JPS5834174B2 - Chitsusosankabutsunojiyokiyohouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing nitrogen compounds,
More specifically, it relates to a method for removing nitrogen oxides and nitrogen dioxide from a gas containing them.

The waste gases generated from various chemical manufacturing processes such as the combustion process, nitric acid manufacturing process, and sulfuric acid manufacturing process in cabins contain nitrogen compounds, which, if released directly into the atmosphere, can cause air pollution. cause

In order to prevent such air pollution, various methods for removing nitrogen oxides from waste gas have been proposed and implemented.

The most commonly used method for removing nitrogen oxides is the alkaline cleaning method, but this method mainly removes water-soluble nitrogen dioxide. is extremely low (water 1 at 50℃
Since the amount dissolved in 0.01 is approximately 0.00451), it is hardly removed.

Therefore, in this alkaline cleaning method, -nitrogen oxide concentration is reduced to t
It cannot be less than o o p, p, m.

- Air oxidation is generally used to remove nitrogen oxides.

By this method, nitrogen monoxide with low water solubility is oxidized to water-soluble nitrogen dioxide, which is dissolved and removed in water or an aqueous alkaline solution.

However, in the conventional air oxidation method, the oxidation rate of nitrogen oxide is low, and in particular, the lower the concentration of nitrogen monoxide to be oxidized, the lower the oxidation rate.

For example, the time required to oxidize nitrogen monoxide contained in the atmosphere by 95 points of its initial concentration with oxygen in the air is approximately 1 hour when the initial concentration is 11,000 ppm, but when the initial concentration is 200 ppm, it takes about 1 hour. Sometimes it takes about 5 hours.

In order to improve the low efficiency of the conventional air oxidation method, a method has been proposed in which nitrogen oxide is oxidized using an oxidizing agent such as hydrogen peroxide, potassium permanganate, or chlorite. .

However, such conventional oxidation methods are also unsatisfactory industrially.

For example, hydrogen peroxide has drawbacks such as being expensive and has a typical feed concentration of 35% and a large weight per available oxygen; and potassium permanganate has drawbacks such as being expensive Moreover, as a result of oxidation, it is reduced to manganese dioxide, which has drawbacks such as difficulty in treating this waste liquid, and if this treatment is done incorrectly, it may cause secondary pollution.

Furthermore, the method using chlorite has the disadvantage that the manufacturing process for chlorite, for example, sodium chlorite, is complicated and therefore expensive, making it difficult to put it into practical use on an industrial scale.

Furthermore, chlorite decomposes rapidly in acidic aqueous solutions, which poses a risk of explosion.

In addition to the conventional oxidation methods mentioned above, catalytic oxidation methods using silica gel, activated carbon, platinum, etc. as oxidation catalysts are also known. Disadvantages include that the catalytic capacity decreases significantly within a short period of time, so that it takes a long time to achieve the desired oxidation.

The purpose of the present invention is to eliminate the drawbacks of conventional nitrogen oxide removal methods, to be able to remove nitrogen oxides efficiently and inexpensively within a short time, and to eliminate the reaction products accompanying this nitrogen oxide removal. The object of the present invention is to provide a method for removing nitrogen oxides that does not cause secondary pollution such as air or river pollution.

In the method for removing nitrogen oxides of the present invention, a nitrogen oxide-containing gas is mixed with a chlorate of 1 mol/l or less and 1 to 80 mol/l of chlorate.
In an aqueous solution containing 1 mol/l or less of chlorate and 1 to 80 mol/l of sulfuric acid or nitric acid, and in the presence of an alkali metal chloride, The method is characterized by contacting with an absorbing liquid consisting of water or an aqueous solution of a basic compound.

