Formation and growth of CO{sub 2} clathrate hydrate shells around gas bubbles or liquid drops

Deep ocean disposal of CO{sub 2} may be required to mitigate rises in its atmospheric levels if other measures are ineffective and the worst global warming scenarios begin to occur. Work at PETC is directed at evaluating the technical feasibility of this option for long-term disposal. At the pressures and temperatures associated with the depths required for effective sequestration of CO{sub 2} (> 500 m), the crystalline CO{sub 2} clathrate hydrate (CO{sub 2} {circ} nH{sub 2}O, 6 < n < 8) can form. Clathrate hydrates are a special type of inclusion compound in which small molecules, such as CO{sub 2}, are held in cavities formed by hydrogen-bonded H{sub 2}O molecules by van der Waals forces. The formation of the CO{sub 2} clathrate hydrate can either facilitate or complicate the sequestration of CO{sub 2} in the ocean. Sequestration would be facilitated if the clathrate hydrates form as solid crystals dense enough to sink and thus increase the residence time of the CO{sub 2} in the ocean. The formation can complicate sequestration if a thin coating of the hydrate forms on the surface of injected bubbles or drops of CO{sub 2}. This complication would hinder dissolution of the CO{sub 2} and permitmore » its rise to unacceptably shallower depths and thus its premature return to the atmosphere. Being able to predict the fate of CO{sub 2} hinges on our understanding of these phenomena and their likely occurrence in ocean disposal scenarios.« less