Hydrate Dissociation Conditions for Mixtures of Air plus Tetrahydrofuran, Air plus Cyclopentane, and Air plus Tetra-n-butyl Ammonium Bromide

Substantial oxygen enrichment is observed in the natural air hydrates formed in Arctic and Antarctic ice sheets. Inspired by this phenomenon, a novel air separation method, utilizing hydrate crystallization, is proposed in our work. The three-phase equilibrium pressure for the air + water system is greater than 15 MPa as the temperature is upon ice point, which makes the air separation impractical by hydrate formation under mild temperature conditions. So, some additives were selected to reduce the phase equilibrium pressure of air hydrates at a fixed temperature. In this work, hydrate dissociation conditions for the air + tetrahydrofuran (THF) + water system (x = 0.0300 and 0.0500), the air + cyclopentane (CP) + water system (x = 0.0300 and 0.0556), and the air + tetra-n-butyl ammonium bromide (TBAB) + water system (w = 0.20 and 0.30) were measured in the temperature ranges of (279.7 to 290.5) K, (284.0 to 296.2) K, and (283.4 to 288.0) K, respectively. The comparison result shows that, in the pressure range of (0 to 1.5) MPa, the promotion effect of these three additives on the air + water system follows TBAB > CP > THF.