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William J Koros - One of the best experts on this subject based on the ideXlab platform.
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natural gas sweetening using a cellulose triacetate hollow fiber membrane illustrating controlled Plasticization benefits
Journal of Membrane Science, 2020Co-Authors: Yang Liu, Zhongyun Liu, Nitesh Bhuwania, Daniel Chinn, Atsushi Morisato, William J KorosAbstract:Abstract Plasticization is a well-understood drawback of polymer membranes in many applications; however, recent studies have demonstrated surprising advantages of this phenomenon for demanding natural gas sweetening for some glassy polymer dense film membranes. Moving beyond dense film membranes, the current study focuses on cellulose triacetate (CTA) hollow fiber membranes to use the benefits of controlled Plasticization for realistic raw natural gas sweetening. Natural gas sweetening can be complicated by co-existence of condensable hydrocarbons, e.g. C2H6, C3H8 and toluene with the main H2S/CO2/CH4 ternary mixture; moreover, the operating temperature and pressure adds another dimension to this important separation. In this study, we consider an aggressive gas composition of high H2S (20 mol.%), low CO2 (5 mol.%), and significant amounts of C2H6 (3 mol.%) and C3H8 (3 mol.%) as well as trace amount of toluene (100–300 ppm) with CH4 comprising the rest of the feed. Various temperatures (35 °C and 50 °C) and pressures (6.9–31.3 bar) are also considered. We show a controlled Plasticization benefit for the CTA hollow fiber membrane, with attractive CO2 and H2S permeance (>110 GPU) and selectivity (22–28) for CO2 and H2S over CH4 at 35 °C and 31.3 bar. The current study represents a major step forward in processes for membrane-based natural gas sweetening using practical asymmetric membranes.
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surprising Plasticization benefits in natural gas upgrading using polyimide membranes
Journal of Membrane Science, 2020Co-Authors: Yang Liu, Wulin Qiu, Zhongyun Liu, Gongping Liu, Nitesh Bhuwania, Daniel Chinn, William J KorosAbstract:Abstract Hydrogen sulfide (H2S) and carbon dioxide (CO2) are acid gases that must be removed from natural gas prior to transmission and use. Here, we report the H2S/CH4 and CO2/CH4 separation performance of two polyimide membranes, i.e. 6FDA-DAM and 6FDA-DAM/DABA (3:2) for various realistic gas compositions and conditions. So-called Plasticization effects of the polyimides are generally viewed as negative features when using such membranes, but we report important applications where H2S is present in the feed and the polyimide membrane Plasticization is actually a tool for performance optimization. In fact, we identify cases where polyimide Plasticization can provide large performance benefits for H2S/CH4 separations. We further analyze the transport mechanisms in terms of sorption and diffusion factors to understand this surprising discovery for various important feeds and conditions. The 6FDA-DAM membrane showed H2S permeability of 495 barrer and H2S/CH4 selectivity of ~31 with CO2 permeability of 301 barrer and CO2/CH4 selectivity of ~19 for a 20% H2S, 20% CO2 and 60% CH4 feed at 35 °C and 46 bar. Such CO2/CH4 performance and higher H2S/CH4 separation performance for aggressive high pressure feeds exceeds that of rubbery polymers, making the glassy materials ideal for processing natural gas feeds containing H2S and CO2.
