Hydrate-Based Gas Storage Application Using Simulated Seawater in the Presence of a Co-Promoter: Morphology Investigation

Abstract

The hydrate morphology pattern plays a critical role in the reactor design for hydratebased gas storage/separation technology. This work investigated the morphology of mixed methane− THF hydrate formation using salt water (3.5 wt % NaCl) instead of pure water at 288.2 K and 8 MPa. The result indicated that the nucleation occurred at the gas/liquid interface and then the hydrates grew along the wall of the crystallizer column. After a specific time interval, the hydrates gradually grew downward until they completely covered the bulk solution. This work applied 500 ppm of copromoters, including sodium dodecyl sulfate (SDS) and three amino acidsvaline, leucine, and methionine to improve the kinetics of mixed hydrate formation. The presence of SDS in the system resulted in distinct mixed hydrate formation patterns. After hydrate nucleation at the gas/liquid interface, most of the hydrates predominantly grew downward and enveloped the solution within a few minutes. Moreover, the mushy hydrates gradually transformed into stiff hydrates over time. Three amino acids resulted in the same hydrate patterns as those formed in the absence of a co-promoter, but the formation was completed more rapidly. The kinetic data indicated that using salt water for the formation of mixed methane−THF hydrates resulted in low hydrate formation kinetics. The presence of SDS significantly enhanced the kinetics of hydrate formation but decreased the final gas uptake by about one-half. Additionally, it was discovered that the presence of amino acids accelerated the hydrate formation kinetics while having a negligible effect on the final methane uptake.

Nucleation Behavior of Single-Gas Hydrates in the Batch-type Stirred Reactor and Their Promotion Effect with Ultrafine Bubbles: A Mini Review and Perspectives

“…Also, because of their large heat capacity, clathrate hydrate crystals may be used as a cold storage media at temperatures higher than that when ice is used . In addition, gas hydrates can selectively remove gases from gas mixtures, , as well as water from aqueous solutions such as with desalination. , …”

“…One hypothesis to explain this memory effect is the “residual structure hypothesis”, which argues that sections of the hydrate crystal structure remain in water, thus leaving behind a “memory” of the crystal structure ,,, (see 2­(a) in Table ). In this explanation’s favor, it is known that a hydrogen bond network exists even with pure water, especially at the low temperatures involved in hydrate formation conditions.…”

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

“…Recently, a huge experimental effort has been directed to enhance methane hydrate kinetics from natural or simulated seawater (2.7-3.5 wt% NaCl) in non-stirred reactors 24,25 .…”

“…For example, Nesterov and Reshetnikov examined pure methane hydrate formation from saline water (3 wt %) in the presence of 0.1 wt % SDS at 275 K. They found that SDS micelles did not form even if the pressure was increased from 8 to 16 MPa . Moreover, Inkong et al tested copromoters of SDS and amino acids for binary CH 4 –THF sII hydrates from a saline solution of 3.5 wt % NaCl at 8 MPa and 288 K. Despite the reduced induction time and increased hydrate formation rate in the presence of SDS, the process resulted in 50% reduction of methane uptake and hydrate yield compared to stand-alone amino acids. , Thus, the effect of SDS addition to saline water is the same in both sI and sII hydrate studies. In addition to the above adverse effects of SDS as a kinetic hydrate promoter (KHP), it has been found that it is not practical for any practical scale-up application due to severe foam formation even at low concentrations .…”

“…22,23 Recently, a huge experimental effort has been directed to enhance methane hydrate kinetics from natural or simulated seawater (2.7−3.5 wt % NaCl) in unstirred reactors. 24,25 To accelerate the hydrate formation rate in such an inhibitory medium, kinetic promoters such as sodium dodecyl sulfate (SDS) and amino acids were used. For instance, Veluswamy et al investigated the kinetic performance of amino acids for sII mixed methane/THF hydrate formation from saline water (3 wt % NaCl) at 283.2 K. The study showed that a low concentration of leucine (200 ppm) could improve the hydrate kinetics at 5 MPa.…”