Browsing by Subject "Membranes"
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Item A mechanistic exploration of oil recovery via selective oil permeation(2023-04-21) Cooper, Carolyn M.; Katz, Lynn Ellen; Kinney, Kerry A.; Seibert, Frank; Lawler, Desmond F; Freeman, Benny DOil-water separations are necessary for the reuse of oil-laden wastewater. For example, oil and gas produced water may have influent oil concentrations of up to 2,000 mg/L that must be reduced to <10–35 mg/L to meet regulatory requirements for non-industrial reuse. However, many conventional oil-water separation processes are unable to achieve these effluent concentrations. Selective oil permeation is a promising membrane-based oil-water separation approach that may be able to meet these treatment goals. The process differs from traditional membrane-based oil-water separations by permeating oil (instead of water) through the hydrophobic membrane. Exploitation of the preferential oil wetting of the membrane surface minimizes viscous fouling and generates an oil permeate stream. Previous investigation of selective oil permeation has demonstrated its ability to recover oil over extended durations. Researchers have hypothesized that mechanistic competition between coalescence and permeation controls oil recovery, results in the development of an oil film at the membrane surface, and leads to transport phenomena that deviate from traditional pore flow models. However, further verification is necessary to validate the existence of hypothesized mechanisms within the process and verify its applicability to produced water treatment. Few studies have investigated mechanistic interactions or process performance (i.e., oil flux, oil recovery, permeate quality) for oil concentrations less than 1%. Even fewer have probed relationships between process performance, operating conditions, and water quality characteristics. Understanding the answers to these outstanding questions is crucial to defining the opportunity space for selective oil permeation. This dissertation is the first set of studies to present results that (1) characterize and provide guidance for enhancing the membrane conditioning process, (2) identify how the operative mechanisms are impacted by system characteristics, operating conditions, and water quality characteristics within this lower oil concentration range, and (3) apply selective oil permeation to produced water. Achieving the outlined objectives will both expand our understanding of the role of the two key mechanisms underlying selective oil permeation (coalescence and permeation) and begin to define the opportunity space for oil recovery via selective oil permeation.Item Development of a new synthetic platform for polyether materials(2019-09-13) Rodriguez, Christina Gissel; Freeman, B. D. (Benny D.); Lynd, Nathaniel; Brennecke, Joan F; Paul, Donald R; Mendoza-Cortes, Jose LThere is considerable current interest in the development of innovative technologies for CO₂ capture and sequestration (CCS) of CO₂. Common separation technologies are cryogenic distillation and chemical absorption, however they suffer from problems associated with high capital and operational costs in addition to environmental impacts. Membrane technology offers an affordable approach for CO₂ capture because of fundamental advantages such as high-energy efficiency, small footprint, operational simplicity, and modularity. Polymeric materials are commonly used as membranes for gas separations due to their lightweight, easy processing, and wide variation in structure and properties. The introduction of polar groups into a polymer matrix has been shown to evoke favorable interactions with CO₂ and the polar ether oxygens present in polyethylene oxide (PEO) are of particular interest. Although PEO has demonstrated potential for CO₂ separations, its weak mechanical strength and tendency to crystallize has opened an opportunity for the exploration of alternative polyether materials. Polyethers are a class of polymers that have the potential for remarkable multi-functionality in a materials platform based on the variety of readily available, inexpensive, and functional monomer precursors called epoxides. The spectrum of methods used to synthesize polyethers each have various advantages and disadvantages, with no single consensus technique for all monomer structures and moieties emerging. The first aspect of this study aims to fill this gap in synthetic techniques in order to explore the potentials of other polyethers for CO₂ separations. A new subset of organoaluminum complexes have been synthesized to initiate and catalyze epoxide polymerizations, which have named mono(μ-alkoxo)bis(alkylaluminum)(MOB) initiators. The main advantages of these new initiators are their one step synthesis and purification as well as their effortless use for polymerizations. They demonstrated control over polymer molecular weight, architecture, composition, and