Ammonia conversion process

FIELD: inorganic compounds technologies.

SUBSTANCE: invention relates to ammonia conversion processes based on two-step catalytic system, which can be employed in production of nitric and hydrocyanic acids and in hydroxylamine sulfate production. Process according to invention comprises passing gaseous ammonia- and oxygen-containing mixture through two-step catalytic system, wherein first downstream step is embodied in a wire catalytic grate stack and second step in one or several layers of block honeycomb material, ratio of second-step hydraulic resistance value to the first-step one exceeding 4. Catalytic system steps are spaced from each other by distance equal to at most 10 and preferably 0.5 to 2 effective thickness of block channel σ calculated in terms of formula σ=2(S/(πn)^1/2 (1-ε^1/2), wherein S represents honeycomb block cross-section area, n number of channels in block, and ε open surface of block. Spacing between the steps is achieved by positioning between them spacing layer of gas-permeable chemically inactive material having hydraulic resistance coefficient below 100, hydraulic resistance of the second step being calculated as summary value of hydraulic resistances of honeycomb and spacing layers.

EFFECT: increased yield of desired products.

4 cl, 6 ex

The invention relates to processes for the conversion of ammonia to two-stage catalytic system, in which the first in the course of the reaction gas mixture of the catalytic step is to package the nets, made of platinum alloys, which may be supplemented platinumellinium nets of gold or palladium, and the second stage - block material of cellular structure containing precious or rare 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 on the packets woven or knitted from wire made of platinum alloys, fine-meshed nets in the pressure range 0.1-1.8 MPa. The reaction is limited by mass transfer, go with extremely high speed and are accompanied by intense heat. In the manufacture of nitric acid under atmospheric pressure conversion of ammonia to nitric oxide occurs when 810-870°C and under pressure of from 0.7 to 1.8 MPa temperature grids reaches 900-940°C. In the production of hydrocyanic acid at a pressure of 0.2 MPa, the gas temperature can reach 1300°C.

In such hard conditions during the industrial mileage (given period of operation nets) occur EIT is sustained fashion chemical and mechanical losses of the wire material of the catalyst, occur as a result of catalytic corrosion of the surface wires. They can be up to 2/3 of the initial load. As a result, the wire activity of the catalyst decreases, and the yield of the target product is reduced, which leads to the need to stop production and reboot expensive catalyst of the first stage. The lifetime of the package nets ranges from 1.5 to 16 months depending on the process conditions. Because high pressure systems calorific catalyst increases, loss of platinum catalyst for a run in them is much higher than at atmospheric pressure, and the lifetime of the package nets significantly shorter.

The intensity of the catalytic corrosion, and hence the number of lost catalyst depend on the physico-chemical properties of catalytic alloy, the composition of the reacting gas flow, temperature and speed. In the case of non-uniform velocity distribution over the cross section of the Converter, which occurs despite the use of contact devices switchgear different designs, catalyst losses also occur unevenly, and this, in turn, causes an uneven change in the dip of the hydraulic resistance of the wire layer and a further increase in non-uniformity in soon the minute flow and losses. Because of this negative current positive feedback conversion efficiency of the process decreases with time.

To prevent or significantly reduce chemical ablation of platinum in the package catalytic nets include special platinovaya mesh, made from gold or palladium. Their use substantially compensates for the above-mentioned positive feedback effect for the following reason. Unevenly (the square package nets) weathered atomic platinum unevenly same is deposited on the surface of the wires catching nets and the areas of high wear package catalytic grids with low hydraulic resistance, correspond to areas of safety nets, having on the contrary, increased hydraulic resistance acquired by overgrowing caught their platinum mesh. As a result, these areas do not experience a significant local increase in velocity head, and hence the intensity of the catalytic corrosion. An additional positive aspect of using platinumplay grids is that as subsidence on them they acquire platinum kataliticheski properties.

Thus, the loss of the platinum source of catalyst depends largely on the design, aktsionnogo design process. A decisive influence on the velocity field of the gas flow with non-uniform distribution at the entrance to the contact device and the lack of action distributing devices may provide hydraulic resistance of the catalytic layer.

