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.

This research aimed to develop the fabrication of mixed matrix membranes (MMMs) utilizing a polymer of intrinsic microporosity (PIM-1) with porous polyimide networks, and to explore their effect on gas transport properties. PIM-1 has been chosen as polymer matrix for its high surface area and high sorption of gases. It is also considered as interesting candidate for membrane gas separation. PIM-1 has been synthesized successfully using high temperature methods (40 min, 160 oC) and low temperature methods (72 h, 65 oC). Porous polyimide networks have been chosen as organic fillers as they have good chemical affinity to polymer matrix and can adhere much better than inorganic fillers. MPN-1 and MPN-2 were synthesized by condensation polymerization of A2 (dianhydride) and B4 (tetraamino). The polymer matrix (PIM-1) and network polyimide fillers were characterized using various characterization techniques, including FTIR, NMR spectroscopy, TGA and N2 sorption analysis. MMMs were fabricated successfully utilizing PIM-1 with 10, 20, and 30wt. % loadings of fillers. The MMMs prepared were homogenous on a macroscale. They characterized using different techniques, such as FTIR spectroscopy, powder x-ray diffraction, and scanning electron microscopy. The gas transport properties of MMMs were obtained using a time lag method. The treatment of MMMs with alcohol showed an increase in the permeability and diffusivity of gases. We aimed in this research to increase solubility of microporous polyimide network (MPN-1) by decreasing the extent of network structure. Different strategies have been utilized. First, using different molar ratios and second, using end-capping modification. The polymers were characterized using various techniques, including FTIR, NMR spectroscopy and TGA. Following this, their CO2 uptake and solubility are also examined.

Whey protein fractionation is an important industrial process that requires effective large-scale processes. Although packed bed chromatography has been used extensively, it suffers from low processing rates due to high back-pressures generated at high flow rates. Batch chromatography has been applied but generally has a low efficiency. More recently, adsorptive membranes have shown great promise for large-scale protein purification, particularly from large-volume dilute feedstocks. A new method for producing versatile adsorptive membranes by combining membrane and chromatographic resin matrices has been developed but not previously applied to whey protein fractionation. In this work, a series of mixed matrix membranes (MMMs) were developed for membrane chromatography using ethylene vinyl alcohol (EVAL) based membranes and various types of adsorbent resin. The feasibility of MMM was tested in bovine whey protein fractionation processes. Flat sheet anion exchange MMMs were cast using EVAL and crushed Lewatit® MP500 (Lanxess, Leverkusen, Germany) anion resin, expected to bind the acidic whey proteins β-lactoglobulin (β-Lac), α-lactalbumin (α-Lac) and bovine serum albumin (BSA). The MMM showed a static binding capacity of 120 mg β-Lac g⁻¹ membrane (36 mg β-Lac mL⁻¹ membrane) and 90 mg α-Lac g⁻¹ membrane (27 mg α-Lac mL⁻¹ membrane). It had a selective binding towards β-Lac in whey with a binding preference order of β-Lac > BSA > α-Lac. In batch whey fractionation, average binding capacities of 75.6 mg β-Lac g⁻¹ membrane, 3.5 mg α-Lac g⁻¹ membrane and 0.5 mg BSA g⁻¹ membrane were achieved with a β-Lac elution recovery of around 80%. Crushed SP Sepharose™ Fast Flow (GE Healthcare Technologies, Uppsala, Sweden) resin was used as an adsorbent particle in preparing cation exchange MMMs for lactoferrin (LF) recovery from whey. The static binding capacity of the cationic MMM was 384 mg LF g⁻¹membrane or 155 mg LF mL⁻¹ membrane, exceeding the capacity of several commercial adsorptive membranes. Adsorption of lysozyme onto the embedded ion exchange resin was visualized by confocal laser scanning microscopy. In LF isolation from whey, cross-flow operation was used to minimize membrane fouling and to enhance the protein binding capacity. LF recovery as high as of 91% with a high purity (as judged by the presence of a single band in gel electrophoresis) was achieved from 150 mL feed whey. The MMM preparation concept was extended, for the first time, to produce a hydrophobic interaction membrane using crushed Phenyl Sepharose™ (GE Healthcare Technologies, Uppsala, Sweden) resin and tested for the feasibility in whey protein fractionation. Phenyl Sepharose MMM showed binding capacities of 20.54 mg mL⁻¹ of β-Lac, 45.58 mg mL⁻¹ of α-Lac, 38.65 mg mL⁻¹ of BSA and 42.05 mg mL⁻¹ of LF for a pure protein solution (binding capacity values given on a membrane volume basis). In flow through whey fractionation, the adsorption performance of the Phenyl Sepharose MMM was similar to the HiTrap™ Phenyl hydrophobic interaction chromatography column. However, in terms of processing speed and low pressure drop across the column, the benefits of using MMM over a packed bed column were clear. A novel mixed mode interaction membrane was synthesized in a single membrane by incorporating a certain ratio of SP Sepharose cation resin and Lewatit MP500 anion resin into an EVAL base polymer solution. The mixed mode cation and anion membrane chromatography developed was able to bind basic and acidic proteins simultaneously from a solution. Furthermore, the ratio of the different types of adsorptive resin incorporated into the membrane matrix could be customised for protein recovery from a specific feedstream. The customized mixed mode MMM consisting of 42.5 wt% of MP500 anionic resin and 7.5 wt% SP Sepharose cationic resin showed a binding capacity of 7.16 mg α-Lac g⁻¹ membrane, 11.40 mg LF g⁻¹ membrane, 59.21 mg β-Lac g⁻¹ membrane and 6.79 mg IgG g⁻¹ membrane from batch fractionation of 1 mL LF-spiked whey. A tangential flow process using this membrane was predicted to be able to produce 125 g total whey protein per L membrane per h.

