En el campo de la cinética de la pirólisis de biomasa se han desarrollado numerosos trabajos de investigación que no acaban de resolver aspectos básicos del proceso. El análisis de resultados termogravimétricos aún requiere el establecimiento de modelos y estrategias de evaluación más apropiadas para los diferentes tipos de biomasa. Esta tesis trata todos estos aspectos desde el punto de vista de la investigación fundamental. Se estudia el comportamiento térmico de biomasas representativas de los residuos de carpintería (madera de pino y haya) y de un cultivo energético (cardo borriquero) por medio de diferentes técnicas termoanalíticas, en el régimen de pirólisis lenta (slow pyrolysis), incluyendo varios pretratamientos de la biomasa para eliminar materia inorgánica y componente extractivo. La primera contribución de esta tesis corresponde a un estudio exhaustivo del efecto de los errores sistemáticos asociados a la experimentación en termogravimetría. El comportamiento térmico de un mismo material es observado en diferentes termobalanzas, bajo condiciones que se consideran equivalentes entre diferentes equipos, y los resultados son analizados estadísticamente. Consecutivamente, para la descripción de la pérdida global de masa, se estudian diferentes aproximaciones cinéticas basadas en reacciones parciales de primer y otros órdenes, por el modelo de pseudocomponentes. Se trata de determinar un conjunto común de parámetros cinéticos que describan satisfactoriamente experimentos provenientes de diversas termobalanzas y bajo diferentes regímenes de calentamiento: lineal y en escalera (aplicación sucesiva de rampas y periodos isotérmicos de calentamiento). Un conjunto común de energías de activación, resultado de la evaluación cinética de muestras pretratadas (lavadas con agua a 80 ºC), es aplicado en la descripción cinética de todos los tipos de experimentos llevados a cabo a lo largo de la tesis.Espectrometría de masas, acoplada simultáneamente a la termogravimetría, es la técnica empleada para el análisis de los productos volátiles. Se aplica una herramienta estadística para analizar la influencia de la composición de las muestras en la descomposición térmica global y en la distribución de productos. Por medio de datos de calibración se estima la producción individual de los principales productos volátiles de la pirólisis. Consecutivamente, se incluye una aproximación de la evolución de dichos productos en el modelo cinético global.El estudio de las reacciones secundarias de pirólisis ha sido también parte importante en esta tesis. A través de la calorimetría diferencial se estudia el calor de reacción de la descomposición primaria y secundaria. Adicionalmente, se analizan los resultados provenientes de un estudio de espectroscopía infrarroja acoplada a termogravimetría, con el objeto de investigar la descomposición secundaria mediante la observación de los perfiles de evolución de los productos volátiles. Finalmente, se prueba y optimiza el desempeño del modelo cinético global para describir la descomposición térmica de muestras bajo condiciones que claramente favorecen la descomposición secundaria.En conjunto, este trabajo de investigación representa un estudio termocinético exhaustivo y profundo de la pirólisis de biomasa. La descomposición térmica se aborda a través de la observación de la interconexión entre los diferentes fenómenos químicos que conforman el proceso. La propuesta de aproximación cinética, que se constituye a lo largo de la tesis, contribuye al entendimiento del proceso como un todo. Puede ser también considerada como un primer paso hacia la aplicación de los modelos cinéticos de pirólisis a otros estudios, requiriéndose la incorporación adicional de fenómenos de transporte y otras consideraciones para su posterior aplicación. / The abundant research literature on the field of biomass pyrolysis kinetics still leaves key issues unsolved. The exploitation of the information provided by thermogravimetry requires the establishing of appropriate models and evaluation strategies for the various biomass materials. The kinetic description of experiments measured at different conditions by exactly the same reaction kinetics is criticized due to some small, but inevitable systematic errors that depend on the experimental conditions. Practical models that predict the evolution of specific products of interest are still expected in the literature. Part of the chemical phenomena referred to the secondary interactions between the primary pyrolysis products has been traditionally avoided when modeling the pyrolytic process. The increased exploitation of herbaceous crops, in addition to the large quantity of woody residues that still remains largely unused, currently ask for a better description of the influence of the heterogeneities on biomass thermolysis.This thesis addresses all these issues in the context of fundamental research. The thermal behavior of biomass materials representative of carpentry residues (pine and beech), and an energy plantation (thistle) is studied by different thermoanalytical techniques, within the range of slow pyrolysis, including various pretreatments to eliminate inorganic matter and extractives. The first contribution aims at deeply observing the extent of systematic errors associated to the experimental part of the thermogravimetric studies. The thermal behavior of the same feedstock in different original equipments, under roughly equivalent experimental conditions, is statistically studied. Then, various approaches based on first and nth-order partial reactions in the summative model of pseudocomponents are employed in order to determine the best kinetic parameters that describe the experiments both at linear and stepwise heating programs and for experiments coming from different sources. A common set of activation energies, coming from the evaluation of water-washed samples, is applied for the kinetic description of all the types of experiments performed along this thesis.Mass spectrometry, simultaneously coupled to thermogravimetry, is used as the volatile product analysis technique. A chemometric tool is applied to help in elucidating the specific influence of the macromolecular composition of the samples on the thermal decomposition and on the product distribution. Making use of calibration data, we estimate the individual production of the major volatile species from slow pyrolysis. Then, an approximation of the vapor-phase product distribution is added to the kinetic mechanism.We are also interested in the study of the secondary biomass pyrolysis. Differential scanning calorimetry is the technique used to observe the information traced by the heat of pyrolysis on the primary and secondary decomposition. Additionally, we analyze results from a Fourier transform infrared spectroscopy device coupled with thermogravimetry, in order to assess the secondary phenomena by considering the evolution profiles of the volatile products, as well. Finally, we test the ability of the best kinetic approach, from the previous kinetic analysis, to describe the global mass loss under conditions that clearly favor secondary vapor-solid interactions.Overall, this research work represents a comprehensive and thorough thermokinetic study of biomass pyrolysis that approaches the thermal behavior by recognizing the connections between different chemical phenomena making up the pyrolytic process. The kinetic proposal, finally built up in this thesis, is a contribution for understanding the process as a whole. Additionally, it can be considered as a first step toward its extension to practical applications, where additional chemical and transport phenomena need to be incorporated.

