Membranes and Membrane Technologies最新文献

The study focuses on the removal of dissolved oxygen from a model monoethanolamine (MEA)-based absorbent to prevent oxidative degradation during the absorption process of flue gas CO₂ removal. A mathematical model was developed to evaluate the deoxygenation parameters in a gas-liquid membrane contactor using composite hollow-fiber membranes with a thin non-porous layer made of a blend of polytrimethylsilylpropyne and polyvinyltrimethylsilane. The modeling results were shown to be in good agreement with experimental data on O₂ removal efficiency. The model was applied to assess the scaling of the membrane system for dissolved O₂ removal to handle an absorbent flow rate of 120 m³/h in a hypothetical CO₂ capture plant using absorption technology. The influence of system parameters (absorbent linear flow rate, membrane contactor length, number of membranes in the contactor, initial O₂ concentration in the absorbent) on O₂ removal efficiency was determined. It was shown that to achieve 90% removal of dissolved oxygen, at least 12 membrane modules with a length of 1 meter and a total membrane area of 1800 m² are required. Various scenarios of dynamically changing external system parameters (oxygen concentration in the feed, absorbent flow rate) were simulated for the designed membrane system to predict the system’s response.

Copolyamide coPA and its metal–polymer complex coPA–Cu²⁺ (MPC)—new polyheteroarylenes—have been synthesized and used to obtain dense nonporous membranes. Some physical properties of the membranes have been determined: density and glass transition temperature, as well as the water contact angle, which showed increased hydrophobicity in the MPC membrane. Thermogravimetric and differential thermal analyses have been used to assess the thermal stability of the membranes. Transport properties have been studied during pervaporation of a toluene/methanol mixture. The coPA and MPC membranes are predominantly permeable to toluene for all feed mixture compositions. In separation of the azeotropic toluene/methanol = 31 : 69 (w/w) mixture, the coPA membrane showed the best separation factor equal to 64, while the MPC membrane had a higher permeability of 26.7 g/(m² h) than the coPA membrane. Based on the sorption studies of membrane samples in toluene and methanol, the degree of equilibrium sorption has been determined. New membranes will be most cost-effective in separating toluene/methanol mixtures with a low toluene content.

The work is devoted to the fabrication of hollow fiber thin-layer composite gas separation membranes with an internal selective layer using interfacial polycondensation followed by deposition of a polydimethylsiloxane (PDMS) layer on a polysulfone membrane substrate. The effect of the concentration of amine (triethylenetetramine (TETA)) and acyl (isophthaloyl chloride (IPC)) components and the conditions of PDMS layer deposition on the change in the gas permeability of composite membranes in O₂/N₂ separation was studied. It was found that after forming the selective layer by the interfacial polycondensation method, hollow fibers with high gas permeability values (≥1000 GPU) were obtained regardless of the monomers used and their concentration, with the O₂/N₂ separation factor α being about 1. After applying an additional layer using 1–3 wt % PDMS solutions, the separation factor was 1.5–3.7. The maximum value of the separation factor was found in a fairly narrow range of TETA concentrations (0.15–0.6%) and at a certain equivalent TETA/IPC ratio. The first maximum (α O₂/N₂ = 3.5) is observed at a weight concentration ratio of TETA/IPC = 0.15/0.26, and the second maximum, at the concentration ratio of TETA/IPC = 0.6/0.15, with the permeability of the composite membranes for oxygen being 107 and 76 GPU, respectively.

Preparation of composite membranes is a complex technological task. To ensure high permeability and selectivity of these membranes, preliminary preparation of a selective layer polymer solution is of importance. In this work, the copolymer of polydecylmethylsiloxane and polymethylpentafluoropropylacrylatesiloxane with a theoretical block ratio of 1 : 1 has been synthesized for the first time. According to ¹Н NMR studies, with increasing the time of hydrosilylation of the reaction mixture from 10 to 50 min the degree of substitution of Si–H bonds increases, with the degree of conversion of pentafluoropropyl acrylate being close to quantitative (100 mol %). A change in the hydosilylation degree affects the nature of the rheological behavior of the solution: in 50 min the polymer solutions change from a Newtonian fluid to a gel-like state, which has a crucial effect on changes in their viscosity and ability to form a uniform defect-free coating on a MFFK‑1 microfiltration support. Based on the data on the surface morphology and elemental analysis and the gas permeability of the membranes, the optimal range of polymer solution viscosity is determined, which allows the production of defect-free composite membranes with the minimal flow of the selective layer polymer into the pores of the support. It has been demonstrated that the polymer flow into the support pores and the thickness of the selective layer can be controlled by changing the viscosity of the polymer solution. It has been revealed that the viscosity of the polydecylmethylsiloxane–polymethylpentafluoropropylacrylatesiloxane copolymer solution on the order of ~0.005–0.006 Pa s is optimal for producing composite membranes.

