Hydrophobization of Polysulfone Hollow Fiber Membranes

The effect of the nature of the pore-forming agent (polyethylene glycol, ethylene glycol, diethylene glycol, glycerol) on the structure and performance of hollow fiber membranes spun from polysulfone solutions in N,N-dimethylacetamide was studied. The membranes have been characterized using various methods (determination of gas permeability and water entry pressure, scanning electron microscopy, contact angle measurement). To increase the hydrophobicity of the selective layer of hollow fibers, a procedure for applying a modifying polydimethylsiloxane layer onto the inner surface of the fiber has been developed, which has made it possible to increase the contact angle from 75°–77° to 115°–151° with retaining their gas transport properties. The composite membranes designed hold promise for use in gas–liquid membrane contactors, and hydrophobized membranes with reduced gas permeability can be used for hydrophobic pervaporation.     

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.     

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.     

Growth in the velocity of mass transfer through the CMX membrane during its aging by operation in intense current regimes

One of the causes for the aging of membranes during their operation in electrodialysis (ED) of solutions is irreversible chemical changes in the ion exchange or reinforcement polymer due to interaction of H⁺ and OH⁻ ions (present in feed solutions or generated in the membrane system under intense current modes) with the matrix or fixed groups in the surface layer of the membranes. The reduction in current efficiency and an increase in energy consumption in the process of electrodialysis are usual consequences of these changes. It has been shown that the degradation of the ion-exchange polymer on the surface of the CMX membrane during its operation in intense current regimes results in the hydrophobization of the membrane surface, which, in turn, causes enhancement of electroconvection. As a result, the limiting current and the mass transfer coefficient of salt ions increase during membrane operation. In the case of desalination of dilute solutions, this growth can reach 50–70% in comparison with the fresh membrane.     

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.     

Cellulose composite membranes for nanofiltration of aprotic solvents

Cellulose composite membranes have been fabricated by casting a cellulose solution in N-methylmorpholine oxide on a nonwoven polyester support. The membranes have been tested for nanofiltration of aprotic solvents. The solvent permeability has changed from 0.11 ± 0.02 to 2.5 ± 0.4 kg/(m² h bar) in the following order: DMSO > NMP > DMFA > THF > acetone, which can be attributed to a decrease in viscosity of the fluids. The rejection of the anionic dyes Orange II (MW 350) and Remazol Brilliant Blue R (MW 626) has been found to range within 15–85% and 42–94%, respectively, on the solvent nature. Sorption experiments have revealed a noticeable difference between certain solvents in interaction with the membrane material: a lower degree of cellulose swelling in THF (37%) and a higher degree in DMSO (230%). In addition, it has been found that the rejection of solutes by the composite membranes correlates with the degree of cellulose swelling. A rejection of ≥90% has been achieved for Remazol Brilliant Blue R, which has the larger molecule, at a cellulose swelling ratio of 100% or higher. Thus, it has been concluded that polymer swelling leads to narrowing the porous structure of the cellulose layer of the composite membrane and, hence, improvement in separation parameters.     

Preparation and ionic selectivity of carbon-coated alumina nanofiber membranes

A novel type of ion-selective membranes based on Nafen^TM alumina nanofibers coated with carbon is proposed. The membranes are produced by filtration of a Nafen nanofiber suspension through a porous support followed by drying and sintering. A thin carbon layer (up to 2 nm) is deposited on the nanofibers by chemical vapor deposition (CVD). Its formation is confirmed by the results of Raman spectroscopy and visually observed in TEM images. According to low temperature nitrogen adsorption experiments, the formation of carbon layer leads to decreasing pore size (the maximum of pore size distribution shifts from 28 to 16 nm) and the corresponding decrease of porosity (from 75 to 62%) and specific surface area (from 146 to 107 m²g^–1). The measurement of membrane potential in an electrochemical cell has shown that the deposition of carbon on the membrane results in high ionic selectivity. In an aqueous KCl solution, the membranes display high anion selectivity with anion and cation transference numbers of 0.94 and 0.06, respectively. The fixed-charge density of membrane has been determined by fitting the experimental data using the Teorell–Meyer–Sievers model. It has been found that the membrane fixed-charge density increases with increasing electrolyte concentration. Possible applications of the membranes produced include nanofiltration, ultrafiltration, and separation of charged species in mixtures. The formation of a conductive carbon layer on the pore surface can be employed for fabricating membranes with switchable ion-transport selectivity.     

