Porous organic polymers (POPs) received great attention in recent years because of their novel properties such as permanent porosity, adjustable chemical nature, and remarkable thermal and chemical stability. These attractive features make POPs very promising candidates for use in gas separation and storage applications. In particular, CO2 capture and separation from gas mixtures by POPs have been intensively investigated in recent years because of the greenhouse nature of CO2, which is considered a leading cause for global warming. CO2 chemical absorption by amine solutions from the flue gas of coal-fired power plants suffers from several challenges such as high-energy consumption in desorption, chemical instability, volatility, and corrosive nature, limiting the widespread use of this technology. To mitigate these limitations, new adsorbents with improved CO2 capturing properties need to be designed, synthesized, and tested. Alternatively, the use of cleaner fuels such as methane can reduce CO2 release or completely eliminates it in the case of hydrogen. However, the on-board storage of methane and hydrogen for automotive applications remains a great challenge. With these considerations in mind, our research goals in this dissertation focus on the systematic design and synthesis of N-rich POPs and their use in small gas (H2 and CH4) storage as well as selective CO2 capture from gas mixtures. In particular, we have studied the effect of integrating pyrene and triazine building units into benzimidazole-linked polymers (BILPs) and covalent organic frameworks (COFs) on gas storage and separation. We have found that pyrene-based BILPs exhibit remarkable selective CO2 capturing capacities under industrial settings (VAS, PSA). However the methane and hydrogen storage capacities of BILPs were found to be only modest especially at high pressure due to their moderate surface area and pore volume. We addressed these limitations by the synthesis of a highly porous imine-linked COF (ILCOF-1), which has very high surface area and improved hydrogen and methane uptakes when compared to BILPs. We have demonstrated that the use of pyrene in BILPs and COFs can direct frameworks growth through - stacking and improve porosity and pore volume whereas the use of triazine is instrumental in improving the binding affinity of the frameworks towards CO2.

Polymers were synthesised containing the methanoanthracene (MA), methanopentacene (MP) and benzomethanoanthracene (BzMA) units to investigate their properties as gas separation membranes. For each monomer type, polymers were successfully synthesised using Tröger’s base (TB) chemistry and cast as free standing films from low-boiling point solvents. Gas permeability tests revealed high selectivities for most of the technologically significant gas pairs. Most interestingly, MA/dimethylethanoanthracene co-polymer, MP-TB and BzMT-TB polymers all show a high degree of selectivity in the separation of a number of technologically significant gas pairs when compared to other state-of-the-art polymers. In particular MP-TB has very high selectivity for the N2/O2 gas pair. Synthetic routes to MP-TB and BzMA-TB involve fewer steps and are significantly cheaper to implement compared to other state of the art TB polymers and high performance PIMs that provide data above the Robeson upper bounds due to their high permeability and selectivity. Co-polymers of MA were synthesised in 1:1, 4:1 and 9:1 ratios. Gas permeability data demonstrated that properties correlate with the monomer composition. Results indicate that inclusion of methano-bridged units into the polymers increased the rigidity of polymer chains, leading to smaller pore widths and improved selectivities compared to polymers such made from more flexible structural units. The first chapter of this thesis introduces the concepts of microporosity, permeability and membrane separation, and describes a number of polymers that have demonstrated properties of interest for separating gas mixtures. Chapter two describes the synthesis and gas permeability data of MA-TB polymer and a series of copolymers incorporating MA. Chapter 3 describes the synthesis of polymers containing the MP structural unit and describes the performance of MP-TB as a membrane for gas separation. Chapter 4 describes a number of polymers synthesised using the BzMA structural unit and chapter 5 reports the synthesis of a number of larger units derived from BzMA including benzomethanotetracene, benzomethanopentacene and dibenzomethanopentacene. Permeability data for TB polymers synthesised from BzMA-type monomers is reported in these chapters.

