Browsing by Subject "Chemical kinetics"

Now showing 1 - 16 of 16
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    A kinetic study of some aromatic sulfinazides
    (Texas Tech University, 1954-01) King, Henry Lee
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    A kinetic study of the acid catalyzed benzidine rearrangement of 2,2'-hydrazonaphthalene
    (Texas Tech University, 1961-08) Burdick, Stanley John
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    Comparison of five kinetic parameter retrieval techniques which are derived from the Michaelis-Menten enzyme kinetic model
    (Texas Tech University, 1989-05) Nguyen, Tuan
    A study of least-squares estimation of Michaelis-Menten kinetic parameters Km and Vmax was performed using five kinetic parameter retrieval techniques. These techniques are derived from five linear plots which are the Direct Linear, Lineweaver-Burk, Eadie- Hofstee, Hanes and Inverse Hanes linear plots. Substrate concentration [S](t) and measured product formation rate V(t) with respect to time were used as the data basis for the system. These data can be obtained by numerical integration of three coupled firstorder ordinary differential equations which represent the Michaelis-Menten mechanism. The problem was to define the most accurate of these techniques, that calculate the Michaelis-Menten parameters Km and Vmax that are closest to one or both theoretical values of Km and Vmax when given Michaelis-Menten substrate concentration and product formation rate that have been perturbed with random noise. The Direct Linear and Eadie-Hofstee are the most accurate retrieval techniques, and the Lineweaver-Burk retrieval technique is the least accurate technique in estimating the Michaelis-Menten parameters Km and Vmax in most cases of all different combinations of the rate constants, values of random data error and numbers of discrete data points chosen in this work without an outlier in perturbed data.
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    Experiments in weak acid dissociation and theories of activated rate processes
    (Texas Tech University, 1991-05) Krishnan, Rajalakshmi
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    Expert system to retrieve optimal kinetic parameters for simple reactions
    (Texas Tech University, 1986-05) Jou, Chon-shin
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    Gas phase oxidation of onion dehydration odors with ozone
    (Texas Tech University, 1977-12) Purkaple, Jerry Dixon
    The kinetics of the reaction between ozone and three identified components associated with onion dehydration odor were studied in a flow reactor. Temperatures in the range of 95-150°F were used in an attempt to estimate the temperature dependence of the reaction rate constant. However, this temperature range was not great enough to establish a meaningful relationship. A homogeneous gas phase model and a heterogeneous model were found to fit the experimental data reasonably well. Due to the mathematical similarities between the two models, no real distinction could be made between them. Initial rate data indicated that the initial reaction was first order with respect to the odor components and of fractional order with respect to ozone.
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    Kinetics and dynamics of adsorption on single crystal semiconductor and metal surfaces
    (2001-08) Reeves, Christopher Thomas; Mullins, C. B.
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    On the representation of model inadequacy : a stochastic operator approach
    (2016-05) Morrison, Rebecca Elizabeth; Moser, Robert deLancey; Oden, John Tinsley; Ghattas, Omar; Henkelman, Graeme; Oliver, Todd A; Simmons, Christopher S
    Mathematical models of physical systems are subject to many sources of uncertainty such as measurement errors and uncertain initial and boundary conditions. After accounting for these uncertainties, it is often revealed that there remains some discrepancy between the model output and the observations; if so, the model is said to be inadequate. In practice, the inadequate model may be the best that is available or tractable, and so despite its inadequacy the model may be used to make predictions of unobserved quantities. In this case, a representation of the inadequacy is necessary, so the impact of the observed discrepancy can be determined. We investigate this problem in the context of chemical kinetics and propose a new technique to account for model inadequacy that is both probabilistic and physically meaningful. Chemical reactions are generally modeled by a set of nonlinear ordinary differential equations (ODEs) for the concentrations of the species and temperature. In this work, a stochastic inadequacy operator S is introduced which includes three parts. The first is represented by a random matrix which is embedded within the ODEs of the concentrations. The matrix is required to satisfy several physical constraints, and its most general form exhibits some useful properties, such as having only non-positive eigenvalues. The second is a smaller but specific set of nonlinear terms that also modifies the species’ concentrations, and the third is an operator that properly accounts for changes to the energy equation due to the previous changes. The entries of S are governed by probability distributions, which in turn are characterized by a set of hyperparameters. The model parameters and hyperparameters are calibrated using high-dimensional hierarchical Bayesian inference, with data from a range of initial conditions. This allows the use of the inadequacy operator on a wide range of scenarios, rather than correcting any particular realization of the model with a corresponding data set. We apply the method to typical problems in chemical kinetics including the reaction mechanisms of hydrogen and methane combustion. We also study how the inadequacy representation affects an unobserved quantity of interest— the flamespeed of a one-dimensional hydrogen laminar flame.
