Package gas-permeable mesh of precious metals for catalytic processes

 

(57) Abstract:

Describes the package gas-permeable mesh of precious metals for catalytic processes, mainly for the catalytic oxidation of ammonia or for recovery of platinum group metals, volatile during the catalytic oxidation of ammonia, including knitted wire mesh made of an alloy based on platinum or palladium, characterized in that the grid connected wire in one or two threads with the formation of the weave "cooking surface with rapport 2, or 3, or 4 needles, and wire made of an alloy of platinum-based, containing, by weight. %: rhodium - 3 - 11, platinum - rest; or palladium 3 - 16, rhodium 3 - 11, platinum - rest; or palladium 3 - 16, rhodium 3 - 11, ruthenium 0,1 - 1,0, platinum - rest; or of an alloy based on palladium-doped tungsten or yttrium-containing, wt.%: tungsten - 3 - 10; palladium - rest; or copper 3 - 10; palladium - rest; or Nickel 3 - 10, palladium - else, while the mesh in the package are angled 90orelative to each other. The technical result - improving the efficiency of the conversion process ammonia. 4 C.p. f-crystals, 2 tab.

The invention relates to the production of nitric acid, namely, the m of the noble metals, which packages are used as catalysts or for the recovery of platinum, a release from the catalyst in the oxidation of ammonia.

Known wire woven mesh of platinum alloys used as catalysts in the oxidation of ammonia (G n HAC and other Industrial products made of precious metals and alloys. M.: metallurgy, 1985, S. 88-89).

However, the woven structure of the grid is not a highly developed surface, which reduces the oxidation of ammonia. In addition, the grid has a low breaking strength.

Known mesh catalyst for the oxidation of ammonia in the form of a package nets made of noble metals (patent Poland N 150285, 01 J 23/44, Appl. 02.03.87, publ. 31.10.90).

The catalyst is made in the form of one or two grids of wire with a diameter of 0.09 mm from an alloy of palladium with rhodium and platinum, or gold, or platinum and gold simultaneously. However, grids, containing gold, increase their cost, and the use is accompanied by high losses of gold.

Known package catalytic grids in the United Kingdom patent N 2062486 (01 J 35/04, Appl. 04.11.80, publ. 28.05.81).

The catalytic metal of the platinum group, however, some grid located at the front of the package, woven from wire having a larger cross-section than the grid located at the rear side of the package. The number of grids in one package is 10 or more.

The disadvantage of catalytic package is a low degree of oxidation of ammonia, because the woven mesh have a smaller contact area with the gas stream. The disadvantages of the known technical solutions is also a large aerodynamic resistance of woven meshes, causing uneven and the pressure drop of the gas flow and therefore decrease the efficiency of the oxidation process.

The technical nature closest to the proposed technical solution are packages of noble metals in the form of a gas-permeable grids produced by the method described in the patent of Russian Federation N 2017520 (01 J 37/00, Appl. 13.03.92, publ. 15.08.94, bull. N 15, CONV. Priority from 16.03.91, N P 4108625.2. Germany).

The grid used for catalytic processes, in particular for the catalytic oxidation of ammonia by air, or for the regeneration of the platinum metal volatilisation during catalytic combustion of ammonia.

Mesh vymazalova 4-12 wt. % palladium and rhodium, or palladium-Nickel alloys with 2-15 wt.% Nickel or palladium-copper alloys with 2-15 wt.% Nickel and copper, the wire has a diameter of 50-120 microns.

Obtained by a specified method of a grid placed in the package, have no seams and welded assemblies inherent in woven nets.

Known grid and have a number of disadvantages.

During the manufacture of nitric acid in the exothermic reactions high fever, along with oxidative atmosphere contributes to large losses of mass of the catalyst in the form of carry-over with the gas of the volatile noble metal oxides that in the absence of alloying alloys reduces the service life of the catalyst gauzes. In addition, non-alloy alloy, which is made known grid, reduces the mechanical properties of the catalyst package.

The task, which was aimed by the invention, is to increase the efficiency of the process of conversion of ammonia due to the high degree of oxidation, reduce the loss of mass of the catalyst, as well as longer service life, net package.

