The interplay between the ion exchange capacity, water content and concentration dependences of conductivity, diffusion permeability, and counterion transport numbers (counterion permselectivity) of CJMA-3, CJMA-6 and CJMA-7 (Hefei Chemjoy Polymer Materials Co. Ltd., China) anion-exchange membranes (AEMs) is analyzed using the application of the microheterogeneous model to experimental data. The structure–properties relationship for these membranes is examined when they are bathed by NaCl and Na2SO4 solutions. These results are compared with the characteristics of the well-studied homogenous Neosepta AMX (ASTOM Corporation, Japan) and heterogeneous AMH-PES (Mega a.s., Czech Republic) anion-exchange membranes. It is found that the CJMA-6 membrane has the highest counterion permselectivity (chlorides, sulfates) among the CJMAED series membranes, very close to that of the AMX membrane. The CJMA-3 membrane has the transport characteristics close to the AMH-PES membrane. The CJMA-7 membrane has the lowest exchange capacity and the highest volume fraction of the intergel spaces filled with an equilibrium electroneutral solution. These properties predetermine the lowest counterion transport number in CJMA-7 among other investigated AEMs, which nevertheless does not fall below 0.87 even in 1.0 eq L−1 solutions of NaCl or Na2SO4. One of the reasons for the decrease in the permselectivity of CJMAED membranes is the extended macropores, which are localized at the ion-exchange material/reinforcing cloth boundaries. In relatively concentrated solutions, the electric current prefers to pass through these well-conductive but nonselective macropores rather than the highly selective but low-conductive elements of the gel phase. It is shown that the counterion permselectivity of the CJMA-7 membrane can be significantly improved by coating its surface with a dense homogeneous ion-exchange film.

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Coating of ion exchange membranes used in electrodialysis with layers of polyelectrolytes is a proven approach that allows for the increasing of the limiting current, the suppressing of sedimentation, the controlling of the intensity of generation of H+ and OH− ions, and also the improving of monovalent selectivity. However, in the case when two materials with the opposite sign of the charge of fixed groups come in contact, a bipolar boundary is created that can cause undesirable changes in the membrane properties. In this work, we used a MK-40 heterogeneous membrane on the surface of which a layer of polyethyleneimine was applied by adsorption from a solution as a model of heterogeneous membranes modified with oppositely charged polyelectrolyte. It was found that, on one hand, the properties of modified membrane were beneficial for electrodialysis, its limiting current did not decrease and the membrane even acquired a barrier to non-selective electrolyte transport. At the same time, the generation of H+ and OH− ions of low intensity arose, even in underlimiting current modes. It was also shown that despite the presence of a layer of polyethyleneimine, the surface charge of the modified membrane remained negative, which we associate with low protonation of polyethyleneimine at neutral pH.

Recently developed and produced by Hefei Chemjoy Polymer Material Co. Ltd., homogeneous CJMC-3 and CJMC-5 cation-exchange membranes (CJMCED) are characterized. The membrane conductivity in NaCl, Na2SO4, and CaCl2 solutions, permeability in respect to the NaCl and CaCl2 diffusion, transport numbers, current–voltage curves (CVC), and the difference in the pH (ΔpH) of the NaCl solution at the desalination compartment output and input are examined for these membranes in comparison with a well-studied commercial Neosepta CMX cation-exchange membrane produced by Astom Corporation, Japan. It is found that the conductivity, CVC (at relatively low voltages), and water splitting rate (characterized by ΔpH) for both CJMCED membranes are rather close to these characteristics for the CMX membrane. However, the diffusion permeability of the CJMCED membranes is significantly higher than that of the CMX membrane. This is due to the essentially more porous structure of the CJMCED membranes; the latter reduces the counterion permselectivity of these membranes, while allowing much easier transport of large ions, such as anthocyanins present in natural dyes of fruit and berry juices. The new membranes are promising for use in electrodialysis demineralization of brackish water and natural food solutions.

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Ultrafiltration and nanofiltration membranes that are traditionally used in baromembrane processes have become increasingly frequently applied in electromembrane and baroelectromembrane processes. In the latter case, two driving forces, an electric field and a pressure gradient, are simultaneously used. This study presents data on the specific electrical conductivity, diffusion permeability, and transport numbers of ions as well as current-voltage characteristics and chronopotentiograms of AMN-P and OPMN-P weakly ionized nanofiltration membranes and a number of track membranes in solutions of NaCl and CaCl 2. The relationship of obtained characteristics with the structure and exchange capacity of membranes is discussed. It is shown that both nanofiltration and track membranes can exhibit a quite high selectivity towards the electrical transport of ions with a certain charge sign. Such selectivity is especially high in respect of the transport of Ca 2+ ions. In the case of an AMN-P membrane, the transport number of Ca 2+ reaches 0.98, while it is noticeably lower for Na + ions. This result correlates well with a known fact about a higher rejection coefficient of doubly charged ions in comparison with singly charged ions in baromembrane processes. Track membrane #115 is also distinguished by high selectivity in respect of cations, the transport number of sodium ions in it is close to 0.96.

Ion-exchange membranes modified with polyelectrolyte layers with alternating charges on fixed groups provide high selectivity among monovalent ions and are therefore promising for use in fractionation of multicomponent solutions by electrodialysis. The structure of such membranes features bipolar boundaries that are capable of raising the system's resistance and lead to establishing the function of H + and OH − ion generation, which is not always a desirable trait in fractionation by electrodialysis. Here, by analyzing potential transients, we estimate the electrical conductivity of MK-40 cation-exchange membranes coated with a layer of polyethylenimine, which is an anion-exchange substance, and the generation of H + and OH − ions at the formed bipolar boundary. We show that the membrane acquires a high resistance (which can be twice as high) due to coating it with such a layer, and the generation of H + and OH − ions, though it emerges already under the conditions of sub-limiting current, does not become a dominant mass transfer process and leads to a change in pH of the diluate by no more than 1.5.