Seawater based mixed methane-THF hydrate formation at ambient temperature conditions

Abstract

We investigate mixed methane-THF hydrate formation at ambient temperature (298.2 K), using natural seawater to make up the hydrate forming solution. The study has been performed with the objective of boosting the economic and operation feasibility of SNG (solidified natural gas) hydrate formation. While high operating temperature and inherently present salts in seawater inhibit rapid hydrate formation with high gas uptake, using amino acids such as L-arginine and L-tryptophan allows a certain level of enhancement in hydrate formation kinetics. A second thermodynamic promoter, 0.3 mol % TBAF (tetra-n-butylammonium fluoride) in the solution facilitates roughly 25% increase in the gas uptake as compared to a counterpart TBAF-free system for the same hydrate formation period. Mapping the hydrate formation morphology reveals subtle details about how the additives employed affect the physical characteristics of hydrates being formed as well as the mechanisms of hydrate growth. This information may be put to good use especially when streamlining the technology for commercial adoption. Finally, the combinatorial hybrid (stirred & unstirred) approach for hydrate formation employed successfully eliminates the stochasticity associated with hydrate nucleation. All systems studied returned induction times of less than or approximately 3 min, with a high degree of reproducibility. Being the first study to investigate SNG hydrate formation at ambient temperature and employing seawater directly, the results obtained in this work set a fundamental benchmark for further research on this economically and operationally inviting prospect, and should be of interest to academic and industry personnel alike.