abstract: Reverse osmosis (RO) membranes are considered the most effective treatment to remove salt from water. Specifically, thin film composite (TFC) membranes are considered the gold standard for RO. Despite TFC membranes good performance, there are drawbacks to consider including: permeability-selectivity tradeoff, chlorine damage, and biofouling potential. In order to counter these drawbacks, polyamide matrixes were embedded with various nanomaterials called mixed matrix membranes (MMMs) or thin film nanocomposites (TFNs). This research investigates the use of graphene oxide (GO) and reduced graphene oxide (RGO) into the polyamide matrix of a TFC membrane. GO and RGO have the potential to alter the permeability-selectivity trade off by offering nanochannels for water molecules to sieve through, protect polyamide from trace amounts of chlorine, as well as increase the hydrophilicity of the membrane thereby reducing biofouling potential. This project focuses on the impacts of GO on the permeability selectivity tradeoff. The hypothesis of this work is that the permeability and selectivity of GO can be tuned by controlling the oxidation level of the material. To test this hypothesis, a range of GO materials were produced in the lab using different graphite oxidation methods. The synthesized GOs were characterized by X-ray diffraction and X-ray photoelectron microscopy to show that the spacing is a function of the GO oxygen content. From these materials, two were selected due to their optimal sheet spacing between 3.4 and 7 angstroms and embedded into desalination MMM. This work reveals that the water permeability coefficient of MMM embedded with GO and RGO increased significantly; however, that the salt permeability coefficient of the membrane also increased. Future research directions are proposed to overcome this limitation. / Dissertation/Thesis / Masters Thesis Civil and Environmental Engineering 2017

The increased demand of fossil fuel along with the depletion of economical crude oil resources, environmental challenges such as the accumulation of CO2 and other greenhouse gases in the atmosphere and the reduction of the dependence on imported oil are some of the motivations for the huge interest in biofuels. Biobutanol produced from ABE fermentation has been considered to be a good partial replacement for fossil fuels. However, challenges such as the need for inexpensive feed-stocks, improved fermentation performance to achieve higher final butanol concentration and higher yield, an efficient method for solvent recovery, and water recycle are the main obstacles to make the production of this alcohol economically viable. Pervaporation, a membrane-based process, is considered to be an attractive separation method to remove butanol from ABE fermentation broth. Among the membranes used for butanol separation, PDMS membranes showed reasonable performance such as good permeability, and appropriate selectivity for butanol separation by pervaporation. However, PDMS membranes need to be improved in terms of performance to be applicable in large scale butanol production plants. In this study, activated carbon nanoparticles have been embedded into the matrix of the PDMS membrane to improve its separation performance and, in particular, the permeation flux and butanol selectivity. Result showed that the presence of nanoparticles improves the PDMS membrane performance up to a certain particle loading. Moreover, it was shown that the operating conditions have a major impact on the pervaporation membrane separation process. The best membrane for pervaporation separation of butanol from binary aqueous solutions was obtained for a 6 wt% particle concentration where the total permeation flux and butanol selectivity increased by 42.6% and 51.9%, respectively, compared to neat PDMS membranes. Moreover, the best performance for the separation of butanol from ABE model solutions was achieved for an 8 wt% nanoparticle loading. Both the selectivity for butanol and the total permeation flux more than doubled in comparison to neat PDMS membranes prepared in this study. Moreover, in order to compare the PDMS/AC mixed matrix membrane performance for pervaporation separation of butanol from binary and ABE model solutions with PDMS membranes available on the market, experiments were also performed with a commercial PDMS membrane. Result of butanol separation from ABE model solutions showed that mixed matrix membranes with 8 wt% nanoparticles loading had a higher permeation flux than that of the commercial membranes. It was clearly shown that the presence of activated carbon nanoparticles in the matrix of the PDMS would be beneficial for the pervaporation separation of butanol from ABE fermentation broths. To better comprehend how the presence of activated carbon nanoparticles in the polymeric membranes enhance the performance of the membranes, a series of numerical simulations were performed. A finite difference model was developed to simulate the mass transfer of permeating components through mixed matrix membranes by pervaporation for a wide range of relative permeability, nanoparticle loading, particle shape, particle size and different filler adsorption isotherms. Finally, an investigation has been performed to optimize the butanol pervaporation separation process from ABE fermentation broth at an industrial scale.