Another method of removing nitrogen oxides according to the present invention is to combine a gas containing nitrogen oxides with a chlorate of 1 to 80 mol/l or less.
In an aqueous solution containing a large amount of hydrochloric acid, or a chlorate of 1 mol/l or less, and sulfuric acid or nitric acid of 1 to 80 weight φ, and in the presence of an alkali metal chloride, The method is characterized by contacting with an absorbing liquid made of an alkaline aqueous solution of a reducing compound.

That is, in the method of the present invention, a gas to be treated containing nitrogen oxides is dissolved in an acidic aqueous solution of chlorate in hydrochloric acid, or in sulfuric acid or nitric acid in the presence of an alkali metal chloride (for example, NaCl or KCI). A first step of bringing the gas into contact with an acidic aqueous solution, and a second step of bringing the gas to be treated, after the treatment, into contact with an absorption liquid consisting of water, an aqueous solution of a basic compound, or an alkaline aqueous solution of a reducing compound. It includes.

In the first step, poorly water-soluble nitrogen oxides are oxidized to easily water-soluble nitrogen dioxide, and in the second step, the nitrogen dioxide produced in the first step is removed by an absorption liquid.

Further, when the gas to be treated obtained in the first step contains chlorine dioxide, chlorine dioxide can also be removed by using an alkaline aqueous solution of a reducing compound as an absorption liquid in the second step.

The nitrogen oxide-containing gas subjected to the method of the present invention is -
Although it contains nitrogen oxide, it may contain other nitrogen compounds, and may further contain sulfur compounds such as sulfur dioxide gas.

The chlorate used in the method of the present invention is a water-soluble chlorate, including NaClO3, KC103, NH4Cl03C
a(CIO3)2. Although Ba(C103)2 and the like can be used, Na C103 is most suitable in view of the price and the difficulty of post-treatment of the reaction product.

The chlorate in the treatment solution is generally used at an aqueous concentration of 1 mol/l or less, preferably 0.01 to 3% by weight,
In order to avoid wasteful consumption of chlorate, it is preferable to use it in as low a concentration as possible.

That is, even if the chlorate concentration in the treatment solution is increased to more than 1 mol/l, the treatment effect will not increase significantly, and this is economically disadvantageous.

For this reason, between treatment operations, the concentration of nitric oxide in the treatment gas and the concentration of chlorate in the treatment liquid are measured, and the required amount of chlorate is added to the treatment liquid according to these concentrations. This is desirable.

In the method of the invention, chlorate is used as an acidic aqueous solution.

Suitable acids used for this purpose are sulfuric acid, hydrochloric acid, or nitric acid, and these acids have a concentration of 1 to 80 kan (by weight).
may be contained in the processing solution in a wide range of high concentrations.

In particular, when the gas to be treated contains sulfur dioxide gas, the sulfur dioxide gas is dissolved in the treatment liquid, and the acid concentration in the treatment liquid is 70%.
The treatment solution remains effective even in the presence of such high concentrations of acid, although it may increase to ~80% (by weight).

However, even if the acid concentration is higher than 80% (by weight), there is no particular advantage in terms of effectiveness, and on the contrary, operational and economical disadvantages become greater.

Furthermore, when the acid concentration is lower than 1 width (weight), the oxidizing effect of nitrogen oxides is significantly reduced.

For example, 250 ppm NO, 900 ppm 5Ox
Boiler exhaust gas containing 02 of 1 and 2,5 weight factor,
When a 50&/l aqueous solution of NaClOs is brought into contact with a treatment solution whose pH has been changed to a range of 0.3 to 4 using HCI at 50°C, the relationship between the pH of the treatment solution and the NO oxidation rate is as follows. As shown in Figure 1.

Also, the pH of each 1φ (weight) aqueous solution of sulfuric acid, nitric acid, and hydrochloric acid
is as follows.

As is clear from FIG. 1, the oxidation rate of NO sharply increases when the pH of the treatment solution is about 0.8 or less.

That is, in order to obtain a sufficient NO oxidation rate, the concentration of acid in the treatment liquid needs to be 1% (by weight) or more.

