Browsing by Subject "Solvents"
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Item A study of controlling resistances during initial solvent evaporation period of asymmetric membrane formation.(Texas Tech University, 1975-05) Majid, S. M ANot availableItem A study of controlling resistances during initial solvent evaporation period of asymmetric membrane formation.(Texas Tech University, 1975-05) Majid, S. M ANot availableItem Assessment of the potential for natural attenuation of chlorinated solvents in contaminated groundwater in the Texas High Plains(Texas Tech University, 2000-12) Kang, Amandeep SinghReese Air Force Base (RAFB), now known as Reese Center is located in the Southern High Plains region of west Texas in Lubbock County. In 1987, concentrations of chlorinated solvents, especially trichloroethene (TCE), were found to be out of compliance with the federal limits. Significant concentrations of perchloroethene (PCE) were also present on site. Pump and treat technologies, which consist of extracting contaminated groundwater and treating it on the surface, have been the traditionally considered technology when significant levels of groundwater contamination exist. Natural attenuation (NA), also called "mtrinsic remediation" has recently been recognized as a potential method for treatment of contaminated groundwater. NA of contaminants includes sorption to soil particles, dilution, dispersion, volatilization, biochemical stabilization, radioactive decay and biodegradation in soils and groundwater. If NA is found to be a viable option at Reese AFB, it can replace the presently employed pump and treat technique and result in monetary gains. A study was conducted to estimate the potential for NA of the TCE present in the Ogallala aquifer at the Reese Air Force Base. Initial assessment of the site showed the existence of three distmct TCE plumes, two on-site and the third off-site. Initial site assessment revealed that one of the plumes exhibited signs of NA. This area is present on-site and consists mostly of the area near the Picnic Lake. A detailed examination of this area was conducted. Plume maps were drawn for the study area using SURFER to study the variation of PCE, TCE, cis-dichloroethene (cis-DCE), and dissolved oxygen (DO) concentrations from 1996 to 1998 (Only data available). These plume maps were then analyzed to study the potential for NA occurring at the site. Data analysis for the study area shows the presence of a large TCE and cis-DCE plume. The TCE plume is located up-gradient and to the northwest of the cis-DCE plume. Data analysis and modeling was used to determme whether the cis-DCE plume is a result of the TCE plume located up-gradient to it. In addition, modeling was used to back track the movement of the TCE plume and locate its possible source as well as assess the future potential of the plume movement.Item Development of nanofiber protective substrates(Texas Tech University, 2004-08) Subbiah, ThandavamoorthyElectrospinning uses high voltage electric field to produce high surface area fibers in the nanometer range. Polymeric nanofibers were prepared by the electrospinning process and were characterized using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). A study on the relationship between process parameters and fiber characteristics was undertaken. The dependence of fiber morphology on the solvent volatility and collector substrate characteristics was critically analyzed. Results on the self assembling nature of the charged fibers over different collector substrates were obtained and reported in the thesis. Defect free nanofiber webs with high specific surface area and low porosities suitable enough to be used as adsorptive filtration membranes were prepared. Polyurethane nanofibers were used as nano metal oxide catalyst carriers by successfully impregnating the catalyst in a single-step electrospinning process. Aerosol filtration abilities of nanofiber membranes were tested and the results are presented.Item Electrochemical Reactions and Mechanisms of Organic and Organometallic Compounds in Aprotic Solvents(Texas Tech University, 1980-08) Root, Duane KeithNot Available.Item Group-Contribution Methods in Estimating Liquid-Liquid Distribution Coefficients(Texas Tech University, 1981-05) Liu, Che KeungNot Available.Item Molecular dynamics study of solvation phenomena to guide