Preparation of steel/titanium dioxide/titanium three-layer composite membranes

Steel/TiO₂/titanium composite membranes have been prepared by magnetron sputtering. The structure of the membrane substrate and that of the selective layers have been studied by scanning electron microscopy. It has been shown that membrane pores from 10 to 150 nm can be obtained by controlling the thickness of the deposited layer. It has been found that the adhesion of the ceramic and metal selective layers to the substrate is 0 according to the GOST 31149-2014 (ISO 2409:2013) classification. The steel/TiO₂/titanium composite membranes possess high selectivity for high-molecular-weight substances and model suspended particles, with the flux of the membranes being on the order of 100 L/(m² h bar) at a deposited-layer thickness of 1.5 μm.     

A novel hybrid material based on polytrimethylsilylpropyne and hypercrosslinked polystyrene for membrane gas separation and thermopervaporation

To improve the membrane permeability and separation properties in gas separation processes and thermopervaporative (TPV) recovery of butanol from model fermentation mixtures, hybrid membranes based on polymers with an extremely high free fractional volume—polytrimethylsilylpropyne (PTMSP) and hypercrosslinked polystyrene (HCL-PS)—have been first prepared and experimentally studied. The composite membranes have been fabricated using the commercial sorbent Purolite Macronet MN-200 exhibiting high sorption capacity for organic solvents. It has been found that in the hybrid membranes, HCL-PS sorbent particles are nonuniformly distributed throughout the volume: they are located in the surface layer of the membrane. It has been shown that the introduction of a small amount of a modifying component (0.5–1.0 wt %) into the PTMSP matrix improves the time stability of transport properties and increase by a factor of 1.5–2 the permeability coefficients of the material to light gases (N₂, O₂, CO₂, CH₄) and butane vapor. It has been found that hybrid PTMSP/HCL-PS membranes have higher separation factors than those of PTMSP membranes in the TPV separation of a butanol/water binary mixture.     

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.     

Ion transport in hybrid membranes based on MF-4SC and silica surface-modified with proton acceptor groups

Methods for synthesizing hybrid MF-4SC membranes containing silica whose surface has been modified with proton acceptor amine-containing groups (3-aminopropyl- and 3-(2-imidazoline-1-yl)-propyl-) are proposed. The incorporation of surface-modified silica particles into the membrane matrix leads to a decrease in the water uptake and exchange capacity compared to a membrane containing pure SiO₂. The proton conductivity and diffusion permeability of NaCl and HCl solutions and the H⁺/Na⁺ ion interdiffusion are studied. The proton conductivity of the membranes containing surface-modified silica is higher than that of the parent membrane and the membrane containing pure SiO₂. It is shown that the surface modification of silica with 5 mol % of nitrogen-containing groups results in a decrease in the diffusion permeability and an improvement in the ion transport selectivity. This extraordinary change in the properties is caused by an increase in the size of the pores and the channels that connect them, along with a significant decrease in the free volume within the pores. At the same time, an increase in the amount of modifying groups to 10 mol % leads to a sharp acceleration of the diffusion permeability and interdiffusion processes because of the formation of through pores in the membrane matrix.     

Membrane separation of gaseous C1-C4 alkanes

The separation of various gaseous hydrocarbons with the aid of polymer membranes is considered; attention is focused on the separation of gaseous C₁–C₄ alkanes, which are the components of natural gas and associated petroleum gases. It is noted that a practically important property of membrane materials is the thermodynamic selectivity of a membrane, which makes it possible to enrich a permeate with heavier alkanes. Up to this point, polyacetylenes exhibited the best transport parameters for the solution of this problem. The second experimental section of this paper describes a study of the separation of CH₄ + C₄H₁₀ binary mixtures on films based on additive poly[3-(trimethylsilyl)tricyclononene-7]. It is demonstrated that this highly permeable saturated glassy polymer exhibits thermodynamic selectivity in experiments with both the individual gases (CH₄ and C₄H₁₀) and their mixtures and provides fivefold butane enrichment of a permeate. The test polymer and others additive Si-containing norbornene polymers are of interest as membrane materials for the separation of hydrocarbon gases.     

