Catchment Gauze
The mechanism of metal losses during production is as follows: During the ammonia oxidation process platinum is lost mainly due to volatilization but mechanical losses can also be an important contributor to overall losses.
The degree of mechanical loss will depend on plant conditions, accounting for 20 to 25% of the total loss.
Palladium oxidizes at temperatures below 750 °Ñ and decomposes to palladium at higher temperatures.
2Pd + O2 = 2PdO 750 °Ñ
2PdO = 2Pd+O2 750 °Ñ
2Pd + PtO2 = Pt + 2PdO
Platinum oxide (Pt2O) lost from catalyst gauzes is reduced to platinum metal and deposited onto the surface of the palladium gauze. Platinum alloys with the palladium to form a solid solution.
Multilayer structure 800 °Ñ
Pd and PdO evaporate 877 °Ñ
PtO2 ↓ Î2 ↓
Pd Vapour
2PdO = Pd + Î2
2Pd + PtO2 = Pt ↓ + 2PdO
Pd Vapour
Pd Metal
Rhodium oxide (Rh2O3) is lost to a much extend and is deposited mechanically onto the catchment surface.
The design and number of gauzes will depend on the following criteria:
| Metal Loss | mg/t |
| Tonnage (100 % Nitric Acid) | t/d |
| Campaign length days | days |
| Burner Diameter | mm |
| Operationg Pressure | MPa |
Installing the catchment gauze pack improves the catalyst performance during the plant operation.
JSC Krastsvetmet supplies individual palladium–based (95% Pd) catchment gauzes made from Pd-Au, Pd-Ni and Pd-W alloys, as well as fully assembled systems enabling quick installation and easy handling and transportation to the site. Depending on the gauze diameter the catchment gauze system can be assembled as a circle, quarters or an eight segment pack. The individual segments are hinged together with stainless steel wire.
Packs for Shipment
Each palladium gauze is separated with a high temperature steel mesh such as Fecral (Fe-Al-Cr).
The two standard separator screens used have the following specification:
Type A: 200 mesh/cm2, 0,18 mm wire dia;
Type B: 49 mesh/cm2, 0,42 mm wire dia.
22 % Ñã, 4,5 % AI, Balance Fe.
