Made available in DSpace on 2014-10-09T12:29:49Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:04Z (GMT). No. of bitstreams: 1 01354.pdf: 3623322 bytes, checksum: c718d54b73549c12892db727707c35bb (MD5) / Tese (Doutoramento) / IEA/T / University of Illinois Urbana - Champaign, Illinois

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Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2010 / Development of safe storage for reactive combustible materials to prevent possible human and environmental hazards as well as ensure and enhance industrial safety can significantly benefit from mathematical modelling of systems. In the recent past, models with varying degrees of sophistication have been developed and applied to the problem of predicting thermal criticality conditions, temperature and concentration profiles of such system. In this thesis, a model showing the temperature history of an nth order exothermic oxidation reaction in a slab of combustible material with variable pre-exponential factor, taking the consumption of the reactant into account in the presence of a convective heating and oxygen exchange at the slab surface with the ambient is presented Both transient and steady state problems are tackled The critical regime separating the regions of explosive and non-explosive paths of a one step exothermic chemical reaction is determined The governing nonlinear partial differential equations are solved numerically by method of lines (MOL), with finite difference schemes used for the discretisation of the spatial derivatives. Moreover, both fourth order Runge-Kutta numerical integration coupled with shooting methods and perturbation techniques together with a special type of Hermite-Pade series summation and improvement method were employed to tackle the steady state problem. The crucial roles played by the boundary conditions in determining the location ofthe maximum heating were demonstrated. In chapter one, the relevant applications together with previous published work on the problem were highlighted The basic mathematical theory and equations needed to tackle the problem were derived in Chapter two. In chapter three, the transient model problem was formulated, analysed and discussed. The steady state problem was formulated and solved in Chapter four. Furtherwork and concluding remarks were highlighted in Chapter five.

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Abstract The tightening environmental legislation and technological development in automotive engineering form a challenge in reactor design of catalytic reactors for automotive exhaust gas abatement. The catalytic reactor is the heart of the exhaust aftertreatment processes, but it can be seen also just as one subsidiary part of vehicles. The aim of this work is to reveal applicable kinetic models to predict behaviour of the particular catalysts and to establish guidelines for modelling procedures and experimentation facilitating catalytic reactor design, especially in the field of automotive exhaust gas abatement. The studies in this thesis include catalyst kinetics with synthetic exhaust gas composition in stoichiometric and net oxidative conditions, DRIFT measurements, and the warm-up of three-way catalysts in real conditions. Knowledge on surface concentrations facilitates kinetic model construction and discrimination. For example, identification of even semi-quantitative surface concentrations may lead to a successful falsification of incorrect kinetic model candidates. Especially, that is clearly seen in cases where models predict the same kind of gas phase behaviour but different kinds of surface concentration profiles. The transient kinetic experiments could give a hint on predominant reaction mechanism, support quantifying of the adsorption capacity and reveal the impact of surface phenomena on reactor dynamics. The level of model complexity should be adapted depending on the purpose of the model. For example, it is mostly convenient for reactor design purposes to perceive only one type of active sites even in a case of mechanical mixture of different catalytic materials; whereas the optimisation of catalyst content demands the management of every prominent site type separately. Or, when a catalytic material has been selected, the stationary kinetic model is, in most cases, adequate for the catalytic converter design and structural optimization for warm-up conditions.

It is well known fact that energy is a big issue for this world and substantial amount of research is going on worldwide for alternative fuels that are environmentally friendly, especially because of the fact that crude petroleum reserves are dwindling. Also, research on alternative fuels is essential for increased energy security. Biodiesel is a renewable, biodegradable, and nontoxic fuel. At present, when homogeneous catalysts are used, biodiesel is primarily produced in batch reactors in which the required energy is provided by heating accompanied by mechanical mixing. Alternatively, ultrasonic processing could be an effective way to attain required mixing while providing the necessary activation energy. We found that, using ultrasonication, a biodiesel yield in excess of 99% can be achieved in a short time duration of five minutes or less in comparison to one hour or more using conventional batch reactor systems. Homogeneous acid or base catalysts dissolve fully in the glycerol layer and partially in the fatty acid methyl esters (biodiesel) layer during the triglyceride transesterification process. Heterogeneous (solid) catalysts, on the other hand, can prevent catalyst contamination making product separation much easier. In the present work, one of the objective was to determine the transesterification kinetics of different pure metal oxide catalysts, mixed metal oxide catalysts, layered double hydroxides with their corresponding yield is presented. It was found that heterogeneous catalysts require much higher temperatures (215oC) and pressures to achieve acceptable conversion levels compared to homogeneous catalysts. For some of the mixed metal oxide solid catalysts a conversion level of 99% was observed. The present study also deals with the catalyst characterization on the basis of their acidity/ basicity and site strength, and surface area. Finally the deoxygenation of fatty acid methyl esters was carried out in order to upgrade the biodiesel. As a result, several aliphatic and aromatic hydrocarbons were detected in the mass spectrometric studies. This dissertation consists of five chapters. Chapter I presents a brief introduction to biodiesel production and the objectives of the study. Chapter II contains a review of literature. Chapter III contains the materials and methods used in this study. In this chapter different principles and theories will be mentioned with regard to the use of ultrasonication towards biodiesel production, reaction kinetics of biodiesel production, catalyst characterizations and thermodynamic analysis of deoxygenation of fatty acid methyl esters. Chapter IV presents the results and its discussions. Finally, Chapter V discusses the summary and conclusions of the study.

Maximizing enzymatic hydrolysis performance can be achieved through the combination of experimental work and modeling. The present work utilizes an enzymatic hydrolysis model based on reaction kinetics, Langmuir adsorption isotherms, and product inhibition of enzymes (β-glucosidase, cellobiohydrolase, and endoglucanase). The model was developed from a 10% w/w corn stover system. Glucose yield sensitivity to changes in parameter values was assessed and linked to biomass and enzyme characteristics. A commercial enzyme cocktail (CEC) was subsequently characterized by FPLC and gel electrophoresis to identify key enzymes/activities, and the CEC was used in the enzymatic hydrolysis of 20% w/w steam-exploded hardwood. The model was applied to experimental data from the enzymatic hydrolysis of the steam-exploded hardwood, which provided characteristic reaction rate and inhibition parameters consistent with cellulose and xylan hydrolysis. These model-based analyses enhanced understanding of hydrolysis at commercially relevant solids loadings, while identifying pathways to improve enzyme cocktails and enhance biomass conversion.

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