Le comportement plastifiant de polymères purs a été bien étudié dans la littérature. Toutefois, il n'y a eu que peu d'études concernant les membranes à matrices mixtes (MMM). Dans le chapitre 2 de cette thèse, le comportement plastifiant de MMM préparés à partir de nanoparticules mésoporeuses Fe(BTC) et du polymère Matrimid® est étudié avec un gaz pur ou en mélange. Les réseaux métaux-organiques (MOF) sous forme particulaires ont présenté une relativement bonne compatibilité avec le polymère. L'incorporation de Fe(BTC) dans du Matrimid® a permis d'augmenter la perméabilité et la sélectivité des membranes. Pour de faibles pressions de 5 bars, les MMM ont une perméabilité au CO2 de 60% plus grande ainsi qu'une sélectivité de 29% plus grande à comparer à la sélectivité idéale de membranes Matrimid®. Il a été observé que la présence de particules Fe(BTC) retardait l'effet plastifiant vers de plus grandes pressions. De plus, cette pression augmente avec le taux de MOF au sein du matériau. Ce retard est attribué à la mobilité réduite des chaînes polymères dans l'entourage des particules Fe(BTC). Egalement, pour des concentrations en MOF plus élevées, les membranes présentent une sélectivité plus ou moins constante sur toute la gamme de pression étudiée. Le chapitre 3 présente ensuite la préparation et le caractère plastifiant des MMMs basées sur trois types de MOFs (MIL-53(Al) (MOF « repirant »), ZIF-8 (MOF « flexible ») and Cu3(BTC)2 (MOF « rigide »)) dispersés dans le Matrimid®. Les performances en gaz pur ou en mélange ont été étudiées en fonction de la quantité de MOF introduite. Parmi les trois systèmes MOF-MMM, les membranes avec le Cu3(BTC)2 ont présenté la plus haute sélectivité alors que les membranes avec du ZIF-8 ont montré une plus grande perméabilité. Ces améliorations sont essentiellement le fait de la structure cristalline du MOF et de son interaction avec les molécules de CO2. Le chapitre 4 décrit la préparation de membranes à base de mélange Matrimid® polyimide (PI)/polysulfone (PSF) contenant des particules de ZIF-8 pour la séparation gazeuse à haute pression. Un mélange optimisé avec un rapport PI/PSF de 3:1 a été utilisé pour une étude sur la stabilité et la performance de ces MMMs incorporant différentes concentration de ZIF-8. PI et PSF étant miscibles, une bonne compatibilité avec les particules de ZIF-8 est observée. Les MMMs PI/PSF-ZIF-8 ont démontré une amélioration significative de la perméabilité en CO2 lors de l'augmentation de la concentration en ZIF-8, ce qui a été attribué à une augmentation modérée de la capacité de sorption et à une diffusion plus rapide au travers des particules de ZIF-8. Lors des mesures en gaz purs, les membranes PI/PSF (3:1) ont présenté une plastification vers 18 bars alors que l'introduction de ZIF-8 repousse cette valeur à 25 bars. En mélange de gaz, les MMMs PI/PSF-ZIF-8 ont abouti à une suppression de la plastification comme l'a confirmé une mesure constante de la perméabilité et de la sélectivité du CH4, et cet effet est plus accentué avec l'augmentation de la concentration en ZIF-8. Les résultats en séparation des gaz avec les MMMs PI/PSF-ZIF-8 montrent une performance supérieure à celle du Matrimid® ce qui laisse augurer un élargissement du spectre d'application de ces membranes, particulièrement pour la séparation du CO2 à haute pression. Dans le chapitre 5, une nouvelle voie de préparation des MMMs via la fusion contrôlée de particules a été introduite. La modification du Matrimid® par du 1-(3-aminopropyl)-imidazole a permis d'améliorer considérablement la compatibilité avec les particules de ZIF-8. Il a ainsi été possible de préparer des MMMs contenant 30% de MOF sans perte de sélectivité. En augmentant la concentration en ZIF-8, les MMMs ont de meilleures performances dans la séparation de mélange CO2/CH4 à comparer au polymère initial. La perméabilité a augmenté de plus de 200% avec une augmentation de 65% de sélectivité pour le mélange CO2/CH4. / The plasticization behavior of pure polymers is well studied in literature. However, there are only few studies on the plasticization behavior of mixed matrix membranes. In Chapter 2 of this thesis, pure and mixed gas plasticization behavior of MMMs prepared from mesoporous Fe(BTC) nanoparticles and the polymer Matrimid® is investigated. All experiments were carried with solution casted dense membranes. Mesoporous Fe(BTC) MOF particles showed reasonably good compatibility with the polymer. Incorporation of Fe(BTC) in Matrimid® resulted in membranes with increased permeability and selectivity. At low pressures of 5 bar the MMMs showed an increase of 60 % in CO2 permeability and a corresponding increase of 29 % in ideal selectivity over pure Matrimid® membranes. It was observed that the presence of Fe(BTC) particles increases the plasticization pressure of Matrimid® based MMMs. Furthermore, this pressure increases more with increasing MOF loading. This delay in plasticization is attributed to the reduced mobility of the polymer chains in the vicinity of the Fe(BTC) particles. Also, at higher Fe(BTC) loadings, the membranes