Open Access
Access granted
Subscription Access
Vol 57, No 13 (2017)
- Year: 2017
- Articles: 7
- URL: https://journal-vniispk.ru/0965-5441/issue/view/11178
Article
Effects of Bulky Substituents on Transport Properties of Membrane Gas Separation Materials
Abstract
In this review membrane gas separation properties of two groups of glassy polymers are considered and compared. The first group comprises highly permeable polymers with large free volume. They contains bulky substituents of the structure MR3, where M = Si, Ge, C, and R = Me, Et, Ph. The second group is represented by polycondensation materials (polyamides, polyimides etc.) with various bulky side groups. It was noted that introduction of such substituents into various main chains of polymers of both groups results in increases in gas permeability, free volume and diffusivity. Robeson diagrams for both cases are considered.
1195-1206
Effect of Protolysis Reactions on the Shape of Chronopotentiograms of a Homogeneous Anion-Exchange Membrane in NaH2PO4 Solution
Abstract
Single-pulse and double-pulse chronopotentiograms of a homogeneous anion-exchange membrane AX in 0.02 M solutions of NaCl (system 1) or NaH2PO4 (system 2) have been recorded in underlimiting and overlimiting current modes. It has been found that in the case of exceeding the limiting current (i > ilimLev) calculated using the convection–diffusion model, the time required to establish a steady state in system 2 increases by more than an order of magnitude compared to system 1. The slow growth of the potential drop is due to a gradual transition of the membrane from the form in which the main counterion is H2PO4– to the HPO42– form. This transition is due to the deprotonation of a part of H2PO4– ions forming HPO42– and protons as they enter the membrane. The participation of H+ in charge transfer in the depleted diffusion layer at a given current density causes a lower value of the potential drop than in system 1 for the same i/ilimLev ratio. In intense current regimes, chronopotentiograms of system 2 exhibit two inflection points. The first point corresponds to the classical Sand transition time and is due to reaching the limiting current of H2PO4– ions (the main charge carrier for i < ilimLev) in the depleted diffusion layer. The second point is associated with a critical current that can be called the second limiting current in the system with NaH2PO4 and has no analogue in the system with NaCl. This current, which is approximately 2ilimLev, corresponds to the state when the membrane is completely transformed into the HPO42– form. Meanwhile, the source of protons due to the transformation of H2PO4– into HPO42– ions as they enter the membrane is exhausted. After reaching this critical value of the potential drop, either the HPO42– deprotonation reaction to give triply charged PO43– ions in the membrane or the water splitting on fixed groups located at the membrane/solution interface may occur.
1207-1218
Methanol Steam Reforming over ZrO2-Supported Catalysts in Conventional and Membrane Reactors
Abstract
Results of a study of the methanol steam reforming (MSR) catalytic process in conventional flow and membrane reactors in the presence of Ni0.2–Cu0.8 and Ru0.5–Rh0.5 catalysts supported on ZrO2 with a monoclinic, tetragonal, and cubic structure have been described. The cubic structure of zirconia has been stabilized with ceria. The samples have been characterized by X-ray diffraction analysis, transmission electron microscopy, and the BET method. It has been shown that the catalytic activity of the composites depends on the type of the metals and the structure of the support. It has been found that the Ru–Rh/Ce0.1Zr0.9O2–δ catalyst exhibits the highest activity, whereas Cu–Ni/Ce0.1Zr0.9O2–δ is the most selective. A comparative study of the MSR process in conventional and membrane reactors with Pd–Ru and modified Pd–Ag membranes has been conducted. The membrane process with a membrane based on a Pd–Ag alloy in the presence of the Ru–Rh/Ce0.1Zr0.9O2–δ catalyst provides a ~50% increase in the hydrogen yield.
1219-1227
Hybrid Membranes Synthesized from a Nafion Powder and Carbon Nanotubes by Hot Pressing
Abstract
Unmodified and hybrid membranes based on Nafion and carbon nanotubes have been synthesized by hot pressing from a mixture of polymer and dopant powders. The water uptake, ionic conductivity under different conditions, and diffusion permeability of the membranes for HCl and methanol solutions have been studied. The hybrid membranes are characterized by high water uptake and proton conductivity in contact with water and low diffusion permeability for hydrochloric acid solution. In contact with water, the conductivity of the samples modified with 1 wt % carbon nanotubes is 0.070 S/cm; the diffusion permeability of a 0.1 M HCl solution is 2.43 × 10–7 cm2/s.
1228-1232
Modification of Track-Etched PET Membranes by Graft Copolymerization of Acrylic Acid and N-Vinylimidazole
Abstract
Photoinduced graft polymerization of N-vinylimidazole (VI) and graft copolymerization of N-vinylimidazole with acrylic acid (AA) onto track-etched polyethylene terephthalate membranes (PET TeMs) with a pore diameter of 450 ± 15 nm have been systematically studied. The effect of different parameters, such as irradiation time, monomer concentration, and solvent nature, has been examined. The samples have been characterized using the instrumental techniques of FTIR and XPS spectroscopies, thermogravimetry, and scanning electron microscopy. The copolymer composition has been determined spectrophotometrically using the Toluidine Blue and Acid Orange dyes. Optimal conditions of AA and VI copolymerization have been found. It has been shown that the surface of modified PET TeMs is reach in functional groups which makes them a promising material for the development of nanosensors and nanocatalysts.
1233-1241
Modeling of Ethylene Absorption from an Ethylene–Ethane Mixture by Silver Nitrate Aqueous Solution in a Hollow-Fiber Membrane Contactor
Abstract
Convection–diffusion mass transfer in a gas–liquid membrane contactor based on porous polysulfone hollow fiber membranes with a mesoporous (dpore ~ 2 nm) structure of the separation layer has been studied. The characteristics of the membrane contactor have been investigated in the recovery of ethylene from its mixture with ethane using an aqueous silver nitrate solution as the absorption liquid. A procedure based on the method of lines is proposed for calculating a mass transfer in hollow fiber contactor with a longitudinal laminar flow in an array of parallel fibers. An ethylene flux, depending on the process conditions, has been found by solving numerically a set of convection–diffusion equations with allowance for both the chemical reaction in the liquid stream and transmembrane transport.
1242-1249
Donnan-Potential Sensors Based on Zirconia-Modified Nafion Membranes Treated under Different Conditions for the Determination of Amino Acids with Several Nitrogen-Containing Groups
Abstract
The effect of heat treatment at varying relative humidity and mechanical deformation on the properties of Nafion perfluorosulfonic cation-exchange membranes and Nafion-based hybrid materials containing hydrated zirconia nanoparticles has been studied. It has been shown that the treatment of the materials makes it possible to change their water uptake, ionic conductivity, and diffusion permeability over wide ranges. Variations in the water uptake and intrapore space volume of the membranes provided by their treatment and modification have led to a decrease in the sensitivity of DP-sensors (the analytical signal is the Donnan potential) to interfering hydroxonium cations in arginine and histidine solutions in 1.5−5 times. The material samples providing a high accuracy of determination of amino acid ions in a concentration range from 1.0 × 10–4 to 1.0 × 10–1 mol/L at pH < 7 have been selected.
1250-1257