Browsing by Subject "Membrane"
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Item A reverse osmosis treatment process for produced water: optimization, process control, and renewable energy application(2009-06-02) Mareth, BrettFresh water resources in many of the world's oil producing regions, such as western Texas, are scarce, while produced water from oil wells is plentiful, though unfit for most applications due to high salinity and other contamination. Disposing of this water is a great expense to oil producers. This research seeks to advance a technology developed to treat produced water by reverse osmosis and other means to render it suitable for agricultural or industrial use, while simultaneously reducing disposal costs. Pilot testing of the process thus far has demonstrated the technology's capability to produce good-quality water, but process optimization and control were yet to be fully addressed and are focuses of this work. Also, the use of renewable resources (wind and solar) are analyzed as potential power sources for the process, and an overview of reverse osmosis membrane fouling is presented. A computer model of the process was created using a dynamic simulator, Aspen Dynamics, to determine energy consumption of various process design alternatives, and to test control strategies. By preserving the mechanical energy of the concentrate stream of the reverse osmosis membrane, process energy requirements can be reduced several fold from that of the current configuration. Process control schemes utilizing basic feedback control methods with proportional-integral (PI) controllers are proposed, with the feasibility of the strategy for the most complex process design verified by successful dynamic simulation. A macro-driven spreadsheet was created to allow for quick and easy cost comparisons of renewable energy sources in a variety of locations. Using this tool, wind and solar costs were compared for cities in regions throughout Texas. The renewable energy resource showing the greatest potential was wind power, with the analysis showing that in windy regions such as the Texas Panhandle, wind-generated power costs are approximately equal to those generated with diesel fuel.Item Assessment of fouling in native and surface-modified water purification membranes(2013-05) Miller, Daniel Joseph Lang; Freeman, B. D. (Benny D.); Paul, Donald R.Fouling is a major obstacle to the implementation of membranes in water purification applications. Hydrophilization of the membrane surface tends to mitigate fouling because hydrophobic interactions between foulants and the membrane are reduced. Polydopamine was deposited onto membranes to render their surfaces hydrophilic. The chemical structure of polydopamine, which was previously ambiguous, was investigated by many spectroscopic techniques. While previously thought to consist of covalently-linked monomers, polydopamine was found to be an aggregate of partly-oxidized dopamine units linked by strong, non-covalent secondary interactions. Polydopamine was also used as a platform for the molecular conjugation of other anti-fouling materials, such as poly(ethylene glycol), to the membrane surface. Membrane fouling was assessed by constant permeate flux crossflow filtration with an oil/water emulsion feed. The threshold flux--the flux at which the rate of fouling significantly increases--was determined by a well-established flux stepping technique. Membrane resistance evolution during fouling was compared for constant flux and constant transmembrane pressure operation using unmodified membranes. Below the threshold flux (slow fouling), good agreement in resistance evolution was found between the two operational modes; above the threshold flux, significant deviation was observed. The effect of polydopamine and polydopamine-g-poly(ethylene glycol) surface modifications was studied under constant flux crossflow fouling conditions. The surface modifications were found to increase the membrane resistance, resulting in higher transmembrane pressures in the modified membranes than in the unmodified membranes at fluxes below the threshold flux. Modified membranes were also compared to unmodified membranes with the same pure water permeance (same initial resistance). In this case, the modified membranes had lower transmembrane pressures during fouling than the unmodified membranes, suggesting that a preferred method of membrane surface modification is to begin with a membrane of higher permeance than required, and then surface-modify it to achieve the desired permeance. The efficacy of polydopamine and polydopamine-g-poly(ethylene glycol) surface modifications in reducing biofouling was also evaluated. Modified membranes showed reduced protein and bacterial adhesion in short-term tests, which are commonly used to assess biofouling propensity. However, long-term operation under hydrodynamic conditions mimicking those of an industrial module showed no benefit of the hydrophilic