Removal of water vapor from humid streams is an energy-intensive process used widely in industry. Effective dehumidification has the potential to significantly reduce energy consumption and the overall cost of a process stream. Membrane-based separations, particularly dehumidification, are an emerging technology that can change the landscape of global energy usage because they have a small footprint, they are easy to scale up, to implement and to operate. The focus of this thesis is to evaluate new directions for the development and use of materials for membrane-based dehumidification processes. It will show advances in the synthesis of new copolymers, a surprising boost in performance with the addition of 2-D materials, propose the use of polybenzimidazole for challenging dehumidification applications, and show how by tuning the nanostructure of a commercially available block copolymer (BCP) it is possible to increase the performance. The design of novel amphiphilic ternary copolymers comprising P(AN-r-PEGMA-r-DMAEMA) allowed selective removal of water vapors from gaseous streams; the effect of varying PEGMA chain length on membrane performance was studied. The membranes showed an excellent performance when the content of the PEGMA segment was 2.9 mol% with a chain length of 950Da. In the mixed-matrix approach, the inclusion of graphene oxide (GO) nanosheets in a different copolymer enhanced the membrane performance by creating selective tortuous pathways for inert gases. The well-distributed GO nanosheets in the defect-free composite membranes resulted in an 8 fold increase in water vapor/N2 selectivity compared to neat membranes. Thirdly, dense polybenzimidazole membranes showed good water vapor permeability, and the addition of TiO2-based fillers with varying chemistry and geometry enhanced the performance of PBI membranes. Lastly, the effect of tuning the morphology of commercially available BCP on dehumidification was demonstrated successfully. The self-assembled morphology formed with cylindrical hydrophobic cores, and the hydrophilic coronas, formed ion-rich highways for fast water vapor transport. Water vapor permeability improved up to 6-fold with the nanostructure modulation more than any membrane reported in the literature. In summary, the work reported in this dissertation has the potential to lay a framework towards tailor-made next-generation membranes aimed for water vapor removal in various dehumidification applications.

