Molecular mechanism for liquid-liquid extraction: Two-film theory revisited

YX Hu and ZP Liu and XG Yuan and XR Zhang, AICHE JOURNAL, 63, 2464-2470 (2017).

DOI: 10.1002/aic.15636

We investigate here the molecular mechanism for liquid-liquid extraction and revisit the classical two-film theory. With equilibrium and non- equilibrium molecular dynamics simulations, we illustrate the kinetics of solute crossing the interface and in particular the structure of the interface at which two stagnant liquid films adhere. Our simulation results show that beyond the two-film theory, the interface is well structured and plays an essential role in solute transfer. We found that at the well-developed interface region the overall density profile exhibits a dip, while the solute concentration shows a significant maximum. Free energy analysis demonstrates the interfacial enrichment of solute molecules serving as a potential well for solute adsorption. Thus, different from the assumption of the two-film theory, our simulations show that there exists a resistance for solute molecules crossing the interface, which could be overcome only at high interface concentration of solute caused by interfacial enrichment. (c) 2017 American Institute of Chemical Engineers AIChE J, 63: 2464-2470, 2017

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