 to 12 by adding a buffer, and measuring the redox potential of the mixture, it is possible to control the concentration of sub- or hypohalite salts. The present invention relates to a method for controlling the concentration of a sub- or hypohalite salt.

To provide a controlled solution that can effectively remove harmful and malodorous gases containing various malodorous components with almost no loss of the controlled solution for cleaning by using the concentration control method of the present invention. can do. Examples of the above-mentioned malodorous components include ammonia, amines, lower fatty acids, hydrogen sulfide, mercaptans, thioethers, alkyl disulfide,
Examples include aldehydes.

Examples of sub- or hypohalite salts whose concentration is to be controlled in the present invention include alkali metal salts or alkaline earth metal salts of halous acids such as chlorous acid, bromic acid, and iodic acid, or hypochlorous acid. , hypobromous acid, hypoiodic acid, and other alkali metal or alkaline earth metal salts of hypohalous acids, among which sodium chlorite, sodium hypochlorite, and sodium hypobromite. Applied to concentration control, etc.

The hydrogen peroxide solution used in the method of the present invention is preferably an aqueous solution, and it is necessary to maintain its pH in the range of 6 to 12 by adding a buffer. Furthermore, by keeping the pH in the range of 6 to 10, the titration error in ORP titration can be kept within ±5%, which is more preferable. Moreover, when the above pH range is set to 8 to 10, the titration error can be further reduced, which is even more preferable. In addition, in the present invention, by using a H ₂ O ₂ solution containing a buffer,
It is less affected by equivalence point fluctuations based on the pH of the solution to be controlled, and the fluctuations can be suppressed within a range of 100 mV, making it possible to reduce control errors. Further, as the hydrogen peroxide solution, for example, soda lime,
When using a hydrogen peroxide solution stored in a container whose opening is sealed with ascarite, pyrogallol, calcium chloride, etc., there is even less change over time, and there is almost no effect on the pH change of the controlled solution. It is the most excellent redox reaction reagent.

The buffer used in the present invention is one that does not react with H ₂ O ₂ , which is a redox reaction reagent, and a controlled solution, such as a NaClO solution, and is widely used as a mixed aqueous solution of a weak acid or weak base and its conjugate base or conjugate acid. For example, borax, boric acid, borates such as monohydrogen boric acid, phosphates such as monohydrogen phosphate and dihydrogen phosphate, citrates such as sodium citrate, or A mixture of these and NaOH, HCl, etc. can be used. In the present invention, such buffers may be used to prepare H ₂ O ₂ solutions having a pH in the range of 6 to 12, preferably 6 to 10, more preferably 8 to 10, and for this purpose, e.g. When using borax, the concentration in the redox reaction reagent is preferably within a range of about 0.005 to 0.2M/.

In the present invention, the total salt concentration in the sub- or hypohalite solution which is the controlled solution is:
From the viewpoint of ORP titration error, it is preferably about 20 wt/v% or less, more preferably about 5 wt/v% or less. Here, the total salt concentration is generated by the deodorizing reaction.
It refers to the concentration of Na ₂ SO ₄ , NaCl and other reaction product salts, salts present in water, salts present in hypochlorite, etc., and is unrelated to the effective chlorine concentration contained in hypochlorite, etc. It is. Also, the pH of the controlled solution
is preferably 5 to 13, more preferably 7 to 11, from the viewpoint of ORP change and titration error, but it is also desirable to have a value of 7 to 11, but it is also possible to solve the problem of CO ₂ content when cleaning harmful gases, or for example
The range of 7.8 to 10 is particularly preferable from the relationship of the dissociation equilibrium of NaClO.

The control method of the present invention will be explained in more detail.

In general, the redox equivalent reaction is expressed by the formula Nox・Vox=NRed・VRed [In the formula, Nox is the specified concentration of the oxidizing agent, NRed is the specified concentration of the reducing agent, Vox is the capacity of the oxidizing agent, and VRed is the capacity of the reducing agent. . ] It is expressed as .

Now, set the set concentration of the controlled solution to be controlled by Nox
The specified amount of liquid to be partially removed is Vox (ml). On the other hand, the concentration of the hydrogen peroxide solution with the specific pH to be mixed with the controlled solution is adjusted to satisfy the relationship of the above formula.
Adjust to NRed regulations. NRed can be determined arbitrarily, but for example, the amount of Vox and hydrogen peroxide solution sent
If the VRed relationship is Vox = VRed, then Nox =
The specified concentration of NRed should be determined so that it becomes NRed.