surfactant design(2009-12) Dalvi, Vishwanath Haily; Rossky, Peter J.Supercritical carbon-dioxide has long been considered an inexpensive, safe and environmentally benign alternative to organic solvents for use in industrial processing. However, at readily accessible conditions of temperature and pressure, it is by itself too poor a solvent for a large number of industrially important solutes and its use as solvent necessitates concomitant use of surfactants. Especially desirable are surfactants that stabilize dispersions of water droplets in carbon-dioxide. So far only molecules containing substantially fluorinated moieties e.g. fluoroalkanes and perfluorinated polyethers, as the CO₂-philes have proved effective in stabilizing dispersions in supercritical carbon-dioxide. These fluorocarbons are expensive, non-biodegradable and can degrade to form toxic and persistent environmental pollutants. Hence there is great interest in developing non-fluorous alternatives. Given the development of powerful computers, excellent molecular models and standardized molecular simulation packages we are in a position to augment the experiment-driven search for effective surfactants using the nanoscopic insights gleaned from analysis of the results of molecular simulations. We have developed protocols by which to use standard and freely available molecular simulation infrastructure to evaluate the effectiveness of surfactants that stabilize solid metal nanoparticles in supercritical fluids. From the results, which we validated against experimental observations, we were able to determine that the alkane-based surfactants, that are so effective in organic fluids, are ineffective or only partially effective in CO₂ because the weak C-H dipoles cannot make up for the energetic penalty incurred at the surfactant-fluid interface by CO₂ molecules due to loss of quadrupolar interactions with other CO₂ molecules. Though the effectiveness of purely alkane-based surfactants in carbon-dioxide can be improved by branching, they cannot approach the effectiveness of the fluoroalkanes. This is because the stronger C-F dipole can supply the required quadrupolar interactions and a unique geometry renders repulsive the fluorocarbons' electrostatic interactions with each other. We have also determined the source of the fluoroalkanes' hydrophobicity to be their size which offsets the effect of favourable electrostatic interactions with water. Hence we can provide guidelines for CO₂-philic yet hydrophobic surfactants.Item A predictive thermodynamic model for an aqueous blend of potassium carbonate, piperazine, and monoethanolamine for carbon dioxide capture from flue gas(2008-05) Hilliard, Marcus Douglas, 1977-; Rochelle, Gary T.The Electrolyte Nonrandom Two-Liquid Activity Coefficient model in Aspen PlusTM 2006.5 was used to develop a rigorous and consistent thermodynamic representation for the base sub-component systems associated with aqueous combinations of K₂CO₃, KHCO₃, MEA, and piperazine (PZ) in a mixed-solvent electrolyte system for the application of CO₂ absorption/stripping from coal fired power plants. We developed a new vapor-liquid equilibrium apparatus to measure CO₂, amine, and H2O vapor pressures at 40 and 60 oC. We found that the volatility of MEA and PZ can be approximated at 50 and 20 ppmv at 40°C for any solvent composition studied in this work, over the CO₂ partial pressure range from 0.01 to 0.1 kPa. Very few solvent compositions exhibited a greater differential capacity than 7 m MEA at 60°C; specifically 11 m MEA, 3.5 m MEA + 3.6 m PZ, 7 m MEA + 2 m PZ, 7 m MEA + 3.6 m PZ, and 5 m K+ + 7 m MEA + 3.6 m PZ. Piperazine exhibited a possible maximum differential capacity of 2.21 mole CO₂/kg-H₂O at a concentration of 7.3 m. At the Norwegian University of Science and Technology, Inna Kim determined the differential enthalpy of CO₂ absorption for aqueous combinations of K₂CO₃, KHCO₃, MEA, PZ, and CO₂, based on a consistent experimental method developed for MEA, from 40 to 120°C for use in this work. In addition, we developed a consistent method to measure the specific heat capacity for a number of similar solvent combinations. We found that the enthalpy of CO₂ absorption increased with temperature because the apparent partial heat capacity of CO₂ may be considered small. Finally, by using a differential scanning calorimeter, we determined the