Conselho Nacional de Desenvolvimento Científico e Tecnológico, CNPq, Brasil

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1980. / Microfiche copy available in Archives and Science. / Bibliography: leaves 152-168. / by Melvin Bruce Fegley, Jr. / Ph.D.

As the world becomes increasingly interconnected, modernized, and populated, the demand for energy across the globe is growing at an unprecedented rate. This growth in energy demand has an undeniable impact on increasingly pressing social issues including, climate change, energy security, energy economy, atmospheric chemistry, and air quality. Finding a way to address these issues on a rapid timescale is more important than ever. A common thread running through all of these challenges is that they can be partially or fully addressed with the development of new chemical energy conversion technologies which, in turn, rely on a comprehensive understanding of gas phase kinetics. Examples of promising technologies include renewable fuels (i.e. methanol and hydrogen) and/or reliable, efficient, and clean engines that can accommodate renewable fuels. The development of such technology would enable the use of renewable fuels, thereby reducing emissions and cutting down on harmful byproducts released into the atmosphere. Computational simulations have become a powerful approach for developing and advancing energy technology in a safe, efficient, and effective manner. These computational approaches model reacting flows and are generally known as computational fluid dynamics (CFD). However, in order for these CFD simulations to work effectively and make meaningful predictions, the sub-models used to describe the underlying chemistry (gas phase kinetics) must be accurate; information about underlying chemistry is provided to computational simulations via a chemical kinetic model/mechanism, which describes the chemical reactions that drive the fuel oxidation within the system being simulated. Regarding combustion specifically, the reliability of predictive simulations depends on the availability of accurate data and models not only for chemical kinetics, but also thermochemistry and transport. Further complicating the problem, combustion and chemical kinetics provide a unique challenge in regard to obtaining accurate predictive models; underlying chemical kinetics mechanisms may require unprecedented accuracy to obtain truly predictive combustion modeling. For example, it has been shown in computational simulations that uncertainties in any of several kinetic parameters can yield uncertainties large enough in the physical system being modeled to cause system failure, thereby reducing the effectiveness of computational design approaches that could accelerate technology development. Hence, a strong need exists to develop a method that significantly reduces uncertainties in chemical kinetics parameters to meet the accuracy demands of advanced computational design tools. To this end, it is useful to draw on inspiration from existing methods in the field of combustion and chemical kinetics as well as tangential fields; the most compelling inspiration can be found in the field of thermochemistry in the form of the Active Thermochemical Tables (ATcT). This work presents a novel, analogous approach for chemical kinetics called MultiScale Informatics, or MSI for short. The MSI approach identifies optimized values and quantified uncertainties for a set of molecular parameters (within theoretical kinetics calculations), rate parameters, and physical model parameters (within simulations of experimental observables) as informed by data from various sources and scales. The overarching objectives of this work are to demonstrate how the MSI approach can be used to determine physically meaningful optimized kinetics parameters and quantified uncertainties, unravel webs of interconnected rate constants in complex reaction systems, resolve discrepancies among data sets, and touch on key elements of MSI’s implementation. To demonstrate how these objectives are met, the MSI approach is used to explore the kinetics of three reaction sub-systems. The studies of these sub-systems will demonstrate some key elements of this approach including: the importance of raw data for quantifying the information content of experimental data, the utility of theoretical kinetics calculations for constraining experimental interpretations and providing an independent data source, and the subtleties of target data selection for avoiding unphysical parameter adjustments to match data affected by structural uncertainties. For the first sub-system explored (CH₃ + HO₂), the MSI approach is applied to carefully selected (mostly raw) experimental data and yields an opposite temperature dependence for the channel-specific CH3 + HO2 rate constants as compared to a previous rate-parameter optimization. While both optimization studies use the same theoretical calculations to constrain model parameters, only the present optimization, which incorporates theory directly into the model structure, yields results that are consistent with theoretical calculations. For the second sub-system explored (HO₂ + HO₂), the MSI approach is applied to carefully selected experimental data, leveraging the hydrogen reaction system from the first study with the addition of high level theory calculations for the reaction of HO₂ + HO₂. Recent high-level theoretical calculations predict a mild temperature dependence for HO₂ + HO₂, which is inconsistent with state-of-the-art experimental determinations that upheld the stronger temperature dependence observed in early experiments. Via MSI analysis of the theoretical and experimental data, alternative interpretations of the raw experimental data that uses HO₂ + HO₂ rate constants nearly identical to theoretical predictions are identified – implying that the theoretical and experimental data are actually consistent, at least when considering the raw data from experiments. Similar analyses of typical signals from low-temperature experiments indicate that an HOOOOH intermediate – identified by recent theory but absent from earlier interpretations – yields modest effects that are smaller than, but may have contributed to, the scatter in data among different experiments. More generally, the findings demonstrate that modern chemical theories and experiments have progressed to a point where meaningful comparison requires joint consideration of their data simultaneously. The third sub-system explored builds a larger web of interconnected reaction systems in an attempt to achieve data redundancy and demonstrate how interpreting coupled reaction systems is necessary to accurately determine many key rate constants. The ability of the MSI method to interpret raw experimental data and untangle rate constant reaction systems is demonstrated. The study also reinforces how implementing theory into the model structure is imperative to yield results that are consistent with experimental data as well as theoretical calculations and achieve physically realistic branching ratios. Finally, this work will present how results from all the studied reaction systems culminate into a complex hydrogen/syngas combustion model validated against data from various combustion experiments.

