Improving electrodialysis based water desalination using a sulfonated Diels-Alder poly(phenylene)

Desalination performance using electrodialysis (ED), and electrochemical and state of water analysis is reported for the acid and sodium forms of a sulfonated Diels-Alder poly(phenylene)s (sPP) series. sPP ionomers had proton conductivities reaching 122 mS/cm with a water uptake of 105 wt%. At this composition, its film conductivity and water uptake in the sodium form decreased to 19 mS/cm and 42 wt%. Atomic force microscopy and x-ray scattering indicate that the rigid poly(phenelyne) backbone results in a highly homogeneous intermediate phase containing large, disperse, and hydrophilic aggregates. Liquid transport experiments revealed that alcohol and sodium chloride diffusion is significantly lesser for the sPP series, which confirms differences in hydrophilic domain size and connectivity. In a working electrodialysis system, sPP (IEC=1.4 meq/g) desalinated 1.0 L of 0.1 wt% NaCl using 5.8 J/g or 5.8 kJ within 44 min. Commercial cation (PC-SK) and anion (PC-SA) exchange membranes designed for brackish water desalination required 8.4 J/g or 8.4 kJ and 79 min for the same volume and concentration. ED performance was adequately modeled by the Nernst-Planck equation, which is comprised of electroosmotic (migration) and diffusion contributions.