This study investigated the effects of temperature and humidity on the photocatalytic oxidation of volatile organic compound (VOCs) over titanium dioxide. Benzene, methyl tert-butyl ether (MTBE), perchloroethylene (PCE), and toluene were selected to investigate the influences of temperature and humidity on photocatalytic conversion. Among these four VOCs, benzene and MTBE were selected for the investigation of reaction pathways and kinetics. This work employed a self-designed annular packed-bed photocatalytic reactor to determine the conversion and reaction rates during photocatalytic degradation of VOCs. Degussa P-25 TiO2 was used as the photocatalyst and a 15 W near-UV lamp (350 nm) served as the light source. Benzene conversions increased with temperature below 160 ºC, but decreased above 160 ºC. Moreover, the conversions of MTBE increased with temperature from 30 to 120 ºC, and the thermocatalytic reaction began above 120 ºC. The conversions of PCE decreased as the temperature increased from 120 to 200 ºC. Toluene conversions almost remained constant at 100~200 ºC. Based on the gas-solid catalytic reaction theory, raising the reaction temperature could promote the chemical reaction rate and reduce reactant adsorption on TiO2 surfaces. The overall reaction rate increased with temperature, indicating that the reduction of reactant adsorption did not affect the overall reaction, and thus the chemical reaction was the rate-limiting step. As the chemical reaction rate gradually increased and the reactant adsorption decreased with temperature, the rate-limiting step could shift from the chemical reaction to the reactant adsorption, while the overall reaction rate decreased with temperature. Additionally, the competitive adsorption between VOCs and water for the active sites on TiO2 resulted in VOCs influent concentration and humidity promoting or inhibiting the reaction rate. The mineralization of benzene and the selectivity of CO and CO2 were not obviously affected under various temperatures, humidities, and influent benzene concentrations. The benzene mineralization ratios ranged from 0.85 to 1.0, to which CO and CO2 contributed approximately 5~20% and 80~95%, respectively. Temperature and humidity variation did not influence the photocatalytic reaction pathway of benzene. Acetone (AC) and tert-butyl alcohol (TBA) were two major organic products for the photocatalysis of MTBE. The addition of water transferred the reaction pathway from producing AC to TBA, while the temperature increase transferred the reaction pathway from producing TBA to AC. A modified bimolecule Langmuir-Hinshelwood kinetic model was developed to simulate the temperature and humidity related promotion and inhibition of the photocatalysis of benzene and MTBE. The competitive adsorption of VOCs and water on the active sites resulted in VOCs influent concentration and humidity promoting or inhibiting the reaction. The reaction rate constant increased with temperature while the adsorption equilibrium constants decreased, confirming that increasing reaction temperature enhanced the chemical reaction, but reduced the adsorption of VOCs and water. Furthermore, the correlation developed here was also used for determining the apparent activation energy of photocatalytic oxidation of VOCs and the adsorption enthalpies of benzene, MTBE, water vapor, and oxygen.

Thèse de doctorat : sciences. Chimie : Ecully, Ecole centrale de Lyon : 2005. / 27 réf.

Thèse de doctorat : sciences. Chimie : Ecully, Ecole centrale de Lyon : 2005. / Titre provenant de l'écran-titre. 27 réf.

The research presented in this dissertation focuses on understanding the dynamics of waves and currents in the presence of wave breaking. The simplest approach, direct numerical simulation of the ocean dynamics, is computationally prohibitive--waves typically have periods of tens of seconds, while currents vary on times from hours to days. This work uses a multi-scale asymptotic theory for the waves and currents (Craik and Leibovich, 1976; McWilliams et al., 2004}, similar to Reynolds-averaged Navier-Stokes, in order to avoid resolving the wave field. The theory decomposes the total flow into the mean flow (current) and fluctuations (waves), then takes a moving time average of the total flow equations to determine the wave forcing on the current. The main challenge is extending this theory to include a physical model for dissipative wave effects, notably breaking, in terms of the wave age, wind speed, and bottom topography. Wave breaking is difficult to observe, model, and predict, because it is an unsteady, non-linear process that takes place over disparate scales in both space and time. In the open ocean, white-capping often covers less than 2% of the surface, yet still plays an important role in the flux of mass, momentum, heat, and chemicals between the atmosphere and ocean. The first part of this dissertation proposes a stochastic model for white-capping events, and examines the stability of the ensemble average of these events. Near the shore, the decreasing ocean depth causes waves to overturn and break. Over time, this drives currents that erode sediment from beaches and deposit it around coastal structures. These currents are often so strong that their effect on the wave field, and thus their own forcing, is significant. A detailed analysis of this phenomena makes up the second part of this dissertation.

