Petroleum Chemistry (v.55, #4)

Physicochemical principles of membrane separation as applied to high purification of gases have been surveyed. The influence of impurity concentration in the feed gas and the membrane material on the separation factor and the role of sorption effects in the membrane material on the permeability and selectivity (separation factor) have been discussed. A mathematical model for the process of high gas purification in a radial membrane module has been developed. The efficiency of gas purification in the radial membrane module has been experimentally determined. The effect of longitudinal mixing in the membrane module on the purification efficiency has been theoretically and experimentally studied. The processes of high gas purification by membrane gas separation with recycle have been considered.
Keywords: membrane gas separation; high purification; sorption; radial membrane module; gases

Poly(phenylene isophthalamide) (PA) membranes modified with detonation nanodiamond (ND) particles have been prepared by solid-phase dispersion of powders of the components. The transport properties of dense film membranes containing up to 5 wt % ND have been studied in the methanol and methyl acetate mass transfer processes using the sorption and pervaporation methods. It has been shown that the sorption-diffusion characteristics of the membranes are improved owing to the incorporation of ND particles in the PA matrix. The experimental data on the pervaporation of a methanol-methyl acetate mixture have been used to calculate the classical parameters flux and separation factor and determine permeability and selectivity, characteristic driving force-normalized properties of the test membrane-penetrant system. The highest flux and separation factor values have been obtained for a membrane containing 3 wt % ND. It has been found that the characteristic properties of the membrane-penetrant system facilitate selective mass transport of a methanol-methyl acetate mixture using PA/ND membranes.
Keywords: pervaporation; membrane; poly(phenylene isophthalamide); nanodiamonds; methanol-methyl acetate mixture

The feasibility of exchange of blood plasma in a three-channel, countercurrent convective-mass exchange apparatus (CCMEA) has been theoretically considered. Fundamental advantages of CCMEA over a blood plasma filter have been noted. Calculations based on a mathematical model show a possibility of attaining a 90% or higher degree of CCMEA plasma exchange in the absence of blood thickening and almost at any flow rate of the blood drawn from and returned to the patient, including a low flow rate, which is very important in procedures of this kind.
Keywords: mass transfer; plasma exchange; plasma filtration; plasmapheresis

Usage of cellulose acetate membranes for the sorption-luminescence determination of pyrene in aqueous media by A. V. Straško; A. B. Shipovskaya; T. I. Gubina; O. N. Malinkina; A. G. Melnikov (292-300).
The applicability of cellulose acetate membranes (CAMs) as a solid matrix for the luminescence determination of pyrene in aqueous micellar solutions is shown. The effect of the concentrations of various surfactants, namely, anionic sodium dodecyl sulfate (SDS), cationic cetyltrimethylammonium bromide (CTAB), and nonionic polyoxyethylene (10) mono-4-isooctyl phenyl ether (TX-100), on the fluorescence of pyrene in aqueous micellar solutions before and after sorption preconcentration and in an adsorbed state on a CAM has been studied. It has been found that the fluorescence intensity of pyrene on the solid-phase matrix increases as a result of pyrene solubilization in surfactant hemimiceles formed on the sorbent surface. The highest degree of pyrene extraction on CAMs has been achieved in the presence of cationic CTAB micelles. The CAM has a negative surface potential (−31.5 ± 2.5 mV), which affects the hydrocarbon recovery. The degree of extractlion and the polarity index of a microenvironment of pyrene molecules in solutions decrease in the order CTAB → SDS → TX-100.
Keywords: cellulose acetate membrane; solid-phase matrix; sorption preconcentration; luminescence analysis; pyrene; aqueous micellar solutions

