mr.crow
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Toluene/water/ethanol azeotrope
We all know the benzene azeotrope used to dry ethanol but I see no reason why toluene can't be used instead.
According to Wikipedia its 12% water, 37% ethanol and 51% toluene boiling at 74.4 deg.
Also sounds like it would work in a dean-stark trap to remove water from a Fischer esterification. Is this a good idea?
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Lambda-Eyde
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Two problems: 1) The azeotrope with toluene contains a lower amount of water and 2) The bp. of the azeotrope with toluene is closer to the bp. of
ethanol than the azeotrope with benzene.
So yes, it would work, but distilling with benzene would be superior.
Edit: No, the azeotrope with toluene contains more water than the azeotrope with benzene. I must have read the table wrong...
Edit2: Do you actually want to dry ethanol or to remove water during a Fischer esterification? If it's the latter, you should look into azeotropes
including the ester as well. I can't come up with any reason for adding toluene (or benzene) to a mix of acetic acid and ethanol (for example), as the
ethyl acetate will form an azeotrope with water and ethanol which separates in a Dean-Stark... Thus eliminating the need for toluene.
[Edited on 11-8-2012 by Lambda-Eyde]
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Nicodem
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Quote: Originally posted by mr.crow  | | We all know the benzene azeotrope used to dry ethanol but I see no reason why toluene can't be used instead. |
The ternary azeotrope with toluene has a higher bp. You would need a much more efficient distillation column in order to break the azeotropic
ethanol/water composition, when compared the same by using benzene.
| Quote: | | Also sounds like it would work in a dean-stark trap to remove water from a Fischer esterification. Is this a good idea? |
The use of a Dean-Stark trap in the esterifications is nothing new. A cursory literature search would give you pleanty of examples. Even Org.
Synth. has several examples:
http://www.orgsyn.org/orgsyn/prep.asp?prep=cv3p0203
http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv9...
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Dave Angel
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I'm currently working on ethanol production mr.crow - are you looking at an immediately practical application to get a >99 % EtOH
end result, or more towards an alternative to increase understanding / options, regardless of the end product? Wikipedia also mentions cyclohexane, which may be more pleasant to use than benzene or toluene - if you have access to it.
I don't wish to derail the specific topic, but unless you're dead-set on a ternary azeotropic method to get near-pure ethanol, I'm getting good
results (as I type, in fact) from 1 L of 15-20 % with a Vigreux column 600 mm, B24); getting over 95%, and have use of CaO, gypsum plaster, and/or 3A
molecular sieves planned to complete the drying as necessary.
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mr.crow
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Thanks everyone.
Benzene seems to work better all around. I hadn't considered how hard it would be to remove the toluene/ethanol azeotrope. Also note the water/ethanol
ratio, toluene removes more water but even more ethanol.
If I need anhydrous I would just the the CaO method or real benzene if it was large scale. Its not that hard to make at home
I am planning on making ethyl benzoate soon using toluene and a dean stark trap.
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mr.crow
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Water/ethanol/toluene fail
I am trying to do a Fischer Esterification using toluene to azeotropically remove water.
My dean-stark trap collects nothing but a clear liquid, not two phases. The boiling point is 76 deg, or the toluene/water azeotrope. The
water/ethanol/toluene azeotrope is supposed to be 74 deg.
Mixing the distillate with sat. NaCl solution caused salt to precipitate and a toluene layer to form.
EDIT:
I solved my own problem. Apparently my thermometer sucks ass and water/ethanol/toluene mixtures do not phase separate.
After collecting the distillate despite the extra water and NaCl it still became a single phase
[Edited on 8-10-2012 by mr.crow]
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Nicodem
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Threads Merged
9-10-2012 at 06:49 |
mr.crow
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I'm a little disappointed no one has any discussion
What is a good solvent system for azeotropic water removal? ethanol screws up water/toluene.
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Nicodem
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If you truly wanted a discussion, you could have at least started one. Complaining about lack of discussion when you show no effort from your side is
lame. Start by describing what exactly do you want to discuss, because as far as I can see, you never described the system from which you want to
remove water. And to what levels? At which temperature? And so on...
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mr.crow
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In my previous two posts I outlined my observations and asked a direct question. Hardly a lack of effort.
Maybe my experience with toluene/water/ethanol mixtures will be useful to someone. Who knows! At this point I don't think its worth it to continue.
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watson.fawkes
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You've only posted part of
an experiment, not anything its entirety. Post the whole procedure. I'm with Nicodem that I don't see anything complete enough to know what's going
on.
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mr.crow
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If you are interested here is my writeup. I don't have a final yield, the crude product is waiting to be vacuum distilled.
Ethyl benzoate by Fischer esterification
150g benzoic acid
300 ml ethanol (95%)
6.5g H2SO4 (10 mol %)
50 mL toluene
Heated to reflux with a dean stark trap. The idea was to separate water/ethanol from water/ethanol/toluene but this didn't happen.
Collected distillate at 76 deg. Should be 74, thermometer is wrong
Distillate was a single phase. Mixing with sat NaCl caused salt to precipitate and toluene layer to form. Adding more distillate turned it into a
single phase again.
After removing liquid from trap temperature rose to ethanol/water temperature. Was above 78 deg, maybe 81.
Refluxed for 6 hours total. Mixed with sat. bicarbonate solution in a sep funnel, vigorous CO2 evolution. Washed organic layer with water. Back-washed
aqueous layers with 35mL toluene recovered from the salt water mixture. Dried organic layers with MgSO4. 200ml of clear liquid remains.
I didn't do such a great job with the workup, it was dark outside at that point. Also forms a slight emulsion, density is very similar to water. The
organic solution was heated to over 140 deg to drive off solvents. ~150mL remained. Smells like weird mint cough medicine.
No, I don't have references. Its such an easy reaction based on many sources. I have tried to develop my own method that was partially successful.
So question: How can I improve the dean stark phase?
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Nicodem
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| Quote: Originally posted by mr.crow | 150g benzoic acid
300 ml ethanol (95%)
6.5g H2SO4 (10 mol %)
50 mL toluene
Heated to reflux with a dean stark trap. The idea was to separate water/ethanol from water/ethanol/toluene but this didn't happen.
|
No phase separation could ever occur from such a system. The difference in bp between ethanol and the ternary azeotrope is of less than 4 K. Do you
know what kind of distillation column you would need to separate two liquids with such a close bp? And you had no column.
Besides, even with a more rationally chosen ratio of reactants that would allow for a phase separation, you can not efficiently remove water in
ethanol esterifications due to the obvious reasons - see the composition of the upper phase of the toluene/ethanol/water ternary azeotrope.
Why did you chose to check this method on an esterification where one of the reactants can be used as the solvent? There is no advantage whatsoever.
Such a reaction does not require water removal. Azeotropic water removal only makes sense when the two reactants are less volatile and one wants to
use a near stoichiometric ratio.
Please read the Kirk-Othmer chapter on esterifications for more information - I posted it in some other thread so UTFSE to download it.
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mr.crow
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Thanks for the detailed response, I have learned a lot. I am glad I have finally been able to communicate my problem.
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