Membranes and Membrane Technologies最新文献

The degree of swelling of the lithium form of the perfluorosulfonic acid membrane Nafion in alcohols (ethanol, 2-propanol), water-alcohol mixtures, and highly polar aprotic solvents (N,N-dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP)) was studied, as well as the thermodynamics of membrane-solvent interaction using microcalorimetry. It was shown that the equilibrium swelling degree of the membrane correlates with the donor number of the solvent and the enthalpy of polymer swelling. The enthalpy of membrane swelling in all studied solvents is negative, indicating polymer solvation. Concentration dependences of the swelling and mixing enthalpies in DMF and NMP were studied in greater detail. The negative values of the swelling enthalpy across the entire concentration range of the solvents indicate good thermodynamic compatibility of the membrane with the solvent and highlight the advantage of using these solvents to produce Nafion dispersions due to their strong solvating properties.

A method has been developed for calculating the rate constants of rate-limiting steps of the water splitting reaction in the generating contacts of heterogeneous bipolar membranes (BPMs) containing particles of a catalytic additive. The method is based on the use of the equation of the current–voltage characteristic of the bipolar region of a heterogeneous BPM that contains generating contacts of two types. For the case when the catalytic additive is a cation exchanger (CE), one of the contacts is formed by CE particles and anion exchanger (AE) particles contained in BPM layers, and the other is formed by catalytic additive particles and AE particles contained in BPM layers. The order of the rate constants for the rate-limiting steps of the water splitting reaction in the studied membranes is consistent with the catalytic activity series, the constants of which are calculated based on the proton transfer reactions between water molecules and ionogenic groups contained in the BPM layers.

The rapidly growing field of portable energy sources requires the search for and development of efficient materials for such devices. To enhance the safety of the most common metal-ion batteries (lithium-ion and sodium-ion), it has been proposed to replace the liquid electrolyte with a unipolar conductive gel-polymer electrolyte based on a Nafion-like electrolyte (Inion) plasticized with aprotic solvents. This study presents the results of investigating the thermal stability, molecular and supramolecular structure, as well as the ionic conductivity of Inion membranes in lithium and sodium forms plasticized with propylene carbonate, using methods including synchronous thermal analysis, IR spectroscopy, small-angle X-ray scattering (SAXS), and impedance spectroscopy.

Tartrate stabilization of wine materials by electrodialysis makes it possible to speed up and automate this process and reduce the loss of valuable components. Widespread implementation of electrodialysis in industrial wine production is hampered by fouling of ion-exchange membranes with wine components and by the very limited range of membranes currently used. This study is devoted to a comparative analysis of properties of relatively inexpensive heterogeneous ion-exchange membranes MA-41, MK-40, AMH-PES, and CMH-PES before and after their use in tartrate stabilization of wine materials by electrodialysis. It is shown that the mechanisms of fouling and its effect on transport characteristics, as well as on the development of electroconvection and generation of H⁺ and OH^– ions, are largely determined by counterions that are transferred through cation-exchange (transition metal cations) and anion-exchange (carboxylic acid anions) membranes. Membranes MA-41 and MK-40 demonstrate higher resistance to fouling during operation of an electrodialysis device for less than 15 h.

The catalytic properties of samples containing Pd and Co metals on carbon supports (IR-pyrolyzed chitosan (CT) with an activated surface and detonation nanodiamonds (DNDs) have been studied in the ethanol steam reforming process. CT is a promising catalyst support due to its developed surface and the presence of nitrogen-containing groups capable of sorbing water molecules. The use of a membrane reactor with a Pd–Ru–In membrane has significantly increased the efficiency of the ethanol steam reforming process due to removing hydrogen from the reaction zone. The hydrogen yield in the membrane reactor increases twofold or more compared to a conventional reactor, while the proportion of reaction byproducts (CO and acetaldehyde) decreases. The highest hydrogen yield (15.8 mol/h per gram of catalyst) in the membrane reactor is achieved using a Pd–Co/CT_KOH catalyst.

