Membranes and Membrane Technologies最新文献

The phenomenon of concentration polarization (CP) in membrane systems refers to the emergence of concentration gradients in solution near the membrane surface due to the selective transport of some solution components through the membrane under the effect of transmembrane driving forces. CP accompanies all types of membrane processes, changing transport conditions and reducing efficiency of separation processes: in most cases, the total transport rate decreases, the energy consumption increases, and the selectivity of the transport process is lost. This review addresses general regularities and specific features of the CP phenomenon in electrodialysis, reverse osmosis, nanofiltration, ultrafiltration, and pervaporation processes, as well as membrane sensing systems and fuel cells. Fundamentals of the CP phenomenon and experimental methods for its investigation are discussed.

The work is devoted to the fabrication of hybrid track-etched polyethylene terephthalate membranes with immobilized silver nanoparticles exhibiting the effect of surface-enhanced Raman scattering. Track-etched membranes were modified with 3-aminopropyltriethoxysilane and 3-mercaptopropyltriethoxysilane using anchor groups based on hydrated forms of aluminum and subsequent immobilization of silver nanoparticles. The resulting track-etched membranes were studied using energy-dispersive X-ray spectroscopy, and the zeta potential of the surface of membrane samples was determined at each modification stage. The presence of silver nanoparticles on the surface of the track-etched membranes was confirmed by scanning electron microscopy, ultraviolet–visible absorption spectroscopy, and surface-enhanced Raman spectroscopy using the test substance 4-aminothiophenol. The proposed approach will help to create sensors based on hybrid track-etched membranes with the possibility of selective sample concentration and further detection of a wide range of substances using surface-enhanced Raman spectroscopy.

The acute shortage of hemodialysis cartridges in Russia, resulting from restrictions imposed by the European Union on the supply of high-tech equipment, has necessitated the development of domestically produced, cost-effective, and efficient hemodialysis membranes. In this study, experimental membranes based on polysulfone were developed and characterized. The effects of different pore-forming agents, polyethylene glycol and polyvinylpyrrolidone, on the structure and transport properties of the membranes have been compared. A non-steady state one-dimensional mathematical model of urea dialysis was proposed, with a key feature being the consideration of the membrane’s microheterogeneous structure. A comparison of the modeling results with experimental data on the time-dependent urea concentration in the dialysate compartment of the dialysis system indicates that the model accurately describes the system under study. A theoretical evaluation of the efficiency of the developed membrane material under conditions relevant to the hemodialysis process has been conducted, along with a comparison of urea removal performance with Nephral ST hemodialysis cartridges from Baxter, a company with a significant presence in the global market. The results have shown that the polysulfone-based membrane produced using polyvinylpyrrolidone demonstrates performance slightly inferior to that of commercially available cartridges, highlighting its potential for use in the production of hollow fiber membranes for hemodialysis cartridges.

A comprehensive characterization of heterogeneous anion exchange MA-40 and MA-41 membranes, differing in the nature of functional groups and the ion-exchange capacity (3.32 and 1.41 mmol/g_dry, respectively), was carried out. The MA-40 membrane contains low basic secondary and tertiary amino groups, while the MA-41 membrane contains predominantly quaternary ammonium bases. Concentration dependences of conductivity and diffusion permeability, current-voltage curves were obtained, and the transport-structural parameters of a microheterogeneous model of membrane in solutions of different natures (salts and acids) containing singly and doubly charged cations and anions (sodium and calcium chlorides, sodium sulfate and sulfuric acid) were determined. The effect of counterions and co-ions on the electrotransport properties of the studied membranes was revealed; it was shown that changes in their properties are determined not only by the nature of the electrolyte but also by the value of the ion-exchange capacity of the samples, as well as the nature of their functional groups.

The problem of low-reagent separation of Na⁺, K⁺, and Li⁺ cations is becoming increasingly important in connection with the search for new technologies for the extraction of lithium from brines and the recovery of this valuable element from already used energy sources. This paper presents the results of testing the electrobaromembrane process, in which the gradients of the electric field and pressure field are directed in opposite directions. The experiments were carried out in a laboratory flow cell, the desalting and concentration chambers of which are separated by a track-etched membrane and limited by MA-41 anion-exchange membranes. The working area of each membrane is 30 cm². The processed solution contains 70, 75, and 55 mmol/L of LiCl, KCl, and NaCl, respectively. It has been shown that at a current density of 11.7 mA/cm² and a pressure difference of 0.20 bar in the desalting circuit, it is possible to ensure an accumulation rate of Li⁺ cations equal to 0.05 mol/(m² h), and a rate of loss of Na⁺ and K⁺ cations from this circuit, equal to –0.09 and –0.25 mol/(m² h), respectively. Factors that can influence the efficiency of separation of Li⁺ and Na⁺, K⁺ are considered.