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chemically cross linkable polyimide membranes for improved transport Plasticization resistance for natural gas separation
Polymer, 2015Co-Authors: Hiroshi Eguchi, Danny J Kim, William J KorosAbstract:Abstract A series of cross-linkable membrane materials based on the 6FDA-DAM:DABA (3:2) polyimide with enhanced transport Plasticization resistance were synthesized to separate CO 2 from CH 4 . Glycidol was used as a cross-linking agent to modify 6FDA-DAM:DABA (3:2) efficiently and form a transesterification reaction-based cross-linking. The conversion was calculated by solution 1 H NMR. These materials were also characterized via density, glass transition temperature, permeation, and sorption measurements. Pure (CO 2 , CH 4 ) and mixed gas (CO 2 /CH 4 ) permeation was studied on dense films of these materials up to 700 psia (1000 psia) for pure CO 2 (50%:50% CO 2 :CH 4 mixed gas) feed. Compared to the 6FDA-DAM:DABA (3:2) membrane, CO 2 -induced Plasticization resistance for cross-linked membranes was enhanced in aggressive feed streams. Under CO 2 feed conditions at 35 °C, Plasticization for the 41% glycidol-modified cross-linked membrane was not observed up to approximately 450 psia. Glycidol-induced cross-linking offers an excellent balance of selectivity, permeability, and Plasticization resistance. The glycidol-modified 6FDA-DAM:DABA (3:2) is competitive with the earlier reported 1,3-propanediol modified materials. Possible issues such as resistance to contaminants may be final determinants in choice of approach; however, this topic was beyond the scope of the current study.
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gas separation performance of 6fda based polyimides with different chemical structures
Polymer, 2013Co-Authors: Wulin Qiu, Donald R Paul, Chienchiang Chen, William J KorosAbstract:Abstract This work reports the gas separation performance of several 6FDA-based polyimides with different chemical structures, to correlate chemical structure with gas transport properties with a special focus on CO 2 and CH 4 transport and Plasticization stability of the polyimides membranes relevant to natural gas purification. The consideration of the other gases (He, O 2 and N 2 ) provided additional insights regarding effects of backbone structure on detailed penetrant properties. The polyimides studied include 6FDA-DAM, 6FDA-mPDA, 6FDA-DABA, 6FDA-DAM:DABA (3:2), 6FDA-DAM:mPDA (3:2) and 6FDA-mPDA:DABA (3:2). Both pure and binary gas permeation were investigated. The packing density, which is tunable by adjusting monomer type and composition of the various samples, correlated with transport permeability and selectivity. The separation performance of the polyimides for various gas pairs were also plotted for comparison to the upper bound curves, and it was found that this family of materials shows attractive performance. The CO 2 Plasticization responses for the un-cross-linked polyimides showed good Plasticization resistance to CO 2 /CH 4 mixed gas with 10% CO 2 ; however, only the cross-linked polyimides showed good Plasticization resistance under aggressive gas feed conditions (CO 2 /CH 4 mixed gas with 50% CO 2 or pure CO 2 ). For future work, asymmetric hollow fibers and carbon molecular sieve membranes based on the most attractive members of the family will be considered.
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Plasticization resistant hollow fiber membranes for co2 ch4 separation based on a thermally crosslinkable polyimide
Journal of Membrane Science, 2011Co-Authors: Chienchiang Chen, Wulin Qiu, Stephen J Miller, William J KorosAbstract:Abstract Decarboxylation-induced thermal crosslinking has been demonstrated to be effective for stabilizing membranes against Plasticization in dense films. This study extends this promising crosslinking approach from dense films to industrially relevant asymmetric hollow fiber membranes. Crosslinkable asymmetric hollow fiber membranes were spun from a carboxylic acid containing polyimide, 6FDA-DAM:DABA. Dope and spinning conditions were optimized to obtain fibers with a defect-free selective skin layer. It is found that slightly defective fibers suffered severe selectivity loss after thermal crosslinking, suggesting that defect-free property is essential to the performance of the resulting crosslinked hollow fiber membranes. The crosslinked fibers were tested for CO2/CH4 separation. The excellent Plasticization resistance under high pressure feeds (with highest CO2 partial pressure of 400 psia) suggests that these robust membranes are promising for aggressive natural gas purification.
Matthias Wessling - One of the best experts on this subject based on the ideXlab platform.
