Measurements and modeling of the hydrate phase equilibria of CO2 in the presence of promoters

Recently, the CO2 hydrate as cold storage medium draws much attention and some thermodynamic promoters are proposed to moderate its hydrate formation condition for reducing energy consumption. In this study, the hydrate phase equilibrium conditions of CO2 in the presence of tetrahydrofuran (THF), cyclopentane (CP), tetrabutylammonium bromide (TBAB) were measured with the isochoric pressure searching method. The hydrate dissociation enthalpies were calculated with Clausius-Clapeyron equation base on the measured data sets. The results showed that the hydrate phase equilibrium temperature of CO2 in the aqueous solution containing promoters increased at least 12 K at 1.5 MPa compared to that of CO2 in the pure water system. The hydrate dissociation enthalpies of (CO2+CP+H2O), (CO2+THF+H2O), (CO2+TBAB+H2O) reached 136.16, 147.07, 205.75 kJ.mol- 1, respectively, which significantly increased than that of (CO2+H2O) (64.93 kJ.mol- 1). A thermodynamic framework was proposed to prediction the hydrate phase equilibria of CO2 in the presence of promoters. The Chen-Guo (C-G) model was used to calculate the fugacity of hydrate phase, the NRTL and developed PMZH models were used to calculate the activity of liquid phase. The CO2 solubility was calculated by the modified Henry's law, and the effect of volatile component in aqueous phase on the composition of gas phase was investigated. The predictions of our proposed model agree well with the measured data in this work as well as literature values.

Automated summary

In this study, the hydrate phase equilibrium conditions and dissociation enthalpies of CO2 in the presence of tetrahydrofuran (THF), cyclopentane (CP), and tetrabutylammonium bromide (TBAB) were measured. The results showed that the presence of promoters increased the hydrate phase equilibrium temperature of CO2 and its dissociation enthalpies significantly. A thermodynamic framework was proposed to predict the hydrate phase equilibria of CO2 in the presence of promoters, and the predictions were in good agreement with the measured data.