The catalyst for the conversion of ammonia

 

(57) Abstract:

The invention relates to catalysts for the conversion of ammonia and can be used to produce oxides of nitrogen in nitric acid and has synthesis. Describes a catalyst for the conversion of ammonia, comprising at least one active component selected from the metals and/or oxides of group VIII in an amount not less than 0.01 wt.% on the media - oxide of silicon and/or aluminium oxide in the form of woven and nonwoven fibrous materials, additionally contains a stabilizer selected from metals and/or metal oxides IIA, IIIA, IVB groups in an amount of 0.01-2.0 wt.% (in terms of metal). The technical result - the development of a catalyst having a high adhesive strength of the applied phase with the carrier, increased thermal stability and mechanical strength. 3 C.p. f-crystals, 1 table.

The invention relates to catalysts for the conversion of ammonia and can be used to produce oxides of nitrogen in nitric acid and has synthesis.

The platinum catalysts used in the oxidation of ammonia to oxides of nitrogen, are very sensitive to impurities in the raw materials, which can get in cont, is their resistance to poisons, thermal stability and reduction catalysts.

Currently used in industry platanoides catalytic oxidation of ammonia possess high activity and selectivity, but the raw materials for their manufacture is expensive and scarce.

Therefore, there is an intensive search and development of cheaper catalysts.

A known catalyst (application of UK N 1590451, IPC3B 01 J 23/56 // B 01 D 53/36; C 01 B 17/78, 21/26, 1981), containing a platinum group metal, which is an intermetallic compound of platinum group metal with aluminum, scandium, yttrium, lanthanide, titanium, zirconium, hafnium, vanadium, niobium or tantalum on the media, which is a refractory oxide. The active component is a coating on the media.

The disadvantage of the catalyst is poor adhesion of the catalytically active components-metals with the surface of the carrier and the catalyst rapidly loses activity.

Known catalyst for the process of production of nitric acid by oxidation of ammonia on the media of foam ceramics or expanded metal mesh structure coated, comp B 01 J 23/40, B 01 J 23/42, 1993). The noble metal is chosen from the group comprising Pt, Pd, Rh, Ru, Os, and mixtures thereof. To obtain a catalyst solution prepared carboxylate salt of a noble metal with a concentration of 1-30% in an organic solvent, is dipped in a solution of the catalyst carrier, removed from the solution-impregnated carrier and maintain the medium at a temperature of 260-800oC to decomposition of the salt and produce metallic electrically conductive coating.

The disadvantage of the catalyst is poor adhesion of the active ingredient with the carrier and therefore, the service life of the catalyst's stability and insufficient, and the catalyst efficiency is low.

Known catalyst of the oxidation of ammonia on the media, representing a cellular structure (application Japan N 57-58213, IPC3B 01 J 23/42, B 01 D 53/36, B 01 J 23/89, 35/04, 1982) of the heat-resistant inorganic material, which form a layer of aluminum oxide with subsequent application of the resulting carrier platinum catalyst or a mixed catalyst containing platinum and cobalt oxide in an amount of 0.1 to 2.0%.

The disadvantage of the catalyst is low, the period of stable operation.

The closest solution is and/or aluminum in the form of threads, fibers, in the form of woven and nonwoven materials and introduce alloying metals selected from the group of Pt, Pd, Rh, Ir, Ag, Au, Fe, Cr, Co, Ni, Mn, Pb, Cu in an amount of 0.001 to 1.0% by weight of the carrier.

The catalyst has a high adhesive strength of the applied phase catalytically active metal with the surface of the carrier, but thermal stability of the catalyst is not high enough.

The problem solved by the present invention is the development of a catalyst having a high adhesive strength of the applied phase with the carrier, increased thermal stability and mechanical strength.

The problem is solved catalyst for the conversion of ammonia, comprising at least one active component selected from the metals and/or oxides of group VIII in an amount not less than 0.01 wt.% on the media - oxide of silicon and/or aluminium oxide in the form of woven and nonwoven fibrous materials. The catalyst contains a stabilizer selected from metals and/or metal oxides IIA, IIIA, IVB groups in an amount of 0.01-2.0 wt.% (in terms of metal).

Elementary fiber glass fiber media have a diameter of 1-20 μm.

As the carrier used fiberglass si is the Catalyst further comprises an oxide of rare earth element in an amount of 0.001-2.0 wt.% (in terms of metal).

For the formation of a high dispersion of the active component in the catalyst composition is administered stabilizers selected from metals and/or metal oxides IIA, IIIA, IVB groups in an amount of 0.01-2.0 wt.%. The introduction of stabilizers prevents the formation of large crystallites of the active component and contributes to the stable operation of the catalyst at high temperatures.

The introduction of a stabilizing component in the catalyst is carried out in various ways: simultaneously with the active ingredient or after application of the active component coating stabilizing metal and/or oxide. High thermal stability is exhibited by catalysts, in which a portion of the stabilizer is introduced into the medium, and the remaining part of the required amount of stabilizer is introduced together with the active component.

The invention is characterized by the presence of stabilizers that allow the active ingredient to be distributed not only on the surface, but in the surface layers of optical fibers. This limits the mobility of the particles of the active phase, including with increasing temperature, which leads to high dispersion and activity of the applied active phases, as well as protects them from the action is s and poisoning.

The proposed catalysts have a very high strength adhesive applied phase catalytically active component and/or its oxide with a surface of the carrier, the resulting catalyst has a high thermostability.

