Chemguy5
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Does water and acetic acid form an azeotrope?
I have a large quantity mixture of acetic acid and H2O. It's got about 60ml of glacial acetic acid in 500ml h2o. I want to recover the acetic acid but
I'm not sure if it forms an azeotrope with water. I know they have close boiling points so fractional distillation is a must correct? Also what is the
highest concentration of acetic acid I can obtain from fractional distillation?
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JJay
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There's no formal azeotrope, but water and acetic acid are very hard to separate. Theoretically, you could achieve 100% acetic acid that way, but it's
going to take a long time.
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Sigmatropic
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Usually high concentration (>90%) of acetic acid are prepared by neutralizing the solution with a base of choice (hydroxides, carbonates,
bicarbonates of sodium or potassium) followed by boiling off the water and drying of the acetate salt. This acetate salt can then be liberated with
concentrated sulfuric acid and distilled from the mixture.
The starting point is usually vinegar at 5-10% acetic acid and is concentrated by fractional crystallization. Therefore you have less liquid to boil
down in the next step.
Since you've got ~12% acetic acid I would recommend the crystallization.
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macckone
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You can separate acetic acid via fractional distillation but you need a reflux ratio of 10 or more so it is very costly in terms of energy. You can
neutralize acetic acid with sodium bicarbonate (both otc and cheap).
Other acids like oxalic acids can be used to release the acetic acid but that is a special reaction with caveats because it can literally blow up in
your face.
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