Development of Mass Transfer Model of Electrochemically Switched Ion Permselective Membrane Separation Process

Abstract

Purposes Electrochemically switched ion permselective (ESIP) is a novel ion selective membrane separation technology, which has been applied for the efficient, continuous and selective separation of low-concentration target ions. However, the ion transfer in the ESIP membrane is disobedient to the Nernst-Planck theory, and the development of mass transfer model of ESIP contributes to the understanding of ESIP separation process. Methods In the ESIP membrane separation system, a modified Nernst-Planck model was proposed to study the mass transfer behavior in the dynamic field coupled with the double pulse potential on the membrane and the cell voltage on the electrode compartment. According to Donnan equilibrium and electroneutrality hypothesis, the steady state model of ion transfer in ESIP membrane separation process was established. The effects of current density, membrane thickness and ionic active site concentration on ion concentration and resistance distribution in membrane separation system were investigated by numerical simulation. Findings The results show that in the diffusion layer of feed solution and the membrane phase, the membrane thickness and the ionic active site concentration have great influence on the ion concentration distribution, and reducing the membrane thickness and increasing the ionic active site concentration are the main ways to improve the ion mass transfer. Under the influence of high current density, thin membrane and ionic active site concentration, resistance in the diffusion layer of feed solution plays a dominant role in the overall resistance, and the ion mass transfer rate can be increased by increasing the flow rate or decreasing the chamber thickness. Conclusions At low current density and thick membrane, the resistance of Donnan layer plays a dominant role, and the ion mass transfer rate is improved by increasing the ionic active sites of the membrane.

Keywords

• electrochemically switched ion permselective membrane
• ion mass transport
• numerical simulation
• concentration distribution
• resistance distribution