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Author: Subject: Phase separations of liquids containing surfactants?
Electra
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[*] posted on 19-12-2013 at 16:00
Phase separations of liquids containing surfactants?


I recently learned about surfactants today and how they can cause immiscable mixtures of liquids to mix together. Say a surfactant, such as CTAB, is used as a catalyst in a reaction, and then following the reaction the mixture has to be separated. Normally the liquids would separate based on their density. Would a surfactant prevent this separation from happening? If so, how would it be dealt with so the liquids can be separated?

[Edited on 20-12-2013 by Electra]
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Aconite
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[*] posted on 26-12-2013 at 12:25


Quaternary ammonium salts are used as *catalysts* and thus very used in very small amounts (say 1-10 mole %). In these small amounts, the phases become only partially miscible- just enough to allow a reaction to take place between the two phases. By no means should there be enough of the catalyst to allow for complete miscibility of the two phases. Because the catalyst is soluble in both phases, at the end of the reaction, it can be washed out via several simple aqueous extractions which are then discarded (presuming the desired product is miscible in the organic phase).
If for some reason you were to use enough of a surfactant to create complete miscibility, it becomes necessary to flood the system with copious volumes of one or both phases to dilute the surfactant enough to where it can be washed out from one phase or the other as mentioned above.
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macckone
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[*] posted on 26-12-2013 at 21:16


As actonite said the surfactants should not be used in sufficient quantities to make the liquids completely miscible.

Some ways of 'neutralizing' the surfactant are also possible.
Various salts, which depend on the surfactant.
Other compounds which degrade the chemical used are also possible.
Various forms of filtration systems can also work.
And depending on the compounds there is always distillation.
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bahamuth
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[*] posted on 27-12-2013 at 06:38


In molecular biology when faced with the OPs problem we just centrifuge until the phases separate.



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