Tetra-n-Butyl Ammonium Bromide (TBAB) forms semi-clathrate hydrates which can incorporate small gas molecules, such as methane and nitrogen at ambient temperatures and atmospheric pressure. Such favourable stability conditions, combined with ease of formation could make semi-clathrates particularly attractive for a large variety of applications. These hydrates have recently been investigated for their use in the separation of gases, and it is proposed that the same technology could potentially be used for storage and transportation of gases. To evaluate the feasibility of using TBAB hydrates for separation and storage purposes, an extensive test programme was conducted to determine: phase stability of the semi-clathrates, gas storage capacity, and composition of the stored gas. The results show that TBAB semi-clathrates have very favourable stability conditions. They can store considerable quantities of gas, and favour small molecules in their structures. These experiments suggest that semi-clathrate hydrates, such as TBAB, could have a significant potential as an alternative for industrial separation, storage, and transportation of natural gas.

Hydrogen is currently considered by many as the “fuel of the future”. It is particularly favoured as a replacement for fossil fuels due to its clean-burning properties; the waste product of combustion being water. While hydrogen is relatively easy to produce, there is currently a lack of practical storage methods for molecular H2, and this is greatly hindering the use of hydrogen as a fuel. Gases are normally stored in vessels under only moderate pressures and in liquid form where possible, which yields the highest energy density. However, to store reasonable quantities of hydrogen in similar volume containers, cryogenic temperatures or extreme pressure are required. Many potential hydrogen storage technologies are currently under investigation, including adsorption on metal hydrides, nanotubes and glass microspheres, and the chemical breakdown of compounds containing hydrogen to release H2. Recent studies have sparked interest in hydrates as a potential hydrogen storage material. The molecular storage of hydrogen in clathrate hydrates could offer significant benefits with regard to ease of formation/regeneration, cost and safety, as compared to other storage materials currently under investigation. Here, we present new experimental hydrate stability data for sII forming hydrogen–water (up to pressures of 180 MPa) and hydrogen–water–tetrahydrofuran systems, the structure-H forming hydrogen–water–methyclycohexane system, and semi-clathrate forming hydrogen–water–tetra-n-butyl ammonium bromide/tetra–n-butyl ammonium fluoride systems.

Cette thèse présente les mesures et l'analyse thermodynamique d'équilibres de phases de systèmes d'hydrates contenant du dioxyde de carbone (CO2), dans le contexte de procédés alternatifs de captage du CO2. Le développement de nouveaux procédés de séparation par voie de cristallisation par hydrates est un point crucial de cette thématique. Les conditions de température et de pression requises et l'utilisation de promoteurs thermodynamiques sont au-delà des opérations habituelles et des bases de données existantes. La connaissance précise des conditions de formation et dissociation d'hydrates de gaz en présence d'additifs chimiques constitue une contrainte importante d'un point de vue thermodynamique et est nécessaire pour la modélisation et l'établissement de la faisabilité de nouveaux procédés industriels impliquant des hydrates de gaz. Dans cette thèse, nous présentons un nouveau dispositif expérimental qui combine techniques statiques et techniques analytiques, ce dernier a été spécialement développé pour mesurer des données d'équilibres des phases hydrate-liquide-gaz à des températures variant entre 233 et 373 K et à des pressions jusqu' à 60 MPa. De nouvelles données d'équilibre de phases des systèmes (CO2 + méthane), (CO2 + azote) et (CO2 + hydrogène) ont été mesurées dans des conditions de formation d'hydrates en suivant la méthode isochorique avec variation de la pression en fonction de la température, et en analysant la composition en phase gazeuse. Les données d'équilibre et les conditions de dissociation d'hydrates générées dans ce travail sont comparées avec les données de la littérature. La fiabilité des modèles thermodynamiques les plus couramment utilisés est aussi étudiée. Les comparaisons entre les données expérimentales et prédites de dissociation d'hydrates suggèrent la nécessité de réajuster les paramètres des modèles thermodynamiques pour les systèmes contenant des hydrates de CO2. En outre, l'effet promoteur du bromure de tetrabutylammonium (TBAB) sur les équilibres des phases des gaz purs et de mélanges contenant du CO2 a été étudié. L'effet le plus important de promotion (réduction de la pression de formation des hydrates > 90%) est observé pour le système (TBAB + azote). Les résultats expérimentaux suggèrent que le CO2 peut être séparé de mélanges de gaz industriels ou de combustion à des températures douces et à de basses pressions à l'aide de TBAB en tant que promoteur thermodynamique. La pression requise pour la formation d'hydrates à partir de mélanges de (CO2 + azote) est réduite de 60 % en présence de TBAB. / This thesis addresses the measurement and thermodynamic analysis of the phase equilibrium behavior of carbon dioxide (CO2) hydrate-forming systems in the context of alternative capture engineering approaches. The development of new technologies based on gas hydrates requires specific temperature and pressure conditions and the utilization of thermodynamic promoters that are beyond usual operations and existing databases. Accurate knowledge of gas hydrates formation and dissociation from thermodynamics point of view in the presence of chemical additives is necessary for modeling purposes and to establish the feasibility of emerging industrial processes involving gas hydrates. In this thesis, a new experimental set-up and method for measuring pressure, temperature and compositional phase equilibrium data of high accuracy are presented. The equipment is based on the ‘static-analytic' technique with gas phase capillary sampling and it is suitable for measurements in a wide temperature range (i.e. 233 to 373 K) and pressures up to 60 MPa. New phase equilibrium data in the (CO2 + methane), (CO2 + nitrogen) and (CO2 + hydrogen) systems under hydrate formation conditions were measured following an isochoric pressure-search method in combination with gas phase compositional analysis. The equilibrium data generated in this work are compared with literature data and also with the predictions of two thermodynamic literature models. Comparisons between experimental and predicted hydrate dissociation data suggest a need of readjusting model parameters for CO2 hydrate-forming systems. In addition, the thermodynamic stability of Tetra-n-Butyl Ammonium Bromide (TBAB) semi-clathrates (sc) with pure and mixed gases was investigated. The largest promotion effect (> 90% reduction in hydrate formation pressure) is observed for (TBAB + nitrogen) sc. The experimental results suggest that CO2 can be separated from highly to low concentrated industrial/flue gas mixtures at mild temperatures and low pressures by using TBAB as thermodynamic promoter. The pressure required for hydrate formation from (CO2 + nitrogen) gas mixtures is reduced by 60% in the presence of TBAB.