Be careful with the gas hydrate equilibrium data measured by stirred autoclave

Abstract

Equilibrium data, one of the essential fundamental data of gas hydrate, is always needed in its prevention and utilization. In this work, a total of 111 sets of hydrate equilibrium data for CO₂-containing natural gas in alcohol/salt solutions were measured in a stirred autoclave or rocking cell by using the isochoric pressure searching method. Some equilibrium data failed in the thermodynamic consistency test. It is speculated, after the hydrate formation and dissociation in the insufficiently stirred autoclave, the last hydrate crystal could be in equilibrium with concentrated or diluted solutions which are different from the initial solution. Fake equilibrium data could be reported. The gas hydrate equilibrium data in some solutions were remeasured in a rocking cell apparatus. All the rocking cell measured equilibrium data passed the thermodynamic consistency test. It seems stirred autoclave are likely to report fake gas hydrate equilibrium data, while rocking cell may be more reliable.