Advanced oxidation processes (AOPs) are commonly used for the destruction of persistent trace organic contaminants (TOrCs) that survive conventional wastewater treatment processes. Three types of AOPs, UV/H2O2, sunlight photolysis and photo-Fenton are experimentally investigated and mathematically quantified to anticipate the fate of TOrCs during oxidation processes, specifically addressing the significant effect of reaction by-products and water matrix on oxidation efficiencies. Hydrogen peroxide UV photolysis is among the most widely used AOPs for the destruction of TOrCs in waters destined for reuse. Previous kinetic models of UV/H2O2 focus on the dynamics of hydroxyl radical production and consumption, as well as the reaction of the target organic with hydroxyl radicals. In this work, we build a predictive kinetic model for the destruction of p-cresol by hydrogen peroxide photolysis based on a complete reaction mechanism that includes reactions of intermediates with hydroxyl radicals. The results show that development of a predictive kinetic model to evaluate process performance requires consideration of the complete reaction mechanism, including reactions of intermediates with hydroxyl radicals. Applying the model to an annular flow-through reactor with reflecting walls, the model mathematically demonstrates that the wall reflectivity significantly enhances the rate of conversion of the target, accounting for the UV light reflection from the reacting walls, as well as the hydrodynamics of the annular flow. Direct and indirect sunlight photolysis is critically important in the breakdown of contaminants in effluent wastewater. The fate of a suite of TOrCs and estrogenic activity were investigated in an effluent-dependent stream. Some TOrCs, which are not sufficiently attenuated through biodegradation and soil adsorption were destructed obviously with distance of travel in the stream. Independent experiments, conducted in batch reactor with 17α-ethinylestradiol (EE2) spiked in effluent showed that attenuation of estrogenic compounds maybe due in part to indirect photolysis caused by formation of reactive species from sunlight absorption. Further investigation was conducted using selective probe compounds to characterize reactive species. And results showed that singlet oxygen generated from excited state of effluent organic matter was responsible for essentially all observed transformations of targets in the effluent in Tucson. To mathematically quantify the photo-Fenton AOP, a kinetic model is proposed for the photolysis of Fe3+ hydroxo complexes at low pH (pH ≤ 3.0). The model incorporates elementary reactions of the Fenton-like and UV/H2O2 system. Iron speciation and photochemical parameters, including the molar absorptivities of light-absorbing species and the quantum yields of Fe3+ and FeOH2+ hydrolysis are experimentally validated. However, the predicted, time-dependent Fe2+ concentrations during Fe3+ photolysis are much lower than measured. The possible missing elements in the model could be (i) quenching of OH radicals by unknown species, or/and (ii) shielding of Fe2+ by unknown compounds at the beginning of the process.