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on the effects of Plasticization in co2 light gas separation using polymeric solubility selective membranes
Journal of Membrane Science, 2011Co-Authors: S Sander R Reijerkerk, D Kitty C Nijmeijer, Benny D Freeman, Claudio P Ribeiro, Matthias WesslingAbstract:Abstract This paper reports pure and mixed gas CO 2 /H 2 and CO 2 /CH 4 membrane separation performance of a highly permeable poly(ethylene oxide) based multi-block copolymer. Permeation and sorption properties have been studied over a wide temperature (−10 °C to +35 °C) and pressure range (up to 25 bar partial pressure of CO 2 ). In particular, we address the effect of Plasticization by CO 2 . A strong dependency of CO 2 permeability on CO 2 concentration in the polymer matrix was observed in pure and mixed gas experiments. Plasticization effects increased the permeability of H 2 and CH 4 in mixed gas experiments compared to their pure gas values. The H 2 permeability was less influenced by Plasticization than the CH 4 permeability due to H 2 's smaller kinetic diameter. As a result, mixed gas selectivities were systematically lower than pure gas selectivities. This difference between mixed and pure gas selectivity is exclusively dependent on the CO 2 concentration in the polymer matrix, which can change with temperature or CO 2 fugacity. Remarkably, the difference between ideal selectivity and mixed gas selectivity scales linearly with the CO 2 concentration in the polymer for all pressures and temperatures considered.
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Materials dependence of mixed gas Plasticization behavior in asymmetric membranes
Journal of Membrane Science, 2007Co-Authors: Tymen Visser, N. Masetto, Matthias WesslingAbstract:The mass transport of asymmetric membranes for the separation of carbon dioxide/methane mixtures is determined by competitive sorption and Plasticization. With increasing feed pressure in mixed gas experiments, the selectivity decreases due to both effects. Distinction whether one or the other mechanism is responsible for the selectivity loss is important since competitive sorption is related to intrinsic material properties and cannot be tailored, whereas Plasticization can be suppressed by various chemical means. This paper describes the systematic analysis for five different asymmetric membranes with respect to the balance between competitive sorption and Plasticization. Four asymmetric membranes where prepared for this study, one membrane was based on a commercial precursor. Of these membranes, three are based on the polyimide Matrimid: pure Matrimid, and blends of Matrimid with polyethersulfone as well as Matrimid with a polyimide P84. These membranes are compared with two other ones: cellulose acetate and polyphenyleneoxide PPO. The blend of Matrimid with P84 shows the highest mixed gas selectivity and is very resistant against Plasticization without any further chemical modification.
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on the subtle balance between competitive sorption and Plasticization effects in asymmetric hollow fiber gas separation membranes
Journal of Membrane Science, 2005Co-Authors: Tymen Visser, G H Koops, Matthias WesslingAbstract:The paper describes the influence of a varying feed composition of CO2/CH4 and CO2/N2 mixtures on the gas separation performance of integrally skinned asymmetric PES/PI hollow fibers with an effective skin thickness of 0.27 ?m. Normally, thin membrane structures (<3 ?m) show accelerated Plasticization behavior induced by CO2 in pure gas measurements. This study shows that introducing an inert gas to the CO2 feed mixture apparently suppresses Plasticization. This effect is more pronounced at higher concentrations of inert gas, supported by a continuous drop in CO2 permeance as a function of CO2 fugacity. At a concentration of 80% inert gas in the feed mixture, the CO2 permeance reduces more than 35% from its initial value, whereas the reduction is 8?10% with 2% inert gas in the feed mixture. However, a mixed gas permeation model predicts for all experimentally used gas compositions similar decreases in CO2 permeance. Plasticization effects seem to be counterbalanced by competitive sorption. This effect becomes larger with increasing inert gas concentration. At 80% inert gas Plasticization effects appear to be completely counterbalanced by competitive sorption. Besides that, for all gas compositions, the separation factor decreases with increasing feed pressure, generally assumed as an indication of Plasticization. However, such a selectivity decrease is also predicted by the dual mode sorption model, which neglects effects of Plasticization. More pronounced indication of Plasticization effects is observed when the N2 permeance decay is followed in time after the membrane has been in contact with CO2 at elevated CO2 partial pressures. A significant enhanced N2 permeance is observed due to polymer network dilation, which decreases very slowly in time. There seems to be a subtle balance between Plasticization and competitive sorption during mixed gas experiments with integrally skinned asymmetric hollow fibers, which results in the observed phenomenon.
