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Vol 58, No 4 (2018)
- Year: 2018
- Articles: 8
- URL: https://journal-vniispk.ru/0965-5441/issue/view/11210
Article
Hydrophobization of Polysulfone Hollow Fiber Membranes
Abstract
The effect of the nature of the pore-forming agent (polyethylene glycol, ethylene glycol, diethylene glycol, glycerol) on the structure and performance of hollow fiber membranes spun from polysulfone solutions in N,N-dimethylacetamide was studied. The membranes have been characterized using various methods (determination of gas permeability and water entry pressure, scanning electron microscopy, contact angle measurement). To increase the hydrophobicity of the selective layer of hollow fibers, a procedure for applying a modifying polydimethylsiloxane layer onto the inner surface of the fiber has been developed, which has made it possible to increase the contact angle from 75°–77° to 115°–151° with retaining their gas transport properties. The composite membranes designed hold promise for use in gas–liquid membrane contactors, and hydrophobized membranes with reduced gas permeability can be used for hydrophobic pervaporation.
279-288
Fabrication of Hollow Fiber Membrane from Polyarylate–Polyarylate Block Copolymer for Air Separation
Abstract
A process has been developed for spinning asymmetric hollow fiber membranes from a polyarylate–polyarylate block copolymer having a separation factor for pure gases in the oxygen–nitrogen pair of α(O2/N2) = 6.3 and an oxygen permeance coefficient of 2.4 Barrer. The effect of the polymer molecular weight, the composition of the dope solution, and the spinning parameters on the gas transport properties of the hollow fiber membrane and its geometry has been studied. The use of a polymer with a molecular weight of 67 kDa, as well as the introduction of surfactants into the dope solution, has made it possible to prepare samples of defect-free membranes with an oxygen permeance of 120 L(STP)/(m2 h bar) and a separation factor of α(O2/N2) = 6.5, which correspond to the selective layer thickness of 60 nm.
289-295
Hybrid Gas Separation Membranes Containing Star-Shaped Polystyrene with the Fullerene (C60) Core
Abstract
A physicochemical study of novel hybrid polymer membranes based on polyphenylene oxide with a star-shaped modifier incorporated into the matrix has been conducted, and the transport properties of the membranes in the gas separation process have been studied. Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) has been selected as the polymer matrix because of the low cost and high mechanical strength of this material. Star-shaped macromolecules (up to 5 wt %) containing six polystyrene arms grafted onto a fullerene(C60) central core have been used as the filler. The structure and physical properties of the resulting membranes have been characterized by scanning electron microscopy, membrane density measurements, differential scanning calorimetry, and thermogravimetric analysis. Film surface has been studied by contact angle measurements. The gas separation properties of the membranes have been studied by the barometric method for the following individual gases: H2, O2, N2, and CH4. Data on the separation properties have been plotted as a Robeson diagram to compare with published data. It has been shown that the incorporation of star-shaped polystyrene into the PPO matrix leads to an improvement of the separation efficiency for selected gas pairs and an increase in selectivity compared with that of the unmodified membrane.
296-303
Ionic Conductivity of Ceria-Doped Ion Exchange Membranes on the Basis of Sulfonated Polynaphthaleneimide
Abstract
Hybrid membrane materials on the basis of sulfonated polynaphthaleneimide doped with ceria have been synthesized, and their ionic conductivity has been investigated. The conditions for membrane synthesis with different dopant contents have been determined. Ceria doping leads to a decrease in the ionexchange capacity of membranes and an increase in their ion conductivity upon contact with water. After 7% ceria doping, the ionic conductivity of the initial membrane (1.9 × 10−2 Ω−1 cm−1) increases up to 3.0 × 10−2 Ω−1 cm−1.
