Using a Single Set of Structural and Kinetic Parameters of the Microheterogeneous Model to Describe the Sorption and Kinetic Properties of Ion-Exchange Membranes

The concentration dependences of the electrolyte sorption, specific electric conductivity, and diffusion permeability of MK-40 and Nafion-117 cation-Ion-exchange membranes in NaCl solutions have been obtained experimentally. Both the membranes contain macropores. The heterogeneous MK-40 membrane contains pores with a size of up to 1 μm between the particles of the ion Ion-exchange resin and polyethylene. The homogeneous Nafion-117 membrane has been subjected to a special thermal pretreatment which results in the formation of macropores. It has been shown for the first time that these experimentally found relationships can be quantitatively described using one set of structural and kinetic parameters of the microheterogeneous model.     

Structure,morphology, and transport characteristics of profiled bilayer membranes

A procedure for the fabrication of profiled cation-exchange bilayer membranes with the homogenized surface based on the commercial membrane MK-40 has been developed. The surface morphology and membrane microstructure have been studied by atomic-force microscopy, electron microscopy, and standard contact porosimetry. The concentration dependences of the electrical conductivity and diffusion permeability of the profiled and bilayer profiled membranes have been studied. It has been shown that the application of an MF-4SK film on the surface of the profiled membrane results in a decrease in its diffusion permeability and some increase in specific conductivity. Based on the data obtained, the transport and structure parameters have been calculated in terms of the microheterogeneous model to assess the influence of the modification on the properties of the support membrane. The current–voltage characteristics of the membranes have been measured in sodium chloride solutions, and it has been shown that profiling leads to an increase in the limiting current by 40%. The investigation of mass transfer of ions in the channels formed by the support and modified membranes has shown that under intense current regimes, the mass transfer coefficient through the profiled bilayer membrane is one and a half times that through the initial profiled membrane.     

An NMR study of a water-methanol solution sorbed in MF-4SK sulfonated cation-exchange membranes

Concentration dependences of self-diffusion coefficients (SDCs), self-diffusion activation energies for water and methanol, and chemical shifts of the protons of the hydroxyl groups δ_OH simultaneously in an external water-methanol solution and the solution sorbed in MF-4SK membranes have been studied by NMR. It has been revealed that the SDC of pure methanol and pure water sorbed in an MF-4SK membrane is 3–5 times lower than that outside the membrane. It has been found that, in the presence of a small amount of methanol, the SDC of water in the membrane is 1.5–2 times higher than the SDC of pure sorbed water. At a solution concentration of 0.1–0.5 mole fraction, the SDC values of water and methanol in the membrane vary only slightly and are about 6 × 10^?6 and 4 × 10^?6 cm²/s, respectively. It has been determined that the δOH value in the membrane is 100–200 Hz higher than that in the external solution. The observed increase in δ_OH and decrease in SDC in the membrane suggest that the state of the solution in the MF-4SK sulfonated cation-exchange membrane has significantly changed compared to the external solution. The effect of the implanted carbon phase (CP) on the SDC of water and methanol and δOH of the solution sorbed in the MF-4SK membranes containing the CP has been studied. It has been revealed that at a methanol mole fraction of up to 0.5, the introduction of 23 wt % CP decreases the SDC of the solution components by no more than 10–20%. At a methanol mole fraction of 0.25–0.5, the self-diffusion activation energies for methanol and water in the external and membrane solutions decrease by 5–7 kJ/mol.     

Study of electrodialysis of a copper chloride solution at overlimiting currents

The electrodialysis of a 0.005 M copper(II) chloride solution simulating electroplating wastewater has been studied. Exceeding the limiting current on an MK-40 cation-exchange membrane leads to the precipitation of copper hydroxide on the membrane surface, which acidifies the solution in the concentration compartment by catalyzing the water dissociation reaction. It has been shown that an MA-40 membrane sorbs up to 15 wt % copper as a result of complexation with functional groups. During the electrodialysis at overlimiting currents, the MA-40 membrane becomes a source of protons to the desalting compartments and the membrane resistance increases because of the formation of copper hydroxide and/or oxide in large pores.     

