Gas hydrate phase equilibria measurement techniques and phase rule considerations

A brief review of the Gibbs phase rule for non-reacting systems and its correct application to clathrate hydrates is presented. Clarification is provided for a common mistake found in hydrate phase-equilibria literature, whereby initial compositions are used as intensive variables to satisfy the Gibbs phase rule instead of the equilibrium values. The system of (methane + carbon dioxide + water) under (hydrate + liquid + vapor) equilibrium is used as a case study to illustrate key points and suggestions to improve experimental techniques are proposed.

► Inconsistencies found in hydrate literature. ► Clarification to the number of variables needed to satisfy and justify equilibrium data. ► Application of phase rule to mixed hydrate systems. ► Thermodynamically consistent format to present data.