The Vespiary
The Hive => Newbee Forum => Topic started by: wyndowlicker on May 19, 2004, 04:47:00 PM
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HEy now,
Im curious to know if molecular seives will dry Ethanol to absolute.Has to be absolute. :P
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Molecular sieves are quite ineffective for drying ethanol. The best way to get absolute ethanol is to perform a regular fractional distillation to get about 95% ethanol. In the next step it is dried with calcium oxide to get about 99.5% ethanol1. From here to super-dry ethanol you can use magnesium as in the Lund and Bjerrum-method2.
[1] Pour about 2 liters of 95-96% ethanol into a 3-litre round-bottomed flask and add 500 g calcium oxide. Fit the flask with a double surface condensor carrying a calcium chloride guard-tube and reflux the mixture gently for six hours. Then reassemble the condensor for downward distillation via a splash head adapter to prevent carry-over of the calcium oxide with the vapour stream. Attach a reciever flask with a side-arm reciever adapter which is protected with a calcium chloride guard-tube. Distill the ethanol gently while discarding the first 20 ml of distillate.
[2] The drying takes advantage of the following reactions:
Mg + 2EtOH --> H2 + Mg(OEt)2
Mg(OEt)2 + 2H2O --> Mg(OH)2 + 2EtOH
Fit a dry 1,5-2 litre round-bottomed flask with a double surface condenser and a calcium chloride guard-tube. Place 5 g clean and dry magnesium turnings followed by 50-75 ml 99,5% ethanol and 0,5 g iodine. Warm the flask until the iodine has dissapeared; if a lively evolution of hydrogen has not set in, add a further half gram of iodine. Continue heating until all of the magnesium has been converted into the ethoxide, then add 900 ml 99,5% ethanol and reflux the mixture for 30 minutes. Distill off the ethanol directly into the vessel in which it will be stored to prevent any unnecessary contact with the air as the product is very hygroscopic. The purity of the distillate is higher than 99.95%. This high purity ethanol can very well be stored over type 4A molecular sieves. Any remaining base (magnesium ethoxide) is preferebly removed using 2,4,6-trinitrobenzoic acid, as this acid does not esterify ethanol no water is introduced into the alcohol.
All info taken from Vogel 5:th ed.
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Hey now,
Thanks for the help Barium.That indeed was what I needed.I think this post will also make it easier to locate the information.Youve made it as simple as possible which takes some talent.I appreciate a straight answer.Im going to have to go look in my vogels for this information. :P