Limited affordable current density of ca. 0.2 A cm−2 is a major drawback in bipolar membrane (BPM) electrodialysis technology. At higher current densities, the diffusion of water into the BPM interface between the anion and cation exchange layers becomes the rate-limiting step for the water dissociation process. The extended use of the BPM setup at such high current densities, however, results in dehydration of the membrane, an increase in its resistance, and irreversible damage to the BPM. A new experimental setup intended to enable high current densities to be safely used is described. The setup comprises a BPM made of a commercial anion exchange membrane to which a thin (<60 μm) sulfonated polyphenyl sulfone layer (TCL) is glued. Between the TCL and an adjacent commercial cation exchange membrane, a solution of polystyrene sulfonic acid (PSSA) is circulated through a net. This setup enables water to diffuse at a high rate through the TCL into the interface where the dissociation process occurs. The composition of the circulating solution prevents the excessive leakage of anions through the TCL into the solution of the basic product. Current densities of 0.4–0.5 A cm−2 were achieved with comparatively low voltage drops on the BPM and without limiting the rate of water diffusion.
- Bipolar membrane
- Water dissociation