Modified alginate composite membranes for the dehydration of acetic acid

Abstract

Alginate composite membranes cross-linked with 1,6-hexanediamine (HDM) or poly(vinyl alcohol) (PVA) were prepared by casting an aqueous solution of alginate and HDM or PVA on a hydrolyzed microporous polyacrylonitrile (PAN) membrane and characterized by pervaporation separation of acetic acid/water mixtures. The influence of hydrolysis of PAN support layer and HDM content in dense layer on separation performance of the composite membrane was studied and it was shown that both could improve the permeation rate and the selectivity of the membrane greatly. The counter cation of alginate coatings as dense separating layer also influenced the pervaporation properties of the membrane, the flux was higher for K + than for Na +, while the separation factor showed an opposite tendency. This sodium alginate (SA) composite membrane cross-linked with HDM has a high separation factor of 161 and a good permeation rate of 262 g/m 2 h for pervaporation of 85 wt.% acetic acid aqueous solution at 70°C. The separation performance varies with feed composition and operating temperature and the results exhibit that the separation factor and the flux of this membrane increase with rise in the operating temperature and water content in feed. However, the cross-linked alginate composite membrane with PVA has much lower separation properties. At the same time, compared to the alcohol/water system, this membrane gives lower separation selectivity for the acetic acid/water mixture regardless of higher boiling point and molecules’ volume of acetic acid. Therefore, the transport mechanism of acetic acid molecules through this kind of membrane is also proposed.