Rapid and energy-dense methane hydrate formation at near ambient temperature using 1,3-dioxolane as a dual-function promoter

Gas storage technologies are vital to a modern energy security and resilience framework. Natural gas storage via clathrate hydrates, also known as Solidified Natural Gas (SNG), is attractive because of its non-explosive nature and high volume density. 1,3-dioxolane (DIOX), an additive with low volatility and less toxicity, has recently emerged as a promising dual-function (thermodynamic and kinetic) promoter for hydrate formation. Herein, we investigate mixed CH4/DIOX (sII) hydrate formation at, a) elevated temperature conditions, and b) introducing 3 wt% NaCl to the system (simulated seawater conditions). Hydrate formation from an aqueous solution containing 5.56 mol% DIOX and 1000 ppm L-tryptophan resulted in an average final methane uptake of 99.76 (+/- 2.85) (v/v; volume of gas at STP/volume of hydrate), when the experimental temperature and methane overpressure employed were 293.15 K and 6.6 MPa, respectively. This equates to 86.8% of the theoretical limit for mixed CH4/ DIOX (sII) hydrates. The average time required for 90% completion of the gas uptake was only 39.89 (+/- 0.96) min. For experiments conducted in the presence of 3.0 wt% NaCl (a thermodynamic inhibitor), the final gas uptake was expectedly lower when compared to the counterpart freshwater system. This was somewhat offset by elevating the initial driving force and adding 1000 ppm of L-tryptophan. The rapid and high-volume methane uptake achieved at near ambient temperature significantly propels the viability of using the mixed CH4/DIOX system for hydrate based natural gas storage. However, further improvement in the kinetic performance is warranted to negotiate hydrate formation from saline water.