frogfot
Hazard to Others
Posts: 212
Registered: 30-11-2002
Location: Sweden
Member Is Offline
Mood: happy
|
|
Glycerin and soap
I posted the very same thread at E&W but they didn't like word "soap", although thread was focusing only on glycerin..
Anyway, thread was locked but I got some thoats about how to purify glycerin without vacuum destillation, gotta share them with someone...
To make long story short. I've heated (~100*C) 1 kg corn oil, 175 g NaOH and 800 ml water, with mechanical stirring for 8 h.
Glycerin was extracted by water while precipitating soap with NaCl. This was done several times. Combined waters was then neutrolised by H2SO4 and
evaporated several times, filtering off precipitating NaCl. In the end I got thick goo that was diluted with alcohol and rests of NaCl was filtered.
Soln was heated to 180*C and destilled in vacuum. Everything came in a fraction of 170*C (must be ~20 torr). I got 61 g clear, thick liquid (57% from
theoretical).
Since vacuum dest is a pain, I tryed to find an alternative way of purification. What if impurities could be removed with activated carbon..
I tested this with saved rests of glycerine from destilling flask. It's basically a brown goo containing glycerin, fatty acids, NaCl and most
probably some organic decomp products.
Goo was dissolved in water, acidifyed by acetic acid and boiled with some activated carbon. On filtering I got clear slightly yellow liquid! (without
acidification it remains brown colored).
So, could activated carbon remove fatty acids and other impurities? If yes, we wouldn't need any vacuum destilling.
In practice one would insert this purifying step while boiling down the extraction waters. Using HCl to acidify. And NaHCO3 to neutrolise (to spare
metallic pot, where everything will be made). Treatement with carbon could be made in a plastic bucket.. evaporation could then be continiued.
In the end, all nonorganic salts could be removed as mentioned before, by adding alcohol.
|
|
|
chemoleo
Biochemicus Energeticus
Posts: 3005
Registered: 23-7-2003
Location: England Germany
Member Is Offline
Mood: crystalline
|
|
Just in case you haven't noticed, there is a related thread, on the making of biodiesel.
Commercial saponification of course extracts glycerin the way you do.
Check this:
http://www.sciencemadness.org/talk/viewthread.php?tid=1694
There are some pics on the layers of liquid you get. But indeed, normally glycerin is distilled in order to purify it.
[Edited on 11-7-2004 by chemoleo]
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
|
|
|
frogfot
Hazard to Others
Posts: 212
Registered: 30-11-2002
Location: Sweden
Member Is Offline
Mood: happy
|
|
Whow! Thats really useful info you posted there.
For some reason I didn't find it with search (probably because you all call it glycerol  ). Anyway, if mods want they can combine/deleate my thread.. But I wanna hear opinions on that activated carbon
purification, even if biodiesel method seems to be much better and simpler. Gonna defineatly try it tomorrow.
[Edited on 12-7-2004 by frogfot]
|
|
|
S.C. Wack
bibliomaster
Posts: 2419
Registered: 7-5-2004
Location: Cornworld, Central USA
Member Is Offline
Mood: Enhanced
|
|
You might want to try purification by crystallization, in addition to the C treatment.
|
|
|
chemoleo
Biochemicus Energeticus
Posts: 3005
Registered: 23-7-2003
Location: England Germany
Member Is Offline
Mood: crystalline
|
|
Crystallisation of glycerol or the fatty acid salts (well....)? or the NaCl? I dont get it 
[Edited on 12-7-2004 by chemoleo]
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
|
|
|
S.C. Wack
bibliomaster
Posts: 2419
Registered: 7-5-2004
Location: Cornworld, Central USA
Member Is Offline
Mood: Enhanced
|
|
Crystallisation of glycerol or the fatty acid salts (well....)? or the NaCl? I dont get it
The glycerol. If this was a great way then industry would do so. This was done in the past, however, and apparently fairly pure glycerol could be
obtained from very impure material. I mention this as purification alternatives are sought here.
Of the pure material, from Merck: "Solidifies after prolonged cooling at 0°, forming shiny orthorhombic crystals, mp 17.8°."
|
|
|
chemoleo
Biochemicus Energeticus
Posts: 3005
Registered: 23-7-2003
Location: England Germany
Member Is Offline
Mood: crystalline
|
|
I was thinking, you could make glyceraldehyde via some bacterial process, react it with NaHSO3 to form the adduct (to purify it) and reduce it in due
course to glycerol - there you got your pure glycerol 
On a more serious note - I doubt crystallisation would work well, becuase the initial product is not clean. I tried once to crystallise
diethanolamine, and despite an MP of 26 deg C, and after more than a week at 4 deg C it didnt crystallise. In the end it did though. And that was a
pure compound.
If I was to make clean glycerin that way, and lacked vacuum destiallation (which really IS the way to go), then I would start with a clean oil,
preferably fully saturated, with little complexity. Make sure it's colourless to start off with. Do your reaction, and don't let the temp.
rise too much. Then raise the pH, and shake with charcoal.
Oh, and btw, glycerol supposedly (as a polyol) dissolves in butanol, while water isn't dissolved - butanol is for instance used to extract other
polyols from complex reactions, as it doesn't dissolve ionics/much water etc.
