Experiments on the Ocean Sequestration
of Fossil Fuel CO2: pH measurements
and hydrate formation

Peter G. Brewer, Edward T. Peltzer and Gernot Friederich
Monterey Bay Aquarium Research Institute
7700 Sandholdt Road
Moss Landing, CA 95039-9644 USA

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.


ABSTRACT

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.


Acknowledgements

This work was supported by a grant to MBARI from the David and Lucile Packard Foundation, and for I.A. and K.Y. by support of the Ship Research Institute. These experiments could not have been carried out without the exceptional support provided by the captain and crew of the R/V Point Lobos, and by the skilled pilots and technicians of the ROV Ventana. We would also like to thank Drs. S. Tsunogai, K.A. Hunter and an anonymous reviewer for their most helpful comments and suggested revisions to an earlier version of this manuscript.


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