end group functionality. Kinetic in-situ fourier-transform infrared spectroscopy (FTIR) studies were used to determine the dependence of alkyl-substituents polymerization rate. The isobutyl-substituted MOB initiator was found to be the most effective towards polymerizing a wide range of functional epoxides. With this new synthetic method available, a polyether membrane platform was developed utilizing commercially available epoxide monomers and incorporating diglycidyl ethers to act as crosslinkers. Kinetic ¹H NMR spectroscopy studies of epichlorohydrin and two diglycidyl ethers revealed complete conversion of both monomer and crosslinker for the formation of homogeneous materials. Tolerance of chemical functionality, realized from previous studies, also enabled membrane formation of several substituted epoxides. A series of crosslinked n-butyl glycidyl ether (nBGE) and poly(ethylene oxide) diglycidyl ether (PEO-dGE) was used to study the variability in transport properties by changing the incorporation of PEO-dGE crosslinker.. These newly synthesized materials showed an improvement in both CO₂ permeability and permselectivity over light gases with increasing amounts of PEO-dGE crosslinker. Gas solubility measurements showed relatively similar CO₂ and N₂ solubilities for all the membranes in the series, which in turn attributed the improvement in CO₂ permeability to an increase in gas diffusivity. When performing CO₂ separations the incoming feed gas typically contains a considerable percentage of water, which can significantly impact transport properties. Given this information, permeability measurements were conducted under humidified conditions and demonstrated that humidity had no noticeable impact on either CO₂ or N₂ permeabilities. These measurements granted a fundamental understanding of the structure-property relationships for these unique class of materials and was aimed at elucidating the capabilities of this new synthetic platformItem Development of new membranes for proton exchange membrane and direct methanol fuel cells(2004-08) Yang, Bo, Ph. D.; Manthiram, ArumugamProton exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC) are drawing much attention as alternative power sources for transportation, stationary, and portable applications. Nafion membranes are presently used in both PEMFC and DMFC as electrolytes, but are confronted with a few difficulties: (i) high cost, (ii) limited operating temperature of < 100 °C, and (iii) high methanol permeability. With an aim to overcome some of the problems encountered with the Nafion membranes, this dissertation focuses on the design and development of a few materials systems for use in PEMFC and/or DMFC. The incorporation of hydrous Ta₂O₅·nH₂O into Nafion membrane as well as the electrodes is shown to help the cell to retain water to higher temperatures. Membrane-electrode assembly (MEA) consisting of the composite membrane shows better cell performance at 100 and 110 °C than that with plain Nafion membrane, and a high power density of ~ 650 mW/cm² at 100 °C is obtained with H₂ - CO mixture as the fuel due to a significant alleviation of the CO poisoning of the catalysts. Sulfonated poly(etheretherketone) (SPEEK) membranes with various sulfonation levels are prepared and investigated in DMFC. With a sulfonation level of ~ 50 %, the SPEEK membranes exhibit low methanol permeability and electrochemical performance comparable to that of Nafion at around 60 °C, making it an attractive low-cost alternative to Nafion. From a comparative study of the structural evolutions with temperature in 2 M methanol solution, it is found that the lower methanol permeability of SPEEK membranes is related to the less connected and narrower pathways for water/methanol permeation. The dry proton conductor CsHSO₄ shows a high proton conductivity of ~ 10⁻³ S/cm at temperatures > 140 °C and water is not needed for proton conduction. However, it is found that CsHSO₄ decomposes to Cs₂SO₄ and H₂S at 150 °C in H₂ atmosphere in contact with the Pt/C catalyst. Thus, new catalyst materials need to be explored for CsHSO₄ to be used in practical high temperature PEMFC. Thin self-humidifying Nafion membranes with dispersed Pt/C catalyst powder are prepared and tested in PEMFC with dry H₂ and O₂. The Pt/C particles provide sites for catalytic recombination of H₂ and O₂ permeating from the anode and cathode, and the water produced at these sites directly humidifies the membrane. The performance of the cell with the self-humidifying membrane operated with dry reactants is ~ 90 % of that obtained with well humidified H₂ and O₂.Item An electrostatic approach for producing nanoparticulate membranes using laser ablation of microparticle aerosols(2011-08) Davis, Claire Elisabeth; Kovar, Desiderio; Becker, Michael F.The Laser Ablation of Microparticle Aerosols (LAMA) process produces nanoparticles by ablating microparticles that are entrained in an aerosol. Two