Membranes and Membrane Technologies最新文献

The object of this work is a new hybrid membrane based on poly(m-phenylene-iso-phthalamide) (PA) modified with a complex filler consisting of equal amounts of heteroarm star-shaped macromolecules (HSMs) and [BMIM⁺Tf₂N^–] ionic liquid (IL). Comparative studies of the structures have been carried out on samples of membranes made of pristine PA and hybrid PA/HSM and PA/(HSM:IL) containing 5 wt % additives. Methods of AFM, X-ray powder diffraction, measurement of density, and contact angles have been used. The transport properties of membranes have been studied in separation of a methanol/n-heptane mixture by the pervaporation method. The actuality of this problem is associated with the process of oil refining. In pervaporation of an azeotropic methanol/n-heptane mixture, the hybrid PA/(HSM:IL) membrane has demonstrated higher performance and separation factor relative to reference membranes. Mechanical tests of the membranes have revealed a high level of properties important for operation (strength and relative elongation) of the hybrid membrane.

An original method of obtaining cation exchange composite heterogeneous membranes involving the low-temperature ion-plasma pretreatment of fibrous systems is proposed. The membranes are obtained by the polycondensation filling of polymer composites via the synthesis and hardening of a strongly acidic sulfo cation exchanger on the surface and in the structure of a novolac phenol-formaldehyde fibrous system. The effect of low-temperature ion-plasma pretreatment on a change in the hydrophilicity, capillarity, and structure of heterogeneous cation exchange composite materials Polykon is investigated.

The influence of lactose on the main transport characteristics of ion-exchange membranes including surface-modified with polyaniline cation-exchange membranes is studied. A pronounced to different extents positive effect of modification of MK-40 and Ralex CMHPES membranes with polyaniline on their biofouling by Bacillus sp. or Shewanella oneidensis MR-1 cell cultures is found which is due to the different conductive surface areas of these membranes. It is revealed that the presence of lactose in a solution leads to a decrease in the electrical conductivity of all the studied membranes; however, the effect the most substantially manifests itself for a modified with polyaniline MK-40 membrane: its electrical conductivity decreases by 15–25%. The diffusion permeability of the anion-exchange and initial cation-exchange membranes weakly depends on the presence of lactose in a solution; however, its 2–2.5-fold decrease is observed in the case of modified with polyaniline cation-exchange membranes. A significant effect of lactose on the current–voltage characteristics of the anion-exchange membranes has been found, which indicates significant adsorption of lactose on their surface under the conditions of an external constant electric field. It is shown that ion-exchange membranes remain quite effective for electrodialysis of solutions of lactoserum but their use in underlimiting current modes will be more effective.

Forward osmosis is considered as an emerging technology that can compete with existing methods of desalination, purification, and concentration of natural and wastewater on the global water market. This review presents possible applications of forward osmosis, technological schemes, and the most striking case studies. The issues of forward osmosis membranes development and improvement, composition and regeneration of draw solutions, membrane fouling are considered. Special attention is paid to the problems arising during forward osmosis operation as well as to energy and economic assessment of new technology. Conclusions are drawn about the status of the commercial implementation of forward osmosis and the main barriers that stand in the way of its development.

Membranes have been fabricated from polyacrylonitrile (PAN) doped with graphene oxide (GO) particles, PAN pyrolyzed by IR irradiation (IR-PAN-a), and nanodiamonds (ND). The pore structure of the resulting membranes has been studied. It has been shown that the addition of carbonaceous components slightly reduces the average pore size of the membranes from 17 to 12–15 nm, thereby leading to a decrease in the water permeability of membranes from 158 to 80.9–119.9 kg/(m² h atm). Doping with particulate additives led to surface hydrophilization: the contact angle of water decreased from 65° to 48°–55°, facilitating the flow of crude oil solutions in toluene by a factor of 2–3 compared to the PAN membrane. However, the addition of GO or IR-PAN-a promoted a significant increase in irreversible membrane fouling. On the other hand, the addition of nanodiamonds not only reduced the overall fouling of the membrane and increased the permeability of the feed mixture from 4.93 to 8.47 kg/(m² h atm), but also made it possible to recover more than 96% of the pure toluene flux. The rejection ratio of ND-doped membranes during the filtration of 10 g/L oil solutions in toluene was 85–89%.

