The influence of Na2SO4 on the CO2 solubility in water at high pressure

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, CO2 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 CO2 in water and aqueous solutions of Na2SO4 was determined in the temperature range between 288 and 368K, pressures up to 14MPa were applied, Na2SO4 concentrations of 0DDT25, 0DDT5 and 1mol Na2SO4/kg water were used, and the CO2 molar fractions were 0DDT0075, 0DDT01 and 0DDT0125. As expected, the data obtained showed that equilibrium pressure increases with temperature and CO2 concentration. A salting out effect is observed. The experimental data were compared to available literature data and the CO2-water data were consistent with literature data, but for the equilibrium pressure of the bubble points in a solution of 1mol Na2SO4/kg water, a systematic overpressure of approximately about 1MPa with respect to some of literature data is found. The system CO2-H2O-Na2SO4 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 %D*DP=4DDT64% 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.