A free energy formalism is developed in order to describe phase equilibria in binary alloys. The proposed phenomenological approach uses a limited number of experimental data to provide a global thermodynamic description of a system including its equilibrium and metastable phase diagrams. Emphasis is placed on the description of short range order by means of the cluster variation method. A microscopic theory is also developed in order to predict the enthalpies of formation of transition metal alloys as well as the short range order dependence of these enthalpies. The theory uses a tight-binding Hamiltonian together with the generalized perturbation method. 0ff~diagonal disorder is taken into account, and charge transfer is treated self consistently in the random alloy. All input parameters to the theory are obtained from ab-initio calculations for the pure elements. In this regard, the model can be considered parameter free. The phenomenological approach has been used to analyzed the Al-Ni, Ni~Cr, and Al~Li systems. It is found that the vibrational entropy of‘ formation plays an important role in the thermodynamics of the Al-Li and Ni-Cr alloys. The approach allows an accurate description of stable and metastable order-disorder or order-order equilibria existing in the Ni-Al or AL~Li systems. The model is used to predict a metastable clustering tendency in Al-Li alloys which appears to have been recently confirmed by experiment. The microscopic theory has been applied to the VB-VIE and IVB-VIIIB (Ni, Pt, Pd) alloys. The calculations are in good agreement with the available experimental data and phase diagram information. It is shown that off-diagonal disorder and electronic self-consistency play a crucial role in the accuracy of the results.

Le lithium est une matière première en demande croissante suite au fort développement des appareils nomades et des véhicules électriques. Ce manuscrit s’intéresse à la production de lithium à partir d’une ressource naturelle : les saumures lithinifères. Une étude bibliographique sur l’extraction du lithium présent dans les saumures a mis en avant que cette dernière requiert des quantités importantes d’énergie, d’eau et de réactifs. Cela met ainsi en évidence l’enjeu environnemental et la nécessité d’améliorer les procédés existants. A cette fin, la présente étude allie la modélisation à un travail expérimental. Le modèle sélectionné pour calculer les coefficients d’activité des éléments dissous dans les saumures est le modèle de Pitzer (1991). Un travail de paramétrisation a été effectué pour mettre au point une base de données thermodynamiques disposant des éléments nécessaires (propriétés des sels, paramètres d’interaction) à la description des systèmes électrolytiques d’intérêt. Après un travail de validation appuyé sur des données expérimentales issues de la bibliographie, cette base de données, associée au logiciel PhreeqC pour les calculs géochimiques, permet de simuler différentes transformations des saumures (dilution, évaporation, ajout de réactifs). L’outil mis en place a permis d’analyser des scenarios exploratoires de production de zabuyelite (Li2CO3) et d’effectuer une étude de sensibilité des paramètres opératoires. Des travaux expérimentaux sur des saumures modèles ont été effectués sur deux pilotes distincts : une enceinte climatique et une unité d’évaporation. Les techniques d’analyses utilisées pour suivre l’évolution de la composition de la saumure et la qualité des cristaux sont la chromatographie ionique, la DRX et l’EDX. Le modèle mis au point permet de décrire les systèmes salés complexes à l’équilibre à 25°C. Il parvient à décrire les essais dans le pilote d’évaporation du LaTEP à condition que l’on émette l’hypothèse que la zabuyelite ne précipite pas au cours du temps (sursaturation nécessaire). Il pourrait certainement être optimisé au niveau thermodynamique (spéciations, constantes de solubilité), mais également en y ajoutant une dimension cinétique et transferts liquide-vapeur. / Lithium is a critical element regarding to the development of portable devices and electric vehicles. This manuscript is dedicated to lithium production from natural lithium bearing brines. A bibliographic review shows that lithium production consumes lots of water, energy and reactive. It underlines environmental issues and the necessity to improve existing processes. In order to achieve this, modeling and experimental work are associated for this study. The Pitzer model (Pitzer, 1991) is used to calculate the activity coefficients of dissolved aqueous species in brines. After parametrization (salt properties, interaction parameters) and validation with experimental data from literature, a database was optimized to allow the description of key electrolytic systems. Associated with phreeQC software, it is possible to simulate transformations of the brine (such as dilution, evaporation, reactions). It can be used as a predictive tool to explore zabuyelite (Li2CO3) production and study the sensibility of the operative parameters (temperature, pH, pCO2). Experimental work on model-brines was done on two separate pilots: a climatic chamber and a crystallization unit. The evolution of the brine composition and quality of crystals produced was monitored by ionic chromatography, XRD and EDX. The model designed in this study can describe the equilibrium of complex brines at 25°C. It can also describe the experiment in the crystallization unit if a hypothesis of supersaturation (Li2CO3) is used. It could be improved thermodynamically with more speciation and solubility constants, and also with kinetics and liquid-vapor transfers.