As mentioned above, chlorate in the treatment solution generates chlorine dioxide due to the presence of hydrochloric acid, sulfuric acid, or nitric acid and an alkali metal chloride, which smoothly oxidizes nitrogen monoxide. I can do it.

That is, when the treatment solution contains chlorate and hydrochloric acid (HCl), the following reaction: NaClO3 + 2HC1- + NaCl + ClO2 7C
12+H20 generates chlorine dioxide.

Furthermore, when the treatment solution contains a chlorate, an acid, and an alkali metal chloride, such as NaCl (or KCI), chlorine dioxide is generated by the following reaction.

As mentioned above, if HC2 or an alkali metal chloride such as NaCl or KCI is present in the acidic treatment solution containing chlorate, ClO2 is smoothly generated from chlorate, and chlorate is not wasted. Consumption can be prevented.

Through the above-described treatment, nitrogen monoxide in the gas to be treated is oxidized to water-soluble nitrogen dioxide, and when absorbed into water, becomes nitrous acid, nitric acid, or denatured into salts of these acids.

Furthermore, when waste gas containing sulfur dioxide gas along with nitrogen oxides is oxidized by the method of the present invention, the sulfur dioxide gas acts as a reducing agent in the presence of an oxidizing agent, converting part or all of the nitrogen oxides into harmless nitrogen. Reduce to gas.

In addition, sulfur dioxide gas turns into sulfuric acid and is recovered as an aqueous solution.

In the first step of the method of the present invention, there are no particular limitations on the amount of SO2, HCl, or alkali metal chloride that should be present in the treatment system.

In the case of SO2, the amount contained in normal industrial waste gas, that is, about 2000 ppm, is sufficient, and in the case of HCI, the amount used as an acid, that is, 1 to 80% by weight, is sufficient, and the amount of alkali 2~ for metal chlorides
It is preferably contained in the treatment liquid at a concentration of 40.9/7.

The gas to be treated containing the water-soluble nitrogen compound thus generated is then contacted with water, an aqueous solution of a basic compound, or an alkaline aqueous solution of a reducing compound.

The above treatment liquid is selected depending on the composition of the waste gas and the aforementioned oxidized gas.

If the waste gas contains sulfur dioxide gas and nitrogen and sulfuric acid are generated by the oxidation treatment as described above, it may be treated with water alone.

In this case, NO2 gas is absorbed by water and converted into HNO2 and HNO3.

Further, the gas to be treated in the first step may be treated in the second step with an aqueous solution of a basic compound such as caustic soda, caustic potash, soda carbonate, ammonia, and slaked lime.

In this case, for example, NO2 gas is converted into NaNO3 and NaNO2 and absorbed in the caustic soda aqueous solution.

The concentration of the basic compound can be arbitrarily determined as desired, but is generally 1 to 4o, y/z.

In addition, if the oxidized gas contains oxidizing gas such as ClO2, a reducing agent such as alkali sulfide (sodium sulfide, potassium sulfide, etc.) should be used to inactivate and dissolve and remove it. ), alkali sulfite (sodium sulfite, potassium sulfite, etc.), or an alkaline aqueous solution of hydrogen peroxide.

(In the presence of reducible substances, hydrogen peroxide acts as a reducing agent.

) The concentration of the reducing agent aqueous solution can be arbitrarily determined as required, but is generally about 0.1 to 10.9/7.

Moreover, the above-mentioned basic compound may be included together with the reducing agent.

Further, the alkaline compound can also be arbitrarily selected from the above-mentioned basic compounds.

In this case, for example, in the case of a caustic soda aqueous solution containing a reducing agent, NO2 is converted to NaNO2 and NaNO3,
ClO2 is reduced to NaC102 or NaCl,
Absorbed in absorption liquid.

By the method of the present invention, gas containing several hundred to several thousand ppm of nitrogen oxides is treated to reduce the concentration of nitrogen oxides in the gas to several to several thousand ppm.
It can be reduced to about several tens of ppm.