The reaction potential at which the relationship of the above formula holds true is the equivalent potential, which is confirmed separately. When the potential of the mixed solution of the controlled solution and the hydrogen peroxide solution is detected by the ORP electrode, if the concentration of the controlled solution is higher than the predetermined concentration of hydrogen peroxide, for example, in the above example, Nox
In a state of ≧NRed, a potential equal to or higher than the equivalent potential is shown, and in this case, the control circuit for feeding the supply liquid is not activated. On the other hand, if the concentration of the controlled solution is consumed due to malodorous gas treatment and becomes thinner than the concentration of hydrogen peroxide, for example in the above example, if Nox < NRed, a potential lower than the equivalent potential is indicated, and this In this case, the control circuit operates and the supply liquid is pumped into the controlled solution, the concentration of the controlled solution increases, and when the state of Nox = NRed returns, the supply liquid is pumped through the control circuit. Stop.

In this way, by mixing a portion of the controlled solution with the hydrogen peroxide solution and causing a redox reaction, the concentration of the controlled solution is controlled to a predetermined set concentration based on the relationship between the reaction potential and the equivalent potential. It is something to do. In particular, in the present invention, the pH of the hydrogen peroxide solution is adjusted within the specified range, so that control errors are significantly reduced.

As a method for supplying a high concentration sub- or hypohalite solution, that is, a supply liquid, by indirect ORP control of the present invention, between two points using a two-point set potential,
Any method can be adopted, such as an ORP control method, a one-point control method and a method in which the control signal is supplied using a timer for a certain period of time from the time the control signal is turned ON, or a method in which ON and OFF supplies are performed using only one point control. Further, contamination of the controlled solution can be prevented by passing it through a filter. Furthermore, the filter is sufficiently effective against colloidal sulfur produced by the reaction between sulfur compounds and NaClO, and even 1000 ppm of colloidal sulfur can be sufficiently filtered out.

The control method of the present invention can be applied or diverted to various other aspects. For example, when a harmful gas containing chlorite (ClO ₂ ) is cleaned with a H ₂ O ₂ solution, the method of the present invention can be used to control the concentration of the H ₂ O ₂ solution by using a NaClO solution as a redox reaction reagent. Or, when cleaning harmful gases containing nitrogen oxides (NOx) with an aqueous solution containing sodium chlorite (NaClO ₂ ), the control method of the present invention may be used to maintain the concentration of NaClO ₂ within a certain range. be able to.

Preferred embodiments of the present invention will be described below according to the flow sheet shown in FIG.

The controlled solution 1 is circulated through a filter 2.
A part of the controlled solution is supplied by the operation of the metering pump 3.
After passing through a filter, it is separated into gas and liquid in a defoaming tank 4 and sent to a mixing tank 5. On the other hand, the same amount of the redox reaction reagent 6, which has a concentration equivalent to the controlled solution having a predetermined concentration, is sent to the mixing tank at the same time as the controlled solution, and when the reaction occurs.
ORP is continuously measured by an ORP meter 7 using a detection electrode. In this case, since the amount of liquid to be fed is the same, there is an advantage that only one pump is required.
As the sub- or hypohalite salt in the controlled solution is circulated through the malodorous gas cleaning device 10, it is consumed and its concentration decreases until a predetermined control concentration is reached, resulting in a large change in ORP. If the ORP control potential is set to a predetermined potential, when that potential is reached, the control circuit 8 is activated, and the supply liquid 9, which is a high concentration solution of sub- or hypohalite salt, is injected to maintain the control concentration. There is.

The present invention will be explained below by giving examples.

Example 1 The concentration of sodium hypochlorite was controlled in the following manner according to the flow sheet shown in FIG.

Control method: Indirect ORP control method with one-point setting Controlled solution: NaClO, PH=5 Redox reaction reagent: Sodium citrate 0.06M/and
0.0226N _H2O2 aqueous solution with addition of _NaOH , PH
=6 Set the control concentration of NaClO (available chlorine) in the above controlled solution to 800 ppm and control ORP to +500 mV. Next, while changing the concentration of the controlled solution using a 1M Na ₂ SO ₃ aqueous solution, we investigated the controllable upper and lower limit concentrations.
They were 890ppm and 820ppm.

Example 2 The PH of the controlled solution was controlled at 8 to 10, and a 0.0282 normal H ₂ O ₂ aqueous solution with PH = 9 to which 0.01 M of borax was added as a redox reaction reagent was used, and the control concentration was 1000 ppm and the control ORP + 400 mV. Set _H2S to 2000 to perform controlled solution concentration changes.
Example 1 except that air containing 21000ppm was used
An experiment was conducted in the same manner. The upper and lower controllable concentration limits were 1070 ppm and 980 ppm, respectively. still
The H ₂ O ₂ aqueous solution sealed with soda lime was used.

