The importance of liquid phase compositions in gas hydrate modeling: Carbon dioxide–methane–water case study

Abstract

Liquid compositions obtained through vapor+liquid+hydrate equilibrium modeling are often neglected and not reported in literature. This work demonstrates the sensitivity and importance of the liquid phase compositions on selected models and parameters. The equations of state used to model two-phase systems are the Soave–Redlich–Kwong, the Valderrama–Patel–Teja and the Trebble–Bishnoi equations of state. The modeling analysis for three-phase systems is based on the Trebble–Bishnoi equation of state along with the model by van der Waals and Platteeuw. The vapor+liquid equilibrium model predictions at gas hydrate formation conditions were found to be greatly dependant on the liquid phase compositions. At the three-phase equilibrium, small modifications in the equation of state’s interaction parameters significantly affected the liquid composition predictions while leaving the vapor compositions mostly unchanged. Lastly, the interaction parameters were optimized for the two phases separately using vapor+liquid equilibrium data. When optimized only for liquid, vapor and liquid compositions were predicted correctly. However, when optimized only for vapor, liquid compositions failed to fit experimental data.