Membranes and Membrane Technologies最新文献

Hydroformylation (or oxo synthesis) is currently one of the most important processes of organic synthesis. Increasing the degree of conversion of this process as well as reducing operating costs seems to be an important direction for its development. A hydroformylation membrane reactor is proposed as an in situ method for separating the catalyst and reaction mixture from the reaction products (aldehydes). This work considers the potential of application of a membrane based on polydecylmethylsiloxane (PDecMS) for a membrane reactor for the hydroformylation of 1-hexene to heptanal. To evaluate the interaction of 1-hexene and heptanal with PDecMS, the sorption of the individual substances and their mixtures at 30 up to 60°C is studied. Sorption isotherms are also obtained for a mixture containing 1-hexene and heptanal which demonstrate selective sorption of heptanal in PDecMS. The transport of 1-hexene and heptanal through a membrane based on PDecMS is studied in the vacuum pervaporation mode at 30 up to 60°C. Based on the obtained experimental data, the temperature dependences of the permeability of 1-hexene and heptanal are plotted. It is shown that the activation energy of transport through a PDecMS membrane is −11.5 kJ/mol for heptanal and −16.4 kJ/mol for 1-hexene. Extrapolation of the temperature dependence of permeability to the operating temperature of hydroformylation (130°C) at a conversion of ~80% shows that, at the permeability of heptanal of 740 mol m⁻² h⁻¹ bar⁻¹ and of 1-hexene, 55 mol m⁻² h⁻¹ bar⁻¹, the flux of heptanal will be 37 kg m⁻² h⁻¹ and of 1-hexene, 5 kg m⁻² h⁻¹. Thus, the permeate will be enriched with the aldehyde.

Synthesis of proton-conducting materials based on track-etched membranes from polyvinylidene fluoride and sulfonated cross-linked polystyrene is described. The synthesis has been carried out by filling the pores of the original or gamma-irradiated track-etched membrane by copolymerization of styrene/divinylbenzene followed by sulfonation of polystyrene with chlorosulfonic acid. The resulting membranes have been studied by scanning electron microscopy and ATR IR spectroscopy. Membrane ionic conductivity, hydrogen gas permeability, ion-exchange capacity, and water absorption were measured. The ionic conductivity at 30°C reaches 51.7 mS/cm, which is almost three times higher than for Nafion®212 membranes; however, the gas permeability of the obtained materials also increases simultaneously.

The review analyzes and summarizes the results of investgations of lithium-conducting polymer electrolytes obtained via ion exchange from the initial H⁺ form of perfluorinated sulfonic cation-exchange membranes of the Nafion family. Salt forms of membranes not only retain the high strength and chemical stability inherent in the parent materials, but also have increased thermal stability (compared to the protonated form). The introduction of plasticizers (dipolar aprotic solvents and their mixtures) and modifying additives makes it possible to achieve a conductivity of 10⁻⁵–10⁻³ S/cm in the ambient temperature range. This makes polymer electrolytes based on lithiated Nafion membranes (Li-Nafion) very attractive for practical use instead of liquid nonaqueous electrolytes in electrochemical power sources. Such research is actively conducted in the field of lithium–oxygen, lithium−sulfur, and lithium-ion batteries, as well as batteries with a lithium metal negative electrode. It is proposed to use Li-Nafion not only as an electrolyte/separator, but also as a functional binder of electrode materials, as a thin barrier layer on a positive electrode or a microporous separator, as an artificial protective layer on the surface of a lithium metal electrode, etc. For all types of considered power sources, the results confirming the prospects for the development of electrochemical systems using Li-Nafion have been obtained.

The deposition of several alternating anion- and cation-exchange surface layers (layer-by-layer method) is a promising technique for the modification of ion-exchange membranes, which makes it possible to essentially increase their selectivity to singly charged ions. This paper presents a one-dimensional model, which is based on the Nernst–Planck–Poisson equations and describes the competitive transfer of singly and doubly charged ions through a multilayer composite ion-exchange membrane. It has been revealed for the first time that, as in the earlier studied case of a bilayer membrane, the dependence of the specific permselectivity coefficient (P_1/2) of a multilayer membrane on the electrical current density passes through a maximum (left( {P_{{{1 mathord{left/ {vphantom {1 2}} right. kern-0em} 2}}}^{{max }}} right).) It has been shown that an increase in the number of nanosized modification bilayers n leads to the growth of (P_{{{1 mathord{left/ {vphantom {1 2}} right. kern-0em} 2}}}^{{max }},) but the flux of a preferably transferred ion decreases in this case. It has been established that (P_{{{1 mathord{left/ {vphantom {1 2}} right. kern-0em} 2}}}^{{max }}) is attained at underlimiting current densities and relatively low potential drop. The simulated dependences (P_{{{1 mathord{left/ {vphantom {1 2}} right. kern-0em} 2}}}^{{max }})(n) qualitatively agree with the known literature experimental and theoretical results.

