Structure Identification and Dissociation Enthalpy Measurement of the CH4 + C3H8 Hydrate Replaced by CO2

Abstract

The CH4-CO2 replacement occurring in natural gas hydrates has attracted significant attention due to its double function for CH4 recovery and CO2 sequestration. This study examined the influence of the CH4-CO2 replacement occurring in the CH4 (90%) + C3H8 (10%) hydrate on the hydrate structure and dissociation enthalpy (ΔHd). The crystalline structure of gas hydrates before and after replacement using CO2 was investigated using powder X-ray diffractometer (PXRD). In addition, 13C NMR was adopted in order to identify the cage-dependent guest molecule distribution in the gas hydrates before and after replacement with CO2. The composition of the hydrate phase was measured using a gas chromatograph. A gradual increase in the extent of the replacement was observed as the driving force (ΔPCO2) increased. A high-pressure micro-differential scanning calorimeter (HP μ-DSC) revealed that the ΔHd values of the hydrates after replacement with CO2 were decreased with large variation depending on ΔPCO2, comparing with those of initial CH4 + C3H8 hydrates.