coatings in limiting biofouling.Item Dendrimers as drug and gene delivery vectors : a self consistent field theory study(2013-08) Lewis, Thomas Wade Stakesby; Ganesan, VenkatThis research focuses on the modeling of dendrimer molecules for their application as delivery vectors within drug and gene therapy systems. We examine how the architecture and composition of dendrimers affect their drug and gene binding efficacies along with their interactions with anionic bilayers. We specifically focus on how the weakly basic nature of dendrimer monomers and the addition of neutral grafts to dendrimer surface groups affect their interactions with drugs, linear polyelectrolytes, and bilayers. By using polymer self-consistent field theory (SCFT) to model such systems, we develop a computationally efficient means to provide physical insights into these systems, which are intended to guide dendrimer design for delivery applications.We study the conformational properties of weakly basic (annealed) polyelectrolyte dendrimers by developing a SCFT model that explicitly accounts for the acid-base equilibrium reaction of the weakly basic monomers. We specifically focus on the role of local counterion concentration upon the charge and conformations of the annealed polyelectrolyte dendrimers. We compare our results to existing polymer scaling theories and develop a strong stretching theory for the dendrimer molecules.We extend the previous study to model the interactions between weakly basic dendrimers and weakly acidic, hydrophobic drug molecules. We specifically examine the effects of excluded volume, electrostatic, and enthalpic interactions on the binding efficacies between dendrimers and drugs under a variety of dendrimer generations, solution pOH conditions, drug sizes, and Bjerrum length values.We study the role of neutral dendrimer grafts on the conformations and drug binding efficacies of dendrimers. We then elucidate how the observed conformational changes affect the charge of the dendrimers. Furthermore, we examine how the presence of grafts affects the steric, electrostatic, and hydrophobic interactions between the drugs and dendrimers under a variety of solution conditions. We compare our results with the binding efficacies observed for non-grafted dendrimers to delineate the conditions under which the grafted dendrimers are better suited as drug hosts.We include semi-flexible, anionic linear polyelectrolyte (LPE) molecules in our grafted dendrimer SCFT framework to model the interactions between dendrimers and negatively charged genetic materials. Specifically, we examine how neutral dendrimer grafts, LPE stiffness, and solution pOH affect the interactions between dendrimers and LPEs. We then use our SCFT potential fields as input into Monte Carlo simulations in order to determine the dendrimer-LPE potentials of mean force and the resulting loop and tail statistics of the dendrimer-adsorbed LPE chains.We incorporate a negatively charged bilayer into our grafted dendrimer SCFT framework to model dendrimer interactions with a cellular membrane. We specifically examine the role of dendrimer grafting length, solution pH, and membrane tension on such interactions. By comparing our results with SCFT calculations of fixed dendrimer conformations and hard sphere nanoparticles in the presence of membranes, we delineate the role of dendrimer flexibility and porosity on the interactions between dendrimers and anionic bilayers.Item Dynamic modeling of membrane swelling in fuel cell manufacturing(2010-12) Silverman, Timothy J.; Beaman, Joseph J.; Meyers, Jeremy P.; Chen, Dongmei; Edgar, Thomas F.; Fahrenthold, Eric P.Fuel cells are promising energy conversion devices, but they have not been widely adopted because of their very high cost. The most expensive component of a fuel cell is the membrane electrode assembly, a polymer film coated with catalyst material. The catalyst layer is fabricated by depositing and drying a liquid ink on the membrane. The membrane can rapidly absorb water from the ink, causing swelling strain sufficient for wrinkling, which can cause defects in the finished product. These challenges limit most catalyst layer fabrication to individual preparation by hand. We seek to understand the swelling phenomenon in a way that enables the control of defects during mass production. Membrane swelling is a transient, three-dimensional, coupled mass transfer, heat transfer and solid mechanics problem. Existing models describe the membrane in fuel cell operating conditions, making use of simplifying assumptions that are not valid for predicting manufacturing defects. We present a new model incorporating effects that are missing from other models. We present simulation results for scenarios relevant to the control of defects. Simple spatial variations in water content can cause curl and wrinkling; we establish criteria for the formation of these defects by simulating the membrane's response when subjected to the full pre-swollen