This paper is dedicated to the determination of the osmotic pressure of multicomponent solutions using aqueous food substances such as fruit and vegetable juices, whey, and lactose as examples. The determination of osmotic pressure as a critical parameter responsible for the efficiency of the membrane separation of multicomponent aqueous mineral-organic solutions is a problem of considerable current interest. An original method for the determination of the osmotic pressure of complex solutions has been developed. A relationship between the osmotic pressures of fruit and vegetable juices and whey and the concentration of lowmolecular-weight solutes (sugars and salt ions) in them has been revealed. A laboratory system for studying the reverse osmosis process has been developed. Experiments with fresh fruit and vegetable juices, curd whey, cheese whey, and lactose were carried out by a dynamic method with the use of a cellulose acetate reverse osmosis membrane with an asymmetric structure. The characteristics of the initial and final products after ultrafiltration are given. Based on the experimental data, the dependence of the osmotic pressure of fruit and vegetable juices, whey, and lactose on the concentration of dry solutes was plotted. The experimental results are discussed.
Keywords: fruit and vegetable juice; whey; lactose; membrane technology; reverse osmosis; osmotic pressure; ultrafiltration; ceramic membrane; polymeric membrane

A laboratory setup has been designed to create the same excess hydraulic pressure at both membrane sides. This setup has been used for the whey ultrafiltration permeate/distilled water system to determine the critical pressure at which pores of an MFFK-3 hydrophobic membrane (Vladipor, Russia) are filled with the liquid phase. This value has been found to be 0.6 MPa. On the basis of several assumptions, it has been supposed that, the membrane pores are partially filled with the liquid phase on the both sides before attaining the critical pressure. This filling leads to a reduction in the distance between the meniscuses of the “hot” and “cold” solutions inside the pore, thereby being theoretically capable of enhancing the membrane flux. The liquid entry pressure (LEP) of this membrane has been also determined, being 130 and 50 kPa for distilled water and whey ultrafiltration permeate, respectivey.
Keywords: hydrophobic membranes; membrane distillation; LEP; whey

Formation of a fuel-cell catalyst layer with a low platinum content by V. V. Sokhoreva; V. M. Golovkov (315-317).
The possibility of decreasing the platinum loading of catalyst layers in fuel cells with a polymer electrolyte membrane, retaining a sufficiently high gas permeability and enhanced electrical and proton conductivity, has been explored. Thin Pt-C catalyst layers have been formed by simultaneous sputter deposition of pyrolytic carbon (of MPG brand) and platinum on both sides of the membrane and on the surface of gas diffusion paper. The magnetron sputtering technique is very promising for the fabrication of Pt-C catalyst layers in a membrane-electrode assembly with a low platinum loading, less than 0.05 mg/cm2. It has been shown that the main parameters determining the electronic properties of the catalyst film depend on the porosity, temperature, and stoichiometry of the catalyst layer.
Keywords: magnetron evaporation; catalytic layer; proton-conducting membrane; polyvinylidene fluoride; ions

Formation of hollow fiber membranes doped with multiwalled carbon nanotube dispersions by T. V. Plisko; A. V. Bildyukevich; V. V. Volkov; N. N. Osipov (318-332).
The structure and properties of dispersions of pristine and covalently modified multiwalled carbon nanotubes (MWCNTs) in N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF) and water have been studied. It has been shown that the dispersions in NMP have the highest stability and smallest particle size. The study of MWCNT dispersions in DMAc with various dispersing polymers, such as polyvinylpyrrolidone (PVP), polyethylene glycol, block copolymers of polyethylene glycol and polypropylene glycol of various molecular weights, ethylenediamine tetrakis(ethoxylate-block-propoxylate) tetrol, and ethylenediamine tetrakis(propoxylate-block-ethoxylate) tetrol has revealed that PVP has the best dispersing capacity. It has been found that the particle size and the yield of MWCNTs dispersed in DMAc depend on the nature and molecular weight of the dispersing polymer, as well as on the solvent quality. Polysulfone hollow fiber ultrafiltration membranes with PVP-modified MWCNT additives (PVP is one of the components of the spinning solutions) have been prepared by the phase inversion method. It has been found that the addition of 0.00084-0.0048% MWCNT in a spinning solution makes it possible to vary the transport properties of the hollow fiber membranes in a wide range.
Keywords: multiwalled carbon nanotubes; carbon nanotube modification; carbon nanotube dispersions; ultrafiltration; hollow fiber membranes; polysulfone