Characterization of Nanocomposite Polymeric Membrane

Composite membrane has good permeability and selectivity for gases, which depends upon the operating conditions. The solubility and diffusivity of the penetrant in the polymer matrix control the transport through non-porous dense membrane. In the present work, the nano sized particles of Co_0.6Zn_0.4Fe₂O₄ were prepared by the co-precipitation method and characterized by the XRD technique with particle size of 10 nm. Nanocomposite polycarbonate membranes were studied before and after irradiation by the ³⁵Cl⁹⁺ ion of 120 MeV at the Nuclear Science Centre, New Delhi. The distribution of nanoparticles throughout the membrane was characterized by the optical microscope. Gas transport properties of H₂, CO₂ and air for these nanocomposite membranes were investigated. It was found that membrane containing nanoparticles shows low permeability with high permselectivity. After irradiation by swift heavy ions (SHI), high gas permeability and high permselectivity has been observed for these nanocomposite membranes.     

Investigation of Structure and Electrical Conductivity in Doped Polyaniline

Polyaniline (PAn) was synthesized chemically and doped with various dopants, such as HCl, HCOOH, I₂ and methylene blue (C₁₆ H₁₈ ClN₃ S), by an immersion method. The structure of these samples was investigated by infrared (IR) spectroscopy and wide-angle X-ray diffraction (WAXD) analysis. Remarkable changes have been observed in the IR spectra of doped PAn, indicating that doping is affecting the chemical structure. The percentage crystallinity was also found to increase after doping. The electrical conductivity (σ) of these samples was measured at various temperatures (T=308K to 423K). Plots of log σ versus T^y, where y=-1/2, -1/3, -1/4, were obtained and used to identity the conduction mechanism. Undoped PAn shows semiconducting behaviour, while doped samples show a variable range hopping mechanism. A primary cell was constructed with HCl-doped PAn as one of the electrodes and a copper plate as the other electrode. It gave an open circuit voltage of 0·38V and a short circuit current of about 5·4mA. © of SCI.     

X-ray diffraction study of doped polyaniline

Polyaniline (PAn), an important conducting polymer, was synthesized chemically. Percentage crystallinity of PAn on doping with various dopants (viz., hydrochloric acid, formic acid, iodine, methylene blue) has been investigated using wide-angle X-ray diffraction analysis. It is observed that percentage crystallinity (Xc %) for PAn increases after doping, and it is different for different dopants. The electrical conductivity measurements of these samples show that there is an increase in electrical conductivity with an increase in crystallinity. © 1996 John Wiley & Sons, Inc.     

Effects of dopants on percolation behaviors and gas sensing characteristics of polyaniline film

Effects of dopants on the correlation between the polyaniline (PAn) film resistance (R) and the reduction charge (Q) injected to the PAn film was investigated in dry acetonitrile solutions during electrochemical reduction by using the double potential step method. The R-Q correlation behaves as S-type curves, leading to the determination of the critical reduction charge (Q_c). The latter represents the reduction charge required for the formation of a continuous partially reduced phase in the PAn film. It was observed that the PAn film doped with sodium dodecylbenzene sulphate (SDBS) yielded a smaller Q_c than that doped with perchlorate, when the PAn films were electrochemically reduced under given conditions. The resistance of the pre-doped PAn film will increase significantly when the film is injected with reduction charge more than Q_c. Hence, a smaller Q_c means that the film can respond to very light reduction (or dedoping), being indicative of better sensing ability toward alkaline and reducing gases. This was confirmed by the increased sensitivity of the PAn/SDBS sensor toward 100 ppm NH₃ vapor, compared with the PAn/ClO₄⁻ sensor.     

Gas transport in halogen-containing aromatic polycarbonates

The gas permeability and permselectivity of a series of halogen-containing polycarbonates are discussed in terms of the fundamental solubility and diffusivity factors. These materials have structural features that hinder interchain packing and intrachain rotational mobility. Both diffusion and solubility coefficients are higher in materials with higher fractional free volumes. Diffusivity selectivities tend to increase with increasing restriction of intrachain torsional mobility. The materials with four bromine atoms substituted on the phenyl rings ortho to the carbonate linkages display a significantly increased diffusivity selectivity relative to conventional polycarbonate. This improvement in the ability of the polymer matrix to discriminate between gas molecules of different sizes is due to a reduction in intrachain torsional mobility. The reduction in chain mobility is indicated by higher glass transition and higher sub-T_g transition temperatures in the bromine-substituted materials. The materials with hexafluoroisopropylidene moieties have high fractional free volumes and exhibit a very significant increase in permeability relative to conventional bisphenol-A polycarbonate. The material with both the hexafluoro and the tetrabromo substitutions displays significant simultaneous increases in permeability and permselectivity relative to conventional polycarbonate.     

