RU2259864C1 - Method of removing nitrogen acids from air - Google Patents

Abstract

FIELD: physical or chemical processes and apparatus.

SUBSTANCE: method comprises flowing air through the chemical absorber of nitrogen acids that is composed of chemically absorbing base that absorbs nitrogen dioxide and sorbent-oxidizer that oxidizes nitrogen mono-acid up to nitrogen dioxide. The chemical absorber is made of n pairs of layers of chemically absorbing base and sorbent-oxidizer. Upon flowing throughout n pairs of the layers, the initial concentration of the nitrogen dioxide drops by a factor of 3ⁿ, where n is the total number of pairs of the layers.

EFFECT: reduced cost and enhanced efficiency.

2 cl, 1 tbl

Description

The invention relates to the field of creating methods for purification of waste gases from chemical industries, as well as methods and means of individual and collective protection of the respiratory system from impurities of nitrogen oxides in the air resulting from accidental emissions or intentional chemical infection, terrorist acts, etc., and can find application in the development of gas masks, protective cartridges, filtering systems for collective use, etc.

One of the most important tasks facing the developers of such protective equipment is to increase the degree of purification of air from harmful impurities. Currently, there are many cleaning methods with which you can achieve more or less acceptable results.

A common method for purification from nitrogen oxides is the catalytic method, which consists in carrying out a heterogeneous reaction for the reduction of nitrogen dioxide (NO ₂ ) to less toxic nitric oxide (NO) and then to nitrogen. The degree of purification using such methods is low, as a rule, does not exceed 90%.

For example, the patent (RU 2147461, class B 01 J 37/04, 2000) describes a catalyst for purifying air from nitrogen oxides, which is obtained by mixing manganese dioxide with a binder - bentonite clay, forming granules, drying, crushing and heat treatment. At the same time, barium hydroxide is introduced into the suspension containing manganese dioxide, which is prepared simultaneously by alkaline treatment of a mixture of manganese dioxide with a water-soluble salt of barium.

The disadvantages of the method of air purification using this catalyst are associated with rapid poisoning of the catalyst as a result of exposure to air moisture and, as a consequence, its instability.

There is also a method for purifying gases from nitrogen oxides using a catalyst obtained by adding a copper nitrate solution and a small amount of water to the powdered active alumina to give the mass plasticity, followed by molding and heat treatment of the granules at 280-300 ° C and impregnating them with a solution of manganese nitrate and repeated heat treatment (Auth. St. USSR No. 986482 dated 03/31/80, class B 01 J 23/84; B 01 D 53/86).

The disadvantages of the cleaning method using this catalyst are associated with the uneven mixing of its ingredients in dry form due to the strong difference in the density of each of the components, which leads to instability of the protective properties and insufficiently high catalytic activity of the obtained catalyst.

A known method of air purification using anionic fibrous materials (L. L. Kukushkina, Z. Z. Abdulkhakova, S. V. Zakharov, MP Zverev. "Capture of nitrogen oxides by fibrous chemisorbent. Ecology and Industry of Russia, 2001, No. 4). To enhance the basicity of anion exchange resin, the authors treated VION AN-1 fiber with a 3% sodium hydroxide solution.

The disadvantage of this and similar methods, in which only anionic nitrogen dioxide absorbers are used, is the fundamental impossibility of achieving a reduction in the concentration of nitrogen oxides in the air stream by more than three times, since during the chemisorption of nitrogen dioxide from three NO ₂ molecules one NO molecule is formed (see below ) Theoretically, nitrogen dioxide is chemisorbed 100%, however, the monoxide (NO) formed in this process is rapidly oxidized to NO ₂ as a result of exposure to ultraviolet radiation, interaction with ozone, or for several other reasons.

Another disadvantage of the above methods is the loss of protective properties when the sorbent is wetted.

Closest to the proposed one is a method of purifying air from nitrogen oxides (RU 2171140, class B 01 J 20/20, 2001), which consists in passing purified air through a chemical absorber of nitrogen oxides, which is a mechanical mixture of two loose components: a carbon sorbent coated with on it potassium carbonate, absorbing nitrogen dioxide, and active alumina with potassium permanganate deposited on it - an oxidizer of NO to NO ₂ .

The disadvantage of this known method (prototype) is that on the modified potassium carbonate carbon sorbent, in addition to the chemical binding of NO ₂ , a partial reduction of NO ₂ to NO occurs, since, as already mentioned, during chemisorption of nitrogen dioxide with a base of three NO ₂ molecules one NO molecule is formed (A.I. Rodionov, V.N. Klushin, N.F. Torocheshnikov. Environmental engineering, M., Chemistry, 1989, p.136). C. the result, in fact, there is a need for oxidation of NO, not only entering the filter element from the outside, but also permanently forming in the filter layer. Obviously, from this point of view, the use of mixed compositions in which both oxidizing NO and reducing NO ₂ components are simultaneously present at all points of the filter layer is irrational, since two competing reactions of mutually opposite directions occur over the entire length of the filter element from the beginning and down to the layers at the exit from it, which leads to a decrease in filter efficiency.

