A systematic investigation of kinetic promoters in seawater hydrate-based technology: Optimizing formation kinetics and storage capacity

Abstract

Addressing the practical constraints of using deionized water for large-scale methane storage, this study explores the use of a 2.5 wt% NaCl solution to simulate seawater conditions at 8.2 MPa and 277.2 K in a quiescent system. The incorporation of NaCl, however, impedes the hydrate formation kinetics. Sodium dodecyl sulfate (SDS) is employed as a kinetic hydrate promoter (KHP). While SDS partially improves hydrate formation kinetics, its application is hindered by foam formation, which poses significant challenges for scaling up the technology. This research further examines the effects of hydrophobic amino acids—valine, leucine, methionine, and tryptophan—as alternative kinetic hydrate promoters. Among the amino acids studied, the ranking of effectiveness under optimal conditions is as follows: tryptophan > methionine > leucine > valine. Tryptophan at its optimal concentration of 1.5 wt% demonstrates the shortest induction time (less than 2 min), the highest gas uptake (approximately 100 mmol gas/mol water), and superior water-to-hydrate conversion (55%). Morphological observations confirm that amino acids promote uniform hydrate growth without foam formation during dissociation, leaving a clear memory solution. These findings underscore the potential of amino acids, particularly hydrophobic ones like tryptophan, as sustainable alternatives to SDS for methane hydrate formation, offering significant advancements in Solidified Natural Gas (SNG) technology with promising applications in gas storage and enhancing energy security.