Effect of Electric Field on Ion Transport in Nanoporous Membranes with Conductive Surface

The effect of an external electric field on the ionic conductivity and selective properties of ceramic membranes based on alumina nanofibers coated with a conductive carbon layer has been studied. It has been shown that the membranes are ideally polarizable in the polarizing voltage range of ?500 to +500 mV and, therefore, can be used for implementing switchable ionic selectivity. Experiments have revealed that the membrane resistance decreases with a change in the applied potential from 0 to ±500 mV. It has been shown that the membrane selectivity can be switched from anion to cation by varying the external potential. The surface charge density of the membranes has been determined in terms of the Teorell–Meyer–Sievers model according to the experimental measurements of the membrane potential.     

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.     

Modified PTFE–PANI membranes for the recovery of oil products from aqueous oil emulsions

Composite membranes have been prepared by modifying a polytetrafluoroethylene membrane with aniline hydrochloride, and the effect of polymerization time on the efficiency of the recovery of petroleum products from aqueous oil emulsions was studied. It has been found that the modification leads to an increase in the degree of oil removal from oil-in-water emulsions by 29%. The specific productivity of the original and modified membranes has been determined with distilled water and water–oil emulsions. It has been found that the specific productivity of the membranes decreases with the time of membrane treatment with ammonium persulfate. The surface of the modified membranes has been studied with the aid of a scanning electron microscope, and the elemental composition of composite membrane surfaces has been examined by X-ray fluorescence analysis. It has been determined that the modification of a polytetrafluoroethylene membrane with aniline hydrochloride leads to an increase in the carbon content and the appearance of nitrogen, oxygen, and sulfur atoms.     

Hybrid membranes based on polybenzimidazole and hydrated zirconia

Hybrid membranes based on polybenzimidazole and hydrated zirconia doped with phosphoric acid have been synthesized. The effect of synthesis conditions on the properties of the resulting materials has been studied. It has been shown that the modification of the membranes makes it possible to increase their proton conductivity. The introduction of hydrated zirconia decreases the amount of phosphoric acid leached out from the membrane exposed to water vapor. The diffusion permeability of composite membranes in solutions of various salts has been studied. Model tests of some samples under fuel cell operating conditions have been performed.     

Electrical conductivity of KCl solutions in pores of track-etched polymer membranes

The dependence of electrical conductivity of KCl solutions in pores of poly(ethylene terephthalate) and polyimide track-etched membranes (PET TM and PI TM) on the solution concentration and pore diameter has been studied by impedance spectroscopy. It has been found that the conductivity values calculated from the experimental results substantially exceed the standard values in the case of small pore diameters and low concentrations of the solutions, with this difference being more pronounced for PET TM. As the solution concentration and pore diameter increase, the conductivity of the solution in pores tends to the standard value. The revealed effect is explained by the presence of a loose layer on the pore walls that results from the polymer degradation induced by irradiation with high-energy ions. The contact of this layer with the solution gives rise to the gel layer, which is filled with the electrolyte and reduces the measured impedance of the membrane.     

Asymmetric track membranes: Relationship between nanopore geometry and ionic conductivity

The revealing of the “diodelike” properties of electrolyte-filled asymmetric nanopores in track membranes has given significant impetus to a detailed study of the properties of “track” nanocapillaries. Studying the behavior of electrolyte solutions in nanovolumes of a given geometry is very important for many applications, such as nanofluid technology, the resistive pulse method for detecting colloidal particles and molecules, modeling of biological membranes, etc. An attempt to find a quantitative relationship between the geometric shape of asymmetric nanopores and asymmetry in electrical conductivity has been made in this paper. The method of chemical etching in the presence of a surfactant was used for the formation of nanopores with different profiles. The pore structure was studied by electron microscopy. It has been found that the rectification ratio increases with the membrane thickness and depends strongly on the curvature of the pore profile in the selective layer. The maximum of the rectification has been observed in a 0.05–0.1M KCl. Simulation of the ionic conductivity of asymmetric nanopores by the Poisson-Nernst-Planck equation qualitatively explains the observed behavior. The effect of the asymmetry of electrical conductivity is well expressed even in cases when the pore radius in the selective layer is substantially greater than the Debye length. The modification of the pore surface by grafting of aminopropyltriethoxysilane results in the sign inversion of electric charge and a sharp change in the current-voltage characteristics of the membranes.     