This dissertation study describes the development of novel heteroepitaxial growth of 3C-SiC layers by chemical vapor deposition (CVD). It was hypothesized that chloride addition to the "traditional" propane-silane-hydrogen precursors system will enhance the deposition growth rate and improve the material quality via reduced defect density. Thermodynamic equilibrium calculations were performed to obtain a criterion for which chloride specie to select for experimentation. This included the chlorocarbons, chlorosilanes, and hydrogen chloride (HCl) chloride containing groups. This study revealed no difference in the most dominant species present in the equilibrium composition mixture between the groups considered. Therefore, HCl was the chloride specie selected to test the hypothesis. CVD computerized fluid dynamic simulations were developed to predict the velocity, temperature and concentration profiles along the reactor. These simulations were performed using COMSOL Multiphysics and results are presented. The development of a high-temperature (1300 °C -1390°C) 3C-SiC growth process resulted in deposition rates up to ~38 µm/h. This is the highest value reported in the literature to date for 3C-SiC heteroepitaxy. XRD FWHM values obtained varied from 220 to 1160 arcsec depending of the process growth rate or film thickness. These values are superior or comparable to those reported in the literature. It was concluded from this study that at high deposition temperatures HCl addition to the precursor chemistry had the most significant impact on the epitaxial layer growth rate. Low-temperature (1000-1250°C) 3C-SiC growth experiments evidenced that the highest deposition rate that could be attained was ~2.5 µm/h. The best quality layer achieved in this study had a FWHM of 278 arcsec; which is comparable to values reported in the literature and to films grown at higher deposition temperatures in this study. It was concluded from this work that at lower deposition temperatures the HCl addition was more beneficial for the film quality by enhancing the surface. Surface roughness values for films grown with HCl additive were 10 times lower than for films grown without HCl. Characterization of the epitaxial layers was carried out via Nomarski optical microscopy, FTIR, SEM, AFM, XRD and XPS.

No description available.

There are two parts in this study. The first part is to test the validity of the assumption of thermodynamic equilibrium between fine particulate (PM2.5) nitrate and ammonium and gas-phase nitric acid (HNO3(g)) and ammonia (NH3(g)). A rough estimation of the characteristic time to achieve thermodynamic equilibrium is first carried out, which suggests that PM2.5 and gas-phase species are in thermodynamic equilibrium. Then equilibrium is tested by calculating the equilibrium concentrations of HNO3(g) and NH3(g) implied by the PM2.5 inorganic composition, temperature and relative humidity observed at the Atlanta Supersite 1999 using ISORROPIA model. The second part of this study is to analyze the ground-level ozone pollution precursor relationships in Hong Kong area. Characteristics of O3 precursors are explored. Trace gases NO and CO, VOCs, absorption coefficient, temperature and solar radiation are associated with the O3 formation. Specific VOC and VOC-sources that contribute most to the formation of photochemical smog are identified. The accuracy of pollutant emission inventories for Hong Kong and PRD region is also assessed. Combined with back trajectory information, dCO/dNOy is used to define whether O3 is locally or regionally occurred. An OBM is used to investigate the relative benefits of various emission-control strategies. Generally the formation of O3 throughout much of Hong Kong area is limited by VOC, in which reactive aromatics are dominant.