Anisotropy of dodecahedral water cages for guest gas occupancy in semiclathrate hydrates

Abstract

Anisotropic dodecahedral cages in semiclathrate hydrates.

CO2 Capture from Flue Gas Based on Tetra-n-butylammonium Fluoride Hydrates at Near Ambient Temperature

“…In addition, particularly high CO 2 selectivity of semiclathrate hydrates compared to structure II gas hydrates was found, ,− although both of these hydrates only have D cages. This is likely due to irregular shapes of the D cages which are available in semiclathrate hydrates. , Semiclathrate hydrates provide differently shaped D cages with various options for the ionic substances. ,,− Because these unique D cages may selectively capture gases, it is expected that semiclathrate hydrates have a further potential to improve their gas selectivity. In our previous studies, we investigated CO 2 capture properties of TBAB, TBAC, TBPB, and TBPC hydrates for CO 2 + N 2 gas. , It was found that TBAB hydrates have high CO 2 selectivity due to the polymorphism of TBAB hydrates which may depend on the aqueous composition and pressure.…”

Structural CO2 capture preference of semiclathrate hydrate formed with tetra-n-butylammonium chloride

“…[4][5][6][7][8][9] The semiclathrate hydrates are also capable of capturing small gases such as methane, carbon dioxide, and nitrogen under relatively mild gas pressures at near ambient temperatures. [10][11][12][13][14][15] Gas capture applications based on the semiclathrate hydrates have received much attention. [16][17][18][19][20][21][22][23] The unique functional properties of such materials are based on their structure as determined by the choice of the ions that make up the salt.…”

“…Contrary to this, methane gas and nitrogen gas were barely present in this type of cage and mostly occupy isotropic D B cages. [12][13][14] Recently, it was reported that the TBAC hydrates have a uniquely high CO 2 selectivity compared to that in semiclathrate hydrates formed with TBAB. 18,20,21 Under gas pressure, TBAC preferentially forms the tetragonal structure, 3,24 while TBAB hydrates prefer the orthorhombic structure.…”

“…18,20,21 Under gas pressure, TBAC preferentially forms the tetragonal structure, 3,24 while TBAB hydrates prefer the orthorhombic structure. 10,13,14,20,23 Such structural differences are likely to affect the gas capture properties of semiclathrate hydrates.…”

“…[25][26][27][28][29][30] Such high coordination numbers in semiclathrate hydrate frameworks may not be possible and can cause high structural disorder. So far, structural studies have only found four hydrogen bonds between water and chloride or bromide in semiclathrate hydrate structures, 10,[12][13][14]24,31 while, as pointed out, these ions often prefer higher coordination numbers in solution. In this study, we investigated structural properties of TBAC + CO 2 hydrates and interactions between water, gas, and ions.…”