Fabrication of Hollow Fiber Membrane from Polyarylate–Polyarylate Block Copolymer for Air Separation

A process has been developed for spinning asymmetric hollow fiber membranes from a polyarylate–polyarylate block copolymer having a separation factor for pure gases in the oxygen–nitrogen pair of α(O₂/N₂) = 6.3 and an oxygen permeance coefficient of 2.4 Barrer. The effect of the polymer molecular weight, the composition of the dope solution, and the spinning parameters on the gas transport properties of the hollow fiber membrane and its geometry has been studied. The use of a polymer with a molecular weight of 67 kDa, as well as the introduction of surfactants into the dope solution, has made it possible to prepare samples of defect-free membranes with an oxygen permeance of 120 L(STP)/(m² h bar) and a separation factor of α(O₂/N₂) = 6.5, which correspond to the selective layer thickness of 60 nm.     

Investigation of pervaporation membranes based on polycarbamide: Effect of residual solvent

Effect of the amide solvent N-methylpyrrolidone occurring in polymer films after their formation on the physicochemical and transport properties of the membranes during pervaporation of a water-isopropanol mixture has been investigated in detail. The objects of study have been new polycarbamide-based membranes a prepared by solvent evaporation from polymer solutions and containing the residual solvent and the membranes from which the residual solvent was removed by special treatment. It has been shown that the removal of the residual solvent increases the density and decreases hydrophilicity of the membrane; in this case, the permeate flux decreases partly during the process of pervaporation, although the separation factor of the water-isopropanol mixture remains high. A composite membrane comprised of a thin selective layer of polycarbamide (～6 μm) and a porous polyphenylene oxide support designed to enhance the flux has been made and investigated.     

Membrane material based on octyl-substituted polymethylsiloxane for separation of C<Subscript>3</Subscript>/C<Subscript>1</Subscript> hydrocarbons

Novel one-step technique has been proposed for octyl-substituted polymethylsiloxane (POMS) synthesis and vulcanization. The technique makes it possible to prepare С₃/С₁ selective gas separation membranes. The fact of POMS formation and vulcanization by hydrosilylation reaction involving 1-octene and polymethylhydrosiloxane has been confirmed by IR spectroscopy data. On the basis of the results obtained by measuring permeability of POMS membranes to permanent gases and propane, a preferred modifier to crosslinker ratio at which polymer films with the best gas transport properties can be obtained has been estimated at 95/5. Experimentally determined permeability coefficients for methane and propane (270 and 1560 barrer, respectively) and ideal propane/methane selectivity of 5.8 allow for the conclusion that POMS obtained in the study has transport properties comparable to those of similar membrane materials reported in the literature as obtained via multistep synthesis.     

Gas permeability through poly(4-methyl-1-pentene) at temperatures above and below the glass transition point

Gas separation properties of polymer films based on semicrystalline poly(4-methyl-1-pentene) (PMP) with T _g = 30°C for permanent gases and some lower hydrocarbons have been experimentally studied in the temperature range of ?20 to 80°C. Experiments have been performed using the differential permeability technique involving the determination of the diffusion coefficient by the characteristic time and functional scaling-up methods. It has been shown that PMP as a biphasic system may be characterized by one diffusion coefficient that includes the contributions of diffusion in the amorphous and crystalline phases. It has also been shown that despite the glass transition (phase transition) at 30°C, the permeability coefficients of the test gases exponentially increase with gas temperature and the temperature dependence curves do not exhibit an inflection in the glass transition region. On the other hand, the Arrhenius plots of the diffusion coefficients show a bend over the entire glass transition range in PMP, with the activation energy of diffusion decreasing with an increase in temperature. This fact demonstrates the unusual, earlier unknown effect of increasing activation energy of diffusion E _D for gases below T _g.     

