A method of converting ammonia

 

(57) Abstract:

The invention relates to the production of nitric acid, in particular to a method of conversion of ammonia using a two-stage catalytic system in aggregates UKL-0,716. The method consists of passing the reaction gas mixture containing ammonia and oxygen-containing gas through a two-stage catalytic system in which the first step along the gas mixture is a layer of platinum mesh, and the second step catalyst bed regular cell structure and over the first step along the gas mixture additionally have a layer of inert nozzles cell structure height 15-30 mm at a distance of not more than 0.4 of its height from the layer of platinum mesh, and the second stage catalytic systems use a layer of catalyst a regular cell structure height 25-40 mm, the present invention allows to increase the output of nitric oxide by 0.1-0.3% and reduce the loss of platinum on 0,005-0.01 g per 1 ton of nitric acid. table 1.

The invention relates to the production of nitric acid, namely the process of conversion of ammonia using a two-stage catalytic system in aggregates UKL-0,716.

-4-0,024 [Patent RU 2119889, 1998].

The method does not significantly improve the degree of conversion of ammonia and reduction of losses of platinum.

Closest to the proposed technical solution is the method of converting ammonia, comprising passing the reaction gas mixture containing ammonia and oxygen-containing gas through a two-stage catalytic system in which the first step along the gas mixture is a layer of platinum mesh, and the second step catalyst bed regular cellular structure, and the second stage catalytic systems use 2-5 spatially separated layers of catalyst a regular cell structure and between catalyst honeycomb structure include a gas-permeable inert material [Patent RU 2145935, 2000].

A known method of converting ammonia has the following disadvantages:

- it does not address the possible vibrations and deflections of the platinum mesh in reverse during gas worby catalyst

- the design of the second stage in the form of a number of layers of the catalyst and increasing, thus, the number of plots of the unsteady gas flow may result in the rejection of time spent on the platinum and block the catalyst from the optimal value, which in turn reduces the selectivity of the process.

- the location in between the layers of the cell structure of the gas-permeable inert material (nichrome mesh, as described in the examples of the patent), can not only enhance the heterogeneity of flow of the reaction mixture, but also to provoke adverse reactions leading to the reduction of output of nitric oxide.

Thus, this method of conversion of ammonia largely retains the shortcomings of known methods, and also does not ensure the achievement of high yields of nitric oxide and a significant reduction in losses of platinum.

In addition, all the methods of oxidation of ammonia have another drawback: the initiation of reaction on the platinum mesh is either flaming rozzhigom device due to the heat of reaction products of combustion of gaseous fuel, hydrogen or a mixture of nitric, or using electronichealthcare element can lead to burning the nets and the phenomenon of precatalyzed at the collector of RU due to heat radiation from the package nets.

The task of the invention is to reduce losses of platinum and an increase in the degree of conversion of ammonia into nitric oxide.

The problem is solved by passing the reaction gas mixture containing ammonia and oxygen-containing gas through a two-stage catalytic system in which the first step along the gas mixture is a layer of platinum mesh, and the second step catalyst bed regular cell structure and over the first step along the gas mixture additionally have a layer of inert nozzles cell structure height 15-30 mm at a distance of not more than 0.4 of its height from the layer of platinum mesh, and the second stage catalytic systems use a layer of catalyst a regular cell structure height 25-40 mm

Inert (cordierite) nozzle honeycomb structure manufactured in accordance with [the Patent 1709705 RF, 1990] and represents sintered at 1250-1270oWith the blocks in the form of square prisms 100x100 mm equivalent diameter of the channel of 3.0-3.5 mm, wall thickness between channels 0.5-0.6 mm, an outside surface 72-76%. The catalyst of the regular honeycomb structure contains oxides of iron and aluminum, made in the form of a honeycomb 100x100 mm with equivale the watts. the certificate in the USSR 1220193, 1994] and KN-CX [Scientific-technical development and industrial testing of extruded catalyst KN-CX second stage oxidation of ammonia in aggregates production of nitric acid under pressure of 7.3 ATA. [Research report KPI. Kharkov. -1986] according to the method described in [Century. And. Vanchurin, C. S. boeskov. The molded catalyst a regular cellular structure of the active mixture for the oxidation of ammonia // Chem. prom. 2000, 3, S. 145-148]. The catalyst of the regular honeycomb structure is placed directly under the package the platinum mesh.

At the height of the inert nozzle honeycomb structure is less than 15 mm, the distance to the platinum layer grids 0,4 more of its height and the height of the catalyst regular structure is less than 25 mm in the operating conditions of the reactor UKL-0,716 unable to provide a satisfactory uniformity of distribution over the cross section of the device, inside the platinum and oxide catalysts, which reduces the selectivity of the process. Increase the height of the cordierite honeycomb nozzle is greater than 30 mm and a bulk catalyst greater than 40 mm is not advisable, as this increases the residence time, which reduces the release of nitric oxide.

