Stability of Clathrate-Hydrate of Carbon Dioxide in Highly Pressurized water.

The fate of CO2 hydrate released in the ocean

“…In a submersible study of hydrothermal field in the Okinawa trough, Sakai et al observed that a CO -rich fluid (containing approximately 86% CO ) was secreted from the sea floor at 1335-1550 m depth; upon contact with seawater at 3)8°C, a thin hydrate layer formed rapidly at the interface of seawater and the effluent. The conditions under which hydrates formed were consistent with the CO -water-hydrate phase diagram developed by Song and Kobayashi (1987), according to which hydrates would form in CO -water systems at pressures greater than 4)5 MPa and temperature less than 283 K. The evidence of formation of CO hydrate in the ocean stimulated the study of CO hydrate and many investigations of formation of CO hydrate in water simulating the deep ocean environment have been conducted (e.g., Aya et al, 1992;Austvik and L+ken, 1992;Golomb, 1993;Golomb et al, 1992;North et al, 1993;Fujioka et al, 1994;Saji et al, 1995). Based on these studies, ocean disposal of anthropogenic CO in the hydrate form at depths (500 m (the pressure and temperature required for hydrate formation can be satisfied at 500 m in many oceans) is believed to be an optimum method to sequester CO in the ocean and it is predicted that the disposed CO hydrate may be sequestered in the deep ocean for a long period of time (Austvik and L+ken, 1992;Golomb, 1993;Golomb et al, 1993;Saji et al, 1992;Noda et al, 1994).…”

“…However, the hydrate particles in the experiments of Saji et al were irregular and their experimental data scattered in a large range from 1)5;10\ m s\ to 1)1;10\ m s\ (the variation is about one order of magnitude). In order to employ more reliable experimental data, we consider a reference CO droplet in seawater at p'4)5 MPa and ¹(283 K. Based on laboratory observations (Aya et al, 1992;Shindo et al, 1993), a hydrate layer would form rapidly on the surface of the droplet. Since the CO and seawater are separated by a hydrate interphase, mass transfer of CO from the droplet to seawater may be expressed as…”

Laboratory Experiments to Simulate Co2 Ocean Disposal

“…During the injection of liquid CO 2 into fresh water or seawater, CO 2 hydrate may form (Aya et al, 1992(Aya et al, , 1997Hirai, et al, 1997): (1) prior to the jet breakup on injector internal passages and on the jet surface; and (2) after jet breakup on the surfaces of liquid CO 2 droplets. A number of studies (Teng & Yamasaki, 1999;Uchida et al, 2000) have examined hydrate formation on the surface of CO 2 droplets; however little work has been done to understand CO 2 hydrate formation prior to jet break up.…”

“…The hydrate film was very thin and elastic. Figure 5.16 is a photo of a tube hydrate.5 The grape and tube types of hydrates were also observed by Aya & Yamane (1992).…”

“…CO 2 hydrate that forms on CO 2 droplet surfaces in the deep ocean following jet breakup restricts the dissolution of the injected CO 2 (Aya et al, 1992;Nishikawa et al, 1995;Wong & Hirai, 1997;Hirai et al, 1997). This impacts the level and extent of acidification of seawater near the discharge location and, potentially, the effectiveness of this CO 2 sequestration technique.…”