Interplay between Forced Convection and Electroconvection during the Overlimiting Ion Transport through Anion-Exchange Membranes: A Fourier Transform Analysis of Membrane Voltage Drops

Electrodialysis (ED) applications have expanded in recent years and new modes of operation are being investigated. Operation at overlimiting currents involves the phenomenon of electroconvection, which is associated with the generation of vortices. These vortices accelerate the process of solution mixing, making it possible to increase the transport of ions across the membranes. In this work, frequency analysis is applied to investigate the interaction between different parameters on the development of electroconvection near anion-exchange membranes, which would provide a basis for the development of ED systems with favored electroconvection. Chronopotentiometric curves are registered and Fast Fourier Transform analysis is carried out to study the amplitude of the transmembrane voltage oscillations. Diverse behaviors are detected as a function of the level of forced convection and current density. The synergistic combination of forced convection and overlimiting currents leads to an increase in the signal amplitude, which is especially noticeable at frequencies around 0.1 Hz. Fast Fourier Transform analysis allows identifying, for a given system, the conditions that lead to a transition between stable and chaotic electroconvection modes.

Automated summary

The use of electrodialysis (ED) has expanded in recent years with the investigation of new modes of operation. Overlimiting currents in ED involve electroconvection and the generation of vortices, which enhance the mixing process and improve ion transport across membranes. This study applies frequency analysis to investigate the interaction of different parameters on the development of electroconvection near anion-exchange membranes, providing insights for the development of ED systems with desired electroconvection. Chronopotentiometric curves and Fast Fourier Transform analysis are used to study transmembrane voltage oscillations. The results show diverse behaviors depending on forced convection level and current density, and the synergistic effect of forced convection and overlimiting currents increases signal amplitude, particularly at frequencies around 0.1 Hz. Fast Fourier Transform analysis identifies the conditions that lead to a transition between stable and chaotic electroconvection modes in a given system.