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Author: Subject: distillation of acetone - failed
Crucible
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[*] posted on 26-6-2010 at 20:06
distillation of acetone - failed


I'm finally ready to fire up my new glassware and decided to start with something simple, distillation of acetone. Acetone being fairly handy and something I'm likely to need in the future. Not sure how much of this shows up in the photo, but I've got a 1L roundbottom flask in a hot water bath, vigreaux column, and west condenser.

I was expecting the acetone to distill fairly rapidly but after 1.5 hours of steady boiling the condensation ring hasn't moved more than halfway up the column. I have it wrapped in 2" fiberglass insulation to eliminate heat loss, but I must still be losing heat somewhere. What am I missing here?

I suppose I could just take the column out, but I'd rather leave it and get a higher purity distillate if possible.

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Skyjumper
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[*] posted on 26-6-2010 at 20:08


Remove the column, The low boiling point of acetone is making the column into basically an air cooled reflux
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not_important
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[*] posted on 26-6-2010 at 21:23


Too low heat input for the losses, that gives a refluxing in the column.

Try a larger waterbath; most of the still pot flask should be immersed in the water and the water should be boiling. The water level can and should be above the level of acetone, when doing higher temperature and vacuum distillations having the bath (or other heat source) like that helps reduce superheating and bumping. Once the reflux ring reaches high enough you can dial back the heat to get to a proper distillation rate.

Use Al foil to 'tent' the top of the flask an joint, and an inverted cone of foil to force steam away from the insulation so that it doesn't get moist. Foil around the insulation and much of the column head doesn't hurt, more to keep away air currents than actual insulation.

[Edited on 27-6-2010 by not_important]
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rrkss
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[*] posted on 26-6-2010 at 21:32


Too little heat input and lack of boiling chips comes to mind.
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zed
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[*] posted on 27-6-2010 at 00:54


In years past, the major percentage of crud in "paint store" acetone, was heavy oily stuff.

It doesn't distill at anywhere near the temperature acetone does.

First off, I'd just do a simple distillation. Good chance, that the product will be good enough for most purposes.
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[*] posted on 27-6-2010 at 06:39


I'd agree with zed - do a simple distillation without reflux to get rid of the high boiling crud & misc contaminants. That's what many people do when producing ethanol ;) Afterwards, a fractional distillation may or may not be necessary depending on what else was in the source material and how pure a result you need.

And the advice on added heat input, shielding the column insulation from water, using alumin(i)um foil as an insulator and as a way to block air currents is all useful.

For distillations under 100C an aluminum foil wrap starting on the flask just above the heating element continuing around the column and up and over the distilling head to the start of the condenser works pretty well for me - no need to use glass wool, etc.
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Crucible
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[*] posted on 27-6-2010 at 09:41


Good advice all. I tightened up the insulation and dialed up the heat and am getting rapid distillation now. I think the real problem was I had the variostat set too low. I'd set it at 60C thinking I didn't want to overdo it. Just goes to show even something as "simple" as solvent distillation isn't ever as simple as it seems. Thanks.

BTW - I only filled my 1L RB with about 700ml of solvent thinking it would be unwise to fill it all the way to the top. What do you think is the max fill level?

[Edited on 27-6-2010 by Crucible]
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[*] posted on 27-6-2010 at 10:17


Usually the max is 1/2 to 2/3 full. Because of the shape if you fill it all the way it will cause a volcanic eruption.

Watch the thermometer and only keep what comes over at 56.5




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[*] posted on 27-6-2010 at 10:52


Thanks for sharing your problems. You were wise to try something easy to start with. It demonstrates how even simple chores are beset with problems that we learn to sidestep. Then later, we forget to pass these little gems of information on as experience, because they are so 'obvious'.

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[*] posted on 27-6-2010 at 11:45


Yes, too little heat is the problem over here. I had the same problem with distilling nitric acid from H2SO4 and NaNO3. I changed the water bath to a bath of a concentrated solution of CaCl2 (drying agent from hardware store). With that, the boiling point of the water bath can be raised 25 C or so and that changed things for the better.

