Figure 5. The relationship between interfacial tension and concentration of two phases.
We have shown that the DIFT varies with the column height in the above text. However, it is still an important issue to analyze the intrinsic influencing factors of DIFT. Comparing to the blank experiments, AC is introduced into the system under mass transfer conditions and the concentration of AC will affect the interfacial tension. In addition, due to the interphase mass transfer, the interface between the two phases will be disturbed (partially attributed to the well-known Marangoni effect), resulting in change of interfacial tension. Preliminary analysis shows that the above two factors are responsible for the dynamic change of interfacial tension under mass transfer conditions. To analyze the contribution of these two factors, the AC concentration profile in the column needs to be measured.
Because of the low fraction of dispersed phase in this experiment, only continuous phase can be led off from the sampling port of the column. The AC concentrations in the continuous phase from different sampling points are measured by titration and the results are shown in Table 3. Though the AC concentration profile of dispersed phase cannot be directly measured, it can be calculated based on the concentration profile of continuous phase through the axial diffusion model 38. The calculation AC concentration profile in dispersed phase is shown in Table 3. The calculated process is described in the Appendix. We can see that the calculated AC concentration in the dispersed phase at the bottom of the column is 1.04 mol/L, which is almost equal to the measured AC concentration at the aqueous phase outlet (1.05±0.03 mol/L). This result proves that the calculated AC concentration in the dispersed phase by axial diffusion model is trustable.