A device for recovery of platinum group metals in catalytic oxidation of ammonia
(57) Abstract:The invention relates to the production of nitric acid, namely to the grids of the precious metals in the form of packets used for recovery of platinum and rhodium, evaporates from the surface of the catalyst in the oxidation of ammonia. The proposed device for the recovery of platinum and rhodium contains grid-traps density 400 - 1024 cells/cm2and the separation of the grid from heat-resistant steel density 49 - 70 cells/cm2forming no more than six layers, the first three of which contain not more than two grids of traps each, and subsequent layers contain one grid-trap. The density of the grids of traps in the direction of the reaction gas increases, dividing grid, one of which is installed at the beginning of the device, and the other at the end, performed by the density of 69 - 180 cells/cm2. Grid-traps made of an alloy based on palladium containing copper and tungsten, in the following ratio, wt.%: copper 4,0-8,0, tungsten 0.3 to 1.0, palladium - rest. In addition, the device may include three layers, the first of which includes no more than two grids of traps lower density, second and third in odnowienie the degree of recovery of platinum, increase service life and reduce consumption of precious metals in the formation of nitric acid. 1 C.p. f-crystals, 1 table. The invention relates to the production of nitric acid, namely to the grids of the precious metals in the form of packets used for recovery of platinum and rhodium, a release from the catalyst in the oxidation of ammonia.During the manufacture of nitric acid by oxidation of ammonia with the use of platinum catalysts at high temperature ablation of the platinum in the oxidation of the filament mesh catalyst to oxides and subsequent evaporation of these oxides, as well as due to mechanical destruction of the nets. These losses amount to 40% by weight of the installed catalyst, in the absence of trapping they become irrecoverable.At the present time for recovery of platinum and rhodium in conjunction with the catalysts in aggregates oxidation of ammonia to set traps, made in the form of service grids of alloys based on palladium.Known grid of metallic palladium or alloys, for example, containing 10% gold and 10% rhodium used for recovery of platinum in the process of katalitin wire oval cross-section. According to this technical solution, okalizacja wire is made by flattening the finished grid.A disadvantage of the known safety nets is the following: mechanical flattening of the grid decreases its strength and may occur curvature of the cells, which leads to uneven density of the fabric and because of this uneven obliteration of individual sections of PGE. In addition, the application package grids with the same density (number of cells per 1 square centimeter) leads to a stronger saturation platinum and sharastani first in the direction of the reaction gas grids forming catching package, which increases the aerodynamic resistance of the system and reduces the efficiency of the capture process.The disadvantages of this package may also include the execution of grids with a high gold content, which increases its cost, and the use of such nets accompanied by a loss of gold.Known mesh of precious metals for recovery of platinum group metals, in particular platinum in the oxidation of ammonia (patent Poland N 107511, 01 J 23/96, Appl. 09.07.77 g, op. 31.12.80 year).The grid on this invention in weaving sod and 20% gold. Heat-resistant substance does not form alloys with the wire used for recovery of platinum group metals. As the heat-resistant substance is an alloy containing 8-20% Nickel and 15-25% chromium or 20-28% of chromium and 3-7% aluminum.However, a disadvantage of catching system containing the above grid is a low degree of recovery of platinum because of the presence of heat-resistant wire, woven into a basic safety net and reducing the surface mesh is used for the deposition of platinum. In addition, woven wire made of heat-resistant substances complicates the refinement of meshes after use. As well as the high gold content increases the cost of the nets.The technical essence and the achieved result closest to the proposed object of the invention is a device for the recovery of platinum group metals on the patent of the Russian Federation N2119381 B 01 J 35/04, Appl. 27.06.97 g, op. 27.09.98,, bull. 27).The device includes a package of safety nets from the base alloy of palladium and the separation of the grid from heat-resistant steel. Safety nets are arranged in layers 2-4 pieces and is made from wire with a diameter of 0.06 to 0.12 mm and a density of 225-1024 cells/cm2and the partition is> Safety nets are made of alloys based on palladium and may contain, by weight. %: platinum - 9,0; tungsten - 0,5; or Nickel - 5,0; tungsten - 0,2; or tungsten - 5,0; yttrium - 0,1; or platinum - 5,0; copper - 5,0; yttrium - 0,1.A disadvantage of the known device is the complexity of its manufacture by installing a layer of meshes of different densities and different from the composition of the alloys.It was established experimentally that in case of implementation of safety nets, containing Nickel, they at the slightest fluctuation in the flow rate of gases capable of coloring, and the presence in the alloy of platinum increases the cost of the entire safety system and decreases the degree of recovery of platinum due to its high initial concentration in the alloy. When installed in the layer 3-4 grid in the operation process is sintering, resulting in increased aerodynamic resistance of the system and decreases the degree of recovery of platinum. In addition, a disadvantage of the known device is increased density (compared to the offer) dividing nets. Although the use of barrier nets made of heat-resisting steel with high density and increases the strength of the package, but also in the maintenance capability of the package.The task, which was sent to the proposed technical solution is to increase the degree of recovery of platinum and rhodium, longer service life safety devices-package and lower attachments of the precious metals.This object is achieved in that the device for recovery of platinum group metals in catalytic oxidation of ammonia, containing layers of grids of traps from an alloy based on palladium and the separation of the grid from heat-resistant steel according to the invention includes catching mesh density 400-1024 cells/cm2and dividing the mesh density 49-70 cells/cm2forming no more than six layers, the first three of which contain not more than two safety nets each, and subsequent layers contain one catching the grid, and the density of safety nets in the direction of the reaction gas increases, dividing grid, one of which is installed at the beginning of the package, and the other at the end, performed by the density 69-180 cells/cm2and catching grid is made from an alloy based on palladium containing copper and tungsten in the following ratio, wt.%: copper - 4,0-8,0; tungsten - 0,3-1,0; palladium - rest.In addition, ustti, and the second and third one catching the mesh higher density.The proposed location of the nets in the package, as determined experimentally, is the most optimal placement of mesh in layers. The batch six-plane is compact and allows you to use all of the layers in the capture process at a lower installation mass, thereby increasing its effectiveness.Setting each of the first three layers on one or two safety nets, the other one provides a uniform and low aerodynamic resistance due to the lack of decrease of pressure is inherent for layers with a large number of grids.The density of the mesh in the direction of the reaction gas is gradually increased from 400 to 1024 cells/cm2, i.e., the first set is more rare grid. This is because immediately after the catalyst is the most intense reaction trapping platinum, and wire mesh rapidly increases in diameter due to the deposition of platinum, but due to their low initial density, they keep their low aerodynamic resistance.Thus, the concentration plasai falls. As a result, the package slowly becomes saturated and can work effectively over the long term.The separation of the grid from heat-resistant steel is separated layers of palladium grids from each other and from the catalyst. To improve the efficiency of trapping the separation of the grid are also manufactured with different densities. Low density (49-70 cells/cm2) dividing nets, which separate layers within the package and prevent the sticking of safety nets, allows not to break the speed of gas flow, and thereby provides a stable aerodynamic resistance, which in turn reduces the number of losses of precious metals.Increased density at the dividing nets combined with the decreasing diameter of the wire from which they are made that increasing the mesh density in 2 times can reduce their weight. In addition, the separator grid with higher density, installed at the end of the package and on the border with catalyst, provide increased mechanical strength of the package and, therefore, its service life. The maximum density at the beginning of the package prevents the rapid obliteration safety nets by equalizing the speed of reaction is tion of the values leads to an increase in aerodynamic resistance of the package and the change of the velocity of the gas stream, contributing to the uneven saturation grids platinum and reduce the service life of the package.Themselves palladium grids are a catalyst for the oxidation of ammonia, and when the saturation of their surface platinum catalytic activity of this system dramatically increases and becomes comparable to the activity of the catalyst based on platinum. Therefore, grid-traps are also used as the second stage of the oxidation reaction of ammonia, which increases the