Electroreduction of molecular oxygen on metal-ion exchanger nanocomposites

The dioxygen electroreduction reaction has been studied on nanosized metal (Cu₀, Ag₀)-ionexchange matrix (macroporous sulfonated cation-exchange resin KU-23, sulfonated cation-exchange membrane MK-4₀) electrode materials. An increase in the half-wave potential of oxygen electroreduction from ∼0.10 to 0.29 V on passing from the Na⁺-to the H⁺-form of the Me₀-ion exchanger nanocomposite indicates the involvement of the H⁺-ion in the step of attachment of the first electron to the oxygen molecule O₂. The reaction of oxygen on the copper-KU-23 nanocomposite is accompanied by the appearance of an additional wave in the polarization curve of oxygen electroreduction in a neutral medium, which is associated with stabilization of hydrogen peroxide, a reaction intermediate, on nanosized copper. In the region of limiting current potentials, the rate-determining step of the array of electrochemical, chemical, and external- and internal-diffusion processes occurring during the electroreduction of oxygen is the external diffusion of O₂ molecules to the electrode surface.     

Effect of Protolysis Reactions on the Shape of Chronopotentiograms of a Homogeneous Anion-Exchange Membrane in NaH<Subscript>2</Subscript>PO<Subscript>4</Subscript> Solution

Single-pulse and double-pulse chronopotentiograms of a homogeneous anion-exchange membrane AX in 0.02 M solutions of NaCl (system 1) or NaH₂PO₄ (system 2) have been recorded in underlimiting and overlimiting current modes. It has been found that in the case of exceeding the limiting current (i > i _lim ^Lev ) calculated using the convection–diffusion model, the time required to establish a steady state in system 2 increases by more than an order of magnitude compared to system 1. The slow growth of the potential drop is due to a gradual transition of the membrane from the form in which the main counterion is H₂PO ₄ ^– to the HPO ₄ ^2– form. This transition is due to the deprotonation of a part of H₂PO ₄ ^– ions forming HPO ₄ ^2– and protons as they enter the membrane. The participation of H⁺ in charge transfer in the depleted diffusion layer at a given current density causes a lower value of the potential drop than in system 1 for the same i/i _lim ^Lev ratio. In intense current regimes, chronopotentiograms of system 2 exhibit two inflection points. The first point corresponds to the classical Sand transition time and is due to reaching the limiting current of H₂PO ₄ ^– ions (the main charge carrier for i < i _lim ^Lev ) in the depleted diffusion layer. The second point is associated with a critical current that can be called the second limiting current in the system with NaH₂PO₄ and has no analogue in the system with NaCl. This current, which is approximately 2i _lim ^Lev , corresponds to the state when the membrane is completely transformed into the HPO ₄ ^2– form. Meanwhile, the source of protons due to the transformation of H₂PO ₄ ^– into HPO ₄ ^2– ions as they enter the membrane is exhausted. After reaching this critical value of the potential drop, either the HPO ₄ ^2– deprotonation reaction to give triply charged PO ₄ ^3– ions in the membrane or the water splitting on fixed groups located at the membrane/solution interface may occur.     

Effect of chromium compounds on the properties of ion-exchange membranes

The transport properties of ion-exchange membranes MK-40 and MF-4SK, MA-40, and MA-41 in solutions of sodium chloride, chromium(III) chloride, and chromium(VI) oxide have been studied. It has been found that the MA-40 and MA-41 membranes retain their transport properties in chromium chloride(III) solutions, whereas the anion-exchange membranes in chromium(VI) oxide solutions undergo partial or complete degradation. The oxidative impact of chromate ions on both the hydrocarbon matrix of the MK-40 membranes and the chemically resistant perfluorocarbon matrix of the MF-4SK membrane has been revealed.     