The permeability of n-butane and methane as well as their mixture through a PDecMS/MFFK composite membrane at reduced temperatures up to 0°C is for the first time studied in this work. According to the data of SEM, the thickness of the selective layer of PDecMS is 5 μm. It is shown that both the permeability coefficient of butane and ideal butane/methane selectivity ({{alpha }_{{{{{{{text{C}}}_{{text{4}}}}{{{text{H}}}_{{{text{10}}}}}} mathord{left/ {vphantom {{{{{text{C}}}_{{text{4}}}}{{{text{H}}}_{{{text{10}}}}}} {{text{C}}{{{text{H}}}_{{text{4}}}}}}} right. kern-0em} {{text{C}}{{{text{H}}}_{{text{4}}}}}}}}}) increase as the temperature decreases from 60 down to 0°C. Thus, the permeability coefficient of butane is 11 400 Barrer at 0°C. It is important to emphasize that the ideal butane/methane selectivity of PDecMS/MFFK of 60 at 0°C is twofold higher than similar values for MDK and PDMS membranes (27 and 32, respectively). This is first of all associated with the difference in the values of the sorption selectivity α^S of these polymers. Thus, the values of (alpha _{{{{{{{text{C}}}_{{text{4}}}}{{{text{H}}}_{{{text{10}}}}}} mathord{left/ {vphantom {{{{{text{C}}}_{{text{4}}}}{{{text{H}}}_{{{text{10}}}}}} {{text{C}}{{{text{H}}}_{{text{4}}}}}}} right. kern-0em} {{text{C}}{{{text{H}}}_{{text{4}}}}}}}}^{{text{S}}}) for PDecMS and PDMS at 0°C estimated based on the enthalpy of sorption are 170 and 95, respectively. In addition, the difference in the activation energies of diffusion of methane in PDecMS, PDMS, and MDK provides a sharper increase in the butane/methane permselectivity for PDecMS when compared to PDMS and MDK in the case of decreasing the measurement temperature. In the case of a C₄H₁₀ (35 vol %)/CH₄ mixture, the butane/methane permselectivity of a PDecMS/MFFK membrane decreases down to 34, which is typical for all the membranes based on polysiloxanes.

Improvement of the chemical stability of hybrid membranes based on perfluorosulfonic acid polymers is necessary to increase the lifetime of fuel cells. This article presents the results of the study of the transport properties and chemical stability of the hybrid Nafion® 212 membranes modified with nanoparticles of hydrated oxides SiO₂, ZrO₂, and TiO₂ by in situ procedure. The influence of the nature of the dopant on the properties of the obtained materials is shown. The chemical degradation of the initial and hybrid membranes has been studied ex situ by treatment with Fenton’s reagent for 240 hours. The stability of materials increases in the series Nafion + SiO₂ < Nafion + ZrO₂ < Nafion < Nafion + TiO₂. For the Nafion + TiO₂ membrane the change in mass as a result of treatment with Fenton’s reagent is two times lower than for the initial Nafion membrane. This reveals an increase in the chemical stability of materials upon the incorporation of TiO₂ nanoparticles due to their ability to bind free radicals. The maximum power of membrane-electrode assembly based on hybrid membranes containing TiO₂ and SiO₂ is higher than that based on Nafion® 212 by 7–10% at RH ~ 100% and t = 65°C.

The effect of pulsed electric field (PEF) parameters on the period-average current densities in the electrodialysis desalination of sodium dihydrophosphate solutions has been studied for the first time. Ir has been shown that, in the case of sodium dihydrophosphate solutions, the PEF effect regularities are generally the same as for the solutions of strong electrolytes. Using the visualization of electroconvective flows in a lean solution near the surface of an anion-exchange membrane, it has been established that the observed distinction in the behavior of membrane systems is caused by weak electroconvection in phosphate-containing solutions. The hypothesis that another reason for the observed distinctions is the effect of a pulsed electric field on the deprotonation of ({{{text{H}}}_{{text{2}}}}{text{PO}}_{4}^{ - }) anions entering the volume of an anion-exchange membrane is put forward.

Composites containing up to 5 wt % montmorillonite (MMT) nanoparticles are created based on natural materials, cellulose acetate and MMT, and film membranes are prepared. The characteristic features of the membrane morphology are studied by scanning electron microscopy. The transport properties of the membranes are studied for the process of separation of a methanol–methyl tert-butyl ether (MTBE) mixture. The degree of equilibrium sorption and diffusion coefficients of methanol and MTBE in the membranes are determined. The pervaporation of a methanol–MTBE mixture is studied in a wide range of feed compositions including the azeotropic point. The best separation factor combined with a high flux is found for a membrane containing 3% MMT. The study of the deformation behavior of the membranes under uniaxial tension shows that they have good mechanical properties, and the elastic modulus increases with the increase in the MMT content while the strength slightly decreases.