showed more or less constant selectivity over the whole pressure range investigated. Chapter 3 subsequently presented the preparation and plasticization behavior of MMMs based on three distinctively different MOFs (MIL-53(Al) (breathing MOF), ZIF-8 (flexible MOF) and Cu3(BTC)2 (rigid MOF)) dispersed in Matrimid®. The ideal and mixed gas performance of the prepared MMMs was determined and the effect of MOF structure on the plasticization behavior of MMMs was investigated. Among the three MOF-MMMs, membranes based on Cu3(BTC)2 showed highest selectivity while ZIF-8 based membranes showed highest permeability. The respective increase in performance of the MMMs is very much dependent on the MOF crystal structure and its interactions with CO2 molecules. Chapter 4 described the preparation of Matrimid® polyimide (PI)/polysulfone (PSF)-blend membranes containing ZIF-8 particles for high pressure gas separation. An optimized PI/PSF blend ratio (3:1) was used and performance and stability of PI/PSF mixed matrix membranes filled with different concentrations of ZIF-8 were investigated. PI and PSF were miscible and provided good compatibility with the ZIF-8 particles, even at high loadings. The PI/PSF-ZIF-8 MMMs showed significant enhancement in CO2 permeability with increased ZIF-8 loading, which was attributed to a moderate increase in sorption capacity and faster diffusion through the ZIF-8 particles. In pure gas measurements, pure PI/PSF blend (3:1) membranes showed a plasticization pressure of ~18 bar while the ZIF-8 MMMs showed a higher plasticization pressures of ~25 bar. Mixed gas measurements of PI/PSF-ZIF-8 MMMs showed suppression of plasticization as confirmed by a constant mixed gas CH4 permeability and a nearly constant selectivity with pressure but the effect was stronger at high ZIF-8 loadings. Gas separation results of the prepared PI/PSF-ZIF-8 MMMs show an increased commercial viability of Matrimid® based membranes and broadened their applicability, especially for high-pressure CO2 gas separations. In Chapter 5, a novel route for the preparation of mixed matrix membranes via a particle fusion approach was introduced. Surface modification of the polymer with 1-(3-aminopropyl)-imidazole led to an excellent ZIF-8-Matrimid® interfacial compatibility. It was possible to successfully prepare MMMs with MOF loadings as high as 30 wt.% without any non-selective defects. Upon increasing the ZIF-8 loading, MMMs showed significantly better performance in the separation of CO2/CH4 mixtures as compared to the native polymer. The CO2 permeability increased up to 200 % combined with a 65 % increase in CO2/CH4 selectivity, compared to the native Matrimid®. Chapter 6 finally discussed the conclusions and directions for future research based on the findings presented in this thesis.

Hybrid membranes represent a promising alternative to the limitations of organic and inorganic materials for high productivity and selectivity gas separation membranes. In this study, the previously developed concept of emulsion-polymerized mixed matrix (EPMM) membranes was further advanced by investigating the effects of surfactant and compatibilizer on inorganic loading in poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)-based EPMM membranes, in which inorganic part of the membranes originated from tetraethylorthosilicate (TEOS). The polymerization of TEOS, which consists of hydrolysis of TEOS and condensation of the hydrolyzed TEOS, was carried out as (i) one- and (ii) two-step processes. In the one-step process, the hydrolysis and condensation take place in the same environment of a weak acid provided by the aqueous solution of aluminum hydroxonitrate and sodium carbonate. In the two-step process, the hydrolysis takes place in the environment of a strong acid (solution of hydrochloric acid), whereas the condensation takes place in weak base environment obtained by adding excess of the ammonium hydroxide solution to the acidic solution of the hydrolyzed TEOS. For both one- and two-step processes, the emulsion polymerization of TEOS was carried out in two types of emulsions made of (i) pure trichloroethylene (TCE) solvent, and (ii) 10 w/v% solution of PPO in TCE, using different combinations of the compatibilizer (ethanol) and the surfactant (n-octanol). The experiments with pure TCE, which are referred to as a gravimetric powder method (GPM) allowed assessing the effect of different experimental parameters on the conversion of TEOS. The GPM tests also provided a guide for the synthesis of casting emulsions containing PPO, from which the EPMM membranes were prepared using a spin coating technique. The synthesized EPMM membranes were characterized using 29Si nuclear magnetic resonance (29Si NMR), differential scanning calorimetry (DSC), inductively coupled plasma mass spectrometry (ICP-MS), and gas permeation measurements carried out in a constant pressure (CP) system. The 29Si NMR analysis verified polymerization of TEOS in the emulsions made of pure TCE, and the PPO solution in TCE. The conversions of TEOS in the two-step process in the two