Izuo Aya and Kenji Yamane
Ship Research Institute
Ministry of Transport
3-5-10 Amanogahara, Katano
Osaka 576-0034, JAPAN
Marine Chemistry (2000) 72: 83-93.
Received: 24 June 1999.
Revised: 9 November 1999.
Accepted: 7 August 2000.
We have carried out a series of in situ experiments to investigate the formation of a CO2 hydrate CO2:5.75 H2O for the purpose of evaluating scenarios for ocean fossil fuel CO2 disposal with a solid hydrate as the sequestered form. The experiments were carried out with a remotely operated vehicle in Monterey Bay at a depth of 619 m. pH measurements made in close proximity to the hydrate seawater interface showed a wide range of values, depending upon the method of injection and the surface area of the hydrate formed. Rapid injection of liquid CO2 into an inverted beaker to form a flocculant mass of hydrate resulted in pH initially as low as 4.5 within a few centimeters of the interface, decaying slowly over 1-2 h towards normal seawater values as dense CO2 rich brine drained from the hydrate mass. In a second experiment, slower injection of the liquid CO2 to produce a simple two-layer system with a near planar interface of liquid CO2 with a thin hydrate film yielded pH values indistinguishable from the in situ ocean background level of 7.6. Both field and laboratory results now show that the dissolution rate of a mass of CO2 hydrate in seawater is slow but finite.