Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: William J. Koros. Vita. Includes bibliographical references.

Thesis (Ph. D.)--Lehigh University, 2004. / Includes bibliographical references and vita.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (Ph. D.)--Lehigh University, 2002. / Includes bibliographical references and vita.

Gas absorption in hollow fibre contactors is being increasingly used due to their enormous surface area/volume ratio. The capability of the hollow fibre membrane modules for the removal of CO 2 and SO2 from a binary gas mixture has been investigated experimentally. Four different modules were used in this study. The membranes in modules one and two were made of microporous polypropylene. The third module was made of non-porous silicone rubber (polydimethylsiloxane) while the latter one was a polyvinylidenefluoride (PVDF) asymmetric hollow fibre membrane. The gas mixtures used in the experiments were composed of 9.5% CO2 and 1% SO2 in N 2 , which was introduced into the hollow fibre lumen, while the absorbent liquid was fed into the shell side of module. The absorbent liquids used were water, aqueous solutions of diethanolamine (DBA) and ammonia at different concentrations (5, 10 and 20 wt%). The effects of different operating conditions on the permeation process have been investigated for co-current and counter-current flow patterns. In addition, to improve the silicone rubber hollow fibre membrane performance, baffles were installed within the shell of the permeator to increase liquid fibre contact. The results obtained showed that the use of baffles within the shell of the permeator improved the separation performance of the non-porous membrane module without any substantial increase in the physical size of the contacting device. Studies also showed that improved performance was observed when the system was operated under a counter-current flow pattern. The results showed that the use of an absorbent liquid in the permeate side of the fibres increased the selectivity of the membranes used, and reduced the need to maintain a high pressure ratio across the membrane. A decrease in the feed gas flow rate or increase in liquid flow rate generally improved the removal of gases. The results showed that the use of aqueous reactive solutions as an absorbing medium in the permeate side of the hollow fibre permeator can significantly improve CO2 removal from the gas mixture. However, the main problem when using a microporous membrane coupled with aqueous solutions of diethanolamine as absorbent was wetting of the microporous membrane by amine solutions. For 862 separation, the highest removal was attained using the microporous membrane coupled with water as absorbent liquid. This demonstrates that a hollow fibre based device can be a very efficient gas liquid contactor. The separation process was simulated with a numerical model based on the effective permeabilities of gases and compared with the experimental results. The model simulations showed good agreement with the experimental observations.

Polybenzimidazoles, a class of aromatic heterocyclic polymers, are well known due to their remarkable thermal stability, mechanical properties and chemical resistance which are often required in extreme operation conditions. Because of these properties, polybenzimidazoles are excellent candidates in various application areas including proton exchange membrane fuel cells, gas separation membranes, reverse osmosis and nanofiltration, and high performance coatings. The following studies are focused on the synthesis, characterization and related properties of polybenzimidazoles and polybenzimidazole based materials. A novel sulfonyl-containing tetraamino-substituted monomer (3,3',4,4'-tetraaminodiphenylsulfone) was synthesized and polymerized with three different diacid monomers to make polybenzimidazoles. The new monomer synthesis route with reduced steps relative to the existing literature method increased the overall yield by a factor of three. The sulfonyl-containing polybenzimidazoles have enhanced solubilities in common organic solvents including dimthylsulfoxide, dimethylacetamide and N-methyl-2-pyrrolidone in comparison with the commercial polybenzimidazole, Celazole®, poly(2,2'-(m-phenylene)-5,5'-bibenzimidazole). The improvements in solubility are attributed to the introduction of polar sulfonyl linking moiety in the monomer. Remarkable thermal stabilities (high T_g, > 428 °C) were demonstrated through Dynamic Mechanical Analysis (DMA) and Thermogravimetric Analysis (TGA). A well designed film casting process was investigated and established. Polybenzimidazoles were fabricated into transparent thin films (20-30 μm thick) for gas transport measurements. These novel polybenzimidazole films exhibited extraordinary gas separation properties, especially for H₂/CO₂ separation. There is a trade-off relationship between gas permeability and selectivity through dense, non-porous polymer membranes that was discovered by Robeson in 1991. The ultimate goal for developing gas separation membranes is to improve both permeability and selectivity simultaneously. Gas permeability is related to the free volume between polymer chains. In order to improve gas permeability, we hypothesized a concept that increasing free volume could be achieved by thermally degrading sacrificial components and volatilizing their byproducts from a glassy matrix. Volatile components were introduced into the films to preoccupy the spaces between polymer chains. Once they were degraded and removed through the thermal treatment, it was hypothesized that the preoccupied spaces would remain empty due to the glassy nature of the matrix at the heat treatment temperature, thus resulting in more free volume. Two post- modification strategies including grafting and blending were utilized to incorporate the volatile components, poly(propylene oxide) and poly(ethylene oxide). Post-modified polybenzimidazole films impressively showed significant enhancements in both gas permeability and selectivity for H₂/CO₂ separation. The H₂ permeability of the post-modified TADPS-OBA polybenzimidazole increased from 3.1-6.2 Barrers to 5.2-7.5 Barrers (up to 66% increase). The selectivity for H₂/CO₂ increased from 7.5-10.5 to 10.1-13.0 (up to 33% increase). The study on the potential effects of water vapor on the separation performance of PBI membranes was discussed in the appendix. / Ph. D.

