Selection of the platinum-rhodium mesh content in nitric acid plants

This post was last edited by Lcy0214 on 2010-4-1 21:22. 1. Pure platinum is used as a catalyst; due to its softness, it has lower thermodynamic properties at normal or high temperatures； Adding rhodium to platinum to form a platinum-rhodium solid solution alloy mesh can improve its thermodynamic properties at room temperature or high temperatures. Adding palladium to platinum-rhodium alloys can enhance the properties of these alloys, improve their catalytic efficiency, increase the antiviral capacity of platinum meshes, and reduce platinum loss. The properties of platinum-rhodium alloys changed regularly as the rhodium content increased ； 2. The properties of various platinum meshes are as follows: Pt90%, Rh10%. Advantages: long service life, high mechanical strength, strong resistance to rhodium poisoning, good high-temperature resistance, strong catalytic activity, low platinum consumption, and light weight. Disadvantages: High rhodium content, poor resistance to rhodium oxidation, high cost; this mesh is suitable for high-temperature and high-pressure oxidation furnaces. Pt95%, Rh5% – Advantages: higher ammonia oxidation rate compared to Pt90%, Rh10%; less rhodium oxide is produced, and the lifespan is longer. Disadvantages: Poor resistance to poisoning; suitable for medium-pressure oxidation furnaces with well-treated ammonia-air filtration. Pt92%, Rh8% – the performance lies between these two options; the choice can be adjusted based on the prices of platinum and rhodium. Pt90%, Rh5%, Pd5%. Advantages: high ammonia oxidation rate, good anti-fouling property of the mesh, and high activity in a short period of time. Disadvantages: Activity decreases significantly after 60 days, it has poor antioxidant rhodium capacity, high platinum consumption, and weak high-temperature resistance. 3. Platinum meshes of various compositions have their own advantages and disadvantages; nitric acid manufacturers should conduct a comprehensive analysis taking into account factors such as the technical characteristics of their production facilities and the prices of precious metals, in order to select the appropriate platinum mesh. The atmospheric pressure method generally uses a ternary alloy (Pt90%, Rh5%, Pd5%), while the pressurized, double-pressurized, and high-pressure methods generally use binary alloys (PtRh10, PtRh5)

Lcy0214 provided quite detailed information; regarding the catalyst used in the nitric acid double-pressure oxidation furnace, we chose PtRh10. The temperature in the oxidation furnace is around 860°C, which is quite high, and this high temperature also imposes restrictions on the level of impurities present in the catalyst.