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Thermodynamic models have been investigated extensively since Johannes van der Waals first devised a mathematical relation capable of predicting both vapour and liquid phases for a mixture at equilibrium. With the advent of modern computing power, these equations of state have gone from their humble empirical beginnings to the comprehensive and fundamentally derived models we have today. One such physically sound model is the Statistical Associating Fluid Theory (SAFT) family of equations, derived from the molecular perturbation theories of the 1980’s. The relative youth of this thermodynamic framework has meant that much work has gone into modification and optimisation of the model recently. The variants of particular interest to this work are the simplified perturbed chain SAFT equations with the Jog & Chapman (sPC-SAFTJC) and Gross & Vrabec (sPC-SAFTGV) polar terms. Each of the polar terms supports one adjustable polar parameter that relates to the quantity of polar segments in the reference fluid but not necessarily its position in the carbon chain. The strength of polar interactions is known to decrease as the functional group moves away from the terminal methyl group and the effects of steric hindrance increase. Thus, in question here is whether the models can account for the change in polar interactions associated with the changing position of the polar group, by only adjusting the values of the existing pure component parameters; that is, in lieu of a position specific parameter. The carbonyl group in ketone molecules is one such polar group, and it is this homologous series that is the focus of this study. The decrease in polar interactions as the carbonyl group in a ketone molecule shifts centrally is apparent from the lower boiling points of the isomers where the polar group is central as compared to those where the functional group is nearer the terminal methyl group. The effect of this functional group shift on binary phase behaviour has not previously been assessed for any system however, as the lack of experimental data attests. Thus, experiments had to be conducted to generate phase equilibrium data for systems comprising each structural isomer of a mid-length ketone with a common second component with no functionality. This limitation was imposed to isolate the cause of experimentally observed phenomena to the shifting polar group alone. The generated data could then be appropriately modelled using the polar sPC-SAFT variants and the capabilities of each model, as outlined above, assessed. To this end, isobaric binary vapour-liquid equilibrium data were measured for 2-, 3- & 4-heptanone with three separate normal alkanes of similar length (n-octane, n-nonane & n-decane) at 40kPa. The apparatus used was a dynamic Gillespie VLE still with temperature and pressure accuracies of 0.03°C and 1.6mbar respectively. Equipment verification was achieved through the reproduction of experimental data for the ethanol/1-butanol system at 1.013bar. The vapour and liquid samples for all nine systems were analysed by gas chromatography with a maximum compositional error of ±0.022 mole fraction. All reported data were found to be thermodynamically consistent using both the L/W and McDermott-Ellis consistency tests. When paired with a common n-alkane, all three structural heptanone isomers displayed similar qualitative trends in phase behaviour. Minimum boiling azeotropes were measured in all nine systems; in the high alkane region for n-octane systems (~98 mole%), the equal concentration region for n-nonane systems (34 mole% to 53 mole%) and in the very dilute n-alkane region for n-decane systems (~3 mole%). The n-nonane systems in particular highlighted the effect of shifting functional group, with completely separate phase envelopes away from the pure alkane composition space evident in a particularly small temperature range. Modelling was performed using in-house developed software, with pure component parameters generated for each system using five different regression procedures. The first was traditional fitting of the segment diameter (σ), segment number (m), segment energy (є/k) and the respective polar parameter (xp, np) to DIPPR correlations of pure component saturated vapour pressure, liquid density and the heat of vaporisation. The latter four procedures included the fixing of the polar parameter according to functional group correlations and the three instances of including the binary VLE data set for each of the three alkanes considered in this work. When applied to the nine binary ketone-alkane systems measured in this work, excellent predictions of the experimental data were in evidence in most cases and only small binary interaction parameters were necessary to correlate the data where pure predictions were poor. The performance of the parameter sets based on the fixing of the polar parameter and the inclusion of VLE data