Phase behavior for carbon dioxide/tetraalkoxysilane systems

Phase diagrams of carbon dioxide (CO2)/tetramethoxysilane (TMOS) and CO2/tetraethoxysilane (TEOS) binary systems were measured. Liquid phase measurements were performed by observing the bubble point pressure with a synthetic method. Vapor phase measurements were conducted with a flow type apparatus. For the CO2/TMOS system, liquid phase lines were measured at temperatures from 313.2 to 393.2 K, and CO2 molar fractions from 0.15 to 0.85, and vapor phase lines were obtained at temperatures 313.2, 353.2 and 393.2 K and pressures up to 12 MPa. For the CO2/TEOS system, measurements were conducted only for liquid phase lines at temperatures from 313.2 to 373.2 K and CO2 molar fractions from 0.25 to 0.75. Phase behavior of these two systems was almost the same with each other. Experimental data were correlated with the Peng–Robinson equation of state (PR EoS), and the molecular interaction parameter kij and lij for both systems were determined. For large difference in the molecular size of CO2 and tetraalkoxysilanes, it was found that the lij could be negligible.