Influences of inorganic salts on the pervaporation properties of zeolite NaA membranes on macroporous supports

Abstract

Zeolite NaA membranes were hydrothermally synthesized on the macroporous supports using varying-temperature hot dip-coating seeding methods, and then were applied to pervaporative dehydration of the alcohol/water/salt mixtures at various temperatures to investigate the influences of salts on the pervaporation performance. Five kinds of salts NaCl, NaNO3, KCl, MgCl2, and CaCl2 were chosen to examine the effects of salt concentration, cations, and anions on the membrane performance. For the model system of ethanol/H2O/NaCl mixture, the water flux decreased largely with increasing salt concentrations which resulted from the reduced water driving force/activity and negative salt physical blocking on the outer membrane surface. For different cations, potassium ion led to the largest flux drop of 58.10%, while sodium ion, calcium ion, and magnesium ion for 25.88%, 22.31%, and 24.91%, respectively. This could be mainly attributed to a joint electrostatic interaction/ion exchange action.Flushing regeneration of the NaA membranes showed that complex flux behaviors were observed for the different salts. The water flux recovered up to 91.23% and 82.47% for the NaCl and NaNO3 system, respectively, indicating that the physical salt blocking effect on the flux drop can be removed therefore is reversible. The water flux recovered to 50.00% and 116.92% for salts of KCl and CaCl2, respectively. The irreversible flux drop probably resulted from the ion exchange and ion blocking effects. This work demonstrates that inorganic salts in the alcohol/H2O mixture decreased the flux or separation selectivity and should be avoided in industrial applications.