Advanced Gas Separation Membrane Materials: Rigid Aromatic Polyimides

Abstract

Permeabilities, solubilities, diffusivities, and selectivities for He/CH₄ and CO₂/CH₄ gas pairs are reported for four aromatic polyimides having systematic variations in intersegrnental packing and intrasegmental mobility. As intersegmental packing is disrupted by bulky substituents, gas diffusivities are generally increased, but diffusivity selectivities of He/CH₄ and CO₂/CH₄ are correspondingly decreased. Simultaneous suppression of intrasegmental mobility and intersegmental packing, however, yields significant increases in both diffusivity and diffusivity selectivity, and consequently in permeability and permselectivity. For example, packing-disrupted and mobility-restricted 6FDA-DAF polyimide provides significantly higher permeabilities and permselectivities than commercially available polymers currently being used as membrane materials.     

Effect of coating method on gas separation by PDMS/PES membrane

In this study, polydimethylsiloxane (PDMS)‐coated polyethersulfone (PES) composite membrane was prepared for gas separation. “Film casting” and “dip‐coating” techniques were used for producing selective PDMS layer on the surface of the PES support. The effects of coating technique and conditions including coating solution concentration and curing temperature on permselectivity of CO₂, CH₄, and N₂ were investigated. The prepared PES support did not provide any selectivity to the gases. When the concentration of PDMS coating solution was increased, initially permeability of CO₂ was rapidly dropped and then gradually reached to an almost constant value. The optimum concentration of coating solution was 5 wt%. Curing temperature showed no pronounced effect on the CO₂ permeability and selectivity. In “film casting” method, double coating showed superior permeability and selectivity. However, triple “dip‐coating” was promising. The selectivity of composite membrane prepared by “dip‐coating” was higher than “film casting” method. CO₂/N₂ and CO₂/CH₄ selectivity of five sequential dip‐coated composite membranes was 45.5 and 9.3, respectively. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers     

壬基酚聚氧乙烯醚硫酸掺杂聚苯胺的电导率研究

以壬基酚聚氧乙烯醚(10)硫酸(NPES)为聚苯胺掺杂剂,研究了掺杂剂及其掺杂反应时间、温度等条件对聚苯胺导电性的影响.结果表明:长链NPES的掺杂能够提高聚苯胺导电性,且随着掺杂反应时间的增加,电导率在20h后即达到最大值0.6S/cm;随着掺杂温度的降低,在冰浴条件下,NPES掺杂聚苯胺的电导率较常温时提高两个数量...     

Effect of Fumed Silica Nanoparticles on the Gas Permeation Properties of Substituted Polyacetylene Membranes

Summary The gas permeability of three substituted polyacetylenes, poly(1-chloro-2-phenylacetylene) (PClPA), poly[1-phenyl-2-(4-trimethylsilyl)phenylacetylene] (PTMSDPA), and poly[1-(trimethylsilyl)-1-propyne] (PTMSP), increased systematically with increasing content of nonporous fumed silica (FS) nanoparticles. For instance, the oxygen permeability coefficient (PO₂) of PClPA containing 30 wt % FS was 86 barrers, which was 10 times higher than that of the unfilled polymer (PO₂=8.6 barrers). The extent of permeability increase with the addition of FS was smaller when the permeability of the original polymer was higher. The order of the permeability increase in FS-filled polymers was as follows: PClPA > PTMSDPA > PTMSP. The addition of FS resulted in the decrease of O₂/N₂ permselectivity of these polymers. The H₂/CH₄ permselectivity largely decreased with increasing FS content in PClPA, while it hardly changed with FS loading in PTMSP. The gas solubility of PClPA was practically independent of FS content, and the increase in gas permeability in filled PClPA resulted from an increase in diffusivity with the addition of FS.     

