The solidified natural gas (SNG) technology via hydrates is a promising and potential method for storing natural gas. It offers a compact mode of natural gas storage with high degree of safety. In this work, we present the synergistic effects of tetrahydrofuran (THF), hollow silica (HS), and sodium dodecyl sulfate (SDS) in enhancing the kinetics of mixed methane−THF hydrate formation at 6 MPa and 293.2 K in an unstirred reactor configuration. HS at the low loading of 0.5% w HS/v in 5.56 mol % THF solution used in the current study is an innovative approach to improve the surface contact area resulting in kinetic enhancement at moderate conditions (low driving force). However, the mixture of 0.5% w HS/v in 5.56 mol % THF solution resulted in a long induction time (about 400 min), which is not favorable for the SNG technology. Addition of SDS decreased the induction time and increased the hydrate formation rate under similar experimental conditions. The induction time significantly decreased with the increase in the SDS concentration. Additionally, the presence of SDS played a key role in influencing the temperature profile and the hydrate morphology during mixed hydrate formation. The methane gas uptake was 0.0591 (±0.0007) and 0.0615 (±0.0023) mol of methane/mol of water without and with SDS, respectively. Thermal stimulation with ΔT = 15 K was employed to recover methane from hydrates. A recovery of 96−98% of the stored methane gas from the hydrates formed with and without SDS was demonstrated. Interestingly, the presence of HS was effective in preventing the foam generation during hydrate dissociation in the presence of SDS.

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The hydrate morphology pattern plays a critical role in the reactor design for hydratebased gas storage/separation technology. This work investigated the morphology of mixed methane− THF hydrate formation using salt water (3.5 wt % NaCl) instead of pure water at 288.2 K and 8 MPa. The result indicated that the nucleation occurred at the gas/liquid interface and then the hydrates grew along the wall of the crystallizer column. After a specific time interval, the hydrates gradually grew downward until they completely covered the bulk solution. This work applied 500 ppm of copromoters, including sodium dodecyl sulfate (SDS) and three amino acidsvaline, leucine, and methionine to improve the kinetics of mixed hydrate formation. The presence of SDS in the system resulted in distinct mixed hydrate formation patterns. After hydrate nucleation at the gas/liquid interface, most of the hydrates predominantly grew downward and enveloped the solution within a few minutes. Moreover, the mushy hydrates gradually transformed into stiff hydrates over time. Three amino acids resulted in the same hydrate patterns as those formed in the absence of a co-promoter, but the formation was completed more rapidly. The kinetic data indicated that using salt water for the formation of mixed methane−THF hydrates resulted in low hydrate formation kinetics. The presence of SDS significantly enhanced the kinetics of hydrate formation but decreased the final gas uptake by about one-half. Additionally, it was discovered that the presence of amino acids accelerated the hydrate formation kinetics while having a negligible effect on the final methane uptake.