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1.
The temperature dependence of gas sorption and transport properties is examined for two polyimide isomers. The permeabilities and solubilities of five gases in these materials are reported over an extensive temperature range from 35 to 325°C. Also, the activation energies for permeation, the heats of sorption, and the activation energies for diffusion obtained for both polyimides are compared and correlated with physical properties of the polymers and penetrants. The influence of temperature on the selective properties of these membrane materials is discussed for three gas separations; He/N2, CO2/CH4, and O2/N2. Thorough analysis of these data provides insight into the influence of the subtle difference in chain structure of the two isomers. The performance of the 6FDA-6Fp DA as a separation membrane at high temperatures suggests that it is an outstanding candidate for use in novel elevated temperature applications. ©1995 John Wiley & Sons, Inc. 相似文献
2.
《Journal of membrane science》1997,126(1):139-149
The silicone rubber (SR) based graft copolymer, SR-graft-poly(acrylic acid) (SR-g-AA), was modified by incorporating silver ion (SR-g-AA-Ag+) for C4 olefin/paraffin gases separation. Olefin could be transported across the complex membrane by the silver ion facilitated transport. The permeation properties, as measured by gas chromatography equipped with a gas permeability analyzer, implied a facilitating effect for olefin. Typical trans-2-butene/n-butane selectivity in the 95.6% grafted complex membrane at 25°C is 4.0. Also, the influences of AA% grafting, measuring temperature and pressure to the permeation properties of C4 gases were studied. In addition, the sorption behaviors of C4 gases in SR based membranes are presented and discussed by the Flory-Huggins equation. Finally, the selectivity of solubility and diffusivity in these SR based membranes are also discussed. 相似文献
3.
N. Muruganandam W. J. Koros D. R. Paul 《Journal of Polymer Science.Polymer Physics》1987,25(9):1999-2026
The effects of molecular structure manipulation of polycarbonates on sorption and transport of various gases were studied using tetramethyl, tetrachloro, and tetrabromo substitutions onto the aromatic rings of bisphenol A polycarbonate. Solubility and permeability measurements were made at 35°C over the pressure range of 1–20 atm for a variety of gases, namely CO2, CH4, O2, N2, and He. A threefold to fourfold increase in permeability was caused by the tetramethyl substitution, whereas the tetrachloro and tetrabromo substitutions reduced the permeability relative to the tetramethyl substitution. Lower activation energies for transport were found for the tetramethyl polycarbonate relative to the unsubstituted polycarbonate. Permeability coefficients were factored into solubility and diffusion coefficients. Sorption levels increased for all substitutions, but among the substituted polymers the levels remain practically the same. Solubility data were analyzed in terms of the dual sorption model. The Henry's law solubility coefficients obtained from this analysis were found to be consistent with a predictive equation developed for rubbery polymers. The usual correlation for predicting the Langmuir sorption capacity of the model overestimates the values for the substituted polycarbonates, and a proposal for the cause of this is offered. Thermal expansion of these polymers was measured using dilatometry, and the results are used in the interpretation of the sorption data. Diffusion phenomena are explained by segmental mobility and free volume considerations. The effects of CO2 exposure history on sorption and transport were also investigated. 相似文献
4.
Two PEG-based copolymers containing two different chain extenders, as hard segments, were synthesized by 4,4′-methylenediphenyl diisocyanate (MDI). The chain extenders were 1,4-butane diol (BDO) and 1,2-ethane diamine (EDA). The application of the polyurethane (PU) and poly(urethane-urea)s (PUU)s synthesized polymers, which were characterized by Fourier transform infrared spectrometer (FTIR), differential scanning calorimetry (DSC) and atomic Force Microscopy (AFM), in the gas permeability was investigated. The obtained results indicated that by replacing the urea linkage in the polymers, the microphase separation of hard and soft segments increased. The synthesized PEG-based copolymers were semi-crystalline at room temperature. According to the DSC results, the crystallinity of the synthesized polyurethanes decreased as temperature increased. In addition, a reduction in mean surface roughness could be seen based AMF information. The gas (carbon dioxide and methane) separation properties of the polymers revealed that by replacing the urea linkage, the diffusivity, permeability and selectivity of the gases increased slightly.The solubility and diffusivity of gases indicated he solubility domination of gas transport in these membranes. However, the sorption coefficient (S) of a particular gas was surprisingly constant for the two synthesized polymers. The CO2 permeability increased with increasing feed pressure, while CH4 permeability remained almost constant at both temperatures of 25°C and 35°C. The increase in temperature led to an increase in the permeability of the gases and a decrease in the gas selectivity for the both synthesized polyurethanes. 相似文献
5.
