Crystal growth of ionic semiclathrate hydrate formed at interface between CO2+N2 gas mixture and tetrabutylammonium bromide aqueous solution

This study reports a visual observation of the formation and growth of ionic semiclathrate hydrate on the surface of a Tetrabutylammonium bromide (TBAB) aqueous solution and CO2+N-2 gas mixture. The composition of CO2+N-2 gas mixture was 20: 80. The experimental temperature range was from 280 K to 290 K, under the pressures of 2.3MPa and 4.7MPa, at w (TBAB) =0.10 and w (TBAB) =0.40, where wTBAB denotes the mass fraction of TBAB in the aqueous solution. At w (TBAB) =0.40, the hydrate crystals were initially observed to grow within the droplet, and followed by lateral growth at the droplet surface; but at w (TBAB) =0.10, the hydrate crystals grew exclusively in the liquid phase and did not cover the droplet surface. Two types of different crystals with different sizes were clearly observed.