Thermal membrane distillation is one of the novel separation methods in the process industry. It involves the simultaneous heat and mass transfer through a hydrophobic semipermeable membrane through the use of thermal energy to bring about the separation of a feed mixture into two streams- a permeate and a retentate stream. Traditionally, studies on this technology have focused on the performance of individual modules as a function of material of the membrane and also configuration of the membrane. However, an investigation into the performance of a network of these modules has not been conducted in the past. A hierarchical parametric programming technique for synthesis of an optimal network of these modules is presented. A global mass allocation representation involving sources and sinks was used to solve the problem and derive criteria for optimality in specific regions of the parametric space. Two case studies have been presented to illustrate the applicability of the presented methodology.

archives@tulane.edu / Converting biomass to fuel and chemicals has attracted significant attention in recent years due to rising energy demands and the need for carbon neutral feedstocks. Lignin and cellulose are typically the main chemical components of biomass and must be depolymerized to yield sugars, which can then be enzymatically converted into alcohols for fuel. However, the depolymerization process yields side products including organic acids, phenols, and other aromatics that inhibit fermentation even at dilute concentrations. Here we investigate silicas with tailored organic surface functionalities as solid-phase adsorbents for selective removal of these chemical species. Two classes of molecules, carboxylic acids and phenol derivatives, were used as model targets for capture using functionalized ordered mesoporous silica (OMS) as a support. Chapter (3) discusses acetic acid capture, where uptake was compared using primary, secondary, tertiary, and quaternary amine grafted OMS. It was found that increasing the degree of methylation on the amine increases uptake when an equimolar functional group surface density is used. However, the aminosilane packing density was found to be crucial to performance with variation depending on the ligand bulk as well as silica support properties. Solutions conditions during uptake were varied to conclude that electrostatic and hydrophobic interactions were the primary uptake mechanisms. In the case of guaiacol, reported in Chapter (4), uptake was compared on OMS surfaces with different hydrophobic functional groups. The key parameter found was that maximizing the amount of hydrophobic functional groups increases guaiacol uptake, but the interfacial surface must concurrently be wettable in aqueous solution. OMS materials were compared and shown to be on par with commercial adsorbents for phenolic molecule uptake, showing potential to improve material performance by incorporating similar functionalities. Chapter (5) describes the synthesis and characterization of colloidally stable, 18 nm silica nanoparticles functionalized with amine groups. It was shown that amine grafting did not impact particle size and that the dispersed particles were stable over 30 days. Ninhydrin, fluorescamine, and carboxylic acid binding showed that the amines are present and accessible on the silica surface. These novel particles could be used in a range of nanotechnology applications. / 1 / Peter Miller

The classical isoelectric trapping (IET) technique, using the multicompartment electrolyzer (MCE), has been one of the most successful electrophoretic techniques in preparative-scale protein separations. IET is capable of achieving high resolution discrimination of proteins, by isolating proteins in between buffering membranes, in their isoelectric state. However, due to the inherent nature of the IET process, IET has suffered several shortcomings which have limited its applicability. During a classical IET separation, a protein gets closer and closer to its pI value, thus the charge of the protein gets closer and closer to zero. This increases the likelihood of protein precipitation and decreases the electrophoretic velocity of the protein, thus making the separation very long. Furthermore, the problems are aggravated by the fact that the instrumentation currently used for IET is not designed to maximize the efficiency of electrophoretic separations. To address these problems, a new approach to IET has been developed, pH-biased IET. By controlling the solution pH throughout the separation, such that it is not the same as the protein’s pI values, the problems of reduced solubility and low electrophoretic migration velocity are alleviated. The pH control comes from a novel use of isoelectric buffers (also called auxiliary isoelectric agents or pH-biasers). The isoelectric buffers are added to the sample solution during IET and are chosen so that they maintain the pH at a value that is different from the pI value of the proteins of interest. Two new pieces of IET instrumentation have been developed, resulting in major improvements in protein separation rates and energy efficiency. A variety of separations, of both small molecules and proteins, have been successfully performed using the pH-biased IET principle together with the new instrumentation.

