On the Importance of Diox Concentration in Promoting Ch4 Hydrate Formation : A Thermodynamic and Kinetic Investigation

Hydrate-based CH 4 storage is a promising technology for safe and economic-viable natural gas storage and transportation as solid CH 4 -hydrate possess advantages in both energy density and storage stability. The quest for an effective and economic-friendly thermodynamic promoter for CH 4 hydrate formation is imminent with the aim of (a) reducing CH 4 hydrate formation P - T condition and (b) increasing both the CH 4 gas uptake rate and final CH 4 storage capacity. In this study, a non-carcinogenic thermodynamic promoter 1,3-dioxolane (DIOX) was systematically investigated with the objective of quantifying the effect of DIOX concentrations (0.15 mol/L - 5.56 mol/L) on the process of mixed CH 4 +DIOX hydrate formation. A series thermodynamic, kinetic, Raman spectroscopy measurement and morphology observation experiments were conducted to elucidate the mechanism of the promotion effect of DIOX at concentrations below the stoichiometric concentration (5.56 mol/L). The DIOX with various concentrations make the thermodynamic phase equilibrium of binary hydrate shift to the region of moderate temperature and pressure. Raman spectra provided evidence of more CH 4 molecules fill the large cages of sII hydrate with the decrease of DIOX concentration. The ratio of CH 4 in large cages to CH 4 in small cages of sII hydrate increases from 0.05 to 0.38 with the decrease of DIOX concentration. The gas uptake rate of CH 4 declined with the decrease of DIOX concentration. We also observed that DIOX concentration is an important factor affecting the morphologies of hydrate formation. These findings provide evaluation methodologies for improving the storage capacity and environmental friendliness, as well as the foundation for application of DIOX in hydrate-based CH 4 storage technology