On the stability of type I gas hydrates in the presence of methanol

Using computer simulations we have studied the stability of type I gas hydrates for different mixtures of methane/methanol at 270 K and atmospheric pressure. In the nanosecond time regime the empty and the methane-filled hydrate are stable with only small perturbations to the water cavity structure. Inclusion of methane stabilizes the lattice structure over the empty hydrate. A hydrate filled with methanol melts in roughly 1 ns with a concomitant destruction of the cavity structure. The resulting mixture is liquidlike in contrast to the icelike hydrate structure. Small amounts of methanol can be incorporated into the hydrate structure; thus a 4 wt % methanol solution is stable, whereas a 7 wt % solution melts. In the stable methanol hydrate cavity structure is maintained, but the perturbations relative to the empty hydrate emphasize the inherent flexibility of these structures. More alcohol can be incorporated into the hydrate if methane is allowed to stabilize the hydrate.