A method of producing a catalyst for ammonia synthesis

 

(57) Abstract:

Describes a method of producing a catalyst for the synthesis of ammonia by oxidation of metallic iron blend containing the promoting additives, education by fusing iron oxide catalyst and promoters of the melt, the melt granulation of the catalyst, subsequent annealing and cooling the obtained granules granulation carried out initially on a moving inclined plane with a flowing stream of water, the resulting pellets are cooled prior to the crystallization catalyst of the melt zone temperature of 1450 - 1350oC, and then cooling the pellets on a moving horizontal surface, moistened with water, with the rapid cooling of the granules on the bottom and a slow - top due to the heat radiation of the granules, the reflected heat shield located above a moving horizontal surface, prior to the final crystallization of the melt at a temperature of 1350 - 1200oC, the resulting granules are then sent to the annealing and cooling. The technical result - obtaining a catalyst with increased activity of small grain size (1-5 mm), with high mechanical strength. 3 C.p. f-crystals, 3 tables.

The invention relates to the production of ka is a way to obtain a pelletized catalyst for ammonia synthesis by melting of the iron oxides with the promoting additives, followed by granulation, whereby cooling of the granules first lead in an upward flow of the gas mixture to 1100 - 1400oC, then in descending stream of water up to 700oC and subsequent annealing granules (USSR Author's certificate N 526099, B 01 J 37/00, 1972).

Also known a technique in which the supplied charge hold over catalyst a floating magnetic field to heat to a temperature above the Curie point and the flow of the heated mixture in the catalyst layer of the floating lead with a speed of 25 to 100 kg/h, and oxygen - 8 - 30 nm3/hour.

The disadvantage of this method is to obtain granules of large size with low mechanical strength and low activity.

The closest solution of the present invention is a method of obtaining a granulated catalyst for the synthesis of ammonia by melting of the iron oxides with the promoters, the granulation of the molten catalyst mass and cooling of the granules from the 1600's to the 50oC. the Granulation and cooling granules from 1600 to 1000oC is carried out in the vapor stream mixture, and then the pellets are directed in the vertical thermal reactor, in which due to the heat released during the cooling of the pellets, first conduct thermal annealing zone is houtem gas supply reductant or oxidant, followed by cooling from 450oC to 50oC in a stream of inert gas. In this method the molten catalyst mass is continuously poured into the vertical flow of air-vapor mixture is directed towards the impinging jet. When this occurs, the division of the stream into droplets, crystallization drops and cooling granules from 1600 to 1000oC. In this way the raw material used metal iron (usually in the form of plates or rods) and a separate promoters, and the breaking and formation of granules occurs without any coercive devices under the influence of gravitational forces and surface tension forces (RF Patent N 913636, B 01 J 37/08, 37/16, C 01 C 1/04, 1977).

The disadvantage of this method is that making under oxidative melting separately iron and promoters does not provide a good enough mixture of iron oxides with the promoters, therefore, the catalyst has a low activity, especially at low temperature synthesis. Spontaneous rupture of the jet on the granules in the ascending flow of vapor mixtures do not provide the small granules of the catalyst in a narrow range of particle size distribution required for radial nozzles columns synthesis, widely implemented at present in the AOI activity of small grain size (1 - 5 mm), with high mechanical strength.

To solve the problem in the method of producing a catalyst for the synthesis of ammonia by oxidation of metallic iron, the melting of the iron oxides with the promoters, granulation Plava catalyst mass, annealing and cooling the obtained granules according to the invention before oxidation pre-prepare a mixture of iron with promoting additives, granulation carried out initially on a moving inclined plane with a flowing stream of water. The resultant pellets are cooled to a temperature of crystallization of the melt in the temperature range of 1450 - 1350oC, and then moving on a horizontal surface, moistened with water, before the end of the crystallization of the melt at a temperature of 1350 - 1200oC and rapid cooling of the pellets from the bottom due to the evaporation of the water film, and a slow - top due to the heat radiation pellets, reflected by the screen, above a moving horizontal surface. The resulting granules are then sent to the annealing and slow cooling to ambient temperature.

As the original mixture using iron powder of high purity mixed with promoting additives is the ora.

The mixture is continuously fed to the oxidation and melting of oxygen. Catalyst melt at a temperature of 1700 - 1500oC served continuously on a moving inclined plane with a flowing stream of water. On an inclined plane is breaking jet granules and cooling to a temperature of crystallization of water (1450 - 1350oC). The change in the slope of the plane and the height of incidence of the jet catalyst Plava on the inclined plane can be obtained pellets of the catalyst in a relatively narrow range of particle size distribution. Next, the granules are transferred to a moving horizontal surface, moistened with water, where the final crystallization of the melt and the initial hardening of the granules. On a moving horizontal surface is the screen that reflects the heat radiation of the granules. Rapid cooling of granules on the bottom and a slow - top allows you to reduce shrinkage of the shell and to increase the density of the granules of the catalyst. Granules with a temperature of 1350 - 1200oC on an inclined plane, on which there is a final separation of the granules from the remainder of the cooling water, get into the annealing chamber, which is the slow cooling of the granules to a temperature environment

As a result of implementation of the proposed method it is possible to obtain a catalyst having high activity, high mechanical strength and mostly small particle size distribution (1 - 2 mm 2 - 3 mm).

