Aqueous Nitrogen-Nanobubble dispersion and supersaturation at elevated pressures up to 277 bara

Abstract

Aqueous nanobubble (NB) dispersion of gaseous species has been studied and applied for various processes near atmospheric pressure, but its fundamental properties are not well understood at elevated pressures. This paper presents an experimental program that measures the gas content of aqueous NB dispersion of nitrogen (N2) at pressures up to 277 bara. The parameters directly set in the experiments were temperature, external pressure, and total volume while the overall composition of aqueous NB dispersion was obtained by constant mass expansion with material balance. The experimental data were analyzed by using a thermodynamic model for calculating an internally consistent set of properties at the experimental conditions.Results show that the N2 content in aqueous NB dispersion increased significantly with the system pressure. For example, the N2 content at 277 bara was 0.29 mol/L for aqueous NB dispersion with deionized (DI) water, which was 2.3 times greater than the inherent solubility of N2 in DI water at the same pressure. The effect of salinity was studied by using 0.88 M NaCl brine in place of DI water, but the N2 contents were similar to those with DI water for the pressures tested in this research. Application of a thermodynamic model using the GERG-2008 equation of state to the experimental data indicates that NBs themselves were unlikely the main storage of N2, but the existence of NBs enabled the supersaturation of the aqueous phase by N2 because of capillary pressure.