Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 112-114). Also available on the World Wide Web.

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Membrane separation technology has recently emerged as a potential alternative technique for removing higher hydrocarbons (C₃₊) from natural gas. For economic reasons, membranes for this application should be organic vapor selective materials such as poly(dimethylsiloxane) (PDMS) or poly(1-trimethylsilyl-1-propyne) (PTMSP). These polymers, often called solubility selective polymers, sieve penetrant molecules based largely on relative penetrant solubility in the polymer. The sorption and transport properties in such polymers have been reported previously. However, most studies present only pure gas sorption and transport properties. Mixture properties, which are important for estimating membrane separation performance, are less often reported. In addition, mixed gas sorption and diffusion data in such polymers, to the best of our knowledge, have never been investigated before. This research work provides a fundamental database of mixture sorption, diffusion, and permeation data in solubility selective polymers. Two solubility selective polymers were studied: poly(dimethylsiloxane) (PDMS) and poly(1-trimethylsilyl-1-propyne) (PTMSP). The vapor/gas mixture was n-C4H10/CH4. CH4 partial pressures ranged from 1.1 to 16 atm, and [subscript n-]C₄H₁₀ partial pressures ranged from 0.02 to 1.7 atm. Temperatures studied ranged from -20 to 50 oC. The pure and mixed gas [subscript n-]C₄H₁₀ and CH₄ permeability and solubility coefficients in PDMS and PTMSP were determined experimentally using devices constructed specifically for these measurements. The pure and mixed gas diffusion coefficients were calculated from permeability and solubility data. In rubbery PDMS, the presence of [subscript n-]C₄H₁₀ increases CH₄ permeability, solubility, and diffusivity. On the other hand, the presence of CH₄ does not measurably influence [subscript n-]C₄H₁₀ sorption and transport properties. The [subscript n-]C₄H₁₀/CH₄ mixed gas permeability selectivities are lower than those estimated from pure gas measurements. This difference is due to both lower solubility and diffusivity selectivities in mixtures relative to those in pure gas. Plasticization of PDMS by [subscript n-]C₄H₁₀ does little to n-C4H10/CH₄ mixed gas diffusivity selectivity. Increases in mixed gas permeability selectivity with increasing [subscript n-]C₄H₁₀ activity and decreasing temperature were mainly due to increases in solubility selectivity. Unlike PDMS, the presence of [subscript n-]C₄H₁₀ decreases CH₄ permeability, solubility, and diffusivity in PTMSP. The competitive sorption and the blocking effects significantly reduce CH₄ solubility and diffusion coefficients in the polymer, respectively. However, similar to PDMS, the presence of CH₄ has no measurable influence on [subscript n-]C₄H₁₀ sorption and transport properties. [subscript n-]C₄H₁₀ /CH₄ mixed gas permeability selectivities in PTMSP are higher than those determined from the pure gas measurements. This deviation is a result of higher solubility and diffusivity selectivities in mixtures relative to the pure gas values. Mixed gas permeability, solubility, and diffusivity selectivities in PTMSP increased with increasing [subscript n-]C₄H₁₀ activity and decreasing temperature. The partial molar volumes of [subscript n-]C₄H₁₀ and CH₄ in the polymers were determined from sorption and dilation data. The dilation isotherms of PDMS and PTMSP in mixtures agree with estimates based on pure gas sorption and dilation measurements. The partial molar volumes of n-C4H10 and CH4 in PDMS are similar to those in liquids. In contrast, the partial molar volumes of [subscript n-]C₄H₁₀ and CH₄ in glassy PTMSP are substantially lower than those in liquids. Several models were used to fit the experimental data. For instance, the FFV model, the activated diffusion model, and the Maxwell-Stefan model were employed to describe the mixture permeability data in PDMS. Based on the Maxwell-Stefan analysis, the influence of coupling effects on permeation properties in PDMS were negligible. The dual mode sorption and permeation models were used to describe the mixed gas data in PTMSP. The dual mode permeability model must be modified to account for [subscript n-]C₄H₁₀ -induced reductions in CH₄ diffusion coefficients (i.e., the blocking effect). The FFV model provides poor correlations in PTMSP. There seems to be other factors, besides FFV per se, contributing to the temperature and concentration dependence of diffusion coefficients in PTMSP.

