Browsing by Subject "Chemical reactions"
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Item A kinetic study of the acid catalyzed benzidine rearrangement of 2,2'-hydrazonaphthalene(Texas Tech University, 1961-08) Burdick, Stanley JohnNot availableItem An examination of modified hierarchical design structure for chemical processes(Texas Tech University, 2003-05) Emets, Stanislav ValerievichThe goal of this work was to examine a modified hierarchical procedure for the conceptual design of chemical processes with chemical reactions. This was achieved by examining several designs of hydrodealkylation (HDA) of toluene to benzene process (a benchmark case in teaching chemical process design), using the modified and the conventional design hierarchies. The conventional design hierarchy as described by Douglas [1] has at least two drawbacks. First, the operation of the chemical reactor is not considered as a separate step of the design exercise, but rather as a part of the recycle structure. Second, the use of a recycle stream is purely an economic decision that should be considered in the unit integration step, after the basic structure of the process is designed. Mann and Hoo [10] proposed a modified hierarchical design structure tor chemical processes that overcomes these drawbacks. Results of this study show that by applying the modified hierarchical design structure to design the HDA process, a more economical plant is designed than one obtained by conventional hierarchical design structure. Specifically, the plant designed by the modified hierarchy requires 70% lower capital investment (bare module cost) and provides an operating loss 50% smaller than that of the conventional design. These economic advantages are obtained mainly due to modifications in the reactor configurations and the elimination of the gas recycle stream. These results indicate that the modified hierarchical design structure for chemical processes with chemical reactions proposed by Mann and Hoo [10] deserves further examination. The results indicate the importance of considering the design of the chemical reactor as a distinct step in the design exercise. The results also indicate that the implementation of a recycle stream should be assessed on the basis of economic considerations, rather than being an inherent part of the design procedure. It is recommended to continue the investigation of the modified hierarchical design structure and expand the study to include the dynamic behavior of the process and the required plant-wide control structure. Also, it is recommended to examine the application of the modified hierarchical design structure to other chemical processes with chemical reactions.Item Chemical vapor deposition of boron carbo-nitride as a potential passivation layer for germanium surfaces(2009-05) Fitzpatrick, Patrick Ryan; Ekerdt, John G.Motivated by the need for a Ge surface passivation layer, chemical vapor deposition of thin (< 10 nm) films of amorphous boron carbo-nitride (BCxNy) on Ge(100) surfaces were studied to assess film continuity, interface bonding, Ge oxidation prevention, and electrical passivation. BCxNy nominally 2.5-5 nm thick continuously covers Ge(100), as determined by ion scattering spectroscopy and two angle resolved x-ray photoelectron spectroscopy (ARXPS) techniques. ARXPS analysis reveals no evidence of an interfacial layer due to elemental intermixing at the BCxNy-Ge(100) interface. High resolution transmission electron microscopy images of HfO₂ / BCxNy / Ge(100) cross-sections reveal abrupt BCxNy-Ge(100) interfaces. XPS was used to track Ge oxidation of BCxNy-covered Ge(100) upon exposure to ambient, 50 °C deionized water, and a 250 °C atomic layer deposition HfO₂ process. If the BCxNy layer is continuous ([greater-than or equal to] ~ 4 nm), the underlying Ge(100) surface is not oxidized despite incorporation of O into BCxNy. Thinner films ([less than or equal to] 3.2 nm) permitted Ge(100) oxidation in each oxidizing environment studied. Ge nanowires with a 5.7 nm BCxNy coating were resistant to oxidation for at least 5 months of ambient exposure. C-V and I-V measurements were made for metal-insulator-semiconductor (MIS) structures fabricated from n-Si(100) and n-Ge(100) wafers passivated with 4.5-5 nm BCxNy. C-rich BC0.61N0.08 films studied up to this point exhibited large amounts of hysteresis and fixed negative charge, so they were abandoned in favor of N-rich BCxNy (0.09 [less than or equal to] x [less than or equal to] 0.15, 0.38 [less than or equal to] y [less than or equal to] 0.52). N-rich BCxNy grown at 275-400 °C showed that lower deposition temperatures resulted in improved electrical characteristics, including decreased hysteresis, lower VFB shift, lower leakage current, and less C-V stretch-out. The electrical improvement is attributed to decreased bulk and interfacial defects in BCxNy deposited at lower temperatures. Even for the lowest growth temperature studied (275 °C), BCxNy-passivated Ge(100) devices had considerable hysteresis and electrical characteristics worsened after a post-metallization anneal. BCxNy-passivated Si(100) devices outperformed similar Ge(100) devices, likely due to the higher interface state densities at the BCxNy-Ge(100) interface associated with the higher relative inertness of Ge(100) to thermal nitridation.Item Coupling reactions of substituted