No description available.

Polymers of Intrinsic Microporosity (PIMs) combine the desirable processability of polymers with a significant degree of microporosity generated from the inefficient packing of their rigid and contorted structures. They are attracting attention for a variety of applications including as membrane materials for gas separations. Over the last 30 years, membranes have become an established technology for separating gases and are likely to play key role in reducing the environmental impact and costs of many industrial processes such as O2 or N2 enrichment from air, natural gas upgrading and hydrogen recovery from ammonia production. This thesis describes the synthesis of a series of novel PIMs, primarily PIM-polyimide structures (PIM-PI) and investigates their potential in such applications. In particular, it focuses on the design and synthesis of solution processable PIMs in order to study how structural differences affect the gas permeability. The first section describes the synthesis of a variety of PIM-PIs using large bulky diamines derived from spirobisindane (SBI) and biphenylfluorene (BPF) structures which are useful monomers for achieving high BET (Brunauer-Emmett- Teller) surface areas (> 650 m2 g-1). The second section describes a whole series PIs based on novel and literature based Tröger’s base (TB) diamine monomers. Most of these exhibited good solubility, excellent thermal stability and intrinsic microporosity, with apparent BET surface areas in the range 450-739 m2 g-1. Notably, a polyimide derived from Me2TB and pyromellitic anhydride demonstrates gas permeability data above the 2008 upper bounds for important gas pairs such as O2/N2, H2/N2 and H2/CH4. The third section aims to enforce rigidity within the polymers further by incorporating differently substituted monomers based on rigid ethanoanthracene (EA) units. This includes the formation of a novel EA-EA based PI with an exceptionally rigid polymeric structure, possessing a BET surface area of 694 m2 g-1. In addition to very high permeability, this polymer demonstrates improved gas selectivity due to its enhanced performance as a molecular sieve, placing it amongst some of the highest performing polymers to date. The final section looks at other ways in which rigidity can be enforced including the formation of TB-polymers and thermally rearranged (TR) polymers and assesses their potential for future investigations.

Nanoporous metal-organic frameworks (MOFs) have attracted tremendous interest due to their potential applications in gas-storage, gas separation, gas sensing, and catalysis. MOFs consist of metal-oxygen polyhedera interconnected with a variety of organic linker molecules, resulting in tailored nanoporous materials. With a judicious choice of organic linker groups, it is possible to fine-tune size, shape, and chemical functionality of the cavities and the internal surfaces. This unique structural feature offers unprecedented opportunities in small-molecule separations as well as chiral separations and catalysis. Prototypical iso-reticular metal-organic frameworks (IRMOFs) have been extensively studied among MOFs due to the simplicity of their synthesis and the variety of their potential applications. IRMOFs are a specific series of metal-organic frameworks developed by Yaghi and his coworkers. All IRMOFs are composed of oxygen-centered Zn4O tetrahedra interconnected with dicarboxylate linkers, forming a cubic type three dimensional (3D) porous network with high surface area. Despite a great deal of research in the synthesis and characterization of MOFs, there have been relatively few reports on the development of their applications, such as the fabrication of MOF thin films and membranes for gas separations. This is mainly due to the challenges associated with relatively difficult heterogeneous nucleation (seeding) and growth of MOFs on supports, and crack formation compared to their counterparts. Thin films and membranes of MOFs have great potentials for applications in membranebased gas separations, reactors, chemical sensors, and nonlinear optical devices. In this dissertation, the fabrication of IRMOF-1 membrane using a novel seeding method and its gas diffusion properties has been demonstrated. Introduction of the new seeding method for MOFs using microwaves resulted in well inter-grown IRMOF membranes showing Knudsen type transport of small gases through its pore. The heteroepitaxial growth of one IRMOF on another produced multi-layered IRMOF membranes. In addition, postsynthetic modification (PSM) of IRMOFs created functionalized membranes with enhanced stability against water as well as reduced crack formation during membrane fabrication. Lastly, hierarchical IRMOFs with improved CO2 adsorption properties were synthesized via PSM with cyanuric chloride.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 176-179). Available also in a digital version from Dissertation Abstracts.