Investigation on the influence of CH4 hydrate dissociation on depressurization replacement efficiency in CO2 hydrate sequestration

Abstract The replacement of CH 4 with CO 2 in marine hydrates has garnered widespread attention due to its potential for energy recovery and CO 2 sequestration. In this study, CH 4 hydrates and replacement process and outcomes with CO 2 were investigated using optical microscopy, differential scanning calorimeter (DSC), and Raman spectroscopy. Optical microscopy experiments showed that CH 4 hydrate formed a solid spherical hydrate film with a thickness of 5–10 μm on the surface of silica gel (SG), which arose from volume expansion associated with the water-to-hydrate phase transition. DSC experiments showed that CO 2 hydrate formation occurred during pure CH 4 decomposition, thereby reducing required CO 2 partial pressure. Finally, replacement ceased when the partial pressure of CO 2 below the partial pressure of CO 2 of the equilibrium pressure of the CH 4 -CO 2 mixed gas hydrate. Pure CH 4 hydrate decomposition simultaneously achieved higher CH 4 recovery (87.9 mol%), CH 4 purity (84.7 mol%), and final system pressure (3.8 MPa). Due to CH 4 hydrate decomposed during replacement procedure (DSC results), the particle size (25–635 μm) minimally affected the replacement rate and efficiency, indicating that the replacement reaction was governed by reaction kinetics in SG. Raman analysis revealed consistent replacement efficiency across hydrate particle depths (0–60 μm).