SU833502A1 - Method of ammonia extraction from gas mixtures - Google Patents

Description

(54) METHOD FOR ISOLATION OF AMMONIA FROM GAS MIXTURES

one

The invention relates to methods for separating ammonia from gas mixtures and can be used in metallurgical, chemical and other branches of the national economy, where there are emissions of gases containing ammonia into the atmosphere.

There is a known method for separating ammonia from gases by its absorption by a solution of ammonium nitrate acidified with acidic acid 1.

The disadvantages of this method are large volumes of circulating solutions and, consequently, the need to have bulky treatment facilities, the resulting solutions must be evaporated to obtain solid ammonium nitrate.

The closest in technical essence and the achieved result to the proposed is a method for the separation of ammonia from gas mixtures by its oxidation on a catalyst with elevated temperature.

Exhaust gases containing 0.03% by volume of NHs and 3% by volume of Og are in contact with the catalyst at 250-450 ° C and a gas flow rate of 1000-100000 hours. In this case, ammonia is oxidized to nitrogen and water by the reaction equation.

4NH 3 + SOg-2N a + The catalyst used contains mainly 0.02-2 mol of copper oxide and 0.5 mol of metal oxide selected from the group of molybdenum, tungsten, vanadium, iron, cerium and the rest of the catalytically active titanium dioxide 2.

The disadvantage of this method is the formation of not only nitrogen and water, but also toxic nitrogen oxides during catalytic oxidation of ammonia. So, at a temperature of 400-450 ° C in gas.x ate ammonia was not found in contact with the catalyst, but nitrogen oxides were found for a catalyst of a given composition in the following amounts,%:

TiOi + CuO13- 82

TiO2 + CuO + 2.0514-45

TiOa-f-VgOi.10-29

The composition of the last cat., Weight. TiO289 and V-iOs I.

The purpose of the invention is to eliminate the formation of nitrogen oxides.

This goal is achieved by the fact that ammonia is liberated by catalytic oxidation of ammonia at elevated temperatures; active alumina containing 6–8% of vanadium pentoxide is used as the vanadium-containing catalyst.

It has been established that contacting an ammonia-air mixture with an ammonia content of 0.1-10% by volume with this catalyst at 400-450 ° C leads to a quantitative oxidation of ammonia to nitrogen and water without the formation of nitrogen oxides.

The catalyst can be easily prepared by impregnating the active alumina granules with saturated aqueous solutions of vanadium soluble salts, such as ammonium vanadate or vanadium oxalate. The impregnated granules are dried. And calcined in air at 500 ° C.

The method of separation of ammonia from gas mixtures is carried out as follows

Through a tube with a catalyst heated to 40-550 ° C, pass the ammonia-air mixture with an ammonia content up to 101. / o. At higher ammonia concentrations, the heat released during oxidation can heat the contact mass to the melting point of vanadium pentoxide, which will lead to a loss of catalyst activity. The gas is passed at a volumetric rate of BOO-OOCH depending on the content of ammonia in the mixture and the required degree of conversion of ammonia to nitrogen.

The selected limits for the content of vanadium pentoxide in the catalyst are defined as follows. Under the same experimental conditions (concentration of ammonia in the gas mixture, temperature and space velocity). An increase in vanadium pentoxide content in the catalyst above 8% does not significantly affect the oxidation rate of ammonia and even decreases due to a decrease in the active surface of the catalyst, and at a content below 6%, the oxidation rate of ammonia decreases sharply.

In tab. Figure 1 shows the effect of temperature on ammonia conversion.

Table 1

Continued gabl, 1

Thus, the optimal temperature range is 400-550 ° C.

In tab. Figure 2 shows the effect of gas volume velocity on the degree of ammonia conversion at a temperature of 500 ° C.

table 2

1oooo

100

ABOUT

98

ABOUT

5000

10,000

95

ABOUT

ABOUT

90

200OO

Thus, with a volumetric rate of up to 20,000, the conversion of ammonia is above 90%.

