Membranes and Membrane Technologies最新文献

This review focuses on the separation properties of membranes based on poly(urethane-imides)—modern products of the chemical modification of polyimides and polyurethanes. The membrane properties of poly(urethane-imides) are reviewed in terms of their chemical design. Membranes based on multiblock (segmented) polymers, polyimides crosslinked by polyurethanes, hybrid poly(urethane-imide) materials, and poly(urethane-imides) subjected to the selective destruction of urethane blocks are considered. The main directions of synthesis of membrane poly(urethane-imides) are described, and reactants and reaction conditions are presented. The transport and separation properties of poly(urethane-imide) membranes in separation, pervaporation, and ultrafiltration processes are addressed in detail. Applications of poly(urethane-imide) membranes are discussed. The review provides insight into the importance of poly(urethane-imide) gas separation and pervaporation membranes for separation processes.

Study has been carried out on the separation of oil–water emulsion using polyamide membranes with a pore size of 0.2 μm treated with corona discharge plasma at a voltage of 5–25 kV for 1–5 min. An increase in the productivity and efficiency of separation of oil–water emulsion with corona-treated polyamide membranes has been revealed. An increase in roughness and a change in the chemical structure of the modified membranes are shown.

Modeling of ion transport in a three-layer system containing an ion-exchange membrane and two adjacent diffusion layers makes it possible to describe the permselectivity of the membrane by determining its fixed charge density. For theoretical analysis of ion transport in such systems, the Nernst–Planck and Poisson equations are widely used. The article shows that, in the galvanodynamic mode of operation of the membrane system when the density of the flowing current is specified, the Poisson equation in the ion transport model can be replaced by the equation for the displacement current. A new model is constructed in the form of a boundary value problem for the system of the Nernst–Planck and displacement current equations, based on which the concentrations of ions, electric field strength, space charge density, and chronopotentiogram of the ion-exchange membrane and adjacent diffusion layers in a direct current mode are numerically calculated. The calculation results of the proposed model are in a good agreement with the results of the modeling based on the previously described approach using the Nernst–Planck and Poisson equations as well as with the analytical assessment of the transition time. It is shown that, in the case of the three-layer geometry of the problem, the required accuracy of the numerical calculation using the proposed model is achieved with a smaller number of computational mesh elements and takes less (about 26.7-fold for the system parameters under consideration) processor time in comparison with the model based on the Nernst–Planck and Poisson equations.

Polynaphthoylenebenzimidazoles (PNBI) with keto (PNBI-СО) and sulfonic (PNBI-SO₂) bridging groups are prepared by the solid-phase polycyclization of films of corresponding polyaminoimides (PANI) synthesized by the polycondensation of 1,4,5,8-naphthalenetetracarboxylic dianhydride with 3,3',4,4'-tetraaminobenzophenone and 3,3',4,4'-tetraaminodiphenyl sulfone in N-methylpyrrolidone, respectively. The polycondensation process and the chemical structure of the resulting PANI and PNBI are controlled by ¹Н and ¹³С NMR and IR spectroscopy. It is shown that variation in the temperature of solid-state polycyclization allows for the synthesis of polymers with various cyclization degrees. The experimental values of gas permeability and diffusion coefficients for He, H₂, N₂, O₂, CO₂, and CH₄ are measured, and the solubility coefficients and ideal selectivity for various gas pairs are calculated. It is found that in terms of the permeability/selectivity ratio completely cyclized PNBI are advantageous over incompletely cyclized ones. This finding should be taken into account when choosing a polymer and a selective layer formation method to develop novel composite membranes. The gas transport characteristics achieved for completely cyclized PNBI-SO₂ and their good film-forming properties combined with a very high thermal stability of this class polymers are of great interest for further expanding the PNBI range and prospects for applying novel polymers of this class in various gas separation processes.

A procedure has been proposed for producing ceramic substrates for filtration membranes based on a narrow fraction of fine fly ash microspheres using cold uniaxial pressing followed by high-temperature firing. It has been shown that increasing the sintering temperature from 1000 to 1150°C leads to a decrease in open porosity from 40 to 24%, a decrease in the average pore size from 1.60 to 0.34 μm, and an increase in the compressive strength from 9.5 to 159 MPa. The resulting substrates are characterized by water permeability values of 1210, 310, 240, 170 L m⁻² h⁻¹ bar⁻¹ at sintering temperatures of 1000, 1050, 1100 and 1150°C, respectively. Experiments on filtration of aqueous suspensions of fine microspheres (d_av = 2.5 µm) and microsilica (d_av = 1.9 μm) through a substrate produced at a sintering temperature of 1150°C have shown the rejection close to 100%. The proposed methodology for using ash waste in the production of membrane materials promotes the development of technologies for the integrated processing of thermal energy waste.

