Membranes and Membrane Technologies最新文献

One-sided modification of homogeneous polymer films of poly(vinyltrimethylsilane) (PVTMS), poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), and polybenzodioxane (PIM-1) by liquid-phase fluorination with a fluorine–nitrogen mixture in perfluorodecalin is carried out in the work. The fluorination time is 10 up to 60 min. It is shown by X-ray diffraction analysis for the samples of PPO that the initial samples include a β nanocrystalline phase (48%) in addition to the amorphous phase and it is found that fluorination does not significantly affect the crystallinity index of the films under study. The effect of the fluorination time on the effective permeability, diffusion, and solubility coefficients of oxygen and nitrogen is studied. It is found that the modification leads to a decrease in both the effective diffusion coefficients and effective solubility coefficients of the gases; here, the resulting growth in the permeability selectivity ranges from 30% for PVTMS to a twofold increase in the case of PPO and PIM-1. It is found that such an improvement in the permeability selectivity is predominantly achieved due to the increase in the solubility selectivity. The values of the effective gas permeability coefficients are obtained for an O₂–N₂ mixture. It is found that the achieved values of separation factors for the modified samples are close to the ideal selectivity of the films. The obtained results demonstrate the possibility of effective application of this method not only for the modification of the homogeneous polymer films of the polymers under study but also for membranes with a selective nonporous layer based on them.

Nanofiltration membranes are used to separate a vapor–air mixture containing organic compounds. The membrane is obtained on a filter paper substrate by pouring with a three-component polymer solution. The surface layers are deposited onto the substrate, sequentially alternating the stages of drying of the membrane. The resulting membrane possesses hydrophilic properties; the porosity of the resulting membrane is 51%. The thickness of the membrane determined by SEM is 98 µm. The retention capacity of the membranes is studied by separating ethanol–air and gasoline–air model mixtures. The membrane permeability of an MAC3 composite membrane during separation of an ethanol–air vapor–air mixture is 11.0 m³ m⁻² h⁻¹ at 0.5 MPa. A high retention capacity of an MAC3 composite membrane is established for xylenes, toluene, and heptane; for other compounds, the efficiency is no higher than 90%. The average retention capacity of the resulting membrane is 87%. Comparative tests on the determination of the gas separation parameters under similar conditions are carried out with a commercial OPMN-P membrane.

One of the promising technologies in demand is biomass processing to obtain various organic substances including energy carriers and valuable chemicals. Developing processes for the bioprocessing of lignin suggest the use of a synthetic biological system that allows the production of lower aliphatic alcohols through the stage of formation of carboxylic acids. Due to the production of alcohols in the form of dilute aqueous solutions, their recovery and concentration are extremely energy-consuming steps. In this paper, we consider the membrane vapor separation method as applied to aqueous solutions containing alcohols and organic acids. The transfer of vapors of water and С₁–С₄ alcohols through commercial pervaporation and gas separation membranes that have not been studied for this purpose, as well as through a laboratory membrane, has been studied. The highest separation performance of water–alcohol mixtures was demonstrated by the Romakon^TM-PM 102 membrane, which was also investigated in the separation of mixtures with acetic acid. On the basis of the experimental data obtained, mathematical modeling of the process of ethanol recovery from the water/ethanol/acetic acid ternary mixture by the membrane vapor separation method was carried out.

In order to increase the efficiency of membranes in the processes of gas separation and thermopervaporative isolation of volatile organic compounds from aqueous media, mixed-matrix membranes based on polytrimethylsilylpropine (PTMSP) with an amount of hypercrosslinked polystyrene (HCPS) particles up to 50 wt % have been obtained and experimentally studied for the first time. The industrial sorbent Purolite Macronet™ MN200 was chosen as HCPS due to its high sorption capacity for volatile organic compounds. It has been found that HCPS particles are nonuniformly distributed over the membrane volume and the membranes show a distinct asymmetry when the HCPS content in PTMSP is more than 30 wt %. In the cross section, the membranes represent composite membranes with a thin selective layer (PTMSP) and a porous support (HCPS). It has been established that the permeability coefficients for light gases increase with an increase in the MN200 concentration in the membrane material from 0 to 20 wt %. The introduction of HCPS in an amount of more than 20 wt % in PTMSP leads to an increase in permeability coefficients by 4–7 times, with the selectivity decreasing. The properties of PTMSP membranes with different HCPS fillings were studied during the thermopervaporative separation of benzene–water, toluene–water, and o-xylene–water binary solutions and a multicomponent BTX–water mixture. It has been found that the permeate flux and the separation factor increase with an increase in the HCPS content in PTMSP for all the studied solutions. The maximum values of the separation factor (>900) for all processed solutions were obtained for PTMSP membranes with a HCPS content of 30 wt %.

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 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 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 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.