In the literature it is unknown how the oxidation of ammonia to recrutare height of 15-25 mm + layer of the platinum mesh (I stage contact) + layer 25-40 mm catalyst regular cell structure (stage II of contact). I.e., the proposed solution is novelty. The proposed location and height of the layer of catalytic systems give an unexpected effect on the increase of nitric oxide and reduced losses of platinum, which cannot be achieved by a simple enumeration or the imposition of known variants.

The invention is illustrated by the following examples.

Example 1 (prototype). The process of conversion of ammonia is carried out in an industrial reactor UKL-0,716 having a diameter of 1500 mm, equipped with a two-stage catalytic system. The first stage in the direction of gas flow is selected layer 9 platinum mesh composition, wt.%: Pt - 81, Pd - 15, Rh - 3.5 and EN - 0,5, and made of wire diameter 0,092 mm number of holes 1024 on 1 cm2. As the second stage uses 4 spatially separated catalyst layer regular honeycomb structure prepared from a mixture of NC-2U), height of each 20-mm equivalent diameter of the channel is 2 mm, a wall thickness between channels 1 mm process Temperature 910oWith the pressure of 7 ATA, the concentration of ammonia in the ammonia-air mixture about 10..%, the rate of ammonia-air mixtures under normal conditions 7 m/s the Output of nitric oxide in these conditions is 95,1% and bisphosphates difference, above the layer of platinum mesh at a distance of 6 mm have a layer of inert nozzle honeycomb structure made of cordierite, height 15 mm, composed of blocks with equivalent diameter of 3.5 mm, the thickness of the walls between the channels of 0.6 mm and an outside surface 72%. At this second stage in the form of a layer of catalyst a regular honeycomb structure prepared from a mixture of NC-2U has a height of 40 mm, an Output of nitric oxide is 95.4% and losses of platinum is 0.135 g per 1 ton of nitric acid.

Example 3. The process is carried out analogously to example 1, with the difference that directly above the layer of platinum grids have a layer of inert nozzles cell structure height 30 mm, made of blocks with equivalent diameter of 3.5 mm, the thickness of the walls between the channels 0.5 mm and an outside surface 76%. At this second stage, composed of catalyst blocks regular cell structure with an equivalent diameter of 3 mm, a wall thickness between channels 0.5 mm and an outside surface 73% and prepared from charge SC-SC, has a height of 25 mm, an Output of nitric oxide is 95.2% and loss of platinum 0,130 g per 1 ton of nitric acid.

Example 4. The process is carried out analogously to example 1, with the difference that the th 20 mm, composed of blocks with equivalent diameter of 3.0 mm, the thickness of the walls between the channels 0.5 mm and a height of 35 mm Release of nitric oxide is to 95.3% and losses of platinum 0,132 g per 1 ton of nitric acid.

The table below shows comparative examples 1-4, showing that the proposed method for catalytic conversion of ammonia can increase the release of nitric oxide by 0.1-0.3% and reduce the loss of platinum on 0,005-0.01 g per 1 ton of nitric acid.

A method of converting ammonia, comprising passing the reaction gas mixture containing ammonia and oxygen-containing gas through a two-stage catalytic system in which the first step along the gas mixture is a layer of platinum mesh, and the second step catalyst bed regular honeycomb structure, characterized in that on the first step along the gas mixture additionally have a layer of inert nozzles cell structure height 15-30 mm at a distance of not more than 0.4 of its height from the layer of platinum mesh, and the second stage catalytic systems use a layer of catalyst a regular cell structure height 25-40 mm.

 

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SUBSTANCE: the invention is dealt with production of nitric acid with the help of oxidation of ammonia by oxygen of the air and absorption of nitrogen oxides by water in installations with uniform pressure at the stages of oxidation of ammonia and absorption of nitrogen oxides. The method of production of nitric acid in the installations with uniform pressure at the stages of oxidation of ammonia and absorption of nitrogen oxides provides, that compression of the air up to a uniform terminal pressure is conducted continuously within one stage without intermediate cooling and after that the compressed and so heated air is divided into two streams, one of which intended for production of nitric acid is directed to be cooled with further mixing with ammonia, and another is fed directly into a fuel combustion chamber connected with a recuperation turbine. The design embodiment of the installation for production of nitric acid provides for usage in the gas-turbine plant as an air engine for compression of air of an axial-flow compressor mounted directly on a common shaft with the recuperation turbine, at which near the outlet of the air engine the line of a compressed air stream is divided into two parts, one of which intended for production of nitric acid is first connected with a compressed air cooler and then with a mixer of ammonia with air, and the second intended for incineration of fuel is directly connected with the recuperation turbine combustion chamber. Besides in the capacity of a the compressed air cooler they use a "boiling" economizer connected to a line of a feed water for a boiler-utilizer and with a vapor collector of the boiler-utilizer by a line of steam-and-water mixture. The line of the air intended for production of nitric acid is also connected through the reheater of ammonia with a nitric acid blowing column. The technical result is simplification of the method, decreased investments and specific consumption of fuel.

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EFFECT: obtaining catalysts with homogenous distribution of active phases and uniform and regulated porosity for optimisation of characteristics in catalytic applications.

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