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The development of functionalized membranes with tunable pores and catalytic properties provides us an opportunity to manipulate the membrane pore structure, selectivity and reactivity. By introducing the functional groups into membrane pores, dissolved metal ions and reactive particles can be effectively immobilized within the polymer matrix for toxic chloro-organic and heavy metal remediation in water. A polyelectrolyte functionalized membrane platform with tunable pore size and ion exchange capacity has been developed for iron/iron oxide nano-catalyst synthesis and chlorinated organic compound (trichloroethylene, TCE and polychlorinated biphenyls, PCBs) degradation. Highly robust polyvinylidene fluoride (PVDF) microfiltration membranes are used as the support with cross-linked polyacrylic acid (PAA) filled in the pores. By varying the environmental pH, PAA hydrogels have either swelling or collapsing behavior, resulting in different effective membrane pore sizes for different separation purposes. Cation exchange groups (i.e. carboxyl groups) in PAA chains prevent the aggregation and leaching of nanoparticles (NPs) during in-situ synthesis and reaction. Depending on the catalyst loading and residence time, TCE and PCBs can be completely degraded by reduction of zero-valent iron and bimetallic iron/palladium NPs, or iron oxide catalyzed free radical oxidation at near-neutral pH. Biphenyl from PCB dechlorination can be further oxidized by hydroxyl radicals (OH•) generated from hydrogen peroxide (H2O2) decomposition. Hydroxybiphenyls and benzoic acid are identified as oxidation products. Line scan and elemental mapping in transmission electron microscopy (TEM) and X-ray photo electron spectroscopy (XPS) characterizations are conducted to understand the effect of iron surface transformation on NP reactivity, and to optimize the membrane functionalization. The same platform can also be used to remove toxic metal selenium in the scrubber water of coal-fired power plants. By reducing the salt concentration in water or increasing the residence time and temperature, the concentration of selenium oxyanions in functionalized membrane permeate can be reduced to less than 10 µg/L. Selenium is captured in membranes by both iron reduction to metallic selenium and iron oxide adsorption. The full-scale flat sheet functionalized membrane and spiral wound modules have also been developed. Iron NPs with alterable loadings are successfully synthesized inside the membrane module for real water applications.

Despite intrinsically high separation performance, conventional polymeric membranes suffer from CO₂ induced plasticization, which reduces CO₂/CH₄ separation efficiency significantly. Covalent ester-crosslinking can improve the plasticization resistance by controlling the segmental chain mobility in the polymer; however, only relatively thick selective skin layers and lower separation productivity have been reported to date. On the other hand, the high cost of crosslinkable polymers makes the approach challenging, especially for large-scale gas separations which require large membrane areas with high feed pressures. Dual-layer hollow fiber spinning can be used to reduce the cost of membrane production by integrating a low-cost supporting core polymer with the expensive crosslinkable sheath polymer. However, the complexity of interfacial interaction between the sheath/core layers and subsequent crosslinking required can delaminate the sheath/core layers and collapse the core layer polymer. This can reduce mechanical strength and the separation productivity significantly. This work aimed to develop thin-skinned high-performing ester-crosslinked hollow fiber membranes with improved CO₂ plasticization resistance. The skin layer thickness of hollow fibers was first optimized by simultaneous optimization of the polymer dope and spinning process variables. Moreover, this study also addresses the solutions of challenging in transitioning the monolithic hollow fiber to composite hollow fiber format. The ester-crosslinked hollow fibers were subjected to high feed pressures and high-level contaminants to probe their CO₂ plasticization and hydrocarbon antiplasticization resistance, respectively. The resultant ester-crosslinked monolithic hollow fibers show significantly reduced skin layer thickness and improved separation productivity under extremely challenging operation conditions. They also demonstrate strong stability under high feed pressures and reversibility after contaminant exposure. Moreover, this study presents a newly discovered core layer material, Torlon®, which demonstrates excellent compatibility with the crosslinkable polymer and superior thermal stability during crosslinking without sheath/core layer delamination or collapse. The characterization under aggressive feed conditions clearly suggests that ester-crosslinked composite hollow fibers can achieve high separation performance and reduce membrane cost simultaneously. This provides a significant advance in state of the art for natural gas separations under realistic operation environments

Thesis (M. S.)--Chemical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: William J. Koros; Committee Member: Amyn Teja; Committee Member: Carson Meredith; Committee Member: Sankar Nair; Committee Member: Wallace W. Carr.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisors: Keith P. Johnston and William J. Koros. Vita. Includes bibliographical references.

Thesis (Ph.D.)--University of Waikato, 2006. / Includes bibliographical references (leaves [186]-203) Also available via the World Wide Web.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 185-195).