This object is achieved in that the package ha is Dov, volatilisation in the oxidation process, including knitted wire mesh made of alloys based on platinum or palladium, according to the invention contains a grid connected wire in one or two threads with the formation of the weave weft surface with repeats 2 or 3, or 4 needles, and the wire can be made of the following alloys, wt.%.

1. Palladium - 3-16

Rhodium - 3-11

Platinum - Rest

2. Rhodium - 3-11

Platinum - Rest

3. Palladium - 3-16

Rhodium - 3-11

Ruthenium - 0,1-1,0

Platinum - Rest

4. Tungsten - 3-10

Palladium - Rest

5. Copper - 3-10

Palladium - Rest

6. Nickel - 3-10

Palladium - Rest

Alloys 4 - 6 doped or tungsten in an amount of 0.1 to 0.5%, or yttrium in the amount of 0,05 - 0,50%.

When set package grid connected from wire of platinum-based first set on a course of movement of the gas and serve as a catalyst for the oxidation of ammonia, followed by installing the package from the nets, knitted from wire based on palladium, which acts as a collector of platinum, evaporates in the process of oxidation of the catalyst.

Neighboring mesh in the package are thus costulae 0,06 - 0.12 mm, and the thickness of the grid is 0.5 to 2.0 mm

Compared to the woven structure of the knitted mesh provides better performance by increasing the surface area and uniform contact with the gas stream.

To improve strength and increase the surface in contact with the gas, a version of the complete mesh of the two wire strands. Increasing the number of threads more than 2 impractical, because it increases the consumption of noble metals and catalytic properties of the grid remain almost unchanged.

The thinner the wire diameter, the less the mass of catalyst in the same surface and catalytic activity, but at the same time, this leads to a reduced service life of the package, and a significant increase in the diameter of the wire does not provide a sufficiently uniform distribution of gas flow and increases the weight of the catalyst. Manufacturer of wire mesh within the claimed diameter is optimal for the efficient operation of the catalyst package, and also allows you to ensure the optimum flow rate of noble alloys with sufficiently developed the working surface of the grid.

Selected type Vya is URS weave, and the uniform distribution of gas flow and low aerodynamic resistance, which is very important for the efficient operation of the package in the ammonia oxidation process. The proposed grid structure has a high tensile strength and resistance to blooming when thread breakage. Another advantage of this grid is the absence of fluctuations.

The number of repeats - the formation of the completed hinge line on each needle for 2, 3 or 4 moves the carriage - provides optimal mesh density.

In order to achieve high mechanical strength and increase the time of contact of the gas with the catalyst, the grid is of a thickness of 0.5 to 2.0 mm

When the bundle set of neighboring mesh laid in such a way that the direction of the loops they form an angle of 90o. This arrangement platinum mesh gives a more even distribution of the material of the catalyst volume and increases the time of contact with the gas, which in turn increases the conversion rate.

Assembled in the same way the package of palladium grids provides improved his catching ability by increasing the surface swept by the gas flow.

Compared with the known alloys used in catalyst grids, the proposed alloys are characterized by a lower content of platinum, and consequently lower losses because the losses of the catalyst grids above all it is part of platinum.

Replacement parts platinum palladium reduce the cost of the catalyst package without compromising its quality, because palladium in a series of catalytic activity in the oxidation of ammonia is in second place after platinum.

The package is made of grids based on palladium, to capture volatilisation of platinum catalyst, also provides increased efficiency of the entire catalytic process due to the fact that palladium grids are a catalyst for the oxidation of ammonia, and when the saturation of their surface platinum catalytic activity of this system increases dramatically and becomes openly the oxidation of ammonia, reducing the amount of platinum catalyst gauzes by 20-40%.

The presence of a platinum alloy for the manufacture of wire rhodium and ruthenium in the claimed limits increases high-temperature mechanical strength of the catalyst, and therefore increases its service life.

Increasing the amount of rhodium in the alloy more than 11 wt.% increases the fragility of the catalyst gauze and reduced activity of the catalyst due to the formation on its surface inactive rhodium oxide.

The increase in the content of ruthenium is more than 1 wt. % leads to the formation of cracks.

In the manufacture of nets from an alloy based on palladium was used tungsten and base metals - copper, Nickel, which have a strengthening effect on palladium. Replacement 3-10 wt.% palladium these components reduces the cost of precious metal without sacrificing his catching ability. As the experiments showed, the increase in base components in the alloy is more than 10 wt. % impractical, because it negatively affects the capture and heat resistance of the alloy.

