We are interested to separate the azeotrope of ethanol and water by freezing. We assume that water will be converted into ice and ethanol remain as liquid at some temperature. Is it possible to separate the azeotrope by this method?
I believe that the mixture of water / ethanol can not be separated of freezing. This process will be hampered by supersaturation, co-condensation.I recommend to read
http://www-llb.cea.fr/WATSURF-2013/Presentations/Seminar/B_Chazallon_Les%20Houches_2013.pdf
This so-called "cold distillation" is sometimes used to make spirits from home-made wine in countries where alcohol cannot be obtained or is heavily taxed. It does not separate out fusel oils, so the resulting rotgut should be consumed with discretion. If you assume that a houshold freezer has a temperature of -20 °C, then you can obtain about 30% ethanol that way, in a lab freezer (-80 °C) about 85%. If you start with the aceotrope (94% ethanol IIRC), freezing will not separate out the remaining water, because the eutectic mixture is close to the azeotrop (https://en.wikipedia.org/wiki/Eutectic_system#/media/File:Phase_diagram_ethanol_water_s_l_en.svg). To get 100% ethanol, you need to react the water with metallic sodium and then re-distill.
A few suggested references:
B.Y. Okamoto, R.H. Wood, P.T. Thompson, "Freezing points of aqueous alcohols. Free energy of interaction of the CHOH, CH2, CONH and C=C functional groups in dilute aqueous solutions", J. Chem. Soc. Faraday Trans. I, 74, 1978, 1990-2007.
J.B. Ott, J.R. Goates, B.A. Waite, "(Solid + liquid) phase equilibria and solid-hydrate formation in water + methyl, + ethyl, + isopropyl, and + tertiary butyl alcohols", J. Chem. Thermodyn., 11(8) 1979, 739-746.
K. Takaizumi, T. Wakabayashi, "The freezing process in methanol-, ethanol-, and propanol-water systems as revealed by differential scanning calorimetry", J. Solution Chem., 26(10) 1997, 927-939.
D.R. Lide (Ed.-in-Chief), "CRC Handbook of Chemistry and Physics", 85th ed., CRC Press, 2004, p. 8-63.
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