Elaboration of composite hollow fiber membranes with selective layer from poly[1-(trimethylsylil)1-propyne] for regeneration of aqueous alkanolamine solutions

The results of research on elaboration of the hollow fiber composite membranes for regeneration of aqueous solutions of alkanolamines in membrane gas-liquid contactor are presented in this work. Asymmetric polysulfone (PSF) hollow fiber UF membranes were used as a porous support, poly[1-(trimethylsylil)-1-propyne] (PTMSP) was employed as a diffusion layer. The influence of PSF hollow fiber casting conditions on hydraulic permeability was studied. Samples of composite membranes were obtained with a defectfree layer of PTMSP and carbon dioxide permeance of 0.26 m³ (STP) (m² h bar)^?1. It was revealed by SEM that the thickness of the PTMSP separation layer is 2.5 microns, where in X-ray spectrometry analysis data and calculations according to resistance-in-series model discovered that the selective layer penetration depth to the pores of the support was 1.4 microns. Calculation by resistance-in-series model showed that 98.6% of resistance to the gas transport is attributed to PTMSP, partially intruded in the pores of the support. Chemical stability of materials which comprise composite membrane makes promising their using for regeneration of aqueous solutions of alkanolamines (pH > 11) from carbon dioxide at a temperature of 100°C and a pressure drop of 10 bar in the membrane gas-liquid contactors.     

Gas separation characteristics of new membrane materials based on poly(ethylene glycol)-crosslinked polymers and ionic liquids

Gas transport characteristics (permeability and diffusion and solubility coefficients for CO₂, O₂, N₂, H₂) of new crosslinked membrane materials synthesized by copolymerization of poly(ethylene glycol) dimethacrylate and poly(ethylene glycol) methyl ether methacrylate in the presence of various ionic liquids have been studied. Comparison of the characteristics of specimens with and without ionic liquids has revealed that the presence of ionic liquids enhances the permeability of the membranes, especially to CO₂. It has been shown that the enhancement of the CO₂ permeability of films incorporating ionic liquid is due to an increase in CO₂ solubility and the increase in selectivity for pairs of gases containing CO₂ is determined by thermodynamic selectivity of separation.     

Hybrid Gas Separation Membranes Containing Star-Shaped Polystyrene with the Fullerene (C<Subscript>60</Subscript>) Core

A physicochemical study of novel hybrid polymer membranes based on polyphenylene oxide with a star-shaped modifier incorporated into the matrix has been conducted, and the transport properties of the membranes in the gas separation process have been studied. Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) has been selected as the polymer matrix because of the low cost and high mechanical strength of this material. Star-shaped macromolecules (up to 5 wt %) containing six polystyrene arms grafted onto a fullerene(C₆₀) central core have been used as the filler. The structure and physical properties of the resulting membranes have been characterized by scanning electron microscopy, membrane density measurements, differential scanning calorimetry, and thermogravimetric analysis. Film surface has been studied by contact angle measurements. The gas separation properties of the membranes have been studied by the barometric method for the following individual gases: H₂, O₂, N₂, and CH₄. Data on the separation properties have been plotted as a Robeson diagram to compare with published data. It has been shown that the incorporation of star-shaped polystyrene into the PPO matrix leads to an improvement of the separation efficiency for selected gas pairs and an increase in selectivity compared with that of the unmodified membrane.     

Effect of Pd–Ru alloy membrane thickness on H<Subscript>2</Subscript> flux from steam reforming products

The influence of the thickness of a Pd–Ru alloy membrane on the H₂ flux from binary mixtures containing about 5 and 20% CO, CO₂, CH₄, and steam has been studied. It has been shown that with a decrease in the membrane thickness from 30 to 10 μm, the negative influence of these impurities on the H₂ flux increases. In experiments with pure H₂, it has been established that a decrease in the membrane thickness does not affect the nature of the rate-limiting step in the H₂ flow mechanism. The values for the effective activation energy of the H₂ permeability of the 30- and 10-μm membranes are 13.6 and 23.4 kJ/mol, respectively. A mathematical model describing the flow of hydrogen from binary mixtures through membranes of various thicknesses with varying temperature and pressure is proposed.     

