卷 1, 编号 2 (2019)

A method is proposed for the removal of water vapor from commercial grade nitrous oxide during its high purification using membrane gas-separation technologies. A single membrane module, a two-stage recirculation unit with the recycling of permeate stream, and two-stage cascades with membranes of different selectivity and experimentally determined the permeability of Lestosil, PVTMS, and CTA test membranes to nitrous oxide have been considered. The optimum values of the main operating parameters of the drying system have been determined, and the energy efficiency of membrane gas separation and low-temperature filtration processes have been evaluated with taking into account the operating costs and purified gas losses.

Long-term (over 20 h) operation of the AMX-Sb membrane in the electrodialysis desalination of 0.02 M NaCl solution in overlimiting current regimes can lead to an increase in experimentally determined limiting current by more than 30% compared to the pristine membrane. This growth is caused by electrochemical degradation of the ion-exchange material at the AMX-Sb/solution interface, which leads to (1) a decrease in hydrophilicity of the membrane surface and (2) the formation of membrane cavities with linear dimensions of 2–3 μm. Both of these effects stimulate electroconvection, which develops in underlimiting current regimes via the mechanism of electroosmosis of the first kind. The resulting microvortex structures deliver a more concentrated solution to the AMX-Sb surface, shifting the limiting state and the onset of the intense generation of H⁺ and OH⁻ ions to higher currents. The study has been carried out using the techniques of voltammetry and impedance spectroscopy, as well as contact angle measurements and optical visualization of the membrane surface.

It has been found that after 300 h of operation of AMX and AMX-Sb anion-exchange membranes (Astom, Japan) in overlimiting current regimes in the process of electrodialysis desalination of 0.02 M NaCl, NH₄Cl, NaH₂PO₄, and KC₄H₅O₆ (KHT) solutions, the limiting currents, \(i_{{\lim }}^{{\exp }}\), determined by graphic processing of current–voltage curves increase in the order NaCl < NaH₂PO₄ < KHT. Their increments relative to those for the “fresh” membrane are 33, 90, and 128%, respectively. The growth in \(i_{{\lim }}^{{\exp }}\) is accompanied by an increase in the thickness of the samples occurring in the NaH₂PO₄ and KHT solutions. In the case of NH₄Cl, the values of \(i_{{\lim }}^{{\exp }}\) decrease. It has been shown that a small decrease in counterion transport numbers during membrane operation has almost no effect on the values of limiting currents. The main contribution to the increase in \(i_{{\lim }}^{{\exp }}\) is apparently made by electroconvection, which develops according to the mechanism of electroosmosis of the first kind. Its development is facilitated by the growth in the number and size of free-standing micrometer-sized cavities on the surface of anion-exchange membranes, the area and linear dimensions of which increase in the order NaCl < NaH₂PO₄ < KHT. These cavities are formed as a result of enhancement of electrochemical degradation of the ion-exchange material and the inert filler polyvinyl chloride at the membrane/solution interface in ampholyte solutions.

Membranes are widely used in modern technology. The demand for different types of membranes and membrane processes is increasing every year. This review summarizes the current state of the art and prospects of membrane science developments including membrane materials for gas separation, pervaporation, and pressure-driven membrane processes; ion-exchange, hybrid, and track-etched membranes; membranes for electrochemical sensors; and mathematical modeling of membrane separation processes and ion and water transport in membrane systems. Studies aimed at improving the selectivity and performance of membranes and their stability are surveyed. New approaches to the synthesis and modification of membranes as well as their advanced applications are discussed.