of the main advantages of this process are that the particles produced are charged (preventing agglomeration) and bare (without a capping layer). Two different techniques are possible to collect the nanoparticles. In this work, the charged state of the particles formed was utilized to collect them electrostatically. This approach has the additional advantage that particles can be selected according to their size. The focus here was a particular application for gas separation. The nanoparticles produced were directly collected in a polymeric liquid, which was then irradiated with ultraviolet light to form a rubbery film. These membranes were tested for olefin/paraffin gas separation, a challenge that finds many applications, notably in the petroleum industry.Item Fundamental gas transport in thermally cross-linked diaminophenylindane (DAPI) containing polyimides(2018-12) Dose, Michelle Elizabeth; Freeman, B. D. (Benny D.); Paul, Donald R.; Riffle, Judy; Lynd, Nathaniel; Sanchez, IsaacThe trust of this work is to critically examine the chemical and morphological structure of thermally cross-linked polyimides and to identify the effect cross-linking has on fundamental gas transport and plasticization resistance of these materials. To accomplish this goal, a polyimide containing diaminophenylindane (DAPI), hexafluoroisopropylindene (6FDA), and diaminobenzoic acid (DABA), referred to as 6FDA-DAPI/DABA, was synthesized and characterized. The thermal cross-linking process was found to occur by thermal decarboxylation of the carboxylic acid groups contained in DABA. Additionally, upon cross-linking, gas permeability was found to increase with increased cross-linking due to an apparent increase in polymer chain spacing. While thermal cross-linking showed improved plasticization resistance to pure CO₂, C₂H₄, and C₂H₆, mixed gas permeation experiments revealed linear 6FDA-DAPI/DABA was more resistant to plasticization than its cross-linked analog. By studying sorption induced dilation, we concluded that linear 6FDA-DAPI/DABA more readily excluded C₂H₆ from the free volume elements, compared to cross-linked 6FDA-DAPI/DABA, correlating well with the minimal plasticization effects observed in the mixed gas experiments. Additionally, the dilation and sorption data were used to estimate the accessible free volume in the polymer-penetrant mixture. While correlating the diffusion coefficients of CO₂, C₂H₄, and C₂H₆ with the penetrant weight fraction showed anomalous behavior, the relative increase in diffusion coefficients with accessible fractional free volume accurately reflected the plasticization behavior observed in mixed gas permeation experiments. Additionally, this dissertation investigated the fundamental transport of gases in thermally rearranged (TR) polymers and polymers of intrinsic microporosity (PIM) to gain an understanding of why these materials tend to perform at or beyond the Robeson Upper Bound for select gas pairs.Item Fundamentals of ion sorption and transport in charged and ligand functionalized membranes(2022-08-10) Sujanani, Rahul; Freeman, B. D. (Benny D.); Ganesan, Venkat; Lynd, Nathaniel A; Dingemans, Theo JPolymeric membranes that selectively control water and ion transport rates are critical to various separation technologies addressing the Water-Energy Nexus. For example, highly selective ion transport across membranes is essential to processes including, reverse osmosis, nanofiltration, electrodialysis, and fuel cells. Developing membranes with enhanced ion transport and selectivity properties could improve the efficiency of existing membrane-based technologies and facilitate the design of new processes for emerging applications (e.g., resource recovery). A detailed fundamental understanding of ion transport in ion selective membranes could permit rational design of new membrane materials with desired separation properties. However, many molecular interactions underpinning ion sorption, diffusion, and selectivity in such materials are poorly understood. This dissertation focused on fundamental studies of aqueous ion sorption and transport in two classes of ion selective membranes: ion exchange membranes (IEMs) and 12-Crown-4-Ether (12C4) ligand functionalized membranes. IEMs contain charged groups tethered to the polymer backbone that enable selective permeation of ions based on charge/valence. Ion sorption properties of commercial IEMs equilibrated with various salts (i.e., NaCl, MgCl₂, Na₂SO₄, and MgSO₄) were characterized experimentally and compared with theoretical predictions to determine the utility of existing models (i.e., Manning’s counter-ion condensation theory and Donnan equilibrium theory), and gaps therein, to describe thermodynamics in charged polymers. These studies demonstrated the importance of counter-ion condensation and ion pairing (a topic rarely considered in hydrated membranes) on ion sorption in IEMs, leading to the development of a