10. Thermodynamics and Applications of CO₂ Hydrates

Gas hydrates are clathrate solid crystalline compounds consisting of a lattice formed by water molecules and entrapped gas molecules inside. They are stable under high pressure and low temperature. CO₂ hydrates, specifically, are composed of CO₂ as the guest molecule and water as the host molecule. CO₂ hydrates have a number of applications including CO₂ capture, cold storage, CO₂ sequestration, and, lately, the direct displacement of methane hydrates with CO₂ to simultaneously produce methane and sequester CO₂. This chapter provides a comprehensive overview of the fundamentals of CO₂ hydrates. The first section gives a general introduction and some basic concepts of gas hydrates. Section 10.2 shifts the focus to the microscopic perspective, looking into how gas hydrates form, the three structures of gas hydrates, and the characteristics of CO₂ hydrates. From there onward, the text focuses specifically on CO₂ hydrates. The physical properties of CO₂ hydrates are considered in Sect. 10.3. Section 10.4 deals with the phase equilibrium of CO₂ hydrate. Experimental methods and the phase diagram are shown in this section. The last section covers the applications of CO₂ hydrates, including the formation and dissociation of CO₂ hydrates, ocean sequestration, and the CH₄ replacement in hydrates by CO₂, which is an attractive potential method to produce natural gas.