Unlocking enhanced gas storage capacity in tuned methane hydrates: Exploring eutectic compositions and water-to-hydrate conversion

Abstract

The tuning effect of gas hydrates has received widespread interest as a promising approach for energy gas storage due to its unique features for enhancing gas storage capacity and formation conditions. However, its practical application has been stagnant because the effect of various factors has still not been revealed to induce the tuning effect. Here, we provide the dominant factors and optimized conditions related to the tuning effect to achieve the practical enhancement of gas storage capacity under mild formation conditions (272.0 K, 2.35 MPa). Based on the tetrahydrofuran (THF)/trimethylene oxide (TMO) + CH4 hydrates, dominant factors that can affect tuning effects such as eutectic composition, the concentration of the promoter, formation methods, and conversion of water-to-hydrate were experimentally examined by employing the in-situ Raman spectroscopy. The tuning effects of hydrates formed from the aqueous solutions (water-borne) were slowly advanced, unlike all hydrates formed from iced particles (ice-borne) which extremely rapidly induced them. It suggests that the eutectic point was the primary factor in water-borne hydrates, whereas the tuning effect in ice-borne hydrates is mainly governed by the formation rate and stochastic nature. Interestingly, our experiments confirmed for the first time that the gas uptake of water-borne tuned gas hydrates may be higher than those of untuned hydrates (i.e. 5.56 mol% stoichiometric concentration). This work provides not only the dominant parameters but also promising strategies for the practical application of tuning effects to efficient hydrate-based gas storage.