Experimental Study on the Use of Nanoparticles to Improve the Efficiency of CO2 Geological Storage

Abstract

Abstract Supercritical CO2 injected into the aquifer in CCS may migrate upward in the aquifer because its density is lower than the density of formation water. As a result, CO2 cannot be stored widely throughout the aquifer, which may reduce CO2 storage efficiency. The objective of this study is to increase the apparent density of supercritical CO2 by dispersing nanoparticles in itself and to improve CO2 storage efficiency by injecting CO2 widely in the aquifers. The n-hexane, which has a similar solubility parameter to supercritical CO2, was used as an alternative solvent to supercritical CO2 in this study. The nanoparticles such as SiO2, Al2O3, TiO2, and ZnO were added and stirred in n-hexane respectively, and their dispersibility was observed after stirring with a magnetic stirrer or ultrasonication for 30 minutes. The dispersibility of nanoparticles in n-hexane was qualitatively evaluated by irradiating the sample with green laser light after stirring and observing the scattered light. The effect of surfactants on improving the dispersibility of nanoparticles was also evaluated using nanoparticles modified with those surfactants. All the nanoparticles were precipitated after 30 minutes of stopping stirring with a magnetic stirrer. The dispersibility of those nanoparticles was improved by ultrasonication and the dispersion was maintained up to about 3 hours. Similar experiments were conducted using nanoparticles modified with surfactants. As a result, improved dispersibility of Al2O3 and ZnO modified with anionic surfactants was obviously observed and laser light scattering was clearly observed for about 2 hours after the stirring was stopped. Finally, it was demonstrated that the dispersion of Al2O3 nanoparticles modified with anionic surfactant was maintained even after 48 hours in n-hexane by ultrasonication. These results indicate that Al2O3 nanoparticles modified with anionic surfactant have high dispersibility in n-hexane, especially with ultrasonication. Anionic surfactants make the surface of nanoparticles hydrophobic, which enhances their dispersibility in nonpolar solvents such as supercritical CO2. Ultrasonication is effective for eliminating agglomeration among nanoparticles and improves their dispersibility in nonpolar solvents.