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Volume 14, Nº 1 (2024)
Articles
Modeling of ion transport in a three-layer system with an ion-exchange membrane based on the Nernst-Planck and displacement current equations
Resumo
Modeling of ion transport in a three-layer system containing an ion-exchange membrane and two adjacent diffusion layers makes it possible to describe the permselectivity of the membrane by determining its fixed charge density. For theoretical analysis of ion transport in such systems, the Nernst–Planck and Poisson equations are widely used. The article shows that in the galvanodynamic mode of operation of the membrane system, when the density of the flowing current is specified, the Poisson equation in the ion transport model can be replaced by the equation for the displacement current. A new model was constructed in the form of a boundary value problem for the system of the Nernst–Planck and displacement current equations. Based on this model, ion concentrations, electric field strength, space charge density and chronopotentiogram of the ion-exchange membrane and adjacent diffusion layers in direct current mode were numerically calculated. The calculation results of the proposed model are in good agreement with the modeling results based on the previously described approach using the Nernst–Planck and Poisson equations, as well as with the analytical assessment of the transition time. It is shown that in the case of the three-layer geometry of the problem, the required accuracy of numerical calculation using the proposed model is achieved with a smaller number of computational mesh elements and takes less (about 26.7 times for the considered system parameters) processor time compared to the model based on the Nernst–Planck and Poisson equations.
3-12
Interlayer resistance of bilayer membrane to gas permeation
Resumo
To describe gas transfer through a bilayer membrane with a thin selective layer on the surface of a highly permeable gutter layer, it was first proposed to take into account the interlayer resistance arising at the boundary of this membrane layers and a model of gas transfer through a bilayer membrane was developed. An analytical expressions for permeability and selectivity of such a membrane taking into account this resistance is obtained. It is shown that the interlayer resistance can noticeably affect the transport characteristics of the membrane. It is found that even in the case of small diffusion resistance to gas permeation of the gutter layer, its sorption and kinetic parameters influence the permeability and selectivity of the membrane as a whole.
13-18
Prospects for the development of hydrogen energy. Polymer membranes for fuel cells and electrolysers
Resumo
Due to increased attention to hydrogen energy and the fact that many countries adopted the programs of its development the question of the prospects for this area becomes relevant. Initially, Russian hydrogen energy development program was focused on producing hydrogen from natural gas. However, owing to the changed international situation and the declared course to the use of “green” hydrogen, the production of which is not associated with the emission of carbon oxides, special attention should obviously be paid to the development of fuel cells (FC) and electrolysers. In this review, the main advantages and disadvantages of fuel cells of various types are considered. Today, the most developed industry is low-temperature fuel cells based on proton-exchange membrane. At the same time, fuel cells based on anion-exchange membranes with OH--ion conductivity are also promising. Their key advantage is the possibility of using significantly cheaper non-perfluorinated membranes and platinum-free catalysts. Considerable attention in the review is paid to fuel cells operating at elevated temperatures.
The second part of this review discusses in detail the membranes currently used in these devices and promising materials that can replace them in the near future.
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Synthesis and gas transport properties of polynaphthoylenebenzimidazoles with keto- and sulfonic bridging groups
Resumo
Polynaphthoylenebenzimidazoles (PNBI) with keto-(PNBI-CO) and sulfonic (PNBI-SO2) bridge groups were obtained by solid-state polycyclization of polyaminoimides (PANI) synthesized by polycondensation of 1,4,5,8-naphthalenetetracarboxylic acid dianhydride with 3,3`,4,4`-tetraaminobenzophenone and 3,3`,4,4`-tetraaminodiphenylsulfone in N-methylpyrrolidone, respectively. The polycondensation process and resulting chemical structure of PANI and PNBI were controlled by 1H NMR, 13C NMR and IR spectroscopy. It is shown that the temperature of solid-state polycyclization change makes it possible to obtain polymers of several of cyclization degrees. The experimental values of the gas permeability and diffusion coefficients for He, H2, N2, O2, CO2, CH4 were obtained. The gas solubility coefficients and the ideal selectivity for various gas pairs were calculated. It has been established that, in terms of the permeability-selectivity ratio, completely cyclized PNBIs occupy a more favorable position compared to incompletely cyclized ones. This result is important for polymer and a method selection to develop a selective layer of new composite membranes. The gas transport characteristics achieved for competely cyclized PNBI-SO2, as well as the film-forming properties, along with the very high thermal stability of polymers of this polymer class, are interest of further expanding the range of PNBI obtained, as well as the prospects for such new polymers using of in various gas separation processes.
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Separation of water-oil emulsion by polyamide membranes treated with corona plasma
Resumo
Studies were carried out on the separation of the water-oil emulsion by polyamide membranes with a pore size of 0.2 μm treated with corona discharge plasma at a voltage of 5–25 kV and a time of 1–5 minutes. An increase in the productivity and efficiency of the separation of the water-oil emulsion by corona-treated polyamide membranes was revealed. Increase of roughness and change of chemical structure of modified membranes are shown.
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Poly(urethane-imides) as perspective materials for the development of gas separation, pervaporation and filtration membranes
Resumo
This review presents the separation properties of membranes based on poly(urethane-imides), polymers that are modern products of the chemical modification of polyimides and polyurethanes. An overview of the membrane properties of poly(urethane-imides) is based on the principles of their chemical design. The following membranes are considered: multiblock (segment) polymers, polyimides crosslinked with polyurethanes, hybrid poly(urethane-imide) materials, poly(urethane-imides) subjected to selective destruction of urethane blocks. In the cases under consideration, ideas are given about the main directions in the synthesis of membrane poly(urethane-imides), reagents and reaction conditions are given. The transport and separation properties of poly(urethane-imide) membranes in the processes of gas separation, pervaporation and ultrafiltration are given in detail. Applications for which poly(urethaneimide) membranes have been developed are described. In general, an idea is given about the importance of poly(urethane-imide) gas separation, pervaporation and filtration membranes for separation processes.
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Памяти Владимира Алексеевича Шапошника
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