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dangerous amateur
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Drying Glycerol
Hi,
I've got 60% Glycerol here and like to dry it.
Can it be done just by boiling the water of?
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PHILOU Zrealone
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Should work because glycerol is quite unvolatile.
So simply heat arround 100°c under a flow of air and mixing until 40% weightloss.
PH Z (PHILOU Zrealone)
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bahamuth
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I doubt simply boiling off the water will do any good, at least you need to raise the temp and lower the pressure to get any effect without destroying
the glycerol. Bubbling hot dry air through a stirred hot solution of glycerol with vigorous stirring under reduced pressure might do the trick.
Glycerol at ~100 degrees Celsius is used to dry ethanol to an anhydrous state, by passing ~95% ethanol/water vapor through the hot glycerol, as not to
liquify the ethanol, but only retain the water.
In the lab, anhydrous glycerol is a treasured thing (at least where I work...) and old unopened bottles of the nearly anhydrous stuff (~99.5 and
above) is useless and is no longer usable as anhydrous material. Opened containers of the anhydrous glycerol is no longer considered anhydrous and is
usually discarded or set to other uses.
Here is some general info I found on glycerol, though I could not find much on the drying of it.
Glycerine - an overview
Let me know if you ever attempt this and if it works, interested in somewhat large scale drying of glycerol myself but never had the incentive to do
so.. And hope you succeed.
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ScienceSquirrel
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Glycerol can be dried by simply heating it above the boiling point of water.
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Nicodem
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Do you have a reference for this?
It sounds quite counterintuitive, given the partial pressure of water vapors above a 60% glycerol/water mixture at 100 °C is still much lower than
the atmospheric pressure. Increasing temperature would bring it to boil, but as the concentration of glycerol raises, so does the partial pressure of
water vapors drop. I guess you could perhaps reach >90% concentrations by distilling off part of the mixture under vacuum, but given the strong
hygroscopicity, the anhydrous state is unlikely to be achieved by mere concentration. Anyway, I guess those interested in drying glycerol could check
the literature on how it is done.
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kristofvagyok
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The most practical purification of glycerol according to my memories is:
Add high excess of n-propanol (300cm of 60% glycerol to 1700cm of n-propanol), boil it and collect the evaporated n-propanol water mixture, distill it
til you get a little more than 1000cm3 of distillate collected, then place the resulting solution in the freezer for a night. The pure glycerol will
crystallize out, filter it on a cooled Büchner (work fast ) and wash the
resulting crystals with chilled acetone or diisopropyl ether.
Distillation on atmospheric pressure won't work.
[Edited on 7-11-2012 by kristofvagyok]
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bahamuth
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Quote: Originally posted by kristofvagyok  | The most practical purification of glycerol according to my memories is:
Add high excess of n-propanol (300cm of 60% glycerol to 1700cm of n-propanol), boil it and collect the evaporated n-propanol water mixture, distill it
til you get a little more than 1000cm3 of distillate collected, then place the resulting solution in the freezer for a night. The pure glycerol will
crystallize out, filter it on a cooled Büchner (work fast) and wash the
resulting crystals with chilled acetone or diisopropyl ether.
Distillation on atmospheric pressure won't work.
[Edited on 7-11-2012 by kristofvagyok] |
Hmm, sounds very expensive and time consuming, regarding that close-to-anhydrous glycerol is relatively cheap...
Though I have found freeze-out-crystallization of simple organics simple and clean (had access to -80 degrees C freezers, Liq. N2 and dry ice), I
imagine this to be too labor intensive if not set up as a continuous process, e.g. as part of a semi-large to large ethanol drying setup...
Edit: Found a reference to what you are describing though not perfectly the same, just needed to borrow some keywords from you
drying of glycerol by distillation with n-propanol
With the original work here:
Purification of Glycerol by Crystallization H. B. Hass and J. A. Patterson Industrial & Engineering Chemistry 1941 33 (5), 615-616
[Edited on 7-11-2012 by bahamuth]
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kristofvagyok
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The method what I have described was from the "purification of organic chemicals" second ed., the big white book, one of the most useful books in a
lab.
Also, I did wrote the recipe from my memories, because I looked up this a while ago... If something was missing, sorry.
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ScienceSquirrel
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| Quote: Originally posted by Nicodem |
Do you have a reference for this?
It sounds quite counterintuitive, given the partial pressure of water vapors above a 60% glycerol/water mixture at 100 °C is still much lower than
the atmospheric pressure. Increasing temperature would bring it to boil, but as the concentration of glycerol raises, so does the partial pressure of
water vapors drop. I guess you could perhaps reach >90% concentrations by distilling off part of the mixture under vacuum, but given the strong
hygroscopicity, the anhydrous state is unlikely to be achieved by mere concentration. Anyway, I guess those interested in drying glycerol could check
the literature on how it is done. |
Will Organic Syntheses do you, see Note3?
Oops I forgot the reference
http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1...
[Edited on 7-11-2012 by ScienceSquirrel]
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PHILOU Zrealone
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First what I have written earlier.
Then if anhydrous is needed: In a closed system now!
Molecular sieves, CaCl2, CaO, silicagel, white CuSO4, anhydrous Na2SO4, P2O5 are good dehydrators...
Then vacuum distil.
PH Z (PHILOU Zrealone)
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bahamuth
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| Quote: Originally posted by PHILOU Zrealone | First what I have written earlier.
Then if anhydrous is needed: In a closed system now!
Molecular sieves, CaCl2, CaO, silicagel, white CuSO4, anhydrous Na2SO4, P2O5 are good dehydrators...