Electrodialysis is increasingly being used for tartrate stabilization of wine, ensuring speed, reproducibility, preservation of valuable components and low environmental impact. In this work, electrodialysis stabilization of wine was carried out using membrane cells formed by pairs of homogeneous (AMX-Sb//CMX-Sb and CJMA-3//CJMC-3) and heterogeneous (MA-41//MK-40 and AMH-PES//CMH-PES) ion-exchange membranes. A comparative analysis of the duration of electrodialysis was performed to reduce the electrical conductivity of the model wine solution by 20%, the degree of extraction of potassium cations and anions (chlorides, sulfates, and tartrates) from its solution as well as energy consumption and pH changes in the desalination and concentration streams. It has been shown that the transport of large, highly hydrated tartaric acid anions in heterogeneous membranes of MA-41 and AMH-PES has steric difficulties. The result of these difficulties is the preferred transfer of chlorides in these membranes, the concentration of which in the model wine solution is an order of magnitude lower than tartrates. The energy consumption required to remove 1 kg of tartrates from the model wine solution is growing in a row: CJMA-3//CJMC-3 < AMX-Sb//CMX-Sb < AMH-PES//CMH-PES < MA-41//MK-40. Replacing the constant electric field mode traditional for electrodialysis with a pulsed electric field mode reduces the energy consumption from 10 to 30% depending on the chemical nature of the membranes.

Nonstationary diffusion problems are considered within the framework of the homogeneous membrane model for a closed membrane cell and a cross-flow cell with a tangential flow of feed solution and permeate in the absence and presence of convection (as applied to dialysis and any pressure-driven membrane process for separating solutions of neutral substances). Characteristic features of a steady state establishment in each of the three cases considered have been revealed, and simple algebraic formulae have been obtained for calculating the time it takes the process to reach a steady state depending on each of the problem parameters. It has been found that membrane characteristics, such as the diffusion coefficient of solute molecules in the membrane and the magnitude of the potential barrier for diffusing components, have a lesser effect on the process stabilization rate than the thickness of the diffusion layer or the flow regime in the case of convective diffusion. It is the additional surface forces, as well as stirring, that make a decisive contribution to the unsteady-state period of the convective diffusion regime. It has been established that purely diffusion processes (for example, dialysis) are not only slower than convective-diffusion processes, but also reach a steady state more slowly. At the same time, it was revealed that the time to reach a steady state in each process is significantly shorter than the characteristic time of the process itself. This fact provides additional justification for the validity of stationary formulations of the problems studied.

At present, the nature of the limiting state of electromembrane systems in solutions of strong electrolytes (e.g., NaCl) is well known. The value of the limiting current in these systems with a rotating membrane disk (RMD) can be calculated quite accurately using the Levich equation. In cases where weak acids and/or their salts are present in the electromembrane system, this equation ceases to be satisfied and the electrodiffusion ion transport is complicated by proton-transfer chemical reactions between these acids, their anions, and water. In this work, the effect of these reactions on the limiting current density in a system with a rotating disk of a cation-exchange membrane and acetic acid has been experimentally studied. The results of voltammetry and their theoretical interpretation using the known mathematical model are presented. Conditions under which the mass transfer rate is limited by the diffusion delivery of acetic acid molecules to the membrane surface, as well as conditions under which the limiting stage is the reaction of their dissociation at the membrane/depleted solution interface, have been revealed.

A model of gas sorption kinetics for a bilayer membrane consisting of a selective polymer layer applied to a highly permeable substrate has been developed. For the first time, analytical expressions for the first and second-order moments of the kinetic sorption curve of the bilayer membrane have been derived. These expressions have been used to propose a method for determining the permeability coefficients of the gas transport through the membrane layers of the bilayer membrane. The results of this work can be applied to evaluate the gas permeability coefficients of composite membranes.

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.