Known [U.S. Pat. Of the Russian Federation No. 2100068, B 01 J 23/78, 01 21/26, 27.12.1997] two-step flow chart, which clearly shows the positive effect of which is located directly after the layer wire platinum source catalyst layer cell block of a catalyst based on a mixed oxide, which serves as the second stage of the oxidation of ammonia. The second stage can substantially equalize the velocity field of the gas flow through the first stage due to its hydraulic resistance, thereby reducing the share of mechanical losses platinum alloy during the run of the nets, and in the case of its catalytic activity she topreverse residual ammonia, reducing attachment platinum source of the catalyst by reducing the number of nets in the first stage, while maintaining the production of the final product.

Also known [U.S. Pat. Of the Russian Federation No. 2119889, 01 21/26, 10.10.98] a 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 is a 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 the speed of sound in these conditions, in the range of 4.8·10^-4-0,024.

In these analogues of the claimed invention is not analyzed and not subject to optimization is such an important factor in ensuring the effectiveness of two-stage catalytic system as the hydraulic resistance layer cell catalyst.

Closest to the proposed technical solution are ways oxidation of ammonia [U.S. Pat. Of the Russian Federation No. 2145935, 01 21/26, 2000; No. 2145936, 01 21/26, 2000], in which this factor should be given due attention, and the second of these patents we have chosen for the prototype.

The main distinctive feature of the method declared in the prototype, consisting 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 is to ensure the relationship value of the hydraulic resistance of the second stage catalytic system to the value of the hydraulic resistance of the first stage in the 0.2-4 units. The task of ensuring the ecene this ratio is solved by deliberately varying the geometrical parameters of the bulk catalyst: hydraulic diameter and length of the channel, the shape of its cross section, wall thickness, number of layers of blocks.

In that case, when there is a correct value of the hydraulic resistance of the second stage (at a given attachment platinum source of catalyst), the homogeneity of the hydrodynamic conditions in the catalyst bed is increased, that is, reduced local differences of speed on certain sections of the package nets, and the positive feedback between these differences and the resulting local changes in the intensity of ablation platinum largely campfires, which leads to a significant reduction of losses in platinum.

The applied method has the disadvantage that it is limited to the case of a significant (tens of mm of water. Art.) hydraulic resistance of the package nets.

Currently, in order to reduce the attachment of platinum and enhance the durability of the wire catalyst tends to use as vysokoporodnyh packages from knitted two - and trehzahodnoy nets and packages from vysokoporodnyh knitted meshes of the firm Degussa, containing the weft yarn [U.S. Pat. DE 10105624, 01 J 35/06, 02.10.02]. The hydraulic resistance of such packets is very small, less than 10 mm water. Art. values, and so declared in the prototype range relations of hydraulic resistances of both stages can arasat the Xia is not enough to compensate for their low straightener actions and ensure uniform distribution of the flow velocity over the cross section of the apparatus, especially when a substantial degree of expansion of the flow at the inlet of the device. Even very significant shrinkage packages from knitted two - and trehzahodnoy nets thickness observed during the operation of packages and leading to a significant increase in resistance, not save the situation. Due to this circumstance would require a significant increase of the hydraulic resistance level formed from a bulk catalyst honeycomb structure.

