Catalyst – Product description
The Iron-Molybdenum catalyst MOC5 is used for the selective oxidation of methanol to formaldehyde in presence of an excess of air in fixed bed converters. It can be used pure (MOC5O) or diluted with an inert (MOC5I) or in a bed made by a combination of pure and diluted catalyst.
Description and chemical composition (Pure Product)
Tabletted rings with outside diameter 4.5-5 mm, internal hole diameter 2-2.2 mm, height 4.5-5 mm of:
| Iron-molybdenum oxide (iron polymolybdate) | |
| Iron content (as Fe) | 11±0.5 % w/w |
| Molybdenum content (as Mo) | 55.5±1.0 % w/w |
| Surface area | 5.5±0.5 m2/g |
| Pore volume | 0.20±0.05 ml/g |
| Physical properties | |
| Appearance | tabletted rings |
| Odour | odourless |
| Colour | grey-green |
| Bulk density (in a 22.1 mm i.d. tube) | 700-750 kg/m3 |
Packaging
The catalyst is delivered in returnable plastic drums, 40 kg per drum (pure) or 20 kg per drum (diluted).
Performance
The catalyst may be employed in multi-tube fixed bed reactors, of different design, of different tube inside diameter and with different heat transfer fluids (HTF). Typically is used in pressureless reactors with tubes inside diameter 22.1 mm and using molten salts as HTF.
The catalyst can work with HTF temperatures from 250 to 320 °C, with hot spot temperature up to 430°C; higher temperatures may reduce the catalyst life due to catalyst syntherization and molybdenum anhydride sublimation.
The catalyst can work with a methanol feed 7 – 9 %vol, below the lower ignition point of the methanol gas mixture.
At reactor outlet oxygen concentration must never be lower than 5 %vol.
The methanol fed to the catalyst must respect standard grade specifications. The following products or elements can act as poisons: chlorides, sulphur, sodium, heavy metals, carbonyls.
The average catalyst consumption, for well managed plants is 1 kg per 22-25 tons of formaldehyde 37% solution produced.