Enhanced Hydrate Growth Kinetics with Hydrate Seeds and Promoter under a Static Reaction System

This work provides fundamental insights into methane hydrate growth kinetics from cyclopentane (CP) hydrate seeds with a surface-active promoter of sodium dodecyl sulfate (SDS) or l-methionine under a static hydrate formation system. The gas consumption rate and the apparent rate constant were determined from the kinetic model during hydrate growth at 275 K and 7 MPa conditions. The quantity of preconstructed hydrate seeds and kinetic promoters was adjusted under a static reaction system. As CP hydrate seeds and SDS have a synergetic effect on promoting heterogeneous nucleation for hydrate growth, the initial apparent rate constant, calculated with initial gas consumption rates, indicating the number of nucleation sites where the hydrate growth occurs, increased with higher seed amounts at 200 and 500 ppm of SDS. However, increasing the seed amount at 1000 ppm of SDS does not improve the initial formation kinetics. l-methionine, one of the hydrophobic amino acids utilized as a kinetic hydrate promoter, did not significantly decrease the interfacial tension between CP and the aqueous phase. With l-methionine, the gas consumption rate did not increase significantly with higher CP amounts because of the limited conversion of CP liquid to hydrate seeds and the small number of nucleation sites. However, the overall methane storage capacity in the l-methionine system increased due to both a lowered initial rate and enhanced water-to-hydrate conversion. These findings provide insights into understanding the fundamental kinetics of hydrate growth and guidelines for optimizing hydrate formation processes to enhance methane storage.