Membranes composed of zeolite crystals, in which gas molecules are transported by surface diffusion, are promising for gas separation applications. Since this mode of mass transfer mechanism is controlled by synergistic adsorption and diffusion phenomena, the separation of gas mixtures is not solely dependent on molecular size. However, undesirable defect pathways in zeolite membranes are often present due to factors such as incomplete crystal growth and/or thermal stresses during membrane synthesis and calcination. These pathways cause molecules to bypass the selective zeolite crystal layer and adversely affect membrane performance. Since the fabrication of defect-free zeolite membranes is very challenging, their widespread adoption for industrial processes has been impeded. Quantification of defects in zeolite membranes is therefore important to improve synthesis protocols of these membranes. In this research, zeolite membranes composed of silicalite crystals have been fabricated using the pore plugging method, and their performance was evaluated by developing a method that can be used to describe the selective and non-selective channels that are present in any zeolite membrane. Unlike the other destructive and sophisticated methods, which already exist to discern this information, the proposed method requires only a limited number of in-situ permeation experiments to be conducted using He – a non-adsorbing gas, and N2 – an adsorbing gas. With this method, the volume fraction, effective length, and size of the selective and non-selective channels of multiple membranes have been quantified, and these parameters were used to predict membrane performance at untested conditions, as well as with untested gases such as CH4 and CO2. In addition, by separating surface diffusion from the flow through the defects in gas separation tests with CO2/N2 mixture, the respective transport diffusivities and exchange diffusivity coefficients, which account for mass transfer in zeolite crystals were determined using the Maxwell-Stefan model. These determined exchange diffusivity coefficients are not equal to each other and challenge the Vignes correlation. In addition, transport diffusivities determined in mixed gas permeation experiments at University of Ottawa have then been validated by large single crystal transport diffusivities for mixed gases that were determined from molecular uptake experiments conducted at University of Leipzig in Germany, using Infra-Red Micro-imaging.

Abstract In this research, a facilitated transport membrane was developed. The reactive membrane consisted of a carrier entrapped in poly(vinyl alcohol) "PVA" matrix cast on a polysulfone support. PVA was selected to hold the reactive carrier because of its hydrophilicity and compatibility with the carrier. Several reactive amines were examined for their suitability as carrier. Among the amines tested as a carrier for CO₂, diethanolamine "DEA" demonstrates a greater improvement in the permeation of CO₂ as well as selectivity over N₂. DEA is a secondary amine and one of the most commonly used amines for gas treating due to its favourable reaction kinetics with acid gases and because of its stability when regenerated. Initially, pure gas permeation was employed for materials selection and membrane preparation procedures. The effects of process conditions on the membrane performance, which involve carrier concentrations, feed pressures and operating temperatures were examined. Then the effects of membrane thickness and long-term stability tests were conducted. Once the appropriate membrane materials and preparation procedures were established, the next phase of the study involved the determination of the actual separation of CO₂/N₂ mixtures. These experiments were carried out by adjusting the feed gas composition, feed pressures and operating temperature. In general, the results obtained with CO₂/N₂ mixtures were in agreement with those obtained with pure gas permeation experiments. It was found that facilitation is more significant at lower CO₂ partial pressure differential across the membrane. At higher partial pressure differentials, the reactive membrane may no longer serve as a facilitating medium due to the saturation of the reactive part of the membrane. Under such conditions the permeance values and selectivity obtained were simply due to the solubility and diffusivity of the CO₂ and N₂ in the membrane matrix. Since it was not possible to analyze concentration profiles inside the thin membrane experimentally, it was decided to analyze the effects of various parameters through the analytical transport equations. The zwitterion mechanism was used to illustrate the kinetics of the CO₂-DEA systems. The mass transport equations were solved numerically. All relevant physicochemical properties needed to implement the mass transport equations were taken from the literatures. The calculated results support the experimental trends that were observed for the CO₂ permeance as a function of partial pressure differentials and carrier concentrations.