In tab. 3 shows the dependence of the conversion of ammonia on the concentration of ammonia in the ammonia-air mixture, at a temperature of 500 ° C and flow rate

5000 hours -

Table 3

The concentration of ammonia in the gas mixture does not significantly affect the degree of conversion of ammonia, however, at an NH 3 concentration of 10 v / v, the catalyst heats up above 650 ° C, which can lead to a decrease in its activity.

In tab. Figure 4 shows the effect of the amount of vanadium pentoxide in the catalyst on the conversion of ammonia.

Table 4 Example, a) Preparation of the catalyst. The granules of active alumina grade А-I (GOST 8136-56) are placed in a saturated solution of ammonium vanadate at 70-80 ° C and kept at this temperature for 1.5-2 hours. The operation is repeated twice, then the granules are separated from solution and calcined at 550 ° C in air for 4-5 hours. The content of vanadium pentoxide in the resulting catalyst was 7.6%. To obtain a catalyst with a VjOj content of 6%, a single impregnation operation is sufficient; to obtain a catalyst with a VgOs content of 8%, it is necessary to perform a double impregnation with a saturated ammonium vanadate solution at the boiling point. b) The release of ammonia from gas mixtures; i Under optimal conditions, the gas mixture obtained by calcining ammonium vanadate in the presence of air is subjected to treatment. The catalyst is active alumina with a content of vanadium pentoxide “7%. The gao-air mixture contains 0.8 vol. % ammonia, 20 mg / m of polyoxide vanadium dust. The contact apparatus described in the example is used, the volumetric gas velocity is 7000, the catalyst temperature is 480-520 ° C, the gas linear velocity is 0.5-0.6 m / s. 500 liters of gas containing 40 liters of ammonia are passed through a catalyst. The degree of ammonia conversion of 98-99%, nitrogen oxides in the exhaust gases was not detected.

 For comparison, under the conditions of this example, the ammonia-air mixture is passed through active alumina, which does not contain, with a granule size of 2-4 mm. The degree of conversion of ammonia is

5-10%. In addition, the ammonia-air mixture is passed through vanadium pentoxide granules obtained by pressing hydrated vanadium pentoxide under pressure of 500 kg / cm2, followed by calcining the granules at 400-450 ° C. The conversion of ammonia is 40-55%.

Experiments were carried out under the same conditions to isolate ammonia from an ammonia – air mixture using the proposed method and the known method. The catalyst according to a known method is a titanium dioxide containing 10-15% vanadium

In tab. 5 shows the comparative data on the release of ammonia from the air mixture containing 1 vol. / o NHa, according to known and proposed methods. Table 5

Claims (2)

Temperature, С Known 88 10 10О 29 100 35 Proposed 60 О93 О 1ОО О rf.- Ammonia conversion degree,%; j3 is the degree of formation of nitrogen oxides,%. As follows from the data table. 5, according to a known method, the complete oxidation of ammonia occurs at lower temperatures, at the same time significant amounts of nitrogen oxides are formed. The proposed method is intended to be used to release ammonia from waste gases from the production of pure vanadium pentoxide. Currently, about 200 kg of ammonia are emitted into the atmosphere with waste gases daily, and therefore the problem of neutralizing production gas emissions is relevant. The application of the proposed method makes it possible to completely eliminate the emission of harmful gases into the atmosphere. DETAILED DESCRIPTION OF THE INVENTION The method for separating ammonia from gas mixtures by oxidation on a vaNadium-containing catalyst at elevated temperatures, characterized in that, in order to prevent the formation of nitrogen oxides, as a vanadium-containing catalyst7., 8 torus using active alumina, 1. Ivanov ME. Ammonia technology containing 6-8% of vanadium. M., “Himi, 1978, p. 185. Information sources, 2. US patent No. 408510, cl. 423-237, taken into account in the examination1978. 833502