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Accelerated Plasticization of thin-film composite membranes used in gas separation
Separation and Purification Technology, 2001Co-Authors: Matthias Wessling, M. Lidon Lopez, H. StrathmannAbstract:Permeation experiments with He, N2, O2 and CO2, have been carried out with double layer composite membranes consisting of a silicone rubber support layer and a thin polyimide layer determining the permeation properties. The estimated thickness of the polyimide layer in the composite membranes was between 1.5 and 4 microns. This paper describes the phenomenon of accelerated Plasticization of such thin polyimide layers used in gas separation membranes. The pressure-normalized fluxes were determined at 5 bars for N2, O2 and in the range of 1?8 bars in the case of He and CO2. Helium permeation decreased with increasing feed pressure and no hysteresis behavior was found for successive increasing and decreasing feed pressure steps. For CO2, the pressure-normalized flux did not follow the typical behavior of glassy polymers but increased continuously with increasing feed pressure. Also, CO2 permeation showed a clear hysteresis effects resulting in an increasing permeability with time and an elevated magnitude in successive decreasing feed pressure steps. Hence, stronger Plasticization effects in the composite membranes must be concluded in comparison with thick single film membranes. The Plasticization effects are significantly pronounced as the polyimide concentration in the solution from which the membranes are cast become more dilute. The latter is interpreted as accelerated Plasticization with decreasing film thickness.
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suppression of gas separation membrane Plasticization by homogeneous polymer blending
Aiche Journal, 2001Co-Authors: A Bos, H. Strathmann, Ineke G M Punt, Matthias WesslingAbstract:Plasticization is a phenomenon frequently encountered in the application of glassy polymeric materials for solution-diffusion membranes. Conventional methods for stabilizing the membrane are either annealing or cross-linking, which hardly influence the selectivity of the membrane, but decrease the permeability. For single-gas experiments, the literature shows that Plasticization can be stabilized by blending a polymer with high Plasticization tendencies with one that is hardly affected by the sorbed molecules. Most permeation experiments are carried out with pure CO2, but little is known about the transport properties determined from mixed gas experiments. Stabilization of Plasticization in mixed-gas experiments for polymer blends of the polyimide Matrimid and polysulfone is reported, as well as transport properties of a new homogeneous polymer blend based on Matrimid and the copolyimide P84. Experimental results show that the material is stabilized against carbon dioxide Plasticization and selectivity for a carbon dioxide/methane mixture significantly improves.
Geoff W Stevens - One of the best experts on this subject based on the ideXlab platform.
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Plasticization of ultra thin polysulfone membranes by carbon dioxide
Journal of Membrane Science, 2010Co-Authors: Colin A Scholes, George Q Chen, Geoff W Stevens, Sandra E KentishAbstract:Abstract Plasticization of gas separation membranes by carbon dioxide permanently alters their performance and increases the possibility of membrane failure. This is amplified in ultra-thin composite membranes, where the active polymeric layer is less than 2 μm. Here, the Plasticization influence of CO 2 is measured on ultra-thin polysulfone composite membranes for a range of active layer thicknesses, at four temperatures. The resulting permeability–pressure isotherms demonstrate Plasticization occurs for all thicknesses at pressures lower than has been reported for dense membranes. These isotherms were quantitatively fitted with an expanded dual-sorption model that takes into account Plasticization of the membrane. The Plasticization potential of CO 2 for polysulfone was found to increase with reduced active layer thickness. Similarly, the Plasticization potential of CO 2 was found to decrease with temperature. These results are consistent with similar research that shows that thin films behave differently to dense membranes.
