Study of the pseudo‐steady‐state kinetics of CO2 hydrate formation and stability

Abstract This article describes a dynamic model for formation and stability of CO 2 ‐hydrate on the interface of liquid CO 2 (LCO 2 ) and ocean water at large depths. Experimental results indicate that a thin film of hydrate naturally forms on the interfaces between LCO 2 and water, and inhibits diffusion between the two phases. Experiments further shows that the flux of CO 2 through the hydrate film is dependent of the CO 2 ‐concentration in the ambient sea water. The model proposed here explains these phenomena by introducing four major mechanisms; diffusion of water to the LCO 2 ‐phase, formation of hydrate in the LCO 2 ‐hydrate interface, decay of hydrate in the water‐hydrate interface, and diffusion of CO 2 through the water phase. The model explains the CO 2 flux not by diffusion through the hydrate film, but suggest a mechanism of continuous hydrate formation and decay. The overall effect is a “moving,” pseudo‐steady‐state hydrate film due to transport of CO 2 through the film. The film velocity is dependent of liquid‐liquid diffusivity parameters and reaction constant, and lacking experimental values of these parameters, an order–of‐magnitude analysis is done by fitting the model to experimentally obtained data for the overall film velocity. The motivation for this work is to elucidate options for CO 2 depositions in deep oceans, of which liquid CO2 sequestration is believed to be one of the most feasible. Spreading of CO 2 from a liquid CO 2 ‐lake and associated lowering of pH in the ecosystem surrounding the lake is of large concern. The work presented here concludes that diffusion of CO 2 in the ocean is largely reduced by the hydrate film and suggests that hydrate formation may alleviate some of the environmental concerns regarding deep ocean sequestration of liquid CO 2 . © 1994 John Wiley & Sons, Inc.