Ocean Disposal of CO 2 : Conditions for Producing Sinking CO 2 Hydrate Jorge Gabitto, 1,2 David Riestenberg, 1 Sangyong Lee, 1,# Liyuan Liang, 1 and Costas Tsouris 1, * 1 Oak Ridge National Laboratory, Environmental Sciences Division, Oak Ridge, Tennessee, USA 2 Chemical Engineering Department, Prairie View A & M University, Prairie View, Texas, USA ABSTRACT Carbon dioxide sequestration at intermediate ocean depths in the form of a sinking CO 2 stream has been shown to be technically feasible. Buoyancy characteristics of CO 2 hydrate particles obtained from a coflow reactor operating under conditions that produce negatively buoyant CO 2 hydrate composite particles were studied. Using a simplified process model, the limiting ratios of CO 2 to water to produce sinking hydrate composite streams were established for pressure and temperature conditions of intermediate ocean depths. A kinetic model involving a mass transfer step and a reaction step was proposed to explain experimental data using a seafloor process simulator. Results suggest that the reactor operates under mass-transfer controlled conditions. Although the density of freshwater is only a few percentage units less than that of seawater, operating conditions derived from freshwater-based studies are significantly different for ambient seawater. Owing to the higher density of seawater, greater conversion of CO 2 to hydrate is needed to obtain a sinking CO 2 composite stream than at the same depth of freshwater. Key Words: Ocean carbon sequestration; CO 2 hydrate; Mass transfer. INTRODUCTION The disposal of anthropogenic greenhouse gases now entering the atmosphere is increasingly becoming a global problem. High atmospheric concentrations of these gases may increase the earth’s average temperature and severely modify the world’s climate. Carbon dioxide (CO 2 ) is one of the most abundant greenhouse gases. Because of the relatively high solubility of the gas, atmospheric-ocean exchange over the large ocean surface could regulate the atmospheric concentration. [1] Additionally, the large storage capacity of the ocean holds an assurance for an active CO 2 injection into the deep ocean to solve this problem. [2,3] For the success of such a strategy, the 703 DOI: 10.1081/DIS-200027332 0193-2691 (Print); 1532-2351 (Online) Copyright # 2004 by Marcel Dekker, Inc. www.dekker.com # Current address: Chemical and Natural Gas Engineering, Texas A&M University Kingsville, Kingsville, TX 78363, USA. *Correspondence: Costas Tsouris, Oak Ridge National Laboratory, Environmental Sciences Division, Oak Ridge, TN 37831-6181, USA; Fax: (865) 241-4829; E-mail: tsourisc@ornl.gov. JOURNAL OF DISPERSION SCIENCE AND TECHNOLOGY Vol. 25, No. 5, pp. 703–712, 2004