Membrane-based gas separation processes are an area of interest owing to their high industrial demand for a wide range of applications, such as natural gas purification from CO2 or H2, and N2 or O2 separation from air. This thesis is focused on developing and investigating polymeric-based membranes. Firstly, novel mixed matrix membranes (MMMs) were prepared, incorporating few-layer graphene in the polymer of intrinsic microporosity PIM-1. Secondly, novel polyphenylene-based polymers of intrinsic microporosity (PP-PIMs) were synthesised. An optimum preparation method of graphene/PIM-1 MMMs (GPMMMs) was established from numbers of experiments. In this study, graphene exfoliation was a step towards GPMMM preparation. Starting from graphene exfoliation in chloroform, as a good solvent for PIM-1, enhancement in graphene dispersibility was obtained with addition of PIM-1. This result helped in GPMMM preparation with high graphene content (up to 4 wt.%). Characterizations techniques such as Raman spectroscopy and scanning electron microscopy (SEM) of GPMMMs, confirmed the few layer graphene content, with morphology changes in the polymeric matrix compared to pure PIM-1.Gas permeability results of GPMMMs showed an enhancement in permeability with low loading graphene (0.1 wt.%) using a relatively low permeability PIM-1 batch, due to high water content. However, less influence of graphene incorporation on permeability was observed with a highly permeable PIM-1 batch. Reduction in permeability over time, termed an ageing effect, is known for a polymer of high-free volume like PIM-1. However, the enhancement of GPMMMs permeability after eight months storage was shown to be retained. Novel PP-PIMs were prepared from novel precursors using a series known organic reactions. PP-PIMs were divided into two groups of polymers based on their polymerization reactions. A group of polymers were prepared from condensation polymerization between bis-catecol monomers and tetrafluoroterephthalonitrile (TFTPN). Another group of polymers were prepared from Diels Alder polymerization between monomers of terminal bisphenylacetylene groups and bis tetraphenylcyclopentadienones (TPCPDs). All of which yielded polymers with apparent BET surface area in the range 290-443 m2 g-1.

In this thesis, a theoretical description of mass transport through membranes used in pervaporation separation processes has been investigated for both dense polymeric membranes and mixed matrix membranes (MMMs). Regarding the dense polymeric membranes, the Maxwell-Stefan model was extended to consider the effect of the operating temperature and membrane swelling on the mass transport of species within the membrane. The model was applied semi-empirically to predict the membrane properties and separation performance of a commercial Polydimethylsiloxane (PDMS) membrane used in the pervaporation separation of butanol from binary aqueous solutions. It was observed that the extended Maxwell-Stefan model has an average error of 10.5 % for the prediction of partial permeate fluxes of species compared to roughly 22% for the average prediction error of the Maxwell-Stefan model. Moreover, the parameters of the model were used to estimate the sorption properties and diffusion coefficients of components through the PDMS membrane at different butanol feed concentrations and operating temperatures. The estimated values of the sorption properties were observed to be in agreement with the literature experimental data for transport properties of butanol and water in silicone membranes while an exact comparison for the diffusion coefficient was not possible due to large fluctuations in literature values. With respect to the MMMs, a new model was developed by combining a one-directional transport Resistance-Based (RB) model with the Finite Difference (FD) method to derive an analytical model for the prediction of three-directional (3D) effective permeability of species within ideal mixed matrix membranes. The main novelty of the proposed model is to avoid the long convergence time of the FD method while the three-directional (3D) mass transport is still considered for the simulation. The model was validated using experimental pervaporation data for the separation of butanol from aqueous solutions using Polydimethylsiloxane (PDMS)/activated carbon nanoparticles membranes and using data from the literature for gas separation application with MMMs. Accurate predictions were obtained with high coefficient of regression (R2) between the calculated and experimental values for both applications.

Separation of CO2, the main global warming causing greenhouse gas, from other flue gases and from biogas has become of great interest due to the predicted effects of global warming that the world is already starting to experience. This research focuses on the separation of CO2 from CH4 and N2 gases using polymeric and mixed matrix membranes. Amine-based poly vinyl alcohol (PVA) polymeric membranes that had previously shown good gas separation results were adapted for use in this research. The physical aging of the adapted membrane was initially analyzed for 37 days and it was observed that the membrane stabilized after 21 days. The adapted membrane was then optimized using a 26 factorial design to improve the membranes’ performance with respect to CO2/N2 and CO2/CH4 selectivity when tested using single gas permeation experiments at near atmospheric conditions. This was done with the membrane components: PVA, formaldehyde, poly (allylamine hydroxide), potassium hydroxide, water and 2-aminoisobutyric acid. Zeolite 13X and ZIF-8 powdered adsorbents were incorporated in the optimized membranes to prepare mixed-matrix membranes with the goal of bettering the separation performance of the membranes. Membrane characterization was done on the best performing membranes through spectroscopy, microscopy, and contact angle measurements. This study concluded with feed pressure tests on the overall best performing membranes. The performance of the fabricated membranes was compared to other polymeric and mixed-matrix membranes and Robeson’s upper bound line. Overall, the polymeric optimized membranes seemed to perform better than the filled mixed matrix membranes due to the introduction of agglomerations and cracks with both the filler materials. Also, the separation performance of the membrane improved with a decrease in pressure. At 1.5 absolute pressure, the optimized membrane was able to achieve a CO2/N2 and CO2/CH4 selectivity of 5.94 and 2.13 respectively with a CO2 permeability of 15,813 Barrer.