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the effect of condensable minor components on the gas separation performance of polymeric membranes for carbon dioxide capture
Energy Procedia, 2009Co-Authors: Colin A Scholes, Sandra E Kentish, Geoff W StevensAbstract:Abstract Polymeric membranes as a carbon dioxide capture technology have a number of advantages over other approaches, including their low cost, high performance separation, ease of synthesis, as well as mechanical and thermal stability. However, condensable components in flue gas, in particular water, undergo competitively adsorption with carbon dioxide within the membranes, resulting in a reduction in CO 2 permeability. Furthermore, on a longer timescale Plasticization of the membrane can occur, turning the glassy polymer to a more rubbery state, which alters both gas permeability and selectivity. Here, the impact of water on three glassy polymeric membranes are studied; polysulfone, Matrimid and 6FDA-TMPDA (a polyimide). The purpose of this work is to model the behavior of gas separation membranes under humid conditions that mimic real flue gas. This will assist in analyzing the performance of glassy gas separation membranes in planned CO 2 capture trials on both pre- and post-combustion carbon capture. Upon exposure to water in the feed, all three membranes, Matrimid, polysulfone and 6FDA-TMPDA experience reduced CO 2 permeability indicative of competitive adsorption. Over a longer timescale, both polysulfone and 6FDA-TMPDA recover some of the loss in permeability performance, due to Plasticization by water. Matrimid displays no Plasticization behavior.
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effects of carbon dioxide induced Plasticization on the gas transport properties of glassy polyimide membranes
Journal of Membrane Science, 2007Co-Authors: Shinji Kanehashi, Sandra E Kentish, Tsutomu Nakagawa, Kazukiyo Nagai, Xavier J Duthie, Geoff W StevensAbstract:Abstract The time dependence of carbon dioxide (CO 2 ) transport properties, such as permeability, solubility, and diffusivity, in glassy polyimide membranes was investigated in terms of membrane preparation protocols ( i.e. , casting solvent and thermal treatment). The polyimide used was 6FDA-TeMPD (4,4-(hexafluoroisopropylidene) diphthalic anhydride) (6FDA)-2,3,5,6-tetramethyl-1,4-phenylene-diamine (TeMPD). The time dependence of CO 2 permeability in the as-cast 6FDA-TeMPD membranes prepared from tetrahydrofuran and dichloromethane showed typical CO 2 -induced Plasticization at pressures over 10 atm. The critical Plasticization pressure at which CO 2 -induced Plasticization begins to affect the gas permeability shifted from nearly 10–30 atm after heat treatment. The increase in CO 2 permeability upon Plasticization is mostly caused by an increase in CO 2 diffusivity. Furthermore, we found that regardless of the membrane preparation protocol, there is a critical CO 2 diffusivity of 73 ± 5 × 10 −8 cm 2 /s at the Plasticization pressure in 6FDA-TeMPD membranes.
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operating temperature effects on the Plasticization of polyimide gas separation membranes
Journal of Membrane Science, 2007Co-Authors: Xavier J Duthie, Sandra E Kentish, Kazukiyo Nagai, Clem E Powell, Greg G Qiao, Geoff W StevensAbstract:Abstract Membrane Plasticization is the process whereby penetrant dissolution causes membrane swelling or dilation, which in turn, can increase membrane diffusivity and solubility and lead to long time frame polymer relaxation processes. In this work, the effect of temperature upon the Plasticization of a rigid polyimide, poly(4,4′-hexafluoroisopropylidene diphthalic anhydride–2,3,5,6-tetramethyl-1,4-phenylenediamine) (6FDA-TMPDA), by carbon dioxide is investigated. It is found that across the full range of temperatures studied, Plasticization has little effect on carbon dioxide solubility as all results can be characterized by a standard dual mode sorption model. However, the effect upon diffusivity is significant and this can be described by both an exponential relationship with penetrant concentration and an Arrhenius relationship with temperature. The polymer relaxation processes induced by Plasticization are also temperature dependent. However, the total proportion of penetrant sorption associated with such relaxation processes is relatively unaffected by temperature. This paper shows that Plasticization effects are dominated by Henry's law dissolution. Conversely, while Henry's law species contribute most to diffusion at high temperatures, at lower temperatures the movement of Langmuir component species also contributes to the total diffusion coefficient.