Tubular metal membranes for cleaning the primary-circuit coolant of a pressurized water reactor (WWER)

The fabrication of tubular microfiltration membranes from PKh18N15 corrosion-resistant steel by the method of radial isostatic pressing and magnetron plasma ion deposition of the surface layer is described. Scanning electron microscopy has been used to study the structure of the substrate and surface layers of the membrane. The flux values of tubular membranes have been found to be 1.39 × 10^?8, 1.88 × 10^?8, and 5.53 × 10^?8 m³/(m² Pa s) for the membranes with pore sizes of 1, 5, and 20 μm, respectively. The possibility of regenerating tubular membranes and restoring their productivity by backwashing has been shown. The service life of the membranes with different pore sizes has been determined during the treatment of make-up water for the sample preparation system of the primary circuit coolant of a pressurized water reactor (WWER).     

Carbon Dioxide Desorption from Amine Solution in a Nonporous Membrane Contactor

Long-term testing of a membrane contactor based on a blend of the nonporous polymers polytrimethylsilylpropyne (PTMSP) and polyvinyltrimethylsilane (PVTMS) has been carried out. The flat-sheet membrane contactor has been tested for CO₂ desorption from an aqueous methyldiethanolamine solution at 100°C. It has been found that the mass transfer parameters (CO₂ flux and stripping efficiency) of the 95%PTMSP/5%PVTMS membrane stabilize after the 7th day of testing. The CO₂ mass transfer coefficient in the membrane contactor has been evaluated, and optimal desorption parameters have been determined.     

Vapor-phase membrane concentration of bioethanol and biobutanol using hydrophobic membranes based on glassy polymers

Pervaporation and vapor-phase membrane separation methods for the recovery of bioalcohols from dilute aqueous solutions have been critically compared. The importance of taking into account the liquid–vapor equilibrium diagram in studies on the separation of binary aqueous–alcoholic liquid media by these methods has been shown. Previously published experimental data on the transport of water, ethanol, and n-butanol vapors in hydrophobic membranes based on the glassy polymers poly(vinyltrimethylsilane) (PVTMS), poly(1-trimethylsilyl-1-propyne) (PTMSP), and poly(4-methyl-1-pentyne) (PMP) have been analyzed. Schemes of butanol and ethanol recovery by the vapor-phase membrane separation process from fermentation broths for the cases of application of water-selective and alcohol-selective membranes have been presented, as well as the results of mathematical simulation of the process and assessment of energy consumption.     

Synthesis of MF-4SC composite membranes exhibiting an anisotropic distribution of zirconia and ion transport asymmetry

Methods for synthesis of MF-4SC composite membranes exhibiting an anisotropic distribution of hydrated zirconia through the thickness have been proposed. The transport and diffusion characteristics of the resulting materials have been studied. It has been shown that the composite membranes with the anisotropic distribution of ZrO₂ exhibit ion transport asymmetry.     

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.     

A Study of Pore Formation and Methanol Vapor Permeability in Stretched Polytetrafluoroethylene Films Used as a Precursor of Composite Ion-Exchange Membranes

Methanol vapor permeability and pore formation features in stretched polytetrafluoroethylene (PTFE) films used as a precursor of composite cation-exchange membranes have been studied. Porous structures of the precursor have been formed via stretching PTFE films in air, toluene, isopropyl alcohol, and CCl₄. Permeability has been determined according to the evaporation of a liquid through a porous film; porosity, according to the increase in the film volume during stretching; pore formation features, according to optical microscopy images of porous films and their transverse microsections. It has been found that, with an increase in the stretch ratio, the porosity of PTFE films increases almost linearly, while the methanol vapor permeability increases exponentially. The permeability of the films stretched in liquids is 20 times higher than the permeability of the films stretched in air at comparable stretch ratio and porosity values. The considerably higher permeability of the films stretched in liquids and the observed differences in their porous structure suggest that the liquids are actively involved in the formation of through pores in the direction connecting the film surfaces, i.e., in the direction that determines the transport and conductive properties of composite membranes based on stretched PTFE films.     

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.