The objective of the invention is to provide a simple and cheap method of purifying air from nitrogen oxides, which will significantly increase the efficiency of the process and will provide almost any high degree of purification of air containing high concentrations of nitrogen oxides, and also will increase the life of the sorbent, reduce its amount with constant efficiency and will provide the possibility of its regeneration.

The solution to this problem is achieved by the proposed method of purifying air from nitrogen oxides, which consists in passing it through a chemical absorber of nitrogen oxides, which includes two components: a chemisorbent base that absorbs nitrogen dioxide, and a sorbent oxidizing agent, which oxidizes nitrogen monoxide to dioxide, in which, according to the invention the cleaned air is passed through a chemical absorber of nitrogen oxides, made in the form of a sequence of n pairs of layers of chemisorbent base and sorbent oxidizer, with the initial concentration After passing through the entire sequence of n pairs of layers, the nitrogen dioxide fraction decreases 3 ⁿ times, where n is the total number of pairs of layers: chemisorbent base + sorbent oxidizing agent and n> 1.

As the chemisorbent base, you can use the fibrous material VION AN-1 in the form of OH ^- or granular anion exchange resin AB-17 in the form of OH ^- .

As the sorbent oxidizing agent, you can use the fibrous material VION AN-1 in the form of MnO ₄ ^- or granular anion exchange resin AB-17 in the form of MnO ₄ ^- .

To regenerate the chemisorbent anion exchange resin, 2% by weight can be treated. NaOH solution in water.

The main difference of the proposed method from the known (prototype) is the formation of a filter layer of a chemical absorber of nitrogen oxides in the form of a sequence of pairs of layers of chemisorbent anion exchange resin in an OH ^- form and an oxidizing agent.

In general terms, the process taking place in the first layer of a pair — in anion exchange resin, can be represented as:

3NO ₂ + 2RCOON ⁺ ... OH ^- → 2RCOON ⁺ ... NO ₃ ^- + NO + H ₂ O

As can be seen from this equation, one molecule of NO is formed from three molecules of nitrogen dioxide during chemisorption.

During the subsequent oxidation reaction, one NO ₂ molecule is formed from one NO molecule. Thus, after passing through one pair of anion exchange resin + oxidizer layers, the concentration of NO ₂ drops three times. Obviously, after passing through n successively arranged pairs of such layers, the concentration of NO ₂ will fall 3 ⁿ times. For example, with the passage of 4 pairs of layers, the degree of purification of the air flow from NO ₂ will be 99%.

The correctness of this consideration is confirmed by the results of tests to clean the air stream from nitrogen oxides. As an example, the table shows the measured dependence on the air flow rate of the efficiency of its purification from nitrogen dioxide when passing through one pair of layers of VION AN-1 anion exchange resin in the form of OH ^- and an oxidizing agent. Tests were carried out under the following conditions: mass of filter material 17 g, initial concentration of nitrogen dioxide 100 mg / m ³ , relative humidity of the gas-air mixture 60%.

Table
Dependence of cleaning efficiency on filtration rate Filtration rate cm / sec 1 5 10 fifteen twenty Cleaning Efficiency (%) 70 68 65 59 fifty

As can be seen from the table, the filtration efficiency at speeds up to 10 cm / s corresponds to a theoretically determined - 2/3. At high speeds, efficiency is expected to decrease. Upon repeated passage through the filter, the concentration of nitrogen oxides again decreases three times. Thus, by placing a sufficient number of chemisorbent-oxidant pairs in the filter element, any sufficiently high degree of purification can be achieved.

Claims (3)

1. The method of purification of air from nitrogen oxides, which consists in passing it through a chemical absorber of nitrogen oxides, comprising two components: a chemisorbent base that absorbs nitrogen dioxide, and a sorbent oxidizer, oxidizing nitrogen monoxide to dioxide, characterized in that the air to be cleaned is passed through chemical absorber of nitrogen oxides, made in the form of a sequence of n pairs of layers of chemisorbent base and sorbent oxidizer, with the initial concentration of nitrogen dioxide after passing through the entire sequence ty n pairs of layers fall 3 ⁿ times, where n is the total number of pairs of layers: chemisorbent base + sorbent oxidizing agent and n> 1. 2. The method according to claim 1, characterized in that the fibrous material VION AN-1 in the form of OH ^- or granular anion exchange resin AB-17 in the form of OH ^{- is} used as the chemisorbent base. 3. A method according to claim 1 or 2, characterized in that as oxidant sorbent fiber material VION AN-1 in the form of MnO ₄ ^- or granular AV-17 anion exchanger in the form of MnO ₄ ^-.