Hydrate-Phase Equilibria
and <sup>13</sup>C NMR Studies
of Binary (CH<sub>4</sub> + C<sub>2</sub>H<sub>4</sub>) and (C<sub>2</sub>H<sub>6</sub> + C<sub>2</sub>H<sub>4</sub>) Hydrates
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Abstract
Three-phase equilibria of hydrate + liquid water + vapor
phases
were investigated at various gas compositions for binary gas mixtures
of (CH<sub>4</sub> + C<sub>2</sub>H<sub>4</sub>) and (C<sub>2</sub>H<sub>6</sub> + C<sub>2</sub>H<sub>4</sub>). Hydrate-phase equilibria
of the binary (CH<sub>4</sub> + C<sub>2</sub>H<sub>4</sub>) hydrate
show significant changes with changing composition, whereas those
of binary (C<sub>2</sub>H<sub>6</sub> + C<sub>2</sub>H<sub>4</sub>) hydrates show little difference because of the similar physical
properties of the two guest species. In addition to macroscopic equilibrium
measurements, solid-state <sup>13</sup>C NMR spectra of hydrate samples
were collected to identify both cavity occupancies of guest components
and hydrate structures. For the binary (CH<sub>4</sub> + C<sub>2</sub>H<sub>4</sub>) hydrate, the large-cavity occupancy of C<sub>2</sub>H<sub>4</sub> molecules increased nonlinearly with increasing C<sub>2</sub>H<sub>4</sub> concentration, which supports nonlinear shifts
of the equilibrium curves. Meanwhile, the large-cavity occupancy of
C<sub>2</sub>H<sub>4</sub> molecules from the (C<sub>2</sub>H<sub>6</sub> + C<sub>2</sub>H<sub>4</sub>) gas mixtures increased linearly
with increasing C<sub>2</sub>H<sub>4</sub> concentration, which is
attributed to linear changes in the distribution or density