A series of mixed matrix membranes based on zeolites incorporated into fluorinated polyimides were fabricated and characterized in this study. The first system consisted of a polyimide (6FDA-6FpDA-DABA) with carboxylic acid groups incorporated into its backbone and amine-functionalized zeolite particles (ZSM-2). FTIR indicated that these functional groups interacted with each other through hydrogen bonding. Both SEM and TEM images revealed good contact between the polyimide and the zeolite. Permeability studies showed a drop in He permeability suggesting there were no voids between the two components. While simple gases such as O2 and N2 followed effective permeabilities predicted by mixing theories, polar gases such as CO₂ did not. The second system fabricated used the same polyimide with amine-functionalized zeolite L. This zeolite differs from ZSM-2 in that zeolite L's pores are not clogged with an organic template, and it possesses 1-D pores as opposed to ZSM-2's 3-D pore structure. XPS and zeta potential experiments were performed to verify the presence of amine groups on the zeolite surfaces. FTIR data showed that after a heat treatment, amide linkages were created between the amine group on the zeolite and the carboxylic acid group of the polyimide. SEM images showed a good distribution of zeolite L throughout the polymer matrix, and no indication of voids between the two components. Permeability experiments were performed to determine if the addition of zeolite L to the polyimide improved its separation performance. The permeability was unchanged between the pure polyimide membrane and the mixed matrix membrane, suggesting there were no voids present within the matrix. Permeability results of larger gases followed a Maxwell Model. A third system was prepared using a poly(imide siloxane) (6FDA-6FpDA-PDMS) and untreated zeolite L. The primary focus of this investigation was to determine if the addition of the flexible segment would promote direct contact with the zeolite surface and remove the need to amine-functionalize the zeolite. Poly(imide siloxane)s were synthesized at 0, 22, and 41 wt % PDMS as verified using 1H-NMR. FTIR was employed to qualitatively verify the successful imidization of the polymers. SAXS patterns and TEM images did not reveal distinct phases indicative of phase separation, however, AFM images did show the presence of phase separation of the surfaces of the poly(imide siloxane)s. Permeability results showed a decrease in selectivity and an increase in permeability as the wt % of PDMS was increased. Permeabilities and selectivities dropped as the zeolite loading was increased from 0 to 20 wt %. Upon increasing the zeolite loading from 20 to 30 wt %, increases in permeability were observed, but both the permeability and selectivity were still below that of the pure polymer. The final system studied employed the 41 wt % PDMS poly(imide siloxane) as the polymer matrix and either closed-ended or open-ended carbon nanotubes as the filler. SEM images showed regions of agglomeration for both types of nanotubes. Helium permeability dropped in both types MMMs, but more so in closed-ended carbon nanotubes MMM. Nitrogen permeability was unchanged for the closed-ended carbon nanotubes MMM, and dropped slightly in the open-ended carbon-nanotube MMM. / Ph. D.

