Investigation of the Efficient Methane Storage via Hydrate Formation Mediated by N‑Acyl Amino Acid-Based Green Surfactants

Enhancing
hydrate formation kinetics is critical for advancing
hydrate-based technologies. However, commonly used promoters are often
toxic, poorly biodegradable, and prone to causing foaming during hydrate
decomposition, limiting their practical applications. This study investigated
five biodegradable N-acyl amino acid surfactantssodium cocoyl
glycinate (SCG), disodium cocoyl glutamate (DCG), sodium cocoyl sarcosinate
(SCS), sodium lauroyl glycinate (SLG), and sodium lauroyl sarcosinate
(SLS)as potential promoters. All five surfactants promoted
methane hydrate formation to varying degrees, with SCG exhibiting
the highest efficacy. At 275.15 K and 6.0 MPa, adding 500 ppm of SCG
significantly reduced the induction time, accelerated hydrate growth,
and achieved a gas uptake of 163.44 v/v, about seven times higher
than that of pure water. Surfactants derived from coconut acid showed
superior performance compared to those based on lauryl acid, and glycine-type
surfactants (SCG, SLG) outperformed sarcosine-type ones (SCS, SLS).
SCG exhibited optimal performance at 500–750 ppm, while excessively
high or low concentrations reduced effectiveness. Elevated initial
pressure generally enhanced hydrate formation, but overly high pressure
could be detrimental. Acidic conditions inhibited hydrate formation,
whereas neutral to mildly alkaline conditions were more favorable.
The shortest induction time was achieved at pH 9.4, though increased
foaming occurred under alkaline conditions. These findings provide
a scientific basis for developing efficient, environmentally friendly
surfactants for hydrate-based gas storage.