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Vol 1, No 3 (2019)
- Year: 2019
- Articles: 7
- URL: https://journals.rcsi.science/2517-7516/issue/view/12864
Article
Russian Multilayer Metal–Ceramic Membranes: Structure, Application, and Perspectives
Abstract
The main trends in modifying the structure of bilayer metal-ceramic membranes developed in Russia to fabricate next-generation multilayer metal–ceramic membranes (MMCM) with a wide range of pore sizes from 0.4 to 100 nm and a narrow pore size distribution have been considered. The examples of MMCM structures of various morphologies, the possibilities of further approach to their modification, and possible applications have been shown. Schematic diagrams of existing and prospective membrane units based on metal–ceramic membranes have been demonstrated. The advantages and promising areas of application of such units are discussed.
127-136
Interfaces in Materials for Hydrogen Power Engineering
Abstract
Hydrogen power engineering is based on the production of hydrogen and subsequent oxidation of it to generate electrical energy. Using the example of ion-exchange membranes, catalysts for low-temperature fuel cells, and catalysts for alcohol steam reforming, the features of the transfer, catalysis, and electrocatalysis in hydrogen power engineering are discussed. Particular attention is paid to the role of interfaces. The occurrence of transport processes in ion-exchange membranes is determined by a system of pores and channels that are formed in the membranes owing to self-organization processes. The main selective transport of counterions occurs in a thin Debye layer at the interface between the polymer and the water solution that fills the pores. The transport of gases in these systems occurs through an electrically neutral solution localized in the center of the pores; it can be controlled by introducing nanoparticles into the pores. Catalytic processes in fuel cells occur at the interface between three phases, namely, the catalyst, the support, and the proton-conducting component. The role of the support in the stabilization and enhancement of the power of fuel cells is discussed. Despite the significant difference, the laws governing the catalytic processes of alcohol steam reforming are similar to those of fuel cells in many respects. The nature of metal catalysts is responsible for the preferred direction of the process, whereas the nature of the support largely determines the catalyst performance.
137-144
Proton-Exchange Hybrid Membranes: A Copolymer of Ethylene Glycol Vinyl Glycidyl Ether and Vinyl Chloride/Polyorganylsilsesquioxane
Abstract
Copolymers of ethylene glycol vinyl glycidyl ether (VGE) and vinyl chloride (VC) have been obtained via radical copolymerization of VGE with VC at 70°C in the presence of the initiator azobisisobutyronitrile. By the sol–gel synthesis involving VGE–VC copolymers and carbofunctional organosilicon precursors, such as N,N'-bis(3-triethoxysilylpropyl)thiocarbamide (BTM) and 2-([triethoxysilylpropyl]amino)pyridine (TEAP), hybrid organic–inorganic membranes possessing proton conductivity after doping with orthophosphoric acid have been fabricated. The proton conductivity of the membranes in the temperature range of 30–80°C is characterized by the values of 3.52–4.88 × 10−3 S cm−1 for VGE–VC/ BTM/H3PO4 and 1.19–2.89 × 10−3 S cm−1 for VGE–VC/TEAP/H3PO4.
145-152
Diagnostics of the Structural and Transport Properties of an Anion-Exchange Membrane MA-40 after Use in Electrodialysis of Mineralized Natural Waters
Abstract
Changes in the structural and transport characteristics of MA-40 anion-exchange membranes after operation in industrial electrodialysis apparatuses have been assessed. Causes for the deterioration of operational properties by the action of various factors in the process of demineralization and concentration of natural waters have been revealed. Samples of the anion-exchange membrane after long-term operation in the working stack of an electrodialysis concentrator, as well as samples taken out from the electrode compartment of the electrodialysis reversal apparatus, have been studied. The most significant change in the structure of the membrane taken out from the electrodialyzer concentrator is an increase in macroporosity, which is the main reason for the growth in the electrical conductivity and water content against the background of a loss of ion-exchange capacity and selectivity. The formation of poorly soluble carbonates and hydroxides both on the surface and in the bulk of a membrane from the electrode compartment of the reversal electrodialyzer leads to the blocking of the functional groups and transport channels, decrease in electrical conductivity, and complication of transport processes.
