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+N₂ gas mixture. The composition of CO₂+N₂ 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.