Abstract In this research, a facilitated transport membrane was developed. The reactive membrane consisted of a carrier entrapped in poly(vinyl alcohol) "PVA" matrix cast on a polysulfone support. PVA was selected to hold the reactive carrier because of its hydrophilicity and compatibility with the carrier. Several reactive amines were examined for their suitability as carrier. Among the amines tested as a carrier for CO₂, diethanolamine "DEA" demonstrates a greater improvement in the permeation of CO₂ as well as selectivity over N₂. DEA is a secondary amine and one of the most commonly used amines for gas treating due to its favourable reaction kinetics with acid gases and because of its stability when regenerated. Initially, pure gas permeation was employed for materials selection and membrane preparation procedures. The effects of process conditions on the membrane performance, which involve carrier concentrations, feed pressures and operating temperatures were examined. Then the effects of membrane thickness and long-term stability tests were conducted. Once the appropriate membrane materials and preparation procedures were established, the next phase of the study involved the determination of the actual separation of CO₂/N₂ mixtures. These experiments were carried out by adjusting the feed gas composition, feed pressures and operating temperature. In general, the results obtained with CO₂/N₂ mixtures were in agreement with those obtained with pure gas permeation experiments. It was found that facilitation is more significant at lower CO₂ partial pressure differential across the membrane. At higher partial pressure differentials, the reactive membrane may no longer serve as a facilitating medium due to the saturation of the reactive part of the membrane. Under such conditions the permeance values and selectivity obtained were simply due to the solubility and diffusivity of the CO₂ and N₂ in the membrane matrix. Since it was not possible to analyze concentration profiles inside the thin membrane experimentally, it was decided to analyze the effects of various parameters through the analytical transport equations. The zwitterion mechanism was used to illustrate the kinetics of the CO₂-DEA systems. The mass transport equations were solved numerically. All relevant physicochemical properties needed to implement the mass transport equations were taken from the literatures. The calculated results support the experimental trends that were observed for the CO₂ permeance as a function of partial pressure differentials and carrier concentrations.

It is well known that clays dispersed in a polymer matrix decrease the permeability of all gases through that membrane. Our objective was to explore the effects on transport when a microporous layered aluminophosphate was added to a polymer matrix. The clay like layered aluminophosphate used contains sheets with 8MR ring openings in the size range of 3-4 Ã . The molecular level dispersion of this material into a polymer matrix is theorized to increase selectivity by molecular sieving. A previous study performed in our laboratory showed an increase in He/CH4 selectivity when this aluminophosphate (8MR-AlPO) was dispersed in a fluorinated polyimide. The increase in selectivity was explained as size sieving by the aluminophosphate sheets where small gas species can pass through the microstructure and large gas species have to take a tortuous path around the sheets. We performed several studies with different polymer materials in the attempt to make composite membranes that corroborated the previously seen increases in gas selectivity. In some cases different surfactants were used to swell 8MR-AlPO. In the first set of studies the methods used to produce the fluorinated polyimide composites were repeated using polydimethyl siloxane (PDMS), a copolymer of a fluorinated polyimide and PDMS, polysulfone, Matrimid, and cellulose acetate as the matrix materials. In general gas permeation studies of these materials showed an overall decrease in permeability with increasing addition of 8MR-AlPO but no substantial increase in selectivity. In an attempt to increase the chances of exfoliating and dispersing the layered aluminophosphate, an in-situ method using poly(etherimide) (PEI) was polymerized in the presence of 8MR-AlPO was employed. Mixed matrix membranes of PEI with 5wt% 8MR-AlPO were successfully fabricated and the transport properties measured. Microscopy revealed that the composites made with the 8MR-AlPO treated with a reactive surfactant showed better dispersion than those treated with the nonreactive surfactants. The permeability of gases changed very little as the result of adding 8MR-AlPO to PEI and no substantial increase in selectivity was observed. Finally, we incorporated a similar layered aluminophosphate with larger 12MR (6-7Ã ) openings into polysulfone. These composites showed barrier behavior but no increases in selectivity. / Ph. D.