efficiency of the entire process and reduces the amount of platinum catalyst gauzes by 20-40%.From the prior art in this field it is known that as the material of which is made of grid-traps, alloys are available based on palladium containing non-ferrous metals. Research to identify material safety nets for the proposed service determined that the most effective of these is based alloy of palladium containing copper.The use of copper in the material of the grids of traps increases their mechanical strength due to the strengthening effect of copper on palladium, reduces the cost of precious metal without sacrificing catching ability of the package.The study of the structures is optimum for the substitution of palladium in the alloy. The decrease in the copper content less than 4% reduces the mechanical strength of the grid, and in addition, reduce the cost of the alloy will be commensurate with the task. The increase in the copper content of more than 8% leads to a rapid deterioration of the grid by reducing erosion resistance of the alloy.The claimed range of the content of tungsten in the alloy for grids modify the microstructure, resulting through the creation of structures regulated by the ratio of the components is achieved by obtaining fine-grained structure, providing the use of such alloy high performance properties.Tungsten greatly increases the resistance of the alloy at the temperature of operation of the grids. In addition, ISPRAS, tungsten accelerates the deposition of platinum on palladium. The content of tungsten in the alloy of 0.3-1.0% allows to increase the tensile strength of the alloy is almost 3 times. When the content of larger quantities (>1%) deteriorating manufacturability grid deteriorates the machinability of the alloy, since the tungsten ternary alloy forms with palladium fragile, reducing the mechanical properties of the alloy.Thus, the use of the alloy manufacturer for the TA and to reduce consumption of palladium.Examples confirming the possibility of carrying out the invention.Package for recovery of platinum and rhodium for the Assembly of high pressure UKL-7 were recruited from six layers and set in the direction of the reaction gas for a package of 8 catalyst mesh density 1024 cells/cm2and the wire diameter 0,092 mm, made of an alloy of platinum-15%palladium-3.5%rhodium-0.5%ruthenium.Safety nets were made of an alloy based on palladium containing copper and tungsten. The tests were performed on grids made of alloys with different content of copper and tungsten (see table).Dividing the grid was made of heat-resistant steel HUT.The order of the set of package (in the direction of the reaction gas) is as follows:
1 layer for the catalyst (start of packet) was established dividing the net density of 69 cells/cm2wire diameter of 0.25 mm, then put 1 safety net density of 400 cells/cm2wire diameter of 0.12 mm, completed the separation layer fabric with a density of 49 cells/cm2wire diameter of 0.4 mm;
2 layer was placed 2 catching mesh density of 400 cells/cm2wire dia is th - installed 2 catching mesh density of 625 cells/cm2wire diameter of 0.09 mm and dividing the mesh density of 70 cells/cm2wire diameter of 0.4 mmIn 2 and 3 layers of mesh had with a turn of the thread at an angle of 45o.4 layer - put 1 safety net density of 1024 cells/cm2wire diameter of 0.09 mm;
5 layer through dividing the net density of 70 cells/cm2wire diameter of 0.4 mm was installed a safety net density of 1024 cells/cm2wire diameter of 0.076 mm;
6 layer through dividing the net density of 70 cells/cm2wire diameter of 0.4 mm was installed a safety net density of 1024 cells/cm2from wire with a diameter of 0.06 mm was Completed layer dividing the net weight of 180 cells/cm2wire diameter of 0.25 mm (end of packet).Package for recovery of platinum and rhodium for Assembly of medium pressure AK-72 were recruited from three layers and was installed in the direction of the reaction gas for a package of 4 catalyst mesh density 1024 cells/cm2and the wire diameter 0,092 mm, made of an alloy of platinum-15%palladium-3.5%rhodium-0.5%ruthenium.
2wire diameter of 0.25 mm was Then placed 1 safety net density of 400 cells/cm2wire diameter of 0.12 mm, which was established 1 safety net density of 400 cells/cm2from wire with a diameter of 0.09 mm was Completed the separation layer fabric with a density of 49 cells/cm2wire diameter of 0.4 mm;
2 layer was set to 1 safety net density of 1024 cells/cm2wire diameter of 0.09 mm, and then dividing the net density of 70 cells/cm2wire diameter of 0.4 mm;
3 layer was set to 1 safety net density of 1024 cells/cm2wire diameter of 0.076 mm and dividing the net weight of 180 cells/cm2wire diameter of 0.25 mm (end of packet).
Copper - 4,0 - 8,0
Tungsten - 0,3 - 1,0
Palladium - Rest
2. The device under item 1, characterized in that it comprises three layers, the first of which includes no more than two grids of traps lower density, vtoro the