Implications of the CH4-Flue Gas Replacement in the Structure H Hydrate System as Revealed by 13C NMR and a High Pressure Micro-Defferential Scanning Calorimeter

Abstract

The CH4-flue gas replacement in naturally occurring gas hydrates has attracted significant attention due to its potential as a method of exploitation of clean energy and sequestration of CO2. In this study, 2,2-dimethylbutane (Neohexane, NH) was used as a sH hydrate former, and the compositions of flue gas were CO2 (10%) + N2 (90%) and CO2 (20%) + N2 (80%). The shifts of the quaternary phase (H-LW-LH-V) equilibrium of initial and replaced hydrates verified that flue gas was successfully replaced with the CH4 in the sH hydrates. The 13C NMR confirmed that the CH4-flue gas replacement reaction proceeded without structural transition and the CO2 molecules also occupied cages of structure H hydrates. A high pressure micro-differential scanning calorimeter (HP μ -DSC) provided reliable hydrate stability conditions and heat of dissociation values in the porous silica gels after the replacement, which confirmed that CH4 in the hydrates was successfully replaced with flue gas. A heat flow change associated with the dissociation and formation of hydrates was not noticeable during the CH4 - flue gas replacement in sH hydrates.