《Journal of Polymer Science.Polymer Physics》2018,56(14):1045-1052
This work reports on the preparation and properties of polydimethylsiloxane (PDMS)/low‐density polyethylene (LDPE) multilayer composite polymer membranes (MCPM) for gas separation applications. The membranes were produced by combining sequential coating with melt‐extrusion/salt leaching techniques. In particular, the gas sorption and permeation properties at different pressure (40–90 psig) and temperature (27–55 °C) are reported with morphology and thermogravimetric properties. The results show that a 20 μm PDMS layer was able to penetrate the microporous LDPE surface layer substrate leading to improved interfacial adhesion. Based on the different gases (CO2, CH4, and C3H8) solubility, permeability, and diffusivity obtained, these membranes are seen as good candidates for industrial gas separations. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1045–1052 相似文献
6.
Polydimethylsiloxane (PDMS) is the most commonly used membrane material for the separation of condensable vapors from lighter gases. In this study, a composite PDMS membrane was prepared and its gas permeation properties were investigated at various upstream pressures. A microporous cellulose acetate (CA) support was initially prepared and characterized. Then, PDMS solution, containing crosslinker and catalyst, was cast over the support. Sorption and permeation of C3H8, CO2, CH4, and H2 in the prepared composite membrane were measured. Using sorption and permeation data of gases, diffusion coefficients were calculated based on solution‐diffusion mechanism. Similar to other rubbery membranes, the prepared PDMS membrane advantageously exhibited less resistance to permeation of heavier gases, such as C3H8, compared to the lighter ones, such as CO2, CH4, and H2. This result was attributed to the very high solubility of larger gas molecules in the hydrocarbon‐based PDMS membrane in spite of their lower diffusion coefficients relative to smaller molecules. Increasing feed pressure increased permeability, solubility, and diffusion coefficients of the heavier gases while decreased those of the lighter ones. At constant temperature (25°C), empirical linear relations were proposed for permeability, solubility, and diffusion coefficients as a function of transmembrane pressure. C3H8/gas solubility, diffusivity, and overall selectivities were found to increase with increasing feed pressure. Ideal selectivity values of 9, 30, and 82 for C3H8 over CO2, CH4, and H2, respectively, at an upstream pressure of 8 atm, confirmed the outstanding separation performance of the prepared membrane. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
7.
The effects of molecular structure and thermal history on the gas transport properties of tetramethyl bisphenol-A polycarbonate (TMPC) and tetramethyl bisphenol-A polysulfone (TMPSF) are reported. The presence of the bulky methyl side groups on the aromatic rings of TMPC and TMPSF inhibits both chain packing and molecular motions in these polymers as compared with standard polycarbonate and polysulfone. The methyl substitution results in significant increases in permeability with little or no loss of selectivity, making these materials promising candidates for membrane-based gas separations applications. Thermal annealing produces a densification of the materials, resulting in decreased permeabilities. Selectivities remained roughly the same or increased slightly upon annealing at temperatures slightly below the glass transition temperature. Thus, thermal annealing may be useful for “fine-tuning” a membrane's properties for applications where improved selectivity is desirable, even at the expense of decreased permeability. 相似文献
8.
