The Role of Stirring and Amino Acid Mixtures to Surpass the Sluggishness of CO2 Hydrates

Clathrate hydrates are attractive materials for storing greenhouse gases such as methane (CH4) and carbon dioxide (CO2). Inefficient water-to-hydrate conversion and sluggishness in kinetics are significant impeding factors. Some additives in lower dosages help accelerate the hydrate conversion process. The aqueous solution with amino acids (0.5 wt %), l-phenylalanine (l-phe), and l-threonine (l-thr) inhibits the CO2 hydrate formation in static (0 rpm) conditions. However, l-methionine (l-met) and l-valine (l-val) are promoters under these conditions. A mild stirring (≥100 rpm) of the aqueous solution favored the hydrate conversion. The overall gas uptake, under continuous stirring, progressively increased by about 15–20%. Another way to improve the storage capacity in l-phe and l-thr aqueous systems in the static reactor is by adding a small quantity of aqueous solutions of l-met or l-val (20% by volume). The overall gas uptake and kinetics under static conditions significantly improved in the l-thr dominant system. However, the gas uptake synergistically improved in mixed solutions with l-phe and l-met, while the gas uptake was insignificant in solution with l-phe and l-val.