coating and drying process. We investigate the sensitivity of wrinkling to nonuniformity in the coating and to processing conditions in the coating line. We propose a rationale for controlling wrinkling caused by these effects and for diagnosing coating defects using the membrane's wrinkling response. We show how the membrane behaves differently depending on whether the coating is applied to one side or to both sides simultaneously. We have designed and constructed a machine to pre-swell the membrane, apply a coating and then dry the coating under controlled tension, speed, temperature and humidity. We present the design and discuss how the machine may be used, together with the membrane model, to predict and control defects in catalyst-coated membranes.Item The effect of synthesis route and ortho-position functional group on thermally rearranged polymer thermal and transport properties(2013-05) Sanders, David Finley; Freeman, B. D. (Benny D.); Paul, Donald R.This dissertation discusses the effect of synthesis route and ortho-position group on the thermal and transport properties of thermally rearranged polymers. Thermally rearranged polymers are polybenzoxazoles formed via the solid state rearrangement of ortho-functional polyimides. In this study, polymers were derived from 3,3'-dihydroxy-4,4'-diamino-biphenyl and 2,2'-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (HAB-6FDA). These HAB-6FDA polymers were synthesized using chemical and thermal imidization, and hydroxyl, acetate, propanoate, or pivalate ortho-position groups were considered. In these polymers, gas permeability increases as a function of conversion for all samples. The polyimide synthesis route does not affect the thermal or transport properties. However, the precursor ortho-position group strongly influences the thermal and transport properties of TR polymers. Additionally, it was determined that an increase in gas diffusivity was the primary cause of increased permeability as a function of thermal rearrangement.Item Electrospinning of silica nanofibers: characterization and application to biosensing(2009-06-02) Tsou, Pei-HsiangElectrospinning is a technique to achieve nanometer scale fibers. Similar to the conventional spin methods of making fabric, the viscous polymer solution is ejected from a spinneret; stretched and solidified in the air, the solution forms the fibers. The different part of electrospinning among others is that the fibers are driven by the electrostatic force, which induces the repulsion inside the liquid and further reduces the diameter. The resultant product is a non-woven membrane, which is porous; and the pore size is around several nanometers to a micrometer wide. In this work, the relationship between the diameter of electrospun silica fibers, experimental parameters such as concentration and voltage, and between pore size of the fiber membrane and experimental time were studied. Materials used in the process are Polyvinylpyrrolidone (PVP), butanol and spin-on-glass coating solution, which act as polymer carrier, solvent, and silica-precursor, respectively. Polymer/silica precursor composite fibers were ejected from the needle of a plastic syringe when an electrical field, as high as several kV/cm, was applied. Then silica fibers were achieved by baking the composite ones at 773 oK for 12 h. Electrospun silica nanofibers were characterized as a function of polymer solution parameters. The calcined fibers were examined by using a field emission scanning electron microscope. The results showed that the fiber diameters decrease with decreasing proportion of polymer and silica precursor, and increase with a higher electric field. Pore sizes, defined as the grid areas enclosed by fibers on nearby layers, were also examined and showed no time-dependent tendency when the electrospin time was between 1-5 min. Fiber membranes were then used as the platform for protein detection. The results were compared with the control, which used glass slides as the platform. The results make it possible to make a more sensitive biosensing device.Item Evaluation of Membrane Treatment Technology to Optimize and Reduce Hypersalinity Content of Produced Brine for Reuse in Unconventional Gas Wells(2012-10-19) Eboagwu, UcheOver 18 billion barrels of waste fluids are generated annually from oil and gas production in the United States. As a large amount of water is used for oilfield operations, treating and reusing produced water can cut the consumption of fresh water in well sites. This research has helped to develop a membrane process train for a mobile produced water treatment unit for treating oilfield produced brine for reuse. To design the process train, over 30 sets of combination tests at pilot laboratory scale were performed using pretreatment, microfiltration and nanofiltration processes. Membrane performance was selected based on high flux separation efficiency, high tolerance for solids and fluid treatments. Over 95 % solids rejection