Colin A. Scholes Jianyong Jin Geoff W. Stevens Sandra E. Kentish 《Journal of Polymer Science.Polymer Physics》2015,53(10):719-728
Highly permeable glassy polymeric membranes based on poly (1‐trimethylsilyl‐1‐propyne) (PTMSP) and a polymer of intrinsic porosity (PIM‐1) were investigated for water sorption, water permeability and the separation of CO2 from N2 under humid mixed gas conditions. The water sorption isotherms for both materials followed behavior indicative of multilayer adsorption within the microvoids, with PIM‐1 registering a significant water uptake at very high water activities. Analysis of the sorption isotherms using a modified dual sorption model which accounts for such multilayer effects gave Langmuir affinity constants more consistent with lighter gases than the use of the standard dual mode approach. The water permeability through PTMSP and PIM‐1 was comparable over the water activities studied, and could be successfully model ed through a dual mode sorption model with a concentration dependent diffusivity. The water permeability through both membranes as a function of temperature was also measured, and found to be at a minimum at 80 ° C for PTMSP and 70 °C for PIM‐1. This temperature dependence is a function of reducing water solubility in both membranes with increasing temperature countered by increasing water diffusivity. The CO2 ‐ N2 mixed gas permeabilities through PTMSP and PIM‐1 were also measured and model ed through dual mode sorption theory. Introducing water vapour further reduced both the CO2 and N2 permeabilities. The plasticization potential of water in PTMSP was determined and indicated water swelled the membrane increasing CO2 and N2 diffusivity, while for PIM‐1 a negative potential implied that water filling of the microvoids hampered CO2 and N2 diffusion through the membrane. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 719–728 相似文献
9.
Diffusion and solubility coefficients have been determined for the CO2?, CH4?, C2H4?, and C3H8-polyethylene systems at temperatures of 5, 20, and 35°C and at gas pressures up to 40 atm. Diffusion coefficients were obtained from rates of gas absorption in polyethylene rods under isothermal-isobaric conditions by means of a new diffusivity apparatus. The concentration dependence of the diffusion coefficients was represented satisfactorily by Fujita's free-volume model, modified for semicrystalline polymers, while the solubility of all the penetrants in polyethylene was within the limit of Henry's law. Semiempirical correlations were found for the free-volume parameters in terms of physicochemical properties of the penetrant gases and the penetrant-polymer systems. These correlations, if confirmed, should permit the prediction of diffusion and permeability coefficients of other gases and of gas mixtures in polyethylene as functions of pressure and temperature. 相似文献
10.
C. Camacho-Zuiga F.A. Ruiz-Trevio S. Hernndez-Lpez M.G. Zolotukhin F.H.J. Maurer A. Gonzlez-Montiel 《Journal of membrane science》2009,340(1-2):221-226
New polysulfone (PSF) copolymers from bis(4-fluorophenyl)sulfone and based on equimolar mixtures of the rigid/compact naphthalene moiety with bulky connectors from bisphenols: tetramethyl, hexafluoro, and tetramethyl hexafluoro, respectively, were synthesized to measure significant physical properties related to the gas separation field. The flexible and transparent polymer dense films TM-NPSF, HF-NPSF and TMHF-NPSF show high glass transition temperatures Tg 230 °C and high decomposition temperatures TD 400 °C (10 wt.% loss, in air). Free volume cavity sizes, as determined by PALS, are in the range of 94–139 Å3. Their gas permeability and selectivity combinations of properties, measured at 35 °C and 2 atm, are very attractive since their selectivity for the pair of gases H2/CH4, O2/N2, and CO2/CH4 are higher than those for commercial PSF membranes, having similar or superior permeability coefficients for the most permeable gases H2, O2, and CO2. Especially important is the tetramethyl naphthalene polysulfone TM-NPSF membrane which reports selectivities for H2/CH4, O2/N2 and CO2/CH4 of 122, 7.6 and 38 with corresponding permeability coefficients (in Barrers) of 17 for H2, 1.2 for O2, and 5.2 for CO2. These results are interpreted in terms of free volume size and glass transition temperature together with the respective contribution of gas solubility and diffusivity to the overall selectivity coefficients. 相似文献
11.
