Molecular insight on CO 2 /C 3 H 8 mixed hydrate formation from the brine for sustainable hydrate-based desalination

Systematic molecular dynamics simulations have been performed to investigate the formation of CO 2 /C 3 H 8 mixed hydrate in brine, to search for the optimal C 3 H 8 content and elucidate the microscopic mechanism for hydrate -based desalination process. Simulation results indicate that the desalination process is significantly affected by the formation kinetics of CO 2 /C 3 H 8 mixed hydrates due to the diverse physical properties of CO 2 and C 3 H 8 molecules in the brine. Specifically, CO 2 molecules are more likely to leave the mixed gas nanobubbles and form hydrates, whereas most of C 3 H 8 molecules remain in gas nanobubbles for a prolonged period. Interestingly, ions can form abnormal CO 2 -occupied and C 3 H 8 -occupied hydrate cages by replacing the water molecule in cages, and some ions can also be adsorbed on the surfaces of the cage -like hydrogen bond network or encapsulated between the hydrate solids. The presence of these ions presents a challenge to separating them due to the strong attraction from the water in hydrate solids. On the other hand, it is confirmed that the C 3 H 8 content with 10 % is optimal for CO 2 /C 3 H 8 mixed hydrate -based desalination, as it promotes the decomposition of mixed gas nanobubbles to form hydrates by suppressing the structural fluctuations in the system. These molecular insights into the effect of C 3 H 8 content on CO 2 /C 3 H 8 mixed hydrate formation in brine may help to develop hydratebased desalination technology.