and greater than 80 % oil removal efficiency were obtained in all these tests. Process train (pre-treatment and membrane) performance was monitored by chemical analysis of permeate and models fitting experimental data for the process. From the results, hydrocarbon rejection was analyzed; total organic carbon rejection was 47.9 %, total carbon content averaged 37.3 % rejection and total inorganic carbon rejection was at 3.66 %. BTEX removal efficiency ranged from 0.98 % to 52.7 % with the progressive pretreatment methods of using cartridge filters. The nanofiltration membrane showed significant reduction in total dissolved solids and in both anionic and cationic species. The process train is seen to follow a sequence of treatment from cartridge and oil removal filter treatment to microfiltration treatment to ultrafiltration, followed by nanofiltration for the purpose of this research. Further research still needs to be done on to determine the kind of analytical test which will give real time feedback on effectiveness of filters. In summary, the process train developed by TAMU-GPRI possesses distinct advantages in treating oilfield produced brine using membrane technology. These advantages include high quality of permeate, reduced sludge and the possibility of total recycle water systems. The small space requirement, moderate capital costs and ease of operation associated with the use of the mobile unit membrane technology also makes it a very competitive alternative to conventional technologies.Item Fabrication and mechanical characterization of graphene based membranes and their use in thermoacoustics(2011-12) Suk, Ji Won; Ruoff, Rodney S.; Liechti, Kenneth M.; Sreenivasan, S V.; Shi, Li; Hall, Neal A.Following the first report on electronic transport measurements of graphene, an atom-thick carbon material, many scientists have devoted effort to understand its fundamental properties. In this work, the mechanical properties of graphene-based materials, including monolayer graphene oxide and chemical vapor deposition (CVD) grown graphene, were determined using membrane structures. Furthermore, a membrane structure was used to demonstrate thermoacoustic sound generation from monolayer graphene. In order to realize the mechanical characterization, reproducible methods to fabricate graphene membranes were developed using dry and wet transfer techniques. A novel dry transfer technique produced graphene-sealed microchambers without trapping liquid inside. An improved wet transfer technique enabled the transfer of graphene onto perforated substrates. Monolayer graphene oxide was mechanically tested using scanning atomic force microscopy (AFM) combined with finite element analysis of the data. The mechanical deformation was measured by scanning AFM tips over the suspended graphene oxide membranes. The Young’s modulus of the membranes was obtained by analyzing the deformation using finite element analysis together with a mapping technique. In addition, membranes with 2 and 3 layers of graphene oxide were identified using transmission electron microscopy and mechanically characterized. Moreover, these same methods were used for measuring mechanical properties of ultra-thin amorphous carbon membranes. Bulge tests, which apply uniform pressure on the suspended membrane, revealed the mechanical behavior of polycrystalline graphene grown on copper foils by chemical vapor deposition. In particular, the effect of grain boundaries on the elastic properties of polycrystalline graphene was studied by correlating its Young’s modulus with the density of grain boundaries within the membranes. It was observed that a large number of grain boundaries softened the graphene membranes. Graphene, along with monolayer hexagonal boron nitride, is the ultimate limit of thin materials. Thus, it is an ideal candidate as a thermoacoustic sound source because of its low heat capacity per unit area. The work presented here provides the first demonstration of thermoacoustic sound generation from large-area monolayer graphene. A fundamental understanding of the influence of the underlying substrates was achieved by comparing the acoustic performance of graphene membranes on various patterned substrates with different porosities.Item Fundamental water and ion transport characterization of sulfonated polysulfone desalination materials(2014-08) Cook, Joseph Reuben; Freeman, B. D. (Benny D.)Sulfonated polysulfones BisAS and BPS were fabricated into dense polymer films, and their water and ion transport properties were systematically characterized. Fundamental NaCl and water transport properties were correlated with polymer chemistry, and water and NaCl permeability were found to increase with degree of sulfonation due to the increasing polymer water content. The BisAS backbone structure was found to result in greater water uptake, increasing water and salt permeability, though the polysulfones show evidence of sensitivity to the thermal casting process as