Membrane with juxtaposed parallel bands - of anion and cation exchange polymers, used for dialysis e.g. demineralisation of sugar

摘要

Prepn. of membranes with parallel juxtaposed bands, alternately anion- and cation-exchanging ('hermaphrodite' membranes) is carried out by (a) running >=1 liq. filament which is a soln. of an anion-exchanging polymer onto a solid support, pref. a reinforcing support for the membrane, (b) running >=1 liq. filament which is a soln. of a cation-exchanging polymer onto the same support, side by side with the first, either simultaneously or successively, (c) evaporating. Solvent, and (d) opt. hot pressing the membrane. Pref. the discharges are made onto a cylinder, using two spinnerets side by side, these being displaced parallel to the axis of the cylinder at a rate such that the cylinder makes one turn as the spinneret is displaced by the width of two bands (one anionic and one cationic). This can be achieved using an Archimedean screw. The membranes are used for selective dialysis and piezodialysis. They permit pref. transport of ionic species,: and hence can be used for the demineralisation of the juice from sugar refineries or the purification of aminoacids.