Suppose I have two liquid mixtures (A+B) and (C+D). The component B is the minor component ~15% in the first mixture. However this component B individually is miscible with all the three liquids A,C and D. What I am curious to know is if I take a drop of A+B and surround it by C+D will the component B get easily extracted? Also what will the interface and interfacial tension of these two phases look like? Will it be stable or will it be dynamic?
You are describing (almost) a classical and common chemical engineering technique known as liquid-liquid or solvent extraction. The main thing your left out is that the mixtures form two immiscible or distinct liquid phases. If they do, you can partially or, in some cases, almost completely transfer one component in one liquid phase to the other phase. The process plays a central role in metallurgical purification, production of high-value organics such as cosmetics and perfumes, separations of oxygenated oils such as vegetable oil and biodiesel, and similar processes. The interface can be completely stable in many cases, though it is possible that the extraction process destabilizes it. The Wikipedia article entitled liquid-liquid extraction provides a good summary. Any engineering separations text will also review this process and the methods for designing systems using it.
Professor Baxter gave to you an excellent answer. I only want to add that you need to know the distribution constant (“KeqB”) of B between A and (C+D):
CB_A=KeqBCB_CD (1)
Where “CB_A” is the volumetric concentration of B in A (g B/volume); “CB_CD” is the volumetric concentration of B in (C+D) (g B/volume). In the situation that you detailed assuming that A is practically immiscible in (C+D) will be a mass transfer of B from the sine of the drop of (A+B) to the sine of (C+D+B). The mass transfer rate depends on B diffusivity both in A and (C+D) and may be the turbulences of liquid phases. The final concentration in both liquid phases will be the required for to satisfy Eq. (1).
Dear Profs Baxter and Alvarado...Thanks for your answers. Sorry I have a few dumb doubts.
The mixture A+B is a proper mixture as B is nicely miscible in A. In that event will extraction even happen? If it does what will the driver be? Also will the interfacial tension change a lot if there is even a slight amount of migration, since B is miscible with the other liquid as well?
There are two potential driving forces for the extraction
1. B is more soluble (preferentially accumulates) in the second phase, and
2. there is no B in the second phase when it enters the extraction vessel.
The first driving force will lead to very effective extraction. The second can still provide some extraction, but it is driven primarily by entropy increasing as B partitions between both phases, so some B will be extracted from the A phase and some will be in the second phase that initially contained no B and both phases will contain some of B at the end of the process.
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