The method of the present invention will be explained in more detail below with reference to Examples.

Example 1 Two bubbling tanks with an inner diameter of 5 crfL are connected in series and the first
150 WL of a mixed solution of sodium chlorate/l and 1.5 mol/l of hydrochloric acid was placed in the tank, and 1 mol/l of caustic soda was placed in the second tank.
0 g/l and hydrogen peroxide 300 ■/l 15
When air containing 11,000 pp of nitrogen monoxide was poured into this bubbling tank at a flow rate of 460 mA' per minute, the nitrogen oxide content of the gas coming out of the second tank was 1.
It was ppm.

Example 2 Under the same conditions as in Example 1 but using 19/l of sodium sulfite instead of hydrogen peroxide, the content of nitrogen oxides in the gas coming out of the second tank was 1 ppm.

Example 3 Under the same conditions as in Example 1, 111/l of sodium sulfide was used instead of hydrogen peroxide, and the nitrogen oxide content of the gas coming out of the second tank was 10 ppm.

Example 4 In the same method as Example 1, 1 part of sodium chlorate was added to the first tank.
When a mixed solution of 0.8 mol/l of hydrochloric acid and 0.8 mol/l of hydrochloric acid was added, the content of nitrogen oxides in the gas coming out of the second tank was Oppm of nitrogen oxide and 18 ppm of nitrogen dioxide.

Example 5 Instead of the device of Example 1, an inner diameter of 95 mm and a height of 1000 m was used.
A mixture of sodium chlorate (1/7) and hydrochloric acid (36 g/l) was circulated in the first column at a flow rate of 3.92 g/min, and the second column was filled with Terraret packing. When a mixture of 7 g of caustic soda and 10 θ/l of sodium sulfite is circulated through the tower at a flow rate of 3.92 per minute, and air containing 11,000 pp of nitrogen monoxide is passed through the tower at a flow rate of 211 per minute, the second
The nitrogen oxide content of the gas exiting from the tower outlet is nitrogen oxide 11
pprn, nitrogen dioxide lppm.

Example 6 Using the apparatus of Example 5, 1:1 of sodium chlorate was added to the first column.
76 g/l of sulfuric acid and 4 g/l of sodium chloride were passed through at a flow rate of 3.92 per minute, water was circulated through the second column at a flow rate of 3.91 per minute, and 2000 ppm of monoxide was produced. Waste gas containing nitrogen and 1200 ppm of nitrous acid gas is
When passed at a flow rate of 11, the outlet gas of the second column has nitrogen oxide of 1
0ppm, nitrogen dioxide 40ppm, sulfur dioxide gas 5ppm
It contained m.

[Brief explanation of the drawing]

FIG. 1 shows the p of the treatment liquid in the first step of the method of the present invention.
It is a graph showing the relationship between H and the oxidation rate of NO.

Claims (1)

[Scope of Claims] 1. A gas containing nitrogen oxides, an aqueous solution containing 1 mol/l or less of chlorate and 1 to 80 weight φ of hydrochloric acid;
Alternatively, contact with an aqueous solution containing 1 mol/l or less of chlorate and 1 to 80 weight sulfuric acid or nitric acid and in the presence of an alkali metal chloride, and then contact with water or a base. A method for removing nitrogen oxides, the method comprising contacting the nitrogen oxides with an absorption liquid consisting of an aqueous solution of a chemical compound. 2. A gas containing nitrogen oxides is converted into an aqueous solution containing chlorate of 1 mol/l or less and hydrochloric acid of 1 to 80 weight φ,
Alternatively, contact with an aqueous solution containing 1 mol/l or less of chlorate and 1 to 80 weight units of sulfuric acid or nitric acid and in the presence of an alkali metal chloride, and then A method for removing nitrogen oxides, the method comprising contacting an absorption liquid consisting of an aqueous solution.