pentaboranes(Texas Tech University, 1973-08) Flukinger, Larry CarlNot availableItem Diastereoselectivity and reactivity of oxoketene and imidoylketene: investigating the pseudopericycle reaction mechanism(Texas Tech University, 2001-05) Shumway, William WalterNot availableItem The effects of pressure variations and chemical reactions on the elasticity of the Lower Tuscaloosa sandstone of the Cranfield Field, Mississippi(2011-08) Joy, Corey Anthony; Sen, Mrinal K.; Tatham, Robert; Spikes, KyleCompliance with current and evolving federal and commercial regulations require the monitoring of injected carbon dioxide for geological sequestration. The goal of this project is to provide geophysicists with tools to quantitatively interpret seismic data for the amount of carbon dioxide retained in subsurface reservoirs. Rock physics can be used to predict the effects on the seismic response of injecting carbon dioxide on the reservoir. However, classical rock physics models fail when chemical reactions alter the microstructure of the host rock. These chemically induced changes can stiffen or soften the rock frame by precipitation or dissolution, respectively, of minerals in the pore space. Increasing pore pressure is another effect of sequestering carbon dioxide. The amount of change in the microstructure due to chemical reactions and pressure variations depends on the reservoir into which the fluid is injected. Therefore, measuring velocities on site-specific subsurface core samples may provide the ability to differentiate between chemical reactions and pressure variations on the elastic properties of the reservoir rock. Core samples come from the Lower Tuscaloosa Sandstone of the Cranfield study area in Mississippi. The experiments consisted of injecting core plugs with carbon dioxide rich brine and measuring compressional and shear velocities at different effective pressures. The elastic moduli of the rock frame are calculated from the measured elastic wave propagation velocities at specific injected pore volumes and effective pressures. Injecting carbon dioxide rich brine into sandstone core samples, which are composed on average of 80% quartz and 20% clay minerals, resulted in softening of the rock frame due to the dissolution of iron bearing minerals. The moduli exponentially decreased with injected pore volumes and were linearly proportional to effective pressure. The bulk modulus and rigidity of the more quartz rich sample decreased by 13% and 6.5%, respectively, due to a combined effect of changing differential pressure from 35 MPa to 27 MPa and injecting CO₂-rich brine. For the more clay rich sample, the moduli decreased by even larger percentages (39.0% and 20.1%, respectively), which could have significant implications on time-lapse seismic data and subsequent estimations of injected CO₂ volumes.Item Heterogenous reactions on atmospheric carbonaceous particles(2005) Nopmongcol, Uarporn; Allen, David T.Elevated particle concentrations in the atmosphere have received significant attention due to their multiple effects from urban to global scales. The sources and formation mechanisms of these air pollutants, however, are poorly understood, especially atmospheric reactions involving oxidation and condensation of gas phase hydrocarbons, catalyzed by atmospheric particles. This work examines these particle catalyzed, gas to particle transformation processes, through detailed photochemical modeling of air quality episodes in Texas. Two heterogeneous reaction pathways were incorporated into a widely used photochemical model. The pathways that were examined were (1) Heterogeneous formation of sulfuric acid on carbonaceous particles and (2) Acid catalyzed condensation reactions of low molecular weight aldehydes. The impact of these pathways on air quality in Texas was examined for a period during which wildfires generated significant amounts of carbonaceous atmospheric aerosol. This episode was chosen for analysis because the rates of the heterogeneous reactions were expected to be significant during this period, leading to observable signals in ambient data. Simulations, together with ambient data, indicated that wood smoke mediated sulfate formation reactions, not accounted for in most current photochemical models, may have led to 5-10 µg/m3 of sulfate formation. In photochemical simulations, wood-smoke mediated sulfate formation was modeled by calculating the rate of impingement of SO2 molecules on the wood smoke particles, and then assuming that a fraction of the impingements resulted in reaction. For reaction probabilities on the order of 0.01, the model predicted magnitudes, spatial distributions and temporal distributions of sulfate concentrations consistent with observations. Simulations, together with ambient data, indicated that acid aerosol mediated organic aerosol formation reactions, not accounted for in most current photochemical models, may have led to 1-5 µg/m3 of organic aerosol. In photochemical simulations, acid mediated organic aerosol formation was modeled by calculating the rate of impingement of aldehyde molecules on acidic particles, and then assuming that a fraction of the impingements resulted in reaction. For reaction probabilities on the order of 0.0005, the model predicted magnitudes, spatial distributions and temporal distributions of organic aerosol consistent with observations. Ambient data and model results in this work demonstrated that the heterogeneous reactions on carbonaceous particles are significant. The methodology developed in this work, most importantly, can be applied to other heterogeneous reactions to be incorporated into a photochemical model.Item Interactions of arenediazonium ions with multidentate ligands(Texas Tech University, 1979-08) Juri, Pedro NorbertoNot availableItem Kinetics and Mechanisms of Chromium (II) Catalyzed Nitrosyl Ligand Exchange Reactions.