Another disadvantage of the known technical solution is that it fails to address the role of the influence of the distance between the levels of the catalytic system on the characteristics of the process, while the current study [V.P.Zakharov, I.A.Zolotarskii, V.A.Kuz'min CFD Simulation of "gauze pad - honeycomb" catalytic system Chem. Eng. J. 91 (2003) 249-255] indicates a promising use of this factor for parameter optimization of the operation of the reactors. The distance between the speed significantly affects the degree of uniformity of distribution of the flow rate of the catalytic layer, and on the intensity of mass transfer. Distant separation steps leads to hydrodynamic autonomy package grids, i.e. supporting the leveling action of the second stage is lost. Moreover, the velocity profile uncontrolled can be deformed between speed and he can priores and global heterogeneity at the entrance to the cell layer. When close enough location steps from each other, the first of them begins to interfere in the process of wrapping the ends of the walls of the channels of the blocks, thereby affecting the nature of the flow in the inlet sections of the channels, where there is a significant intensification of mass transfer due to the implementation mode of unsteady vortex (turbulence in the flow). Dense planting of service grid cell layer leads to a complete suppression zone recirculation flow at the inlet edges of the walls of the channels, which has a positive impact on the intensity of mass transfer, if not sharp concentration depletion of parietal layer of gas, leading ultimately to the deterioration of mass transfer for a considerable length of the channels. However, the close contact of the speed achieved their maximum hydrodynamic interaction and the positive impact of proximity on the global heterogeneity of the workflow (distributing ability of the second stage) due to the significant increase in the input resistance of the channels. However, this situation is also undesirable, as it is accompanied by the occurrence of small-scale (comparable to the thickness of the wall of the channel and its diameter) inhomogeneities of the flow in the body of the first stage, which inevitably leads to the loss of global d is myroodah properties of the second stage. Unwanted locally-jet nature of the penetration flow through the package in this case contributes to accelerated local depletion of platinum source of catalyst due to its high ash on the portions corresponding to the entrances to the channels. In contrast, the portions corresponding to the ends of the walls of the channels, the use of this catalyst is reduced. From the above it follows that a necessary compromise in ensuring optimum properties of global and local uniformity of the velocity field.

The invention solves the problem of eliminating the above mentioned disadvantages of the prototype and is aimed at further reduction of mechanical and chemical losses of platinum alloy and increase the yield of the target product, for example, in the process of nitric acid, and has synthesis is nitric oxide, and in the process of obtaining hydrogen cyanide is HCN.

To achieve elimination of the basic drawback can increasing the hydraulic resistance of the second stage by increasing its thickness or number of spatially separated layers of blocks in it, but it can lead to excessive longitudinal dimensions of this level. More reasonable this increase is to ensure that by reducing the flow area of the cell catalyst by reducing the hydraulic diameter of the channels while maintaining their number per unit square is square, that is, by increasing the thickness of the walls of the channels. However, calculations show that the integral mass transfer in cellular catalyst remains almost unchanged due to the fact that the lower conversion in the channels due to the linear increase of the gas velocity and a corresponding increase of the Reynolds number, which determines the process of transfer in the channels, is completely compensated by the increase of masatake on the end surfaces of the blocks facing to the incident flow. If it is economically feasible, in order to ensure uniformity of flow distribution in catalytic layer, the second step can be done using cell blocks, made of chemically inert heat-resistant material.

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 as the gas level is the package catalytic wire mesh, made of a platinum alloy, and the second stage is one or more layers of a block of cellular material with hydraulic resistance, more than 4 times greater hydraulic resistance of the first stage, and catalytic stage located at a distance of not more than 10 and preferably 0.5 to 2 effective thickness of the wall of the channel unit δ calculated according to the formula δ=2(S/(πn))^l/2·(1-ε^1/2), where S is the cross-sectional area of the cell block, n is the number of channels in the block and ε - open surface of the block by placing between the spacer gas-permeable layer of chemically inert material having a coefficient of hydraulic resistance lower than 100, and the hydraulic resistance of the second stage are calculated as the total value of the hydraulic resistance of the cell and the spacer layers.

As part of the package grids of the first stage are used platinovaya grid, and the hydraulic resistance of the first stage are calculated as the total value of the hydraulic resistance of the package and catalytic platinumplay nets.

You can use cell blocks, made of catalytic material, which is, for example, mixed oxides of the General formula ((2-x)MgO·xMeO)·(2-y)Al₂O₃-(5+y+(2-x))SiO₂where x=0-2; y=0-0 .5, Me=Mn, Fe, Co, Ni, Cu, Cr, V or mixtures thereof, forming a frame structure of cordierite and having an effective thickness of a wall of the channel δ 1,0-3,0 hydraulic diameter of the channel, the value of which lies in the range 1-20 mm

You can use cell blocks, made of chemically inert heat-resistant material and having effectively is active wall thickness of the channel δ in 1,0-3,0 hydraulic diameter of the channel, the value of which lies in the range 1-20 mm