A new polymeric material with a polyoxanorbornene backbone and carbamoylmethylphosphine oxide, CMPO, ligand pendant groups has been synthesized, characterized, and studied. The ability of the material to selectively partition actinides utilizing a biphasic extraction strategy was tested. The polymeric materials had significantly higher (> 5-25 times) ability to extract Th4+ than the monomeric system. The molecular weight of the material affected the extraction and separation abilities. The lower molecular weight material extracted more ions, but was less discriminate for thorium(IV) over cerium(III), lanthanum(III), and europium(III), than the higher molecular weight material. Structural modifications to this system were made by creating block copolymers. The influence of additional functionalities, created by the addition of new polymeric blocks, was investigated. The ability of the material to selectively partition actinides utilizing both solid-liquid and liquid-liquid extraction strategies was tested. Extraction efficiencies comparable to liquid-liquid extractions were achieved in the solid-liquid extractions. The extraction behavior of the materials was significantly altered by the incorporation of new blocks. The incorporation of glycol chains into the system caused an increase in the uptake of thorium(IV) over the homopolymers. The incorporation of blocks of glycol chains and blocks of cross-linked hydroxcoumarian increased the selectivity significantly (XTh/Eu 2.3 – 4.5 times higher) over the homopolymer. These materials show tremendous promise as modular polymeric scaffolds. A novel emissive tetradentate platinum complex with electropolymerizable ethylenedioxythiophene groups has been synthesized and characterized. This material has been developed for use as the active layer in polymer light-emitting diodes. Electropolymerization offers ease of processing by depositing thin films directly onto an electrode during the polymerization process. Additionally because the emitter is covalently bound in the polymer, it cannot aggregate as is the case with some small molecule emitters. The platinum complex displayed emission peaks at 510 nm and 544 nm. Electropolymerization resulted in a conductive and emissive thin film, with an emission maximum at 453 nm.

No description available.

No description available.

Membrane separations provide a potentially attractive technology over conventional processes due to their advantages, such as low capital cost and energy consumption. The goal of this thesis is to design hybrid membranes that facilitate specific gas separations, especially olefin/paraffin separations. This thesis focuses on the designing dendrimer-based hybrid membranes on mesoporous alumina for reverse-selective separations, synthesizing Cu(I)-dendrimer hybrid membrane to facilitate olefin/paraffin separations, particularly ethylene/methane separation, and investigating the influence of solvent, stabilizing ligands on facilitated transport membrane. Reverse-selective gas separations have attracted considerable attention in removing the heavier/larger molecules from gas mixtures. In this study, dendrimer-based chemistry was proved to be an effective method by altering dendrimer structures and generations. G6-PIP, G4-AMP and G3-XDA are capable to fill the alumina mesopores and slight selectivity are observed. Facilitated transport membranes were made to increase the olefin/paraffin selectivity based on their chemical interaction with olefin molecules. Two approaches were explored, the first was to combine facilitator Cu(I) with dendrimer hybrid membrane to increase olefin permeance and olefin/paraffin selectivity simultaneously, and second was to facilitate transport membrane functionality by altering solvents and stabilizing ligands. Promising results were found by these two approaches, which were: 1) olefin/paraffin selectivity slightly increased by introducing facilitator Cu(I), 2) the interaction between Cu(I) and dendrimer functional groups are better known.

abstract: Complex samples, such as those from biological sources, contain valuable information indicative of the state of human health. These samples, though incredibly valuable, are difficult to analyze. Separation science is often used as the first step when studying these samples. Electrophoretic exclusion is a novel separations technique that differentiates species in bulk solution. Due to its ability to isolate species in bulk solution, it is uniquely suited to array-based separations for complex sample analysis. This work provides proof of principle experimental results and resolving capabilities of the novel technique. Electrophoretic exclusion is demonstrated at a single interface on both benchtop and microscale device designs. The benchtop instrument recorded absorbance measurements in a 365 μL reservoir near a channel entrance. Results demonstrated the successful exclusion of a positively-charged dye, methyl violet, with various durations of applied potential (30 - 60 s). This was the first example of measuring absorbance at the exclusion location. A planar, hybrid glass/PDMS microscale device was also constructed. One set of experiments employed electrophoretic exclusion to isolate small dye molecules (rhodamine 123) in a 250 nL reservoir, while another set isolated particles (modified polystyrene microspheres). Separation of rhodamine 123 from carboxylate-modified polystyrene spheres was also shown. These microscale results demonstrated the first example of the direct observation of exclusion behavior. Furthermore, these results showed that electrophoretic exclusion can be applicable to a wide range of analytes. The theoretical resolving capabilities of electrophoretic exclusion were also developed. Theory indicates that species with electrophoretic mobilities as similar as 10-9 cm2/Vs can be separated using electrophoretic exclusion. These results are comparable to those of capillary electrophoresis, but on a very different format. This format, capable of isolating species in bulk solution, coupled with the resolving capabilities, makes the technique ideal for use in a separations-based array. / Dissertation/Thesis / Ph.D. Chemistry 2012

