Abstract
Abstract Classical and chronopotentiometric characterization of the electrodialysis module at the same concentrations of diluate and concentrate was performed. Limiting current was determined from the Cowan-Brown plot, the current efficiency and the mean transport number of counterions – from the concentration changes on the exit of the ED module. The electric resistance was determined from the chronopotentiometric curve. For electric currents higher than the limiting one, the transition time (inflection point) was observed. Thus, having such curves for different values of electric current, the limiting current can be roughly estimated. To estimate a mean counterion transport number from the transition time, an equation, analogous to the Sand equation, should be developed which include both types of membrane.
Highlights
Electrodialysis (ED) is a membrane process driven by the electric force which found application in many different areas [1, 2]
The main characteristics of the membrane stack used in the ED system, working in given conditions include the limiting current, current efficiency, module electric resistance, which determine energy efficiency of the process
It can be used for the determination of ion transport numbers in a single membrane [9] and of the system resistance [10]
Summary
Electrodialysis (ED) is a membrane process driven by the electric force which found application in many different areas [1, 2]. The main characteristics of the membrane stack used in the ED system, working in given conditions (electrolyte, concentration, flow velocity, etc.) include the limiting current, current efficiency, module electric resistance, which determine energy efficiency of the process. [5,6,7,8] It can be used for the determination of ion transport numbers in a single membrane [9] and of the system resistance [10]. Koter module contains two types of ion-exchange membranes which can differ in the degree of concentration polarization at their surfaces. We may expect that the limiting current, Ilim, covers a certain range of values and the transition time observed for a single membrane in the overlimiting current range for the ED stack may not be clearly seen.
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