This work explores the fabrication and permeability testing of mixed matrix membranes (MMM) utilising a polymer of intrinsic microporosity (PIM-1) and various fillers. PIM-1 has been chosen for this work due to its high apparent surface area and high sorption of gases. PIM-1 also is a good candidate for gas sorption applications due to the film forming properties of the polymer. The fillers utilised in this work are Metal Organic Frameworks (MOFs) and organic cages, which have been chosen due to the gas sorption properties they exhibit. The MOFs used are micro and nanoparticles of Zeolitic Imidazole Framework-8 (ZIF-8), copper based MOF HKUST-1 and chromium based MOF MIL-101. Micro particles of magnesium based MOF Mg-MOF-74 were also looked at as well as cage 3, nano cage 3 and reduced cage 3. Comparable surface areas of the MOFs compared to those quoted in the literature have been obtained. Successful PIM-1/Filler MMMs were synthesised utilising PIM-1 and the fillers outlined above with various loadings of filler. The highest loading achieved was with a 10:6.4 PIM-1/nanoZIF-8 ratio. All MMMs apart from PIM-1/Mg-MOF-74 MMM were homogenous on a macroscale with scanning electron microscopy proving the dispersion of fillers. Gas transport properties of the MMMs were determined using predominantly a time lag method. PIM-1/ZIF-8 MMMs were also tested using a chromatographic method and using a gas sorption experiment. A range of gases were tested including CO2, N2, CH4, O2, He and H2. Ideal selectivities were also calculated with focus on the gas pairs O2/N2, CO2/CH4 and CO2/N2.When comparing the two permeability methods using the PIM-1/nanoZIF-8 MMM, lower permeability results were found from the time lag method. This was concluded to be due to the aging effect brought about by the vacuum used in the time lag method. The chromatographic method produced positive results with high selectivities, breaking Robeson’s upper bound, for the gas pair O2/N2. All other fillers tested showed an increase in permeability and stable selectivity with an increase in the amount of filler. MIL-101 and Cage 3 were the most successful fillers with high permeabilities of 35600 and 37400 Barrer respectively, encroaching on that of PTMSP. Mg-MOF-74 and reduced cage 3 MMM however, had a detrimental effect on the permeability. Aging data was also investigated which showed that for the majority of MMM the permeability followed the trend of PIM-1. microHKUST-1 and cage 3 of 10:3 loading were shown to give promising results with 10000 and 14300 Barrer respectively compared to 7200 Barrer for PIM-1. Although a loss in permeability is seen, it is still above that of PIM-1 at the same point of aging. These results give a positive indication that MMMs have the potential to provide resistance against aging, a major problem in using high free volume polymers in industrial applications.

Mixed Matrix Membranes (MMMs) have received worldwide attention during the last decades. This is due to the fact that the resulting materials can combine the good processability and low cost of polymer membranes with the diverse functionality, high performance and thermal properties of the fillers. This work explores the fabrication and application of MMMs. We focused on the design and fabrication of nanofillers to impart target functionality to the membrane for water treatment, protective coating and gas separation. This thesis is divided into three sections according to the application including: I- Water Treatment: This part is divided into three chapters, two related to the membrane distillation (MD) and one related to the oil spill. Three different nanofillers have been used: Periodic mesoporous organosilica (PMO), graphene and carbon nanotube (CNT). Those nanofillers were homogeneously incorporated into polyetherimide (PEI) electrospun nanofiber membranes. The doped nanoparticle not only improved the mechanical properties and thermal stability of the pristine fiber but also enhanced the MD and oil spill performance due to the functionality of those nanofillers. II- Protective coating: This part includes two chapters describing the design and the fabrication of a smart antibacterial and anti-corrosion coating. In the first project, we fabricated colloidal lysozyme-templated gold nanoclusters gating antimicrobial-loaded silica nanoparticles (MSN-AuNCs@lys) as nano-fillers in poly(ethylene oxide)/poly(butylene terephthalate) polymer matrix. MSN-AuNCs@lys dispersed homogeneously within the polymer matrix with zero NPs leaching. The system was coated on a common radiographic dental imaging device that is prone to oral bacteria contamination. This coating can successfully sense and inhibit bacterial contamination via a controlled release mechanism that is only triggered by bacteria. In the second project, the coaxial electrospinning approach has been applied to fabricate smart core-shell nanofiber for controlled release of anti-corrosion material. Acetal-dextran was used as a pH controlled shell of the fibers and polyvinyl alcohol (PVA) as a hydrophilic core. Caffeine, as an anti-corrosion inhibitor was encapsulated in the fiber core to test its potential application as an anticorrosion coating. The almost negligible release was noticed at neutral pH. In acidic pH due to corrosion, the fibers quickly respond by releasing caffeine cargo. III- Gas separation: We describe the synthesis and application of novel ethylene-diamine-based PMO. The novel nanoparticles were homogeneously incorporated into polydimethylsiloxane to fabricate a MMMs thin layer on a porous polyacrylonitrile support. Our results prove that our PMOs can be used as nanofillers to enhance the CO2 selectivity of the PDMS polymer.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22895号 / 工博第4792号 / 新制||工||1749(附属図書館) / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 SIVANIAH Easan, 教授 田中 庸裕, 教授 今堀 博 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