Surface-bound particulates containing radionuclides in the environment can become airborne through the process of resuspension. Once airborne, these radionuclides can be inhaled or ingested to deliver an internal dose of ionizing radiation. To that end, the resuspension factor method is a powerful tool for predicting a person's exposure to airborne particles from surface contaminations, and therefore is used to determine protective and intervening measures. The resuspension factor is calculated as the ratio measured airborne to surface mass concentration and has been found to generally decrease exponentially with time. Current models of the resuspension factor are empirical and have failed to predict recent measurement, motivating a stronger basis and physical model for the system. Additionally, federal guidances conservatively suggest an unphysical model of particulate radioactivity impact wherein the entirety of the radiation is absorped. For this dissertation, two- and three-compartment catenary models were derived which build on measured resuspension rate constants under various influences. These models were fit to a set of historic observations of resuspension factors using an instrumental uncertainty-weighting to resolve the large variances early in time which otherwise inflate calculations. When compared to previous resuspension models, our physical models better fit the data achieving reduced-chi-squared closer to 1. An experiment was undertaken to validate our basic environment resuspension models in an urban environment without wind. A resuspension chamber is constructed by placing an acrylic tube atop a poured concrete surface and lowering a low-volume air sampler head from above. Europium oxide powder was dispersed upon the surface or from above the air sampling height to emulate ideal compartmentalized release scenarios, and air is sampled on an hourly, daily, or weekly basis. Sampler filters then were evaluated for Europium content using neutron activation and gamma spectroscopy. Hourly measurements following airborne release are within an order of magnitude of early-timeframe historic resuspension factors (~10^−6 m^−1), whereas daily and weekly measurements from surface release demonstrate a gradual decrease in resuspension factor (∼10^−8 m^−1). These results support a need to critically assess the resuspension factor definition and its relationship to "initial suspension" and the indoor background, non-anthropogenic resuspension. Finally, a simulated model was generated to demonstrate loss of alpha radiation from relevant transuranic radioparticles. This was accomplished using the Geant4 Monte Carlo particle transport code. This basic model demonstrated a clear loss of average intensity and energy of exiting particles which are both directly related to the absorped dose. The data shows a loss from 10 to 90% of intensity to occur at particle sizes approaching the range of alphas within them, and a loss of roughly half the initial alpha energy at around the same particle sizes. The results establish a first-order baseline for a particulate self-absorption model which complement existing dosimetry models for inhaled radionuclides.

This investigation provides a comprehensive experimental dataset and kinetic model for biomass gasification, over a wide temperature range (1150-1350 °Ï¹) in CO2, H2O and the combination of these two reactant gases over the mole fraction ranges of 0 to 0.5 for H2O and 0 to 0.9 for CO2. The data come from a unique experimental facility that tracks continuous mass loss rates for poplar wood, corn stover and switchgrass over the size range of 6-12.5 mm. In addition, the data include char size, shape, surface and internal temperature and discrete measurements of porosity, total surface area, pore size distribution and composition. This investigation also includes several first-ever observations regarding char gasification that probably extend to char reactivity of all types and that are quantified in the model. These include: the effect of ash accumulation on the char surface slowing the apparent reaction rate, changes in particle size, porosity and density as functions of burnout, and reaction kinetics that account for all of these changes. Nonlinear least-squares regression produces optimized power-law model parameters that describe gasification with respect to both CO2 and H2O separately and in combination. A single set of parameters reasonably describes rates for all three chars. Model simulations agree with measured data at all stages of char conversion. This investigation details how ash affects biomass char reactivity, specifically the late-stage burnout. The ash contents ratios in the raw fuels in these experiments are as high as 40:1, providing a clear indication of the ash effect on the char reactivity. The experimental results definitively indicate a decrease in char reaction rate with increasing initial fuel ash content and with increasing char burnout -- most pronounced at high burnout. This investigation postulates that an increase in the fraction of the surface covered by refractory material associated with either higher initial ash contents or increased burnout decreases the surface area available for reaction and thus the observed reaction rate. A quantitative model that includes this effect predicts the observed data at any one condition within the data uncertainty and over a broad range of fuel types, particle sizes, temperatures, and reactant concentrations slightly less accurately than the experimental uncertainty. Surface area, porosity, diameter, and density predictions from standard models do not adequately describe the experimental trends. Total surface area increases slightly with conversion, with most of the increase in the largest pores or channels/vascules not measurable by standard surface area techniques but most of the surface area is in the small pores. Porosity also increases with char conversion except for abrupt changes associated with char and ash collapse at the end of char conversion. Char particle diameters decrease during these kinetically controlled reactions, in part because the reaction is endothermic and therefore proceeds more rapidly at the comparatively warmer char surface. SEM images qualitatively confirm the quantitative measurements and imply that the biomass microstructure does not appreciably change during conversion except for the large pore diameters. Extant char porosity, diameter, surface area, and related models do not predict these trends. This investigation suggests alternative models based on these measurements.

