Energy analysis and phase equilibrium in clathrate hydrate-based simultaneous carbon capture and desalination

To develop a technology that simultaneously performs clathrate hydrate-based carbon capture and desalination, phase equilibrium conditions of clathrate hydrate-forming systems consisting of carbon dioxide–nitrogen mixed gases and sodium chloride aqueous solutions were measured. The energy requirement associated with seawater desalination and the second stage of a multistage carbon dioxide separation process was also examined. Using mixed gases with carbon dioxide mole fractions ranging from 0.61 to 0.68 in equilibrium with sodium chloride aqueous solutions with mass fractions from 0.035 to 0.105, the measured phase equilibrium temperatures ranged from 269.8 K to 275.8 K, with corresponding equilibrium pressures ranging from 2.12 MPa to 4.02 MPa. Under the assumed operating pressure of 2.8 MPa, the sum of the energy required to supply the cold thermal energy and compress the gas corresponds to 199 kWh–220 kWh when expressed per ton of carbon dioxide captured, and 68.5 kWh–75.6 kWh when expressed per cubic meter of water obtained. A large fraction of the energy is consumed for supplying cold thermal energy to remove the enthalpy change of clathrate hydrate formation and for gas compression. Therefore, the results indicate that effective utilization of cold thermal energy from liquefied natural gas regasification, operation at lower temperatures and pressures, and the introduction of guests that enable operation at reduced pressures are promising strategies for reducing the overall energy demand. These strategies may facilitate the development of hydrate-based technologies for simultaneous carbon capture and desalination of high-salinity water streams, including produced water and seawater.