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Vol 13, No 1 (2023)
Articles
Electrochemical Properties and Specific Selectivity of Ion-Exchange Membranes in Borate-Nitrate Electrolyte Solutions
Abstract
Electrochemical characteristics of heterogeneous cation- and anion-exchange Ralex membranes and the mechanism of transfer of ions of salt, boric acid and its anions through membranes at different pH values were investigated by the method of rotating membrane disk (RMD). It is shown that boric acid is transported mainly through an anion exchange membrane. At pH 9.5, the limiting stage of anion transfer through the anion exchange membrane is the reaction of tetrahydroxyborate \({\text{B}}\left( {{\text{OH}}} \right)_{4}^{ - }\) anion formation. The study of the electrodialysis separation of a solution of sodium nitrate and boric acid showed that the electrodialysis method makes it possible to effectively separate the components of the mixture, while the value of the specific selectivity coefficient \({{P}_{{{{\text{B}} \mathord{\left/ {\vphantom {{\text{B}} {{\text{NaN}}{{{\text{O}}}_{{\text{3}}}}}}} \right.} {{\text{NaN}}{{{\text{O}}}_{{\text{3}}}}}}}}}\) = (0.02–0.06), depending on the voltage on the electrodialyzer.
3-14
Optimization of the Hydrodynamic Regime in the Flow Electrodializator Cell
Abstract
Electrodialysis is a water treatment and wastewater treatment technology that uses an electric field gradient and ion exchange membranes to separate ions in aqueous solutions. Studies conducted using this technology have shown the influence of the hydrodynamic regime on the efficiency of the process, the rate of mass transfer and polarization concentration. The article presents experimental results, mathematical calculations and numerical modeling in the universal software system of analysis by the Ansys finite element method. Theoretical calculated results show a good correlation with the results of hydrodynamic processes in the apparatus obtained experimentally. The hydrodynamic regime in the channel of the electrodialyzer cell has been studied, the influence of the mesh geometry on the distribution of fluid flow over the membrane surface has been shown, and the change in flow velocity and pressure depending on the structure of the mesh has been described.
15-22
Physico-Chemical Properties and Performance Characteristics of Perfluorined Membranes Bulk Modified with Platinum during Operation in Proton Exchange Membrane Fuel Cell
Abstract
The results of application of platinum bulk modified perfluorinated membranes in proton exchange membrane fuel cell are presented. The change in physicochemical and transport characteristics of the membranes after modification with platinum and at different stages of their operation in the PEMFC are also discussed. The thickness, radius pore distribution obtained by the standard contact porosimetry method, the concentration dependences of the conductivity, and the current-voltage characteristic are studied. The influence of copper in bimetallic electrocatalyst on the characteristics of the perfluorinated membrane are considered. An increase in the efficiency of PEMFC with both commercial and bimetallic catalysts and platinum bulk modified membranes due to the formation of a self-humidifying structure is found.
23-32
Practical Manufacturing of Asymmetric Hollow Fiber Membranes for Gas Separation Made of Poly(2,6-dimethylphenylenoxide-1,4)
Abstract
The regularities of manufacturing of hollow fiber membranes made of poly(2,6-dimethylphenylene oxide-1,4) for gas separation were studied. The phase inversion method was used to manufacture the membranes. The dependence of the separation characteristics of the membrane on such spinning parameters as the type of solvent, the exposure time of the polymer solution in the “air” gap, and the type of non-solvents (coagulants) has been studied. The characteristics of the membrane were obtained by determining their gas permeability. It is shown that higher separation and gas transport characteristics of the PPO membrane are obtained using the wet spinning method. An intrinsic selectivity of 4.8 ± 0.4 was obtained at a specific oxygen permeability (20°C) – (P/l) 790 ± 82 [m3 (s.t.p.) m–2 s–1 kPa] for oxygen–nitrogen system. The developed membranes are promising for use in case for producing nitrogen and oxygen-enriched air.
33-41
Method of Liquid-Phase Fluorination of Polymers to Increase the Selectivity of the Air Separation
Abstract
The one-sided modification of homogeneous polymer films of polyvinyltrimethylsilane (PVTMS), poly(2,6-dimethylphenyl-1,4 oxide) (PPO), and polybenzodioxane (PIM-1) was carried out by liquid-phase fluorination method using a fluorine-nitrogen mixture in perfluorodecalin. The fluorination time ranged from 10 to 60 min. For PPO films the amorphous and β-nanocrystalline phase (48%) was found by X-ray diffraction analysis of the original films. It was shown that fluorination does not significantly affect the degree of PPO crystallinity. The effect of fluorination time on the effective coefficients of permeability, diffusion, and solubility of oxygen and nitrogen has been studied. It was found that the fluorination leads to a decrease in both effective diffusion coefficients and effective gas solubility coefficients, while the resulting increase in permeability selectivity ranged from 30% for PVTMS to a 2 times increase in the case of PPO and PIM-1. It has been noted that this improvement in permeability selectivity is achieved mainly by the solubility selectivity increasing. The permeability of O2/N2 mixture for original and modified films was studied. It was found that the achieved values of the separation factors are close to the ideal selectivity. The results obtained demonstrate the possibility of effective application of the liquid-phase modification method not only for the homogeneous polymer films of the studied polymers treatment, but also for membranes with a selective non-porous layer based on them.
42-55
Air Cleaning from Organic Compounds Using a Nanofiltration Composite Membrane Based on Cellulose Acetate and a Commercial Membrane of OPMN-P Brand
Abstract
Nanofiltration membranes were used to separate the vapor–air mixture containing organic compounds. The membrane was obtained on a filter paper substrate by pouring with a three-component polymer solution. The surface layers were deposited on the substrate by sequentially alternating the stages of membrane drying. The resulting membrane has hydrophilic properties, the porosity of the resulting membrane is 51%. The membrane thickness determined by SEM was 98 µm. The retention capacity of the membranes was studied by separating model mixtures of ethanol–air and gasoline–air. The membrane permeability of the MAC3 composite membrane during separation of the ethanol–air vapor-air mixture was 11.0 m3/m2h at a pressure of 0.5 MPa. The high retention capacity of the MAC3 composite membrane was established for xylenes, toluene, and heptane; for other compounds, the efficiency is no more than 90%. The average retention capacity of the resulting membrane was 87%. Comparative tests to establish gas separation parameters under similar conditions were carried out with a commercial membrane brand OPMN-P.
56-64
Polymer Membranes for Vapor-Phase Concentration of Volatile Organic Products of Biomass Processing
Abstract
The biomass processing is one of the demanded promising technologie including energy carriers and valuable chemical reagents. The developed processes of lignin bio-processing suggest the use of a synthetic biological system that allows obtaining lower aliphatic alcohols through the stage of formation of carboxylic acids. Due to the production of alcohols in the form of dilute aqueous solutions, their recovery and concentration are extremely energy-consuming stages. In this paper, a vapor-phase membrane separation method is considered in application to aqueous solutions containing alcohols and organic acids. The transfer of vapors of water, C1–C4 alcohols and acetic acid through commercial pervaporation and gas separation membranes, which have not been previously studied for this purpose, has been investigated. RomakonTM-102 PM membrane demonstrated the highest separation of water-alcohol mixtures. Based on the experimental data obtained, mathematical modeling of the process of ethanol recovery from triple mixture “water/ethanol/acetic acid” by the vapor-phase membrane method was carried out.
65-80