Fabrication of high-performance PVA/PAN composite pervaporation membranes crosslinked by PMDA for wastewater desalination

The pyromellitic dianhydride(PMDA) crosslinked poly(vinyl alcohol)(PVA) was coated on top of the PAN ultrafiltration membrane to form a PVA/PAN composite PV membranes for wastewater desalination. The composite membranes have high application value in industrial wastewater treatment. By varying the membrane fabrication parameters including the weight percent(wt%) of the PMDA, the crosslink temperature and duration, membrane with the best desalination performance was obtained. The composite membrane with a 2-lm-thick PVA selective layer containing 20 wt% of PMDA and being crosslinked at 100 °C for 2 h showed the highest Na Cl rejection of 99.98% with a water flux of 32.26 L/(m~2 h)at 70 °C using the 35,000 ppm Na Cl aqueous solution as feed. FTIR spectroscopy, wide-angle X-ray diffraction, thermogravimetric analysis and scanning electron microscope have been used to characterize the structures and properties of both the crosslinked PVA dense films and PVA/PAN composite membranes. The effects of the concentrations of PMDA,the crosslinking time and temperature to the membrane water contact angle, swelling degree, salt rejection and water flux were systematically studied.     

铝合金聚四氟乙烯复合膜的摩擦学性能

利用阳极氧化技术处理铝合金表面，制备铝合金聚四氟乙烯复合膜，该复合膜既具有氧化铝的硬度特性，又具有聚四氟乙烯的润滑性能。阳极氧化层的硬度越大，复合膜摩擦学性能越好。     

基膜热处理对复合膜气体分离性能的影响

制备了用于有机蒸汽正庚烷/氮气分离的PDMS/PVDF复合膜,研究了PVDF基膜热处理温度和时间对复合膜的分离性能的影响,用XPS和SEM对PVDF基膜表面结构的变化进行了研究。结果表明,393.2K、12min热处理后的PVDF基膜表面的C-O、C=O极性官能团增加,增强了表面极性,使得PDMS活性层和PVDF基膜能够紧密结合,而且复合膜的分离性能达到最佳值。在固定测试条件下,分离因子αC7H16/N2为445.7,渗透速率JC7H16和JN2为1.9×10-7、4.26×10-10mol/(m2.s.Pa)。     

Separation of molasses distillery slop on UFM-50®, UPM-50M®, OPMN-P®, and OFAM-K® porous membranes

Experimental data on the pressure gradient-dependent flux through UPM-50M, UFM-50, OPMN-P, and OFAM-K membranes in the separation of molasses distillery slop have been obtained. During the separation of the molasses distillery slop, a dynamic fluid membrane forms above the surface of the active layer on the test semipermeable membrane, which is compacted with increasing pressure and serves as an additional membrane. Evidence has been presented that the reverse osmosis membrane OFAM-K is superior for use at an effective working pressure of P = 4.0 MPa in the separation of the molasses distillery slops to the OPMN-P, UPM-50M, and UFM-50 membranes in terms of performance criteria (environmental friendliness, economy, import substitution, production of a discolored flow (volume) of permeate with good solute permeation and retention parameters) based on the results of statistical processing of experimental data.     

Effect of process parameters of manufacturing of composite fibrous membranes on their structure and ion selectivity

The porous structure of Polikon K composite ion-exchange membranes based on polyacrylonitrile fibers has been studied by standard contact porosimetry. Differences in maximum porosity, internal specific surface area, macropore volume, and other structural characteristics attributed to the use of different molding pressures during the preparation of the membranes have been revealed. According to the analysis of the porometric curves measured in octane and water, it has been found that the volume of hydrophobic pores in the Polikon membranes is an order of magnitude lower than the total volume of hydrophilic pores. The ion selectivity of the membrane materials has been estimated from the porometric curves. A comparison of the ion transport numbers measured by the potentiometric method to the calculated values has shown that they are in good agreement.     

Preparation of composite membranes with bulk or supported catalyst layers

The preparation of composite catalytic membranes as a type of heterogeneous catalysts is considered. The necessity of the use of a catalyst material (bulk or supported) for the formation of the functional layers (selective or catalytic) of a catalytic membrane is substantiated. The procedure for the preparation of a catalytic membrane includes two stages: the initial formation of functional layers from a catalyst precursor followed by its activation. Changes in pore structure characteristics at different stages of preparation are exemplified by membranes with catalysts based on molybdenum compounds. The composite membrane structure has been formed from a precursor by chemical vapor deposition. Composite membranes based on a molybdenum carbide catalyst have been prepared using porous base layers with different porous structures. The effect of the stage of activation on the pore structure characteristics of a catalytic composite membrane has been experimentally demonstrated.