153-167
Transport Characteristics of Homogeneous and Heterogeneous Ion-Exchange Membranes in Sodium Chloride, Calcium Chloride, and Sodium Sulfate Solutions
Abstract
Structural (volume fractions of the gel phase and the intergel solution) and transport (electrical conductivity, diffusion permeability, transport numbers of counterions and coions) characteristics of cation-exchange (CMX, MK-40) and anion-exchange (AMX, MA-41) membranes in NaCl, CaCl2, and Na2SO4 solutions have been studied. The investigated membranes have the same chemical nature of the ion-exchange matrix and similar values of ion-exchange capacity, but they differ in the degree of heterogeneity and chemical nature of the reinforcing materials. The difference in the properties between heterogeneous (MK-40 and MA-41) and (conventionally) homogeneous (CMX and AMX) membranes is due to the fact that the heterogeneous membranes have macropores, whereas the homogeneous membranes do not have such pores. It has been shown that the largest macropores, which basically determine the high diffusion permeability of heterogeneous membranes, are formed at the boundaries of reinforcing fabric threads and the composite material. Regarding the influence of the electrolyte nature, the sorption of coions of the membrane gel phase (not containing macropores) is of primary importance; the sorption of coions, as well as diffusion permeability and the transport number of coions, increase in the order: 1 : 2 < 1 : 1 < 2 : 1, where the first numeral is the charge of the counterion and the second one is that of the coion. An important role, especially in the case of heterogeneous membranes, is played by the electrolyte diffusion coefficients in the electroneutral solution that fills the central part of meso- and macropores.
168-182
Diffusion Transport of Water and Methanol Vapors in Polyvinyltrimethylsilane
Abstract
The specifics of diffusion of water and methanol vapors in nonporous polymer films based on polyvinyltrimethylsilane (PVTMS) have been studied. The vapor diffusion coefficients have been determined by measuring the kinetics of unsteady flow through the membrane (differential method) and subsequent processing the results by functional scaling . The kinetic curves have been found to deviate from those described by classical Fick’s law. It has been theoretically shown that such deviations can be due to the formation of associates of penetrant molecules inside the membrane, and a modified method for calculating diffusion coefficients has been proposed for this case. The behavior of the diffusion coefficients of water and methanol vapors in PVTMS in the temperature range of 50–90°C and the vapor activity range of 0.3–0.9 has been studied. The activation energies of diffusion of water and methanol vapors in PVTMS have been determined to be 23 and 44 kJ/mol, respectively, and the effective kinetic diameters of the molecules have been calculated to be 0.29 and 0.37 nm, respectively. The proposed approach opens the possibility for systematic studies of the diffusion kinetics of vapors of different organic compounds with an assessment of their kinetic contribution to the membrane permselectivity.
183-189
Modified Microheterogeneous Model for Describing Electrical Conductivity of Membranes in Dilute Electrolyte Solutions
Abstract
Many transport properties of ion-exchange membranes can be described in terms of the microheterogeneous model using a single set of parameters. However, the model is applicable in a limited concentration range of electrolyte solutions. In this paper a new modification of this model is proposed, taking into account the contribution of the electrical double layer (EDL) at the internal boundaries of the gel phase and the intergel solution of the membrane to describe the electrical conductivity of membranes in dilute electrolyte solutions. The model suggests that the EDL thickness in the internal solution phase increases with dilution of the external solution. Since EDL is more conductive than the electroneutral part of the solution, it is possible to describe the concentration dependence of the electrical conductivity of membrane more precisely as compared with the basic version of the microheterogeneous model. Comparison of the concentration dependences of the electrical conductivity of membranes shows a good agreement between the experimental and calculated data.
190-199