Insights into CO2 hydrates formation and dissociation at isochoric conditions using a rocking cell apparatus

Abstract

In order to study the hydrate-liquid–vapour-equilibria (HLVE), the isochoric pressure search method is one of the most sought-after methods through which the characteristics of the hydrate formation and dissociation processes of a given hydrate-former substance can be traced. This method contains three temperature driven segments that are known as: (i) fast cooling step, (ii) isothermal step and (iii) a slow heating step applied to a given water + hydrate-former system under closed conditions. In this work, we have carried out a study to determine the effect of various variables on the formation/dissociation process of CO2 + H2O hydrate systems such as cooling rate, heating rate, isothermal segment temperature and its length, rocking rate, initial pressure and operating temperature. These variables may influence the characteristic shape of the p-T loops and thereby might affect the precise determination of kinetics and thermodynamics parameters. The experiments have been conducted using a rocking cell apparatus where nearly 50 experiments using 10 different versions of the isochoric pressure search method have been carried out. This work primarily shows practicalities of how to obtain the hydrate equilibrium curve more efficiently and accurately. The large number of experiments provide qualitative indications of the combined mass transfer and kinetics. This information might have implications towards the use of hydrate technology for energy and environmental related applications.