were consistent and of a high quality for both models, with near identical parameters generated in all four cases for each of the nine systems. The parameter sets generated in this fashion were shown to be applicable not only to the systems measured in this work, but also successfully predicted the independently measured experimental data of the n-hexane/4-heptanone system. It was thus concluded that either of these regression alternatives are viable for the generation of accurate component parameters, and the choice of VLE data set included is trivial. The pure predictions of the sPC-SAFTGV model were generally better than its sPC-SAFTJC counterpart, particularly in the case of the traditionally regressed parameter sets. sPC-SAFTGV displayed constant qualitative agreement with the experimental data for each of the heptanone isomers with a given n-alkane. The quality of the predictions of sPC-SAFTJC, however, worsened significantly as the polar interactions diminished from 2- to 4-heptanone, with no predictions even possible for the least polar isomer. This was attributed to the different perturbation theories used in the development of these terms, but a more detailed study would be necessary to confirm this. This work thus shows an apparent inability of the sPC-SAFTJC equation of state to account for the decreasing polar interactions associated with the carbonyl group in a ketone molecule shifting centrally, while sPC-SAFTGV produces qualitatively good fits for all three isomers. These flaws can be overcome through the incorporation of VLE data in the regression procedure if such data is available, or otherwise through the use of group specific correlations for fixing the polar parameter value. / AFRIKAANSE OPSOMMING: Sedert Johannes van der Waals die eerste wiskundige verhouding ontwikkel het wat beide die damp- en vloeibare fases van 'n mengsel by ewewig kon voorspel, is die veld van termodinamiese modellering al deeglik ondersoek. Na die koms van die moderne rekenaars het hierdie vergelykings van hul nederige empiriese wortels gegroei tot die omvattende, fundamentele modelle wat ons vandag het. Een so 'n fundamenteel gebaseerde familie van vergelykings is die ‘Statistical Associating Fluid Theory’ (SAFT) modelle, wat afgelei is vanaf molekulêre versteuringsteorieë, ontwikkel in die 1980s. Hierdie relatiewe jong modelle het in die afgelope ruk aansienlike aanpassing en optimering ondervind. Modelvariante van besondere belang tot hierdie werk, is die vereenvoudigde versteurde ketting of ‘simplified perturbed chain’ SAFT vergelykings, met Jog & Chapman (sPC- SAFTJC) en Gross & Vrabec (sPC- SAFTGV) polêre terme. In die sPC-SAFT toestandsvergelyking word elkeen van die polêre terme ondersteun deur een polêre veranderlike. Hierdie veranderlike is afhanklik van die aantal polêre segmente in die verwysingsvloeistof, maar nie noodwendig hul posisie in die koolstofketting nie. Daarteen is dit bekend dat die polêre interaksies tussen molekules swakker word soos die polêre groep wegbeweeg van die terminale metielgroep, en steriese hindernis ʼn groter rol begin speel. Dus is die vraag of die model die verandering in die polêre interaksie, as gevolg van veranderende posisie van die polêre groep, kan voorspel deur in plek van ʼn posisie afhanklike parameter, slegs ʼn aanpassing van die polêre waardes van die suiwer komponente te maak. Die karbonielgroep in ketoon molekules is een so 'n polêre groep, en ʼn homoloë reeks ketone word in hierdie studie ondersoek. Die afname in die polêre interaksie soos wat die karbonielgroep in 'n ketoon molekule weg skuif vanaf die terminale metiel groep is sigbaar deur die afname in kookpunt van die verskillende isomere. Hierdie effek van die funksionele groepsposisie op binêre fasegedrag is nog nie voorheen vir enige stelsels geëvalueer nie en geen eksperimentele data is vrylik beskikbaar nie. Om hierdie tekortkoming in die literatuur aan te spreek, is eksperimentele fase ewewig data gemeet. ʼn Reeks stelsels is ondersoek wat elk bestaan uit ʼn struktuurisomeer van ʼn mid-lengte ketoon en ʼn tweede komponent met geen funksionele bydrae. Eksperimente is so opgestel om die effek van die skuiwende polêre groep op die fasegedrag te isoleer en kwalitatief te ondersoek. Die gegenereerde data is dan gemodelleer met behulp van die polêre sPC- SAFT variante, soos hierbo gespesifiseer, en die vermoëns van