(54d) A New Model for the Solubility of Sulphur Dioxide in Aqueous Solutions at Higher Ionic Strength

An extended model for the description of phase and chemical equilibria in aqueous systems containing chloride or bromide in the presence of sulphur dioxide has been developed using new thermodynamical data and Pitzer's activity coefficient model. Solubility data for SO2 in these solutions are substantial for the process design of flue gas cleaning devices using seawater. This process is used by industrial facilities (e.g. refineries, combustors, smelteries) in coastal areas [1, 2]. However, up to now no thermodynamical data were available to effectively design these flue gas cleaning devices.

The following systems have been investigated: HCl/SO₂/N₂/H₂O, NaCl/SO₂/N₂/H₂O, HBr/SO₂/N₂/H₂O and NaBr/SO₂/N₂/H₂O. The required ionic strength (up to 5 mol/kg) was adjusted by addition of the strong electrolytes HCl, NaCl, HBr, and NaBr, respectively. In the liquid phase the model considers the following species: H₂O, Na⁺, Cl^-, Br^-, H⁺, OH^-, SO₂(aq), HSO₃^-, SO₃^2-, S₂O₅^2-, SO₂Cl^- and SO₂Br^-. In the gas phase nitrogen, sulphur dioxide and water are relevant for the pressure calculation.

The equilibrium measurements were carried out in a closed apparatus with in-situ-UV-spectroscopy.

The relevant binary interaction parameters of Pitzer's ion activity coefficient model [3] were adjusted to fit calculated gas solubilities and UV extinctions to experimental data. The model includes the Sechenov approach modified by Weisenberger and Schumpe [4] to account for the solubility of gases in electrolytes.

The presentation will outline the measured gas solubilities as well as spectroscopic data for the systems addressed and discuss data prediction by the newly evolved model.

[1] M. Radojevic, Chemistry in Britain, 1996, 32, 47

[2] G. B. G. Nyman, A. Tokerud, Oil & Gas Journal, 1991, 89, 52

[3] K.S. Pitzer, J. Phys. Chem. 1973, 77, 268

[4] S. Weisenberger, A. Schumpe, AIChE J., 1996, 42(1), 298 – 300