Le CO2 est capté par formation de clathrates hydrates sous l'action d'un promoteur de cristallisation thermodynamique. Les clathrates hydrates sont des composés d'inclusion non stœchiométriques formés de molécules d'eau organisées en réseau de cavités piégeant des molécules de gaz. Ce procédé de captage consiste à piéger de façon sélective le dioxyde de carbone dans les cavités des clathrates hydrates et à le séparer ainsi des autres gaz. Les hydrates mixtes de cyclopentane (CP) + gaz ont été étudiés dans le cadre du projet FUI ACACIA et du projet européen ICAP. Les premières expériences se sont focalisées sur l'étude des équilibres quadri phasiques (gaz CO2/N2, eau liquide, cyclopentane liquide et hydrate). Le cyclopentane est un promoteur thermodynamique qui forme des hydrates mixtes de CO2 + N2 + CP à basse pression et température modérée. La pression d'équilibre des hydrates mixtes est réduite jusqu'à 97% par rapport à la pression d'équilibre initiale des hydrates de gaz. La sélectivité de captage du CO2 dans les hydrates mixtes est augmentée et le volume de gaz stocké est de 40 m3gaz/m3hydrate. Une seconde étude expérimentale, conduite en présence d'une sonde FBRM (Focused Beam Reflectance Measurements) et d'une émulsion stable directe de CP/eau, a montré que la cinétique de cristallisation des hydrates mixtes de CP + CO2 est limitée par la diffusion du gaz à l'interface gaz/liquide. La sonde FBRM permet de détecter parfaitement l'apparition de la nucléation. Le changement de profil de la distribution en longueurs de corde (CLD) est non seulement lié à l'apparition des mécanismes de cristallisation (dont l'agglomération) mais aussi à la disparition des gouttes de CP au profit des hydrates qui cristallisent par un mécanisme à cœur rétrécissant.

The first project in this work used classical molecular dynamics to study the ice recrystallization inhibition potential of a series of carbohydrates and alcochols, using the hydration index, partial molar volumes and isothermal compressibilities as parameters for measuring their cryogenic efficacy. Unfortunately, after 8 months of testing, this work demonstrates that the accuracy and precision of the density extracted from simulations is not sufficient in providing accurate partial molar volumes. As a result, this work clearly demonstrates that current classical molecular dynamics technology cannot probe the volumetric properties of interest with sufficient accuracy to aid in the research and development of novel cryoprotectants.The second project in this work used molecular dynamics simulations to evaluate the Gibbs free energy change of substituting CO2 in sI clathrate hydrates by N2,CH4, SO2 and H2S flue gas impurities under conditions proposed for CO2 capture (273 K, 10 bar). Our results demonstrate that CO2 substitutions by N2 in the small sI cages were thermodynamically favored. This substitution is problematic in terms of efficient CO2 capture, since the small cages make up 25% of the sI clathrate cages, therefore a significant amount of energy could be spent on removing N2 from the flue gas rather than CO2. The thermodynamics of CO2 substitution by CH4, SO2 and H2S in sI clathrate hydrates was also examined. The substitution of CO2 by these gases in both the small and large cages were determined to be favorable. This suggests that these gases may also disrupt the CO2 capture by sI clathrate hydrates if they are present in large concentrations in the combustion flue stream. Similar substitution thermodynamics at 200 K and 10 bar were also studied. With one exception, we found that the substitution free energies do not significantly change and do not alter the sign of thermodynamics. Thus, using a lower capture temperature does not significantly change the substitution free energies and their implications for CO2 capture by sI clathrate hydrates.

The objective of this study was to synthesize and characterize new energetic polycyclic "cage" compounds. As part of a program involved in the synthesis of new polynitropolycyclic compounds, 2,6-dinitro-5-methoxy- 7-carbomethoxypentacyclo[5. 3 .0 . 0* • * . CP • i ° . 0* •8]decane has been synthesized. This is a model system which can be used to study (1) the effect of nitro substitution on the photolability of carbon-carbon double bonds and (2) to develop methods for avoiding Haller-Bauer cleavage in cage /3-keto esters when synthesizing polynitro-substituted cage compounds.