Effect of preparation conditions on nanostructural features of the NAFION® type perfluorinated proton conducting membranes

Features of the fine structure of three samples of perfluorinated Nafion® type membranes—Nafion-115, its Russian analogue MF-4SK, and a new similar material PFM-E produced according to our novel water-emulsion technique—have been characterized using the small-angle neutron scattering technique. A difference in the regularity of common elements of fine structure (cylindrical channels) in the membranes has been revealed. Nafion-115 has the most regular structure with a diffraction peak corresponding to the double channel diameter and an additional broad maximum in the scattering curve indicating a long-range order in the arrangement of straight cylindrical channels. For MF-4SK, in addition, twisted and less ordered channels have been observed. In the PFM-E sample channels have a tortuous and branched structure with diameters similar to Nafion-115. Only a short-range order (40–50 Å) in the arrangement of the channels has been detected, and correlation in their mutual orientation at longer distances is weakened. It has been supposed that the observed branched structure of the channels promotes an increase in water content and an improvement in proton conductivity.     

Sensors based on zirconia-modified perfluorinated sulfonic acid membranes sensitive to organic anions in multiionic aqueous solutions

The effect of modification of perfluorinated sulfonic acid membranes with zirconia on their conducting properties and electrode-active properties for potentiometric sensors whose analytical signal is the Donnan potential (DP) has been studied. It has been found that the incorporation of ZrO₂ particles into the membrane matrix results in an increase in the ionic conductivity, as compared with unmodified membranes, and the proton diffusion coefficient changes nonmonotonically. Membranes with a gradient dopant distribution along the sample length provide for a partial decrease in the cation-exchange function of DP sensors because of a decrease in the concentration of fixed cation-exchange groups and due to the sorption of coions. This results in an increase in the sensor sensitivity to organic and sulfur-containing anions in multiionic aqueous solutions. Multivariate calibration methods with a nonorthogonal experimental design were used to evaluate the effects of the concentrations and nature of counterions and coions and pH in the test solutions on the characteristics of DP sensors.     

Structure and gas permeability of nanoporous metal oxide coatings produced by the alkoxide method

Peculiarities of the preparation of selective nanoporous metal oxide coatings on the surface of macroporous rutile support (pore size 0.1 μm and mixed aluminum and titanium oxides (pore size 0.05 μm) are presented. Gas selective coatings of empirical formula of P _x Ti_{1 ? 0.5x} O_{2 ± δ} with uniform distribution of nanosized pores have been obtained with the alkoxide method using titanium alkoxide and ettriol phosphite (precursor of the phosphorous-containing component) at their various total concentrations. Surface morphology of the obtained membranes has been investigated and major parameters of gas selective coatings have been determined. It has been shown that the dependences of the He, N₂, CO₂, and C₃H₈ gas permeability on temperature and pressure drop are consistent with the molecular regime of gas flow. The reproducible effect of permeability anisotropy of ～502?60% is observed when the integral vacuum method is used.     

Characteristics of PD-sensors based on hybrid perfluorinated membranes in aqueous solutions of inorganic electrolytes and lysine

The characteristics of PD-sensors based on MF-4SC perfluorosulfonic cation-exchange membranes, particularly those containing surface-functionalized silica nanoparticles, in HCl, NaCl, KCl, CaCl₂, and lysine monohydrochloride solutions have been studied. It has been revealed that the degree of hydration of inorganic cations has a dominant effect on the magnitude of PD-sensor response in individual electrolyte solutions. It has been shown that the response and sensitivity of PD-sensors based on hybrid materials with respect to lysine cations increase with increasing concentration of amino groups grafted to SiO₂. This feature is attributed to an increase in the counterion concentration in the film owing to a decrease in the water uptake and enhancement of the interaction between the counterions and the functional groups (sulfo groups of membrane, amino groups of dopant) in membrane.     