Sulfonated poly(arylene ether sulfone)s are a class of engineering thermoplastics well-known for their mechanical properties and chemical/oxidative stability. The research in this dissertation focuses on modifying the structure of sulfonated poly(arylene ether sulfone)s to improve membrane performance. Blends of a 20% disulfonated poly(arylene ether sulfone) (BPS20) with poly(ethylene glycol) (PEG) were investigated with the objective of promoting water flux across a reverse osmosis membrane. It was considered desirable to investigate poly(arylene ether sulfone)s with a hydroquinone unit that could be controllably post-sulfonated without degradation, providing a polymer with controlled sulfonation through controlling hydroquinone content. It also avoided the disadvantages noted previously in polymers with post-sulfonated biphenol units. Initial experiments focused on determining sulfonation conditions to confirm quantitative sulfonation of the hydroquinone without side reactions or degradation. A polymer with 29 mole % hydroquinone-containing units was used to study the rate of sulfonation. Successful post-sulfonation was confirmed and reaction conditions were applied to a series of polymers with varying hydroquinone comonomer contents. These polymers were sulfonated, characterized and evaluated for transport properties. Of interest was the high sodium rejection in the presence of calcium, which in the directly copolymerized disulfonated materials is compromised. The post-sulfonated poly(arylene ether sulfone)s showed no compromise in sodium rejection in a mixed-feed of sodium chloride and calcium chloride. In the membrane electrolysis of water, Nafion's high permeability to hydrogen, particularly above about 80 C, results in back-diffusion of hydrogen across the membrane. This reduces efficiency, product purity, and long-term electrode stability. Hydrophilic-hydrophobic multiblock copolymers based on disulfonated and non-sulfonated poly(arylene ether sulfone) oligomers feature a lower gas permeability. Various multiblock compositions and casting conditions were investigated and transport properties were characterized. A multiblock poly(arylene ether sulfone) showed a significant improvement in performance over Nafion at 95°C. Multiblock hydrophilic-hydrophobic poly(arylene ether sulfone)s have been extensively investigated as alternatives for proton exchange membrane fuel cells. One concern with these materials is the complicated multi-step synthesis and processing of oligomers, followed by coupling to produce a multiblock copolymer. An streamlined synthetic process was successful for synthesizing membranes with comparable morphologies and performance to a multiblock synthesized via the traditional method. / Ph. D.

Junior enlisted personnel are the workforce of the U.S. Army and a recruiting pool for Warrant and Officer Candidate School training programs. Before fulfilling their initial obligation of 8 years, 25 to 30 percent of enlistees receive separation orders from the Army. Consequently, attrition in this group has created a substantial problem in maintaining a trained and ready Army. The purpose of this correlational study was to understand what factors contribute to unfilled service of enlisted personnel. Specifically, this study focused on the number of years of service before departure, the cause of the early separations, and the subcategories as factors contributing to early separations. This was in comparison to the recruiting results of first-term, junior enlisted personnel. The data for this study came from the U.S. Department of Defense Demographics reports for years 2008 through 2013. These data were analyzed using a factor analysis procedure. The findings indicated 5 subcategories of early separations: Failure to meet military requirements, behavior unbecoming a soldier, inability to achieve the minimum Army standards, individual voluntarily requests for discharge, and serving their minimum active duty contractual obligations. The factor analyses revealed the percentage of variance of the early separations were most significant for individual voluntary requests for discharge and serving the minimum active duty contractual obligations. The positive social change implications stemming from this study include recommendations to the Defense Department to support eliminating the females’ exemptions from registering. This will allow all eligible individuals to register with the Selective Service, thereby advancing the integration of women into combat arms positions throughout the military services.