Thesis (Master)--İzmir Institute of Technology, İzmir, 2004. / Includes bibliographical references (leaves. 82-84).

Thesis (M. Sc.)--University of Alberta, 2010. / Title from pdf file main screen (viewed on June 11, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science in Chemical Engineering, [Department of] Chemical & Materials Engineering, University of Alberta. Includes bibliographical references.

Until present, many researchers relied on the conventional plug flow dispersion models to analyse the concentration profiles obtained from the tracer injection experiments to evaluate the dispersion coefficients in packed beds. The Fickian concept in the limit of long time duration is assumed to be applicable and it implies that the mean-square displacement of the tracer profile is constant with time and the concentration profile is Gaussian. There were very few studies on identifying the conditions under which this assumption is valid and delineate the range of applicability of the existing plug flow dispersion models. If the time scales of a tracer injection experiment are not sufficient for a tracer to traverse the bed radius and sample the velocity variations, this could give rise to persisting non-Fickian transients where the mean-square displacement of the tracer profile is not constant with time and the concentration profile deviates from the normal Gaussian distribution. These transients cannot be predicted by the conventional plug dispersion models. An extended axial non-Fickian macroscopic dispersion model is derived to describe the transient development of a solute tracer when injected into a fluid flowing through a cylindrical packed bed or empty tube and some non-Fickian effects in the dispersion process. The flow profile in beds packed with uniform particles exhibits radial non-uniformity due to the oscillatory variation in porosity because of the wall confinement (wall effect). Compared with the axial plug flow dispersion model, the extended model contains time-dependent coefficients such as the transient axial dispersion coefficient and higher order derivatives (higher than second order) of the cross-sectionally averaged concentration. Including them provides some insight on non-Fickian transport in the dispersion process. The model provides time criteria on the basis that the effelongitudinal dispersion coefficient in the packed bed reaches its asymptotic value and the non-Fickian transients will die out. Some experimental conditions in the literature were checked by these criteria and found to be either marginally satisfied, or not satisfied at all, which indicates that the Fickian concept is not valid. The model results for tracer dispersion in cylindrical packed beds show that the longitudinal dispersion coefficient converges to its asymptotic value on a time scale proportional to R2/(DT) where R is the column radius and (DT) is the area averaged lateral dispersion coefficient. The extended model encouraged study of the consequences of the additional dispersion terms in other applications such as the pulse spread in the field of capillary column inverse gas chromatography (CCIGC). CCIGC is used to evaluate the solute-polymer diffusion coefficient Dp and the partition coefficient K at infinite dilute conditions. The tube geometry in CCIGC is more complex than the conventional Taylor dispersion problem due to the polymer coating on the inside of the capillary wall. The extended CCIGC model presented in this study has advantages over the previous models by including the effects of Taylor dispersion and higher order derivatives of the pulse area-averaged concentration. Taylor dispersion effect causes more pulse spread in the longitudinal direction and by not including it in the CCIGC regression models may cause a significant error in the measured Dp values. The extended CCIGC model provides for the first time criteria on capillary dimensions for the transient coefficients (multiplying the second and higher order derivatives) to become constant and for the non-Fickian effects associated with the higher order derivatives to be neglected. Model results show that Taylor dispersion effect has a significant effect on the elution profiles at high values of Dp and/or low values of gas diffusion coefficients Dg and it can be used to increase the sensitivity range of the previous CCIGC models at extremely low and high Dp values.

No description available.