Thesis (MTech (Chemistry))-- Cape Peninsula University Technology, 2012 / The inclusion behaviour of a series of hydroxyl hosts with a variety of liquid guests has been investigated. The host 9-(4-methoxyphenyl)-9H-xanthen-9-ol (A1), C20H16O3, forms inclusion compounds with aniline (ANI), 3-picoline (3PIC), morpholine (MORPH), Nmethylacetamide (NMA) and N-methylformamide (NMF). Their structures have been elucidated and correlated with their thermal behaviour. The inclusion compounds A1ANI and A1MORPH were successfully solved in space group P21/c, whereas A13PIC was solved in 𝑃ī. Non-isothermal kinetics of desolvation were performed for A13PIC and A1MORPH. The packing of A13PIC and A1MORPH is characterized by (Host)(Guest) hydrogen bonds, whereas A1ANI is stabilised by (Host)(Host) hydrogen bonding. Three structures were obtained for the host A1 and the guest N-methylacetamide, with structural formulas of C20H16O3 C3H7NO (A1NMA), C20H16O3 2C3H7NO (A12NMA) and 2C20H16O3 2C3H7NO (2A12NMA). The packing of A1NMA, A12NMA and 2A12NMA are characterized by (Host)-OHO-(Guest) and (Guest)-NHO-(Guest) hydrogen bonds, which gave hydrogen bonding patterns of 𝐶2 2(7), 𝐶3 3(11) and 𝐶4 2(11) respectively. The hydrate A1NMFH2O was successfully solved in the triclinic space group 𝑃ī. The A1NMFH2O hydrogen bond pattern may be described according to Etter’s notation as 𝑅4 2(8) and 𝑅6 6(16). The host 9-(3-methoxyphenyl)-9H-xanthen-9-ol (A2), C20H16O3, forms inclusion compounds with morpholine (A2MORPH), N-methylacetamide (A2NMA) and N-methylformamide (A2NMF), with host-guest ratios 1:1. The crystal structure of the apohost was solved in Pbca with Z=8. The structures of A2MORPH and A2NMF were solved in 𝑃ī, whereas A2NMA was solved in P21/n. The packing of these structures is stabilised by (Host)(Guest) hydrogen bonds. The host 5-(4-methoxyphenyl)-5H-dibenzo[a,d]cyclohepten-5-ol (A26), C22H18O2, forms inclusion compounds with aniline (A26ANI) and morpholine (A26MORPH). A26MORPH and A26ANI crystallised in the space groups Pc and 𝑃ī respectively. The packing of these structures are characterized by (Host)-OHO-(Host) hydrogen bonding. A guest exchange reaction was performed. The host compounds 5-(4-chlorophenyl)-5H-dibenzo[a,d]cyclohepten-5-ol (C21H15OCl), 5-[3(trifluoromethyl)phenyl]-5H-dibenzo[a,d]cyclohepten-5-ol (C22H15OF3) and 5-(naphthalen-1-yl)-5H-dibenzo[a,d]cyclohepten-5-ol (C25H18O) form inclusion compounds with morpholine. All three structures were solved in 𝑃ī with the host molecules hydrogen bonded to the morpholine guests.