Surface-modified cation exchange materials are obtained based on industrial MK-40 heterogeneous and MF-4SK homogeneous cation-exchange membranes by in situ oxidative polymerization of aniline under electrodialysis conditions. The conduction and diffusion characteristics of the initial and modified membranes in solutions of sulfuric acid and nickel sulfate are studied. It is shown that the modification of the membranes with polyaniline leads to a decrease in their electrical conductivity and diffusion permeability without sacrificing high selectivity. The diffusion permeability of the cation-exchange membranes is higher in solutions of nickel sulfate in comparison with solutions of sulfuric acid, while an inverse dependence is found for anion-exchange membranes. The competitive transport of sulfuric acid and nickel sulfate during electrodialysis separation and concentration of their mixture using initial commercial and modified cation-exchange membranes paired with an MA-41 anion-exchange membrane is studied. It is shown that applying a layer of polyaniline with positively charged groups onto one of the surfaces of MK-40 or MF-4SK cation-exchange membranes leads to a decrease in the transport of a doubly charged nickel cation both in the separation and concentration modes over the entire range of current densities. The highest repulsion effect is observed in the case of the use of homogeneous modified membranes, where the selective permeability coefficient P(H₂SO₄/NiSO₄) increases from 0.7–1.7 up to 32.5–19.7 depending on the current density. It is found that the use of surface-modified with polyaniline cation-exchange membranes makes it possible to concentrate a solution containing 0.1 mol-equiv/L (4.9 g/L) H₂SO₄ and 0.1 mol-equiv/L (7.7 g/L) NiSO₄ with simultaneous separation to sulfuric acid with a concentration of about 2.4 mol-equiv/L (120 g/L) and a solution of nickel sulfate. Here, the concentration of nickel sulfate in the concentrate does not exceed 0.13 mol-equiv/L (10 g/L).

The permeability of individual lower hydrocarbons and in a С₁/С₄ mixture is studied for the first time for films based on PTMSP of the new cis-enrich configurational composition (the content of cis-units in the samples is 80 and 90%). The methane permeability of freshly prepared cis-regular PTMSP films (90% cis-units) and exposed to air for a month is higher than the corresponding values of PTMSP films containing 80% cis-units. The X-ray diffraction data indicate a looser packing of cis-regular PTMSP. The introduction of antioxidant Irganox 1076 into the PTMSP films leads to a decrease in the initial level of methane flux. At the same time, the permeability of the films with the added Irganox decreases much more slowly over time (for a month) compared with the films without the added antioxidant. The permeability of individual lower hydrocarbons through PTMSP films without and with the added Irganox 1076 increases in the sequence С₁ < C₂ < C₃ < C₄. The value of the separation factor in the n-butane/methane mixture attains 33, which is almost 7 times higher than selectivity for individual components. A high level of n-butane permeability for cis-enrich PTMSP is maintained at least for a month of film storage in air.

Polysulfones are synthesized in aprotic dipolar solvents, such as dimethylacetamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide, in a wide range of molecular weights from 42 000 to 184 000 g/mol for hollow-fiber membranes spinning for the first time. Dependence of the thermal and mechanical properties of polysulfones on molecular weight characteristics is investigated. A comparison of the mechanical properties of the synthesized PSF and commercial PSF Ultrason S 6010 (BASF, Germany) and PSF-150 (JSC Institute of Plastics, Russia) shows that the synthesized polymers are not inferior to their commercial analogs and some samples even surpass them in terms of the elastic modulus and strength. According to the dynamic viscosity of spinning solutions, promising PSF samples are chosen to form porous hollow-fiber supports. It is demonstrated that the hollow-fiber supports based on PSF with a molecular weight of 110 000 g/mol have a high nitrogen permeability of 47.5 m³/(m² h bar). These supports show promise for casting composite membranes with a thin selective layer.

The physicochemical properties of experimental heterogeneous MK-40 and MA-41 membranes with different ratios of ion-exchange resin and polyethylene binder in their composition have been studied. It is shown that the specific electrical conductivity in 0.01–1 M NaCl solution decreases triply for cation-exchange membranes and doubly for anion-exchange ones with a decrease in the content of ion-exchange resin in the membranes from 69 to 55%. It has been established that the diffusion permeability of anion-exchange membranes is more sensitive to their composition and naturally increases with an increase in the ion-exchange resin proportion in the composition. Information on the influence of the heterogeneous membrane composition on its structure obtained by the method of standard contact porosimetry is supplemented by the calculation of transport-structural parameters of the microheterogeneous and extended three-wire models of the ion-exchange membrane.

Ion-exchange membranes with high specific selectivity to singly charged ions are in demand in various industries. One of the ways to increase the specific selectivity can be the formation on the membrane surface of a thin layer with a charge opposite to the charge of membrane fixed groups. The possibility of forming such a layer due to the specific interaction of calcium ions with the sulfonate groups of the membrane during treatment with a high-intensity electric current in a CaCl₂ solution has been investigated. The ability of heterogeneous (MK-40, Ralex CMH) and homogeneous (CMX, CJMC-5) sulfonated cation-exchange membranes to specifically adsorb calcium ions on their surface has been studied. It has been shown that the CMX membrane exhibits this ability to the greatest extent, which is due to a higher density of (-{text{SO}}_{3}^{ - }) groups on its surface compared to other studied membranes. It has been found that formation of a thin positively charged layer on the surface of the CMX membrane increases the membrane permselectivity coefficient ({{P}_{{{{{text{N}}{{{text{a}}}^{{text{ + }}}}} mathord{left/ {vphantom {{{text{N}}{{{text{a}}}^{{text{ + }}}}} {{text{C}}{{{text{a}}}^{{{text{2 + }}}}}}}} right. kern-0em} {{text{C}}{{{text{a}}}^{{{text{2 + }}}}}}}}}}) by 69%. Moreover, the presence of such a layer does not lead to an increase in undesirable water splitting, which occurs when widely used polyelectrolytes with amino groups are applied as modifiers.