The method is illustrated by the following examples.

Example 1. Iron powder obtained by the decomposition of carbonyl iron, in the amount of 100 kg is mixed with the promoting additives (4 kg Al2O33 kg CaO and 1.7 kg K2CO3) and a binder (1 kg of powder graphite). The resulting mixture was formed into tablets 10 x 10 mm and continuously sent to oxidative crucible in which due to the heat of oxidation reaction of iron is melting a mixture of iron oxide with promoters at a temperature of 1600oC. Performance of the crucible 150 kg per hour.

The obtained catalyst melt with a temperature of 1600oC continuous stream of drops on a moving inclined plane, cooled by water flow. On an inclined plane is a jet fragmentation into small pellets, which together with the water flowing over the surface plane. At the end of the inclined plane separates the hot pellets from the flow of water: water is due to forces of adhesion with the surface of the tion parallel to the inclined plane and get on moving in the horizontal direction of the plane, moistened with water. On the inclined surface of the first cooling granules with 1600oC to a temperature close to the temperature of crystallization catalyst Plava (about 1450oC).

Over the horizontally moving surface has a heat-resistant screen reflecting the radiant energy of the hot pellets. Thanks to this device is directional crystallization of water in the granules of catalyst from the bottom up, which reduces shrinkage and increases the durability of the pellets. For horizontally moving surface is solidified granules and cooling up to 1350oC. Next, the pellets are sent on an inclined plane, on which there is a final separation of the granules from the remnants of water in the annealing chamber, in which the slow cooling of the granules to 60oC and then in a separate container to the environment. The duration of cooling for at least 24 hours. To prevent pereokislenie the surface of the granules in the annealing chamber bottom serves nitrogen to maintain an inert atmosphere in the layer of the cooled catalyst. Coming from the annealing chamber, the catalyst is directed to the sieving and packing.

Example 2. Postoperatory catalyst, passivated and unloaded from the columns of the synthesis containing not less than 65% Femethwhere evenly distributed promoting additive (4,5% Al2O3at 3.5% CaO, 1.5% of K2O). The temperature in the oxidation crucible 1500oC, on the inclined plane of the granules are cooled to 1350oC, on the horizontal plane up to 1200o. The amount of oxidizing the crucible spent catalyst 150 kg per hour, the plant capacity 190 kg per hour.

Example 3. Proceed as in example 1, but as the source of the charge using the charge in the form of a mixture of powder iron tablets with promoters in an amount of 5 kg and spent catalyst - 95 kg with a content of 75% iron metal. Pellets are cooled on an inclined plane to 1425oC, horizontal up to 1300oC.

Example 4. Proceed as in example 1, but as a starting raw material, a mixture of 30 kilograms of pills powder iron with promoters and 70 kg of spent catalyst containing metallic iron 70%. Pellets are cooled on an inclined plane to 1400oC and horizontal - up to 1250oC.

The catalysts obtained by the present method and prototype have the characteristics shown the constituent particle size distribution (mainly pellets size 1 - 2 mm 2 - 3 mm) with high mechanical strength and high activity designed for use in modern radial nozzle columns for the synthesis of ammonia.

1. A method of producing a catalyst for the synthesis of ammonia by oxidation of metallic iron blend containing the promoting additives, education by fusing iron oxide catalyst and promoters of the melt, the melt granulation of the catalyst, subsequent annealing and cooling the obtained granules, characterized in that the granulation is conducted initially on a moving inclined plane with a flowing stream of water, the resulting pellets are cooled prior to the crystallization catalyst of the melt zone temperature of 1450 - 1350oC, and then cooling the pellets on a moving horizontal surface, moistened with water, with the rapid cooling of the granules on the bottom and a slow - top due to the heat radiation of the granules, the reflected heat shield located above a moving horizontal surface, prior to the final crystallization of the melt at a temperature of 1350 - 1200oC, the resulting granules are then sent to the annealing and cooling.

2. The method according to p. 1, characterized in that as metallic iron ihtiosiformnye exhaust catalyst, containing metallic iron with uniformly distributed therein promoting additives.

4. The method according to p. 1, characterized in that the mixture using iron powder with promoters in a mixture with passivated spent catalyst containing a mixture of 5 - 30% iron powder.

 

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