In this study, pervaporation, a membrane-based process was studied for in-situ separation of butanol. This technique has a great potential due to its high selectivity, low energy requirement and high efficiency. The primary objective was to improve the performance of the Polydimethylsiloxane (PDMS) membrane for the pervaporation separation and the recovery of butanol by adding nanoparticles into its matrix to make mixed matrix membrane (MMM). These nanoparticles included zinc-based Metal Organic Frameworks (MOFs) and zinc oxide. Different particle sizes of zeolitic imidazolate framework (ZIF-8) were synthesized. The separation performance of MMMs incorporating different sizes of ZIF-8 nanoparticles was compared to the performance of mixed matrix membranes incorporating zinc oxide as well as pure PDMS membrane. Different characteristics of ZIF-8 and their impact on the performance of the host membrane were discussed. Result showed that the presence of nanoparticles improves the PDMS membrane performance up to a certain particle loading. Moreover, it was shown that the particle size and interfacial bond between polymer and particles have a major impact on the pervaporation membrane separation process. The best membrane for pervaporation separation of butanol from binary aqueous solutions was obtained for the 8 wt% small-size ZIF-8/PDMS MMM where the total permeation flux and butanol selectivity were increased by 350% and 6%, respectively, compared to neat PDMS membranes. In addition to the MOFs, nanotubes are considered emerging nanostructured materials for use in membrane separation applications due to their high molecular diffusivity and unique geometry. Recent progress has also been made on the modification of nanotube surface functionality, and the fabrication of nanotube mixed matrix membranes as well as the ability to align them in MMMs. Since numerous types of nanotubes are available and the process of producing well-aligned nanotube MMMs is very challenging, a theoretical model using finite difference method (FD) was used to gain a deeper understanding on the effect of nanotubes on the separation performance of mixed matrix membranes. A series of numerical simulations were performed and the effects of various structural parameters, including the tubular filler volume fraction, orientation, length-to-diameter aspect ratio, and permeability ratio, were assessed. The results showed that the relative permeability is enhanced by vertically-aligned nanotubes and further increased with an increase of the permeability ratio, filler volume fraction and the length-to-diameter aspect ratio. In addition, comparing the simulation results with existing analytical models for the prediction of the relative permeability acknowledges a need to develop a new correlation that would provide more accurate predictions of the relative permeability of MMMs with embedded nanotube fillers.

No description available.