This investigation provides a comprehensive experimental dataset and kinetic model for biomass gasification, over a wide temperature range (1150-1350 °Ï¹) in CO2, H2O and the combination of these two reactant gases over the mole fraction ranges of 0 to 0.5 for H2O and 0 to 0.9 for CO2. The data come from a unique experimental facility that tracks continuous mass loss rates for poplar wood, corn stover and switchgrass over the size range of 6-12.5 mm. In addition, the data include char size, shape, surface and internal temperature and discrete measurements of porosity, total surface area, pore size distribution and composition. This investigation also includes several first-ever observations regarding char gasification that probably extend to char reactivity of all types and that are quantified in the model. These include: the effect of ash accumulation on the char surface slowing the apparent reaction rate, changes in particle size, porosity and density as functions of burnout, and reaction kinetics that account for all of these changes. Nonlinear least-squares regression produces optimized power-law model parameters that describe gasification with respect to both CO2 and H2O separately and in combination. A single set of parameters reasonably describes rates for all three chars. Model simulations agree with measured data at all stages of char conversion. This investigation details how ash affects biomass char reactivity, specifically the late-stage burnout. The ash contents ratios in the raw fuels in these experiments are as high as 40:1, providing a clear indication of the ash effect on the char reactivity. The experimental results definitively indicate a decrease in char reaction rate with increasing initial fuel ash content and with increasing char burnout -- most pronounced at high burnout. This investigation postulates that an increase in the fraction of the surface covered by refractory material associated with either higher initial ash contents or increased burnout decreases the surface area available for reaction and thus the observed reaction rate. A quantitative model that includes this effect predicts the observed data at any one condition within the data uncertainty and over a broad range of fuel types, particle sizes, temperatures, and reactant concentrations slightly less accurately than the experimental uncertainty. Surface area, porosity, diameter, and density predictions from standard models do not adequately describe the experimental trends. Total surface area increases slightly with conversion, with most of the increase in the largest pores or channels/vascules not measurable by standard surface area techniques but most of the surface area is in the small pores. Porosity also increases with char conversion except for abrupt changes associated with char and ash collapse at the end of char conversion. Char particle diameters decrease during these kinetically controlled reactions, in part because the reaction is endothermic and therefore proceeds more rapidly at the comparatively warmer char surface. SEM images qualitatively confirm the quantitative measurements and imply that the biomass microstructure does not appreciably change during conversion except for the large pore diameters. Extant char porosity, diameter, surface area, and related models do not predict these trends. This investigation suggests alternative models based on these measurements.

The objective of this dissertation is the development of computer simulation-based models for the modeling of upper ionosphere, starting from the first principles. The models were validated by exact analytical benchmarks and are seen to be consistent with experimentally obtained results. This area of research has significant implications in the area of global communication. In addition, these models would lead to a better understanding of the physical processes taking place in the upper ionosphere.

Rapid consumption of energy storage and serious environmental pollution demand more advanced combustion strategies and more renewable fuels. Development of chemical kinetic models and suitable selection of fuels are key factors in evolving and optimizing new engine and combustion concepts. Alkenes are typical composition of gasoline as well as typical intermediates in the oxidation of larger alkanes and alcohol, while isoprene is one of the important alkenes impacting both the atmospheric pollution and energy depletion. Isoprene is one of the most important species in the atmosphere chemistry, dominating the carbon flux emitted by vegetation and accounting for forty percent of non-methane biogenic emissions globally. Isoprene has been recognized not only as a noteworthy precursor to polycyclic aromatic hydrocarbons but also as a promising fuel additive. Isoprene has been extensively investigated in the atmosphere chemistry, but its role as a critical diolefin in combustion chemistry has received less attention. Only A few researchers studied isoprene chemistry by carrying out pyrolysis experiments and theoretical calculations. To better understand the combustion chemistry of isoprene, this work presents a detailed experimental and kinetic modeling investigation. This study explored the chemical kinetics of isoprene oxidation in ignition delay times and speciation measurements. Our shock tube experiments for ignition delay times covered the temperatures of 680 – 1470 K, pressures of 1 – 30 bar, and equivalence ratios of 0.5 – 2. We measured laser-based time-resolved CO speciation in a low-pressure shock tube at temperatures of 900 – 1470 K, pressures of 1 and 4 bar, and equivalence ratios of 0.5 and 1. Major species concentrations were measured in a jet-stirred reactor at 680 – 1280 K, 1 bar, and φ = 0.5 – 2. Afterwards, we used 1,3-butadiene as a basis to develop fuel-specific isoprene sub-mechanism and coupled it with a C0-C5 core sub-mechanism. Finally we developed a comprehensive kinetic model including 1585 species and 6884 reactions and achieved a good agreement between the model’s predictions and the experiments. To our knowledge, this study is the first comprehensive effort to describe the process and provides valuable insights into isoprene oxidation. The work reported in the thesis also facilitates the better understanding of combustion chemistry of diolefins.