Example 3 The pH of the controlled solution was controlled to 9, and 0.01M/pH of borax was added as a redox reaction reagent.
= 9 using a 0.197 normal H ₂ O ₂ aqueous solution, control concentration
Set to 7000 ppm, control ORP + 400 mV, and increase H ₂ S to 4000 ~ 4000 to change the concentration of the controlled solution.
Example 1 except that air containing 18000 ppm was used
An experiment was conducted in the same manner. The upper and lower controllable concentration limits were 7100ppm and 7000ppm, respectively. still
The H ₂ O ₂ aqueous solution sealed with soda lime was used.

Example 4 The pH of the controlled solution was controlled at 12, and sodium citrate was added as a redox reaction reagent at 0.06 M/ml.
Using 0.0226 normal H ₂ O ₂ aqueous solution with PH = 6 added with NaOH, control concentration 800 ppm, control ORP + 400 m
An experiment was conducted in the same manner as in Example 1 except that the voltage was set to V. The upper and lower concentration limits that can be controlled are
They were 950ppm and 780ppm. The H ₂ O ₂ aqueous solution sealed with ascarite was used.

Example 5 The PH of the controlled solution was controlled to 12, and a 0.0226N H ₂ O ₂ aqueous solution with PH = 12 to which 0.08M borax and NaOH were added as redox reaction reagents was used.
An experiment was conducted in the same manner as in Example 1 except that the control concentration was set to 800 ppm and the control ORP + 200 mV. The upper and lower concentration limits that can be controlled are 1010ppm and 1010ppm, respectively.
It was 940ppm. The H ₂ O ₂ aqueous solution sealed with ascarite was used.

Example 6 The pH of the controlled solution was controlled to 13, and 0.01M/pH of borax was added as a redox reaction reagent.
=9 using 0.0282 normal H ₂ O ₂ aqueous solution, control concentration
An experiment was conducted in the same manner as in Example 1 except that the setting was 1000 ppm and control ORP + 400 mV. The upper and lower controllable concentration limits were 1200 ppm and 1100 ppm, respectively.

Example 7 The pH of the controlled solution was controlled to 13, and 0.08M/pH of borax was added as a redox reaction reagent.
Using a _0.0282 normal _H2O2 aqueous solution of =12, control concentration
An experiment was conducted in the same manner as in Example 1 except that the setting was 1000 ppm and control ORP + 200 mV. The upper and lower controllable concentration limits were 1600 ppm and 1500 ppm, respectively.

Reference Example 1 The sealing effect when a hydrogen peroxide solution, which is a redox reaction reagent in the present invention, was sealed with a sealant was investigated. In other words, borax 0.01M/as a buffering agent
The H ₂ O ₂ solution is continuously suctioned at a constant rate from a H ₂ O 2 storage tank containing H 2 O ₂ , and the H Figure 2 shows the rate of decrease in ₂ O ₂ concentration.
From the figure, the reduction rate after 5 days of continuous suction is 2% in the former (solid line), but 10% in the latter (dotted line), and when a sealant is used, it is not used. The sealing effect was five times better than that without.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing a preferred embodiment of the method for controlling halide salts of the present invention. In Figure 1, 1 is a controlled solution, 2 is a filter, 3 is a metering pump, 4 is a defoaming tank, 5 is a mixing tank, 6 is a redox reaction reagent, 7 is an ORP meter,
8 is a control circuit, 9 is a supply liquid, and 10 is a foul-smelling gas cleaning device. FIG. 2 is a graph showing the sealing effect when the redox reaction reagent of the present invention is sealed with a sealant.

Claims (1)

[Claims] 1. Take out a part of the solution in which the concentration of subhalite or hypohalite is to be controlled, and mix it with a hydrogen peroxide solution whose pH has been adjusted to 6 to 12 by adding a buffer. A method for controlling the concentration of a sub- or hypohalite salt, characterized in that the concentration of the sub- or hypohalite salt is controlled by measuring the redox potential of the mixed solution. 2. The concentration control method according to claim 1, wherein the hydrogen peroxide solution has a pH of 6 to 10. 3. The concentration control method according to claim 2, wherein the hydrogen peroxide solution has a pH of 8 to 10. 4. Claims 1 to 3, characterized in that the hydrogen peroxide solution used is a hydrogen peroxide solution stored in a container whose opening is sealed with soda lime, ascarite, pyrogallol, calcium chloride, etc. The concentration control method according to any one of paragraphs.