The required distance between the levels is ensured by placing between them, for example, a wire mesh or packages of such meshes (grids). The spacer layer in the case of possession of a significant hydraulic resistance can combine their function with the function of the distributor flow and affect the degree of uniformity of the velocity distribution on the combined catalytic layer. The hydraulic resistance of the second stage in this case are calculated taking into account the hydraulic resistance of the spacer layer. With sufficient to ensure the right balance between the hydraulic resistance of the catalytic steps of the accuracy of the joint resistance of the spacer and the cell layers can be defined as the total value of their resistances;

in the case of use as part of the package grids of the first stage platinumplay nets its hydraulic resistance calculate, taking into account their hydraulic resistance. Based on the well-known result [Ershin S.A., Kadieva L.G. ABOUT hydraulic soprotivlenie and the refractive action of fine-meshed nets, " Izv. An SSSR, MIG, 1988, No. 2, pp.109-115], the hydraulic resistance of the package grids can be defined as the total knowledge is giving hydraulic resistance of each of the grids of the package;

- in order to reduce the flow area of the layer block of a catalyst using the catalyst honeycomb structure, the thickness of which is 1.0-3.0 hydraulic diameter of the channel of the catalyst, lying in the range 1-20 mm;

- block the catalyst honeycomb structure may contain oxides of base metals and represents, for example, mixed oxides of the General formula ((2-x)MgO·xMeO)·(2-y)Al₂O₃·(5+y+(2-x))SiO₂where x=0-2; y=0-0 .5, Me=Mn, Fe, Co, Ni, Cu, Cr, V or mixtures thereof, forming a frame structure of cordierite and is characterized by a thermal expansion coefficient equal to 10^-7-10^-5To^-1in the temperature range up to 900°he may further comprise oxides with spinel structure, perovskite, hexaline, corundum and other silicates;

- if it is economically feasible, in order to ensure uniform flow distribution over the surface of the catalytic layer, you can use cell blocks, made of chemically inert heat-resistant material and having an effective thickness of a wall of the channel δ 1,0-3,0 hydraulic diameter of the channel, the value of which lies in the range 1-20 mm

The invention is illustrated by the following examples.

Example 1. (Prototype) Process carried out on industrial Assembly about what svojstva weak nitric acid to the diameter of the reactor for the oxidation of ammonia 1600 mm 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 910°C. the oxidation of ammonia to nitric oxide is carried out on a two-stage catalytic system, where the first step is the package that includes 22 of woven wire, made of a platinum alloy, diameter 0,092 mm and a spacing of 1 mm mesh. As the second stage used a single layer cell block catalyst height 44 mm Block has a square cross-section with a side 51,3 mm, the channels have a circular cross-section with a diameter of 3.65 mm and are located at the nodes of a square grid of 9×9. The porosity (open surface) of the catalytic unit 0,322. Package grid placed directly on the layer of blocks, without the spacer strip. Cell catalyst has the composition: 1,8MgO·0,3FeO·2Al₂O₃·4,9SiO₂with the frame structure of cordierite and coefficient of thermal expansion CTE equal to 7·10^-6K^-1.

The hydraulic resistance of the package grids - 12 mm Vogt, hydraulic resistance layer cell block catalyst - 48 mm Vogt, 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 4. The output of nitric oxide p and this is 92,0%.

Example 2. The process is conducted as in example 1 with the difference that in the second stage use cell catalyst of manganese cordierite composition 1,5MgO·0,4MnO·2Al₂O₃·5,1SiO₂with a coefficient of thermal expansion CTE 5·10^-6To^-1and with the hydraulic channel diameter of 2.6 mm and the porosity of the block of 0.16. The height of the block layer of the catalyst 49 mm. In this case, the hydraulic resistance of the second stage is increased to 192 mm water. century, 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 16. The output of nitric oxide is 94.2 percent.

