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EmmisonJ
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after reading the patents it seems like distillation with a column packed with dry cornmeal would work because it seems like all they did was
pass the azeotropic ethanol/water vapors through dry corn grain and it will happily absorb the water vapor allowing the almost anhydrous ethanol to
pass through. does anyone see anything wrong with this procedure?
| Quote: | 1. dehydrate cornmeal
| Quote: | | To make the corn meal suitable for use it is heated with 50° C. to 60° C. air to dryness. According to the patent, the corn meal exhibits a capacity
to absorb only about 0.0225 gram water per gram of dry corn meal. |
Reference: http://www.patentstorm.us/patents/4868346/description.html
based on the quote above, cornmeal can absorb 0.0225g of water per 1g of dry cornmeal. working with 50ml of 95% EtOH means we need to absorb
2.5ml/2.5g of water. 2.5/0.0225 = ~112, so we need 112g of cornmeal. let's play it safe and use a little overkill with 150g. so heat 150g of cornmeal
to 60C until it is dry (not sure how long, will look for visual indicator)
2. setup for fractional distillation, charge the distilling RBF with 50ml 95% EtOH and pack the vigreux column with 150g dry cornmeal. put a cotton
ball on the bottom of the column to keep particles from falling into the distilling flask then load it up with the cornmeal on top of the cotton ball
3. distill the 95% EtOH, as the ethanol/water vapors pass through the cornmeal, the cornmeal should absorb the water vapors allowing only the ethanol
vapors to pass through. the ethanol vapors are then condensed and collect in the receiving flask as 99+% EtOH
4. the EtOH must be stored sealed with a desiccant to keep it 99% EtOH, but is better to be prepared right before it is needed
other references of interest are
http://www.freepatentsonline.com/4333740.html
http://www.freepatentsonline.com/4345973.html |
[Edited on 16-5-2009 by EmmisonJ]
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not_important
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"packed" is too strong a word, the starchy material must be in a reasonably open & porous form. It will swell to a lesser or greater extent as it
absorbs water, if too tightly packed it will seal the column shut. You must insure that water does not condense in the column, else
strong swelling can occur.
This is a detailed paper on the process, using corn grits:
http://journeytoforever.org/biofuel_library/ethanol_grits.ht...
other carbohydrates can be used:
http://www.nt.ntnu.no/users/skoge/prost/proceedings/aiche-20...
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EmmisonJ
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Quote: Originally posted by not_important  | | "packed" is too strong a word, the starchy material must be in a reasonably open & porous form. It will swell to a lesser or greater extent as it
absorbs water, if too tightly packed it will seal the column shut. You must insure that water does not condense in the column, else
strong swelling can occur. |
very good call, thanks. you're absolutely right, it could swell and seal the column shut which could lead to a dangerous pressure buildup in the
heated distilling flask full of hot alcohol
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EmmisonJ
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cotton ball won't work, i just tried out that idea and paid close attention as the heat built up to any signs of pressure. basically i had a neck
that was capped and every so often i would briefly uncap it to release excess pressure if any.
well the EtOH began condensing faster and faster on the bottom of the cotton ball so i just took that as a sign to pull the plug on the experiment.
a better idea would be to either just use a sieve if you have any available. else, use a desiccant stored in the 95% EtOH in its liquid phase then
distill it afterwards
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not_important
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| Quote: Originally posted by EmmisonJ |
well the EtOH began condensing faster and faster on the bottom of the cotton ball so i just took that as a sign to pull the plug on the experiment.
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Right there it says the needed conditions were not met. The column must be preheated above the boiling point of the EtOH-H2O azeotrope so that only
vapour contacts the carbohydrate; liquid in the absorption column means you failed to provide required conditions.
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EmmisonJ
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| Quote: Originally posted by not_important | [Right there it says the needed conditions were not met. The column must be preheated above the boiling point of the EtOH-H2O azeotrope so that only
vapour contacts the carbohydrate; liquid in the absorption column means you failed to provide required conditions.
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yep bad practice on my end. all the patents (IIRC) say they use a column that is jacketed and run hot water through it. now i know why, thanks
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EmmisonJ
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after reading up a bit it sounds like if you use sieves that they will leave a powder from their outer surface which will initially be suspended in
the EtOH causing it to appear cloudy. letting it settle and decanting EtOH from the top is the remedy for this.
i was curious though how fine of a particulate is this powder, can it be filtered/vac filtered out with 101-103 filter paper?
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DougTheMapper
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Personally, I'd set up a distillation apparatus and add an excess of anhydrous MgSO4 to the boiling flask.
MgSO4 (anh.) is easily obtained with epsom salts and an oven.
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grind
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An extremely simple method to remove a few percent of water in ethanol is to distill the ethanol in vacuum. The azeotropic composition is dependent on
the pressure, and if I remember correctly, 95% ethanol should be distilled at approx. 50 mbar. With a very good column, of course.
That´s what I´ve heard. I never tried it, but it sounds good.
The industrial way to produce absolute ethanol consists of the distillation of the ethanol/water-mixture with benzene. At first a ternary mixture
(benzene/water/ethanol) comes over, absolute ethanol remains. You need a very good column, and you can´t substitute benzene with toluene (what is
generally possible in only very few cases although often suggested!).
Concerning the dehydration with molecular sieves - you should distill the ethanol after such a treatment. No one guarantees that your molecular sieves
are completely free from (ethanol-) soluble impurities...
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Barium
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| Quote: Originally posted by grind | | The industrial way to produce absolute ethanol consists of the distillation of the ethanol/water-mixture with benzene. |
AFIK, cyclohexane is nowdays used instead of benzene. To 95% ethanol, obtained by fermentation, is added fifteen times more cyclohexane than the
amount of water the azeotrope contains. By distillation at ordinary pressure a ternary mixture containing 5% water, 20% ethanol and 75% cyclohexane
comes over at 62 deg C. Ethanol with a purity of about 99,7% comes over at 78 deg C and the remaining cyclohexane at 81 deg C. The remaining
impurities (acetic acid and ethyl acetate) is removed by reaction with sodium hydroxide followed by another distillation.
From a raw fermented mixture containing 8-10% ethanol is obtained a first distillate containing 55% ethanol by simple distillation. A second
distillation gives 85% ethanol and a third gives 90%. After eight distillations 95% ethanol is obtained.
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