The gas‐transport properties of poly[2,6‐toluene‐2,2‐bis(3,4‐dicarboxylphenyl)hexafluoropropane diimide] (6FDA‐2,6‐DAT) have been investigated. The sorption behavior of dense 6FDA‐2,6‐DAT membranes is well described by the dual‐mode sorption model and has certain relationships with the critical temperatures of the penetrants. The solubility coefficient decreases with an increase in either the pressure or temperature. The temperature dependence of the diffusivity coefficient increases with an increase in the penetrant size, as the order of the activation energy for the diffusion jump is CH4 > N2 > O2 > CO2. Also, the average diffusion coefficient increases with increasing pressure for all the gases tested. As a combined contribution from sorption and diffusion, permeability decreases with increases in the pressure and the kinetic diameter of the penetrant molecules. Even up to 32.7 atm, no plasticization phenomenon can be observed on flat dense 6FDA‐2,6‐DAT membranes from their permeability–pressure curves. However, just as for other gases, the absolute value of the heat of sorption of CO2 decreases with increasing pressure at a low‐pressure range, but the trend changes when the feed pressure is greater than 10 atm. This implies that CO2‐induced plasticization may occur and reduce the positive enthalpy required to create a site into which a penetrant can be sorbed. Therefore, a better diagnosis of the inherent threshold pressure for the plasticization of a glassy polymer membrane may involve examining the absolute value of the heat of sorption as a function of pressure and identifying the turning point at which the gradient of the absolute value of the heat of sorption against pressure turns from a negative value to a positive one. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 354–364, 2004 相似文献
12.
《Journal of membrane science》1997,134(2):143-150
The transport phenomena of oxygen and nitrogen across a pure polycarbonate (PC) and a cobalt(III) acetylactonate (Co(acac)3) containing PC membrane was studied. Co(acac)3 was added into a polycarbonate membrane to enhance its oxygen solubility. The oxygen sorption isotherms was measured. It was found that the oxygen solubility decreased sharply as pressure increased, especially at low pressure region. On the contrary, the oxygen permeability increased slightly with respect to pressure. Both the solution-diffusion model and traditional dual mobility model were unable to explain the inconsistent pressure dependency between solubility and permeability. Instead of adopting Langmuir-Henry sorption model, a modified dual mobility model which incorporates BET-type isotherm to describe oxygen sorption. The diffusivity of molecules moving at the first adsorbed layer was assumed to be different from those moving at higher layers. This modified dual mobility model satisfactorily described both the pressure dependency of oxygen solubility and permeability. It was also found that the increase of oxygen/nitrogen selectivity was not due to the elevation of oxygen to nitrogen solubility ratio but due to the mobility ratio of oxygen to nitrogen at the higher adsorption layers. 相似文献
13.
Separation of small molecules using novel rolltruded membranes. I. Apparatus and preliminary results
A novel membrane production technique, rolltrusion, has been developed for the preparation of permselective polymeric membranes for both gas and vapor separations and pervaporation applications. Pinhole-free thin films with a regulated three-dimensional morphology comprising crystalline and amorphous regions have been produced with improved mechanical properties in three dimensions. Because rolltrusion is a solid-state processing technique, it is not restricted by solubility constraints inherent in the common solvent-based thinfilm production techniques. Consequently it can be extended to include commercially available engineering plastics that have not been used as membranes previously because of their limited solvent solubility. These polymers are interesting because of their applicability to temperatures in excess of 200 to 300°C in harsh chemical environments, compared with the ca. 150°C ceiling usually encountered in the most rugged of solvent-cast polymers. In the first part of this series we detail an automated experimental permeation apparatus that permits testing of both single-component and multicomponent gases and vapors over a temperature range of ?73 to 273°C. Currently, modifications to the permeation cell are underway to permit pervaporation studies in the apparatus. To illustrate the operation of the apparatus, and to some degree the effect of rolltrusion processing, experimental permeability, diffusivity, solubility, and actual gas separation factors (via gas chromatography) are detailed for several light gases in rolltruded isotactic poly(propylene) (iPP) and in the thermally and chemically resistant thermoplastic, poly(ether ether ketone) (PEEK). Permeation temperatures to at least 225°C have been studied using PEEK, representing the first published experimental permeability and gas-separation results for such engineering polymers at temperatures above 200 °C. © 1992 John Wiley & Sons, Inc. 相似文献
14.