(Texas Tech University, 1974-12) Roberts, Richard LeeNot Available.Item Phase space theory, variational transition-state theory, and classical trajectory studies of gas-phase chemical reactions(Texas Tech University, 1989-05) Song, KihyungThis dissertation is a collection of works on theories of gas-phase chemical reactions. Three main topics are included: phase space theory, microcanonical variational transitionstate theory, and the classical trajectory method. Phase space theory was applied to the reaction (H2O)OH- (CO2.H2O) HCO3-. The available experimental data on this reaction was successfully reproduced by taking into account the dissociation of the HCO3- ion using a dissociation energy of 1.8 eV, which is in good agreement with the reported value. The decomposition of the bromobenzene cation was studied using a variational method developed by Chesnavich. This study showed that the existence of multiple transitionstates strongly depends upon the transitional mode potential. A microcanonical variational method was developed and applied to two systems, HO2 and HeH2+. The HO2 study revealed that a bottleneck in the angular part of the potential can produce multiple transition-states. Also, multiple transition-states are more Ukely to exist for systems with lower well-depth. The HeH2+ study supports this trend. More detailed calculations conserving angular momentum gave similar results. A life-time estimate for the system trapped between the two transition-states was performed with a pseudo-complex assumption. For the HeH2+ system, this lifetime is equal to -200 fs, which is within the limit of experimental detection. The origin of the dynamic threshold for collision-induced dissociation was studied using the boundary trajectory method. This study showed no correlation between the curvature of the minimum energy path potential and the dynamic threshold. The results suggest that the dynamic and energetic thresholds are equal only when an exchange reaction channel is presentItem Item Reactor performance prediction for the reaction of sulfur dioxide with manganese dioxide(Texas Tech University, 1969-05) Graham, Roy RussellNot availableItem The acid-catalyzed reactions of some N, N'-dimethylhydrazoaromatics(Texas Tech University, 1976-05) Walzel, Gerald LNot availableItem The Kinetics and Mechanisms of the Iridium(IV) - Sulfur(IV) reaction in a bBffered Chloride Medium(Texas Tech University, 1973-08) Stapp, Eldon LloydNot Available.Item The reaction of 2,4-dinitrophenylhydrazine with beta-alkylthio ketones and beta-dialkylamino ketones(Texas Tech University, 1968-06) Gayley, Owen ClarkNot availableItem The reaction of 2.4-dinitrophenylhydrazine with alpha, beta-unsaturated ketones and beta-alkoxy ketones(Texas Tech University, 1962-08) Fang, Li-TzuNot availableItem The reactions of trimethyl group Va Lewis bases with simple boron Lewis acids.(Texas Tech University, 1975-05) Mente, Donald CharlesNot availableItem Theories of chemical reactions: the orbiting transition state for linear molecules, classical dynamics of association and dissociation in collinear reactions(Texas Tech University, 1987-08) Grice, Marvin EdwardIn this dissertation we examine two topics in the theory of chemical reactions. The first involves statistical theory of reaction dynamics, particularly that of the orbiting transition state (i.e., phase space theory). The second involves a classical dynamics study of a simple system. In Part 1 we examine two approximations to the orbiting transition state sum of states for systems containing linear molecules. The first is a low angular momentum approximation which was originally introduced by Klots and shown by him to be exact in the limit of zero angular momentum. The second is an "integral" approximation in that it is designed to work well when the sum of states is integrated over a large range of angular momenta, a situation in which the Klots approximation usually fails. Part 2 reports a study of the classical dynamics of collinear collision induced dissociation and association at energies slightly above the diatom dissociation threshold. The method of Andrews and Chesnavich is used to define the banding of the reagents' phase space into reactive, nonreactive, dissociative, associative and nonassociative regions for fixed total energy. In the bound region of the reagent diatom phase space, two dynamically distinct reactive bands, surrounded by companion dissociative bands, are embedded within a nonreactive region, while in the nonbound region of the reagent's phase space, association bands are seen that are simple extensions across the dissociation threshold of the reactive and nonreactive bands. The dynamics also varies smoothly across the dissociation threshold. No evidence was found for the existence of periodic or "trapped" trajectories at the energies of this study.