Discharging carbon dioxide (CO2) to seafloors in the form of CO2-hydrates can potentially store CO2 in virtually unlimited quantity. Realizing the process requires a thorough understanding of CO2-hydrate forming behavior in seawater conditions. One of the major concerns is the gravitational stability of the produced bulk CO2-hydrates. The objective of this study was to seek the optimum procedure for producing bulk CO2-hydrates with densities greater than seawater density. This objective was achieved by direct visualization of CO2-hydrates through the glass windows of a reactor under various pressure and temperature conditions with mixing methods of CO2-bubbling and water-dropping. CO2-bubbling into the water phase was observed to produce bulk CO2-hydrates with densities less than water density due to the excessive CO2 trapped in the bulk hydrates. Water-dropping into the CO2 phase was observed to produce bulk CO2-hydrates with densities greater than water density due to the excessive water trapped in the bulk hydrates. Water-dropping was therefore identified as a favorable mixing method for producing CO2-hydrates with gravitational stability for depositing onto seafloors.
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