Constructional material of packings

In chap. 4.2 it was alreadj pointed out in how far the chemical nature of the material of which the column packing is made may influence the separation. The materials in question are glass, porcelain, earthenware, various metals and their alloys and recently also plastics. Glass or a ceramic material is in general preferred on account of its resistance to corrosion and low price. Porcelain should be hard-baked and free from iron, as catalytic effects may otherwise occur. For high efficiencies packing made of 18 8 stainless steel wire or wire gauze is unsurpassed. 

The differences in the separating effect found with wire-gauze packing made of various alloys are explained by Fuchs [133], on the strength of work done by Forsythe et al. [134], as being due to differences in the wettability of the metals and to 

The basic advantages of packings made of plastics as compared to other materials are [137]  

The relatively high separating efficiency of packings made of plastic material with a low wettability is interpreted by Teller [138] as resulting from the formation of an interstitial hold-up due to the low energies of adhesion involved c,f. chap. 4.2). This hold-up extends the residence time of the liquid phase in the column. Teller s polyethylene Tellerettes (Fig. 356) yield a relative free vohune of 83%. They are shaped such that the two phases encounter relatively small solid surfaces by which they are divided and diverted. 

Tests have shown that the polymers polytetrafluoroethylene and polypropylene arc suitable packing materials for columns using concentrated sulphuric acid or acid water as liquids [143]. 

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