Presence of inclusions in high manganese steel are a major concern in the steel making industry, since these particles affect the processing and properties of the steel. During the refining of high manganese steel in the ladle furnace, the types of inclusions present and their growth in the liquid steel, or during solidification of the steel, caused by the addition of manganese and other alloying elements are to be examined. This research developed a kinetic model for the presence and growth of inclusions in the liquid high manganese steel for the ladle metallurgy process. The diffusion of dissolved elements, and the seed of inclusions for the growth and consumption of inclusions, were both addressed in the model. The present model for inclusions was coupled to the updated kinetic model for slag-steel reactions in the ladle furnace for high manganese steel. The coupled model allows for verifying the process analysis plant data for the highest manganese concentration presently available in the steel industry. Finally, an analysis of the coupled kinetic model was performed to compare the effect of the different processing conditions, and the presence and growth of inclusions in the high manganese steel from the ladle metallurgy process. / Thesis / Master of Applied Science (MASc)

In biochemical networks, complex dynamical features such as superlinear growth and oscillations are classically considered a consequence of autocatalysis. For the large class of parameter-rich kinetic models, which includes Generalized Mass Ac- tion kinetics and Michaelis-Menten kinetics, we show that certain submatrices of the stoichiometric matrix, so-called unstable cores, are sufficient for a reaction network to admit instability and potentially give rise to such complex dynami- cal behavior. The determinant of the submatrix distinguishes unstable-positive feedbacks, with a single real-positive eigenvalue, and unstable-negative feedbacks without real-positive eigenvalues. Autocatalytic cores turn out to be exactly the unstable-positive feedbacks that are Metzler matrices. Thus there are sources of dynamical instability in chemical networks that are unrelated to autocatalysis. We use such intuition to design non-autocatalytic biochemical networks with su- perlinear growth and oscillations.

Master of Science / Department of Grain Science and Industry / Subramanyam Bhadriraju / During heat treatment, the ambient temperature of grain-processing facilities is raised to 50-60°C for at least 24 hours to manage stored-product insects. Young larvae (first instars) of the red flour beetle, Tribolium castaneum (Herbst), are the most heat tolerant stage at 50-60°C. A thermal death kinetic (TDK) model predicted survival of T. castaneum young larvae exposed to six constant elevated temperatures between 42 and 60ºC. The model is based on logarithmic survival of T. castaneum as a function of time and logarithmic reduction in larval survival as a function of temperature. The model was validated with 12 independent temperature datasets collected during heat treatments of pilot-scale and commercial grain-processing facilities. Young larval survival in plastic boxes/vials with flour was used to validate model predictions. The heating rate to 50°C from the ambient among the 12 datasets ranged from 0.9-7.8°C/h. Mean absolute deviations between observed and predicted larval survival for 10 of the 12 datasets ranged from 2.1-11.4%; it was 16.2 and 18.3% for two other datasets. The TDK model can be used to predict survival of young larvae of T. castaneum based on time-dependent temperature profile obtained at any given location during heat treatment of grain-processing facilities. In three commercial grain-processing facilities heat treatments were conducted for 24-27.7 hours using forced-air gas heaters. Temperatures attained and survival of 20 eggs, 20 young larvae, and 20 adults of T. castaneum in bioassay vials at various locations were determined. Across all three facilities, 5 out of 2720 adults in 136 vials, 1 out of 960 young larvae in 48 vials, and 0 out of 1760 eggs in 88 vials were alive at the end of the heat treatment. In each facility, the time in hours for 1% predicted survival of T. castaneum young larvae was positively related to how quickly temperatures reached 50°C, and negatively related to rate of heating to 50°C from the ambient, time above 50°C in hours, and the maximum temperature. Bioassays with T. castaneum life stages and the TDK model can be used to gauge effectiveness of facility heat treatments.