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In reference to my previous question: Separation of methyl acrylate from ethanol I have successfully get rid of acrid odor by treating ethanol with sodium hydroxide and filtering out the precipitate, but after distillation, there is "thinner" odor, possible benzene, toluene or similar aromatic hydrocarbon. Also, the remainder after distillation has orange color (before distillation it was pale yellow), which is possibly due to tetracene.

The question is the same, how can I get rid of these aromatics, probably benzene, easy way? Distillation is here not very good method because of similar boiling points (80.1 °C benzene, 78 °C ethanol).

I also do not know how can benzene get into ethanol, maybe it is by-product of previous reaction with sodium hydroxide with something in UV resin?

Tom
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  • Now I am not quite sure it is benzene as contaminant (or maybe it is not the only one). For some time at the beginning of distillation, I observe something is boiling at 74 °C, +- 1 °C. and after that it raised to 78 °C for ethanol. What could it be, if it has "thinner" odor? – Tom Sep 23 '23 at 08:37

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The melting points of benzene and of ethanol are quite far apart: ~279 K and ~159 K, respectively. Also, solubility tends to decrease at low temperature.

On a small scale, greatly chilling the mix to separate it would not be economically feasible, but on a large scale, an efficient countercurrent heat exchanger would require little energy to chill, separate and then return the effluents to room temperature.

In cold climates, applejack and slivovitz is often made by "freeze distillation".

BTW, many warm-blooded animals have a rete mirabile, a system of blood vessels acting as a countercurrent heat exchanger to get oxygen to limbs, while retaining heat in the body core.

DrMoishe Pippik
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  • Thank you for answer, these are all physical methods, but is there any chemical method to separate them? I mean to add reagent(s) to mixture which will react with benzene but not with ethanol and then it can be easier to separate via filtration, sedimentation etc.? – Tom Sep 23 '23 at 02:34
  • Anyway, I will try this "freeze distillation". I will simply put the mixture in freezer and try to separate solid parts via cold filtration, which can be done in freezer as well. Is that correct? – Tom Sep 23 '23 at 02:42
  • I am still curious about this "freeze distillation", I think it would not be so easy, because otherwise it would be enough for absolute ethanol to freeze e.g. 50% ethanol and separate away the ice from water. I think that mixture will have different behavior and different freezing point. Same could be for mixture of ethanol with benzene. – Tom Sep 23 '23 at 08:40
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    Benzene ethanol have a low boiling azeotrope about 10degrees lower you are possibly seeing this get a better column. Apple jack is made by keeping a barrel of hard cider outdoors The barrel freezes from the outside in by Spring there is a liquid core with eutectic ethanol and apple flavorings in the center ready to be tapped. This worked in the northern climes and may be a lost art with global warming. Freezing probably will not work check the ethanol-benzene phase diagram to see why. [or if it will work] – jimchmst Sep 23 '23 at 20:21
  • @jimchmst, not shuah its a lost aht... down east, them revenuahs don't see a still ;-) – DrMoishe Pippik Sep 24 '23 at 00:11