运用ANSYS5.4作水平井钻杆转向轨迹参数试验

在水平径向钻进中 ,钻杆在其内部高压驱动下通过转向器由垂直方向向水平方向转向 ,在约 0 3m最小曲率半径内发生大于 90°的弯曲 ,而且转向轨迹是由多个参数描述的。对此 ,井运用ANSYS5 4软件完成了所设计的α、R、δ数值试验并对数值试验数据作了处理。分析表明 ,在其它转向轨迹参数不变的情况下 ,偏角α在所设计的范围内变动时 ,钻杆通过转向器的阻力波动较小 ;最小弯曲半径R在所设计的范围内变动时 ,钻杆通过转向器的阻力随着R的增大而减小 ;矫直偏量δ在所设计的范围内变动时 ,当δ >0 ,随着δ的增大钻杆通过转向器的阻力Fz 上升很快 ,而当δ <0 ,阻力Fz 随δ的减小下降较慢     

Electrochemically active surface of nanodispersed copper in ion-exchange matrix

Copper nanoparticles have been formed in ion exchange matrices KU-23 and MK-40 by chemical deposition. The size of the metal particles has been determined using scanning electron microscopy, X-ray powder analysis, and transmission electron microscopy. It has been found that the major contribution to the electrochemically active surface of the nanocomposite based on granular ion-exchange carrier make copper particles of a size of 37–47 nm regularly distributed on the bulk of the polymer. In electrode materials based on ion exchange membranes MK-40, copper nanoparticles on the surface are in general electrochemically active.     

Preparation of metal-polymer composite membranes with conductance asymmetry

The structure and electrochemical properties of a poly(ethylene terephthalate) track membrane, one side of which was coated with thin aluminum layers by thermal vacuum evaporation, have been investigated. It has been found that the deposition of the aluminum layer on the surface leads to the creation of metal-polymer composite membranes that exhibit in electrolyte solutions conductance asymmetry, the rectification effect similar to the p-n junction in semiconductors. This is due to a change in pore geometry of the composite membranes and to the existence in pores of the interface between the original membrane and the aluminum layer, which bear oppositely charged functional groups on their surface in aqueous solutions. Information on ion transport in the membranes has been obtained by impedance spectroscopy.     

CO2/CH4 separation using prepared and characterized poly (ether-block-amide)/ZIF-8 mixed matrix membranes

In this study, poly (ether-block-amide) (Pebax-2533) based mixed matrix membranes were prepared by incorporating various contents of synthesized zeolitic imidazole framework (ZIF-8) nanoparticles into the polymer matrix. The membranes were fabricated via a solution casting–solvent evaporation technique. The results of gas permeation through the membranes revealed that the addition of the ZIF-8 into the polymer matrix enhances both permeability and CO₂/CH₄ selectivity values. As an example, for the mixed matrix membrane comprising 25 wt% of ZIF-8, CO₂ permeability and ideal CO₂/CH₄ selectivity values are 269.73 Barrer and 9.31, respectively, while the corresponding values are 187.54 Barrer and 7.25 for the neat membrane.     

Influence of argon modified atmosphere packaging on the growth potential of strains of Listeria monocytogenes and Escherichia coli

Modified atmosphere packaging (MAP) based on carbon dioxide (CO₂) – nitrogen (N₂) gas mixtures has been applied to maintain the safety and quality of ready-to-eat (RTE) meat products. The use of argon (Ar) gas as a supplement to CO₂–N₂ mixtures or as substitute for N₂ is a current approach to enhance the effectiveness of MAP. As there is limited information on the effect of Ar MAP on the growth behaviour or the survival of pathogenic bacteria in RTE foods, the aim of the present study was to assess the influence of Ar in MAP on the growth of Listeria monocytogenes and Escherichia coli strains under different conditions. For this purpose, a CO₂–N₂ (20:80) atmosphere was compared with a CO₂–N₂–Ar (30:30:40) and CO₂–Ar (30:70) atmosphere based on the assessment of bacterial growth (δ) on a gelatin-agar medium and ham. Additionally, a shelf life monitoring study was performed to evaluate the effect of these treatments on the background microflora of ham. The findings suggest that under the CO₂–N₂ MAP the product matrices supported the growth (δ > 0.5 log CFU g⁻¹) of L. monocytogenes throughout an observation period of 21 days at 4 ± 2 °C. On the contrary, both MAP containing Ar were equally able to reduce the δ below 0.5 log CFU g⁻¹. In this regard it was irrelevant whether L. monocytogenes was inoculated in depth (per slice) or at the surface (top slice) of the ham. Regarding the influence of the different gas atmospheres on E. coli all gas mixtures applied had the capacity to reduce the δ of E. coli below −0.5 log CFU g⁻¹. Further, shelf-life extension could not be managed with the gas atmospheres considered.     

