Synergistic and antagonistic effects of amino acids in clathrate hydrates of greenhouse gases

Abstract

Gas hydrates are the indispensable materials in curtailing greenhouse gas emissions, particularly given their larger volumetric compressibility. However, sluggish and inefficient conversions are notable hindrances, which can be surpassed by using certain additives. We used aqueous solutions with 0.5 wt % amino acids (l-phe, l-met, l-cys, l-val, and l-leu) as additives. Individually all are suitable promoters for CH4 hydrates, while the same is true for CO2 hydrates also excepting l-phe. However, a small amount of l-met or l-cys can assist the l-phe rich solution as a better promoter for CO2 hydrates. The solution mixture synergistically enhances the gas uptake by a factor of 10. The addition of l-val or l-leu shows an antagonistic effect, and the CO2 hydrate conversion is insignificant until the solution mixture became rich in l-val or l-leu. Ex-situ micro-Raman studies unambiguously confirm the solid phase as clathrate hydrate. The perturbations in the OH-stretching mode due to synergistic or antagonistic effects in amino acids mixed solutions are small but subtle.

Keywords

• CO2- and CH4- hydrates
• Synergistic and Antagonistic effects
• Amino acids
• Mixed solutions
• Kinetic promoters
• Raman spectroscopy