The technique of Inverse Gas Chromatography (IGC) was employed for the study of the interactions between various organic solvents with various types of the major inorganic materials (clay minerals and sand) found in Albertas oil sands. Heat of adsorption (-H) was measured for each solvent with respect to each of the four studied inorganic materials. The calculation we used was based on the Infinite Dilution Thermodynamics approach used by Katsanos et. al. [Journal of Chromatography A. 795, 133-184 (1998)]. Retention time data is converted into Retention Volume; H is then obtained by a plot vs. 1/T. The solvents studied were straight chain, branched and cyclic alkanes, alkenes, aromatics, and ketones. The inorganic materials studied were kaolinite, illite, illite-smectite mixed layer, and sand. Our results show that solvents had significantly less affinity for sand when compared to the three types of clay studied. Additionally, solvent affinity to illite had appreciable difference when compared to kaolinite and the mixed layer of illite-smectite. Furthermore, increase in carbon number leads to increased adsorption to the clay. Branched or cyclic alkanes have slightly lower adsorption to clay when compared to straight chain alkane of the same carbon number. Double bonds significantly increase solvent affinity to clay, but have no effect on sand. Lastly, alcohols and ketones have very high affinity to clay that no elution occurred when either solvent was injected into the GC and only ketone eluted when sand was the stationary phase in the GC column. / Chemical Engineering

For elucidating catalytic processes and enhancing process efficiency, the characterisation of porous catalysts is crucial. While the chemical characterisation of the catalyst surface, e.g. by infrared and X-ray photoelectron spectroscopy, is standard practice, the energetic characterisation of surface sites is often neglected, although all heterogeneously catalyzed reactions take place at the surface. Inverse gas chromatography is a gas phase method to investigate a large number of physico-chemical, morphological and energetical surface properties of particles, granulates or fibers. In this dissertation, silica materials with well-defined surface properties and a large specific surface area (porous glass beads, pyrogenic silica) were investigated. For potential catalytic and sensoric applications, the silica material was additionally grafted with organofunctional silanes. The overall aim of this Thesis was to apply IGC-theories to different silicas before and after surface modification, to examine the potential of this characterisation method. The validity of the results was set against its limitations, to verify the IGC as sensitive method even for small changes of physico-chemical surface properties. It was observed that the physicochemical properties of the surface are predominatly determined by silanol and siloxane groups. In particular the LEWIS-acid silanol groups strongly interact with LEWIS-basic polar probe molecules. This results in high values for free surface energy with a dominant polar component and an overall LEWIS-acidity of the silica. Measurements indicated specific surface areas respectively to the applied probe molecule. In particular 2-propanol showed strong interactions, a very high surface area, but also a heterogenous adsorption behaviour. According to PAPIRERs Patchwork model of condensation approximation, two different states of adsorption were found. With DFT-simulation these were identified as low energetic hydrogen bonds between 2-propanol and siloxan and as high energetic hydrogen bonds between 2-propanol and silanol groups. Nevertheless, all of the IGC findings point to a reduction of the acidity of silica and an increase in hydrophobicity by surface modification due to the loss of silanol groups with the silane grafting. Finally, the IGC can be presented as a many-faceted useful tool for surface characterisation. Its variability and sensitivity expands most other classical methods. Complex surface properties like free surface energies, acid-base functionality, kinetic parameters, specific surface area and surface heterogenity can be determined from single chromatographic peaks with the respective theories. Throughout the investigation, a new non-linear parameter estimation approach was introduced in contrast to the common linear computation models. Therefore, an increasing number of involved probe molecules and also the use of bipolar probes yields in statistical more reliable results.

No / In this paper, molecular modelling was used to investigate the nature of probe/surface interactions during the analysis of Dß-mannitol using inverse gas chromatography (IGC). IGC was used to experimentally measure the dispersive components of surface free energy () and the specific components of free energy of adsorption () of Dß-mannitol by calculating the retention time of non-polar (n-alkanes) and polar (tetrahydrofuran and chloroform) probes, respectively. The results showed that Dß-mannitol surface is acidic in nature because the basic probe had more interaction with the surface as compared to acidic probe. Cerius2 software package was used to model the two morphologically important surfaces, which showed the presence of surface hydroxyl groups. Molecular dynamics simulations were performed in Cerius2 to model the adsorption of the same probes (n-alkanes, tetrahydrofuran and chloroform) on the Dß-mannitol surfaces. The adsorption energies calculated from the simulation showed a close match to those determined experimentally. The calculated values are slightly higher for all probes except chloroform, but as a single perfect crystal was modelled without considering the effect of impurities, solvent and other physical factors this is not unexpected.

