Modeling of the streaming potential through porous bipolar membranes

The streaming potential of a porous bipolar membrane (BM) composed of a cation-exchange layer (CEL) and an anion-exchange layer (AEL) is presented theoretically. The theoretical approach is based on the motion equation, the nonlinear Poisson-Boltzmann equation and the flow conservation law. It is shown that the global streaming potential (SPG) of the bipolar membrane is mainly dependant on such parameters as the zeta potential, pore radius, porosity and thickness of each layer. If all the above-mentioned parameters of each layer are equal, SPG is zero, which means that the bipolar membrane reaches the isoelectrical state. Furthermore, with other parameters unchanged, SPG decreases with the increase of the absolute values of zeta potential and thickness of CEL, and increases as the pore radius and porosity of CEL increases. The effect of AEL on SPG is opposite to that of CEL. Such results were also validated by qualitative experiments.