Sciencemadness Discussion Board - Concentrate ethanol?

Concentrate ethanol?

j_smith - 7-12-2006 at 17:56

What's the best method to concentrate 95% ethanol (as in Everclear) up to ~98%? I only need about 2 liters for a fulminate synthesis...
I've got access to a pretty well-equipped lab, but it would be up to me to purchase any necessary chemical supplies, so nothing exotic, please.

enhzflep - 7-12-2006 at 18:14

Firstly, isn't that % about the range of the azeotrope?

Second, why would you bother? You're adding it to a solution of (less than)70% nitric acid and mercury nitrate. I never did anything with store bought solvent grade(as in denatured to prevent drinking) ethanol except add the mercury nitrate/nitric solution to it.

"Only" need about 2 litres for a fulminate synth

. My memory's a little hazy on this, but don't you get something like 1/10 (or more) the weight of ethanol back as MF?

Furch - 7-12-2006 at 18:53

Try refluxing the ethanol with magnesium turnings and magnetic stirring, till all the magnesium has reacted (either turned into visuable salt crystals or gone into solution as Mg2+). If you use an excess of magnesium, this procedure should remove denaturating agents such as ketones too - they are converted to the enolate with Mg2+ as counter ion.

Per kilo of denatured ethanol (approx 1.25 liters) you have 50 grams of water, that's roughly 3 moles... Magnesium has an atomic mass of about 24 u, times 3 makes about 75 grams, divided by 2 (one Mg atom interacts with two molecules of water) makes about 40 grams, with a couple of grams for good measure.

Reflux about 60 grams of mangesium with 2 liters of the denatured ethanol, then distill. Left in the distilling flask should be Mg(OH)2.

- Furch

[Edited on 8-12-2006 by Furch]

[Edited on 8-12-2006 by Furch]

Furch - 7-12-2006 at 22:09

Also, don't forget using a drying tube containing anhydrous calcium chloride or the like on top of the reflux condenser.

- Furch

turd - 8-12-2006 at 01:31

Quote:

Try refluxing the ethanol with magnesium turnings and magnetic stirring, till all the magnesium has reacted (either turned into visuable salt crystals or gone into solution as Mg2+). If you use an excess of magnesium, this procedure should remove denaturating agents such as ketones too - they are converted to the enolate with Mg2+ as counter ion.

Will not work. There's a book called "Purification of laboratory chemicals" with the correct procedure.

Furch - 8-12-2006 at 03:10

Will work.

This is a well established laboratory procedure for preparation of absolute ethanol, or "super dry ethanol".

Reference: "Vogel's practical chemistry".

- Furch

turd - 8-12-2006 at 05:53

Hogwash. Magnesium doesn't react with 95% ethanol. Read that reference again and more carefully this time.

Furch - 8-12-2006 at 08:13

I'm sorry to say that I don't have Vogel's at hand right now...

However a quick Google search shows that elemental magnesium can indeed be employed as drying agent for ethanol.

Anyway, I'll get back to you after I've read that particular passage in Vogel's more carefully again - possibly with an apolagy!

Sincerely,
Furch

XxDaTxX - 8-12-2006 at 09:15

I wouldn't call 3A molecular sieves "exotic" would you?

Mg the prep you speak of produces >99% and is only used for things prepping sodium reduction solvents, but one usually starts from 99%. The formation of enough alkoxide to dehydrate 2L of 95 ..... well that would produce quite a bit of hydrogen. If you've done it before you'd choose the sieves as well.

[Edited on 8-12-2006 by XxDaTxX]

Furch - 8-12-2006 at 09:38

I'm sorry... I don't see the problem with formation hydrogen gas? Just ventilate...

I don't consider molecular sieves exotic either... Though if I had to compare, I'd say they are more exotic than magnesium turnings.

XxDaTxX - 8-12-2006 at 10:05

Like I said .... you have to start with 99%. The point about H2 was just if you could hypothetically kickstart your reaction, it would create more than normal amounts of gas being that you started from 95% and you want to do a whole 2L.

Furthermore, you must usually activate the Mg before the alkoxide forms, even starting with freshly delivered 99%.

Also, what would you rather do? Mg, add a little EtOH, activate, warm, wait for H2 evolution to subside, add remaining EtOH, reflux, distill, and remove bases that came over

.... or throw some molecular sieves in and take a nap?

[Edited on 8-12-2006 by XxDaTxX]

Furch - 8-12-2006 at 10:44

Well... To answer your question, I would have to say that I'd rather use magnesium turnings... As I don't own molecular sieves

Anyway, as you seem to have the strongest will and rethorical skills, molecular sieves seem to be the best way to go about the problem.

Sincerely,
Furch

Thanks for the replies

j_smith - 8-12-2006 at 16:32

First thing, Everclear is not denatured. It is sold as an alcoholic beverage...people actually drink it! So no need for the Mg route...

Second, and best part, a colleague loaned me his 3A molecular sieve. It's some sort of synthetic zeolite. All I can say is WOW. Simple, easy, cheap (LOL). I had no idea of that particular application drying ethanol. You could even use corn meal as a sieve!

Magpie - 8-12-2006 at 18:08

As a side note I am also impressed with molecular sieves. I dried my homemade diethyl ether (made from 95% ethanol) to a point good enough for a Grignard reaction. I used 4A sieves and believe that they not only removed the water but also any unconverted ethanol.