Polymer – clay nanocomposites have improved thermal, mechanical, and barrier properties when compared with the pure polymer. The objective of this study was to examine if gas separation performance could be improved by introducing a layered nanopourous aluminum phosphate with a large aspect ratio into a polymeric matrix. The aluminum phosphate has eight membered rings, which could potentially serve as a size selective medium. A hexafluorinated polyimide, 6FDA-6FpDA-8%-DABA, was used as the polymeric matrix. The polyimide and the aluminum phosphate were synthesized separately according to well documented procedures. The two materials were blended and fabricated into nanocomposite membranes. The effect of mixing temperature and percentage of layered aluminum phosphate added to the polymer on the permeation properties were examined. These factors had a direct effect on the degree of intercalation and exfoliation of the nanocomposite structure. Transmission FTIR, TEM, DMTA, and X-ray diffraction were used to characterize the morphology, structure, and composition of these nanocomposite films. The permeation properties of the nanocomposite membranes were evaluated using pure gases (He, O₂, N₂, CH₄, CO₂) at 35°C and a feed pressure of 4 atm. In general, the permeability decreased and the selectivity coefficients increased when adding 10 wt% aluminum phosphate to the polyimide. Furthermore, the membranes showed size selectivity, consistent with the pore size in the layered aluminum phosphate. / Master of Science

Membrane separations provide a potentially attractive technology over conventional processes due to their advantages, such as low capital cost and energy consumption. The goal of this thesis is to design hybrid membranes that facilitate specific gas separations, especially olefin/paraffin separations. This thesis focuses on the designing dendrimer-based hybrid membranes on mesoporous alumina for reverse-selective separations, synthesizing Cu(I)-dendrimer hybrid membrane to facilitate olefin/paraffin separations, particularly ethylene/methane separation, and investigating the influence of solvent, stabilizing ligands on facilitated transport membrane. Reverse-selective gas separations have attracted considerable attention in removing the heavier/larger molecules from gas mixtures. In this study, dendrimer-based chemistry was proved to be an effective method by altering dendrimer structures and generations. G6-PIP, G4-AMP and G3-XDA are capable to fill the alumina mesopores and slight selectivity are observed. Facilitated transport membranes were made to increase the olefin/paraffin selectivity based on their chemical interaction with olefin molecules. Two approaches were explored, the first was to combine facilitator Cu(I) with dendrimer hybrid membrane to increase olefin permeance and olefin/paraffin selectivity simultaneously, and second was to facilitate transport membrane functionality by altering solvents and stabilizing ligands. Promising results were found by these two approaches, which were: 1) olefin/paraffin selectivity slightly increased by introducing facilitator Cu(I), 2) the interaction between Cu(I) and dendrimer functional groups are better known.

This research project investigated physical aging and carbon dioxide plasticization behavior of glassy polymer films. 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. The effect of film thickness on CO₂ permeation and sorption was studied extensively through carefully defined and controlled methods that provide a basis for future study of plasticization behavior. 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. 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. For a series of different polymers, the extent of plasticization response tracks with CO₂ solubility. There is little data available for gas sorption in thin glassy polymer films. In this work, a novel method involving spectroscopic ellipsometry is used to obtain simultaneously the film thickness and CO₂ sorption capacity for thin glassy polymer films. This allows a more comprehensive look at CO₂ permeability, sorption, and diffusivity as a function of both CO₂ pressure and exposure time. Like the gas permeation data, these experiments suggest that thin film sorption behavior is substantially different than that of thick film counterparts. Dynamic ellipsometry experiments show that refractive index minima, fractional free volume maxima, and CO₂ diffusivity maxima correlate well with observed CO₂ permeability maxima observed for thin Matrimid® films. These experiments demonstrate that plasticization and physical aging are competing processes. Aging, however, dominates over long time scales. Over time, CO₂ diffusivity is most affected by these competing effects, and the evolution of CO₂ diffusivity is shown to be the main contributing factor to changes in CO₂ permeability at constant pressure. / text