Yes / Globular proteins are important both as therapeutic agents and excipients. However, their fragile native conformations can be denatured during pharmaceutical processing, which leads to modification of the surface energy of their powders and hence their performance. Lyophilized powders of hen egg-white lysozyme and β-galactosidase from Aspergillus oryzae were used as models to study the effects of mechanical denaturation on the surface energies of basic and acidic protein powders, respectively. Their mechanical denaturation upon milling was confirmed by the absence of their thermal unfolding transition phases and by the changes in their secondary and tertiary structures. Inverse gas chromatography detected differences between both unprocessed protein powders and the changes induced by their mechanical denaturation. The surfaces of the acidic and basic protein powders were relatively basic, however the surface acidity of β-galactosidase was higher than that of lysozyme. Also, the surface of β-galactosidase powder had a higher dispersive energy compared to lysozyme. The mechanical denaturation decreased the dispersive energy and the basicity of the surfaces of both protein powders. The amino acid composition and molecular conformation of the proteins explained the surface energy data measured by inverse gas chromatography. The biological activity of mechanically denatured protein powders can either be reversible (lysozyme) or irreversible (β-galactosidase) upon hydration. Our surface data can be exploited to understand and predict the performance of protein powders within pharmaceutical dosage forms.

Les silices pyrogéniques sont très utilisées comme charge pour les polysiloxanes mais elles sont l’un des principaux constituants des superisolants thermiques. Cependant, l’échelle nanométrique de ces silices et leur chimie de surface (groupes silanol) est également responsable de leur aptitude à adsorber la vapeur d’eau, ce qui a pour conséquence d’altérer leurs propriétés d’isolant thermique au cours du temps, notamment lors de leur stockage dans des conditions non contrôlées. Malgré son importance industrielle ce phénomène n’a fait l’objet dans la littérature que d’une seule étude assez limitée.En effet, initialement la surface de ces silices ne sont que partiellement hydroxylées et la présence de ponts siloxanes tendus, susceptibles de réagir avec l’eau va mener à une évolution de leurs propriétés de surface en présence d’humidité.Une première étude a porté sur les silices N20, T30 et T40 (Wacker Chemie AG) sont obtenues par combustion de SiCl4 dans un mélange air/H2, de surfaces spécifiques égales respectivement à 200, 300 et 400 m2/g. Elles ont été vieillies à température constante 22,5 ± 0,1 °C, dans une enceinte fermée, sous humidité relative (HR) contrôlée : 62, 75, 84, 92 et 100%.L'adsorption d'eau a été suivie par gravimétrie. La masse d’eau adsorbée, par unité de surface augmente à la fois avec HR et la surface spécifique. Cette augmentation qui peut atteindre près de 60% de la masse initiale pour une HR de 100%, est liée à l’augmentation de l’hydrophilie de la surface de la silice liée à la formation de nouveaux groupes silanol. Nous avons démontré que cette augmentation suit une cinétique du 1er ordre et que la constante cinétique passe par un maximum pour une RH égale à 84%.L’augmentation du nombre de silanol superficiels a été confirmée par leur dosage chimique. Leur densité superficielle augmente d’environ 50%, passant de 2,4 SiOH/nm2 à 3,6 SiOH/nm2 pour l’HR égale à 100%.La spectroscopie IR atteste clairement d’une diminution nette des silanol isolés au profit de silanol fortement liés par pont hydrogène. Les spectroscopies RMN du proton et du silicium confirment l’augmentation de la densité locale en groupes silanols.L’évolution des propriétés superficielles des silices vieillies environ 1000 h a été suivie par chromatographie inverse à dilution infinie (CGI-DI) et concentration finie (CGI-CF).La CGI-DI pratiquée avec des sondes alcanes linéaires et cycliques démontre que le vieillissement n’affecte que très faiblement tant la composante dispersive de l’énergie de surface que leur rugosité à l’échelle moléculaire, autrement dit qu’il ne modifie pas la morphologie de la surface. Notamment la rugosité superficielle des silices T30 et T40 n’est pas affectée.La variation de l’hétérogénéité