Influence of surface wettability on methane hydrate formation in hydrophilic and hydrophobic mesoporous silicas

The methane hydrate (MH) formation process in confinement was investigated using high-pressure methane sorption experiments on two wet materials with similar pore size distributions, B – PMO (hydrophobic) and MCM – 41 (hydrophilic). Their methane sorption isotherms possess two discrete methane gas consumption steps at ~10 bar and ~ 30 bar at 243 K. A systematic analysis reveals that external water and the so-called ‘core water’ inside the pore is rapidly consumed in the first step to form bulk-like hydrate, whereas adsorbed water is slowly consumed in the second step to form less stable confined hydrates at higher pressures. Synchrotron powder X-Ray results confirm methane hydrate structure I and reveal that bulk ice is swiftly and fully converted to hydrate in MCM – 41, whereas inactive bulk ice co-exists with MH in B – PMO at 6 MPa demonstrating the huge impact of the surface wettability on the water's behavior during MH formation.