Vol 56, No 10 (2016)

Membrane technology is characterized by high efficiency, compatibility and flexibility of various membrane processes in integrated systems, low power consumption, high stability and environmental safety of processes, comparative ease and simplicity of controlling and scaling-up, as well as a unique functional flexibility of the membrane processes. This is why the membrane technology is considered as a promising way to reduce anthropogenic emissions of carbon dioxide into the atmosphere. Gas–liquid membrane contactors are a prime example of high-performance hybrid processes using membrane technologies. Integrating several separation methods in one device (membrane contactor) makes it possible to retain benefits of membrane technology, such as small size and flexibility, complementing them with high separation selectivity typical of CO₂ absorption. This review presents the basic principles of operation and design of membrane contactors, and a wide range of materials, membranes, and liquid absorbents for membrane CO₂ absorption/stripping are considered. Particular attention has been paid to current studies on CO₂ removal from thermal power plant flue gas, natural gas, biogas, and syngas. The examples of pilot-scale and semi-commercial implementation of CO₂ absorption/stripping in membrane contactors have been given.

Thin-film membranes based on polyphenylene oxide composites with a varying concentration of heteroarm star-shaped polymers (1, 3, and 5 wt %) comprising arms of polystyrene and poly(2-vinylpyridine)- block-poly(tert-butylmethacrylate) diblock copolymer grafted onto a common fullerene C₆₀ core have been developed. The transport properties of the membranes have been studied in the pervaporation separation of a methanol–ethylene glycol mixture. An increase in the star-shaped polymer content in the membrane leads to an increase in the flux and separation factor of the membranes. Sorption studies have revealed that the sorption activity of methanol in the membranes is higher than that of ethylene glycol. The introduction of star-shaped polymer additives into the membrane composition leads to an increase in the degree of equilibrium sorption of the two components of the mixture subjected to separation. The formation of transport channels in pervaporation membranes during sorption in deuterated methanol has been first studied using the small-angle neutron scattering method. Comparative analysis of the data on neutron scattering on the original dry samples, the samples saturated with deuterated methanol, and the samples dried after sorption has shown that the structural uniformity of the composite membranes is higher than that of the matrix polymer. According to scanning electron microscopy, the morphology of the composite membranes is a system of closed cells.

The effectiveness of a number the test samples of new antiscalants (lightly crosslinked polymers of acrylic and methacrylic acids and crosslinking agents based on allyl ethers and other compounds, and a copolymer of maleic anhydride and methacrylic acid) has been experimentally compared with that of traditionally used scale inhibitors based on hydroxyethylidene diphosphonic acid, nitrilotriphosphonic acid, and the commercial inhibitor Aminat-K. The results of the experimental study of the kinetics of formation and buildup of the crystalline deposit of calcium carbonate in the presence and the absence of scale inhibitors depending on the composition of feedwater and the yield of a filtrate are reported. The experiments have been performed with the use of feedwater from the Moscow water-supply line. Equations for determining the rates of formation of calcium carbonate deposits in membrane devices in the presence of an inhibitor depending on the chemical composition of feedwater and the filtrate yield have been derived; these equations make it possible to recommend a work-cycle time before chemical cleaning operations.

This study has been focused on the influence of the conditions of electrochemical template synthesis (i.e., potential difference and temperature of electrolyte solutions) on the structural and conductive properties of cobalt nanotubes. Polyethylene terephthalate track-etched membranes with a pore density of 1 × 10⁹ ions/cm² have been used as a template. Scanning electron microscopy, X-ray diffraction, and energy dispersive analysis have been used for a comprehensive elucidation of the dimensionality, chemical composition, and crystal structure of the synthesized samples. The optimum conditions for the synthesis of cobalt nanotubes with a minimum crystallographic anisotropy have been determined. It has been shown that controlling the synthesis conditions by changing electrolyte solution temperature and applied potential difference, one can vary the electrical and conductive properties of cobalt nanotube arrays, which have promising application in magnetic recording storage devices, high-precision magnetic field sensors, and optical devices.

A number of electromembrane processes used for the regeneration and purification of chromium plating electrolytes based on chromic acid and its recovery from the rinse water have been described, as well as the solution to the problem of stabilization of the chemical composition of the chromium plating electrolytes based on trivalent chromium salts using the electromembrane method.