new thermodynamic framework that accounts for both phenomena. In some cases, good quantitative agreement was observed between theoretical predictions and experimental data, using no adjustable parameters. Given that commercial membranes exhibit limited selectivity between ions of the same valence (e.g., Li⁺ vs. Na⁺), the influence of fixed ligand sites on ion transport in hydrated polymers was also investigated. Permeability, solubility, and diffusivity of LiCl, NaCl, and MgCl₂ were measured in a series of 12C4 functionalized membranes. In some cases, 12C4 membranes exhibited an unusual, LiCl/NaCl permeability selectivity higher than previously reported values among hydrated polymers under single salt conditions (i.e., ~2.3). These results provided an improved fundamental understanding of host-guest interactions in hydrated polymers and potential guidelines for designing ion selectivity in membranes.Item Germanium and silicon nanowires for use in water purification(2022-05-11) Sullivan, William (M.S. in chemical engineering); Korgel, Brain Allan, 1969-Germanium and silicon nanowires present an exciting opportunity for broadening the scope of membrane fouling mitigation research. Germanium nanowires provide a highly effective model system for investigating how to incorporate silicon nanowires into polymeric membranes, while providing relative ease in synthesis and workability compared to silicon nanowires. Silicon nanowires present an exciting area of investigation for fouling mitigation for two main reasons: they can be surface passivated to achieve desired chemical properties and they are photoactive. This work explores how to effectively incorporate germanium nanowires into polymeric membranes as a model to be used for silicon nanowires. Then the integration of silicon nanowires is further explored to determine the most effective methods of silicon nanowire incorporation into polymeric membranes. Successful integration of silicon nanowires into polymeric membrane systems is demonstrated, providing the groundwork for further exploration of the use of nanowires in water purification, specifically for fouling mitigation.Item Investigating molecular effects on membrane structure, dynamics and function(2019-05-01) Anderson, Cari Michelle; Webb, Lauren J.; Elber, Ron; Baiz, Carlos R; Eberlin, Livia S; Gordon, VernitaBiological membranes are heterogeneous structures with complex electrostatic profiles arising from lipids, sterols, membrane proteins, and water molecules. We investigated the effect of cholesterol and its derivative 6-ketocholestanol (6-kc) on membrane electrostatics by directly measuring the dipole electric field (F [arrow above F] [subscript d] ) within lipid bilayers containing cholesterol or 6-kc at concentrations of 0−40 mol% through the vibrational Stark effect (VSE). We found that adding low concentrations of cholesterol, up to ∼10 mol %, increases F [arrow above F] [subscript d], while adding more cholesterol up to 40 mol% lowers F [arrow above F] [subscript d]. In contrast, we measured a monotonic increase in F [arrow above F] [subscript d] as 6-kc concentration increased. We proposed that this membrane electric field is affected by multiple factors: the polarity of the sterol molecules, the reorientation of the phospholipid dipole due to sterol, and the impact of the sterol on hydrogen bonding with surface water. We used molecular dynamics simulations to examine the distribution of phospholipids, sterol, and helix in bilayers containing these sterols. At low concentrations, we observed clustering of sterols near the vibrational probe whereas at high concentrations, we observed spatial correlation between the positions of the sterol molecules. This work demonstrated how a one-atom difference in a sterol changes the physicochemical and electric field properties of the bilayer. Additionally, we set out to understand how a small molecule interacts with the lipid bilayer differently based on its charge. Our laboratory had previously reported that tryptophan permeated through a phosphatidylcholine lipid bilayer membrane at a faster rate when it was positively charged (Trp+) than when negatively charged (Trp−), which corresponded to a lower potential of mean force (PMF) barrier determined through simulations. In the work described here, we demonstrated that Trp+ partitions into the lipid bilayer membrane to a greater degree than Trp− by interacting with the ester linkage of a phosphatidylcholine lipid, where it is stabilized by the electron withdrawing glycerol functional group. These results are in agreement with tryptophan’s known role as an anchor for transmembrane proteins, though the tendency for binding of a positively charged tryptophan is surprising. We discussed the implications of our results on the mechanisms of unassisted permeation and penetration of small molecules within and across lipid bilayer membranes based on molecular charge, shape, and molecular