Toward Economical Seawater-Based Methane Hydrate Formation at Ambient Temperature: A Combined Experimental and Computational Study

Abstract

Clathrate hydrates are emerging as a novel storage medium for safe and compact methane storage. However, their industrial-scale applicability is hindered by sluggish formation kinetics and intense energy cooling requirements. The present study is the first report on binary methane-tetrahydrofuran (THF) formation using the combination 1 of seawater and an unstirred reactor at ambient temperature (298.2 K) that would improve the process economics. Acidic zeolites with different Si/Al ratios (USY-40 and USY-10) as well as aliphatic (L-valine) and aromatic (L-tryptophane) amino acids are employed as environmentally benign kinetic hydrate promoters. The experimental study is combined with DFT calculations to shed light on the role of kinetic promoters in hydrate formation. The set of experimental data revealed that hydrophobic zeolites with a higher Si/Al ratio performed better than the more hydrophilic ones. Moreover, the aliphatic amino acid L-valine showed better kinetic promotion performance for hydrate formation in natural and artificial seawater than the aromatic amino acid L-tryptophan.The optimization of the experimental condition allowed a controlled hydrate growth boosting the gas uptake to 40 mmol gas/mol water, which is the highest reported under mild conditions using seawater. In addition, the induction time is reduced to less than 10 minutes, and a methane recovery of 97% is reached without any foaming signs. Thus, this study demonstrates the possibility of controlling the stochastic nature of nucleation and hydrate growth by properly manipulating the reaction system. Our results provide a better understanding of hydrate nucleation enhancement under realistic conditions and open the door for a possible application of these environmentally benign kinetic hydrate promoters (KHPs) for synthetic natural gas (SGH) on a continuous process and industrial scale.

Effect of Glucose on CH4 Hydrate Formation in Clay Nanopores and Bulk Solution: Insights from Microsecond Molecular Dynamics Simulations

“…50−52 Molecular dynamics (MD) simulations have been often employed to investigate the microscopic behavior of gas hydrates from the molecular scale. 53−57 Based on MD simulation, some studies had reported that lignin, 58 protein, 47 humic acid, 59 fatty acid, 60 amino acid, 61 and other organic matters 62,63 exhibit different effects on the formation and growth of gas hydrate. Furthermore, some MD simulation results found that clay mineral surfaces can repel organic matter or form organo-mineral complexes, significantly influencing the wettability of the clay surface.…”

“…Park and coworkers observed that CH 4 hydrate solids can stably intercalate within montmorillonite interlayers under conditions of lower pressure and higher temperature, suggesting that a portion of such clay mineral surface actively involved in promoting CH 4 hydrate formation . Recently, Ren et al reported that montmorillonite shortens the induction time of gas hydrate formation by providing additional nucleation sites but retards the growth kinetics of gas hydrate due to hindered mass transfer. , Several experimental studies have found that the phase equilibrium of CH 4 hydrate is inhibited in porous media composed of solid particles. − Our previous study revealed that clay surfaces affect gas hydrate formation by changing the concentration of guest molecules and ions via the adsorption of water molecules, ions, and guest molecules. , On the other hand, the abundant organic matter in hydrate reservoirs will also affect the formation behavior of gas hydrates. , Liu and coworkers found that organic matter can kinetically promote gas hydrate formation by enhancing gas–water contact, and this effect was further enhanced by sulfur-containing acid-dissolvable organic matters. , Some studies revealed that organic matter molecules inhibit the formation of gas hydrates by association with water molecules. , It is worth noting that recent studies have observed that organic matter and clay minerals have a synergistic effect on the formation of gas hydrates, which significantly shortens the induction time for gas hydrate formation. − Molecular dynamics (MD) simulations have been often employed to investigate the microscopic behavior of gas hydrates from the molecular scale. − Based on MD simulation, some studies had reported that lignin, protein, humic acid, fatty acid, amino acid, and other organic matters , exhibit different effects on the formation and growth of gas hydrate. Furthermore, some MD simulation results found that clay mineral surfaces can repel organic matter or form organo-mineral complexes, significantly influencing the wettability of the clay surface. , The interaction between organic matter and clay surfaces complicates the formation processes of gas hydrates.…”