Rapid methane storage via sII hydrates at ambient temperature

Abstract Mixed CH4-THF hydrate formation has been studied with the objective of advancing the operational and economic feasibility of hydrate formation. In this regard, the possibility of achieving rapid kinetics of hydrate formation at ambient temperature (298.2 K) has been explored. It was found that at a relatively moderate initial driving force of 5.4 MPa (9.5 MPa initial pressure at 298.2 K), we report mixed CH4-THF hydrate formation with a methane uptake of 40.2 (±0.9) mmol of gas/mol of water gas uptake achieved in 1.5 h of hydrate formation. Further, by synergistically combining with a benign kinetic promoter, hydrophobic amino acid L-tryptophan in low concentration (500 ppm), the kinetic performance could be rapidly enhanced with 81.3 (±3.7) mmol of gas/mol of water gas uptake obtained in 1.5 h. This gas uptake capacity equates to roughly 69% of the theoretical gas uptake limit for sII hydrates of CH4 and THF. For a lower initial driving force of 3.1 MPa (7.2 MPa initial pressure), similar kinetic performance could not be replicated. This indicates that when the temperature is fixed as a rate limiting step at a rather high value as 298.2 K in the present case, sufficient driving force is required in the form of a high initial pressure so as to achieve rapid hydrate formation. Finally, by using hybrid combinatorial approach which combines stirred (to enable fast nucleation) and unstirred reactor configuration for hydrate formation, we were able to significantly reduce the stochasticity of hydrate nucleation with the overall average nucleation time in the study being 1.4 (±0.8) minutes.