The glassy copolyimide 6FDA-DAM:DABA was investigated as a polymer backbone for membranes used in aggressive sour gas separation applications. An esterification crosslinking mechanism enabled the synthesis of materials with augmented H₂S/CH₄ selectivity and plasticization resistance. These materials make use of polyethylene glycol (PEG) crosslinking agents and are referred to as PEGMC polymers. Rigorous dense film characterization of the novel crosslinkable materials indicates that excellent H₂S/CH₄ selectivity (24) is achievable while still maintaining high CO₂/CH₄ selectivity (29) under high pressure ternary mixed gas (CO₂/H₂S/CH₄) feeds. Defect-free asymmetric hollow fiber membranes were formed and appropriate crosslinking conditions were determined, allowing for the characterization of these fibers under realistic sour gas feed conditions. Also, a PDMS post-treatment was used to give ultra-high permselectivity for aggressive feeds. Using several mixed gas feeds containing high concentrations of CO₂ and H₂S at feed pressures up to 700 psig, it is shown that the crosslinked asymmetric hollow fiber membranes developed and manufactured through this work are capable of maintaining excellent separation performance even under exceedingly taxing operating conditions. For example, CO₂/CH₄ and H₂S/CH₄ permselectivity values of 47 and 29, respectively, were obtained for a 5% H₂S, 45% CO₂, 50% CH₄ feed at 35°C with 700 psig feed pressure. An extremely aggressive 20% H₂S, 20% CO₂, 60% CH₄ mixed gas feed with 500 psig feed pressure was also used; the maximum CO₂/CH4 and H₂S/CH₄ permselectivity values were found to be 38 and 22, respectively.

No description available.

Les Metal-Organic Framework (MOF) sont des adsorbants très prometteurs pour la séparation des gaz. Formés de centres métalliques reliés par des ligands organiques, ces matériaux présentent une structure organisée avec des pores de taille contrôlée ainsi que des surfaces et des volumes poreux très élevées. La possibilité de faire varier à la fois le centre métallique et le ligand organique donne aux MOFs une très grande diversité qu'on ne retrouve pas chez les zéolithes et les charbons actifs.L'objectif de cette étude a été d'évaluer le potentiel des MOFs en tant qu'adsorbants pour quatre procédés de séparation de gaz. En raison du grand nombre de MOFs disponibles, il a été nécessaire d'élaborer une stratégie pour identifier les matériaux les plus prometteurs dans chaque cas. Cette méthodologie comprend quatre étapes : une étape de criblage, une étape expérimentale, une étape de calcul et une étape d'évaluation.Pour l'étape de criblage, un nouvel appareil dit « à haut débit » a été développé pour mesurer des isothermes approximatives. Ensuite, un certain nombre de matériaux ont été retenus pour faire une étude plus approfondie de leurs propriétés d'adsorption. Des isothermes très précises ont été mesurées par gravimétrie tandis que les enthalpies d'adsorption ont été obtenues par microcalorimétrie. Dans l'étape de calcul, le modèle IAST a été utilisée pour prédire les sélectivités à partir des données en gaz pur. Enfin, les adsorbants ont été classés à l'aide d'un nouveau paramètre de sélection qui regroupe la sélectivité, la capacité efficace et l'enthalpie d'adsorption, où l'importance de chacun des paramètres peut être ajustée en fonction des besoins du procédé. / Metal-Organic Frameworks (MOFs) are seen to be one of the most promising classes of adsorbents for gas separations. Consisting of metal clusters connected by organic linkers to form a fully crystalline network, these materials have record breaking surface areas and pore volumes as well as a wide variety of pore structures and sizes. This, coupled with the possibility to use virtually any transition metal as well as functionalized linkers, gives MOFs the chemical and physical versatility often lacking in traditional adsorbents such as zeolites and activated carbons.The purpose of this study was to evaluate the potential of MOFs as adsorbents for four gas separations of interest to the petrochemical industry. Because of the diversity and number of MOFs available, a methodology was needed to help identify the most promising materials in each case. The proposed methodology comprises four stages: a screening step, an experimental step, a computational step and finally an evaluation step. For the first stage, a high-throughput setup was developed to measure rough adsorption isotherms. A number of materials were then selected for a more thorough investigation of their adsorption properties. Highly accurate isotherms were measured gravimetrically while precise adsorption enthalpies were obtained by microcalorimetry. Step three involved predicting the co-adsorption behaviour from the pure gas isotherms using the Ideal Adsorbed Solution Theory. Finally, the adsorbents were ranked based on a new selection parameter regrouping selectivity, working capacity and adsorption enthalpy where the importance of each term can be adjusted depending on the requirements of the process.