A method of converting ammonia

 

(57) Abstract:

The invention relates to processes of high-temperature catalytic conversion of ammonia to two-stage catalytic system, where the first step in the direction of gas flow containing at least ammonia and oxygen, is a grid layer made of alloy containing platinum, and the second stage catalysts containing precious metals in the production of nitric and hydrocyanic acid, and has synthesis. The problem to which the present invention is directed, is to reduce investments and losses of PGM and increase the yield of the target product. The essence of the method consists in passing the reaction gas mixture containing ammonia and oxygen-containing gas through a two-stage catalytic system in which the first step in the direction of gas flow is a layer of platinum mesh, and the second step catalyst bed regular cell structure in relation to the value of the hydraulic resistance of the second stage catalytic system to the value of the hydraulic resistance of the first stage of 0.2 to 4, and use the catalyst honeycomb structure, porosity, characterizing the volume of voids, liblicense the result is to increase the yield of the target product, the reduction of investments and losses of platinum. 9 C.p. f-crystals.

The invention relates to processes of high-temperature catalytic conversion of ammonia to two-stage catalytic system, where the first step in the direction of gas flow containing at least ammonia and oxygen, is a grid layer made of alloy containing platinum, and the second stage catalysts containing noble metals. The scope of the invention extends to the use of nitrogen and hydrocyanic acid, and has synthesis.

High-temperature catalytic conversion of ammonia is carried out usually at atmospheric and elevated pressures (0.1 - 1.8 MPa) is woven or knit from the platinum filaments grids (an alloy of platinum with rhodium or platinum with rhodium, palladium and / or other platinum group metals). The reaction is accompanied by intense heat, comes with extremely high speed and is limited by mass transfer processes.

The temperature of the gas in the production of hydrocyanic acid at a pressure of 0.2 MPa can reach 1300oC.

In the production of nitric acid in the conversion of ammonia to nitric oxide at a pressure of from 0.the first pressure of the process occurs at 810 - 870oC with access 97 - 98%. The rest of the ammonia is consumed in the formation of nitrogen. The conversion of ammonia are characterized by low hydrodynamic resistance (several tens of mm of water.article ) and high linear speeds (up to 15 m/s) [Pickwell P., Nitric acid plant optimization, Chem. and Ind. 4, 21(1981)114]. Depending on the process conditions, the service life of the platinum package nets ranges from 1.5 to 16 months.

For all processes of high-temperature ammonia conversion performed on the platinum grids are characterized by significant loss of platinum during the industrial process.

When carrying out catalytic reactions on platinum there is loosening of the corrosion resistance of the surface of the catalyst. Education during the oxidation of ammonia crystal structures is accompanied by an increase up to 20 times the catalyst surface (increasing the diameter of the platinum catalyst of the thread) and losses of platinum in the form volatile oxides of platinum (chemical loss) and mechanical entrainment of catalyst particles. By the end of the path, the first surface along the gas grid is reduced, mainly as a result of loss of platinum. Catalytic corrosion occurs with various IC is each grid, and loss of platinum for each grid. During the run the nets loss of platinum, accompanying the corrosion of the surface grids can be up to 2/3 of the initial load. In the process of producing hydrocyanic acid, where the temperature of the interaction of the reagents is much higher than the temperature in the process of nitric acid, catalytic grid become even more brittle and tends to fusion grids. Loss of platinum also depend on the physico-chemical properties of the alloy.

However, to a much greater extent than by the composition of the catalyst, loss of platinum depends on technological parameters and structural design process. In systems under pressure process is carried out at a higher temperature. Increase the heat density of the catalyst, the linear velocity and the gas density. As a consequence, the direct loss of catalyst (for mileage) is significantly higher than at atmospheric pressure, which leads to a much shorter lifetime of service grids. Measurements of the velocity distribution in the contact devices show that there is considerable heterogeneity of the flow cross section of the apparatus. Despite the use of different switchgear Croesus the remaining two thirds of the area. Changing hydrodynamic conditions in the Converter has a significant influence on the magnitude of the losses of platinum.

A decisive influence on the velocity field of the gas flow with non-uniform distribution at the entrance to the contact device has a hydraulic resistance of the catalytic layer. The regular layer structure formed cell block catalyst, located directly after the platinum layer grids, allows not only to reduce the attachment of platinum by reducing the number of nets in the first stage, but also to reduce losses in the process of mileage grids while maintaining production of the product [RF Patent N 2100068, IPC 6 B 01 J 23/78, BI No. 36, 1997].