Fine purification of silane for removal of chlorosilanes by membrane gas separation

The membrane separation of a silane, dichlorosilane, trichlorosilane, and tetrachlorosilane gas mixture has been theoretically and experimentally studied. The ideal separation factors have been determined experimentally and their values in the separation cell at pressures P ₁ and P ₂ have been found. The separation factor has been calculated for different ratios of flows in the compartments of a membrane module. The silane cleaning process for the removal of highly penetrating impurities in a radial membrane module and in a membrane module with a feed tank has been calculated.     

The effect of stopping alcoholic fermentation on the variability of H,C and O stable isotope ratios of ethanol

Stopping fermentation using chemical or physical agents is an oenological procedure carried out in order to leave a pleasant amount of residual sugar in the wine. This process is typically used in the production of some Italian sweet wines (such as the famous Moscato d’Asti), where alcoholic fermentation is stopped once the alcoholic content reaches 4.5–10%. In this study, we investigated the effect of stopping fermentation on the isotopic values of (D/H)_I, (D/H)_II, δ¹³C and δ¹⁸O of ethanol obtained from wine. We examined 126 samples obtained by partially fermenting five different must samples (N = 4 fresh musts, N = 1 desulphited must) and 18 commercial Italian sweet wines. Fermentation stage was positively correlated with the δ¹³C and, in particular, the (D/H)_II values of ethanol, but not with the (D/H)_I and δ¹⁸O values. Partially fermented musts and traditional sweet wines were characterized by lower δ¹³C and (D/H)_II isotopic values. The (D/H)_II values were outside the normal range of variability for natural wines, which means that particular care must be taken in assessing the (D/H)_II of sweet wines in order to avoid misinterpreting the results.     

Diffusion characteristics of surface-modified ion-exchange membranes based on MK-40, MF-4SK, and polyaniline

Asymmetric membrane materials based on MK-40 membranes modified with a thin layer of MF-4SK perfluorinated ion-exchange resins with incorporated polyaniline have been studied. The diffusion characteristics of the resulting composites have been analyzed. It has been proved that the membranes with polyaniline undergo a decrease in diffusion permeability, which indicates an increase in selectivity. The modified membranes exhibit a higher cation transport rate. The diffusion coefficients of individual cations in mixed cationic membranes have been estimated. It has been shown that the introduction of small amounts of polyaniline leads to an increase in the proton transport rate.     

Intensification of separation of oil-in-water emulsions using polysulfonamide membranes modified with low-pressure radiofrequency plasma

Effect of low-pressure radiofrequency capacitively-coupled plasma parameters on the separation of model “oil-in-water” emulsions using UPM-20 polysulfonamide membranes with a pore size of 0.01 μm has been studied. Atmospheric air has been used as a plasma gas. The plasma treatment time is 1, 5, 4, and 7 min at a plasma torch anode voltage of U _a = 1.5–7.5 kV. The separated medium is a 3% emulsion based on the industrial oil I-20A; the stabilizer is the surfactant Kosintol-242. The highest performance is observed in the case of membranes treated with plasma for 7 min. It is found that plasma treatment leads to an increase in the emulsion separation efficiency from 90 to 99%. It has been shown that the plasma treatment contributes to the surface hydrophilization of the membranes owing to the formation of oxygen-containing functional groups. The membrane exhibits a contact angle of water of α = 59.6° before treatment and α = 19.5° after a 4-min plasma treatment at U _a = 7.5 kV. Atomic force microscopy reveals that the plasma treatment leads to a change in the surface structure of the membranes, namely, to a decrease in their roughness. The internal structure of the membranes also undergoes changes which result in an increase in their crystallinity.