elke model is beoordeel. Isobariese binêre fase ewewig data is by 40kPa gemeet vir damp-vloeistof stelsels bestaande uit 2, 3 & 4 heptanoon, gemeng met drie verskillende normaal alkane van vergelykbare kettinglengte (n-oktaan, n-nonaan & n-dekaan). Die apparaat wat gebruik was is 'n dinamiese Gillespie VLE eenheid met temperatuur- en drukakkuraatheid van 0,03°C en 1.6mbar, onderskeidelik. Die akkuraatheid van die toerusting is bevestig deur eksperimentele data vir ʼn etanol/1-butanol stelsel by 1.013bar te reproduseer. Die damp en vloeibare monsters vir al nege stelsels is ontleed deur gaschromatografie met 'n maksimum komposisionele fout van ± 0,022 (molfraksie). Alle data is as termodinamies konsekwent gevind deur van beide die L/W en McDermott-Ellis konsekwentheidstoetse gebruik te maak. Mengsels van die drie strukturele isomere van heptanoon met ʼn gemene n-alkaan het tydens eksperimente soortgelyke kwalitatiewe tendense in fasegedrag getoon. Gedurende eksperimente is die lae kookpunt asiotrope gemeet vir al nege stelsels. Die asiotrope verskyn in die hoë alkaan konsentrasies (~98 mol%) vir n-oktaan stelsels, medium konsentrasies (34 mol% tot 53 mol%) vir n-nonaan stelsels en baie verdunde konsentrasies (~ 3 mol%) vir n-dekaan stelsels. Die n-nonaan stelsels beeld veral die effek van die verskuiwing van die funksionele groep uit, met diskrete fasegrense wat duidelik apart staan van die suiwer alkaan ruimte, binne ʼn klein temperatuurverskil. Modellering van die stelsels is uitgevoer met behulp van sagteware wat in-huis ontwikkel is. Suiwer komponent data is gegenereer vir elke stelsel deur van vyf verskillende regressie prosedures gebruik te maak. Die eerste is die tradisionele passing van die segment deursnee (σ), segment nommer (m), segment energie (є/k) en die onderskeie polêre parameters (xp, np) op DIPPR korrelasies van die suiwer komponent versadigde dampdruk, vloeistof digtheid en die hitte van verdamping. Die oorblywende vier prosedures sluit in die bepaling van die polêre parameter deur funksionelegroep korrelasies, en drie gevalle waar die binêre VLE data vir elk van die drie alkane ingesluit is. Deur hierdie prosedures op die modellering van die nege binêre ketoon/alkaan stelsels toe te pas, is uitstekende passings van die eksperimentele data verkry met slegs baie klein binêre interaksie parameters nodig waar voorspellings minder akkuraat was. Die prestasie van die parameter stelle, gebaseer op die bepaling van die polêre parameter en die insluiting van VLE data, is konsekwent en van 'n hoë gehalte vir albei modelle, met 'n byna identiese parameters gegenereer in al vier gevalle vir elk van die nege stelsels. Die parameter stelle wat op hierdie metode gegenereer is, is nie net toepaslik gevind op eksperimentele data gemeet in hierdie werk nie, maar ook op onafhanklike data vir die n-heksaan/4-heptanoon stelsel. Daar is tot die gevolgtrekking gekom dat beide van die regressie alternatiewe lewensvatbaar is vir die generasie van akkurate suiwer komponent parameters, en dat die insluiting van die VLE data triviaal is. Die suiwer sPC - SAFTGV voorspelling was oor die algemeen beter as die suiwer sPC- SAFTJC model met die voorspelling van data, veral in die geval van passings gedoen met parameters verkry vanaf tradisionele regressie metodes. sPC- SAFTGV het ʼn voortdurende, kwalitatiewe ooreenkoms met eksperimentele data getoon vir elk van die nege stelsels. Daarteen het voorspellings deur sPC- SAFTJC beduidend verswak soos die polêre interaksies afgeneem het vanaf 2- na 4- heptanoon, met geen akkurate voorspelling moontlik vir die minste polêre isomeer nie. Die verskynsel kan toegeskryf word aan die verskil in versteuringsteorieë wat gebruik word in die ontwikkeling van die onderskeie toestandsvergelykings, maar ʼn meer in-diepte ondersoek is nodig om hierdie teorie te bevestig. Hierdie werk toon dus 'n skynbare onvermoë van die sPC - SAFTJC toestandsvergelyking om die verandering in polêre interaksie, as gevolg van die veranderende posisie van die polêre groep, vir die karbonielgroep in ʼn ketoon te voorspel, terwyl die sPC-SAFTGV toestandsvergelyking goeie kwalitatiewe passings vir al drie isomere bied. Hierdie tekortkominge kan oorkom word deur VLE data, indien beskikbaar, in die regressie prosedure in te sluit, of deur die gebruik van groep spesifieke korrelasies vir die aanpassing van die polêre parameter.