Separation technologies with polymeric membranes are widely studied and have a wide range of applications. The membrane's heart is a dense selective layer whose permeability should strongly depend on the permeating species' properties. In turn, permeability depends on the diffusivity and solubility of the permeating species in the selective layer, which are considered intrinsic properties of the polymer forming the selective layer. When developing new membrane materials, the ultimate objective is to exceed the famous "upper bound" limit by achieving simultaneously higher selectivity and higher permeability. This objective is impossible without a reliable and accurate characterization method to determine the selective layer's intrinsic transport properties. The time-lag method is the most common membrane characterization technique, initially developed for polymeric membranes. However, as the membrane technology and material science advance, the selective layer structure becomes more complex and not limited to organic polymers. As a result, the time-lag method needs to be reviewed and adapted to these more complicated cases, which was the main objective of this thesis. Numerical simulation of dynamic gas permeation experiments is a powerful tool to examine different aspects of the time-lag method. Therefore, we have established a comprehensive variable-mesh finite-difference scheme, which was used throughout the thesis. It allowed us to investigate the effect of different random and resolution errors and an extrapolation error on the resulting time lag of an ideal membrane. We then considered more complex systems, particularly those of glassy polymers and mixed matrix membranes, to investigate the effect of different transport mechanisms on the results of dynamic and steady-state gas permeation experiments. In parallel, we also focused on developing a novel gas permeation system that would monitor dynamic gas permeation experiments based on pressure decay at the feed side. All the existing constant-volume gas permeation systems rely on monitoring pressure to rise at the membrane's permeate side. Although this work is still ongoing, we have made considerable progress. Among the numerous contributions made through this thesis, there are three of particular significance. We have developed an analytical model to predict mixed matrix membranes' relative permeability with the uniformly dispersed non-permeable fillers of different shapes. The model requires three structural parameters arising from the filler's shape and size, and it is superior to all existing analytical models, including the famous Maxwell model. We have also demonstrated that the diffusivity of mixed matrix membranes determined by the time-lag method depends on the number of layers of dispersed particles. In the limiting case of a single layer of uniformly impermeable fillers, it is possible for the diffusivity determined by the time-lag method to be greater than that of the host polymer, which might appear as counterintuitive in the absence of defects at the polymer-particle interface. In the case of glassy polymers, it is possible to observe an upward deviation from the steady-state flux, resulting from a non-instantaneous equilibrium between permeating species in Henry's and Langmuir adsorption sites.

No description available.

The vast majority of commercial gas separation membrane systems are polymeric because of processing feasibility and cost. However, polymeric membranes designed for gas separations have been known to have a trade-off between permeability and selectivity as shown in Robeson's upper bound curves. The search for membrane materials that transcend Robeson's upper bound has been the critical issue in research focused on membranes for gas separation in the past decade. To that end, many researchers have explored the idea of mixed matrix membranes (MMMs). These membranes combine a polymer matrix with inorganic molecular sieves such as zeolites. The ideal filler material in MMMs should have excellent properties as a gas adsorbent or a molecular sieve, good dispersion properties in the polymer matrix of submicron thickness, and should form high quality interfaces with the polymer matrix. In order to increase gas permeance and selectivity of polymeric membranes by fabricating MMMs, we have fabricated mixed matrix membranes using carbon nanotubes (CNTs) and nano-sized mesoporous silica. Mixed matrix membranes containing randomly oriented CNTs showed that addition of nanotubes to a polymer matrix could improve its selectivity properties as well as permeability by increasing diffusivity. Overall increases in permeance and diffusivity for all tested gases suggested that carbon nanotubes can provide high diffusivity tunnels in the CNT within the polymer matrix. This result agreed well with molecular simulation estimations. In order to prepare ordered CNTs membranes, we have developed a simple, fast, commercially attractive, and scalable orientation method. The oriented CNT membrane sample showed higher permeability by one order of magnitude than the value predicted by a Knudsen model. This CNT membrane showed higher selectivities for CO₂ over other gas molecules because of preferential interaction of CO₂ with the amine functionalized nanotubes, demonstrating practical applications in gas separations. Recently, mesoporous molecular sieves have been used in MMMs to enhance permeability or selectivity. However, due to their micrometer scale in particle size, the composite membrane was extremely brittle and tended to crack at higher silica loading. In this study, we have developed fabrication techniques to prepare MMMs containing mesoporous MCM-41 nanoparticles on the order of ~50 nm in size. This smaller nanoparticle lead to higher polymer/particle interfacial area and provides opportunity to synthesize higher loading of molecular sieves in polymer matrix up to ~80 vol%. At 80 vol% of nano-sized MCM-41 silica loading, the permeability of the membrane increased dramatically by 300 %. Despite these increases in permeability, the separation factor of the MMMs changed only slightly. Therefore, these nanoscale molecular sieves are more suitable for commercialization of MMMs with very thin selective layers than are micro-sized zeolites or molecular sieves. / Ph. D.