XxDaTxX - 8-12-2006 at 18:38

Quote:

Originally posted by j_smith
First thing, Everclear is not denatured. It is sold as an alcoholic beverage...people actually drink it! So no need for the Mg route...

Second, and best part, a colleague loaned me his 3A molecular sieve. It's some sort of synthetic zeolite. All I can say is WOW. Simple, easy, cheap (LOL). I had no idea of that particular application drying ethanol. You could even use corn meal as a sieve!

The kicker is .... REUSABLE. You're welcome.

Tsjerk - 8-12-2006 at 19:00

And that kicker is even more a kicker if you have experience with drying molecular sieves. It's to simple, just trow it in an oven at 90 degrees an wait. In just an hour its dry.

I ones had 15 grams of 3A sieves which were a little bit wet (mostly methanol) and within 45 minutes it reduced to 10 grams. They turned from brown to a colour which was more a dark coloured white. I got them from a bottle of absolute dry methanol and I wanted to use them for drying THF.

[Edited on 9-12-2006 by Tsjerk]

[Edited on 9-12-2006 by Tsjerk]

j_smith - 8-12-2006 at 20:57

That's the best part. Not only CHEAP, but

REUSABLE!

I love chemistry :cool:

cbfull - 8-12-2006 at 23:56

In the past when I was researching the subject the suggested reagent was calcium oxide (also called quicklime). I don't know where to get it other than chemical suppliers but it reacts with the water irreversibly to calcium hydroxide, and requires re-distillation.

You could probably try calcium sulfate (drierite) or even baked magnesium sulfate (epsom salts) for that matter.

Another method might be to use silica gel (the non indicating variety, cobalt is toxic) if the wet ethanol is cold. I say cold because the silica gel tends to absorb the water rather quickly generating much heat and causing the gel pieces to crack apart as it absorbs too fast. To remedy this you might start with silica gel already wetted with DRY ethanol, and slowly add the 95% ethanol with stirring to avoid exposing the gels to too much water too fast.

Just an idea but I bet it would work.

cyberzed - 10-12-2006 at 10:02

Absolute, or 99.5% water-free, Ethanol is frequently necessary in many organic operations. It is quite easy to prepare from the azeotrope with water such as "Everclear" brand grain alcohol, "moonshine" or "Rectified Spirits" (an old term for the same thing).

Dehydrate 75g of fresh anhydrous Calcium Oxide in a vacuum dessicator for 24 hours (a bit redundant, I know) or heat in an oven at 200C for 2 hours, then immediately transfer to the vacuum dessicator until use. Setup glassware for simple refluxing with a water-cooled condenser and a Calcium Chloride guard tube. Place 350mL of Ethanol into the flask, quickly add the Calcium Oxide and hold at gentle reflux on the water bath or heating mantle for 6 hours. Allow the mixture to stand overnight, then distill off the alcohol, discarding the first few mL (it may be more convenient to just vent the condenser to the atmosphere for the first couple of minutes after distillation has commenced). Yield should be better than 315mL. Store the absolute Ethanol in a tightly closed glass container as it will pick up water from the air rapidly.

Calcium oxide can be prepared by heating Calcium Carbonate to a temperature above 825°C where it wil liberate CO2 and form Calcium Oxide.

unionised - 10-12-2006 at 14:25

Fresh quicklime is likely to be a better dessicant than a vacuum dessicator. It willalso rapidly pick up CO2 from the air at 200C so I think you would be better off not bothering to try to dry it.

Dehydrating ethanol

MadHatter - 10-12-2006 at 18:58

People who distill ethanol for fuel often run it through anhydrous rock salt. This is my
preferred method. Do it and redistill the liquid to remove any traces of NaCl.

evil_lurker - 10-12-2006 at 21:09

3A sieves rule supreme for drying ethanol.

On Ebay you can get 5 pounds capable of absorbing 15%+ of their weight in water for around $30.

No mess. No fuss. Chunk in. Let sit for a few days. Pour off. Your done. No need for redistillation.

EmmisonJ - 15-5-2009 at 07:39

Quote: Originally posted by j_smith

You could even use corn meal as a sieve!

does anybody have any information on using corn meal as a sieve to dry out 95% ethanol to 99% ethanol?

aside from this http://journeytoforever.org/biofuel_library/ethanol_grits.ht...

EmmisonJ - 15-5-2009 at 08:16

ah, found this http://www.patentstorm.us/patents/4868346/description.html

Elawr - 15-5-2009 at 11:03

Anhydrous CuS04 will also work, but I'm uncertain of solubility of Cu++ in etOH so distilling afterward might be prudent. It is easily prepared by heating the pentahydrate to 200 C until all the blue color is gone, and you are left with grey-white ashlike powder.

EmmisonJ - 15-5-2009 at 17:11

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]

not_important - 16-5-2009 at 00:19

"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...

EmmisonJ - 16-5-2009 at 05:20

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

EmmisonJ - 16-5-2009 at 14:05

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

not_important - 17-5-2009 at 04:01

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.

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.

EmmisonJ - 17-5-2009 at 10:59

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.

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

EmmisonJ - 29-5-2009 at 06:20

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?

DougTheMapper - 20-6-2009 at 19:21

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.

grind - 5-7-2009 at 04:25

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...

Barium - 5-7-2009 at 09:43

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.