Efeito de surfactantes sobre o coeficiente volumétrico de transferência de massa de oxigênio da interface gás-líquido

Abstract

In this study, the effects of ionic surfactants (sodium dodecyl sulfate and humic acids) in the transfer of oxygen are investigated in a cylindrical reactor and in a prismatic tank with oscillating grid. For the first time, a systematic study is shown in a wide range of surfactant concentration, below and above the critical micelle concentration (CMC). In both systems the presence of surfactant in the water reduces the volumetric coefficient of oxygen transfer. In the cylindrical reactor (bubble aeration), the maximum reduction of the volumetric mass transfer coefficient (KLa) was observed in a 0.3 mM dodecyl sodium sulfate concentration prior to CMC. The results are discussed on the basis of molecular interactions between water molecules, air bubbles and surfactant molecules. To better understand the experimental findings, a mathematical model was developed based on the estimated volumetric mass transfer coefficient. The forecasts agree well with the experimental results and point to a maximum reduction of 41% in KLa, regardless of the air flow rate into the cylindrical reactor. The model was successfully tested in the prediction of KLa data reported in the literature under the influence of different surfactants. For experiments in the prismatic tank with oscillating grid (surface aeration) and presence of humic acids, a similar behavior was observed independently of the grid oscillation frequency. There was, however, high experimental variability making it difficult to adjust the model to this data set, what could be compensated by conducting experiments at triplicate. Thus, it is believed that these results can be used to predict future experimental results.