well. Additionally, water and ion permeability and sorption values were determined for select polymers when exposed to a feed consisting of mixtures of monovalent and divalent cation salts. The divalent cations were found to sorb into the polymer much more favorably than the monovalent sodium, similarly to charged materials found in the literature. The sodium permeability of sulfonated polysulfones was found to increase in the presence of divalent cations by ratios of 2 to 5 times more than when exposed to an equivalent increase in feed charge concentration of monovalent cations. It has been hypothesized the more strongly charged divalent cations are neutralizing the sulfonate charges and suppressing Donnan exclusionary effects that reduce salt transport in charged polymers.Item Investigation and design of an actively actuated lower-limb prosthetic socket(2009-12) Montgomery, John Thomas; Crawford, Richard H.; Barr, Ronald E.A prosthetic socket worn by an amputee must serve a wide variety of functions, from stationary support to the transfer of forces necessary to move. Fit and comfort are important factors in determining the therapeutic effectiveness of a socket. A socket that does not fit the subject well will cause movement problems and potentially long-term health issues. Because a subject's residual limb changes volume throughout the day, it is desirable that the socket adapt to accommodate volume changes to maintain fit and comfort. This thesis presents research to manufacture adaptive sockets using selective laser sintering (SLS). This additive manufacturing process allows freedom to design a socket that has both compliant areas that can adapt to changes to the residual limb, as well as rigid regions to provide necessary support for the limb. A variety of concepts are discussed that are intended for manufacture by SLS, and that feature flexible inner membranes in various configurations. For each concept the membrane will be inflated or deflated to match the limb’s change in volume and the thesis also presents a study to determine SLS machine parameters for optimal build results. A series of experiments was created to understand the ability of SLS manufactured plastics to be inflated and the possible performance.Item Localization and functional interactions of fibronectin and associated basement membrane proteins during embryonic heart development(Texas Tech University, 1984-08) Kitten, Gregory TThe early embryonic heart is composed of two, cylindrical epithelial layers, an inner endothelium and an outer myocardium. The cardiac jelly (CJ), an a cellular accumulation of extra cellular matrix (ECM), fills the space between the two layers. All cardiac endothelial cells (EC) do not follow an identical course of differentiation. Some of the EC of the atrio ventricular (AV) and outflow tract (OT) regions undergo an epithelial-mesenchymal transition to form mobile cardiac mesenchymal (CM) cells while in other regions (e.g., ventricle), EC differentiate along the lines of a typical vascular endothelium. The mechanisms controlling the biphasic differentiation of EC and the subsequent migration of CM cells are poorly understood. Although the CJ lies between two epithelia and is spatially equivalent to a basement membrane (BM), it has not traditionally been considered to be organized into a BM-like structure. The potential significance of this observation lies in the possibility that BM, or their individual components (i.e., fibronectin (FN), laminin (LH), type IV collagen, and heparan sulfate proteoglycan (HSPG)), may function as the regulatory site o f " epithelial differentiation and morphogenesis. The temporal changes in the localization and the functional involvement of the BM components FN, LM, type IV collagen, and HSPG were investigated with respect to (1) EC attachment and differentiation and (2) CM cell attachment and migration. A cryofixation technique was developed in order to determine the in situ immunohistochemical distribution of the BM components in the CJ. Results indicated that the CJ exists IJS the fusion between a larger, myocardially derived BM and an attenuated, endothelial associated BM. Except for FN, the individual BM components were not all present during early stages. Instead, they appeared in a sequential manner, suggesting that all components of an adult-type B'A are not required to initiate the assembly of a structural and functional BM during development. In the AV and OT, FN lippeared as a progressively expanding gradient of material with the greatest density nearer the myocardium. An in vitro collagen gel bioassay was employed to directly test whether FN or other BM components play a role in EC and CM cell attachment, differentiation, and migration. Biochemical analysis and results from experiments using probes directed against the BH components indicated that mora than one mechanism of attachment, involving FN and/or HSPG, exist during EC development and CM cell migration.Item Membrane