Improved Experimental Determinations of Phase Equilibria and Structural Transitions of Mixed Gas Hydrates under Isothermal Conditions

Abstract

Investigations on the intrinsic properties of gas hydrates with multiple guests are essential to scientific and technological fields. In particular, even though evaluating and designing a hydrate phase process require isothermal phase equilibria, it is difficult to obtain extensive data with various components and compositions in a short period of time due to the static-analytic method. The present study introduces a new experimental determination on hydrate phase equilibria using continuous dissociation induced by extremely slow vapor volume expansion at a constant temperature. When a syringe pump is automatically operated at the microliter level during the dissociation process, the endothermic dissociation can be traced from the temperature readings. The validity and stability of the proposed technique were evaluated using pure CH4 hydrates, and repeated measurements of three-phase (L-w-H-v) equilibrium conditions are used to optimize the volumetric expansion rates. Then, an experimental approach is applied to incipient CH4 + C2H6 hydrates and identifies the structural transition behavior. This method is thought to provide extensive data and further improvements in terms of hydrate phase equilibria with multiple gas components.