有机磺酸掺杂聚苯胺的气敏性能

采用化学氧化聚合法,以苯胺为单体,过硫酸铵为氧化剂,在不同的酸性介质中合成了聚苯胺(PAn),采用傅里叶红外光谱和TG-DTA技术埘聚苯胺掺杂前后的结构变化和热稳定性进行了分析,结果表明,掺杂剂的加入降低了聚苯胺分了链的分解温度,与HCl掺杂相比,有机磺酸掺杂的聚苯胺具有更好的热稳定性.研究了不同质子酸掺杂对聚苯胺气敏性能的影响,结果表明有机磺酸掺杂的聚苯胺比PAn-HCI对目标气体具有更好的灵敏性,其中结果最好的PAn-SSA在室温下对1000×10-0NH3的灵敏度达到了15.47,而且响应时间小于20 s,恢复时间小于2 min,响应恢复性能良好.测试了不同酸掺杂聚苯胺灵敏度的长期稳定性,结合TG-DTA的分析结果,说明与PAn-HCI相比,有机磺酸掺杂的聚苯胺具有更好的环境稳定性.     

Gas separation properties of new polyoxadiazole and polytriazole membranes

The gas separation properties of new aromatic poly-1,2,4-triazole and poly-1,3,4-oxadiazole membranes have been systematically investigated. Various functional groups were incorporated as pendent groups onto the polymer backbone of poly-1,2,4-triazoles. A wide permeability/selectivity spectrum was covered with the choice of functional groups incorporated into the polymer backbone of poly-1,3,4-oxadiazoles. High permeabilities were found for poly-1,3,4-oxadiazoles with a 1,1,3-trimethyl-3-phenylindane (PIDA-POD) and a 4,4′(2,2′-diphenyl)hexafluor propane (HF-POD) unit in the polymer backbone, while incorporation of a 4,4′-diphenyl ether unit (DPE-POD) results in a polymer with a low permeability but an extremely high selectivity. While the permeabilities vary over four orders of magnitude, the solubility remains almost constant and, therefore, the increase in permeability is mainly due to an increase in diffusivity. The permeability is discussed in terms of the polymer free volume.     

Influences of van der waals volume of substitute groups on CO2 permselectivity of polyimide‐A molecular simulation study

Polyimide (PI) as a typical glassy polymer material was investigated by molecular simulation to reveal the relationship between polymer molecular structure and its gas separation properties. The influences of van der waals volume (V_w) on CO₂ permselectivity of PI polymers (with four kinds of backbone substitute groups and a series of side substitute groups from small to large volume) and V_w was proposed as an intermediate to establish the relationship between the substitute group and permselectivity. The results show that the CO₂ permeability (P) simply increases and CO₂/N₂ selectivity (S) decreases with the increasing V_w of side substitute groups. The linear fitline of P‐V_w is much suitable to describe and predict the effect of the increasing V_w of side substitute group on improving permeability by analyzing the experimental and calculated CO₂ permeability. The increasing V_w of backbone substitute group can slow down the increasing of CO₂ permeability, but result in the decreasing first and then recovering to the original level. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41082.     

导电聚苯胺/聚乙烯醇复合乳液的制备研究

以聚乙烯醇为树脂基体 ,通过乳液氧化聚合同步搀杂有机酸 ,研究了聚苯胺 /聚乙烯醇复合乳液的制备。结果表明 ,过硫酸铵的用量对聚苯胺的产率影响较大 ,当氧化剂 /苯胺的摩尔比达到 2时 ,产率为95% ,高于溶液法的原料比例。十二烷基苯磺酸和聚乙烯醇 (88%醇解度 )对聚苯胺乳胶的粒径亦有影响。在聚苯胺 /聚乙烯醇复合膜中 ,当聚苯胺含量超过 2 0 %后 ,电导率趋向稳定 ,可达 2 .3 s/ cm     

Effect of doping treatment on gas transport properties and on separation factors of polyaniline memebranes

