Abstract
The formation, dissociation, and reformation of cyclopentane (CP) hydrate in a sub-millimeter-sized capillary were conducted in this work, and the morphology of CP hydrate was obtained during above processes, respectively. The influences of the supercooling degree, i.e., the hydrate formation driving force, on CP hydrate crystals’ aspect and growth rate were also investigated. The results demonstrate that CP forms hydrate with the water melting from ice at the interface between the CP and melting water at a temperature slightly above 273.15 K. With the action of hydrate memory effect, the CP hydrate in the capillary starts forming at the CP-water interface or CP–water–capillary three-phase junction and grows around the CP–water interface. The appearance and growth rate of CP hydrate are greatly influenced by the supercooling degree. It indicates that CP hydrate has a high aggregation degree and good regularity at a high supercooling degree (or a low formation temperature). The growth rate of CP hydrate crystals greatly increases with the supercooling degree. Consequently, the temperature has a significant influence on the formation of CP hydrate in the capillary. That means the features of CP hydrate crystals in a quiescent system could be determined and controlled by the temperature setting.
Highlights
That means the features of CP hydrate crystals in a quiescent system could be determined and controlled by the temperature setting
Hydrates are a kind of crystalline compound, which is usually formed by water and gas molecules at the proper temperature (T) and pressure (P) [1,2]
We focused on CP hydrate crystal formation, dissociation, and reformation in a
Summary
Hydrates are a kind of crystalline compound, which is usually formed by water and gas molecules at the proper temperature (T) and pressure (P) [1,2]. Most common gases, such as CH4 , CO2 , N2 , O2 , tetrahydrofuran (THF), and cyclopentane (CP), are able to form hydrates at different T-P conditions [3,4]. Water molecules (host molecules) build cavities with a specific shape and size through a hydrogen-bond interaction, and gas molecules (guest molecules) are encaged in the cavities and stabilize the cavity structure [5,6]. Different guest molecules should form hydrates with different structures, i.e., structure I, II, and H [8,9]
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