La thèse porte sur la modélisation de la transformation de l'austénite en ferrite dans les aciers en mettant l'accent sur les conditions thermodynamiques et cinétiques aux interfaces alpha/gamma en cours de croissance de la ferrite. Dans une première partie, la thèse se concentre sur la description des équilibres thermodynamiques entre alpha et gamma à l'aide de la méthode CalPhad. Nous avons développé un nouvel algorithme hybride combinant la construction d'une enveloppe convexe avec la méthode classique de Newton-Raphson. Nous montrons ses possibilités pour des aciers ternaire Fe-C-Cr et quaternaire Fe-C-Cr-Mo dans des cas particulièrement difficiles. Dans un second chapitre, un modèle à interface épaisse a été développé. Il permet de prédire l'ensemble du spectre des conditions à l'interface alpha/gamma au cours de la croissance de la ferrite, de l'équilibre complet au paraéquilibre avec des cas intermédiaires des plus intéressants. Nous montrons que de nombreux régimes cinétiques particuliers dans les systèmes Fe-C-X peuvent être prévus avec un minimum de paramètres d'ajustement, principalement le rapport entre les diffusivités de l'élément substitutionnel dans l'interface épaisse et dans le volume d'austénite. Le troisième chapitre porte sur l'étude d'un modèle de champ de phase. Une analyse approfondie des conditions à l'interface données par le modèle est réalisée en utilisant la technique des développements asymptotiques. En utilisant les connaissances fournies par cette analyse, le rôle de la mobilité intrinsèque d'interface sur la cinétique et les régimes de croissance est étudié, à la fois dans le cas simple d'alliages binaires Fe-C et dans le cas plus complexe d'alliages Fe-C-Mn / Transformation in steels focusing on the thermodynamic and kinetics conditions at the alpha/gamma interfaces during the ferrite growth. The first chapter deals with the determination of thermodynamic equilibria between alpha and gamma with CalPhad thermodynamic description. We have developed a new hybrid algorithm combining the construction of a convex hull to the more classical Newton-Raphson method to compute two phase equilibria in multicomponent alloys with two sublattices. Its capabilities are demonstrated on ternary Fe-C-Cr and quaternary Fe-C-Cr-Mo steels. In the second chapter, we present a thick interface model aiming to predict the whole spectrum of conditions at an alpha/gamma interface during ferrite growth, from full equilibrium to paraequilibrium with intermediate cases as the most interesting feature. The model, despite its numerous simplifying assumptions to facilitate its numerical implementation, allows to predict some peculiar kinetics in Fe-C-X systems with a minimum of fitting parameters, mainly the ratio between the diffusivities of the substitutional element inside the thick interface and in bulk austenite. The third chapter deals with the phase field model of austenite to ferrite transformation in steels. A thorough analysis on the conditions at the interface has been performed using the technique of matched asymptotic expansions. Special attention is given to clarify the role of the interface mobility on the growth regimes both in simple Fe-C alloys and in more complex Fe-C-Mn alloys

