Microscopic observations of clathrate-hydrate films formed at liquid/liquid interfaces. I. Morphology of hydrate films

• Published in: Chemical engineering science 2001-07, Vol.56 (14), p.4331-4338
• Main Authors: Kobayashi, Izushi, Ito, Yusuke, Mori, Yasuhiko H.
• Format: Article
• Language: English
• Subjects: Chemistry; Clathrate hydrate; Convective transport; Crystallization; Exact sciences and technology; Gas hydrate; Gas-liquid interface and liquid-liquid interface; General and physical chemistry; Mass transfer; Morphology; Surface physical chemistry
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/S0009-2509(00)00544-3

This study aims to obtain cross-sectional views of clathrate-hydrate films each formed at the interface between a liquid-water phase and a hydrophobic hydrate-former phase. For this purpose, an experimental scheme was devised which permitted us to observe, through a high-resolution microscope, cross sections of a ring-shaped hydrate film formed over the surface of each discoid drop of HCFC-141b (CH 3CCl 2F) held stationary in a narrow space between two transparent plates filled with flowing, or quiescent, water. We found that the hydrate films, once exposed to a shear flow of water and then held in a quiescent medium of water, continued to thicken at a much higher rate than the films which had been held exclusively in a quiescent water medium since their formation. The former films kept their surface/internal texture much coarser, in the course of their thickening, than the latter films which showed very fine texture throughout. When continuously exposed to a steady water flow, the hydrate films kept their thickness constant. The steady-state thickness thus recognized showed a negative dependency on the flow velocity. A temperature rise, slightly exceeding the thermodynamic stability limit for the hydrate, caused each hydrate film once grown at a lower temperature to undergo crystal dissociation simultaneously throughout its thickness, in which numerous HCFC-141b droplets, a few micrometers in diameter, were evolved and migrated into the adjacent water phase.