Novel Amino Acid Derivatives for Efficient Methane Solidification Storage via Clathrate Hydrates without Foam Formation

Although anionic surfactants are considered the most efficient kinetic gas hydrate promoters for gas storage applications, gas recovery and reuse of surfactants are difficult due to high foam formation during hydrate melting. Additionally, most anionic surfactants are toxic, which has an intense environmental effect. In this study, novel amino acid derivatives (ACDs) were developed as the first class of superior promoters compared to surfactants without foaming during the formation and recovery of gas hydrates. The results of high-pressure autoclave experiments indicated that all ACDs significantly enhanced the kinetics of methane hydrate formation at 500 ppm. ACD5 derived from leucine showed the best promotion effect in distilled water by providing a total mole consumption of 436.1 mmol. ACD5 increased the degree of water-to-hydrate conversion from 39.6% in pure water to 94.3%, which was higher than in sodium dodecyl sulfate (SDS) solution (87.8%). Moreover, differential scanning calorimetry experiments demonstrated that ACDs could form methane hydrates at relatively lower temperatures than pure water. They increased the onset temperature of methane hydrate formation from −15 °C in pure water to −12 °C at 500 ppm. A higher promotion activity than SDS was also observed for ACDs in salt water, suggesting that seawater can be used to produce methane hydrate instead of pure water to reduce gas storage costs. Besides, visual observations revealed that no foam was formed during melting hydrates and releasing methane in the presence of ACDs. These findings show that a slight modification of amino acids makes them efficient candidates for improving gas hydrate formation for seawater desalination and gas storage applications.