Method for recovering platinum in a nitric acid plant

Claim 1

In the method for the recovery of platinum and/or rhodium lost from a platinum-containing catalyst during ammonia oxidation processes at temperatures above 850°C. by bringing said lost platinum and/or rhodium into contact with a foraminate element; the improvement which comprises utilizing for recovery purposes a foraminate element fabricated from a material consisting essentially of palladium and nickel, characterized by (a) a novel configuration whereby the initial product of mesh size (N) and wire diameter (d ) for said element is greater than at least about 0.2 and (b) where, for a given nitrogen throughput, the weight recovery efficiency (η' ) is a function of the wire diameter (d ) and mesh size (N) combination and weight recovery efficiency is improved by increasing the mesh size (N) at a given wire diameter or increasing the wire diameter (d ) for a given mesh size.

Claim 29

A method for recovering platinum lost from a platinum-containing catalyst gauze in a nitric acid plant, wherein the catalyst gauze is replaced periodically, the period being the catalyst gauze cycle length "Tp", wherein at least one recovery gauze consisting of at least a major proportion of palladium is placed closely adjacent to the catalyst gauze downstream of the catalyst gauze, characterized in that the recovery gauze cycle length "T", as calculated from the formula is in the range of from about 0.9 Tp to about 1.1 Tp, wherein W is the weight of the recovery gauze sheet, η is the recovery efficiency of the recovery gauze sheet as calculated according to the formula wherein "ξ is the volumetric void fraction of the gauze which is less than about 0.76-but greater than 0; "Sc" is the Schmidt number for the diffusion of oxidized platinum in the effluent from the catalyst gauze; "Re" is the Reynolds number based on the wire diameter and average velocity of the process stream just upstream of the recovery gauze, i.e., Re = G d w , where "G" is the mass velocity of the gaseous stream fed to the catalyst; "C" is the appropriate mass transfer correlation coefficient for the geometry of the gauze; "a" is the specific bulk surface area of the gauze; "m" is the appropriate mass transfer correlation exponent for the configuration of the gauze; "d w " is the diameter of the wires in the gauze, and "b" is the amount of platinum lost from the catalyst gauze for each ton of nitrogen (in ammonia) converted; and "L" is the loading or amount of nitrogen (in ammonia) passed over each square meter of the catalyst gauze per day.

Claim 30

A method for recovering platinum lost from a platinum-containing catalyst gauze in a nitric acid plant, wherein the catalyst gauze is replaced periodically, the period being the catalyst gauze cycle length "Tp", wherein at least one recovery gauze consisting of at least a major proportion of palladium is placed closely adjacent to the catalyst gauze downstream of the catalyst gauze, characterized in that the recovery gauze cycle length "T", as calculated from the formula is in the range of from about 0.9 Tp to about 1.1 Tp, wherein W is the weight of the recovery gauze sheet, η is the recovery efficiency of the recovery gauze sheet as calculated according to the formula wherein "ξ is the volumetric void fraction of the gauze which is less than about 0.76-but greater than 0; "Sc" is the Schmidt number for the diffusion of oxidized platinum in the effluent from the catalyst gauze; "Re" is the Reynolds number based on the wire diameter and average velocity of the process stream just upstream of the recovery gauze, i.e., Re = G d w , where "G" is the mass velocity of the gaseous stream fed to the catalyst; "C" is the appropriate mass transfer correlation coefficient for the geometry of the gauze; "a" is the specific bulk surface area of the gauze; "m" is the appropriate mass transfer correlation exponent for the configuration of the gauze; "d w " is the diameter of the wires in the gauze, and "b" is the amount of platinum lost from the catalyst gauze for each ton of nitrogen (in ammonia) converted; and "L" is the loading or amount of nitrogen (in ammonia) passed over each square meter of the catalyst gauze per day.

