Membranes and Membrane Technologies最新文献

Improvement of the chemical stability of hybrid membranes based on perfluorosulfonic acid polymers is necessary to increase the lifetime of fuel cells. This article presents the results of the study of the transport properties and chemical stability of the hybrid Nafion® 212 membranes modified with nanoparticles of hydrated oxides SiO₂, ZrO₂, and TiO₂ by in situ procedure. The influence of the nature of the dopant on the properties of the obtained materials is shown. The chemical degradation of the initial and hybrid membranes has been studied ex situ by treatment with Fenton’s reagent for 240 hours. The stability of materials increases in the series Nafion + SiO₂ < Nafion + ZrO₂ < Nafion < Nafion + TiO₂. For the Nafion + TiO₂ membrane the change in mass as a result of treatment with Fenton’s reagent is two times lower than for the initial Nafion membrane. This reveals an increase in the chemical stability of materials upon the incorporation of TiO₂ nanoparticles due to their ability to bind free radicals. The maximum power of membrane-electrode assembly based on hybrid membranes containing TiO₂ and SiO₂ is higher than that based on Nafion® 212 by 7–10% at RH ~ 100% and t = 65°C.

The effect of pulsed electric field (PEF) parameters on the period-average current densities in the electrodialysis desalination of sodium dihydrophosphate solutions has been studied for the first time. Ir has been shown that, in the case of sodium dihydrophosphate solutions, the PEF effect regularities are generally the same as for the solutions of strong electrolytes. Using the visualization of electroconvective flows in a lean solution near the surface of an anion-exchange membrane, it has been established that the observed distinction in the behavior of membrane systems is caused by weak electroconvection in phosphate-containing solutions. The hypothesis that another reason for the observed distinctions is the effect of a pulsed electric field on the deprotonation of ({{{text{H}}}_{{text{2}}}}{text{PO}}_{4}^{ - }) anions entering the volume of an anion-exchange membrane is put forward.

Composites containing up to 5 wt % montmorillonite (MMT) nanoparticles are created based on natural materials, cellulose acetate and MMT, and film membranes are prepared. The characteristic features of the membrane morphology are studied by scanning electron microscopy. The transport properties of the membranes are studied for the process of separation of a methanol–methyl tert-butyl ether (MTBE) mixture. The degree of equilibrium sorption and diffusion coefficients of methanol and MTBE in the membranes are determined. The pervaporation of a methanol–MTBE mixture is studied in a wide range of feed compositions including the azeotropic point. The best separation factor combined with a high flux is found for a membrane containing 3% MMT. The study of the deformation behavior of the membranes under uniaxial tension shows that they have good mechanical properties, and the elastic modulus increases with the increase in the MMT content while the strength slightly decreases.

This work shows the possibility of formation of membranes with an asymmetric porous structure based on copolyimide/nanodiamonds (coPI/ND) composites. The influence of nanodiamonds as well as variation of the nature of the solvent by introducing an ionic liquid on the structure and thermal properties of the membranes is investigated by X-ray diffraction analysis, thermogravimetric analysis, scanning electron microscopy, and IR spectroscopy. The transport properties of the membranes are investigated in the process of ultrafiltration of aqueous solutions of proteins. The effect of the additions of an ionic liquid on the optimization of transport characteristics is carried out. It is shown that membranes based on coPI/ND composites possess increased hydraulic performance: the introduction of up to 3 wt % ND and use of an ionic liquid as a cosolvent lead to increase in the flux up to 600 L m⁻² h⁻¹ bar⁻¹ compared to a membrane based on PA.

The bipolar heterogeneous membrane has been obtained by applying a layer of phosphoric acid ion exchanger paste on a water-based wet rough cation exchange membrane, followed by drying and hot pressing with an anion exchange membrane. It is shown by the method of electrochemical impedance that the obtained membrane at a current density of 1.1 A/dm² has a bipolar overvoltage of 0.26 V. This is comparable to the overvoltage of the bipolar region of industrial membrane MB-3 (0.29 V) and is much lower than the same value for industrial bipolar membrane MB-1 (2.86 V) and membrane MB-2 (8.04 V). The process of obtaining acid and sodium hydroxide from solutions of sodium chloride and sodium nitrate in an electrodialyzer with three-chamber elementary cells consisting of the obtained bipolar membrane and monopolar membranes Ralex CMH and Ralex AMH has been investigated. Integral current efficiencies and productivities for acid and alkali are higher, and energy consumptions and contaminations of the produced acid and alkali solutions with salt ions are lower than when using the industrial MB-3 membrane.

