Effect of Ion Specificity on Thermodynamic Inhibition of CH4 and CO2 Hydrates: An Experimental and Modeling Study

Abstract

The effects of iodide salts and ion specificity on the thermodynamic inhibition of CH₄ and CO₂ hydrates have not been thoroughly investigated. In this study, we employ the isochoric pressure-search method to measure the dissociation temperature (272.48 – 286.54 K) and pressure (1.38 – 11.24 MPa) of CH₄ and CO₂ hydrates in iodide solutions with concentrations of 6.24 wt% and 12.48 wt%. The measured data are subsequently used to validate a thermodynamic model integrating the Pitzer model into the van der Waals-Platteeuw (vdW-P) model for predicting the dissociation pressure of gas hydrates. The model can accurately predict the dissociation conditions of CH₄ and CO₂ hydrates in iodide solutions. The experimental results reveal that the inhibition effect of iodide salts on CH₄ and CO₂ hydrates is enhanced with an increasing salt concentration. Additionally, the dissociation temperature suppression of CH₄ and CO₂ hydrates is correlated with water activities of different salt solutions to investigate the effect of ion specificity on the thermodynamic inhibition of these hydrates. Our analysis demonstrates that ion specificity exists in the thermodynamic inhibition of CO₂ hydrate but does not apply to CH₄ hydrate. In addition, anions play a major role in the thermodynamic inhibition of CO₂ hydrate.