Сrosslinked polymer memranes are obtained by the heat treatment of films prepared from a solution of a mixture of bromine-containing poly(1-trimethylsilyl-1-propyne) (PTMSP) and polyfunctional amine polyethyleneimine (PEI) as a crosslinking agent. Crosslinked products are identified from IR spectra, elemental analysis data, and stability of reaction products to a solvent (CCl₄), in which the original brominated PTMSP is soluble. According to the IR spectra, the crosslinking reaction occurs via reactive C–Br bond in bromine-containing PTMSP with the participation of PEI amino groups at a temperature above 90°С. The crosslinking of bromine-containing PTMSP makes it resistant to organic solvents. An increase in the content of PEI in the mixture correlates with the proportion of bromine atoms involved in the reaction. For brominated PTMSP films crosslinked by PEI transport parameters for individual gases and in the mixture n-butane/methane (98.4 mol % methane and 1.6 mol % n-butane) are studied. In the sequence PTMSP–brominated PTMSP-Br–PTMSP-Br/PEI (before crosslinking)–PTMSP-Br/PEI (after crosslinking) permeability for individual gases decreases. Crosslinked PTMSP in the mixture methane/n-butane demonstrates high permeability coefficients of n-butane (({{P}_{{n{text{-}}{{{text{C}}}_{{text{4}}}}{{{text{H}}}_{{10}}}}}}) = 12 000 Barrer) and selectivity for n-butane separation from a mixture with methane (({{alpha }_{{n{text{-}}{{{text{C}}}_{{text{4}}}}{{{text{H}}}_{{10}}}{text{/C}}{{{text{H}}}_{4}}}}}) = 13).

In this work, mixed matrix membranes (MMMs) were obtained based on polyimides synthesized from a mixture of diethyltoluene diamine (DETDA) isomers and BPDA and 6FDA dianhydrides by introducing metal-organic framework compounds ZIF-8 and ZIF-67 in a concentration of up to 20 wt % in chloroform solution. The starting polyimides were synthesized by one-stage high-temperature catalytic polycondensation in a benzoic acid melt. The studied MMMs were treated with sc-CO₂ followed by decompression. The gas transport and gas selective properties of the original and modified membranes were studied. Experimental values of the effective coefficients of permeability and diffusion of gases for He, H₂, O₂, N₂, CO₂, CH₄ were obtained, and the effective solubility coefficients of these gases were calculated. It was found that treatment of the studied MMMs in sc-CO₂ can significantly increase the level of gas permeability of membranes with gas selectivity at the level of initial values, while the achieved effect of changing the permeability of membranes depends on the gas, the nature of the matrix, and the concentration of the introduced particles. It was found that the treatment effect persists over time with a slight decrease in permeability of gases, which remains at a level significantly higher than the initial values. The demonstrated effect of improving gas transport properties when treating MMMs based on polyimide matrices 6FDA-DETDA and BPDA-DETDA in sc-CO₂ can be used for further application of the proposed modification method in order to increase gas transport through MMMs based on other polymers, including highly permeable ones.

Hollow fiber membranes originally developed in the 1960s for the reverse osmosis process have since then become widely used for diverse separation processes. The advantages of hollow fiber membranes include the low energy consumption, ease of operation and, among the most important ones, highly efficient operation in a small footprint (a large membrane area can be packed into a module unit). The production of hollow fiber membranes involves many spinning parameters to be controlled. The list of these parameters, in particular, includes the viscosity of the spinning solution, the design and geometric parameters of the spinneret, the extrusion speed of the polymer solution, the composition and temperature of the bore fluid, the type of external coagulant, the air gap distance, the draw ratio, etc. The effect of these parameters on the properties of hollow fiber membranes is reviewed. Research data pertaining to the modification of polymers, both commercially available and at the stage of their synthesis, are also presented in the context of membrane applications. In addition, the preparation of membranes using non-toxic or less toxic solvents is discussed.

Analytical expressions for the specific coefficients of electrical conductivity and electrodiffusion of a bilayer ion exchange membrane have been obtained in terms of thermodynamics of irreversible processes and the homogeneous model of a fine-pore membrane. The influence of the physicochemical parameters of the modifying layer and the electrolyte concentration on the obtained values of the coefficients at fixed physicochemical characteristics of the substrate has been explored using mathematical modeling. It has been shown that the conductivity and electrodiffusion of the modified membrane increase with increasing the space charge density of the modifying layer when the signs of the space charges of the membrane layers are identical and decrease when they differ or the thickness of the modifying layer increases. With increasing electrolyte concentration, these characteristics of the modified membrane increase regardless of the sign of charges of the membrane layers. The obtained analytical expressions can be used in modeling electromembrane processes and predicting the characteristics of new surface-modified ion exchange membranes.

The article presents an analysis of the kinetic data on dry reforming of methane (DRM) in reactors with traditional (TC) and membrane catalysts (MC). The kinetic experiment in reactors with the TC and MC is performed in the temperature range of 820–900°С at CH₄ : CO₂ = 1 : 1. The experiment reveals intensification of the reaction of methane cracking; its rate constant increases by an order of magnitude. This difference in the DRM data obtained for the studied catalysts is explained by the fact in the case of the MC mass transfer is intensified due to the thermal slip phenomenon. A mathematical description corresponding to the kinetic scheme of the DRM process is proposed, and the rate constants of direct and reverse reactions in both reactors are determined. The DRM process carried out on the TC yields water vapor, while in the case of the MC syngas is produced. On the TC the DRM process is accompanied by the accumulation of carbon deposits (CDs), while on the MC this accumulation is absent. On the TC the DRM process is characterized by three main reactions (methane cracking, gasification of CDs with carbon dioxide and/or water vapor, and reverse water gas shift) which are assumed to be reversible under the experimental conditions. It is found that the gasification of CDs on the TC occurs in the reverse reaction of methane cracking; on the MC, in the reactions of CDs gasification with water vapor (mostly) and carbon dioxide. In the case of the MC, the process is characterized by the irreversible reactions of methane cracking and CDs gasification with water vapor and carbon dioxide. The reverse water gas shift reaction on the MC remains reversible, and its rate constants of direct and reverse reactions are an order of magnitude lower than similar rate constants on the TC.