Claim 32

A method for recovering platinum lost from a platinum-containing catalyst gauze in a nitric acid plant, wherein the catalyst gauze is replaced periodically on a catalyst gauze cycle length "Tp", wherein at least one recovery gauze sheet consisting of a major proportion of palladium is placed closely adjacent to the catalyst gauze downstream of the catalyst gauze, characterized in that the geometric configuration of the recovery gauze is chosen such that the average recovery efficiency over the catalyst gauze cycle length exceeds 1 - exp (-3.45/L · 7 ) .

Claim 33

A method for recovering platinum lost from a platinum-containing catalyst gauze in a nitric acid plant, wherein the catalyst gauze is replaced periodically on a catalyst gauze cycle length "Tp", wherein at least one recovery gauze sheet consisting of a major proportion of palladium is placed closely adjacent to the catalyst gauze downstream of the catalyst gauze, characterized in that the geometric configuration of the recovery gauze is chosen such that the average recovery efficiency over the catalyst gauze cycle length exceeds 1 - exp (-3.45/L · 7 ) .

Claim 38

The method of claim27 wherein a multiplicity of recovery gauze sheets is provided, at least two of the sheets having a recovery gauze cycle length of from about 0.9 to about 1.1 Tp, and at least one of those two sheets has an average recovery efficicency over the catalyst cycle Tp in excess of 1 - exp (-3.45/L ·7 ).

Claim 39

A method of recovering platinum in a nitric acid plant in which the catalyst includes platinum, is scheduled to be changed substantially periodically, the period being the "catalyst gauze cycle length", comprising the step of inserting a recovery gauze into the stream of the plant downstream from the catalyst, characterized in that the recovery gauze consists essentially of a major proportion of palladium and a minor proportion of nickel, the geometrical configuration of the recovery gauze being such that but upon use, the recovery gauze swells such that the single sheet average recovery efficiency over the catalyst cycle exceeds that indicated in the table where L is the nitrogen loading of the plant:

Claim 40

A method of recovering platinum in a nitric acid plant in which the catalyst includes platinum, is scheduled to be changed substantially periodically, the period being the "catalyst gauze cycle length", comprising the step of inserting a recovery gauze into the stream of the plant downstream from the catalyst, characterized in that the recovery gauze consists essentially of a major proportion of palladium and a minor proportion of nickel, the geometrical configuration of the recovery gauze being such that but upon use, the recovery gauze swells such that the single sheet average recovery efficiency over the catalyst cycle exceeds that indicated in the table where L is the nitrogen loading of the plant:

Claim 42

A method of making a gauze for recovery of platinum lost from a platinum-containing catalyst in a nitric acid plant, comprising (1) measuring the flow rate, conditions and composition of the gaseous stream to be treated with the gauze, then (2) determining the physical properties of the stream, either by measurement or calculation; (3) determining the mass velocity (G), dynamic viscosity (µ) , and Schmidt No. (Sc) for the process stream in which the gauze is to be employed; (4) estimating the recovery efficiency of a selected gauze sheet based on the assumption that platinum recovery is essentially mass transfer limited; and fabricating a woven wire mesh sheet from wire consisting essentially of a major proportion of palladium and a minor proportion of an alloying metal, characterized in that the mesh size and wire diameter of the mesh are chosen such that upon use in the plant, over the catalyst cycle length of the plant, the sheet will recover a larger fraction of the platinum presented to it than is indicated for the nitrogen loading in the following table:

Claim 43

A method of making a gauze for recovery of platinum lost from a platinum-containing catalyst in a nitric acid plant, comprising (1) measuring the flow rate, conditions and composition of the gaseous stream to be treated with the gauze, then (2) determining the physical properties of the stream, either by measurement or calculation; (3) determining the mass velocity (G), dynamic viscosity (µ) , and Schmidt No. (Sc) for the process stream in which the gauze is to be employed; (4) estimating the recovery efficiency of a selected gauze sheet based on the assumption that platinum recovery is essentially mass transfer limited; and fabricating a woven wire mesh sheet from wire consisting essentially of a major proportion of palladium and a minor proportion of an alloying metal, characterized in that the mesh size and wire diameter of the mesh are chosen such that upon use in the plant, over the catalyst cycle length of the plant, the sheet will recover a larger fraction of the platinum presented to it than is indicated for the nitrogen loading in the following table:

