Explicating the amino acid effects for methane storage in hydrate form.

ABSTRACT

Methane emissions increase day by day into the atmosphere and influence global temperatures. The necessity to capture these emissions at the source point is a primary concern. Several methods/techniques are being adopted to capture these emissions. The methane hydrates could be a viable method among them. The present study exposes various amino acids' effects in methane hydrate formation. The formation temperatures are around ∼268 to 273 K except for l-cys, which is about ∼277 K. The required subcooling for hydrates to trigger is high and is increasing in the order l-thr > l-met > l-phe > l-val > l-cys. The methane hydrate conversion is high in the presence of nearly all the amino acids with methane uptake capacity of ∼80-85%, except l-thr, for which it is only 30% of the total uptake capacity. The side chain of l-thr comprises the hydroxyl group, making it a polar and uncharged amino acid. It is ascertained that hydroxyl groups alone can form hydrogen bonds with water, increasing the hydrophilicity and solubility of molecules, causing lesser conversion in the l-thr system. The gas uptake kinetics is faster in l-met and l-phe systems (t 90 ∼ 40 min), and sluggish kinetics is observed in l-cys, l-val, and l-thr systems. The investigations positively indicate using amino acids, l-met, l-phe, l-cys, and l-val as efficient materials for methane gas capture and storage in hydrate form, although not l-thr. Amino acids are readily dissolvable in water and could be easily pelletized for methane gas storage and transportation.