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    Parametric uncertainty and sensitivity methods for reacting flows
    (2014-05) Braman, Kalen Elvin; Raman, Venkat
    A Bayesian framework for quantification of uncertainties has been used to quantify the uncertainty introduced by chemistry models. This framework adopts a probabilistic view to describe the state of knowledge of the chemistry model parameters and simulation results. Given experimental data, this method updates the model parameters' values and uncertainties and propagates that parametric uncertainty into simulations. This study focuses on syngas, a combination in various ratios of H2 and CO, which is the product of coal gasification. Coal gasification promises to reduce emissions by replacing the burning of coal with the less polluting burning of syngas. Despite the simplicity of syngas chemistry models, they nonetheless fail to accurately predict burning rates at high pressure. Three syngas models have been calibrated using laminar flame speed measurements. After calibration the resulting uncertainty in the parameters is propagated forward into the simulation of laminar flame speeds. The model evidence is then used to compare candidate models. Sensitivity studies, in addition to Bayesian methods, can be used to assess chemistry models. Sensitivity studies provide a measure of how responsive target quantities of interest (QoIs) are to changes in the parameters. The adjoint equations have been derived for laminar, incompressible, variable density reacting flow and applied to hydrogen flame simulations. From the adjoint solution, the sensitivity of the QoI to the chemistry model parameters has been calculated. The results indicate the most sensitive parameters for flame tip temperature and NOx emission. Such information can be used in the development of new experiments by pointing out which are the critical chemistry model parameters. Finally, a broader goal for chemistry model development is set through the adjoint methodology. A new quantity, termed field sensitivity, is introduced to guide chemistry model development. Field sensitivity describes how information of perturbations in flowfields propagates to specified QoIs. The field sensitivity, mathematically shown as equivalent to finding the adjoint of the primal governing equations, is obtained for laminar hydrogen flame simulations using three different chemistry models. Results show that even when the primal solution is sufficiently close for the three mechanisms, the field sensitivity can vary.
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    Reactor performance prediction for the reaction of sulfur dioxide with manganese dioxide
    (Texas Tech University, 1969-05) Graham, Roy Russell
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    Sigma bond activation of the hydrogen molecule by cooperative interaction with a boron cation, a lithium anion, and a beryllium atom
    (Texas Tech University, 1999-05) Sharp, Stephanie Baxter
    Sigma bond activation, making a sigma bond more reactive, has been one of tht' most extensively studied areas of chemistry for the past decade. Sigma bonds are the strongest bonds and therefore reactions that involve the breaking of such bonds have large activation energies. Without a doubt, the three most popular sigma bonds are H-H. C-H, and C-C which have been studied extensively in the chemical and physical sciences, and are the driving force behind many industrial processes. Activation of a sigma bond requires a reduction in the energy necessary to break the bond, and historically this has involved an interaction with a transition metal. The selective activation of alkanes has been identified as one of the Holy Grails of current chemical investigation [1].
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    The kinetics and mechanisms of the copper (II) - catalyzed iron (III) - sulfur (IV) reaction in a chloride medium
    (Texas Tech University, 1972-08) Zeck, Otto Frank
    The object of the work reported in this dissertation is the mechanistic study of the oxidation of sulfur(IV) in acidic aqueous solutions. Iron(III) perchlorate was used as the oxidant, but the reaction was carried out in a chloride medium. Thus, the dominant iron(III) species was a monochloroiron(III) complex even though iron(III) was originally added as the perchlorate salt. The term, iron (III), is used to designate the reactive iron complex where the iron is in the +3 oxidation state. The reaction was found to be catalyzed by copper(II). Copper(II)- catalyzed reactions of hydrated iron(III) and sulfur(IV) have been previously studied, ' as have uncatalyzed reactions of iron(III) and sulfur(IV).2'^"1^ The possible products of the reaction are sulfate and dithionate ions. Under most conditions, both reactions 1 and 2 occur to give a mixture of dithionate and sulfate in solutions containing no catalysts.
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    The kinetics of endothermic solid state decompositions
    (Texas Tech University, 1970-12) Sveum, Larry K
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    The theory of nonisothermal kinetics
    (Texas Tech University, 1965-05) George, Thomas D.
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    Toxicological effects and kinetics of perchlorate on fishes
    (Texas Tech University, 2003-08) Park, June-Woo
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