To analyze the DIFT influencing factors, the AC concentration in both liquids as well as the DIFT are displayed together as shown in Figure 5. As a comparison, the static interfacial tension for two phases in equilibrium state is also displayed in the figure. The static interfacial tension was measured by pendent drop method (LSA100 Surface Analyzer, LAUDA).
It can be found from Figure 5 that the static interfacial tension between the two phases decreases with the increase of the AC concentration (in both phases) under equilibrium conditions. When the concentration of AC continues to increase, the static interfacial tension between the two phases reaches a platform when the AC concentration in aqueous phase (Ca ) is higher than a critical point. The critical point of Ca is approximately 0.3 mol/L. However, under mass transfer conditions in the column, the dynamic interfacial tension between the two phases decreases continuously with the increase of aqueous phase concentration. Comparing these two curves, we can derive that the effect of concentration change on dynamic interfacial tension has been pretty weak because the concentration in the column is much higher than the critical point. Therefore, the main reason for the decrease of dynamic interfacial tension is the disturbing effect of mass transfer.
In order to further analyze the relationship between dynamic interfacial tension and mass transfer, the equilibrium relation of AC in both phases was measured and displayed in Figure 5 as the equilibrium line. The AC concentrations of both phases in the column are displayed as the operation line in Figure 5. The concentration difference between the equilibrium line and the operating line is the mass transfer driving force. It can be clearly seen that the larger the mass transfer driving force is the larger the difference between DIFT and static interfacial tension is. Larger driving force leads to higher mass transfer rate. Thus, the above results illustrate that the dynamic interfacial tension decreases with the increasing of mass transfer rate, probably due to the disturbing effect of mass transfer on the interface.
To quantitatively analyze the effect of the mass transfer rate on the DIFT, the mass transfer flux at different height of the column is calculated based on mass conservation. The calculating result is shown in Figure 6. Though an empirical correlation equation cannot be established due to the small number of data points, the results provides the first quantitative relation between the mass transfer flux and the DIFT. A method to quantitatively study the DIFT in columns is proposed.