interactions within the bilayer structure.Item Physical aging of thin and ultrathin glassy polymer films(2010-05) Rowe, Brandon William; Paul, Donald R.; Freeman, B. D. (Benny D.); Ganesan, Venkat; Eldridge, R B.; Kulkarni, SudhirThis research effort investigated the influence of confinement on the physical aging behavior of thin and ultrathin glassy polymer membranes. Membrane permeability changes with time due to physical aging, and for reasons not completely understood, the rate of permeability change can become orders of magnitude faster in films thinner than one micron. Special experimental techniques were developed to enable the study of free standing, ultrathin glassy polymer films using gas permeability measurements. The gas transport properties and physical aging behavior of free-standing glassy polysulfone (PSF) and Matrimid® films from 18-550 nm thick are presented. Physical aging persists in glassy films approaching the length scale of individual polymer coils. The membranes exhibited significant reductions in gas permeability and increases in selectivity with aging time. Additionally, the influence of physical aging on the free volume profile in thin PSF films was investigated using variable energy positron annihilation lifetimespectroscopy (PALS). The films exhibited decreasing o-Ps lifetime during physical aging, while o-Ps intensity remained constant. The o-Ps lifetime was reduced at lower implantation energies, indicating smaller free volume elements near the film surface. Thin films aged dramatically faster than bulk PSF and the PALS results agree favorably to behavior tracked by gas permeability measurements. The physical aging behavior of ultrathin films with different previous histories was also studied. The state of these materials was modulated by various conditioning treatments. Regardless of the previous history, the nature of the aging response was consistent with the aging behavior of an untreated film that was freshly quenched from above Tg, i.e., permeability decreased and pure gas selectivity increased with aging time. However, the extent of aging-induced changes in transport properties of these materials depended strongly on previous history. The properties of these ultrathin films deviate dramatically from bulk behavior, and the nature of these deviations is consistent with enhanced mobility and reduced Tg in ultrathin films, which allows them to reach a lower free volume state more quickly than bulk material. The Struik physical aging model was extended to account for the influence of film thickness on aging, and was shown to accurately describe the experimental data.Item Polyamide desalination membrane characterization and surface modification to enhance fouling resistance(2010-05) Van Wagner, Elizabeth Marie; Freeman, B. D. (Benny D.); Sharma, Mukul M.; Paul, Donald R.; Bonnecaze, Roger T.; Lawler, Desmond F.; Mickols, William E.The market for polyamide desalination membranes is expected to continue to grow during the coming decades. Purification of alternative water sources will also be necessary to meet growing water demands. Purification of produced water, a byproduct of oil and gas production, is of interest due to its dual potential to provide water for beneficial use as well as to reduce wastewater disposal costs. However, current polyamide membranes are prone to fouling, which decreases water flux and shortens membrane lifetime. This research explored surface modification using poly(ethylene glycol) diglycidyl ether (PEGDE) to improve the fouling resistance of commercial polyamide membranes. Characterization of commercial polyamide membrane performance was a necessary first step before undertaking surface modification studies. Membrane performance was found to be sensitive to crossflow testing conditions. Concentration polarization and feed pH strongly influenced NaCl rejection, and the use of continuous feed filtration led to higher water flux and lower NaCl rejection than was observed for similar tests performed using unfiltered feed. Two commercial polyamide membranes, including one reverse osmosis and one nanofiltration membrane, were modified by grafting PEGDE to their surfaces. Two different PEG molecular weights (200 and 1000) and treatment concentrations (1% (w/w) and 15% (w/w)) were studied. Water flux decreased and NaCl rejection increased with PEGDE graft density ([microgram]/cm2), although the largest changes were observed for low PEGDE graft densities. Surface properties including hydrophilicity, roughness and charge were minimally affected by surface modification. The fouling resistance of modified and unmodified membranes was compared in crossflow filtration studies using model foulant solutions consisting of either a charged surfactant or an oil in water emulsion containing n-decane and a charged surfactant. Several PEGDE-modified membranes demonstrated improved fouling resistance compared to unmodified membranes of similar