The article presents experimental studies of the hybrid process of regeneration of used oils based on two interrelated processes of coagulation and ultrafiltration. The hypothesis that the process of coagulation due to aggregation of particles and organic substances contributes to the formation of a more porous sediment layer, which reduces pore blockage and increases filtration efficiency, has been checked. The aim of this study is to determine the most effective parameters of the baromembrane process by describing changes in the properties of deposits in a tubular ceramic membrane during ultrafiltration of waste oils. At the first stage, experiments were carried out on a Jar reactor with two different coagulants: an aqueous solution of diaminomethanal and a mixture of ethanolamine and propane-2-ol, and the effect of coagulants on the process of flake formation has been investigated by micrography of droplet samples and paper chromatography. At the second stage, studies of the ultrafiltration process have been carried out. Coagulation and ultrafiltration experiments have shown different permeability of the process. The effect on the permeate flow depends on the nature and composition of the coagulant. As a result of experiments, it has been shown that more stable flakes are formed under the influence of an aqueous solution of diaminomethanal and, as a result, a longer operation of the membrane element without a drop in permeability is observed.

A non-steady state mathematical model of the separation of a solution of an amino acid (phenylalanine) and a mineral salt (NaCl) by the neutralization dialysis (ND) method in a circulating hydrodynamic mode has been proposed. The model takes into account the characteristics of the membranes (thickness, ion-exchange capacity, electrical conductivity) and the solution (concentration and nature of the components) and the flow rate of the solution in the dialyzer compartments. The new model, unlike the known models, takes into account the transport of phenylalanine cations and anions across membranes and diffusion layers of the ND system. In addition, the model takes into account the ability of an amino acid to undergo protonation/deprotonation reactions. Comparison of the simulation results with experimental data suggests that the model adequately describes the ND of solutions of a phenylalanine–NaCl mixture. It has been shown that, for a given pair of membranes (CSE cation-exchange membrane and ASE anion-exchange membrane, Astom, Japan) and studied concentrations, the pH of the mixed solution remains relatively low throughout the entire process, and the rate of decrease in the electrical conductivity is lower than that for an individual NaCl solution. The loss of phenylalanine in the ND process has been determined according to analysis of the experimental data and simulation results.

The transport of oxygen, nitrogen, and hydrocarbons C₁–C₄ in polyimides based on 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and biphenyl-3,3',4,4'-tetracarboxylic acid dianhydride (BPDA) and diethyl toluene diamine (DETDA) has been studied. The dependences of the diffusion coefficient on the diffusant effective diameter and the solubility coefficients on the Lennard–Jones potential of pair interaction have been considered. It is shown that the diffusion coefficients of butane are out of the linear dependence of the logarithm of the diffusion coefficient on the square of the effective diameter of the diffusant, which may indicate the plasticization of polymers with butane at a pressure of 1 atm. The permeability of mixtures of gases O₂–N₂ (29 : 71 v/v) and CO₂–CH₄ (62 : 38 v/v) has been studied. There are no significant differences in the gas separation parameters in comparison with the experiment for individual gases; however, for a mixture of CO₂–CH₄, a slight increase in the separation factor has been found as compared to the ideal selectivity. The data on the measurement of sorption isotherms and solubility coefficients O₂, N₂, and CH₄ are also presented in the article. Gas solubility coefficients have been found to be close to the values obtained indirectly as P/D.

The free solvent transport number in an MF-4SK perfluorinated membrane in solutions of alkaline metal chlorides and hydrochloric acid is for the first time calculated within the framework of a capillary model based on the data of standard contact porosimetry and membrane conductometry. The reasons for the change in the structural characteristics and specific conductivity upon varying the nature of the counterion are discussed. The portion of through mesopores in MF-4SK homogeneous and MK-40 heterogeneous sulfonated cation-exchange membranes is estimated using the experimental data on the water transport numbers in solutions of electrolytes of different natures.