R. Messalem et al., NOVEL ION-EXCHANGE SPACER FOR IMPROVING ELECTRODIALYSIS - II - COATEDSPACER, Journal of membrane science, 138(2), 1998, pp. 171-180
Ion-conducting spacers were prepared by applying an ion-exchange coati
ng to commercially available polypropylene netting. Homogeneous and he
terogeneous types of coating were used. Homogeneous anion-exchange coa
ting consisted of bromomethylated and aminated polysulfone, homogeneou
s cation-exchange coating of sulfonated polysulfone. All heterogeneous
coatings consisted of ground ion-exchange resin, embedded in crosslin
ked poly(vinyl alcohol). All the coated spacers increased the rate of
desalting of sodium chloride solutions, at concentrations of 20 mM or
less. The effect increased with the ion-exchange capacity of the space
r per unit area. The spacers suppress polarization, leading to increas
ed current efficiency and decreased cell resistance. As expected, larg
est decrease of cell resistance is obtained in dilute solutions, <3 mM
. The dearest effect on efficiency was observed in ED with heterogeneo
us ion-exchange membranes, which are by themselves highly polarizing.
Most experiments were carried out with anion-exchange spacers, minimiz
ing the water splitting which takes place at the surface of the ion-ex
change membrane. Introduction of an anion-exchange spacer near the het
erogeneous anion-exchange membrane and a cation-exchange spacer near t
he heterogeneous cation-exchange membrane led to a dramatic increase i
n current efficiency. (C) 1998 Published by Elsevier Science B.V.