Studies have shown that the process of conversion of ammonia proceeds effectively on the catalysts with the active component and the stabilizer of a silicate glass-fiber media.

Analyzing this positive compared with the prototype, we can identify the following chemical and physical causes, which ensured the achievement of qualitative change in the process parameters ammonia conversion:

a) was that entered into the fiberglass carrier of the active component and the stabilizer give it a special status on the stability level of catalytic activity at high temperatures;

b) the small size of the elementary fibers (1-20 ám) glass fiber media, the proposed catalyst provides the intensification of the process by reducing diffusion difficulties.

When used as a carrier silica glass material in the form of woven patterns can be used different is the Diameter of the thread, textile 1 mm, this thread formed by twisting elementary fibers with a diameter of 7-9 μm.

Media obtained from conventional silicate glasses, in which the content of silicon dioxide ranges from 50 to 99.9 wt.%.

The inner surface of the carrier varies from 0.1 m2/g to 200 m2/g by dosed leach processing of the original fiberglass materials in acidic media.

Depending on the requirements to the level of intensity of the process can be used additives of rare earth elements in an amount of 0.001-2.0 wt.%.

The choice of the optimal catalyst in mastering it in a production environment should be determined by the requirements to the level of intensity of the process, its selectivity, degree of purification of the final product, as well as economic assessments of the effectiveness of the technological scheme.

The active ingredient can be introduced into the silicate glass fiber media in different ways. In Russian patent N 2069584, 1996 (author Barelko and others ) mentioned method based on the introduction of catalytically active metal in the stage of forming the molten glass. Preparation of catalysts, test data are given below, p is onestage media in solutions of salts of the injected metal.

Thus, the essential distinguishing features of the claimed invention is that:

the catalyst additionally contains a stabilizer;

stabilizer selected from metals and/or metal oxides IIA, IIIA, IVB group.

The experiments were conducted in a laboratory reactor with a diameter of 55 mm, which laid the catalytic packages.

On the catalytic package is a stream of ammonia-air mixture with the concentration of ammonia 12 vol.%. The flow rate of the ammonia-air mixture 1 m3/h, the linear velocity of the gas stream 15 cm/s initiating the reaction by using a special rossignolo device, and after the transition reaction in automatic mode initiation is terminated. Analysis activity (conversion rate) is determined by the standard method by sampling the ammonia-air mixture and nitrous gases with subsequent titration. To determine thermal stability of the catalyst maintained at a temperature of 900-1000oC for a specified time and then under the same conditions determine the degree of conversion of ammonia.

To test the resource characteristics of the catalysts (duration) of the individual samples was laid in premisesfor and test results.

The following examples illustrate the proposed solution.

Example 1

For the preparation of the catalyst containing 0.1 wt.%, Pd take fibrous material, consisting of 96% SiO2in the form of woven fibers having a diameter of 5 μm. Prepare a solution of palladium chloride in 5% hydrochloric acid solution, add the calculated quantity of chloride of zirconium. Stand in the impregnating solution, the media 3 hours, raise the temperature to 80oC, the carrier is dried and calcined at a temperature of 400oC.

Example 2

For the preparation of the catalyst used fibrous media with the content of SiO250 wt.%. Prepare an impregnating solution containing a definite number of platinum tetrachloride and India, the media is kept in an impregnating solution of 3 hours and up to 4 hours the temperature to 450oC.

Example 3

Similar to example 2, only notable characteristic of the media, and the stabilizer is used as the Sol TiO2.

Example 4

Similar to example 2, only as the active component further comprises rhodium, iron, and as stabilizers - barium.

Example 5

Similar to example 2, only the quality is x2">

Example 6

Similar to example 1, except that as the active component contains cobalt, and as a stabilizer calcium and promoter - cerium.

Example 7

Similar to example 2, only as the active component further comprises palladium and rhodium, as a stabilizer further comprises magnesium. As the rare earth element is cerium, which is introduced together with the active component.

Example 8

Similar to example 2, only as the active component further comprises iridium and osmium and promoter - praseodymium, and as a stabilizer, titanium and aluminum.

Example 9 (prototype)

Similar to example 2, is characteristic of the media and the fact that platinum in the amount of 0.05 wt.% introduced at the stage of preparation of the media and the rest of the calculated amount injected into the catalyst by impregnation of the support.

Tests have shown that the introduction of stabilizers selected from metals and/or metal oxides IIA, IIIA, IVB groups, in an amount of 0.01-2.0 wt.% in the catalyst leads to stabilization of physico-chemical properties of the inventive catalyst in terms of 850-950oC, which contributes to production of Wahoo is the reason for the decline of output of nitric oxide.

1. The catalyst for the conversion of ammonia, comprising at least one active component selected from the metals and/or oxides of group VIII in an amount not less than 0.01 wt. % media - oxide of silicon and/or aluminium oxide in the form of woven and nonwoven fibrous materials, wherein the catalyst additionally contains a stabilizer selected from metals and/or metal oxides IIA, IIIA, IVB groups in an amount of 0.01 - 2.0 wt.%, in terms of metal.

2. The catalyst p. 1, characterized in that the elementary fibers of the glass fiber media have a diameter of 1 to 20 μm.

3. The catalyst p. 1, characterized in that as the carrier is used fiberglass silicate material with a silicon dioxide content of 50 to 99.9 wt.% and having a surface of 0.1 - 200 m2/,

4. The catalyst p. 1, characterized in that it further contains an oxide of rare earth element in the number 0,0021 - 2.0 wt.%, in terms of metal.

 

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