superficielle avec le vieillissement a été déterminée, en termes de fonctions de distribution des énergies d’adsorption de l’isopropanol, par CGI-CF.Le processus de vieillissement conduit, comme attendu, à une augmentation de la composante de haute énergie liée à l'apparition de nouveaux groupes silanol par ouverture nucléophile des ponts siloxane. Le glissement du maximum de cette composante vers les hautes énergies montre la formation d’un nouveau type de silanol plus interactif par liaison hydrogène.Ces résultats confirment la réactivité des silices de combustion vis-à-vis de l'eau lorsqu’elles sont exposées à une humidité relative élevée. L'eau est chimisorbée sur la surface de la silice par une réaction d'ouverture des ponts siloxane. L'étude de l'influence de la variation de l'humidité relative, montre qu’il existe un seuil (HR50%) au-dessous duquel ces silices restent stables par rapport à la vapeur d'eau. [...] / Pyrogenic silicas , produced by combustion of SiCl4 into a mixture hydrogene/air, are widely used as filler for polysiloxanes, but also as one of the main components of super-thermal insulating. However, the nanoscale of these silicas and surface chemistry (silanol groups) is also responsible for their ability to adsorb water vapour, which alters their insulation and reinforcement properties, especially when stored in uncontrolled conditions. Initially the surface of pyrogenic silicas is partially hydroxylated, silanol groups, but presents also strained siloxane bridges, which can react with adsorbed water, leading to a change in their surface properties when exposed to the atmospheric moisture. Despite its industrial importance, this phenomenon has been rarely studied in the literature, except a single study, which was rather limited.Our study was focused on a set of six pyrogenic silicas, having specific surface areas comprised between 150 to 400 m2 / g. They were aged at constant temperature 22.5 ± 0.1 ° C in a closed chamber under controlled relative humidity (RH): 62, 75, 84, 92 and 100%.The water adsorption was followed gravimetrically. The mass of water adsorbed per unit area increases with both HR and the specific surface area. This increase, which can reach nearly 60% of the initial mass at 100% RH, is induced by the increase of their surface hydrophilicity due to the formation of new silanol groups. But, the study of the influence of the variation in RH, indicates that a threshold exists around HR50%, below which these silicas are stable.Finally, fitting the gravimetric curves, it was evidenced that the water sorption follows a first order kinetics and that the kinetic constant goes through a maximum for an HR equal to 84%. This increase of silanol density was testified by chemical titration. It increases by about 50%, from 2.4 to 3.6 SiOH/nm2 for ageing under 100% RH, but is dependent of the specific surface area and surface roughness. IR spectroscopy clearly indicates a net decrease of isolated silanol band correlated with an increase of H-bounded silanol. Proton and silicon NMR spectroscopies confirm the increase of the local density silanol groups on the aged silca surface.Finally, the evolution of the surface properties of these silica samples, aged during about 1000 h, was followed by inverse gas chromatography in infinite dilution (IGC-ID) and at finite concentration (CGI-FC) conditions.The CGI-ID was performed using linear and cyclic alkane probes. It shows that the ageing process affects only very slightly both the dispersive component of surface energy and the nano-roughness at the molecular level of all studied, indicating that the surface morphology is quite unchanged. Then; the variation of their surface heterogeneities with ageing time, in terms of the distribution functions of the probe adsorption energies, was assessed by CGI-CF, using isopropanol as probe.The aging process leads, as expected, to an increase of the high energy component related to the appearance of new silanol groups by nucleophilic opening of siloxane bridges by water confirming the reactivity of fumed silicas toward water when exposed to a high RH. All our observations, existence of a threshold, maximum for the kinetic constant and decrease of the chemisorbed of water amount with both specific surface area and surface roughness is supported by a model for the ageing process. [...]

