Vol 57, No 2 (2017)

Separation of the gas mixtures 7.7 vol % nitrogen in ammonia and 5.5% carbon monoxide in ammonia in one-compressor multistage membrane devices with one and two separation steps has been compared. The apparent values of selectivity have been determined for these gas mixtures. Expressions relating the degree of separation to the stage cut and the degree of purification to the product loss have been experimentally obtained. The degree of purification has been shown to increase with the number of stages despite of the fact that the degree of separation at individual stages is lower than in a single membrane module.

Transport properties of the new polytriazole and polynaphthalenediimide membrane materials have been observed. According to impedance data, the sulfonated polynaphthalenediimide membrane obtained in dimethylsulfoxide demonstrates the maximum value of ionic conductivity. Modification of a membrane material with silica leads to transport properties improvement.

Seawater desalination by reverse osmosis is widely used for drinking and utility water supply. But the formation of sparingly soluble salts in membrane devices remains a major problem, complicating the operation of reverse-osmosis (RO) membrane systems. The most effective measure to prevent the calcium carbonate and sulfate scaling of membranes is the technology of dosing inhibitors into feed water. Although a variety of effective scale inhibitors have been developed over the last two to three decades, research in this area is currently focused on the development of new types of reagents, the so-called “green” antiscalants, which do not contain phosphorus and are readily biodegradable. The use of such inhibitors does not cause eutrophication of water bodies by RO desalination concentrates discharged into them. The use of scale inhibitors has become particularly demanded in the case of desalination of seawater, since the water is alkalized and an increase in the pH sharply increases the scale deposition rate. In this study, six new phosphorus-free “green” antiscalants have been tested and compared with conventional inhibitors (Aminat-K). Experimental relationships that made it possible to determine the rate of formation of calcium carbonate in membrane devices and to compare the performance of different scale inhibitors in reducing the rates at different pH values are presented.

Effect of low-pressure radiofrequency capacitively-coupled plasma parameters on the separation of model “oil-in-water” emulsions using UPM-20 polysulfonamide membranes with a pore size of 0.01 μm has been studied. Atmospheric air has been used as a plasma gas. The plasma treatment time is 1, 5, 4, and 7 min at a plasma torch anode voltage of U_a = 1.5–7.5 kV. The separated medium is a 3% emulsion based on the industrial oil I-20A; the stabilizer is the surfactant Kosintol-242. The highest performance is observed in the case of membranes treated with plasma for 7 min. It is found that plasma treatment leads to an increase in the emulsion separation efficiency from 90 to 99%. It has been shown that the plasma treatment contributes to the surface hydrophilization of the membranes owing to the formation of oxygen-containing functional groups. The membrane exhibits a contact angle of water of α = 59.6° before treatment and α = 19.5° after a 4-min plasma treatment at U_a = 7.5 kV. Atomic force microscopy reveals that the plasma treatment leads to a change in the surface structure of the membranes, namely, to a decrease in their roughness. The internal structure of the membranes also undergoes changes which result in an increase in their crystallinity.