Direct measurement of formation and dissociation rate and storage capacity of dry water methane hydrates

Dry water (DW) has been recently demonstrated to be an effective medium for methane storage in a hydrated form. Here, a series of experiments have been carried out on dry water methane hydrates (DW–MH) to investigate their formation and dissociation rates, storage capacity and structural characteristics. The result shows that the storage capacity of MH increases at least 10% by using DW relative to using surfactants like sodium dodecyl sulfate (SDS) solution. Also, it is found that controls on pressure–temperature (P–T) condition have influences on the induction and reaction time of DW–MH formation, i. e. the induction and reaction time are much shorter when the reaction cell is cooled to ~ 3 °C first. On the basis of Raman spectra, the hydration number is calculated as 5.934 ± 0.06 at different positions of the DW–MH, which suggests that the sample is very homogeneous. The dissociation process of the DW–MH sample exhibits a rapid release of methane gas at the first stage of dissociation. Although hydrate dissociation is prevented by the effect of self preservation, most methane gas has released from the hydrate, however, before the self preservation occur.

Research highlights
► Storage capacity of methane hydrate increases at least 10% by using dry water.
► Cooling first can enhance the formation rate of dry water methane hydrate.
► Hydration number is measured as 5.934 ± 0.06 by Raman Spectroscopy.
► Effect of self preservation occurs after most methane released from hydrate.