When ice is compressed alongside a gas, crystalline 'host - guest' inclusion compounds known as gas clathrate hydrates form. These compounds are of interest not only for their environmental and possible technological impact as gas storage and separation materials, but also for their ability to probe networks not readily adopted by the pure `host' water molecules, and to study the interactions between water and gas molecules. Despite the pressure dependent crystal structures being fully determined for a large variety of `guest' gas species there is still relatively little known about the crystal structures in small guest gas systems such as H2 hydrate. The majority of structural studies have been done with x-ray diffraction and report a number of conflicting structures or hydrogen contents for the four known stable phases (sII, C0, C1 and C2). As this is a very hydrogen rich system the most ideal method to study the structure is neutron diffraction, which is able to fully determine the location of the hydrogen atoms within the structure and would allow a direct measurement of any hydrogen ordering within the host structure and the H2 content. In this work the phase diagram of the deuterated analogue of the H2-H2O system is explored at low pressures (below 0.3 GPa) with neutron diffraction. In the pressure/temperature region where the sII phase is known to be stable, two metastable phases were observed between the formation of sII from ice Ih and that this transition sequence occurred in line with Ostwald's Rule of Stages. One of these metastable phases was the C0 phase known to be stable in the H2-H2O system above 0.5 GPa, and the other is a new structure not previously observed in this system and is dubbed in this work as C-1 . Prior to this work the C0 phase has been reported with various structures that were determined with x-ray diffraction, and here the crystal structure and H2 content at low pressure are determined with neutron diffraction. The C0 phase was found to form a similar host structure to those of the previous studies with spiral guest sites but is best described with highly mobile H2 guests and a higher symmetry space group which make it the same structure as the spiral hydrate structure (s-Sp) recently observed in the CO2 hydrate system. In addition to this structure being determined at pressure a sample of C0 was also recovered to ambient pressure at low temperature and its structure/H2 content is presented as it was warmed to decomposition. The crystal structure of the C-1 phase was determined to be similar to ice Ih and a sample was recovered to ambient pressure to study its decomposition behaviour. Evidence for a similar structure in the helium hydrate system at low pressure is also reported here. This work was then extended to higher pressures with the recent developments of a hydrogen-compatible gas loader and large-volume diamond anvil cells. Several test experiments on gas-loaded Paris-Edinburgh presses are described on systems that are similar to hydrogen-water like urea-hydrogen and neon-water. And a further preliminary high pressure study on the deuterated analogue of the H2- H2O system in a diamond anvil cell between 3.6 and 28 GPa shows decomposition behaviour as pressure was increased.

Thermoelectric phenomena couple thermal and electric currents, allowing for solid-state conversion of heat into electricity. For decades Radioisotope Thermoelectric Generators have supplied power to NASA satellites and deep space probes. A more accessible application to consumers is the automotive industry's aspiration to incorporate thermoelectrics into active waste heat recovery systems. Higher power demands require these new thermoelectric devices to operate at higher temperatures and higher efficiencies, justifying new materials research. Recently, clathrates have gained interest for thermoelectric applications due to the unique properties they possess.These properties are directly related to their crystal structure. Therefore, clathrates are not only of interest from the standpoint of potential thermoelectric applications but are also of scientific interest as they presents an opportunity to investigate fundamental properties of group-IV elements in novel crystal structures. Clathrates are a class of novel open-structured materials in which molecules or atoms of one species are completely enclosed within a framework comprised of another species. This work presents a systematic investigation of the electrical properties of type I clathrate alloys, specifically Si-Ge alloys, for the first time. A series of Ba8Ga16-ySixGe30-x+y clathrates with varying Si content were synthesized and their structural and transport properties were studied. Two additional series of type I clathrates were also synthesized and characterized and their properties compared to those of the Si-Ge alloys in order to develop an understanding of their structure-property relationships. The increasing Si content correlates to a dramatic increase in Seebeck coefficient even as the resistivity decreases, suggesting the complex interaction between the Ba and the Si substitution within the Ga16Ge30 framework significantly modifies the band structure.

Diquinoline molecules have been shown previously to have interesting inclusion properties. Of the nine new, targeted molecules produced for this work, seven formed inclusion compounds, and their solid-state structures are discussed herein. Chapter 2 shows the effect that substituting a hydrogen atom with a chlorine atom has on the inclusion properties. This comes about because of the additional intermolecular attractions that are now possible, and a wider range of guest molecules is included as a result. A new homochiral aromatic 'swivel offset face-face (OFF)' interaction is observed. Chapters 3 and 4 deal with the effect of adding extra aromatic planes to the target molecules, two or four planes, respectively. Each of these host molecules formed dimeric host-host units that are extremely similar across all crystal structures. These dimers mainly employed aromatic edgeface (EF) interactions. Chapter 5 looks at the effect of combining the modifications described in Chapters 2-4, namely additional aromatic surfaces and atom substitution. The resulting host molecule specifically includes polyhalomethane guests. In addition, this host molecule formed two concomitant pseudo-dimorph compounds with chloroform-d. The diquinoline host molecule presented in Chapter 6 incorporated an isomeric central linker ring to the other compounds. Although only a single crystal structure could be obtained, 1H NMR spectroscopy experiments show other small aromatics may be included. The effect of electron donating chemical substituents was examined in Chapter 7. These compounds were found to be quite insoluble, and did not produce crystals suitable for X-ray analysis. The host molecules in Chapter 8 contain electron withdrawing nitro groups. The two isomeric compounds that act as inclusion hosts show quite different properties. One of these hosts forms a series of inclusion compounds with water, in which the site occupancy of the guest can range from 0-100% without change to the overall structure. All the X-ray structures described have been analysed in crystal engineering terms, and their supramolecular interactions described in detail.