Computational chemistry examination of the bond dissociation enthalpies of tungsten and main group elements. Includes quantification and calibration of theoretical methods to address the question of bond strengths including component σ and π molecular bonds.

M. Tech. Chemical and Metallurgical Engineering / Focuses on developing a reproducible, regenerable, effective and affordable adsorbent for the removal of fluoride, phosphorus and arsenic from water. The adsorption media should perform at room or low temperatures. To perform basic mathematical modelling to aid in adsorber design. The specific objectives are as follows: to apply a simple thermo-chemical process to convert limestone into a robust adsorption media ; to pelletize thermo-chemically converted limestone using organic binders ; to determine the effect of binders on arsenic, fluoride and phosphate removal from water and to apply basic models to interpret breakthrough results.

The research addresses two groups of reactions: chlorine atom reactions with fluorinated propenes and methyl amines. Most of the reactions were studied over a range of temperature and pressure with the goals of (i) assessing the potential importance of the reactions in atmospheric chemistry and (ii) obtaining kinetic and thermochemical information of fundamental physical–chemical interest. In the studies reported herein, laser flash photolysis (LFP) was coupled with time resolved atomic resonance fluorescence (RF) spectroscopic detection of chlorine atoms to investigate chlorine atom kinetics.

Here I report the hydrothermal chemistry of scandium, examining the behavior of the Sc³⁺ cation in various systems, including phosphates, phosphites, phosphonates and carboxylates. In total, 27 different materials, 23 of which are novel, have been synthesised and their structures solved. Seven different scandium phosphate-based materials have been successfully synthesised using amines and alkali hydroxides as structure directing agents, producing chain, layer and framework materials. Thermal analysis of these materials indicated that they were not stable upon removal of the template, because there are hydrogen bonding networks between the template and free OH groups on the phosphate groups. Certain conditions lead to the crystallization of either kolbeckite, Sc(PO₄).2H₂O, or a langbeinite-type structure, (NH₄)₂Sc₂(HPO₄)(PO₄)₂, which are dense frameworks. Investigation of scandium phosphites leads to the formation of more thermally stable frameworks. Investigation of scandium phosphite-based materials using different structure directing agents yielded three framework phosphite materials and one layered phosphite / phosphate. The use of lithium hydroxide and ethylenediamine within scandium phosphite systems resulted in the crystallization of a gainesite type framework, (LiSc(HPO₃)₂)and (H₃N(CH₂)₂NH₃)₂Sc₄(HPO₃)₈, which distorts in order to accommodate the amine, but not the lithium cation. Decreasing the potential for the formation of hydrogen bonding networks in the phosphite systems led to the formation of framework structures, however these structures did not retain their crystalline integrity upon removal of the template. In order to impart structure directing properties upon scandium-based materials but avoid the formation of hydrogen bonding networks upon which the crystalline integrity is dependent, scandium phosphonates were investigated. Seven different scandium phosphonate materials have been synthesised, two of which have been solved from powder diffraction data, and one from a combination of powder diffraction data, molecular modeling and single crystal data. Synthesis of scandium phosphonate materials yielded two thermally stable, porous materials with reversible water adsorption properties, NaSc(CH₃PO₃)₂•H₂O and Sc₂(O₃PCH₂(NHC₅H₁₀NH)₋CH₂PO₃)₃4H₂O. The success of this approach led to the examination of scandium carboxylate metal organic framework materials. The incorporation of Sc³⁺ into microporous carboxylate frameworks yielded three aliphatic scandium carboxylates and six aromatic scandium carboxylates. The scandium analogue of MIL-53 shows potential for gas adsorption studies, as well as illustrating that scandium carboxylates can be isostructural to metal carboxylate materials already published. The scandium terephthalate, Sc₂(O₂CC₆H₄CO₂)₃, is a small pore framework material with an unprecedented structure type, the adsorption properties of which have been examined using a variety of different small gas molecules and hydrocarbons, including X-ray analysis of the structures whilst adsorbing different molecules. ⁴⁵Sc MAS NMR has been performed on the materials prepared pure and characterized in this thesis, in order to establish a library of chemical shifts for scandium in different framework environments.