Removal of polynuclear aromatics from diesel fuel has become a focus of intense research due to the stringent environmental legislation associated with clean fuels. In this work, selective ring opening of model compound decalin over the set of catalysts comprising of 1) Ir-Pt supported on mesoporous Zr-MCM-41, large and medium pore zeolites like HY and H-Beta and 2) Ni-Mo/carbide on HY, H-Beta, Al-SBA-15, ¥ã- alumina and silica alumina were studied. All the catalysts were extensively characterized by BET surface area measurement, CO-chemisorption, XRD, FTIR, TPR and TPD of ammonia. Ring opening of decalin was studied on these catalysts in a trickle-bed reactor in a temperature range of 200- 400 ¡ÆC, pressure range of 2-7 MPa and LHSV of 1 to 3 h- 1. 31.7 and 65.0 wt.% of RO yield and selectivity were observed on Ir-Pt/HY catalyst at 220 ¡ÆC, whereas 34.0 and 40.0 wt.% of ring opening yield and selectivity were observed on Ni-Mo carbide/HY catalyst at 240 ¡ÆC. From the model compound studies, Ir-Pt/HY, Ni-Mo carbide/HY and Ni-Mo carbide/H-Beta were selected for study of hydrotreated light gas oil in a trickle bed reactor. Ni-Mo carbide/HY performed better over other catalysts and increased the cetane index of hydrotreated light gas oil by 12 units at 325 ¡ÆC. A first order kinetic model was fitted for the hydrotreated light gas oil study. 89, 111 and 42 KJ/gmol of activation energies was observed for dearomatization, aromatization and naphthenes cracking steps, respectively. The thermodynamic equilibrium calculations reveal that the selectivity of ring opening products of decalin can be maximized by favoring the formation of unsaturated compounds at higher operating temperatures. Energetics of dealkylation and ring opening reactions of naphthenes in gas phase and on the surface of Br©ªnsted acid sites were calculated using quantum chemical simulations. In iv gas phase, ratio of Arrhenius activation energies for forward and reverse reactions of RO and dealkylation reactions are 1.92 and 1.82 respectively. Deakylation on different level clusters revealed that surface reaction is the rate controlling.

Removal of polynuclear aromatics from diesel fuel has become a focus of intense research due to the stringent environmental legislation associated with clean fuels. In this work, selective ring opening of model compound decalin over the set of catalysts comprising of 1) Ir-Pt supported on mesoporous Zr-MCM-41, large and medium pore zeolites like HY and H-Beta and 2) Ni-Mo/carbide on HY, H-Beta, Al-SBA-15, ¥ã- alumina and silica alumina were studied. All the catalysts were extensively characterized by BET surface area measurement, CO-chemisorption, XRD, FTIR, TPR and TPD of ammonia. Ring opening of decalin was studied on these catalysts in a trickle-bed reactor in a temperature range of 200- 400 ¡ÆC, pressure range of 2-7 MPa and LHSV of 1 to 3 h- 1. 31.7 and 65.0 wt.% of RO yield and selectivity were observed on Ir-Pt/HY catalyst at 220 ¡ÆC, whereas 34.0 and 40.0 wt.% of ring opening yield and selectivity were observed on Ni-Mo carbide/HY catalyst at 240 ¡ÆC. From the model compound studies, Ir-Pt/HY, Ni-Mo carbide/HY and Ni-Mo carbide/H-Beta were selected for study of hydrotreated light gas oil in a trickle bed reactor. Ni-Mo carbide/HY performed better over other catalysts and increased the cetane index of hydrotreated light gas oil by 12 units at 325 ¡ÆC. A first order kinetic model was fitted for the hydrotreated light gas oil study. 89, 111 and 42 KJ/gmol of activation energies was observed for dearomatization, aromatization and naphthenes cracking steps, respectively. The thermodynamic equilibrium calculations reveal that the selectivity of ring opening products of decalin can be maximized by favoring the formation of unsaturated compounds at higher operating temperatures. Energetics of dealkylation and ring opening reactions of naphthenes in gas phase and on the surface of Br©ªnsted acid sites were calculated using quantum chemical simulations. In iv gas phase, ratio of Arrhenius activation energies for forward and reverse reactions of RO and dealkylation reactions are 1.92 and 1.82 respectively. Deakylation on different level clusters revealed that surface reaction is the rate controlling.

