Kinetic evidence for the effect of salts on the oxygen solubility using laboratory prototype aeration system

This study is dedicated to an accurate evaluation of thermodynamic and kinetic aspects in the oxygenation process of water/salt solutions. Oxygenation has been analyzed by means of kinetic study of oxygen dissolution from the oxygen mass transfer coefficient (KLa) and oxygen transfer rate (SOTR). A stirred, submerged aerated 4-liter system has been designed and the operational conditions have been optimized by studying the influence of hydraulic head, air flow and salinity of water using an optical oxygen sensor. Concerning the thermodynamic phase equilibria, experimental and modeling results are obtained from different binary systems (water/air) and ternary systems (water/air/salts). This information is necessary to predict the composition of the gas phase during the process and is also important for an implementation in a process simulation. The oxygen mass transfer coefficients were firstly measured, by monitoring in the time the oxygen concentration in various synthetic liquid phases containing different salts (NaCl, KCl, LiCl). When compared to clean water, noticeable increase of KLa was observed; the variation of KLa and SOTR with the solution salinity was modeled and found dependent on the nature of cation in the salt added. For all cases, an increase of KLa with increasing salinity was observed but, when the results are correlated with salt molar concentration, very important relation attributed to different salts has been obtained. The present study clearly confirmed the importance to define the experimental conditions before to describe and to model appropriately the gas-liquid mass transfer phenomena.