dissolution temperature for aqueous mixtures of unloaded piperazine, which inferred an effective operating range for solutions of concentrated piperazine, greater than 5 m PZ, over a loading range between 0.25 to 0.45 mole CO₂/2·mol PZ. Through unit cell x-ray diffraction, we were able to identify and characterize the presence of three solid phases (PZ·6H₂O, KHCO₃, and KvPZ(COO)₂) in aqueous mixture combinations of K₂CO₃, KHCO₃, PZ, and CO₂.Item Solvent determination for thermally stable polymers - PDIAB(Texas Tech University, 1976-05) Dangayach, Kailash C BNot availableItem Solvent Effects in the Diels Alder Reaction(Texas Tech University, 1971-05) Silber, ErnestoNot Available.Item Solvent extraction in the vapor phase(Texas Tech University, 1936-06) Watkins, Alva EugeneNot availableItem Stabilization of colloidal dispersions in supercritical carbon dioxide(2005) Dickson, Jasper Lane; Johnston, Keith P., 1955-Over the past decade, compressed carbon dioxide (CO2) has emerged as a possible alternative to traditional organic solvents in various industrial processes. Compared to other compressible fluids, CO2 is particularly appealing since it is inexpensive, relatively non-toxic, non-flammable, and possesses a mild critical point. Unfortunately, the solvent strength of CO2 is limited due to its lack of a permanent dipole moment and weak van der Waals interactions. To accommodate CO2’s limited solvation capacity, emulsions and colloidal dispersions are often stabilized with fluorinated surfactants and polymers. However, even for the most CO2-philic fluoropolymers, pressures above 100 bar are typically required to achieve good solvent conditions. In an attempt to increase the industrial applicability of CO2, a majority of this research is focused on the development of novel approaches to stabilize emulsions and colloids in liquid CO2 at low pressures. The use of solid particles in lieu of classical surfactants is demonstrated to allow for the stabilization of emulsions consisting of water and CO2 at low CO2 densities since stability is not dependent on tail solvation. The stability of these emulsions is shown to be highly dependent on the particle hydrophilicity and its subsequent contact angle at the water-CO2 interface. Concentrated dispersions of inorganic silica particles are stabilized at pressures as low as the vapor pressure through the formation of a cross-linked polymeric shell around the solid core. The presence of the polymeric shell allows for dispersibility by weakening the Hamaker interactions between the core-shell particles. The density-dependent interparticle interactions between these dispersed core-shell nanoparticles are quantified in terms of a diffusional second virial coefficient using dynamic light scattering. Finally, the water-CO2 and the solid-CO2 interfaces are investigated. Using high-pressure pendant-drop tensiometry, the water-CO2 interfacial tension is measured for a family of surfactants in order to investigate the relationship between surfactant molecular architecture and interfacial activity. Measurements of the CO2/water/solid contact angle on well defined homogeneous substrates as a function of CO2 pressure provide fundamental insight into the specific interactions between CO2 and the solid interface.Item Synthesis, properties, and applications of ionic liquids(Texas Tech University, 2002-05) Dzyuba, Sergei VNot availableItem The effect of structural modifications on solvent interactions with siloxane polymers(Texas Tech University, 1978-05) Chen, Ko-ChiGas-Liquid chromatography (GLC) was used to investigate the sensitivity of GLC data to structural modification in a series of alkyl- and fluoroalkyl- substituted siloxane polymers. Experimental data at 55°C, 70°C, 85°C and essentially atmospheric pressure for each solute in the siloxane polymer systems at infinite dilution are presented. Infinite-Dilution pseudo activity coefficients (Ω∞) and thermodynamic quantities (e. g., ∆Hm, ∆Gm, ∆Sm) were obtained from data taken at 55°C, 70°C and 85°C. The significance of the results to melting transition in polymers, glass transition in polymers, polymer solubility, and the effect of polymer structural modification with solubility are discussed. It is concluded that gas chromatography is a valuable tool for studying the structure of polymers and their interaction with compounds of lower molecular weight.