The role of thermal path on the accuracy of gas hydrate phase equilibrium data using isochoric method

The aim of this paper is to investigate the role of thermal path on the accuracy of gas hydrate phase equilibrium data using isochoric method. In this regard, methane hydrate equilibrium conditions have been typically determined using different heating paths – continuous and stepwise. The step-heating path, with proper size and duration of temperature increment, provided the most accurate data of methane hydrate phase equilibrium conditions compared with other experimental data available in literature. We have concluded that equilibrium step-heating path had the potential for determining reliable hydrate phase diagrams, irrespective of the present components in the system. Generally, the sufficient time given to each isothermal step is based on approaching a constant number of moles of gas phase through partial hydrate dissociation whereas the size of temperature increment is limited by the amount of gas encaged in hydrate cages.Moreover, the advantage of isochoric method for pure gas systems in utilizing a section of hydrate phase diagram instead of the distinctive condition, at which the last piece of hydrate disappears, is confirmed. Finally, the possibility of obtaining hydrate phase diagram of pure gas systems at arbitrary pressures was examined by purging the system before hydrate dissociation process.

► Step-heating path provides more reliable gas hydrate equilibrium data (Lw-H-V).
► Larger increment in isothermal steps needs more time to approach equilibrium state.
► Pure gas step-heating curve is in close agreement with hydrate equilibrium curve.
► Its probable to obtain pure gas hydrate data at arbitrary pressure by gas purging.