Donald R Paul - One of the best experts on this subject based on the ideXlab platform.
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gas permeation in thin films of high free volume glassy perfluoropolymers part ii co2 Plasticization and sorption
Polymer, 2015Co-Authors: Rajkiran R Tiwari, Zachary P Smith, Haiqing Lin, Benny D Freeman, Donald R PaulAbstract:Abstract Carbon dioxide (CO2) Plasticization and sorption effects in both thick and thin films of “high free-volume” glassy perfluoropolymers were studied by monitoring CO2 permeability and by observing changes in the film thickness and refractive index with ellipsometry measurements. The film thickness, aging time, thermal history and CO2 exposure protocols have significant effect on the absolute CO2 permeability and Plasticization behavior of both thick and thin films. The extent of CO2 Plasticization increases as film thickness decreases and as the aging time is increased. The as-cast films showed higher Plasticization compared to films which were annealed above Tg; however, the CO2 permeability of both the as-cast and annealed films continuously decreased during the depressurization step unlike other glassy polymers. In general, the various CO2 exposure protocols revealed lower CO2 Plasticization for perfluoropolymers compared to other reported glassy polymers. The extent of CO2 sorption obtained from the ellipsometry measurements was found to decrease with the decrease in the excess volume and increase in the aging time for perfluoropolymers; in addition, the structural differences among the various glassy polymers resulting in different polymer–gas interactions also affects the overall sorption characteristics. The lower Plasticization in perfluoropolymers compared to Matrimid was also confirmed from the smaller percent increase observed for the experimental diffusion coefficient compared to the theoretically predicted diffusion coefficient from the dual sorption-mobility model. The Langmuir sorption parameter, C H ′ , and solubility at infinite dilution, S0, obtained from fitting dual sorption-mobility model to sorption data, showed an excellent linear correlation with (Tg-35) °C. The CO2 diffusivity and permeability data obtained for thin films of various glassy polymers also showed a strong correlation with free volume. The somewhat unusual behavior of thin films of AF 2400 in comparison to other glassy polymers studied to date is believed to be related to the low cohesive energy density expected of perfluorinated structures and its high free volume resulting from the bulky dioxole comonomer.
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gas separation performance of 6fda based polyimides with different chemical structures
Polymer, 2013Co-Authors: Wulin Qiu, Donald R Paul, Chienchiang Chen, William J KorosAbstract:Abstract This work reports the gas separation performance of several 6FDA-based polyimides with different chemical structures, to correlate chemical structure with gas transport properties with a special focus on CO 2 and CH 4 transport and Plasticization stability of the polyimides membranes relevant to natural gas purification. The consideration of the other gases (He, O 2 and N 2 ) provided additional insights regarding effects of backbone structure on detailed penetrant properties. The polyimides studied include 6FDA-DAM, 6FDA-mPDA, 6FDA-DABA, 6FDA-DAM:DABA (3:2), 6FDA-DAM:mPDA (3:2) and 6FDA-mPDA:DABA (3:2). Both pure and binary gas permeation were investigated. The packing density, which is tunable by adjusting monomer type and composition of the various samples, correlated with transport permeability and selectivity. The separation performance of the polyimides for various gas pairs were also plotted for comparison to the upper bound curves, and it was found that this family of materials shows attractive performance. The CO 2 Plasticization responses for the un-cross-linked polyimides showed good Plasticization resistance to CO 2 /CH 4 mixed gas with 10% CO 2 ; however, only the cross-linked polyimides showed good Plasticization resistance under aggressive gas feed conditions (CO 2 /CH 4 mixed gas with 50% CO 2 or pure CO 2 ). For future work, asymmetric hollow fibers and carbon molecular sieve membranes based on the most attractive members of the family will be considered.
