Formation of bilayer clathrate hydrates

Abstract

We report molecular dynamics (MD) simulation evidence of a new family of two-dimensional (2D) clathrate hydrates. Particular attention is placed on the effect of size and hydrophilicity of guest-molecule on the formation of 2D clathrate hydrates.Among MD simulations undertaken, spontaneous formation of bilayer (BL) clathrate hydrates in nanoslits are found with five different hydrophobic guest molecules, namely, ethane (C 2 H 6 ), ethene (C 2 H 4 ), allene (C 3 H 4 ), carbon dioxide (CO 2 ) and hydrogen (H 2 ) molecules, respectively. Our simulations suggest that the host cages in water framework are likely BL-hexagonal cages with single occupancy for H 2 , or BL-heptagonal cages for CO 2 . With further increase of guest size, the host cages for C 2 H 6 , C 2 H 4 , and C 3 H 4 are BL-octagonal cages with single occupancy, and their long molecular axis tends to be normal to the surface of clathrate hydrates. In addition, for hydrophilic guest molecules such as NH 3 and H 2 S which can form strong hydrogen bonds with water, we find that most guest molecules can preferentially displace water molecules from lattice sites of water framework, instead of being separately trapped within water cages. Structural analogy between the 2D and 3D clathrates enlightens us to predict stability of several bulk gas hydrates, namely, "ethane clathrate III", "CH 4 ice-i" and "H 2 ice-i". Our findings not only can enrich clathrate structures in the hydrate family but also may improve understanding of the hydrate formation in microporous media.

CO Separation from H2 via Hydrate Formation in Single-Walled Carbon Nanotubes

“…However, when the pore size is reduced to subnanometer, the hydrogen-bonding network in water is disrupted by the highly confined environment, thereby affecting the kinetics of crystallization. − In 2D nanoconfinement, monolayer or bilayer gas clathrates can be formed under thousands of atmospheric pressures, ,, while quasi-one-dimensional (Q1D) core–sheath n -gonal ( n = 5–8) hydrogen hydrates can be formed spontaneously within single-walled carbon nanotubes (SW-CNTs) . Also, the formation of Q1D heptagonal and octagonal hydrogen hydrates can be seen under ambient pressure when the SW-CNTs are immersed in the dilute H 2 aqueous solution …”

Displacement behavior of methane in organic nanochannels in aqueous environment

“…Thus, it is necessary to study the interaction between gas and water in the organic nanochannels (Li et al, 2016(Li et al, , 2017aShen et al, 2019). Although the phase change, the occurrence state and the flow mechanism of water/gas molecules in nanopores have been the research hotspots in natural science and many engineering fields (Hummer et al, 2001;Dammer and Lohse, 2006;Bai and Zeng, 2012;Zhao et al, 2014bZhao et al, , 2015Kou et al, 2015;Lee and Aluru, 2015;Wang et al, 2016;Li et al, 2019aLi et al, , 2019b. In view of the particularity of shale pore structure and reservoir property, the research on gas in confined space in petroleum engineering field is still very limited.…”

Experimental studies on hydrogen hydrate with tetrahydrofuran by differential scanning calorimeter and in-situ Raman

“…To clear formation mechanism of hydrate containing hydrogen, some calculations and experiments were ever carried out from the microscopic point of view. Zhao et al [37] reported that guest molecules with various size and hydrophilicity presented different characteristics when they were participating in the process of hydrate formation in microscopic media. Moreover, Raman shift changed involving into guest-host hydrogen bonding, according to the results reported by Lim et al [38] in the system with diazine isomers.…”