Les oxydes d’actinides sont des matériaux hygroscopiques. L’adsorption de l’eau à leurs surfaces est susceptible d’entrainer des modifications quant à la nature ou à son état. Dans le cas des oxydes à fort débit de dose, vient s’ajouter les effets de radiolyse de l’eau, entrainant sa décomposition et générant du dihydrogène. Ces deux aspects, étude de surface et radiolyse de l’eau, ont été étudiés ici. L’étude de la génération de dihydrogène par radiolyse de l’eau adsorbée à la surface a montré que cette génération linéaire dans les premiers temps atteint une concentration stable au bout de plusieurs heures. Cet état stationnaire a été très peu observé, et est absent dans le cas d’humidité importante. Un conditionnement dans une atmosphère contenant du dihydrogène a permis de mettre en lumière une réaction de consommation du dihydrogène par le matériau. Ces expériences ont permis de faire émerger un modèle cinétique basé sur deux réactions de production et de consommation de dihydrogène. La première correspond à la décomposition de l’eau sous l’effet du rayonnement, et pour la seconde il est suspecté une réduction partielle de la surface avec la formation d’une phase sous-stœchiométrique en surface. Cependant, aucune technique d’analyse de surface n’a permis de mettre en évidence formellement cette phase. La chromatographie gazeuse inverse est une technique peu intrusive vis-à-vis des couches d’eau adsorbée du fait des températures et des pressions mis en jeux et de l’absence de dépôt d’énergie. Cette technique a été employée sur des oxydes de thorium et d’uranium. Sur oxyde de thorium, il en résulte un impact de la température de calcination, avec un maximum d’énergie de surface pour une calcination à 650°C. Par ailleurs, il a été montré que la préparation du dioxyde de thorium pouvait impacter l’état de sa surface. En effet, il a été observé une déshydratation de l’oxalate de thorium au fil du temps, impactant la structure de ce dernier. Cette modification se répercute sur la surface de l’oxyde final par une chute de l’énergie de surface et par une modification sur la répartition des sites d’adsorption en surface. Néanmoins un traitement chimique de l’oxalate permet de retrouver la réactivité de surface et une distribution des sites d’adsorption. L’hydratation de la surface montre une augmentation de l’énergie de surface, mais cette augmentation n’est observée que pour des hydratations de longues durées. / Actinide oxides are hygroscopic materials. The adsorption of water on their surfaces is likely to cause changes in the nature or condition. In the case of oxides with a high dose rate, the effects of radiolysis of the water causes the decomposition of water and generates hydrogen. These two aspects: surface study and radiolysis of water have been studied here.The study of the generation of dihydrogen by radiolysis of water adsorbed on the surface has shown that this linear generation in the early stages reaches a stable concentration after several hours. This stationary state has been very little observed, and is absent in the case of significant humidity. Conditioning in a dihydrogen-containing atmosphere made it possible to highlight a reaction of consumption of dihydrogen by the material. These experiments led to the emergence of a kinetic model based on two reactions of production and consumption of dihydrogen. The first corresponds to the decomposition of the water under the effect of the radiation, and for the second it is suspected a partial reduction of the surface with the formation of a sub-stoichiometric phase on the surface, however no technique of analysis of surface has not formally highlighted this phase.Inverse gas chromatography is a technique that is not very intrusive with respect to the adsorbed water layers because of the temperatures and pressures involved and the absence of energy deposition. This technique has been used on oxides of thorium and uranium. On thorium oxide, this results in an impact of the calcination temperature, with a maximum of surface energy for calcination at 650 ° C. In addition, it has been shown that the preparation of thorium dioxide can impact the state of its surface. Indeed, it has been observed dehydration of thorium oxalate over time, impacting the structure of the latter. This modification affects the surface of the final oxide by a drop-in surface energy and a change in the distribution of surface adsorption sites. Nevertheless, a chemical treatment of oxalate makes it possible to recover the surface reactivity and a distribution of the adsorption sites. The hydration of the surface shows an increase in surface energy, but this increase is observed only for hydrations of long duration.Keywords: water sorption, radiolysis, plutonium, inverse gas chromatography, thorium, uranium