Gas permeation experiments of H₂, O₂, CO₂, N₂, and CH₂ were carried out with freestanding films of the conjugated polymer polyaniline (PANi). At first annealed to remove residual solvent, PANi membranes were doped (i.e., protonated) in a strongly acidic medium (HCl 4M), undoped in a basic medium (NH₄OH 1M), and redoped in a slightly acidic medium (HCl 10^?2M). Protonation and deprotonation kinetics were studied by elementary analysis Gas permeation experiments were performed with the annealed, doped, undoped, and redoped PANi films. The gas transport mechanism was clearly influenced by the diffusivity factor and it obeyed a Fickian diffusion model. From the variations in permeability coefficients with the doping treatment, gases could be divided in two subgroups comprising H₂, O₂, and CO₂ on one hand and N₂ and CH₄ on the other. After the doping–undoping–redoping process, gas fluxes were increased by 15% for the smaller gases and were decreased by 45% for the larger gases. As a consequence gas separation factors were approximately doubled for a gas pair involving the two subgroups and these were unchanged for a gas pair involving only one subgroup. The highest O₂/N₂ and CO₂/CH₄ selectivity coefficients were, respectively, equal to 14 and 78. © 1995 John Wiley & Sons, Inc.     

Gas separation properties of aromatic polyetherimides from 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride and 3,5-diaminobenzic acid or its esters

The gas transport properties of a series polyetherimides, which were prepared from 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride (HQDPA) with 1,3-phenylenediamine or 3,5-diaminobenzic acid (DBA) or its esters are reported. The effects of carboxylic group (—COOH) and carboxylic ether groups (—COOR), at five positions of 1,3-phenylenediamine moiety, on H₂ CO₂, O₂, and N₂ permeability, diffusivity, and solubility of the polyetherimides were investigated. The gas permeability, diffusion, and solubility coefficients of the polyetherimides containing COOR are bigger than those of HQDPA-PDA, but the ideal separation factors and ideal diffusivity selectivity factors are much smaller than that of HQDPA-PDA because COOR decreases chain segmental packing efficiency and increases chain segmental mobility. The permeability coefficients of HQDPA-DBA to H₂, CO₂, and O₂ are bigger than those of HQDPA-PDA; the ideal separation factors for gas pairs H₂/N₂, CO₂/N₂, and O₂/N₂ are also much bigger than those of HQDPA-PDA. Both the diffusion coefficients of CO₂ and O₂ and the ideal diffusivity selectivity factors for CO₂/N₂ and O₂/N₂ are bigger than those of HQDPA-PDA because COOH decreases both chain segmental packing efficiency and chain segmental mobility. The copolyimides, which were prepared from 3,5-diaminobenzic acid and 3,5-diaminobenzic esters, have both high permeability and high permselectivity. © 1997 John Wiley & Sons, Inc.     

Gas permselectivity properties of high free volume polymers modified by a low molecular weight additive

The permselectivity properties of mixtures of the highly substituted polymers tetramethylhexafluoro polysulfone (TMHFPSF) and tetramethylhexafluoro bisphenol A t-butyl isophthalate (TMHFBPA-tBIA) with a low molecular weight glassy additive Kenflex A (denoted here as KXA) were measured for different gases and compared with the permselectivity properties shown by the base, unsubstituted polymers polysulfone (PSF) and bisphenol A t-butyl isophthalate (BPA-tBIA). The results show that the selectivity-permeability balance of polymer membranes may be appropriately tailored by a combination of chemical and physical alterations of the base polymer. The addition of modest amounts of KXA (ca. 20 wt %) into TMHFPSF or TMHFBPA-tBIA leads to materials whose permeability/selectivity combination is better than that of the unsubstituted materials, PSF or BPA-tBIA. The polymer TMHFPSF responds more beneficially to the incorporation of KXA than TMHFBPA-tBIA. At the same level of permeability, mixtures based on TMHFPSF have higher selectivity factors for H₂/CH₄ and CO₂/CH₄ than those based on TMHFBPA-tBIA. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 403–415, 1998     

Carbon molecular sieve membranes derived from Matrimid® polyimide for nitrogen/methane separation