Closest to the proposed technical solution is the method of catalytic oxidation of ammonia, which consists in passing the reaction gas mixture containing ammonia and oxygen, through a two-stage catalytic system in which the first step in the direction of gas flow is a layer of platinum mesh, and the second step - cell catalyst of regular patterns, and the jets of the gas mixture moving in the cell channels of the catalyst supporting ratio of the average operating speed to skorogo, the efficiency of the catalytic system is largely dependent on the degree of homogeneity moving through it, the gas stream. During the mileage given period of operation nets) package platinum grids can lose, as mentioned above, up to 2/3 of the initial weight. Moreover, due to uneven distribution of the velocity field in the cross section of the Converter losses of platinum in each point of the square grids also occur unevenly, as in vneshnediffuzionnoe mode they depend on consumption of reagents (ammonia and oxygen) through a unit area of the grids and the gas flow speed. Thus, the initial non-uniformity of the velocity field characteristic for a given reactor design, results in an uneven distribution of the losses of platinum, which, in turn, causes an uneven drop resistance layer and a further increase in non-uniformity in flow rate and losses of platinum. The efficiency of the process decreases with time. Layer cell block catalyst, firstly, due to its regular structure, can align the velocity field of the gas flow through two-stage catalytic system. Secondly, due to its as the platinum layer grids, in addition to heterogeneous (occurring on the catalyst surface) reactions may have unwanted side homogeneous reaction, reducing the effectiveness of the process. For example, during the oxidation of ammonia to nitric oxide formed nitric oxide can interact with ammonia in the gas phase [Karavaev M. M., Zasorin A. P., Kleschev N. F., Catalytic oxidation of ammonia, M. , Chemistry, 1983, S. 232]. This homogeneous reaction, reducing the yield of the target product, nitric oxide, proceeds as between catalyst and in the channels of the cell block. In the work that we have adopted for the prototype, do not consider the influence of the homogeneous component of the process. Thus, it is not optimized placement layer cell block of the catalyst and its geometric characteristics from the viewpoint of improving the overall conversion of ammonia and to minimize losses of nitrogen oxides due to the occurrence of adverse reactions in the gas phase.

The block layer of the catalyst, due to its regular structure, uniform velocity field of gas through the platinum package grids, reducing the proportion of mechanical losses and increasing the efficiency of use of the platinum mesh. A decisive influence on the velocity field of the gas stream Loya cell catalyst regular patterns, which, in turn, also depends on the geometrical parameters of the bulk catalyst: the form of the ratio of hydraulic diameter and wall thickness, the height of a single channel.

The problem to which the present invention is directed, is to reduce the losses of platinum and increasing the yield of the target product, for example, in the process of nitric acid, and it has synthesis nitric oxide, in the process of obtaining hydrogen cyanide is HCN.

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 in the direction of gas flow is a layer of platinum mesh, and the second step catalyst bed regular cell structure in relation to the value of the hydraulic resistance of the second stage catalytic system to the value of the hydraulic resistance of the first stage of 0.2 - 4.

As shown by the analysis of existing structures converters, the minimum hydraulic resistance layer cell block of the catalyst, which starts to affect the positive effect is 0.2 hydraulic resistance of the layer p is RA more than 4 times compared to the layer patentnyh grids can lead to reduced system performance.

Additional differences between the proposed method:

at the second stage use cell catalyst porosity, characterizing the volume of voids or open surface of which is 0.1 - 0.6,

at the second stage catalytic system using multiple spatially separated layers of honeycomb catalyst

each individual layer of the cell block of the catalyst have a distance of less than 60 mm from the adjacent layer, mainly at the distance of 0.5 - 1 wall thickness of the channel block,

between the layers of honeycomb catalyst regular patterns include a gas-permeable inert material,

the height of each layer of the catalyst honeycomb structure is not more than 0.5 Re dewhere Re is the Reynolds number, equal to 1 5 104de- hydraulic diameter of the channel cell catalyst is 1 to 20 mm,

use the catalyst honeycomb structure having a wall thickness (0.1 - 1.0) de,

use the catalyst honeycomb structure, containing in its composition oxides of base metals,

use the catalyst honeycomb structure is On)f, where A is a cation of Ca, Sr, Ba, Mg, Be, Ln, or a mixture thereof, B - cations of Mn, Fe, Ni, Co, Cr, Cu, V or mixtures thereof, x = 0-2, y = 1 - 2, z = 0.8 - 1.7; MemOn- aluminium oxide and/or silicon oxide, zirconium, chromium, aluminum silicates, oxides of rare earth elements (REE), or mixtures thereof, m = 1 to 3, n = 1 - 2, k and f - wt.%, when the ratio k/f = 0.01 - 1, wt.%: iron oxide 70 - 94, aluminum oxide, 1 - 29, the silicon oxide and/or oxides of rare-earth elements, zirconium oxide 1-29,

use the catalyst honeycomb structure, specific surface area greater than 5m2/,

The invention is illustrated by the following examples.