Grid-based alloys of palladium alloyed with tungsten or yttrium, which greatly increases their about the use of knitted meshes of the proposed alloys in accordance with this invention provides improved oxidation of ammonia, reducing the weight loss of the catalyst package, reducing the deadweight losses of noble metals and reducing the weight of the package.

Examples of carrying out the invention

Example 1. The package is suitable for the oxidation of ammonia to nitric oxide and is a number of knitted nets stacked on top of each other and form a package. The number of grids depends on the type of reactor and may range from a few to tens.

The grid is connected to the knitting machine. View mating - surface weft with repeats 2 or 3, or 4 needles. The screen cloth is knitted from wire in one or two strands from an alloy of platinum-based (see table 1). The wire diameter was 0,06 -0,12 mm, the strength of the wire - 400 - 800 H/mm2extension to 2 - 6%.

The thickness of the finished knitted mesh was 1.5 mm, specific weight of 8.0 g/DM2.

When the bundle set of neighboring mesh was placed in such a way that the direction of the loops in adjacent grids formed angle 90o.

Characteristics of the package and the results of testing are presented in table 1.

Example 2. Package nets designed to capture platinum, evaporating with platinum catalyst. The package consists of a knitted mesh of alloys ass 4 needles. The screen cloth is connected with one or two wires of an alloy based on palladium. Wire diameter ranged from 0.06 to 0.12 mm, the Strength of the wire - 400-800 H/mm2elongation - 2-6%. The thickness of the finished knitted mesh of 0.5-2.0 mm, specific weight of 5.0-10.0 g/DM2depending on the wire diameter. When the bundle set of neighboring mesh was placed in such a way that the direction of the loops in them formed an angle of 90o.

Characteristics of the meshes and the results of their testing are shown in table 2.

Compared to similar devices offer a package of knitted gas-permeable grids provides:

increasing the degree of conversion of ammonia to NO;

reducing the weight loss of the catalyst;

increasing the mechanical strength;

increased service life;

the reduction of investment precious metals.

1. Package gas-permeable mesh of precious metals for catalytic processes, mainly for the catalytic oxidation of ammonia or for recovery of platinum group metals, volatile during the catalytic oxidation of ammonia, including knitted wire mesh made of an alloy based on platinum or palladium, characterized in that the grid connected wire in one of the Jena from an alloy of platinum-based contains, wt%:

Rhodium - 3 - 11

Platinum - Rest

or

Palladium - 3 - 16

Rhodium - 3 - 11

Platinum - Rest

or

Palladium - 3 - 16

Rhodium - 3 - 11

Ruthenium - 0,1 - 1,0

Platinum - Rest

or from an alloy based on palladium-doped tungsten or yttrium-containing, wt.%:

Tungsten - 3 - 10

Palladium - Rest

or

Copper - 3 - 10

Palladium - Rest

or

Nickel - 3 - 10

Palladium - Rest

when this mesh in the package are angled 90orelative to each other.

2. The package p. 1, wherein the mesh is made of wire with a diameter of 0,06 - 0,12 mm

3. The package p. 1, characterized in that the thickness of the knitted mesh is 0.5 to 2.0 mm

4. The package p. 1, wherein the wire is made of an alloy based on palladium-doped tungsten in an amount of 0.1 to 0.5%.

5. The package p. 1, wherein the wire is made of an alloy based on palladium-doped yttrium in the amount of 0,05 - 0,50%.

 

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FIELD: supported catalysts.

SUBSTANCE: invention claims a method for preparation of catalyst using precious or group VIII metal, which comprises treatment of carrier and impregnation thereof with salt of indicated metal performed at working pressure and temperature over a period of time equal to or longer than time corresponding most loss of catalyst metal. According to invention, treated carrier is first washed with steam condensate to entirely remove ions or particles of substances constituted reaction mixture, whereupon carrier is dried at 110-130oC to residual moisture no higher than 1%.

EFFECT: achieved additional chemical activation of catalyst, reduced loss of precious metal from surface of carrier, and considerably increased lifetime.

5 cl, 9 ex

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