Functionalized silica materials are synthesized for various environmental applications. The overall objective is functionalization with sulfur-containing moieties for mercury sorption and as a platform for nanoparticle synthesis. The first objective is quantifying this functionalization for various silica platforms. The second objective is development of effective mercury sorbents, for both aqueous mercury and elemental mercury vapor. Third, those sorbents are incorporated into mixed matrix membranes (MMM) for aqueous mercury sorption. Fourth, functionalized silica materials are developed as platforms for the synthesis of reactive metal nanoparticles (NP) for the degradation of trichloroethylene. Thiol-functionalized silica is used as a sorbent for aqueous mercury, and a novel functionalized material (thiol-functionalized silica shell surrounding a carbon core) has been developed for this application. Total capacity and kinetics of aqueous mercury sorption were determined. The silica-coated carbon was functionalized with thiol and sulfonate moieties for regeneration under mild conditions. Finally, the sorbent particles were incorporated into polysulfone to form a mixed matrix membrane (MMM) for toxic metal capture under convective-flow conditions. High loadings (up to 50% particles, base particles of ~80 nm) were achieved in the MMM. The particles are well-dispersed which can lower mass transfer resistance to the sorption sites. The MMM also imparts several practical advantages such as ease of sorbent handling. Silica functionalized with tetrasulfide silane is used for mercury vapor sorption. Sorption kinetics and dynamic capacity depend upon pore structures of the functionalized material. The particles are thermally stable and exhibit a glass transition in the tetrasulfide silane coating, with high total sorption capacity achieved by addition of copper sulfate. Temperature effects on mercury sorption indicate a chemisorptive mechanism. Silica particles functionalized with sulfonate moieties were used as a platform for the synthesis of dispersed iron nanoparticles. These NP are applied for degradation of trichloroethylene (TCE), a persistent, toxic, and widespread pollutant. The particles were stabilized against agglomeration. Natural product reducing agents, such as ascorbic acid, adsorb to the particle surface and can protect against oxidation. These particles were demonstrated for the reductive as well as oxidative degradation of TCE.

Mixed matrix membranes (MMM) offer one potential path toward exceeding the Robeson upper bound of selectivity versus permeability for gas separation performance while maintaining the benefits of solution processing. Many inorganic materials, such as zeolites, metal-organic frameworks, or carbon nanotubes, can function as molecular sieves, but as stand-alone membranes are brittle and difficult to manufacture. Incorporating them into a more robust polymeric membrane matrix has the potential to mitigate this issue. In this work, phase inversion polymer solution processing for the fabrication and testing of asymmetric flat sheet mixed matrix membranes was employed with CVD-derived multiwall carbon nanotubes (MWCNTs) dispersed in a polyethersulfone (PES) matrix. The effect of MWCNT loading on membrane separation performance was examined. Notably, a distinct enhancement in selectivity was measured for several gas pairs (including O2/N2) at relatively low MWCNT loading, with a peak in selectivity observed at 0.1 wt% loading relative to PES. In addition, no post-treatment (e.g. PDMS caulking) was required to achieve selectivity in these membranes. In contrast, neat PES membranes and those containing greater than 0.5 wt.% MWCNT showed gas selectivity characteristic of Knudsen diffusion through pinhole defects. These results suggested that at low loading, the presence of MWCNTs suppressed the formation of surface defects in the selective layer in flat sheet mixed matrix membranes. Additionally, a bench-scale, single-filament hollow fiber membrane spinning line was designed and purpose-built at the University of Kentucky Center for Applied Energy Research (CAER). Hollow fiber membrane spinning capability was developed using polyethersulfone (PES) solution dopes, and the process was expanded to include polysulfone (PSf) as well as mixed matrix membranes. The effects of key processing parameters, including the ratio of bore to dope velocities, the spinning air gap length, and the draw-down ratio, were systematically investigated. Finally, direct hollow fiber analogues to flat sheet mixed matrix membranes were characterized. Consistent with the flat sheet experiments, the mixed matrix hollow fiber membranes showed a local maximum in selectivity at a nominal loading of 0.1 wt.% MWCNT relative to the polymer, suggesting that the pinhole suppression effect introduced by MWCNTs was not limited to flat sheet membrane casting. The development of asymmetric hollow fiber mixed matrix membrane processing and testing capability at the UK Center for Applied Energy Research provides a platform for the further development of gas separation membranes. Using the tools developed through this work, it is possible to further push the frontiers of mixed matrix gas separation by expanding the capability to include more polymers, inorganic fillers, and post treatment processes which previously have been focused primarily on the flat sheet membrane geometry.