Example 1. (Prototype) Process carried out at the industrial unit of production of weak nitric acid to the diameter of the reactor for the oxidation of ammonia 1500 mm oxidation of ammonia to nitric oxide is carried out on a two-stage catalytic system, where the first stage in the direction of gas flow have a catalytic package consisting of 9 woven platinum mesh wire diameter of 0.092 mm number of holes 1024 on 1 cm2with the composition of the platinum alloy: Pt - 81, Pd - 15, Rh - 3.5 and Ru - 0.5%. As the second stage in the direction of gas flow using a single layer cell block catalyst height 50 mm with hydraulic diameter of the channel 7 mm and a thickness of the article is SUB>2O3- 25, aluminosilicate fiber - 5. The concentration of ammonia in the ammonia-air mixture 10%, the absolute pressure of 7 ATA, the normal speed of the ammonia-air mixture 7 nm/s, operating temperature 910oC. the Hydraulic resistance of the package nets - 48,0 mm water.art., hydraulic resistance layer cell block catalyst - 6.0 mm water.art., the ratio of the value of the hydraulic resistance of the second stage to the value of the hydraulic resistance of the second stage is 0,126. The output of nitric oxide is 90.1%. The service life of the catalyst of the first stage is 2300 hours.

Example 2. The process is conducted as in example 1, a two-stage catalytic system, where the first stage in the direction of gas flow have a catalytic package consisting of 9 woven platinum grids, with the difference that in the second stage use cell catalyst with a hydraulic diameter of the channel of 3.2 mm and a wall thickness of 1.6 mm composition, wt.%: iron oxide - 84, alumina - 13, the silicon oxide - 2 and zirconium oxide - 1. The height of the block layer of the catalyst 50 mm Porosity block 0.44. Between catalytic steps include a gas-permeable nichrome mesh height 1.5 mm In this case, hidraulicas the value of the second stage to the value of the hydraulic resistance of the first stage is of 0.51. The output of nitric oxide is 93.2%. The service life of the catalyst of the first stage is 2900 hours.

Example 3. The process is conducted as in example 1 with the difference that in the second stage used a single layer of honeycomb catalyst height 100 mm with hydraulic channel diameter 5.5 mm and a wall thickness of 1.5 mm, the Porosity of the block 0.60. In this case, the hydraulic resistance of the second stage is 13 mm water.art., the ratio of the value of the hydraulic resistance of the second stage to the value of the hydraulic resistance of the first stage 0,26. The output of nitric oxide is 93.3%. The service life of the catalyst of the first stage 3100 hours.

Example 4. The process is conducted as in example 3 with the difference that the second stage consists of two layers of honeycomb catalyst height of each 50 mm of the composition, wt.%: iron oxide - 80, alumina - 10, the silicon oxide - 5 and oxides of rare earth elements - 5.

Between the cell layers of the catalyst include a gas-permeable nichrome mesh height 1.5 mm In this case, the number Re for the channel block is 1600, the height of one layer of honeycomb catalyst is 0,006 from Re dehydraulic resistance of the second stage was the resistance of the first stage is 0,435. The output of nitric oxide is 93.8%. The service life of the catalyst of the first stage 3200 hours.

Example 5. The process of conversion of ammonia to hydrogen cyanide in the process of producing hydrocyanic acid is carried out on a two-stage catalytic system, where the first step along the gas is catalytic package consisting of 3 platinum meshes with the thread diameter 0.098 mm Second stage during gas are the three layers of the cell block catalyst height 50 mm with hydraulic channel diameter of 3 mm and a wall thickness of 2 mm, Porosity of the catalytic unit is 0.36. Cell catalyst has the composition: 10 wt. % ferrite, lanthanum-aluminum oxide. The reaction mixture composition, %: ammonia - 11, methane - 10, oxygen - 16, the nitrogen - rest. The pressure is atmospheric, the normal speed of the ammonia-air mixture 2.5 nm/s, operating temperature 1026oC. the Hydraulic resistance of the package nets - 57.1 mm water. Art. , hydraulic resistance layer cell block catalyst - 120 mm of water.art., the ratio of the value of the hydraulic resistance of the second stage to the value of the hydraulic resistance of the first stage is 2.1. 3 new meshes converts 94.3% of the total number of processed and the stage catalytic system 98.1%. Mileage catalytic system is 1 year instead of the scheduled operation period of three platinum grids - 3 months.