Cette thèse est consacrée à l'étude des processus d'ondes au voisinage des chocs dans les plasmas spatiaux. La propagation des ondes de Langmuir dans un plasma présentant des inhomogénéités aléatoires de densité a été modélisée numériquement; les résultats obtenus ont été comparés aux données des instruments WHISPER et WBD à bord des satellites CLUSTER. Les résultats de modélisation et l'étude statistique portant sur l'intensité des ondes de Langmuir observées dans le préchoc terrestre et le vent solaire ont montré que le théorème central limite n'est pas applicable aux statistiques sur l'intensité, du fait du nombre insuffisant d'inhomogénéités. Il en résulte que la fonction de distribution de probabilité pour le logarithme des énergies d'ondes n'atteint pas la distribution normale. D'autre part la détection à distance de la zone quasi-perpendiculaire du front de choc terrestre a pu être effectuée en analysant la modulation des ondes de Langmuir et celle des ondes électrostatiques avec fréquence décalée à proximité de la limite du pré-choc. Il a été montré que la probabilité d'observation de la non-stationnarité du front de choc augmente avec le nombre de Mach du choc. Enfin le rayonnement de transition des électrons relativistes au front de choc quasi-perpendiculaire a été calculé pour expliquer le mécanisme de l'émission électromagnétique observée par les satellites près du front de choc interplanétaire le 22 janvier 2004. Les paramètres du calcul correspondent aux véritables paramètres de l'évènement. Le spectre du rayonnement de transition établi théoriquement a son maximum dans le même domaine de fréquence que pour les mesures.

Semiconductor photocatalysis has received considerable attention in recent years as an alternative for treating water polluted with hazardous organic chemicals. The process, as a means of removal of persistent water contaminants such as pesticides, which exhibit chemical stability and resistance to biodegradation, has attracted the attention of many researchers. To a lesser extent, it has also been studied for decontamination of water containing toxic metals. Precious and common metals enter waters through washing, rinsing, pickling and surface treatment procedures of industrial processes, such as hydrometallurgy, plating and photography. As a result we are living in an environment with a multitude of potentially harmful toxic metal ions. In contrast, the demand for metals increases significantly with the development and growth of industry. Even though research on the photocatalytic recovery of waste and noble metals has escalated in the past 10 years, the practical implementation of these processes is not yet justified. The successful implementation of large scale reactors, for industrial application, has to consider several reactor design parameters that must be optimised, such as reactor geometry and the utilization of radiated energy. In this study the effect of various parameters such as initial platinum(IV)chloride concentrations, initial sacrificial reducing agent (ethanol) concentrations, catalyst (TiO2) concentration, pH, temperature and light intensity has been investigated as a first step towards optimising a photocatalytic batch and photocatalytic flow reactor. Langmuir–Hinshelwood kinetics has been applied to calculate the photocatalytic rate constant kr as well as the adsorption equilibrium constant Ke for both the initial platinum(IV) dependency as well as the initial ethanol concentration dependency. The results in this study may be used in future work for the optimisation and comparison of both batch and flow reactors towards the industrial implementation of these processes. / Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2012.

Semiconductor photocatalysis has received considerable attention in recent years as an alternative for treating water polluted with hazardous organic chemicals. The process, as a means of removal of persistent water contaminants such as pesticides, which exhibit chemical stability and resistance to biodegradation, has attracted the attention of many researchers. To a lesser extent, it has also been studied for decontamination of water containing toxic metals. Precious and common metals enter waters through washing, rinsing, pickling and surface treatment procedures of industrial processes, such as hydrometallurgy, plating and photography. As a result we are living in an environment with a multitude of potentially harmful toxic metal ions. In contrast, the demand for metals increases significantly with the development and growth of industry. Even though research on the photocatalytic recovery of waste and noble metals has escalated in the past 10 years, the practical implementation of these processes is not yet justified. The successful implementation of large scale reactors, for industrial application, has to consider several reactor design parameters that must be optimised, such as reactor geometry and the utilization of radiated energy. In this study the effect of various parameters such as initial platinum(IV)chloride concentrations, initial sacrificial reducing agent (ethanol) concentrations, catalyst (TiO2) concentration, pH, temperature and light intensity has been investigated as a first step towards optimising a photocatalytic batch and photocatalytic flow reactor. Langmuir–Hinshelwood kinetics has been applied to calculate the photocatalytic rate constant kr as well as the adsorption equilibrium constant Ke for both the initial platinum(IV) dependency as well as the initial ethanol concentration dependency. The results in this study may be used in future work for the optimisation and comparison of both batch and flow reactors towards the industrial implementation of these processes. / Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2012.

Thesis (Ph. D.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains viii, 144 p. : ill. (some col.). Includes abstract. Includes bibliographical references.

Stuttgart, Univ., Diss., 2000.

Thesis (M.S.)--U.S. Naval Postgraduate School, 1960. / "Controlled Thermonuclear Processes, UC-20" -t.p. "TID-4500 (15th Ed.)" -t.p. Includes bibliographical references (p. 26-27).