CO2 nanobubbles as a novel kinetic promoter in hydrate-based desalination

The use of CO2 nanobubbles (NBs) was investigated as a sustainable kinetic promoter of gas hydrate formation in hydrate-based desalination (HBD) that does not require any separation steps from the recovered water. Stable CO2 NBs (8.07 ± 0.21× 107 bubbles/mL with 103.15 ± 2.47 nm mean radius and −6.35 ± 1.17 mV zeta potential) were generated and tested in HBD experiments conducted at 274.15 K and 3.58 MPa. The colloidal stability of CO2 NBs increased under pressure: their concentration increased and their size decreased. Low concentrations of dissolved chloride salts reduced the size of CO2 NBs, while high concentrations increased the likelihood of NBs' agglomeration. The induction time for CO2 hydrate formation in the presence of CO2 NBs was reduced by 86.04 %. The desalination results confirmed that CO2 NBs played a significant role in accelerating the process based on the memory effect mechanism. In the presence of CO2 NBs, water recovery reached 68.85 ± 1.82 % and 63.37 ± 2.76 % with an ion removal efficiency of 41.35 ± 6.16 and 40–50 % in a single-stage HBD process for 0.5 M NaCl and synthesized seawater solutions, respectively. These findings could unlock the potential for the further development of HBD of natural saline solutions as well as its deployment in near-zero liquid discharge industrial processes.