Aqueous Nanobubble Dispersion of CO<sub>2</sub>at Pressures Up To 208 bara
Hao Wang, Tesleem Lawal, Sofiane H. Achour, Kai Sheng, Ryosuke Okuno
Abstract
This paper presents an experimental program for generating an aqueous nanobubble dispersion of CO 2 at elevated pressures up to 208 bara. It directly sets total volume, external pressure, and temperature, and the overall composition is determined by constant mass expansion of aqueous nanobubble dispersion to a low pressure (e.g., atmospheric pressure) with material balance. Results with deionized water show that the CO 2 content in the aqueous nanobubble dispersion increased with the system pressure. The largest CO 2 concentration, 2.3 mol/L, was obtained at 207.8 bara, which was 42.9% greater than the inherent solubility of CO 2 in water at 207.8 bara. The maximum solubility enhancement, 52.8%, in comparison to the inherent solubility, was observed at 138.9 bara. Generation of an aqueous nanobubble dispersion of CO 2 was also tested with a buffer solution based on sodium formate, which resulted in 1.52 mol/L of CO 2 at 208 bara. This was 77% greater than the inherent solubility of CO 2, 0.86 mol/L, in a sodium chloride solution with the same ionic strength. An important observation from the thermodynamic analysis of experimental data is that nanobubbles themselves may not be the main storage of CO 2, but their existence can increase the level of supersaturation of the aqueous phase by CO 2 . This was consistent with the direct measurement of bubble properties using nano tracking analysis, where the CO 2 content as bubbles was much smaller than the inherent solubility of CO 2, even with a bubble number density of 10 8 mL –1 and a bubble radius greater than 100 nm.