types of emulsions were very close to each other. In the case of the one-step process, the conversions in the TCE emulsion were significantly greater than those in the emulsion of the PPO solution in TCE. Consequently, the conversions of TEOS in the EPMM membranes made in the two-step process were greater than those in the EPMM membranes made in the one-step process. The latter ranged between 10 - 20%, while the highest conversion in the two-step process was 74% in the presence of pure compatibilizer with no surfactant. Despite greater conversions and hence the greater inorganic loadings, the EPMM membranes prepared in the two-step process had glass transition temperatures (Tg) only slightly greater than the reference PPO membranes. In contrast, despite relatively low inorganic loadings, the EPMM membranes prepared in the one-step process had Tgs markedly greater than PPO, and showed the expected trend of an increase in Tg with the inorganic loading. These results indicate that in the case of the one-step process the polymerized TEOS was well integrated with the PPO chains and the interactions between the two phases lead to high Tgs. On the other hand, this was not the case for the EPMM membranes prepared in the two-step process, suggesting possible phase separation between the polymerized TEOS and the organic phase. The latter was confirmed by detecting no selectivity in the EPMM membranes prepared by the two-step process. In contrast, the EPMM membranes prepared in the one-step process in the presence of the compatibilizer and no surfactant showed 50% greater O2 permeability coefficient and a slightly greater O2/N2 permeability ratio compared to the reference PPO membranes.

In this study, the effect of compatibilizers on the gas separation performance of polycarbonate (PC) membranes was investigated. Membranes were prepared by solvent evaporation method. They were characterized by single gas permeability measurements of O2, N2, H2 and CO2 as well as scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and Fourier transform infrared spectrometry (FTIR). Membranes containing 0.5 to 10 w% p-nitroaniline (pNA) were prepared to study the effect of compatibilizer concentration on the membrane performance. Permeabilities of all gases decreased but selectivities increased with pNA concentration. The membranes with 5 w% pNA showed a selectivity of 114.5 for H2 over N2, 53.9 for CO2 over N2 and 13.4 for O2 over N2 at room temperature, whereas, the H2/N2, CO2/N2 and O2/N2 selectivities for pure PC membranes were 43.5, 20.6 and 5.6, respectively. The N2 permeabilities through pure PC membrane and 5 w% pNA/PC membrane were 0.265 and 0.064 barrer, respectively. The glass transition temperature of the membranes decreased with increasing pNA concentration. FTIR spectra showed that the peaks assigned to nitro and amine groups of pNA shifted and/or broadened. The DSC and FTIR results suggested an interaction between PC and pNA. The effect of type of compatibilizer was also studied. The compatibilizers were 4-amino 3-nitro phenol (ANP), Catechol and 2-hydroxy 5-methyl aniline (HMA). Similar to membranes prepared with pNA, membranes prepared with these compatibilizers had a lower permeability and glass transition temperature but higher selectivity than pure PC membranes. Their FTIR spectra were also indicated a possible interaction between PC and compatibilizer. In conclusion, PC/compatibilizer blend membranes for successful gas separation were prepared. Low molecular weight compounds with multifunctional groups were found to effect membrane properties at low concentration range, 0.5-5 w%.

Metal-organic frameworks (MOFs) are hybrid organic-inorganic micro- or mesoporous materials that exhibit regular crystalline lattices with rigid pore structures. Chemical functionalization of the organic linkers in the structures of MOFs affords facile control over pore size and physical properties, making MOFs attractive materials for application in gas-separating membranes. A wealth of reports exist discussing the synthesis of MOF structures, however relatively few reports exist discussing MOF membranes. This disparity owes to challenges associated with fabricating films of hybrid materials, including poor substrate-film interactions, moisture sensitivity, and thermal instability. Since even nanometer scale cracks and defects can affect the performance of a membrane for gas separation, these challenges are particularly acute for MOF membranes. The focus of this work is the development of novel methods for MOF film and membrane fabrication with a view to overcoming these challenges. The MOF film production methods discussed herein include in situ synthesis using ligand-modified or metal-modified supports and rapid thermal deposition (RTD).

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Koros, William; Committee Member: Beckham, Haskell; Committee Member: Eckert, Charles; Committee Member: Henderson, Cliff; Committee Member: Meredith, Carson. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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