The influence of Na 2SO 4 on the CO 2 solubility in water at high pressure

Abstract

Supercritical water oxidation (SCWO) is a very efficient process for the destruction of organic wastes. In this type of processes, conversions higher than 99% can be achieved with residence times shorter than a minute. The effluent of this process is a mixture of water, CO 2 and inorganic salts. For modeling this process, it is necessary to have reliable experimental data of the system water–carbon dioxide–inorganic salts. These data are scarce in literature, especially at high pressures. The solubility of CO 2 in water and aqueous solutions of Na 2SO 4 was determined in the temperature range between 288 and 368 K, pressures up to 14 MPa were applied, Na 2SO 4 concentrations of 0.25, 0.5 and 1 mol Na 2SO 4/kg water were used, and the CO 2 molar fractions were 0.0075, 0.01 and 0.0125. As expected, the data obtained showed that equilibrium pressure increases with temperature and CO 2 concentration. A salting out effect is observed. The experimental data were compared to available literature data and the CO 2–water data were consistent with literature data, but for the equilibrium pressure of the bubble points in a solution of 1 mol Na 2SO 4/kg water, a systematic overpressure of approximately about 1 MPa with respect to some of literature data is found. The system CO 2–H 2O–Na 2SO 4 was modeled using the Anderko–Pitzer EOS, specially developed for water–salt systems at high temperatures and pressures. Experimental data were used for obtaining parameters in the range of pressure and temperature of the data. In this range they differ with an average deviation of %Δ P = 4.64% in total pressure from the experimental results. However, extrapolated results from the Anderko–Pitzer EOS are poor. In order to extend the region of applicability of the EOS, it will be necessary to adjust the parameters in the appropriate range of temperature and concentration.