Vol 56, No 4 (2016)

The presented nonisothermal technique for investigation of membrane gas separation (using MDK-1 membrane as an example) demonstrates possibilities of rapid assessment of the separation power of commercial membranes for both individual components and various mixtures in the temperature range of‒20 to +40°C. The efficiency of the membrane process under these conditions (cross-flow membrane module model) for separation of propane–methane mixtures has been evaluated. It has been shown that the permeability of methane decreases with a decrease in temperature in the Arrhenius coordinates and the propane permeability increases. The separation selectivity in the mixture decreases by more than twofold in comparison with the ideal selectivity. Nevertheless, a significant improvement of separation has been observed at lower temperatures, with the recovery of the desired product and its purity being variable in a wide range depending on the practical goal. The nonisothermal technique is supposed to be useful for rapid selection of conditions (temperature, pressure, components to be separated) for efficient application of polymeric membranes for separation of hydrocarbon-containing mixtures that are close in composition to real gas sources.

Membrane technologies using novel types of ion-exchange membranes comprising nanoparticles of inorganic substances—hybrid materials—have been vigorously developed in recent years. This modification leads to significant changes in the system of pores and channels and in the transport properties of the membranes. Owing to the changes, these materials exhibit considerable advantages over conventional membranes. This brief review analyzes the prospects for the use of hybrid ion-exchange membranes in water treatment systems, electrolysis cells, electrochemical current-generation devices, and sensors and in catalysis and gas separation processes.

The results of a pilot study of the structure and properties of cellulose diacetate filtration membranes with solid fillers are reported; thermally treated millet thresh waste (millet glume) was used as a filler. The porosimetric parameters of the initial polymer and solid fillers, the rheological properties of molding solutions, and the operational characteristics of the resulting composite membranes were determined.

The influence of the concentration and molecular weight of polyethylene glycol (PEG, 400–40000 g mol^–1) on the phase state and viscosity of ternary polysulfone–polyethylene glycol–N,N-dimethylacetamide solutions has been studied. It was shown that an increase in PEG molecular weight (MW) results in a decrease in the region of existence of homogeneous solutions on the phase diagram due to polymer incompatibility, and in an increase in the viscosity of polymer solutions. At a constant PEG concentration (5%) the viscosity depends on PEG MW in a complicated way: in the range of PEG molecular weights 1000–6000 g mol^–1 the viscosity is nearly unchanged, but when the PEG MW exceeds 6000 g mol^–1 a sharp increase in the viscosity of the polymer solutions is observed. It was shown that changes in the membrane performance are determined by PEG concentration in the dope solution. At a PEG concentration of 5% an increase in PEG MW results in an increase in membrane performance and a decrease in the rejection capability; at an increase in PEG concentration in the dope solution up to 25% the maximum pure water flux was observed for PEG-400. The bubble point test showed that with an increase in PEG molecular weight a fraction of large pores, which can be considered as selective layer defects, increases.

Nonuniform electric field formed near pores of a metal-coated track-etched membrane retains on the membrane surface particles having a higher dielectric permittivity compared with the surrounding medium. A feasibility of separating suspensions (for example, rutile slurry in distilled water) by dielectrophoresis on metal-coated track-etched membranes has been experimentally shown.

Using the optical method developed in this study and based on the absorption of light from an external reference source by a solid (suspended particles), the concentration profile of settling particles along the flow of a suspension through an extended “transparent” system that model deep-bed filtration with allowance for gravity has been experimentally determined. At a constant differential pressure across the inlet and outlet of the filtration cell, a flow rate of the suspension over time has been measured. By using methods of continuum mechanics, the continuity equation for a selected moving volume of the suspension has been derived, with the change in mass of particles in the volume being proportional to the concentration in unit volume of the porous membrane filter with variable porosity. From the concentration of particles deposited along the depth of the filter, the proportionality factor for the proposed relation of the rate of deposition of particles on the porous skeleton to the concentration of particles in the suspension has been found.