Sciencemadness Discussion Board

Drying Glycerol

dangerous amateur - 7-11-2012 at 06:01

Hi,

I've got 60% Glycerol here and like to dry it.

Can it be done just by boiling the water of?

PHILOU Zrealone - 7-11-2012 at 06:25

Should work because glycerol is quite unvolatile.
So simply heat arround 100°c under a flow of air and mixing until 40% weightloss.

bahamuth - 7-11-2012 at 07:42

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.

ScienceSquirrel - 7-11-2012 at 08:06

Glycerol can be dried by simply heating it above the boiling point of water.

Nicodem - 7-11-2012 at 08:38

Quote: Originally posted by ScienceSquirrel  
Glycerol can be dried by simply heating it above the boiling point of water.

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.

kristofvagyok - 7-11-2012 at 10:28

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:D) 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]

bahamuth - 7-11-2012 at 11:10

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:D) 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:P

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]

kristofvagyok - 7-11-2012 at 11:59

Quote: Originally posted by bahamuth  
Edit: Found a reference to what you are describing though not perfectly the same, just needed to borrow some keywords from you:P

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

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.

ScienceSquirrel - 7-11-2012 at 12:55

Quote: Originally posted by Nicodem  
Quote: Originally posted by ScienceSquirrel  
Glycerol can be dried by simply heating it above the boiling point of water.

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]

PHILOU Zrealone - 7-11-2012 at 13:22

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.

bahamuth - 7-11-2012 at 15:11

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.

ScienceSquirrel - 7-11-2012 at 15:39

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.

dangerous amateur - 10-11-2012 at 04:42

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?




Lambda-Eyde - 10-11-2012 at 06:36

What's wrong with plastic? I've seen 99% glycerol from Merck in HDPE bottles.

dangerous amateur - 10-11-2012 at 13:06
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.

kristofvagyok - 10-11-2012 at 13:47

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.

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.

thejerseyrebel - 23-1-2016 at 15:50

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

MeshPL - 27-1-2016 at 02:24

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.

Praxichys - 27-1-2016 at 05:48

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.

S.C. Wack - 27-1-2016 at 09:09

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 726 times

UC235 - 27-1-2016 at 09:24

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.

MeshPL - 28-1-2016 at 02:09

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.

kecskesajt - 30-1-2016 at 01:40

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 :D

Detonationology - 30-1-2016 at 09:25

Sounds like you boiled the glycerol.

bluamine - 2-2-2016 at 07:52

Can we use any drying agents to do so? (Like calcium oxide)

Detonationology - 2-2-2016 at 08:40

Quote: Originally posted by bluamine  
Can we use any drying agents to do so? (Like calcium oxide)

Any compound used to dry the glycerol would likely become suspended in the mixture and would be difficult to separate, even with a vacuum filter. I have nothing but excellent results drying glycerol in a home oven at 350˚F. You can do the same on a hotplate. If it begins to fume or smoke, it's too hot.

Mabus - 2-2-2016 at 11:55

Quote: Originally posted by Detonationology  
Quote: Originally posted by bluamine  
Can we use any drying agents to do so? (Like calcium oxide)

Any compound used to dry the glycerol would likely become suspended in the mixture and would be difficult to separate, even with a vacuum filter. I have nothing but excellent results drying glycerol in a home oven at 350˚F. You can do the same on a hotplate. If it begins to fume or smoke, it's too hot.

What about centrifugation? I don't think calcium hydroxide is very soluble in glycerol.

Detonationology - 2-2-2016 at 13:07

I don't have much practical experience using a centrifuge, but seems like a waste of chemicals and time. As I said, I have dried glycerol from my local pharmacy in an oven for a reaction with oxalic acid to make very dry formic acid. As long as the glycerol is baked thoroughly at a high temp for a long duration, and the oxalic acid is reasonably dry, the product is nearly anhydrous.

[Edit] And NEVER bake oxalic acid, benzoic acid, salicylic acid, etc. in your oven or you will be hated by your family and yourself.

[Edited on 2-2-2016 by Detonationology]