remodeling in epsilon proteobacteria and its impact on pathogenesis(2012-05) Cullen, Thomas Wilson; Trent, Michael Stephen; Whiteley, Marvin; Harshey, Rasika M.; Stevens, Scott W.; O'Halloran, Terry J.Bacterial pathogens assemble complex surface structures in an attempt to circumvent host immune detection. A great example is the glycolipid known as lipopolysaccharide or lipooligosaccharide (LPS), the major surface molecule in nearly all gram-negative organisms. LPS is anchored to the bacterial cell surface by a anionic hydrophobic lipid known as lipid A, the major agonist of the mammalian TLR4-MD2 receptor and likely target for cationic antimicrobial peptides (CAMPs) secreted by host cells (i.e. defensins). In this work we investigate LPS modification machinery in related ε-proteobacteria, Helicobacter pylori and Campylobacter jejuni, two important human pathogens, and demonstrate that enzymes involved in LPS modification not only play a role in evasion of host defenses but also an unexpected role in bacterial locomotion. More specifically, we identify the enzyme responsible for 4'-dephosphorylation of H. pylori lipid A, LpxF. Demonstrating that lipid A depohsphorylation at the 1 and 4'-positions by LpxE and LpxF, respectively, are the primary mechanisms used by H. pylori for CAMP resistance, contribute to attenuated TRL4-MD2 activation and are required for colonization of a the gastric mucosa in murine host. Similarly in C. jejuni, we identify an enzyme, EptC, responsible for modification of lipid A at both the 1 and 4'-positions with phosphoethanolamine (pEtN), also required for CAMP resistance in this organism. Suprisingly, EptC was found to serve a dual role in modifying not only lipid A with pEtN but also the flagellar rod protein FlgG at residue Thr75, required for motility and efficient flagella production. This work links membrane biogenesis with flagella assembly, both shown to be required for colonization of a host and adds to a growing list of post-translational modifications found in prokaryotes. Understanding how pathogens evade immune detection, interphase with the surrounding environment and assemble major surface features is key in the development of novel treatments and vaccines.Item Water and salt transport structure/property relationships in polymer membranes for desalination and power generation applications(2012-12) Geise, Geoffrey Matthew; Paul, Donald R.; Freeman, B. D. (Benny D.)Providing sustainable supplies of water and energy is a critical global challenge. Polymer membranes dominate desalination and could be crucial to power generation applications, which include reverse osmosis (RO), nanofiltration (NF), forward osmosis (FO), pressure-retarded osmosis (PRO), electrodialysis (ED), membrane capacitive deionization (CDI), and reverse electrodialysis (RED). Improved membranes with tailored water and salt transport properties are required to extend and optimize these technologies. Water and salt transport structure/property relationships provide the fundamental framework for optimizing polymer materials for membrane applications. The water and salt transport and free volume properties of a series of sulfonated styrenic pentablock copolymers were characterized. The polymers' water uptake and water permeability increase with degree of sulfonation, and the block molecular weights could be used to tune water uptake, permeability, and selectivity properties. The presence of fixed charge groups, i.e., sulfonate groups, on the polymer backbone influence the material's salt transport properties. Specifically, the salt permeability increases strongly with increasing salt concentration, and this increase is a result of increases in both salt sorption and diffusivity with salt concentration. The data for the sulfonated polymers, including a sulfonated polysulfone random copolymer, are compared to those for an uncharged polymer to determine the influence of polymer charge on salt transport properties. The sulfonated styrenic pentablock copolymer permeability data are compared to literature data using the water permeability and water/salt selectivity tradeoff relationship. Fundamental transport property comparisons can be made using this relationship. The effect of osmotic de-swelling on the polymers and the transport properties of composite membranes made from sulfonated styrenic pentablock copolymers are also discussed. The sulfonated styrenic pentablock copolymers were exposed to multi-valent ions to determine their effect on the polymer's salt transport properties. Magnesium chloride permeability depends less on upstream salt concentration than sodium chloride permeability, presumably due to stronger association between the sulfonate groups and magnesium compared to sodium ions. Triethylaluminum was used to neutralize the polymer's sulfonic acid functionality and presumably cross-link the polymer. The mechanical, transport, and free volume properties of these aluminum neutralized polymers were studied.