Membranes and Membrane Technologies最新文献

Surface-modified cation exchange materials are obtained based on industrial MK-40 heterogeneous and MF-4SK homogeneous cation-exchange membranes by in situ oxidative polymerization of aniline under electrodialysis conditions. The conduction and diffusion characteristics of the initial and modified membranes in solutions of sulfuric acid and nickel sulfate are studied. It is shown that the modification of the membranes with polyaniline leads to a decrease in their electrical conductivity and diffusion permeability without sacrificing high selectivity. The diffusion permeability of the cation-exchange membranes is higher in solutions of nickel sulfate in comparison with solutions of sulfuric acid, while an inverse dependence is found for anion-exchange membranes. The competitive transport of sulfuric acid and nickel sulfate during electrodialysis separation and concentration of their mixture using initial commercial and modified cation-exchange membranes paired with an MA-41 anion-exchange membrane is studied. It is shown that applying a layer of polyaniline with positively charged groups onto one of the surfaces of MK-40 or MF-4SK cation-exchange membranes leads to a decrease in the transport of a doubly charged nickel cation both in the separation and concentration modes over the entire range of current densities. The highest repulsion effect is observed in the case of the use of homogeneous modified membranes, where the selective permeability coefficient P(H₂SO₄/NiSO₄) increases from 0.7–1.7 up to 32.5–19.7 depending on the current density. It is found that the use of surface-modified with polyaniline cation-exchange membranes makes it possible to concentrate a solution containing 0.1 mol-equiv/L (4.9 g/L) H₂SO₄ and 0.1 mol-equiv/L (7.7 g/L) NiSO₄ with simultaneous separation to sulfuric acid with a concentration of about 2.4 mol-equiv/L (120 g/L) and a solution of nickel sulfate. Here, the concentration of nickel sulfate in the concentrate does not exceed 0.13 mol-equiv/L (10 g/L).

The permeability of individual lower hydrocarbons and in a С₁/С₄ mixture is studied for the first time for films based on PTMSP of the new cis-enrich configurational composition (the content of cis-units in the samples is 80 and 90%). The methane permeability of freshly prepared cis-regular PTMSP films (90% cis-units) and exposed to air for a month is higher than the corresponding values of PTMSP films containing 80% cis-units. The X-ray diffraction data indicate a looser packing of cis-regular PTMSP. The introduction of antioxidant Irganox 1076 into the PTMSP films leads to a decrease in the initial level of methane flux. At the same time, the permeability of the films with the added Irganox decreases much more slowly over time (for a month) compared with the films without the added antioxidant. The permeability of individual lower hydrocarbons through PTMSP films without and with the added Irganox 1076 increases in the sequence С₁ < C₂ < C₃ < C₄. The value of the separation factor in the n-butane/methane mixture attains 33, which is almost 7 times higher than selectivity for individual components. A high level of n-butane permeability for cis-enrich PTMSP is maintained at least for a month of film storage in air.

Polysulfones are synthesized in aprotic dipolar solvents, such as dimethylacetamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide, in a wide range of molecular weights from 42 000 to 184 000 g/mol for hollow-fiber membranes spinning for the first time. Dependence of the thermal and mechanical properties of polysulfones on molecular weight characteristics is investigated. A comparison of the mechanical properties of the synthesized PSF and commercial PSF Ultrason S 6010 (BASF, Germany) and PSF-150 (JSC Institute of Plastics, Russia) shows that the synthesized polymers are not inferior to their commercial analogs and some samples even surpass them in terms of the elastic modulus and strength. According to the dynamic viscosity of spinning solutions, promising PSF samples are chosen to form porous hollow-fiber supports. It is demonstrated that the hollow-fiber supports based on PSF with a molecular weight of 110 000 g/mol have a high nitrogen permeability of 47.5 m³/(m² h bar). These supports show promise for casting composite membranes with a thin selective layer.

The physicochemical properties of experimental heterogeneous MK-40 and MA-41 membranes with different ratios of ion-exchange resin and polyethylene binder in their composition have been studied. It is shown that the specific electrical conductivity in 0.01–1 M NaCl solution decreases triply for cation-exchange membranes and doubly for anion-exchange ones with a decrease in the content of ion-exchange resin in the membranes from 69 to 55%. It has been established that the diffusion permeability of anion-exchange membranes is more sensitive to their composition and naturally increases with an increase in the ion-exchange resin proportion in the composition. Information on the influence of the heterogeneous membrane composition on its structure obtained by the method of standard contact porosimetry is supplemented by the calculation of transport-structural parameters of the microheterogeneous and extended three-wire models of the ion-exchange membrane.

Ion-exchange membranes with high specific selectivity to singly charged ions are in demand in various industries. One of the ways to increase the specific selectivity can be the formation on the membrane surface of a thin layer with a charge opposite to the charge of membrane fixed groups. The possibility of forming such a layer due to the specific interaction of calcium ions with the sulfonate groups of the membrane during treatment with a high-intensity electric current in a CaCl₂ solution has been investigated. The ability of heterogeneous (MK-40, Ralex CMH) and homogeneous (CMX, CJMC-5) sulfonated cation-exchange membranes to specifically adsorb calcium ions on their surface has been studied. It has been shown that the CMX membrane exhibits this ability to the greatest extent, which is due to a higher density of (-{text{SO}}_{3}^{ - }) groups on its surface compared to other studied membranes. It has been found that formation of a thin positively charged layer on the surface of the CMX membrane increases the membrane permselectivity coefficient ({{P}_{{{{{text{N}}{{{text{a}}}^{{text{ + }}}}} mathord{left/ {vphantom {{{text{N}}{{{text{a}}}^{{text{ + }}}}} {{text{C}}{{{text{a}}}^{{{text{2 + }}}}}}}} right. kern-0em} {{text{C}}{{{text{a}}}^{{{text{2 + }}}}}}}}}}) by 69%. Moreover, the presence of such a layer does not lead to an increase in undesirable water splitting, which occurs when widely used polyelectrolytes with amino groups are applied as modifiers.