Example 3. The process is conducted as in example 2, with the difference that between the catalytic steps include the spacer grid of nichrome wire with a diameter of 1 mm with a step of weaving 10 mm, having a thickness h=2 mm Effective thickness of the wall of the channel cell block δcalculated by the formula δ=2(S/(πn))^l/2·(1-ε^1/2), where S=51,3²mm²- the cross-sectional area of the block, n=81-number of channels in the block and ε - porosity (open surface) of the block is 3.8 mm Distance between levels h is 0.53 for the effective wall thickness of the channel unit δand the value of δ 1,46 times greater than the amount of hydraulic d is ametra channel. The value of the coefficient of hydraulic resistance of the spacer grid is 0.3, which provides the hydraulic resistance of 0.6 mm vods With this soprotivlenie 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 of 16.05. The output of nitric oxide is a 94.6%.

Example 4. The process is conducted as in example 3 with the difference that the cell blocks are made of chemically inert heat-resistant material. The output of nitric oxide is 92,2%.

Example 5. The process is conducted as in example 4 with the difference that in the package catalytic meshes included two platinovaya mesh, made of gold wire with a diameter of 0.076 mm with a pitch of 0.3 mm, the Hydraulic resistance of these nets - 5 mm Vogt given 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 11.3. The output of nitric oxide in the beginning of the run platinumplay grids is 92,3%.

Example 6. The process is conducted as in example 1 with the difference that the channels of the cell block have a circular cross-section with a diameter of 3.2 mm, and between catalytic steps include a package of four spacer grids, izgotovlennyh of nichrome wire with a diameter of 1 mm with a step of weaving 5 mm, with regard to partial absorption of the amount of thickness h=6 mm Effective thickness of the wall of the channel cell block δ is 3,23 mm Distance between levels h is 1,86 from the effective wall thickness of the channel unit δand the value of δ approximately 1% greater than the amount of the hydraulic diameter of the channel. The value of the coefficient of hydraulic resistance of the package the spacer grids is 3,15, and the value of its hydraulic resistance - 6,16 mm vods With this in mind, the resistance ratio of the magnitude of the hydraulic resistance of the second stage, with a total value in 88,46 mm Vogt the value of the hydraulic resistance of the first stage is 7,37. The output of nitric oxide is 92,8%.

As seen from the above examples, the proposed method for catalytic conversion of ammonia can improve 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, which consists in passing gaseous ammonia and oxygen-containing mixture through a two-stage catalytic system in which the first mixture during step is to package catalytic wire mesh, and the second stage is one or more layers of a block of cellular material is material, characterized in that the ratio of the magnitude of the hydraulic resistance of the second stage to the value of the hydraulic resistance of the first stage is more than 4, and stage catalytic systems have one from another at a distance of not more than 10 and preferably 0.5 to 2 effective wall thickness of the channel unit δcalculated by the formula δ=2(S/(πn))^l/2·(1-ε^1/2), where S is the cross-sectional area of the cell block, n is the number of channels in the block and ε - open surface of the block by placing between the spacer gas-permeable layer of chemically inert material having a coefficient of hydraulic resistance lower than 100, and the hydraulic resistance of the second stage are calculated as the total value of the hydraulic resistance of the cell and the spacer layers.

2. The method according to claim 1, characterized in that the package grids of the first stage are used platinovaya grid, and the hydraulic resistance of the first stage are calculated as the total value of the hydraulic resistance of the package and catalytic platinumplay nets.

3. The method according to claim 1, characterized in that use cell blocks, made of catalytic material, which is, for example, mixed oxides of the General the th formula ((2-x)MgO· hmeo)·(2-y)Al₂O₃·(5+y+(2-x))SiO₂where x=0-2; y=0-0,5, Me=Mn, Fe, Co, Ni, Cu, Cr, V or mixtures thereof, forming a frame structure of cordierite and having an effective thickness of a wall of the channel δ 1,0-3,0 hydraulic diameter of the channel, the value of which lies in the range 1-20 mm

4. The method according to claim 1, characterized in that use cell blocks, made of chemically inert heat-resistant material and having an effective thickness of a wall of the channel δ 1,0-3,0 hydraulic diameter of the channel, the value of which lies in the range 1-20 mm