Kanchan Ghosal Rey T. Chern Benny D. Freeman Raj Savariar 《Journal of Polymer Science.Polymer Physics》1995,33(4):657-666
CO2, CH4, O2, and N2 permeability and solubility of unmodified and aryl-nitrated polysulfone were determined at 35°C and pressures up to 20 atm. The degree of nitration was varied from 0 to 2 nitro groups per repeat unit. The permeability and diffusion coefficients for all gases decreased with increasing degree of nitro substitution. The decrease in gas diffusivity is attributed to a combination of decreased fractional free volume and decreased torsional mobility with increasing degree of substitution. The solubilities of N2, O2, and CH4 do not show a systematic dependence on degree of substitution. However, CO2 solubility apparently goes through a minimum as the degree of substitution is increased. CO2 solubility may be influenced by a competition between increases in polymer polarity (favoring higher solubility) and lower free volume (favoring lower solubility) that accompanies increases in the polar nitro substituent concentration. CO2/CH4 solubility selectivity increases monotonically as the degree of substitution increases. CO2/CH4 permselectivity and diffusivity selectivity increased with increasing degree of substitution. © 1995 John Wiley & Sons, Inc. 相似文献
15.
Betty Wong Zhiyi Zhang Y. Paul Handa 《Journal of Polymer Science.Polymer Physics》1998,36(12):2025-2032
An in situ gravimetric technique, employing an electrobalance, is described for determining the solubility and diffusivity of gases in polymers over extended ranges of temperature and pressure. Solubilities of CO2 in polystyrene at 35°C were measured as a test case; the results are in excellent agreement with the literature values determined by the pressure decay method. Solubility and diffusivity results are also reported for PVC-CO2 at 35°C and for PS-1,1,1,2-tetrafluoroethane at 30, 90, and 120°C. A comparison with other studies shows the in situ method to be more efficient and precise than the ones based on weighing the gas-saturated polymer under ambient conditions. The kinetics of gas sorption were analyzed in terms of two data reduction techniques to derive diffusion coefficients. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2025–2032, 1998 相似文献
16.
The present work tries to introduce a high‐performance nano‐composite membrane by using polydimethylsiloxane (PDMS) as its main polymer matrix to meet some specific requirements in industrial gas separations. Different nano‐composite membranes were synthesized by incorporating various amounts of nano‐sized silica particles into the PDMS matrix. A uniform dispersion of nano‐particles in the host membranes was obtained. The nano‐composite membranes were characterized morphologically by scanning electron microscopy and atomic force microscopy. Separation properties, permeability, and ideal selectivity of C3H8, CH4, and H2 through the synthesized nano‐composite membranes with different nano‐particle contents (0.5, 1, 1.5, 2, 2.5, and 3 wt%) were investigated at different pressures (2, 3, 4, 5, 6, and 7 atm) and constant temperature (35°C). It was found out that a 2 wt% loading of nano‐particles into the PDMS matrix is optimal to obtain the best separation performance. Afterwards, sorption experiments for the synthesized nano‐composite membranes were carried out, and diffusion coefficients of the gases were calculated based on solution‐diffusion mechanism. Gas permeation and sorption experiments showed an increase in sorption and a decrease in diffusion coefficients of the gases through the nano‐composite membranes by adding nano‐particles into the host polymer matrix. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
17.
Experimental data on gas sorption and polymer swelling in glassy polymer—gas systems at elevated pressures are presented for CO2 with polycarbonate, poly(methyl methacrylate), and polystyrene over a range of temperatures from 33 to 65°C and pressures up to 100 atm. The swelling and sorption behavior were found to depend on the occurrence of a glass transition for the polymer induced by the sorption of CO2. Two distinct types of swelling and sorption isotherms were measured. One isotherm is characterized by swelling and sorption that reach limiting values at elevated pressures. The other isotherm is characterized by swelling and sorption that continue to increase with pressure and a pressure effect on swelling that is somewhat greater than the effect of pressure on sorption. Glass transition pressures estimated from the experimental results for polystyrene with CO2 are used to obtain the relationship between CO2 solubility and the glass transition temperature for the polymer. This relationship is in very good agreement with a theoretical corresponding-states correlation for glass transition temperatures of polystyrene-liquid diluent mixtures. 相似文献
18.