A commercial polyimide, Matrimid® 5218, was pyrolyzed under an inert argon atmosphere to produce carbon molecular sieve (CMS) dense film membranes for nitrogen/methane separation. The resulting CMS dense film separation performance was evaluated using both pure and mixed N₂/CH₄ permeation tests. The effects of final pyrolysis temperature on N₂/CH₄ separation are reported. The separation performance of all CMS dense films significantly exceeds the polymer precursor dense film. The CMS dense film pyrolyzed at 800 °C shows very attractive separation performance that surpasses the polymer membrane upper bound line, with N₂ permeability of 6.8 Barrers and N₂/CH₄ permselectivity of 7.7 from pure gas permeation, and N₂ permeability of 5.2 Barrers and N₂/CH₄ permselectivity of 6.0 from mixed gas permeation. The temperature dependences of permeabilities, sorption coefficients, and diffusion coefficients of the membrane were studied, and the activation energy for permeation and diffusion, as well as the apparent heats of sorption are reported. The high permselectivity of this dense film is shown to arise from a significant entropic contribution in the diffusion selectivity. The study shows that the rigid ‘slit-shaped’ CMS pore structure can enable a strong molecular sieving effect to effectively distinguish the size and shape difference between N₂ and CH₄.     

Effect of fractional free volume and Tg on gas separation through membranes made with different glassy polymers

The aim of this work is to study how the characteristics of the polymer used to manufacture gas separation membranes influence its permeability and selectivity. It has been shown that the gas diffusivity decreases with the kinetic diameter of the gas except for CO₂, probably due to its high condensability. While solubility increases with the gas condensation temperature and clearly with the glass transition temperature of the polymer for each gas. The permeabilities of CO₂, CH₄, O₂, N₂ increase for increasing glass transition temperatures. Nevertheless only the selectivity of CO₂ versus the other gases increases significantly when polymers with high glass transition are used. The Robeson limit in a selectivity‐versus‐permeability plot is approached for CO₂/CH₄ when T_g increases. This distance to the Robeson limit, for this pair of gases, results to decrease for increasing T_g. For the case of the O₂/N₂ selectivity remains approximately constant with an appreciable increase in permeability for polymers with increasing T_g. Permeability increases due to the corresponding increase in fractional free volume, FFV, that appears for increasing glass transition temperatures, T_g. This correlation of FFV with T_g has been confirmed by obtaining FFV by different methods. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

The preparation of SPEEK/phosphate salts membranes and application for CO2/CH4 separation

SPEEK/phosphate salts membranes were prepared and utilized for CO₂/CH₄ separation. SPEEK with abundant –SO₃H groups and EO groups on polymer chains would be beneficial for CO₂ transport. The doped phosphate salts (NaH₂PO₄, Na₂HPO₄ and Na₃PO₄) with different acid‐base properties increased the water content in the membrane, and water was expected to increase both the solubility and diffusivity of CO₂ in the membrane. All membranes were characterized by FTIR, TGA, and XRD. The CO₂ permeability and CO₂/CH₄ selectivity of SPEEK/Na₃PO₄ membranes were higher than that of SPEEK/NaH₂PO₄ and SPEEK/Na₂HPO₄ membranes. Compared to the pure SPEEK membrane, the CO₂ permeability and CO₂/CH₄ selectivity of SPEEK/Na₃PO₄?10 membrane were increased by 144% and 65%, respectively. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43399.     

Sorption, diffusion, and permeation of light olefins in poly(ether block amide) membranes

Sorption, diffusion, and permeation of three olefins (i.e., C₂H₄, C₃H₆, and C₄H₈) in poly(ether block amide) (PEBA 2533) membranes at different temperatures and pressures were investigated. This is pertinent to olefin recovery from resin off gas in polyolefin manufacturing. The relative contribution of solubility and diffusivity to the preferential permeability of olefins over nitrogen was elucidated. It was revealed that the favorable olefin/nitrogen permselectivity was primarily attributed to the solubility selectivity, whereas the diffusivity selectivity may affect the permselectivity negatively or positively, depending on the operating temperature and pressure. The olefin permeability is in the order of C₄H₈>C₃H₆>C₂H₄, the same order as their solubility in the membrane. In general, a low temperature favors both the permeability and selectivity. With an increase in pressure and/or a decrease in temperature, the sorption uptake of the olefin in the membrane increases progressively, and the diffusivity and hence the permeability are also enhanced because of the increased membrane plasticization/swelling caused by the penetrant sorbed in the membrane. At a given temperature, the pressure dependence of solubility and permeability could be described empirically by an exponential function. The limiting solubility at infinite dilution was correlated with the reduced temperature, and the hypothetical diffusivity at zero pressure was related to temperature by the Arrhenius equation.