Preparation of polyelectrolyte complex membranes by the electric-field enhanced method and investigation of the effect of preparation conditions on the membranes’ pervaporation performance

In this study, multilayered polyelectrolyte complex membranes (PECMs) were formed on top of the polyacrylonitrile (PAN) substrate membrane by using the electric-field enhance method. It was found that the treatment of NaOH on the polyacrylonitrile substrate membrane could improve the affinity between the polyelectrolyte solution and the substrate membrane. It also makes the substrate denser, causing higher selectivity but lower flux.

The pervaporation performance of the multilayered polyelectrolyte complex membranes is influenced by the PH value of the polyelectrolyte solution. The ionization degree of the –COOH functional group of the PAN substrate membrane and the ionization degree of the -NH2 functional group of the PEI polyelectrolyte are influenced by the PH value of the PEI polyelectrolyte solution. The ionization degree of the –COOH functional group of the PAA polyelectrolyte and the ionization degree of the -NH2 functional group of the PEI layer are influenced by the PH value of the PAA polyelectrolyte solution. Prepared by using adequate PH value of PEI and PAA polyelectrolyte solution, the polyelectrolyte complex membrane will have higher ionic cross-linking density and higher selectivity of the pervaporation of the isopropanol aqueous solution. With suitable conditions which the PH value of PEI polyelectrolyte solution is 8 and the PH value of PAA polyelectrolyte solution is 6, polyelectrolyte composite membranes with on PEI/PAA bilayer exhibited a flux of 1123 (g/m2hr) and a permeate water concentration of 98.2 wt % for the dehydration of 90 wt % of isopropanol aqueous solution at 50°C.

In addition, it was found that the pervaporation performance of the polyelectrolyte complex membrane depends on the direction of the electric field and applied voltage during the fabrication process. Compared to the
polyelectrolyte complex membrane prepared in positive electric field, the polyelectrolyte complex membranes prepared in negative electric field have higher flux and lower permeate water concentration. With the increasing applied voltage of the negative electric field, flux of the polyelectrolyte complex membrane increases and the permeate water concentration of the polyelectrolyte complex membrane decreases.