Fabric selection for solid-liquid filtration

The key parameters in fabric selection have been described (Hardman, 1994) as the thermal and chemical conditions, filtration requirements, equipment considerations and cost. 

By comparison, as other polymer types are of higher density and generally more expensive, they tend to be used where their physical and/or chemical properties significantly out-perform those of polypropylene. For example, fibres and filaments in the polyamide family, whilst unable to compete with polypropylene in strongly acidic conditions, are notably tougher and more durable than polypropylene. As a result, they are often found in less demanding chemical environments where high resistance to harsh abrasive 

E = Excellent, VG = Very Good, F = Fair, G = Good and P = Poor. 

Polyester fibres are also tougher than polypropylene, and are again used where oxidising conditions are present, but on this occasion acidic conditions preclude the use of nylon. Polybutylene terephthalate (PBT) is a particularly tough variation but, like Polyamide 11, is also only available in monofilament form. On the other hand, unlike polypropylene and polyamide, all polyester fibres/filaments are severely degraded by strong alkaline conditions, the ester link in the molecular chain being attacked as shown in Fig. 7.9. 

The presence of steam, which may be used for example to express more product from the filter cake in oils and fats filtration, will also cause polymer chain scission through hydrolysis, again leading to rapid fibre degradation. 

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