Membranes and Membrane Technologies最新文献

This work is devoted to the removal of dissolved oxygen from a model absorbent based on monoethanolamine (MEA) to prevent its oxidative degradation during the absorption purification of flue gases from carbon dioxide. Composite membranes based on porous ceramic and polymeric supports with a thin selective layer of poly[1-(trimethylsilyl)-1-propyne] or its blend with polyvinyltrimethylsilane are developed, and gas-liquid membrane contactors are created on their basis. It is shown that the use of these contractors in the vacuum mode allows the removal of up to 60% of dissolved oxygen from the model sorbent.

The paper suggests exact formulae for calculating the electromigration, diffusion, and convective transference numbers of counterions in the cell model of a charged membrane depending on the physicochemical parameters and equilibrium concentration of the electrolyte. The cell model was previously developed to calculate all the kinetic coefficients of the Onsager matrix, and the asymmetry of the cross coefficients was established. A limiting case of an ideally selective membrane is studied in detail, for which approximate formulae for transference numbers are obtained. The obtained dependences are illustrated by graphs by way of example of an MK-40 cation-exchange membrane after conditioning at room temperature. The proposed calculation procedure for transference numbers is applicable to any single-layer membranes in solutions of a binary electrolyte.

The results of a theoretical analysis of the influence of the electroosmotic flow on the electromigration and convective transport of competing ions separated by the electrobaromembrane process are presented. Separated ions of the same charge sign move in an electric field through the pores of a track-etched membrane to the corresponding electrode, while a commensurate convective counterflow being created by the pressure drop across the membrane. A simplified model based on the convective electrodiffusion equation and the Hagen–Poiseuille equation allows the analysis of experimental data using only the effective transport numbers of ions in the membrane as fitting parameters. Using a 2D mathematical model described by the system of Nernst–Planck, Navier–Stokes, and Poisson equations, it is shown that the electroosmotic flow can cause the effective transport numbers of competing ions to exceed their values in solution, even if these ions are coions for the membrane.

The paper presents the results of a study of water uptake, ionic conductivity, and Donnan potential in systems with perfluorosulfonic acid membranes in the H⁺, Li⁺, Na⁺, and K⁺ ionic forms and solutions of inorganic electrolytes. The properties of commercial membranes Aquivion E87-05S and Nafion 212, as well as membranes obtained from dispersions of Nafion 212 in solvents of various nature (N,N-dimethylformamide, 1-methyl-2-pyrrolidone, mixtures of isopropyl alcohol with water in a volume ratio of 80–20) have been studied. The effect of the number of functional groups, the length of the side chain of polymer macromolecules, and the morphology of the polymer in membranes on their equilibrium and transport properties depending on the nature of the counterion has been determined. The effect of relaxation and electrophoretic factors on the transfer of alkali metal ions through the system of pores and channels of perfluorosulfonic acid membranes is discussed. The slope of the concentration dependences of the Donnan potential for all highly hydrated membranes in the H⁺ form has been found to be close to the Nernstian one, while the selectivity to alkali metal ions increases for membranes with the highest ion exchange capacity or the lowest amount of sorbed water and diffusion permeability due to the exclusion of co-ions from the membrane phase.

Amino acids that are ampholytes can be effectively separated and purified by the method of neutralization dialysis (ND), whose advantage is the ability to control the pH value of the solution without adding reagents. An important task is to optimize the parameters of the ND process to ensure minimal losses of amino acids during their isolation from mixed solutions. An experimental study of the process of demineralization of the phenylalanine and sodium chloride equimolar mixture by the ND method is carried out. It is established that varying the concentration and flow rate of acid and alkali solutions in the corresponding compartments of the dialysis cell allows for regulating the pH value of the solution being desalted and controlling the amount of amino acid losses. Halving the acid concentration (from 0.10 to 0.05 M) allowes reducing the losses of phenylalanine from 18.3 to 16.4%, and using a lower solution flow rate in the acid compartment (0.75 instead of 1.50 cm s^–1) makes it possible to reduce these losses to 14.2%. At the same time, in all experiments, the electrical conductivity of the solution being desalted decreases by 90%, which suggests a high demineralization rate and the effectiveness of the method used to isolate phenylalanine from the mixed solution.

