Membrany i membrannye tehnologii

Due to its high mechanical strength and other outstanding properties the ultra-high molecular weight polyethylene (UHMWPE) is a promising material for membrane preparation. In this work, it was shown that thermally induced phase separation (TIPS) method can be used for preparation of UHMWPE membranes from a mixture of this polymer with decalin even without subsequent drawing of the films. Two ways of decalin removal from the membrane precursor were used: drying from solvent at ambient conditions and extraction into iso-propanol with subsequent drying in air. It was shown that the former way leads to significant shrinkage and thus to membranes with a thickness of ~14 μm, porosity of ~24%, permeance of ~150 l/m² h bar, bubble point of ~1.7 bar and tensile strength of ~8.6 MPa. The structure and properties of the samples prepared using the latter way of decalin removal depend on the duration of the extraction stage. It was established that the decrease of extraction time from 24 to 1 hour results in a decrease of membrane porosity (from ~86 to ~81%) and permeance (from ~1700 to ~1550 l/m² h bar), and an increase of tensile strength (from ~0.73 to ~0.92 MPa), while elongation at break (~280%), melting temperature (~136.5°C) and crystallinity degree (~82%) remain almost unchanged. The main reasons for the observed tendencies are discussed. The obtained data showed that changing the conditions of solvent removal may be used as an effective method of controlling the structure, physico-mechanical and transport properties of the membranes.

Palladium-containing membranes are used for hydrogen separation and purification. However, for sufficiently thin membranes, the permeation flux can be limited by the kinetics of surface processes. In the present study, in order to overcome the limitation of the transition through the surface, the developed Pd₇₆Ag₁₄Au₁₀ alloy membranes were modified with a nanostructured surface layer. The modification was carried out by deposition of penta-branched bimetallic Pd-Pt nanoparticles on the membrane surface. An increase in the hydrogen flux was observed in a wide temperature range (25°–400°C). The highest values of the permeation flux density were demonstrated for membranes with a penta-branched modifier – up to 52.43 mmol s^–1 m^–2 at 400°C. It is assumed that the complex morphology of the nanoparticles, as well as the presence of a synergistic effect from the combination of Pd and Pt, contribute to a decrease in activation barriers and an increase in catalytic activity. The developed membranes demonstrated high and stable selectivity over time, which opens up wide possibilities for their use in steam reforming reactors for producing high-purity hydrogen.

The development of membrane processes requires new materials for the production of highly efficient membranes. In this work, a composite based on P84 copolyimide with the additives of a new modifier of the titanosilicate mineral natisite was created. For this purpose, natisite was synthesized and identified. The P84/natisite composite (5 wt.%) prepared in a DMF solution was used to obtain a dense membrane. The features of the physicochemical, mechanical and gas transport properties of the P84/natisite membrane were studied in comparison with the P84 membrane. Transport properties were estimated by the permeability of He, O₂, N₂ and CO₂ through the membranes. The value of gas permeability through the membranes made of the composite is lower compared to pure P84, and the selectivity of the separation of gas pairs H₂/N₂, CO₂/N₂ and O₂/N₂ is improved due to the inclusion of the natisite modifier. It has been shown that the introduction of 5 wt.% natisite additives does not have a significant effect on the physical and mechanical properties of the P84/natisite (5%) membrane, which meet the industrial requirements.

Resource-saving and environmentally friendly electrodialysis (ED) is finding an increasing number of applications involving the separation and purification of organic acids and the extraction of their anions from wines, juices and biochemical waste products. Gaining information about the transport of these anions, particularly tartaric acid (H₂T) anions, is key to improving ED efficiency. In this study, the transport of tartrates across the CJMA-3 anion exchange membrane was investigated using voltammetry, chronopotentiometry and ED experiments. It was shown that when using a Na_xH_(2–x)T solution with pH 9.0, which contains only doubly charged tartrate anions T^2–, the transfer patterns do not differ from those well known for strong electrolytes. If a solution has a pH of 2.5 or 3.0, it contains a mixture of H₂T acid molecules and singly charged HT^– anions. Upon entering the membrane, HT^– anions dissociate. Protons are excluded from the depleted solution by the Donnan effect, and the resulting doubly charged T^2– anions are transported through CJMA-3. A decrease in the concentration of HT^– in the near-membrane depleted solution stimulates the irreversible dissociation of H₂T. Under the influence of an electric field, protons are removed from the reaction zone and move into the solution, and anions into the membrane. Therefore, the transfer of tartrates through the anion exchange membrane occurs even if the feed solution mainly contains acid molecules. The implementation of these mechanisms causes empirical limiting currents to exceed theoretical limiting currents many times over. The energy consumption for the extraction of 20% tartrates from a 0.022M solution is Na_xH_(2–x)T 0.22 (pH 9.0), 0.32 (pH 3.0) and 0.57(pH 2.5) kW h/kg. The duration of ED in this case increases in the series: pH 3.0 << pH 9.0 < pH 2.5.

The article discusses the possibility of using electrodialysis for processing weak aluminate solutions for the purpose of causticization and obtaining strong alkaline solutions is being studied. A three-chamber electrodialysis cell of our own design is described. The cell uses heterogeneous cation exchange membranes MK-40; titanium alloy VT1-0 is used as the cathode and anode material. Electrodialysis was carried out at an interpolar distance of 3–5 cm and a current density of 0.5–3.0 A/dm² to obtain cathodic (concentrated caustic alkali solution) and anodic (aluminum hydroxide and desalinated solution) products. The optimal operating parameters for the process of electrodialysis concentration of an aluminate solution were selected – the current density is about 2 A/dm² with an the interpolar distance of 4 cm. It was determined that the soda content in the solution within an hour decreases from 55 to 25–30% at various operating parameters of the electrolylysis process. The degree of concentration of total alkali in the solution at the selected process parameters after an hour reaches 1.40–1.45.