New Morphology of CO₂ Hydrate Crystal near the Edge of Porous Media

Crystal growth characteristics determine the formation of carbon dioxide (CO2) hydrate. This study experimentally realized the regulation of CO2 hydrate growth mode from multidimensional to one-dimensional based on multiphase transportation theory inside porous media and succeeded visually observing the ray type growth process of many hydrate crystals at the interface between bulk gas and porous media. There are a few nucleation points in each experimental case, and from which the hydrate bud crystals of approximately 0.74 mm in diameter grow above on the porous media, reaching 26 mm long at most. Analysis of mass transfer within porous media revealed that the continuous growth of hydrate buds is driven by water self-transportation among pores. That is why that either large particle (over 0.8 mm diameter) or low water saturation (less than 30%) inhibits the effective growth of hydrate buds. In particular, by dynamic tracking in continuous images, the growth rates under different water saturation and particle size conditions are quantified, and the one-dimensional growth rate of hydrate is determined as 0.04 mm/s. This study unveils the mystery growth mechanism of CO2 hydrate for the first time and is extremely significant to future researches on the fundamental and application of various gas hydrates.