Characterizing the interactions of solvent molecules with ions is fundamental in understanding the thermodynamics of solution chemistry. These interactions are difficult to observe directly in solution because the number of solvent molecules far exceed that of ions. This lend the gas phase to be the ideal medium in the study ion-solvent interactions on a molecular level. Ionized polycyclic aromatic hydrocarbon (PAH) molecules can readily form hydrogen bonds with neutral solvent molecules in aqueous and interstellar medium. Previous research has been done for stepwise solvation of small molecules such as benzene+, pyridine, and phenylacetylene. The similarity in these results show that these organic ions can be considered prototypical model systems for aromatic ion-neutral solvent interactions. The goal of this dissertation is to demonstrate that naphthalene can act as a prototypical model of PAH ions for ion-solvent interactions. Two types of experiments are considered throughout this dissertation using ion mobility mass spectrometry: (1) ion-neutral equilibrium thermochemistry and (2) mobility measurements. For thermochemistry experiments, the naphthalene radical cation was injected into the drift cell containing helium and/or neutral solvent vapor and the enthalpy and entropy changes were measured by varying the drift cell temperature and measuring the equilibrium constants. The results of these studies showed that small polar molecules bind to naphthalene with similar energy based on the measured by the enthalpy changes. Unsaturated aliphatic molecules behave similarly, but with much lower binding energy. Aromatic ions tend to bind to the naphthalene with lower binding energy than that observed with the benzene ion. The results for small polar molecules were compared to similar studies using the phenyl cation. The second series of experiments required the coexpansion of the naphthalene and benzene or pyridine. Injecting theses dimers into the drift cell allowed the measurement of reduced mobility on the dimers at a series of temperatures. These were used to calculate the average collision cross section and thus give insight in to the structure of these aromatic dimers. Structures were determined by comparing these results to those predicted by DFT calculations.

A química do selênio é um assunto de crescente interesse devido a sua presença em diversos ambientes químicos, em particular, na atmosfera terrestre. A ausência de estudos sobre espécies relativamente simples contendo 2-4 átomos motivou este projeto, que se concentrou na investigação teórica rigorosa de uma serie de espécies moleculares: SeF, SeCl, SeBr, HSeF, HFSe, HSeCl, HClSe, HSeBr, HBrSe e de vários isômeros na superfície de energia potencial 1[H, S, Se, Cl]. Propriedades espectroscópicas de um conjunto de estados eletrônicos e o calor de formação das moléculas SeF, SeCl e SeBr foram determinados. Juntamente com os novos resultados desta investigação, sugerimos uma revisão e correção de alguns dados teóricos e experimentais da literatura. Aspectos energéticos, estruturais e espectroscópicos associados aos pontos estacionários nas superfícies de energia potencial singleto [H, Se, X], X = F, Cl e Br, e [H, S, Se, Cl] também foram caracterizados, assim como determinados os calores de formação dos isômeros mais estáveis. Barreiras energéticas para os vários processos de isomerização foram estimadas bem como o gasto energético envolvido nas diferentes possibilidades de dissociação dos isômeros mais estáveis. No caso dos sistemas triatômicos ainda estimamos as constantes de velocidade para as reações de isomerizações direta e reversa. Nesse contexto, esperamos que este trabalho possa servir como uma referência para estudos teóricos e experimentais futuros desses sistemas e/ou de outros de complexidade idêntica. / The chemistry of selenium is a subject of increasing interest due to its presence in many chemical enviroments, specially in the Earth\'s atmosphere. The lack of studies of relatively simple species containing 2-4 atoms has motivated this project which was focused on a rigorous theoretical investigation of a series of molecular especies: SeF, SeCl, SeBr, HSeF, HFSe, HSeCl, HClSe, HSeBr, HBrSe, and the isomers on the 1[H, S, Se, Cl] potential energy surface. Spectroscopic properties of a set of electronic states and the heat of formation of SeF, SeCl, and SeBr were determined. Along with the new results from this investigation, we showed that some theoretical and experimental data reported in the literature be revised and corrected. Energetic, structural, and spectroscopic aspects associated with the stationary points on the singlet potential energy surfaces [H, Se, X], X = F, Cl e Br, and [H, S, Se, Cl] were also characterized, and the heats of formation of the most stable isomers evaluated. Energetic barriers for the various processes of isomerization were estimated, as well as the energy involved in the dierent possibilities of dissociation of the most stable isomers. In the case of triatomic systems, we still estimated the rate constants for the direct and reverse reactions. In this context, we expect that this work should serve as reference in future theoretical and experimental studies on these systems and/or others of similar complexity

