Solid–liquid–vapor phases of water and water–carbon dioxide mixtures using a simple analytical equation of state

Abstract

Recently we have proposed a unified analytical equation of state (EOS) for solid–liquid–vapor phases, and successfully applied the EOS for the solid–liquid–vapor states of pure substances, as well as binary mixtures. The present study is an extension of the earlier EOS work to water and its binary mixtures with carbon dioxide. It is found that the proposed EOS can describe reasonably well the thermodynamic properties of water (having unordinary melting/freezing behaviors) around the triple point, although to set up the EOS parameters requires a special procedure different from the ordinary compounds like CO 2. A simplified version of EOS for water has also been developed by sacrificing accuracy in some of the water properties, in order to model water-containing mixtures. Using such a simplified EOS of water, we examine the feasibility of phase behavior prediction including the solid (clathrate hydrate) state for binary mixtures of water and CO 2. All important three-phase (triple-point) equilibrium lines (vapor–liquid–liquid, solid–liquid–liquid, solid–liquid–vapor equilibria) are fairly well predicted, using only the information of vapor–liquid equilibrium data and the quadruple points. Results are still tentative but are encouraging for further improvement. This is a completely new way to model the clathrate-forming system.