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carbon dioxide Plasticization and conditioning effects in thick vs thin glassy polymer films
Polymer, 2011Co-Authors: Norman R Horn, Donald R PaulAbstract:Abstract Recent studies have shown that thin glassy polymer films undergo physical aging more rapidly than thick films. This suggests that thickness may also play a role in the Plasticization and conditioning responses of thin glassy films in the presence of highly-sorbing penetrants such as CO2. In this paper, a carefully designed systematic study explores the effect of thickness on the CO2 Plasticization and conditioning phenomena in Matrimid®, a polyimide commonly used in commercial gas separation membranes. Thin films are found to be more sensitive than thick films to CO2 exposure, undergoing more extensive and rapid Plasticization at any pressure. The response of glassy polymers films to CO2 is not only dependent on thickness, but also on aging time, CO2 pressure, exposure time, and prior history. Finally, thin films experiencing constant CO2 exposure for longer periods of time exhibit an initial large increase in CO2 permeability, which eventually reaches a maximum, followed by a significant decrease in permeability for the duration of the experiment. Thick films, in contrast, do not seem to exhibit this trend for the range of conditions explored.
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the effects of crosslinking chemistry on co2 Plasticization of polyimide gas separation membranes
Industrial & Engineering Chemistry Research, 2002Co-Authors: John D Wind, Donald R Paul, Claudia Staudtbickel, William J KorosAbstract:To suppress undesirable Plasticization effects in CO2/CH4 separations, crosslinkable 6FDA-based copolyimides were synthesized by using 3,5-diaminobenzoic acid (DABA) as one of two diamine monomers. DABA contains a carboxylic acid group that can be used to crosslink the polymer chains with ethylene glycol and aluminum acetylacetonate. These chemistries were compared for effectiveness in suppressing CO2 Plasticization on the basis of pure CO2 permeation and sorption data up to 800 psia. The time and pressure dependencies of permeation and sorption were analyzed to characterize the Plasticization phenomenon and how it can be controlled by covalent crosslinking. Mixed-gas permeation data are reported up to a total feed pressure of 850 psia for the separation of 50:50 CO2/CH4 mixtures at 35 °C. Selectivity losses with increasing feed pressure are modeled to further understand the effects of Plasticization, dual-mode sorption, gas-phase nonidealities, and bulk flow on membrane performance. Additionally, a short...
H. Strathmann - One of the best experts on this subject based on the ideXlab platform.
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Accelerated Plasticization of thin-film composite membranes used in gas separation
Separation and Purification Technology, 2001Co-Authors: Matthias Wessling, M. Lidon Lopez, H. StrathmannAbstract:Permeation experiments with He, N2, O2 and CO2, have been carried out with double layer composite membranes consisting of a silicone rubber support layer and a thin polyimide layer determining the permeation properties. The estimated thickness of the polyimide layer in the composite membranes was between 1.5 and 4 microns. This paper describes the phenomenon of accelerated Plasticization of such thin polyimide layers used in gas separation membranes. The pressure-normalized fluxes were determined at 5 bars for N2, O2 and in the range of 1?8 bars in the case of He and CO2. Helium permeation decreased with increasing feed pressure and no hysteresis behavior was found for successive increasing and decreasing feed pressure steps. For CO2, the pressure-normalized flux did not follow the typical behavior of glassy polymers but increased continuously with increasing feed pressure. Also, CO2 permeation showed a clear hysteresis effects resulting in an increasing permeability with time and an elevated magnitude in successive decreasing feed pressure steps. Hence, stronger Plasticization effects in the composite membranes must be concluded in comparison with thick single film membranes. The Plasticization effects are significantly pronounced as the polyimide concentration in the solution from which the membranes are cast become more dilute. The latter is interpreted as accelerated Plasticization with decreasing film thickness.