Gas transport properties of semicrystalline films of poly(2,2,4,4-tetramethyl cyclobutane carbonate) (TMCBPC) were studied. Permeability coefficients for He, O2, N2, CH4, and CO2 at 35°C for pressures between 1 and 20 atm are reported as well as sorption isotherms for N2, CH4, and CO2 at the same conditions. The permeability coefficients for TMCBPC are larger than corresponding values for the aromatic bisphenol-A polycarbonate (PC) and tetramethyl bisphenol-A polycarbonate (TMPC), even though the TMCBPC films are semicrystalline. These results are explained on the basis of the larger free volume available for permeation in this polymer. Significant TMCBPC plasticization by CO2 was also observed and this causes typical time-dependent behavior. The plasticization process starts at very low pressures compared with the behavior of aromatic polycarbonates PC and TMPC. This early onset of plasticization seems to be related also to the larger free volume in the amorphous phase of TMCBPC which favors high gas sorption. The diffusion coefficients for TMCBPC are also larger than those reported for the aromatic polycarbonates PC and TMPC. Ideal gas separation factors were found to follow the usual trend; that is, as permeability increases, the ideal separation factor decreases. © 1993 John Wiley & Sons, Inc. 相似文献
19.
Although poly(4-vinylpyridine) is believed to have good gas permselectivity, the intrinsic gas permeation property is rarely reported in the literature. The objective of this work is to study the the intrinsic gas permeation property of poly(4-vinylpyridine) using a free-standing film. Because of its brittleness and strong adhesion with most solid surfaces, a free-standing poly(4-vinylpyridine) film was therefore prepared from casting on a liquid mercury surface. The permeation behavior of He, H2, O2, N2, CH4, and CO2 through the film was tested over a pressure range of 252 to 800 cm Hg at 35°C. The permeability and solubility decrease slightly with an increase in pressure, whereas the diffusivity increases as pressure increases. The pressure-dependent phenomenon can be explained using the partial immobilization model and the dual sorption model. An effective gas molecule diameter, which is defined as the square root of the product of gas collision and kinetic diameters, was used to correlate the diffusivity and gas molecule size, and an empirical equation was derived. Solubility is also a strong function of gas physical properties such as critical temperature and Lennard–Jones force constant, which are the measures of gas condensability and molecule interaction, respectively. In general, higher solubility in a polymer is obtained for gases with greater condensability and stronger interaction. Typical gas permeabilities of poly(4-vinylpyridine) measured at 619 cm Hg and 35°C are: 12.36 (He), 12.64 (H2), 3.31 (CO2), 0.84 (O2), 0.14 (CH4), and 0.13 (N2) barrers. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2851–2861, 1999 相似文献
20.
Hydrocarbon solubility,permeability, and competitive sorption effects in polymer of intrinsic microporosity (PIM‐1) membranes
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Colin A. Scholes Jianyong Jin Geoff W. Stevens Sandra E. Kentish 《Journal of Polymer Science.Polymer Physics》2016,54(3):397-404
The sorption and permeation of pentane, hexane, and toluene through highly permeable polymer of intrinsic microporosity (PIM‐1) membranes were investigated. It was established that the hydrocarbons sorbed strongly within the micro‐void regions of the PIM‐1 membrane. The sorption concentration was similar for the paraffins, pentane and hexane, but greater for aromatic toluene at high vapor activities. The magnitude of the hydrocarbon permeability was associated with the critical temperature of the hydrocarbon. The PIM‐1 membrane displayed selectivity for the three hydrocarbons over CO2. As a consequence, the presence of the three hydrocarbons dramatically reduced the permeability of CO2 and N2 under mixed gas–vapor conditions to 68%–95% below the dry gas value. For all three hydrocarbons the N2 permeability was more strongly impacted than CO2 permeability, and hence the ideal CO2/N2 selectivity of PIM‐1 increased. It was determined that CO2 and N2 solubility decreased because of hydrocarbon competitive sorption while CO2 and N2 diffusivity also decreased because of anti‐plasticization, which was due to the presence of hydrocarbon clusters within the membrane structure. There was a clear correlation between the magnitude of anti‐plasticization and the critical temperature of the hydrocarbon. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 397–404 相似文献