This study investigates the electrodialysis processing of a dilute sodium chloride solution using commercial anion-exchange membranes—heterogeneous MA-41, homogeneous Neosepta AMX, and an experimental homogeneous membrane MA-1. The rate of desalination and the limiting current value for the examined anion-exchange membranes increase in the order of MA-41, MA-1, AMX. It has been found that for commercial membranes, the desalination process under a constant potential difference across the membrane is accompanied by a transition to an overlimiting state and the development of coupled effects of concentration polarization. For the AMX membrane, beneficial mass transfer is enhanced by electroconvection, whereas for the MA-41 membrane, the salt ion flux decreases due to the occurrence of water dissociation. For the MA-1 membrane, decreasing the solution concentration leads to a transition of the system to a pre-limiting state, which may be associated with a significant contribution of equilibrium electroconvection to ion transfer in dilute solutions in electromembrane systems with this membrane. This difference in the properties of the MA-1 and AMX membranes results in higher mass transfer coefficients for the MA-1 membrane compared to the AMX membrane at potential jumps of 1 and 2 V. The most optimal operating mode for the MA‑1 membrane is a potential jump in the electromembrane system of 1 V, where specific energy consumption is 0.24 kWh/mol. Under comparable conditions, the specific energy consumption for the AMX membrane is 0.34 kWh/mol.

Surface modification of heterogeneous MA-41 anion-exchange membranes with cerium oxide particles, including those with a surface functionalized with phosphoric acid groups, was carried out. The resulting composite membranes were characterized by SEM, TGA, IR spectroscopy, and voltammetry. For membranes in various ionic forms, their conductivity, the number of anion transfers, as well as the selective permeability coefficients of singly and doubly charged anions in the process of electrodialysis desalting were determined. The modifying layer of cerium oxide practically does not change the conductivity of the membranes, but increases their selectivity to singly charged anions. Thus, the value of the selective permeability coefficient (P({text{C}}{{{text{l}}}^{ - }}{text{/SO}}_{4}^{{2 - }})) of the modified MA-41 membrane increases from 0.82 to 1.01, and (P({text{NO}}_{3}^{ - }{text{/SO}}_{4}^{{2 - }})) increases from 1.38 to 1.60.

For the first time, poly(phenylene sulfones) (PPSFs) with chlorine and hydroxyl terminal groups are synthesized and tested for casting high-performance flat-sheet ultrafiltration membranes. The synthesis of PPSFs is carried out in dimethylacetamide at various ratios of 4,4'-dihydroxydiphenyl and 4,4-dichlorodiphenyl sulfone monomers. Two samples with the predominant content of hydroxyl (PPSF-ОН) and chlorine (PPSF-Cl) terminal groups are studied by NMR spectroscopy, GPC, and DSC methods. The coagulation values of polymer solutions in N-methyl-2-pyrrolidone (NMP) and the mechanical properties and hydrophilicity of polymer materials are determined. Both PPSF samples exhibit high tensile strength values at a level of 16 MPa. Using the method of precipitation of PPSF solutions in NMP with PEG-400 additives into water flat-sheet porous asymmetric membranes with a mesoporous (a pore diameter of about 7 nm) thin outer layer and fingerlike macropores in the substrate layer are obtained. An increase in the proportion of hydroxyl terminal groups enhances the hydrophilicity of the polymer. This, in turn, allows for the preparation of flat-sheet membranes from PPSF-ОН with a water permeability of 66 L/(m² h bar), which is 1.5 times higher than the water permeability of the PPSF-Cl membrane. Meanwhile, both membranes demonstrate a Blue Dextran (M_w = 70 000 g mol^–1) rejection of 99.9%.

A comprehensive study of hemocompatibility and gas permeability of 1,2-disubstituted polyacetylenes, namely poly(1-trimethylsilyl-1-propyne) and poly(4-methyl-2-pentyne), was carried out. The polymers were synthesized started from 1-trimethylsilyl-1-propyne and 4-methyl-2-pentynemonomers on the catalytic systems NbCl₅ and NbCl₅/n-Bu₄Sn to form homopolymers containing 50 and 55% cis-units, respectively. The comparison of the obtained polyacetylenes and the thermoplastic polyolefin, poly(4-methyl-1-pentene) that currently is widely used as a thin-film coating of hollow fiber membranes for extracorporeal membrane oxygenation of blood (ECMO), was performed. The investigated polymers are highly hemocompatible as shown by morphofunctional status of blood cells analysis and mesenchymal multipotent stromal bone marrow cells culture of tissue donors. In terms of hemocompatibility, poly(4-methyl-2-pentyne) was superior to poly(1-trimethylsilyl-1-propyne) and was comparable to poly(4-methyl-1-pentene). The studied polyacetylenes were shown to be significantly more permeable on oxygen and carbon dioxide than poly(4-methyl-1-pentene): poly(1-trimethylsilyl-1-propyne) is more permeable in 320 and 400 times, whereas poly(4-methyl-2-pentyne) is more permeable in 60 and 90 times, respectively. These parameters can significantly reduce the contact area of membranes with blood and reduce the size of oxygenators. Since poly(4-methyl-2-pentyne) has the high gas permeability in combination with the hemocompatibility comparable to poly(4-methyl-1-pentene), this polymer can be recommended as a promising material of a selective membrane layer for ECMO technology.

To describe gas transport through a bilayer membrane with a thin selective layer on the surface of a highly permeable gutter layer, it is for the first time proposed to take into account the interlayer resistance arising at the boundary of two membrane layers and a model of gas transport through a bilayer membrane is developed. Analytical expressions for the permeability and selectivity of such a membrane are obtained taking into account this resistance. It is shown that interlayer resistance can noticeably affect the transport characteristics of the membrane. It is found that, even in the case of a low diffusion resistance to gas transport of the gutter layer, its sorption and kinetic parameters affect the permeability and selectivity of the membrane as a whole.