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suppression of gas separation membrane Plasticization by homogeneous polymer blending
Aiche Journal, 2001Co-Authors: A Bos, H. Strathmann, Ineke G M Punt, Matthias WesslingAbstract:Plasticization is a phenomenon frequently encountered in the application of glassy polymeric materials for solution-diffusion membranes. Conventional methods for stabilizing the membrane are either annealing or cross-linking, which hardly influence the selectivity of the membrane, but decrease the permeability. For single-gas experiments, the literature shows that Plasticization can be stabilized by blending a polymer with high Plasticization tendencies with one that is hardly affected by the sorbed molecules. Most permeation experiments are carried out with pure CO2, but little is known about the transport properties determined from mixed gas experiments. Stabilization of Plasticization in mixed-gas experiments for polymer blends of the polyimide Matrimid and polysulfone is reported, as well as transport properties of a new homogeneous polymer blend based on Matrimid and the copolyimide P84. Experimental results show that the material is stabilized against carbon dioxide Plasticization and selectivity for a carbon dioxide/methane mixture significantly improves.
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co2 induced Plasticization phenomena in glassy polymers
Journal of Membrane Science, 1999Co-Authors: A Bos, Matthias Wessling, Ineke G M Punt, H. StrathmannAbstract:A typical effect of Plasticization of glassy polymers in gas permeation is a minimum in the relationship between the permeability and the feed pressure. The pressure corresponding to the minimum is called the Plasticization pressure. Plasticization phenomena significantly effect the membrane performance in, for example, CO2/CH4 separation processes. The polymer swells upon sorption of CO2 accelerating the permeation of CH4. As a consequence, the polymer membrane loses its selectivity. Fundamental understanding of the phenomenon is necessary to develop new concepts to prevent it. In this paper, CO2-induced Plasticization phenomena in 11 different glassy polymers are investigated by single gas permeation and sorption experiments. The main objective was to search for relationships between the Plasticization pressure and the chemical structure or the physical properties of the polymer. No relationships were found with respect to the glass-transition temperature or fractional free volume. Furthermore, it was thought that polar groups of the polymer increase the tendency of a polymer to be plasticized because they may have dipolar interactions with the polarizable carbon dioxide molecules. But, no dependence of the Plasticization pressure on the carbonyl or sulfone density of the polymers considered was observed. Instead, it was found that the polymers studied plasticized at the same critical CO2 concentration of 36±7 cm3 (STP)/cm3 polymer. Depending on the polymer, different pressures (the Plasticization pressures) are required to reach the critical concentration.
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suppression of co2 Plasticization by semiinterpenetrating polymer network formation
Journal of Polymer Science Part B, 1998Co-Authors: A Bos, Matthias Wessling, Ineke G M Punt, H. StrathmannAbstract:CO2-induced Plasticization may significantly spoil the membrane performance in high-pressure CO2/CH4 separations. The polymer matrix swells upon sorption of CO2, which accelerates the permeation of CH4. The polymer membrane looses its selectivity. To make membranes attractive for, for example, natural gas upgrading, Plasticization should be minimized. In this article we study a polymer membrane stabilization by a semiinterpenetrating polymer network (s-ipn) formation. For this purpose, the polyimide Matrimid 5218 is blended with the oligomer Thermid FA-700 and subsequently heat treated at 265°C. Homogeneous films are prepared with different Matrimid/Thermid ratios and different curing times. The stability of the modified membrane is tested with permeation experiments with pure CO2 as well as CO2/CH4 gas mixtures. The original membrane shows a minimum in its permeability vs. pressure curves, but the modified membranes do not indicating suppressed Plasticization. Membrane performances for CO2/CH4 gas mixtures showed that the plasticizing effect indeed accelerates the permeation of methane. The modified membrane clearly shows suppression of the undesired methane acceleration. It was also found that just blending Matrimid and Thermid was not sufficient to suppress Plasticization. The subsequent heat treatment that results in the s-ipn was necessary to obtain a stabilized permeability.