Three methods for modification of polyacrylonitrile (PAN) ultrafiltration membranes with polyelectrolytes are considered: (1) bulk modification by introducing polyacrylic acid (PAA) into the casting solution, (2) surface modification by using aqueous solutions of polyethyleneimine (PEI) as a coagulation bath, and (3) a combination of methods 1 and 2. In all three cases, modification of membranes with polyelectrolytes leads to effective hydrophilization of the surface of ultrafiltration membranes (the contact angle decreases from 41° to 15°–25°). It has been found that the bulk modification of PAN membranes by introducing 0.05–0.2 wt % PAA into the casting solution leads to a decrease in the pure water flux from 110 to 96 L/m² h. The maximum polyvinylpyrrolidone K30 rejection coefficient of 96% was observed at a PAA concentration of 0.05 wt %; with a subsequent increase in the PAA content, the rejection coefficient decreases to 70–73%. Surface modification of PAN membranes with polyethyleneimine leads to a more than twofold increase in their water flux (up to 233–294 L/m² h), while the rejection coefficient for polyvinylpyrrolidone K30 was 82–96% depending on the PEI concentration in the coagulation bath. It is shown that the combined modification method reduces the water flux to 44 L/m² h, which is associated with the formation of a polyelectrolyte complex and compaction of the membrane structure. It has been found that the combined modification method allows obtaining ultrafiltration PAN membranes with a high flux recovery ratio after filtration of model solutions of polyvinylpyrrolidone (73–100% compared to 65% for the unmodified membrane) and humic acids (80% compared to 73% for the unmodified membrane).

Composite materials based on cation-exchange membranes MK-40 and ceria, including phosphate-functionalized, have been obtained and characterized by SEM, TGA, and IR spectroscopy. The conductivity of the membranes in the sodium form decreases from 6.2 to 3.5 mS/cm and in the calcium form, increases slightly from 1.3 to 1.6 mS/cm. It has been shown that selectivity to divalent ions grows. For example, during electrodialysis desalination selective permeability coefficients Р(Ca²⁺/Na⁺) and Р(Mg²⁺/Li⁺) increase to 3.6 and 6.6, respectively. Furthermore, additional phosphate functionalization of ceria improves the fouling resistance of the materials.

Due to the rapid development of hydrogen energy, increased attention is paid to the preparation of polymer ion-exchange membranes for low-temperature fuel cells. The paper presents the results of studying transport properties and chemical stability of hybrid materials based on a perfluorosulfonic acid polymer membrane with a short side chain Aquivion and hydrated oxides of silicon, titanium, and cerium obtained by the in situ method. Modification of the Aquivion membrane with hydrated silicon and titanium oxides leads to an increase in the proton conductivity of the membranes by 10–40% but, in the case of silica, is accompanied by a gain in gas permeability. The advantage of hybrid membranes Aquivion + SiO₂ is their higher conductivity at reduced humidity (RH = 32%) compared to Aquivion. It is found that membranes based on perfluorosulfonic acid polymers with a short side chain (Aquivion) have higher chemical stability than those with a long one (Nafion^®212). The introduction of hydrated titanium and cerium oxides leads to the preservation of high proton conductivity after membranes treatment with Fenton’s reagent along with their high chemical stability due to the ability of dopants to capture free radicals.

Approximately 90 million barrels of crude oil are processed daily worldwide, with separation processes such as distillation accounting for 10–15% of global energy consumption. In this regard, the scientific community is faced with the ambitious task of finding alternative fractionation technologies that are not based on the volatility of individual components of complex liquid mixtures. The driving force of ultrafiltration is the pressure difference across the membrane. Therefore, separation occurs without phase transitions and with significantly lower energy consumption compared to distillation. In recent years, there has been a growing interest in the development of membrane technologies for the purification and reuse of used lubricating oil. One of the key challenges in membrane filtration of oil and lubricants is their high viscosity. This review examines two approaches to reducing the viscosity of such systems: filtration at elevated temperatures and pre-dilution of the feedstock followed by filtration. A literature analysis revealed that in most cases, ultrafiltration with ceramic membranes is employed in the former approach, while the latter uses more cost-effective polymer membranes. Special attention in the review is given to the issues of membrane fouling and regeneration.

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.