The concern about fossil fuel reserves depletion, pollution due to extensive use of conventional fuels and stricter standards for emission are the forces that drive research on alternative fuels. Amongst these are the biodiesel in which the use of vegetable oils has become an attractive to replace diesel from petroleum because of its physico-chemical characteristics and no toxic emissions. This work aimed to study the effect of diferente variables on conversion of peanut oil to biodiesel; determine the influence of temperature and pH in the purification process in order to optimize the amount of water used and study the thermodynamic equilibrium of the system biodiesel-glycerine-alcohol (decreasing the production of effluents). The process of production and purification of peanut biodiesel obtained by transesterification was studied. In this reaction was used sodium hydroxide (NaOH) as a basic catalyst, anhydrous ethanol and peanut crude oil (non-degummed) in a pilot production unit. In the purification process was used sulphuric acid diluted in distilled water and drying agent (magnesium sulphate). A 22 factorial design was performed to determine the influence of chemical variables on the amount of water required for thepurification. The variables for the production process were: temperature (30o, 70oC), stirring speed (150 rpm, 350 rpm), molar ratio oil/alcohol (1:4 and 1:10), amount of catalyst (0,5% and 1,5%) and reaction time (0,5 h, 2 h). For the purification process the variables analysed were: temperature (30o and 70oC) and pH (2 and 5). For the study of the system´s thermodynamic equilibrium was used purified biodiesel, jacketed glass reactor with circulating water, titration with biodiesel and glycerine. The evaluation parameter for the production process is the conversion to biodiesel determined by gaseous chromatography and for the purification process were the amount of water utilized and the determination of the influence of the temperature on the system´s thermodynamic equilibrium. The conversion to biodiesel varied between total saponification to a conversion of 87%. In the purification was observed that the effect of the pH variable could be ignored and the effect of the temperature and the interaction of the temperature and pH can be considered. The thermodynamic equilibrium of the system biodiesel/glycerine/alcohol and the tie lines did not have its behaviour influenced by the different temperatures, not influencing the miscibility of the mixture. / A preocupação com o esgotamento das reservas de combustíveis fósseis, a poluição devido ao grande uso de combustíveis convencionais e as normas rigorosas em relação às emissões são as forças que impulsionam as pesquisas com combustíveis alternativos. Dentre estes, temos o biodiesel no qual o uso de óleos vegetais tem se tornado uma alternativa atrativa em substituição ao diesel do petróleo devido às suas características físico-químicas e emissões não tóxicas. Esse trabalho teve como objetivos estudar o efeito de diferentes variáveis na conversão do óleo de amendoim a biodiesel; determinar a influência da temperatura e do pH no processo de purificação, a fim de otimizar a quantidade de água utilizada e, estudar o equilíbrio termodinâmico do sistema biodiesel-glicerina-álcool (diminuindo a produção de efluentes). Foi estudado o processo de produção e purificação do biodiesel de amendoim, obtido através da reação de transesterificação. Nessa reação foi utilizado hidróxido de sódio (NaOH) como catalisador básico, etanol anidro e óleo de amendoim bruto (não-degomado) em uma unidade piloto de produção. No processo de purificação foi utilizado ácido sulfúrico diluído em água destilada e agente dessecante (sulfato de magnésio). Um planejamento fatorial 2² foi realizado a fim de se determinar a influência das variáveis químicas na quantidade de água requerida para a purificação. As variáveis para o processo de produção foram: temperatura (30° e 70°C), velocidade de agitação (150 rpm e 350 rpm), razão molar óleo/álcool (1:4 e 1:10), quantidade de catalisador em massa (0,5% e 1,5%) e tempo de reação (0,5 h e 2 h). Para o processo de purificação foram analisadas as variáveis: temperatura (30° e 70°C) e pH (2 e 5). Para o estudo do equilíbrio termodinâmico foi utilizado o biodiesel purificado, reator de vidro com camisa de circulação de água, titulação com glicerina e biodiesel. O parâmetro de avaliação para a produção é o rendimento em biodiesel determinado por cromatografia gasosa e para o processo de purificação, a quantidade de água utilizada e a determinação da influência da temperatura no equilíbrio termodinâmico do sistema. A conversão a biodiesel variou de total saponificação até uma conversão de 87%. Na purificação, foi observado que o efeito da variável pH pode ser desprezado e o efeito da temperatura e da interação dessas duas variáveis pode ser considerado. O equilíbrio termodinâmico do sistema biodiesel/glicerina/álcool e suas tie lines não sofreram influência de comportamento nas diferentes temperaturas estudadas, não influenciando na miscibilidade da mistura.