As seen from the above examples the proposed method for catalytic conversion of ammonia reduces the loss of platinum and to increase the yield of target products and may find wide application in the manufacture of nitric and hydrocyanic acid, and has synthesis.

1. Method of catalytic conversion of 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 the ratio of the magnitude of the hydraulic resistance of the second stage catalytic system to the value of the hydraulic resistance of the first stage is 0.2 - 4.

2. The method according to p. 1, wherein the used catalyst honeycomb structure, porosity, characterizing the volume of voids or open surface of which is 0.1 - 0.6.

3. The method according to p. 1, characterized in that the second stage of the AC is s.

4. The method according to PP.1 and 3, characterized in that each layer of the catalyst honeycomb structure have a distance of less than 60 mm from the adjacent layer, mainly at the distance of 0.5 - 1 wall thickness of the channel block.

5. The method according to PP.1 and 3, characterized in that between the layers of the catalyst honeycomb structure include a gas-permeable inert material.

6. The method according to PP.1 and 3, characterized in that the height of each layer of the catalyst honeycomb structure is not more than 0.5 Re dewhere Re is the Reynolds number, equal to 1 5 104de- hydraulic diameter of the channel of the catalyst is 1 to 20 mm

7. The method according to p. 1, wherein the used catalyst honeycomb structure having a wall thickness (0.1 to 1.0) dewhere de- hydraulic diameter of the channel of the catalyst is 1 to 20 mm

8. The method according to p. 1, wherein the used catalyst honeycomb structure, containing in its composition oxides of base metals.

9. The method according to PP.1 and 8, characterized in that the used catalyst honeycomb structure, which is a mixed oxide of General formula (AxByO3z)k(MemOn)fwhere a is an oxide of aluminium and/or silicon oxide, zirconium, chromium, aluminum silicates, oxides of rare earth elements (REE), or a mixture thereof; m = 1 to 3; n = 1 or 2; k and f - wt.%, when the ratio k/f = 0.01 to 1,% by weight: iron oxide 70 - 94, aluminum oxide, 1 - 29, the silicon oxide and/or oxides of rare-earth elements, zirconium oxide, 1 - 29.

10. The method according to PP.1 and 9, characterized in that the used catalyst honeycomb structure, the specific surface area is greater than 5 m2/,

 

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EFFECT: the invention ensures the increased conversion of ammonia and the decreased share of the platinoids included in the mesh catalytic agent production processes providing for the catalytic conversion of ammonia in the flow sheet of the chemical goods production.

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EFFECT: increased catalyst activity.

8 cl, 2 tbl, 3 ex

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EFFECT: increased degree of conversion and degree of trapping of platinum, and prolonged lifetime of grids.

5 cl, 6 ex

FIELD: chemistry.

SUBSTANCE: invention pertains to the method of obtaining porous substances on a substrate for catalytic applications, to the method of obtaining porous catalysts for decomposition of N2O and their use in decomposing N2O, oxidising ammonia and reforming methane with water vapour. Description is given of the method of obtaining porous substances on a substrate for catalytic applications, in which one or more soluble precursor(s) metal of the active phase is added to a suspension, consisting of an insoluble phase of a substrate in water or an organic solvent. The suspension undergoes wet grinding so as to reduce the size of the particles of the substrate phase to less than 50 mcm. The additive is added, which promotes treatment before or after grinding. A pore-forming substance is added and the suspension, viscosity of which is maintained at 100-5000 cP, undergoes spray drying, is pressed and undergoes thermal treatment so as to remove the pore-forming substance, and is then baked. Description is also given of the method of obtaining porous catalysts on a substrate for decomposing N2O, in which a soluble cobalt precursor is added to a suspension of cerium oxide and an additive, promoting treatment, in water. The suspension is ground to particle size of less than 10 mcm. A pore-forming substance, viscosity of which is regulated to approximately 1000 cP, is added before the suspension undergoes spray drying with subsequent pressing. The pore-forming substance is removed and the product is baked. Description is given of the use of the substances obtained above as catalysts for decomposition of N2O, oxidation of ammonia and reforming of methane with water vapour.

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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