Pd60%Cu40% alloy membranes are modified with nanostructured coatings to intensify the low-temperature (25–100°С) transport of hydrogen. Classical palladium black and filamentous particles are deposited as surface modifiers by electrodeposition. The experimental data confirm that the deposition of the modifying layer on both surfaces of the Pd60%Cu40% alloy membranes can considerably reduce surface limitations for the process of hydrogen transfer. In the low-temperature hydrogen transport processes, the developed membranes demonstrate high and stable fluxes up to 0.36 mmol s^–1 m^–2 and high hydrogen permeability up to 1.33 × 10^–9 mol s^–1 m^–2 Pa^–0.5. For the Pd60%Cu40% alloy membranes modified with nanofilaments hydrogen permeability is up to 1.3 times higher compared with the membranes modified with classical black and up to 3.9 times compared with the uncoated membranes. The Pd60%Cu40% alloy membranes also exhibit a high level of H₂/N₂ selectivity, up to 3552. The strategy of surface modification of palladium-based membranes can shed new light on the development and manufacture of high-performance and selective membranes for ultrapure hydrogen production units.

In this work, the production of sodium hydroxide by the method of bipolar electrodialysis from a solution of sodium carbonate using bipolar membranes MB-3 has been studied. For research, a laboratory electrodialyzer-synthesizer with a three-chamber unit cell has been used. The membrane package of the electrodialyzer has contained five elementary cells, the active area of each membrane being 1 dm². To compare the obtained mass transfer characteristics, the process of preparation of sodium hydroxide from sodium sulfate has been additionally studied. It has been shown that the use of sodium carbonate as the initial solution makes it possible to increase the concentration of the resulting alkali from 0.92 to 1.7 M under comparable process conditions compared to the preparation of sodium hydroxide from a sodium sulfate solution. When sodium carbonate is used, the alkali current efficiency is more than 70% in all experiments, while when alkali is obtained from a sodium sulfate solution, the current efficiency drops sharply to 0.4–0.5% when the concentration exceeds 0.8 M NaOH. The energy consumption for the transfer of one kg of alkali is in the range of 2.8–13.9 kWh/kg at operating current densities of 1–3 A/dm².

The object of this work is a new hybrid membrane based on poly(m-phenylene-iso-phthalamide) (PA) modified with a complex filler consisting of equal amounts of heteroarm star-shaped macromolecules (HSMs) and [BMIM⁺Tf₂N^–] ionic liquid (IL). Comparative studies of the structures have been carried out on samples of membranes made of pristine PA and hybrid PA/HSM and PA/(HSM:IL) containing 5 wt % additives. Methods of AFM, X-ray powder diffraction, measurement of density, and contact angles have been used. The transport properties of membranes have been studied in separation of a methanol/n-heptane mixture by the pervaporation method. The actuality of this problem is associated with the process of oil refining. In pervaporation of an azeotropic methanol/n-heptane mixture, the hybrid PA/(HSM:IL) membrane has demonstrated higher performance and separation factor relative to reference membranes. Mechanical tests of the membranes have revealed a high level of properties important for operation (strength and relative elongation) of the hybrid membrane.

An original method of obtaining cation exchange composite heterogeneous membranes involving the low-temperature ion-plasma pretreatment of fibrous systems is proposed. The membranes are obtained by the polycondensation filling of polymer composites via the synthesis and hardening of a strongly acidic sulfo cation exchanger on the surface and in the structure of a novolac phenol-formaldehyde fibrous system. The effect of low-temperature ion-plasma pretreatment on a change in the hydrophilicity, capillarity, and structure of heterogeneous cation exchange composite materials Polykon is investigated.

The influence of lactose on the main transport characteristics of ion-exchange membranes including surface-modified with polyaniline cation-exchange membranes is studied. A pronounced to different extents positive effect of modification of MK-40 and Ralex CMHPES membranes with polyaniline on their biofouling by Bacillus sp. or Shewanella oneidensis MR-1 cell cultures is found which is due to the different conductive surface areas of these membranes. It is revealed that the presence of lactose in a solution leads to a decrease in the electrical conductivity of all the studied membranes; however, the effect the most substantially manifests itself for a modified with polyaniline MK-40 membrane: its electrical conductivity decreases by 15–25%. The diffusion permeability of the anion-exchange and initial cation-exchange membranes weakly depends on the presence of lactose in a solution; however, its 2–2.5-fold decrease is observed in the case of modified with polyaniline cation-exchange membranes. A significant effect of lactose on the current–voltage characteristics of the anion-exchange membranes has been found, which indicates significant adsorption of lactose on their surface under the conditions of an external constant electric field. It is shown that ion-exchange membranes remain quite effective for electrodialysis of solutions of lactoserum but their use in underlimiting current modes will be more effective.