Then vacuum distil. |
I suspect glycerol to have a stronger affinity to water than CaCl2, silica gel and Na2SO4. At least they will not dry
the glycerol completely. Though I have no proof of this but scouring the net I find lots of use for glycerol as a moderately strong desiccant in some
cases. Molecular sieves would probably work, as would probably anhydrous CuSO4 and CaO. P2O5 will dehydrate your
glycerol to acrolein.
Even if the desiccants above will dehydrate the glycerol, they will give their water (or at least some of it) back when the temperature is high enough
for the glycerol to distill even under reduced pressures, except CaO though.
In one of my above links; Glycerol - An overview, they state a boiling point of 152 degrees Celsius at 5 mmHg, in which is all but the CaO will give
their water back at the reduced pressures, excluding the phosphorous pentoxide.
But of course this whole discussion depends on how dry the OP really needs it; when someone mentions "dry" to me I at least think they mean anhydrous
or as close as possible to that.
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ScienceSquirrel
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For some purposes eg the synthesis of acrolein and nitroglycerine dry could be defined as maybe 98 - 99% or better and that is good enough to give
good yields of the desired product.
Very dry would be maybe 99.9 or 99.99%.
Distilling under dry nitrogen in flame dried Schlenk apparatus from molecular sieves might get you close to anhydrous but I guess it would still
contain a few molecules of water.
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dangerous amateur
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Thank you for your answers.
Well, in fact I'm indeed thinking about some little nitration experiments. I know that it's not necessary to have 99%, but I since I'm very low on
acids I do not want to waste it just for absorbing water.
As a matter of principle.
Unfortunately I don't have a destillation apparatus (yet).
But I got another bottle of pure glycerine from a friend. Should have 99%. But as so many other stuff, it came in a plastic bottle
Is it worth to be decanted into a proper glass vessel?
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Lambda-Eyde
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What's wrong with plastic? I've seen 99% glycerol from Merck in HDPE bottles.
This just in: 95,5 % of the world population lives outside the USA
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dangerous amateur
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| Quote: |
What's wrong with plastic? I've seen 99% glycerol from Merck in HDPE bottles. |
Take a look at that nice PDF bahamuth posted, Page nine.
Humidity at my storage place is about 60%.
That means over time it will settle at 75% Now if it's in a glass bottle with proper cap this wont happen, or at least take a very long time.
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kristofvagyok
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| Quote: Originally posted by dangerous amateur |
Take a look at that nice PDF bahamuth posted, Page nine.
Humidity at my storage place is about 60%.
That means over time it will settle at 75% Now if it's in a glass bottle with proper cap this wont happen, or at least take a very long time.
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I still don't get it. We've got a LOT chemicals shipped in HPDE bottles and they do not absorb more water than other chems what are kept in glass.
Why would the be glycerine unpure if it is stored in a 60% humidity room in a HDPE bottle? If is closed well, then you can keep it in the HDPE flask
under water also.
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thejerseyrebel
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so I tried this with some impure glycerin with cacl2 but when I transferred it to another container with cacl2 I saw hydrochloric acid fumes pouring
out with the molten glycerin. I have absolutely no idea why the road salt grade cacl2 reacted though the glycerin is quite contaminated and needs to
be decolorized
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MeshPL
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Molecular sieves should work, they are quite a powerful dessicant. Although a huge excess will be required to overcome glycerol's affinity to water.
Silica gel could work. It should be noted that due to simmilarity of glycerol to water most dessicants will dissolve e.g. sodium sulphate, calcium
chloride, copper sulphate... basic and acidic dessicants may simply dissolve.
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Praxichys
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Bubbling dry air through the glycerol solution with progressive warming would work well. You would have to stop below the temperature where
decomposition becomes rapid, so something less than 280°C. It could then be vacuum fractionated from its decomposition/oxidation products. Oxidation could be significant enough to warrant the use of an inert gas rather than air, and would undoubtedly result in a purer product.
Azeotropic drying using toluene and a dean-stark trap might work but would probably be slow since this relies on the partial pressure of water in
glycerol at only 110°C.
I would be hesitant to use solid desiccants because glycerol is quite viscous and will be difficult to filter from fine solids. Further, if the
desiccant works well enough the glycerol could solidify. Besides, it is not practical to remove 40% water using solid desiccants. Even 5% would be
quite high for something like that.
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S.C. Wack
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| Quote: Originally posted by thejerseyrebel | | so I tried this with some impure glycerin with cacl2 but when I transferred it to another container with cacl2 I saw hydrochloric acid fumes pouring
out with the molten glycerin. |
If one is going to try calcium chloride drying of glycerol, it'll be in a vacuum desiccator with a separate container for each. Perhaps you've made an
addition compound that would be expected with an -ol. There would some old literature on that out there for the finding for sure if someone cared.
The IEC article mentioned years ago is definitely worth posting somewhere, so here it is.
Attachment: iec_33_615_1941.pdf (261kB)
This file has been downloaded 738 times
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UC235
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It will be much harder to dry glycerol than to just go buy some that is already dry. Unless you're trying to work up biodiesel waste for some reason,
you can buy it in bulk for $2/kg.
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MeshPL
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What about making some magnesium methoxide? (by simply boiling magnesium in methanol) And adding it to glycerol so that magnesium hydroxide and
methanol are formed. Magnesium hydroxide could be filtered and methanol evaporated.
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kecskesajt
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I tried evaporating water and ended up in a fog in the kitchen where I can't even see the clock in the other side of the room
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Detonationology
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Sounds like you boiled the glycerol.
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bluamine
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Can we use any drying agents to do so? (Like calcium oxide)
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