(457c) Morphological Investigation of Cyclopentane Hydrates: Effect of Cyclopentane Activity and Surface Active Agents

Clathrate hydrates, which are generally termed gas hydrates when natural gas is a guest molecule, generate interest because of the potential negative consequences of hydrate plug formation for transport of natural gas and hydrogen, and because of their potential application in CO2 sequestration, or as phase change materials in refrigeration. Proper analysis of hydrates in any scenario will require knowledge of the dynamic processes of formation and dissociation as well as understanding of their rheological and morphological properties. This work addresses the last one of these issues related to model oil-field emulsions. Cyclopentane forms clathrate hydrates at atmospheric pressure and is used as the guest molecule in hydrates. Morphological behavior of a single water drop immersed in a hydrocarbon phase containing cyclopentane under hydrate forming conditions is presented. It has been found that the concentration of cyclopentane in the external hydrocarbon phase affects the thermodynamics and kinetics of the process as well as micro-structural characteristics of hydrates. The equilibrium dissociation temperature and the rate of hydrate formation decreases with a drop in cyclopentane activity (concentration). Hydrate formation preferentially occurs at the water-hydrocarbon interface leading to formation of a hydrate shell around a water drop. Generally crude oils carry a significant amount of natural surfactants, e.g. asphaltenes, inspiring us to study the effect of surface active agents over the hydrate morphology. Results are reported for different surfactants present only in either the hydrocarbon or water, or in both the phases; naturally-occurring surface active agents from crude oil have also been studied. Our results indicate that head group area of a surfactant significantly affects the sequence of events in hydrate formation, and thus modifies the final morphology. Bulky head group surfactants present in the hydrocarbon phase lead to a mushy / dendritic morphology while a faceted / polycrystalline shell is found in their absence. Interaction of two water drops during the process of hydrate formation possesses a significant value to understand a global emulsion behavior during plug formation and results on this problem will be described.