Les premiers travaux relatifs aux combinaisons des métaux alcalins avec le silicium ou le germanium datent du milieu du siècle dernier. Sainte-Claire Delville (1857) (1), Winkler (1864) (2) puis Vigouroux (1869) (3) (4), qui entreprirent les premières recherches dans cette voie ne décelèrent en fait aucune réaction entre le silicium et le sodium. Moissan (1902) (5) (6), après avoir réalisé la synthèse d'un siliciure de lithium auquel il attribua la formule Li₆Si₂, montra que le silicium réagissait sous vide avec le sodium ou le potassium pour former de petites quantités de siliciures difficiles à séparer des produits de départ, et qu'il ne put identifier. Les premiers essais concernant les germaniures alcalins donnèrent en revanche des résultats beaucoup plus concluants. En 1930 Dennis et Skow (7) après avoir porté à 1000°C un mélange équimoléculaire de germanium et de sodium dans un creuset de fer isolèrent un germaniure de sodium correspondant à la formule NaGe...

Ce travail de thèse présente les résultats obtenus lors de l'étude des mécanismes élémentaires à l'origine de la forte conduction protonique mesurée dans le cas de clathrates hydrates d'acides forts. Une méthodologie combinant diffusion neutronique, résonance magnétique nucléaire et simulation de dynamique moléculaire "ab-initio" a permis de modéliser les différents processus dynamiques impliqués, se produisant sur des temps allant de la nanoseconde à la femtoseconde. Le modèle proposé explique la forte conduction de ces systèmes aqueux par la délocalisation à longue distance de leurs protons résultant d'un mécanisme de type Grotthuss gouverné par la relaxation des molécules aqueuses environnant les protons en excès.

The first project in this work used classical molecular dynamics to study the ice recrystallization inhibition potential of a series of carbohydrates and alcochols, using the hydration index, partial molar volumes and isothermal compressibilities as parameters for measuring their cryogenic efficacy. Unfortunately, after 8 months of testing, this work demonstrates that the accuracy and precision of the density extracted from simulations is not sufficient in providing accurate partial molar volumes. As a result, this work clearly demonstrates that current classical molecular dynamics technology cannot probe the volumetric properties of interest with sufficient accuracy to aid in the research and development of novel cryoprotectants.The second project in this work used molecular dynamics simulations to evaluate the Gibbs free energy change of substituting CO2 in sI clathrate hydrates by N2,CH4, SO2 and H2S flue gas impurities under conditions proposed for CO2 capture (273 K, 10 bar). Our results demonstrate that CO2 substitutions by N2 in the small sI cages were thermodynamically favored. This substitution is problematic in terms of efficient CO2 capture, since the small cages make up 25% of the sI clathrate cages, therefore a significant amount of energy could be spent on removing N2 from the flue gas rather than CO2. The thermodynamics of CO2 substitution by CH4, SO2 and H2S in sI clathrate hydrates was also examined. The substitution of CO2 by these gases in both the small and large cages were determined to be favorable. This suggests that these gases may also disrupt the CO2 capture by sI clathrate hydrates if they are present in large concentrations in the combustion flue stream. Similar substitution thermodynamics at 200 K and 10 bar were also studied. With one exception, we found that the substitution free energies do not significantly change and do not alter the sign of thermodynamics. Thus, using a lower capture temperature does not significantly change the substitution free energies and their implications for CO2 capture by sI clathrate hydrates.