A series of composite ion-exchange membranes based on an heterogeneous cation-exchange MK‑40 membrane and polyaniline is obtained under the conditions of electrodiffusion of a monomer and an oxidizing agent. The process of polyaniline synthesis on the membrane surface is accompanied by recording of chronopotentiograms and pH of the solution leaving the desalination compartment. The initial cation-exchange MK-40 membrane and obtained composites based on it are studied by voltammetry and chronopotentiometry in solutions of NaCl, CaCl₂, and MgCl₂ in the same flow-type electrodialysis cell, in which the composites are obtained. To calculate the transport numbers of counterions in the membranes in solutions of CaCl₂ and MgCl₂ by chronopotentiometry, the apparent fraction of the conductive membrane surface in a solution of NaCl is calculated based on the experimental data on the potentiometric transport numbers of counterions in the membrane. The conditions for the synthesis of polyaniline on the surface of an heterogeneous MK-40 membrane which result in the preparation of samples with selectivity to singly charged ions are found out.

Comprehensive characterization of basic MK-40 and Ralex CMH heterogeneous cation-exchange membranes and composite membranes with polyaniline based on them is performed including the determination of specific electrical conductivity and diffusion permeability; measurement of current–voltage curves in solutions of sodium, calcium, and magnesium chlorides and hydrochloric acid and curves of distribution of water with respect to the bond energies and effective pore radii as well as assessment of the transport structural parameters of a microheterogeneous model. The time of synthesis of polyaniline on the surface of cation-exchange membranes for obtaining samples with an anisotropic structure and asymmetric electric transport properties is determined by successive diffusion of a solution of an oxidizing agent and a monomer through the membrane into water. It is shown based on the analysis of the electric transport properties, structural characteristics, and model transport structural parameters of the membranes in solutions of singly and doubly charged ions that the obtained materials are promising for use in the processes of electrodialysis desalination of multicomponent solutions.

The thermo-oxidative stability and gas transport properties of poly(4-methyl-2-pentyne) (PMP) samples of the mixed configurational composition (50% cis-units) in the presence of phenolic antioxidants Irganox 1076, Irganox 1010, Vulkanox BHT, and Rianox 1520 differing in the nature and structure of substituents on the benzene ring is studied. The annealing of PMP films at 140°С demonstrates that the films with the added Irganox 1076 and Irganox 1010 maintain the strength and stability of gas transport properties for at least 150 h of total heating after moderate decrease in permeability (∼30%) for the first 48 h of heating. PMP films with Vulkanox BHT and Rianox 1520 upon 48 h of heating at 140°С show an increase in gas permeability coefficients, indicating the onset of polymer degradation, and after 100 h of heating they are destroyed. The wide-angle X-ray diffraction of the films with the most effective stabilizers Irganox 1076 and Irganox 1010 reveals a decrease in interchain distances upon annealing which provides evidence for an increase in the packing density of macromolecules as a result of thermally activated relaxation.

Significant increase of ion selectivity has been observed for Nafion membranes modified by poly(diallyldimethylammonium chloride) (PDADMAC) in the presence of lower aliphatic alcohols and NaCl. It has been found that addition of the salt into the alcohol-containing modification solutions results not only in decrease of diffusional permeability towards vanadyl ions P but also in simultaneous two- to threefold growth of proton conductivity σ in comparison with the membranes modified in the alcohol-water solutions in the absence of the salt. As a result, ion selectivity of the membranes calculated as σ/P ratio has been increased in ∼4 orders of magnitude as compared with pristine Nafion 112 membrane. Conceivable mechanism of the ion selectivity increasing is proposed for the membranes modified by PDADMAC in the presence of lower aliphatic alcohols and NaCl.

In this work, poly(4-methyl-2-pentyne) (PMP) with quaternary ammonium salts has been functionalized in order to increase CO₂ selectivity. Functional groups have been introduced by a two-stage method: (i) bromination of the initial polymer and (ii) addition of tertiary alkylamines, namely trimethylamine (TMA) and trimethylamine (TEA). It has been established that the optimal amount of introduced functional groups, while maintaining the mechanical properties of the polymer, is up to 5 mol %. The results of organoelemental analysis and IR spectroscopy confirm the PMP functionalization. X-ray diffraction patterns of the samples indicate an increase in the interchain distance in the series initial PMP–brominated PMP–functionalized PMP. TGA data confirm high thermal and thermal-oxidative stability. The coefficients of permeability, solubility, and diffusion of PMP samples containing TMA and TEA salts have been determined for individual gases. An increased ideal selectivity for the separation of gas pairs CO₂/N₂ by 2–3 times and CO₂/CH₄ by 1.5–2 times has been achieved while maintaining the permeability at a high level.