(PS Actuyally I would also try the biodiesel method to see whether the glycerol there is cleaner)
[Edited on 13-7-2004 by chemoleo]
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
|
|
|
frogfot
Hazard to Others
Posts: 212
Registered: 30-11-2002
Location: Sweden
Member Is Offline
Mood: happy
|
|
Tested to crystallise pure glycerin at 0*C, nothing happened in a day. Now when you say such things could take weeks.. would it crystallise at 9*C (my
fridge temp)? ..I forget to refresh ice-bath.. so thats why I'm asking.
Other method is so nice!! Since the other thread is focused on biodiesel I thoat to tell results from glycerin purification here..
Btw, ethanol (95%) doesn't work because of water. Everything have to be dry because water will hydrolise formed esters and make it much harder
for layers to separate. And theres not much water that's needed to screw things over (it's so small compared to big fatty acids).
Anyway, you all probably know this link but here it is, lots of info:
http://journeytoforever.org/biodiesel_make.html
I used methanol, and got nice layer separation after couple of minutes. Bottom layer was acidifyed by dilute H2SO4. This gave two layers: aqueous
glycerin/Na2SO4/H2SO4 in bottom and liquid free fatty acids in top.
Bottom layer was made basic by NaHCO3, boiled down and alcohol was added to precipitate NaCl/NaHCO3.
It was then heated to 180*C, more alcohol and to 180*C again.
On cooling to r.t. his gave thick yellow liquid (like honey) much more clearer than that raw glycerin I got from soap procidure! And thats without
even purifying.
Haha, screw the soap procidure! If it took me 3 days to process 1 kg, now it can be done in 3 hours! With less effort, less chems and better yield.
The biodieslel is a big byproduct for me.. probably gonna use it in pyro fireballs. 
Btw, I'd keep purification as simple as possible, hope freezing will work.
[Edited on 13-7-2004 by frogfot]
|
|
|
S.C. Wack
bibliomaster
Posts: 2419
Registered: 7-5-2004
Location: Cornworld, Central USA
Member Is Offline
Mood: Enhanced
|
|
Well, Sarg made a nice product by crystallization industrially for years starting in the 1870's, but did not leave handy notes.
I found a good old (1873) article on the net including the discovery of crystalline glycerol...in Swedish...it begins at the bottom of this page and
goes on a few more. I've no idea how dull or interesting it might be to you.
http://www.lysator.liu.se/runeberg/tiphyche/1873/0306.html
Seed crystals seem to get mentioned a lot. And centrifuges to strip off the impurities from the crystals. Saw a mention of Cl2 to induce
crystallization as well.
And this:
http://l2.espacenet.com/espacenet/viewer?PN=US2233606&CY...
Butanol shows up again. There is a DLI book on glycerin mentioned on the sciencemadness library page, and that was the main source of my earlier
statement about obtaining pure crystals from impure material.
[Edited on 13-7-2004 by S.C. Wack]
|
|
|
frogfot
Hazard to Others
Posts: 212
Registered: 30-11-2002
Location: Sweden
Member Is Offline
Mood: happy
|
|
Thanx alot for the links. I didn't quite understand first text since it's some kind of old Swedish?? (a bit hard to read) But the patent
really describes it all. Although as you've said, one needs seed crystalls..
As I understand solvent is just to thin out glycerine, to make it less viscouls and therefore make it easier for crystalls to form. They also mention
many other solvents that can be used, more available ones like EtOH and MeOH. Although yield is 40%.. (or did I miss something..)
Btw, product from my previous post had some fatty acids, since on dilution with water it became a bit turbid. Turbidity increased on acidification.
I've retested procidure but now I treated glycerin with carbon. Result is much better! No indication of fatty acids and product is nearly
colorless
Although I got only ~30% yield. I'll try to come up where the rest went. Since reaction goes to 100%, loss must be in extractions.. maby some
glycerin is adsorben on carbon.. dunno.
EDIT:
Maby some glycerin is in diesel. Extraction with water could be made directly after the transesterification step. Although I don't know how this
would affect further purification/quality of diesel..
[Edited on 13-7-2004 by frogfot]
|
|
|
axehandle
Free Radical
Posts: 1065
Registered: 30-12-2003
Location: Sweden
Member Is Offline
Mood: horny
|
|
| Quote: |
Thanx alot for the links. I didn't quite understand first text since it's some kind of old Swedish?? (a bit hard to read) But the patent
really describes it all. Although as you've said, one needs seed crystalls..
|
No no no no no. It's Danish, written in 1873. 
[Edited on 2004-7-13 by axehandle]
My PGP key, Fingerprint 5D96 E09E 365D 1867 2DF5 C2FE 4269 9C19 E079 CD35
\"Verbing nouns weirds the language!\"
|
|
|
frogfot
Hazard to Others
Posts: 212
Registered: 30-11-2002
Location: Sweden
Member Is Offline
Mood: happy
|
|
Oki, transesterification gave fair yields, 84%, if what I got is a pure product...
After experimenting some I wrote up a procidure (saponification is also mentined), if anyone is interested:
www.frogfot.com/synthesis/glycerol.html
Biodiesel seems to dissolve glycerol to some extent, so, extracting diesel many times should increase yields.. But I suspect that using too big
ammounts of water will decrease yield since I heard that glycerol evaporates with water steam.
Any idea if thats a big loss at atmospheric pressure?
In industry they evaporate aqueous glycerol under vacuum, and since boiling points of water and glycerol comes closer under vacuum, more glycerol
should be lost, right? But since industry doesn't care about this, maby loss ain't that big.. or?
Heh, Axehandle, so I could understand a little Danish.. cool
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