304-308
A Study of Pore Formation and Methanol Vapor Permeability in Stretched Polytetrafluoroethylene Films Used as a Precursor of Composite Ion-Exchange Membranes
Abstract
Methanol vapor permeability and pore formation features in stretched polytetrafluoroethylene (PTFE) films used as a precursor of composite cation-exchange membranes have been studied. Porous structures of the precursor have been formed via stretching PTFE films in air, toluene, isopropyl alcohol, and CCl4. Permeability has been determined according to the evaporation of a liquid through a porous film; porosity, according to the increase in the film volume during stretching; pore formation features, according to optical microscopy images of porous films and their transverse microsections. It has been found that, with an increase in the stretch ratio, the porosity of PTFE films increases almost linearly, while the methanol vapor permeability increases exponentially. The permeability of the films stretched in liquids is 20 times higher than the permeability of the films stretched in air at comparable stretch ratio and porosity values. The considerably higher permeability of the films stretched in liquids and the observed differences in their porous structure suggest that the liquids are actively involved in the formation of through pores in the direction connecting the film surfaces, i.e., in the direction that determines the transport and conductive properties of composite membranes based on stretched PTFE films.
309-316
Study of Separation Behavior of Activated and Non-Activated MOF-5 as Filler on MOF-based Mixed-Matrix Membranes in H2/CO2 Separation
Abstract
In this study, cubic and tetragonal structures of MOF-5 (C-MOF-5 and T-MOF-5) were successfully synthesized, characterized and incorporated into cellulose acetate (CA) polymer matrix in the range of 6, 9 and 12 wt % to fabricate mixed matrix membranes (MMMs). The effects of smaller pore size of T-MOF-5 and more ZnO molecules in T-MOF-5, on the H2 and CO2 permeation properties of C-MOF-5/CA and T-MOF-5/CA MMMs were investigated. The all novel MMMs were prepared using the solution casting method and characterized by FTIR, TGA and SEM. SEM images as well as results of FTIR and TGA analyses confirmed good adhesion between both MOF-5s and CA matrix. Addition of both C-MOF-5 and T-MOF-5 into the CA improved the gas transport properties of the CA, especially in H2 separation. The H2/CO2 selectivity continued the increasing trend at 9 wt % and did not significantly reduce even at 12 wt % due to good adhesion between both MOF-5s and CA. The highest H2/CO2 selectivity was obtained at 12 and 9 wt % loading of C-MOF-5 and T-MOF-5, respectively. By changing the filler from C-MOF-5 to T-MOF-5, the increasing and reducing of adsorption site of H2 and CO2 (respectively), and also reducing in pore size, caused the appearance of H2 permeability to not change much but the CO2 permeability to reduce. Accordingly, the H2/CO2 selectivity in all T-MOF-5/CA MMMs is higher than that in all C-MOF-5/CA MMMs. According to obtained results, the activated MOFs (i.e., C-MOF-5 in this study) are not always the best choices for separation process.
317-329
Carbon Dioxide Desorption from Amine Solution in a Nonporous Membrane Contactor
Abstract
Long-term testing of a membrane contactor based on a blend of the nonporous polymers polytrimethylsilylpropyne (PTMSP) and polyvinyltrimethylsilane (PVTMS) has been carried out. The flat-sheet membrane contactor has been tested for CO2 desorption from an aqueous methyldiethanolamine solution at 100°C. It has been found that the mass transfer parameters (CO2 flux and stripping efficiency) of the 95%PTMSP/5%PVTMS membrane stabilize after the 7th day of testing. The CO2 mass transfer coefficient in the membrane contactor has been evaluated, and optimal desorption parameters have been determined.
330-337
Use of a Hybrid Membrane–Sorption System with Three Adsorbers for Producing Oxygen-Enriched Air
Abstract
A three-adsorber ejector membrane–sorption system for separating gas mixtures is proposed for obtaining a product enriched in a weakly sorbable component. The system consisting of a pressure-swing adsorption unit and a hollow fiber membrane module has been experimentally studied for air enrichment with oxygen. Various cyclograms of operation and sorbent regenerating methods have been considered. The efficiency of the proposed system has been compared with that of other systems intended for the same purpose.
338-345