initial water flux, possibly due to steric hindrance imparted by the PEG chains. Fouling resistance was higher for membranes modified with higher molecular weight PEG. Fouling was more extensive for feeds containing the cationic surfactant, potentially due to electrostatic attraction with the negatively charged membranes. However, fouling was also observed in the presence of the anionic surfactant, indicating hydrodynamic forces are also responsible for fouling.Item Surface modification of water purification membranes to improve fouling resistance in oily water filtration(2015-12) Kasemset, Sirirat; Freeman, B. D. (Benny D.); Sharma, Mukul M.; Paul, Donald R; Sanchez, Isaac C; Ellison, Christopher J; Emrick, Todd SOne of the biggest challenges in using water purification membranes is fouling. Surface modification using hydrophilic materials can reduce hydrophobic interactions between membrane surface and hydrophobic foulants, thereby alleviating fouling. In this Ph.D. research, polydopamine (PDA), a highly hydrophilic and universal coating agent, was used to surface-modified reverse osmosis (RO) and ultrafiltration (UF) membranes. PDA modification conditions (e.g., dopamine coating solution concentration, coating time, and pH of coating solution) control PDA deposition and can directly influence the modified membrane properties. Thus, the influence of PDA modification conditions on membrane physical, permeation, selective, and fouling properties were investigated systematically. A fundamental understanding relating the physical and permeation properties and the fouling characteristics of PDA-modified membranes was established. The RO membranes were modified with PDA at various modification conditions. Permeate fluxes during pure water and oil/water emulsion filtrations were studied. The PDA modification increased the permeate fluxes during oil/water emulsion filtration (thus, improved membrane fouling resistance) relative to unmodified membranes regardless of the initial dopamine concentration or deposition time used. However, these changes were only observed for the membranes coated under alkaline conditions, suggesting that the PDA did not deposit well under acidic condition. For UF membranes, molecular weight cutoff (MWCO) and pure water permeance decreased with increasing initial dopamine concentration or deposition time. A permeability and selectivity tradeoff was also observed. Membrane mean pore size and pore size distribution (modeled using log-normal pore size distribution) were investigated via modelling using a hindered solute transport model, Hagen-Poiseuille equation, and a stagnant film model. The PDA modification increased UF membrane surface hydrophilicity regardless of the coating conditions used, but it did not clearly change surface roughness or zeta potential (i.e., surface charge). Membrane fouling propensity was characterized using threshold flux. Compared to unmodified membranes, the threshold flux increased at minimal PDA coatings, but decreased at excessive PDA coatings. These threshold flux changes were likely governed by a tradeoff between surface hydrophilicity increase and pure water permeance decrease. Excessive PDA coatings resulted in decreased pure water permeance and possibly, pore blockage and pore size reduction, leading to higher local permeate flux causing severe fouling and decreased threshold flux.Item A theoretical formulation for flexoelectric membranes(2015-05) Sermollo, Nebiyu Barsula; Huang, Rui, doctor of civil and environmental engineering; Landis, Chad MFlexoelectricity is electric polarization induced by a strain gradient. This phenomenon has been observed in different types of materials. It has been studied and documented that biological membranes possess this flexoelectric property. Research by Brownell et al. has shown that the inner-ear hair cells elongate or shrink as a result of external stimuli. This shrinking and elongation of the cells is due to the wrinkling and flattening of the cell membrane surrounding the hair cells. To study this biomechanical response, a soft, elastomeric membrane under loading by in-plane forces, moments and voltage across the membrane is considered. This membrane is assumed to have the flexoelectric property. Using a thermodynamic approach, a set of constitutive equations are derived that relate the physical quantities (forces, moments, voltage) to the state variables (strains, curvatures, electric displacement). The accuracy of these equations is tested by using them to estimate the flexoelectric coefficient of certain materials following a procedure established by Cross et al. Additionally, a critical membrane thickness is found which ensures a positive-definite Helmholtz free energy for the membrane, guaranteeing a stable system. Finally, a model for the wrinkling and flattening of the cell membrane surrounding the inner-ear outer hair cells is developed using the derived constitutive equations.