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Category: Industrial Processes
Subject: Questions about platinum/rhodium catalyst gauzes used for ammonia oxidation
Q: In a gauze pack used for ammonia oxidation, how are the number of gauzes, the mesh size of the gauze and the wire diameter determined.
How is the percentage of rhodium in the catalyst decided?
The number and structure of the catalyst gauzes in a gauze pack will depend on the type of plant in which it will be used. The parameters that are important in making these decisions are: the operating pressure of the burner; the capacity of the plant (tonnes /day); the campaign length; and the diameter of the burner.
For the gauze material, generally 5%Rh/95%Pt is the alloy material used as wire to knit or weave the gauzes for nitric acid production. This material gives the optimum conversion efficiency. However, alternative alloys including ternary materials, including palladium, are also used.
By comparison, the alloy generally used for manufacturing Caprolactam and Hydrogen Cyanide is 10% Rh/90% Pt.
Answer posted February 2005
Submitted by: Mr Dharmeshwaran Natesan
Affiliation: Retd. Chemist, Ordnance Fys.
Answered by: Garry Crooks
Affiliation: Johnson Matthey Noble Metals