Ionomer‐coated filtration membranes as an alternative to ion‐exchange membranes for demineralization by electrodialysis

Abstract

Industrial application of ion‐exchange membranes, the key component of many electro‐membrane processes, is often hindered due to their high cost—result of complex fabrication methods and use of highly engineered precursors. As an alternative to conventional anion‐exchange membrane (AMX), this study focuses on the fabrication of cation‐coated filtration membranes (CCFM‐Type 1 and CCFM‐Type 2) by depositing a thin layer of crosslinked branched polyethyleneimine (PEI)‐based ionomer on top of the porous substrate. The use of commodity precursors (PEI) in combination with energy efficient fabrication processes ensures a low end‐cost for CCFMs. The properties and the performances of these membranes are evaluated and compared with AMX. Though ionic conductance of both CCFMs is found to be lower than AMX, similar electrochemical behavior is observed for all three membranes. In terms of performance, the highest NaCl demineralization rate is given by CCFM‐Type 2, while whey demineralization rate for all three membranes is similar. Energy consumption during both processes is increased for CCFMs probably due to noticeably higher global resistance which the ED system reaches during the process. These promising results suggest the possible application of these cost‐effective CCFMs in electrodialysis demineralization processes as an alternative to commercial AMX at an industrial level.

Impact of Hierarchical Cation-Exchange Membranes’ Chemistry and Crosslinking Level on Electrodialysis Demineralization Performances of a Complex Food Solution

“…Overall, a low thickness of the ion-exchange layer is beneficial for the conductivity of the membrane. Indeed, ionomer coatings contribute to a decrease in conductivity of the hCEM [ 12 ]; therefore, maintaining low thickness is seen as beneficial for the performance of the membrane. Finally, hCEMs were significantly thicker than the reference (+66%), due to a significant contribution of the substrate.…”

“…To combine the desirable transport properties of homogeneous materials with the stability and simple fabrication of heterogeneous membranes, novel hierarchically structured anion-exchange membranes have been recently developed [ 11 , 12 ]. Hierarchical ion-exchange membranes (hIEMs) are composed of a highly porous substrate coated with a thin layer of ion-exchange polymer.…”

“…This concept allows for decoupling the mechanical and transport properties of the membrane individually. Moreover, this approach enables limiting the thickness of the ionomer layer (well below 50 μm), which favors the conductivity and enables material savings on the ionomer precursors [ 11 , 12 ]. Recently, it has been reported that cation-exchange coatings of hierarchical exchange membranes (hCEMs) can be fabricated using UV curable formulations containing urethane acrylate oligomers and monomers [ 13 ], or using UV-initiated radical polymerization of formulations containing acrylic oligomers and monomers [ 14 ].…”

Impact of Formulation of Photocurable Precursor Mixtures on the Performance and Dimensional Stability of Hierarchical Cation Exchange Membranes

“…As the mechanical properties of the composite membrane are governed by the supporting layer, the ion-exchange performance of the membrane can be tuned by the selection of monomers which form an ionomer of a structure that normally would not possess mechanical properties to form a self-supported membrane. 20 The UV curing employed in the fabrication of ionomer coatings leads to the shrinkage of the coating layer when the liquid formulation of monomers hardens under UV exposure. Ionomers formed by the radical polymerization of sulfonated low-molecular-weight functional monomers with cross-linkers such as, for example, divinylbenzene (DVB), are prone to shrinkage since the dense and highly cross-linked polymer network is formed.…”

Recent developments of polysaccharide‐based double‐network hydrogels

“…The molecular chains in the fully chemically cross‐linked network are linked to each other by irreversible covalent bonds. The most common chemically cross‐linked agents are glutaraldehyde, 123 PEGDE, 124 genipin, 125 epichlorohydrin (ECH), 126 gelatin methacryloyl (GelMA), 127 and N,N‐methylene bis‐acrylamide (MBAA) 128 . Yang et al 129 used ECH cross‐linked regenerated cellulose (RC) and MBAA cross‐linked PAAm to form a dual chemically cross‐linked network (Figure 12A).…”