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.