Characterization of Poly(Acrylic) Acid-Modified Heterogenous Anion Exchange Membranes with Improved Monovalent Permselectivity for RED

Abstract

The performance of anion-exchange membranes (AEMs) in Reverse Electrodialysis is hampered by both presence of multivalent ions and fouling phenomena, thus leading to reduced net power density. Therefore, we propose a monolayer surface modification procedure to functionalize Ralex-AEMs with poly(acrylic) acid (PAA) in order to (i) render a monovalent permselectivity, and (ii) minimize organic fouling. Membrane surface modification was carried out by putting heterogeneous AEMs in contact with a PAA-based aqueous solution for 24 h. The resulting modified membranes were firstly characterized by contact angle, water uptake, ion exchange capacity, fixed charge density, and swelling degree measurements, whereas their electrochemical responses were evaluated through cyclic voltammetry. Besides, their membrane electro-resistance was also studied via electrochemical impedance spectroscopy analyses. Finally, membrane permselectivity and fouling behavior in the presence of humic acid were evaluated through mass transport experiments using model NaCl containing solutions. The use of modified PAA-AEMs resulted in a significantly enhanced monovalent permselectivity (sulfate rejection improved by >35%) and membrane hydrophilicity (contact angle decreased by >15%) in comparison with the behavior of unmodified Ralex-AEMs, without compromising the membrane electro-resistance after modification, thus demonstrating the technical feasibility of the proposed membrane modification procedure. This study may therefore provide a feasible way for achieving an improved Reverse Electrodialysis process efficiency.

Surface Modifications of Anion Exchange Membranes for an Improved Reverse Electrodialysis Process Performance: A Review

“…Dip coating is the process of immersing a membrane during a controlled period of time into a solution containing a modifying agent, to create an additional layer with desirable characteristics onto the surface of the membrane [53,54]. In a different approach, the solution used can also be in direct contact with only one side of the membrane, using two-compartment cells, in order to prepare one-side monolayer modifications [55], as represented in Figure 4. The importance of optimizing the modification conditions (i.e., immersion time and modifier concentration) as well as selecting the appropriate modifying agent to obtain a stable anionic polyelectrolyte layer on the surface of different Neosepta AEMs was discussed and demonstrated in 1995 [56], when two different anionic polyelectrolytes, namely a polycondensation product of sodium naphthalene and formaldehyde, and polystyrene sulfonic acids, respectively, were considered.…”

“…In particular, heterogeneous Ralex AEMs were modified by direct contact (during 24 h) with poly(acrylic) acid (PAA)-based solutions, which represents the use of a non-toxic and stable modifying agent [59,60]. The authors reported an improved surface hydrophilicity and monovalent membrane permselectivity as a function of different concentrations of PAA, without compromising the membrane electro-resistance [55].…”

“…Dip coating is the process of immersing a membrane during a controlled period of time into a solution containing a modifying agent, to create an additional layer with desirable characteristics onto the surface of the membrane [ 53 , 54 ]. In a different approach, the solution used can also be in direct contact with only one side of the membrane, using two-compartment cells, in order to prepare one-side monolayer modifications [ 55 ], as represented in Figure 4 .…”

Electrochemical Impedance Spectroscopy of Anion-Exchange Membrane AMX-Sb Fouled by Red Wine Components

“…Electrochemical impedance spectroscopy (EIS) is increasingly being used to study IEM fouling [ 26 , 27 , 28 , 29 , 30 , 31 ]. The method of equivalent electrical circuits (EEC) is most often applied for the interpretation of experimental spectra [ 28 , 29 , 30 , 31 ].…”

“…Electrochemical impedance spectroscopy (EIS) is increasingly being used to study IEM fouling [ 26 , 27 , 28 , 29 , 30 , 31 ]. The method of equivalent electrical circuits (EEC) is most often applied for the interpretation of experimental spectra [ 28 , 29 , 30 , 31 ]. For example, an increase in the ohmic resistance of a membrane, which is determined by processing a high-frequency EIS arc using the EEC method, is the basis for online registration of the effect of fouling on the transport characteristics of membranes in reverse and conventional ED [ 30 , 31 ].…”