Carlos Lange Bassani

Approche Multi-Échelles pour les Hydrates de Gaz tenant compte de la Structure, de la Cinétique de Croissance, de l'Agglomération et de la Transportabilité dans des Conditions d'Écoulement Polyphasique: Un problème signalé par les compagnies pétrolières est le colmatage des conduites d'écoulement à cause des hydrates de gaz, un cristal qui se forme et s'agglomère provoquant des obstructions. La stratégie de gestion des hydrates consiste à laisser les hydrates se former, tout en assurant leur écoulement stable. Cette thèse décrit quantitativement une partie des processus hors équilibre de la cristallisation en considérant plusieurs concepts multi-échelles omis jusqu'à présent à la littérature. Les hydrates sont des particules poreuses et hydrophiles qui agissent comme des éponges emprisonnant l'eau, dont la cristallisation se produit principalement dans les parois capillaires. La perméation à travers les particules poreuses fournit de l'eau à sa surface externe, favorisant la formation de ponts liquides après la collision des particules, ce qui conduit à l’agglomération. Des sous-refroidissements plus élevés favorisent un scellement rapide des particules, diminuent les taux de perméation et amènent les particules à être inertes au sens de l'agglomération. De plus, les additifs aux propriétés tensioactives diminuent la vitesse de perméation, ce qui explique leurs effets anti-agglomérants. Plusieurs mécanismes sont discutés lors de la modélisation de la cinétique de croissance et de l'agglomération en utilisant un bilan de population couplé avec un modèle d'écoulement polyphasique en régime permanent. À des fins d'ingénierie, le modèle est simplifié en un critère qui détermine la production stable des systèmes à l’huile continue, donnant lieu à un nouveau nombre adimensionnel qui relie les nombres de Damköhler et de Reynolds.

The shape of nanocrystals is crucial in determining their surface area, reactivity, optical properties, and self-assembly behavior. Traditionally, shape control has been achieved through empirical methods, highlighting the need for a more refined theoretical framework. A comprehensive model should account for the kinetic factors at distinct stages of the shape formation process to identify the key determinants of nanocrystal morphology. By modulating kinetics at terraces, ledges, and kinks, we reveal that the primary factors are the adatom nucleation energies and the geometry of growth islands. Transient sites dominate the growth process, leading to kinetically trapped, metastable shapes. We illustrate these concepts with face-centered cubic nanocrystals, demonstrating diverse shape evolutions, including surface roughening and the preservation of crystal symmetry in cubes, octahedra, rhombic dodecahedra, and their truncated variants. This study reveals the mechanisms driving the formation of cubic nanocrystal shapes and offers guidance for their precise synthesis.

We explore the potential of nanocrystals (a term used equivalently to nanoparticles) as building blocks for nanomaterials, and the current advances and open challenges for fundamental science developments and applications. Nanocrystal assemblies are inherently multiscale, and the generation of revolutionary material properties requires a precise understanding of the relationship between structure and function, the former being determined by classical effects and the latter often by quantum effects. With an emphasis on theory and computation, we discuss challenges that hamper current assembly strategies and to what extent nanocrystal assemblies represent thermodynamic equilibrium or kinetically trapped metastable states. We also examine dynamic effects and optimization of assembly protocols. Finally, we discuss promising material functions and examples of their realization with nanocrystal assemblies.

Clathrate hydrates are crystals formed by guest molecules that stabilize cages of hydrogen-bonded water molecules. Whereas thermodynamic equilibrium is well described via the van der Waals and Platteeuw approach, the increasing concerns with global warming and energy transition require extending the knowledge to non-equilibrium conditions in multiphase, sheared systems, in a multiscale framework. Potential macro-applications concern the storage of carbon dioxide in the form of clathrates, and the reduction of hydrate inhibition additives currently required in hydrocarbon production. We evidence porous mesomorphologies as key to bridging the molecular scales to macro-applications of low solubility guests. We discuss the coupling of molecular ordering with the mesoscales, including (i) the emergence of porous patterns as a combined factor from the walk over the free energy landscape and 3D competitive nucleation and growth and (ii) the role of molecular attachment rates in crystallization–diffusion models that allow predicting the timescale of pore sealing. This is a perspective study that discusses the use of discrete models (molecular dynamics) to build continuum models (phase field models, crystallization laws, and transport phenomena) to predict multiscale manifestations at a feasible computational cost. Several advances in correlated fields (ice, polymers, alloys, and nanoparticles) are discussed in the scenario of clathrate hydrates, as well as the challenges and necessary developments to push the field forward.

Gas hydrate formation is a main flow assurance concern in oil and gas production. Understanding the effects of the introduction of solid particles in the slug flow is essential to improve the efficiency and safety of multiphase production. The purpose of the present work is the experimental characterization of solid‐liquid‐gas slug flow with the presence of dispersed hydrate‐like particles. Experimental tests were carried out with inert polyethylene particles of 0.5‐mm diameter with density similar to gas hydrates (938 kg/m³). The test section comprised a 26‐mm ID, 9‐m length horizontal duct of transparent Plexiglas. High Speed Imaging and resistivity sensors was used to analyze the slug flow unit cell behavior due to the introduction of the solid particles and to measure the unit cell translational velocity, the slug flow frequency, the bubble and slug lengths, and the phase fractions. Two distinct concentrations of solid particles were tested (6 and 8 g/dm³). © 2018 American Institute of Chemical Engineers AIChE J, 64: 2864–2880, 2018