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The effect of acyl chloride chemical structure on the ethanol aqueous solution dehydration through the poly(thiol ester amide) thin-film composite membrane prepared by reacting 2-aminoethanethiol (AETH) with trimesoyl chloride (TMC) or succinyl chloride (SCC) on the surface of the modified asymmetric polyacrylonitrile (mPAN) membrane was investigated. SEM/EDX, ATR-FTIR and water contact angle were applied to analyze the S element, chemical structure, and hydrophilicity of the poly(thiol ester amide) active layer of the composite membrane. In order to estimate the variation in the free volume of the poly(thiol ester amide) active layer and correlate that with the pervaporation performance, positron annihilation spectroscopy (PAS) experiments were conducted, in which a variable monoenergy slow positron beam was used. Doppler broadening S parameters of annihilation radiation energy spectra showed a significant variation with the acyl chloride chemical structures of the poly(thiol ester amide) active layers. The S parameters of the AETH–TMC/mPAN thin-film composite membrane were found to be lower than those of the AETH–SCC/mPAN thin-film composite membrane. In the ethanol aqueous solution dehydration, the AETH–TMC/mPAN thin-film composite membrane exhibited a lower permeation rate and a higher water concentration in the permeate than the AETH–SCC/mPAN. This is in good agreement with the analysis by positron annihilation spectroscopy. The solution effect dominated the pervaporation separation behavior of the poly(thiol ester amide) thin-film composite membrane with TMC substituting for SCC in the poly(thiol ester amide) active layer. The AETH–TMC/mPAN membrane was found to exhibit superior performance compared with some membranes discussed in the literature. © 2008 Elsevier B.V. All rights reserved.

Effect of chemical structures of amines on the performance of isopropanol dehydration by pervaporation through the polyamide thin-film composite membranes prepared by various amines reacting with TMC on the surfaces of the modified asymmetric polyacrylonitrile (mPAN) membranes was investigated. ATR-FTIR, SEM, AFM and water contact angle were used to characterize the chemical structures, morphologies and hydrophilicity of the polyamide active layers of the composite membranes. To investigate the correlation between the free volume of polyamide active layer and pervaporation performance, the free volume variation of the polyamide active layers was probed by positron annihilation spectroscopy (PAS) experiments performed using the slow positron beam. It was found that the pervaporation performance for separating 90 wt.% aqueous isopropanol solutions at 25 °C decreased in the order of EDA–TMC/mPAN membrane > MPDA–TMC/mPAN membrane > PIP–TMC/mPAN and HDA–TMC/mPAN membranes. The relationship between the performance of isopropanol dehydration and the physicochemical properties of the polyamide layers, that is, the free volume, surface roughness and hydrophilicity seemed very well.

A series of aromatic polyimide membranes were synthesized using direct polycondensation of various diamines containing flexible ether groups and bulky substituents with various aromatic dianhydrides. It is expected to promote the gas permeability of the polyimide membrane and maintain similarly gas selectivity by introduction of bulky groups. It was found that the gas permeability of aromatic polyimide membranes increased and the gas selectivity decreased with increasing fractional free volume and d-spacing. In addition, the gas permeability had good correlation with the γ-transition temperature and the thermal expansion coefficient. The bulky hexafluoroisopropylidene group introduced into the polyimide backbone could efficiently promote the gas permeability while the gas selectivity decreased slightly. Because the gas diffusivity coefficient and diffusivity selectivity controlled gas permeability and selectivity, respectively, the diffusivity effect dominated the gas separation behavior. The sorption behavior of aromatic polyimide membrane can be well explained using the dual-sorption model. The experimental data indicated that the aromatic polyimide membrane had excellent oxygen/nitrogen separation performance.

Living ring-opening metathesis polymerization (ROMP) of a norbornene derivative containing carbazole group, 5-( N -carbazolyl methylene)-2-norbornene (CbzNB), was carried out to prepare pervaporation membranes for aqueous alcohol solution separation. The linear dependence of the number average molecular weight ( Mn ¯ ) on the [M]/[I] ratio ([M], monomer concentration; [I], initiator concentration) and low polydispersity (PDI) demonstrated a living polymerization of CbzNB. Hydrogenation of poly(CbzNB), poly(H-CbzNB) increased the polymer thermal stability. The water molecules preferentially permeate through the poly(H-CbzNB) membranes. The feed compositions, degree of swelling and molecular size effects of the alcohols on the pervaporation performances were investigated. The separation factor and the permeation rate increase with increasing ethanol concentration in the feed.

In the present work, a novel aromatic polyamide was prepared by direct polymerization of 4,4′-hexafluoroisopropylidenedibenzoic acid with diamine of 2,2′-dimethyl-4,4′-bis(aminophenoxy)diphenyl by triphenyl phosphite and pyridine in N-methyl-2-pyrrolidinone. The effects of coagulation media on the membrane morphology and the vapor permeation performances of aqueous ethanol solution through wet phase inversion prepared asymmetric polyamide membrane were investigated. The Young’s modulus increases and membrane porosity of the asymmetric polyamide membrane decreases with increasing the molar volume of coagulation medium. The diffusivity of coagulation medium ranks in the following order: water>methanol>ethanol>n-propanol. The membrane morphology and membrane formation properties were characterized by SEM, Fourier transform infrared (FT-IR)–attenuated total reflectance (ATR), light transmission, and DMA, etc. Optimum vapor permeation results, a separation factor of 21 and permeation rate of 657 g/m2 h, were obtained with the asymmetric polyamide membrane prepared from the ethanol (coagulation medium) system.

The pervaporation and vapor permeation performances of a series of fluorine-containing aromatic polyamide membranes for various alcohol mixtures were investigated. Compared with pervaporation, vapor permeation effectively increases the permselectivity of water. The solubility of alcohol in an aromatic membrane is higher than that of water, but the diffusivity of water across the membrane is higher than that of the alcohols. In addition, the relationship between the polymer structure and pervaporation performance was obtained. It was found that the permeation rate can be increased by the introduction of bulky substituted groups and arylene ether groups into the polymer backbone.

For dehydrating aqueous alcohol solution by pervaporation, a fluorine-containing aromatic polyamide membrane was synthesized. The fluorine-containing polyamides were prepared by direct polycondensation of 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, BAPPH, with various aromatic diacids by triphenyl phosphite and pyridine in N -methyl-2-pyrrolidinone. The novel aromatic polyamides were examined by elemental analysis, FTIR, and X-ray diffraction. The aromatic polyamides were crystalline except (A-B 2 ). The effects of feed composition, degree of swelling, and the molecular size of alcohols on pervaporation performances were investigated. Water molecules preferentially permeate through the aromatic polyamide membranes. A separation for water of 36 and a 383 g/m 2 h permeation rate with a 90 wt% feed ethanol concentration was obtained.