Том 58, № 13 (2018)

The results of studies of mass transfer through a polyamide composite reverse-osmosis membrane in the demineralization of dilute solutions of six strong electrolytes are summarized. The relation of the electrolyte concentration at the surface of the reverse-osmosis membrane, at which its true selectivity tends to zero, to the specific water flux and the sum of the hydration numbers of the cations and anions of this electrolyte has been revealed. It has been shown that at a low salinity of the feed solution, the product of the molar electrolyte flux and the sum of the hydration numbers of its cations and anions for the test membrane is almost independent of the electrolyte type. An analysis of the dependence of the solute flux on the transmembrane pressure, concentration, and temperature in the electrolyte concentration range of 0.2 to 20 mol/m³ in the feed solution, as well as the experimentally determined activation energy of the NaCl flux, has led to the conclusion that there is an additive component of the electrolyte flux, whose contribution to the total flux is insignificant at high concentrations and becomes determining at concentrations below 2–5 mol/m³.

Fluorinated copolymers with different compositions and geometric structures have been prepared from 1-trimethylsilyl-1-propyne and its fluorinated containing analogue 1-(3,3,3-trifluoropropyldimethylsilyl)-1-propyne and then studied. The copolymers combine resistance to different hydrocarbons with high permeability coefficients and high selectivity of n-butane separation from its mixture with the noncondensable hydrocarbon methane. High microporosity of the copolymers is confirmed by the results of the determination of the pore volume and pore surface area using low-temperature sorption of nitrogen and the investigation of the film surface by atomic force microscopy (AFM). It has been found that microporosity, which determines the transport properties of the copolymers, depends on both their comonomer composition and the microstructure formed at the stage of polymer synthesis catalyzed by a certain catalyst system. In particular, the copolymers produced in the presence of a TaCl₅–Ph₃Bi catalyst have a greater pore size and a larger pore surface area relative to copolymers with a similar composition formed in the presence of the NbCl₅–Ph₃SiH system. The high values of gas transport parameters of the obtained copolymers and their selectivity for recovery of condensable hydrocarbons from vapor–gas mixtures together with resistance to higher hydrocarbons make these copolymers promising membrane materials, e.g., for use in natural gas conditioning processes or separation of C₃₊ hydrocarbons from associated petroleum gas.

The influence of the electrical and geometrical heterogeneity of the surface of heterogeneous sulfonated cation-exchange membranes on their current–voltage characteristic (CVC) has been experimentally studied. The objects of the study have been experimental samples of Ralex CM Pes membranes manufactured by MEGA a.s. (Czech Republic). A series of experimental membranes Ralex has been produced by hot rolling using an ion-exchanger with different particle sizes. The particle size of the ion-exchanger was controlled by its milling time from 5 to 80 min. It has been found that in the swollen state of the membranes, the ratio of conducting (ion-exchanger particles) and inert (polyethylene) areas on the membrane surface remains constant regardless of the milling time of the sulfonated cation-exchanger. At the same time, the dimensions of the conductive areas and the distance between them decreased and the surface microrelief became smoother. The influence of changes in the membrane surface properties on the CVC parameters has been revealed. With an increase in the ion-exchanger milling time corresponding to a decrease in the spacing of electrical heterogeneity of the surface, a reduction in the length of limiting-current plateau and a decrease in the resistance of the second and third regions on the current–voltage curve were observed. It has been assumed that the main cause of changes in the current–voltage characteristics is an increase in the intensity of heteroelectroconvection.

The affinity of polar extractants (propylene carbonate, dimethylsulfoxide, dimethylformamide, triethylene glycol and dimethylacetamide) and benzene, toluene, p-xylene and m-xylene (so-called BTX fraction) for PIM-1 material was evaluated. The mass-transfer coefficients of selected solvents were determined in organic solvent nanofiltration process. All solvents showed a good affinity toward PIM-1 polymer; while the large values of sorption and PIM-1 swelling degree were in the case of benzene (1.63 g/g, 192%), toluene (1.72 g/g, 186%) and xylenes (1.61–1.76 g/g, 147–170%); while these values for selected polar solvents were in the range of 1.09–1.48 g/g and 83–108%, respectively. The values of sorption and swelling degree were successfully correlated with Hansen’s solubility parameters. Values of permeability coefficients of nonpolar solvents through PIM-1 membranes were 1.5–5.5 times higher than those for polar solvents. With increasing affinity of the solvent toward polymer, the values of the permeability coefficients also increased.