Les systèmes de stockage thermochimique s’avèrent être de bonnes alternatives aux technologies actuelles pour le stockage saisonnier ou intersaisonnier de la chaleur, car l’énergie est stockée sous forme d’un potentiel chimique et donc, il n’y a pas de pertes thermiques pendant la durée de stockage. Un grand nombre d’études a été mené sur le développement de réacteurs thermochimiques intégrés au système de stockage, et peu d’étude ont été menées sur les technologies de réacteur séparé du réservoir de stockage. Ces dernières présentent cependant l’avantage, entre autres, de dissocier la puissance thermique du réacteur et la capacité de stockage de l’installation, ce qui permettrait d’augmenter la densité de stockage.Cette étude se penche sur le développement d’un réacteur thermochimique à lit mobile fonctionnant avec des sels hydratés sous air humide, adapté à des applications aux réseaux de chaleur. Un prototype de réacteur, développé et construit durant cette étude, a permis d’analyser le fonctionnement du réacteur. Cette étude a, entre autres, mis en évidence l’impact des passages préférentiels de l’air sur les performances du réacteur (température et puissance), ainsi que l’importance du titre de vapeur de l’air à l’entrée du réacteur sur ces performances. Il apparaît également que la circulation du solide abaisse sensiblement le point d’équilibre atteint par la réaction.De plus, deux modèles mathématiques ont été développés : un modèle analytique 1D et un modèle 2D prenant en compte les phénomènes de transfert de matière et de chaleur au sein de la zone réactive. Le modèle 2D, validé avec les résultats expérimentaux, a été exploité à l’aide du logiciel de simulation par éléments finis COMSOL Multiphysics afin de mener une étude théorique sur le fonctionnement et les performances du réacteur. Cette étude numérique a porté sur l’influence des conditions opératoires (débit et taux d’humidité de l’air, vitesse du solide) sur les performances et le rendement du système et a permis la comparaison des réacteurs à lit mobile par rapport aux réacteurs à lit fixes, communément développés pour des applications de stockage thermochimique. Cette étude a montré l’importance de la régulation de la vitesse du solide pour l’optimisation des performances du réacteur à lit mobile.L’ensemble de cette étude a permis de mettre en évidence les avantages et les limitations d’un réacteur à lit mobile pour des applications de stockage thermochimique / Thermochemical storage systems prove to be good alternatives to current technologies for seasonal or inter-seasonal storage of heat, because energy is stored as a chemical potential and therefore, there is no heat loss during the storage period. Nowadays, a large number of studies have been conducted on the development of thermochemical reactor integrated in the storage system, andlittle study has been conducted on reactor technologies separated from the storage system. The latter, however, have the advantage, among others, of separating the thermal power produced or consumed and the storage capacity of the installation, which would increase the storage density.This study investigates the development of a moving-bed thermochemical reactor operating with hydrated salts and humid air cross-flow, suitable for district heating applications. A reactor prototype, developed and built during this study, allowed to analyze the functioning of the reactor. This study has, among others, highlighted the impact of the preferential air flow path on the reactorperformances (temperature and power), as well as the importance of the air humidity at the reactor inlet on these performances.In addition, two mathematical models have been developed : a 1D analytical model and a 2D model taking into account the heat and mass transfer phenomena within the reactive area. The 2D model, validated with the experimental results, was exploited using the finite element simulation software COMSOL Multiphysics to conduct a theoretical study on the functioning and the performances of the reactor. This numerical study focused on the influence of operating conditions (air flow rate and moisture content, solid flow rate) on the performances and the efficiency of the system and allowed the comparison of moving bed reactor over fixed bed reactors, commonly developed for thermochemical storage applications. This study has shown the importance of solid velocity control for optimizing the performances of the moving bed reactor.This study has highlighted the advantages and limitations of moving bed reactors for thermochemical storage applications