GB2036108A

GB2036108A - Woven Grids for Recovery of Precious Metals

Info

Publication number: GB2036108A
Application number: GB7849530A
Authority: GB
Original assignee: Mennica Panstwowa; Instytut Nawozow Sztucznych
Current assignee: Mennica Panstwowa; Instytut Nawozow Sztucznych
Priority date: 1978-12-21
Filing date: 1978-12-21
Publication date: 1980-06-25
Also published as: GB2036108B

Abstract

A woven grid for the recovery of platinum metals volatilising from a catalyst during the oxidation of ammonia in the production of nitric oxide is characterised in that some thicker wires are woven into the warp and/or weft. The difference in thickness may be from 30% to 1000% and the sets may be one thicker wire to every 10 to 200 thinner wires.

Description

SPECIFICATION A Grid of Precious Metals for the Recovery of Platinum Metals Escaping from a Catalyst During the Reaction, and Especially of Platinum During Oxidation of Ammonia The invention relates to a grid of precious metals for the recovery of platinum metals volatilising from a catalyst during a reaction, and especially of platinum volatilising during the oxidation of ammonia in the production of nitric oxide and nitric acid, In reactions conducted in the presence of catalysts containing platinum metals, at the incandescence temperature, a loss in the precious metals content of the catalyst occurs. Part of the platinum metals is voiatilised from the catalyst by the flowing reactants and is present in the end products of the reaction.Another part of the platinum metals deposits upon the inner surfaces of the reactors and in the pipe lines of the installation.

Part of the platinum metals escaping from the catalyst cannot be recovered. The costs thus arising considerably affect the economy of the process, especially the costs of the process of ammonia oxidation.

For the recovery of platinum escaping from the catalysts during the reaction according to publication No. 1 686 of Johnson Matthey s Company the grids used are made of a palladiumgold alloy having a different thickness of wire in one of the grids. The grids for the recovery of platinum, become brittle in use due to the diffusion of platinum into the palladium-gold alloy. In order to increase their strength several grids are spotwelded into a unit which is then fitted within the installation in the flow path of the reactants, behind the catalytic grids.

Another solution of the problem according to Polish patent No. 80333 consists in the presence of separating grids made of heat-resisting materials, inserted between the recovery grids, especially grids composed of heat resisting steels.

It has however been proved that the known methods of increasing the strength and the durability of the recovery grids have drawbacks as the flow of reactants through a unit of welded grids separated by heat-resisting grids is considerably reduced as a result of the additional resistance created at the welded points or due to the grids made of heat-resisting material. The resulting increased strength of the grid pack impedes the whole catalytic process due to the increased pressure drop. An additional drawback of the use of separating grids made from heat resisting material is a decrease in the activity of the recovery grids due to their contamination by the volatilisation of products from the heat resisting grids.

It has become evident that the grids according to the invention eliminate the drawbacks and unexpectedly enable the recovery of larger quantities of platinum metals volatilising during the reaction to be achieved, thus having an advantageous effect upon the progress of the process and increasing the effectiveness of the recovery of the platinum metals.

The grid according to the invention is woven from wires of different thicknesses, which are made from the same precious metals that have been used for the recovery of the platinum metals.

The differences in the wire thicknesses and the arrangement of the thicker wires in the woven structure depend upon the type of catalytic process. In processes operated at atmospheric pressure especially in the processes of ammonia oxidation, it is preferable to employ grids in which the difference in the thickness of the wires in the weave is from 30 to 400%.

In medium-pressure processes the preferred grids are those in which the thickness difference in the woven wires is from 60 to 600%.

In high-pressure processes the preferred grids are those in which the thickness difference in the woven wires is from 100 to 1000%.

The differences in the wire thickness as in the woven grids is related to the density of the grid and to the arrangement of the thick wires in relation to the thin wires.

It is advantageous to insert the thick wires every 10 to 100 thin wires when there is but a slight difference of thickness, whereas when there is a considerable difference in the thickness it is sufficient to insert them after every 1 5 to 200 thin wires.

The thick wires in the weave may be in the warp and in the weft; however, a undirectional arrangement with all such wires being woven into the warp or into the weft is also advantageous, and it considerably simplifies the manufacture of the grid.

The grid according to the invention is characterized by a considerably increased strength, when compared with a grid using the same wire thickness throughout the weave.

The grids, according to the invention, assembled in a unit are in direct contact one with another, and the surfaces of particular wires are utilized to the maximum degree for the process of recovery of the platinum metals.

The grid according to the invention advantageously affects the process of the recovery process, increasing its effectiveness.

Claims

1. A grid of precious metals for the recovery of platinum metals volatilising from a catalyst during a reaction, especially a platinum grid used for the oxidation of ammonia, characterised in that it contains wires having a greater thickness in th,Q weave made from the known precious metals used for the recovery of the said platinum metals, the differences in the thickness of the wires being from 30 to 1000%.

