Synthesis of a monovalent selective cation exchange membrane to concentrate reverse osmosis brines by electrodialysis

Abstract In this work, novel monovalent selective cation exchange membranes (CEMs) with different mixtures of polyvinylidene fluoride (PVDF) and sulfonated PVDF (S-PVDF) were synthesized. The selected composite membranes were modified by surface polymerization of polyaniline (PANi) to improve their monovalent cation selectivity. PANi was doped with p-toluene sulfonic acid (pTSA) or l -valine (2-amino-3-methylbutanoic acid) and the selectivity of each CEM was determined. Membrane properties, such as chemical composition, water uptake, ion exchange capacity, permselectivity, contact angle and crystallinity were measured. The influence of the applied voltage was also studied. The newly developed membranes were used for electrodialytic concentration of NaCl from synthetic reverse osmosis (RO) brine. Doped membranes with pTSA (SNaMg = 0.13, SNaCa = 3.59) and valine (SNaMg = 0.09, SNaCa = 0.8) have a higher selectivity for sodium than the composite ones (SNaMg = 0.63, SNaCa = 6.82). Moreover, the increase of applied voltage results in an increase of the selectivity for monovalent ions.