Claim 44

A method for recovering platinum lost from the platinum-containing catalyst of a nitric acid plant in which the catalyst is scheduled to be changed substantially periodically, the period being the "catalyst gauze cycle length", comprising the step of inserting into the flow stream downstream of the catalyst gauze at least one sheet of recovery gauze containing a major proportion of palladium, characterized in that the geometrical configuration of the recovery gauze sheet is selected such that the average recovery efficiency of the gauze over the catalyst cycle of the plant will be: more than 49% if the plant operates at a loading of between 10 and 15 short tons of nitrogen in ammonia per square meter of catalyst gauze per day; more than 41% if the nitrogen leading is between 15 and 20 tons per square moter per day; more than 35% if the nitrogen loading is between 20 and 25 tons per square meter per day; more than 31% if the nitrogen leading is between 25 and 30 tons per square meter per day; more than 28% if the nitrogen loading is between 30 and 35 tons per square meter per day; more than 25% if the nitrogen loading is between 35 and 40 tons per square meter per day; more than 23% if the nitrogen loading is between 40 and 45 tons per square meter per day; more than 22% if the nitrogen leading is between 45 and 55 tons per square meter per day; more than 19% if the nitrogen leading is between 55 and 65 tons per square meter per day; more than 17% if the nitrogen loading is between 65 and 75 tons per square meter per day; more than 16% if the nitrogen loading is between 75 and 85 tons per square meter per day; more than 14% if the nitrogen loading is between 85 -and 100 tons per square meter per day; and more than 13% if the nitrogen loading is over 100 tons per square meter per day.

Claim 45

A method for recovering platinum lost from the platinum-containing catalyst of a nitric acid plant in which the catalyst is scheduled to be changed substantially periodically, the period being the "catalyst gauze cycle length", comprising the step of inserting into the flow stream downstream of the catalyst gauze at least one sheet of recovery gauze containing a major proportion of palladium, characterized in that the geometrical configuration of the recovery gauze sheet is selected such that the average recovery efficiency of the gauze over the catalyst cycle of the plant will be: more than 49% if the plant operates at a loading of between 10 and 15 short tons of nitrogen in ammonia per square meter of catalyst gauze per day; more than 41% if the nitrogen leading is between 15 and 20 tons per square moter per day; more than 35% if the nitrogen loading is between 20 and 25 tons per square meter per day; more than 31% if the nitrogen leading is between 25 and 30 tons per square meter per day; more than 28% if the nitrogen loading is between 30 and 35 tons per square meter per day; more than 25% if the nitrogen loading is between 35 and 40 tons per square meter per day; more than 23% if the nitrogen loading is between 40 and 45 tons per square meter per day; more than 22% if the nitrogen leading is between 45 and 55 tons per square meter per day; more than 19% if the nitrogen leading is between 55 and 65 tons per square meter per day; more than 17% if the nitrogen loading is between 65 and 75 tons per square meter per day; more than 16% if the nitrogen loading is between 75 and 85 tons per square meter per day; more than 14% if the nitrogen loading is between 85 -and 100 tons per square meter per day; and more than 13% if the nitrogen loading is over 100 tons per square meter per day.

Claim 49

A method of recovering platinum lost from the platinum-containing catalyst in a nitric acid plant, comprising the step of inserting at least one recovery gauze sheet containing a major proportion of palladium into the reaction stream downstream of the catalyst pack, the recovery gauze sheet being characterized in that the void fraction is less than .76.

Claim 50

A method of recovering platinum lost from the platinum-containing catalyst in a nitric acid plant, comprising the step of inserting at least one recovery gauze sheet containing a major proportion of palladium into the reaction stream downstream of the catalyst pack, the recovery gauze sheet being characterized in that the void fraction is less than .76.