2. A grid according to claim 1 characterised in that the thicker wires in the weave are woven between the thinner wires after every 10 to 200 of the thinner wires.

3. A grid according to claim 1 and 2

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

SPECIFICATION A Grid of Precious Metals for the Recovery of Platinum Metals Escaping from a Catalyst During the Reaction, and Especially of Platinum During Oxidation of Ammonia The invention relates to a grid of precious metals for the recovery of platinum metals volatilising from a catalyst during a reaction, and especially of platinum volatilising during the oxidation of ammonia in the production of nitric oxide and nitric acid, In reactions conducted in the presence of catalysts containing platinum metals, at the incandescence temperature, a loss in the precious metals content of the catalyst occurs. Part of the platinum metals is voiatilised from the catalyst by the flowing reactants and is present in the end products of the reaction.Another part of the platinum metals deposits upon the inner surfaces of the reactors and in the pipe lines of the installation.

Part of the platinum metals escaping from the catalyst cannot be recovered. The costs thus arising considerably affect the economy of the process, especially the costs of the process of ammonia oxidation.

For the recovery of platinum escaping from the catalysts during the reaction according to publication No. 1 686 of Johnson Matthey s Company the grids used are made of a palladiumgold alloy having a different thickness of wire in one of the grids. The grids for the recovery of platinum, become brittle in use due to the diffusion of platinum into the palladium-gold alloy. In order to increase their strength several grids are spotwelded into a unit which is then fitted within the installation in the flow path of the reactants, behind the catalytic grids.

Another solution of the problem according to Polish patent No. 80333 consists in the presence of separating grids made of heat-resisting materials, inserted between the recovery grids, especially grids composed of heat resisting steels.

It has however been proved that the known methods of increasing the strength and the durability of the recovery grids have drawbacks as the flow of reactants through a unit of welded grids separated by heat-resisting grids is considerably reduced as a result of the additional resistance created at the welded points or due to the grids made of heat-resisting material. The resulting increased strength of the grid pack impedes the whole catalytic process due to the increased pressure drop. An additional drawback of the use of separating grids made from heat resisting material is a decrease in the activity of the recovery grids due to their contamination by the volatilisation of products from the heat resisting grids.

It has become evident that the grids according to the invention eliminate the drawbacks and unexpectedly enable the recovery of larger quantities of platinum metals volatilising during the reaction to be achieved, thus having an advantageous effect upon the progress of the process and increasing the effectiveness of the recovery of the platinum metals.

The grid according to the invention is woven from wires of different thicknesses, which are made from the same precious metals that have been used for the recovery of the platinum metals.

The differences in the wire thicknesses and the arrangement of the thicker wires in the woven structure depend upon the type of catalytic process. In processes operated at atmospheric pressure especially in the processes of ammonia oxidation, it is preferable to employ grids in which the difference in the thickness of the wires in the weave is from 30 to 400%.

In medium-pressure processes the preferred grids are those in which the thickness difference in the woven wires is from 60 to 600%.

In high-pressure processes the preferred grids are those in which the thickness difference in the woven wires is from 100 to 1000%.

The differences in the wire thickness as in the woven grids is related to the density of the grid and to the arrangement of the thick wires in relation to the thin wires.

It is advantageous to insert the thick wires every 10 to 100 thin wires when there is but a slight difference of thickness, whereas when there is a considerable difference in the thickness it is sufficient to insert them after every 1 5 to 200 thin wires.

The thick wires in the weave may be in the warp and in the weft; however, a undirectional arrangement with all such wires being woven into the warp or into the weft is also advantageous, and it considerably simplifies the manufacture of the grid.

The grid according to the invention is characterized by a considerably increased strength, when compared with a grid using the same wire thickness throughout the weave.

The grids, according to the invention, assembled in a unit are in direct contact one with another, and the surfaces of particular wires are utilized to the maximum degree for the process of recovery of the platinum metals.

The grid according to the invention advantageously affects the process of the recovery process, increasing its effectiveness.

Claims

1. A grid of precious metals for the recovery of platinum metals volatilising from a catalyst during a reaction, especially a platinum grid used for the oxidation of ammonia, characterised in that it contains wires having a greater thickness in th,Q weave made from the known precious metals used for the recovery of the said platinum metals, the differences in the thickness of the wires being from 30 to 1000%.

2. A grid according to claim 1 characterised in that the thicker wires in the weave are woven between the thinner wires after every 10 to 200 of the thinner wires.

3. A grid according to claim 1 and 2 characterised in that the thicker wires have been woven undirectionally into the warp or into the weft of the grid.

New Claims or Amendments to Claims filed on 12 February 1980.

New or Amended Claims:

1. A grid of precious metals for the recovery of platinum metals volatilising from a catalyst during a reaction, especially a platinum grid used for the oxidation of ammonia, characterised in that it contains wires having a greater thickness in the weave made from the known precious metals used for the recovery of the said platinum metals, the differences in the thickness of the wires being from 30 to-l 0009/0.