In Situ Characterization of Mixed CH₄–THF Hydrates Formed from Seawater: High-Pressure Calorimetric and Spectroscopic Analysis

Clathrate hydrate-based sustainable technologies have received considerable interest in various industrial applications, wherein solidified natural gas (SNG) technology has revealed an incredible potential for storing natural gas (methane) in the safest and compact form. Herein we elucidated seawater-based mixed CH₄–THF hydrate to comprehend the economic feasibility of SNG technology. High pressure in situ calorimetric and vibrational spectroscopic (Raman spectroscopy) analyses were carefully performed to expand physical insights into the formation and dissociation behavior of mixed hydrates in a seawater environment. Experiments were performed to study the inhibition or promotional effect of salt on formation/three-phase equilibrium and dynamics of cage occupancy of mixed hydrates in the presence of saltwater (3.0 wt % NaCl), synthetic seawater (3.83 wt % salinity), and actual Singapore seawater (2.72 wt % salinity) while utilizing a stoichiometric amount of THF (5.56 mol %). Though salts are known for hydrate inhibition, unusual rapid hydrate formation events were observed at ambient temperature in the presence of seawater. Additionally, experiments were performed to study the effect of pressure driving force for the promotional effect of seawater in mixed hydrate formation. Our findings highlight the potential of engaging natural seawater to enhance the economic feasibility of SNG technology for natural gas storage and transportation.