But the CaCl2/water bath is a mess, you get white solid everywhere and it is not pleasant to work with it. If you really intend to do distillations more frequently, get yourself a heating mantle. Soon after my struggles with distiling HNO3 I decided to buy a heating mantle and with that, distillation rocks.

A 500 ml heating mantle, second hand, should be available for somewhere between EUR 50 and EUR 100. Such a heating mantle also is suitable for 250 ml. You could also buy a 250 ml heating mantle and with that you can also use a 100 ml flask for smaller distillations. I have done the latter. If I want to distill larger quantities, then I change somewhat more often. Smaller setups have the advantage of having less losses.

[Edited on 27-6-10 by woelen]




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[*] posted on 27-6-2010 at 18:26


It can be surprising to discover how much heat it lost from a column, and how much energy is needed to bring a fractionation column up to operational temperature. I believe you've just be surprised :-).

Remember that to get a fractionation effect you need some reflux going back down the column, generally several times greater than the take-off flow.

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[*] posted on 27-6-2010 at 23:18


I distill hardware store acetone from time to time. I use a Snyder column. It comes over pretty fast. The Snyder starts rattling almost as soon as the heat is applied. The acetone I get is quite clean as a rule. I keep the acetone waste in a special container so I can clean it up. Your problem is clearly not enough heat. You might get more heating with an oil bath. I use one when I want really high heat or need particularly even heating. I got one at a thrift store. The control is such that I can regulate the bath temperature to within a deg C. (I do have to take a little ribbing about it.) If you subbed oil for the water in that Pyrex pot you would get more rapid heating and better heat transfer from the hot plate. You would also avoid the problems that steam sometimes causes. Another option is keep an eye on Ebay for a mantle. I have a variac you could buy when you're ready to upgrade. Happy hunting.
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Crucible
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[*] posted on 1-7-2010 at 16:06


Thanks to everyone for the helpful tips. They are appreciated.

Quote: Originally posted by Mr. Wizard  
Thanks for sharing your problems. You were wise to try something easy to start with. It demonstrates how even simple chores are beset with problems that we learn to sidestep. Then later, we forget to pass these little gems of information on as experience, because they are so 'obvious'.


That's a problem I've run into with a lot of the information on the net and in chem books. There's a lot that is too 'obvious' to mention. This site has been a great resource for me, and everyone has been super helpful even when I ask 'obvious' questions.

[Edited on 2-7-2010 by Crucible]
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[*] posted on 1-7-2010 at 16:11


Quote: Originally posted by not_important  

Remember that to get a fractionation effect you need some reflux going back down the column, generally several times greater than the take-off flow.


Ah. I wasn't really checking the reflux. It's one of the things I don't like about having insulation on the column. I can't see what's going on inside very well.
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[*] posted on 8-7-2010 at 10:25


It's that fk'ing hotplate. I don't know how else to break it to you, but I think it's a pile of shit and should probably go in the bin. If it couldn't distill acetone, that'd worry me. Either start again or just buy a genuine hotplate. As a committed DIYer, I'd say buy a import hotplate.

Acetone would be a blindfold easy evaporation for a number of the people posting. I know I could do it with zero effort.

I seriously think that plate is going to cost you more in terms of effort than it'd cost to just buy a genuine plate. You can get them used for tens of dollars. The fact acetone is your first distillation indicates that you are in no way near ready to start working with things that require explosion proof hotplates. I don't have one and I work with things far more hazardous.

Acetone boils at 56C. My plate will go to 380C and, often, that's not high enough, even though it's 6-7 times more than yous. You can buy a hotplate from china, with a digital display, that'll go to that for $150 - 200.

Use the oven hotplates or a portable hotplates. Or...

BUY A HOTPLATE.

A* for trying. F- for results.

I'm trying to save you time, effort and money. That plate, as it is, isn't going to work; at all.

If it can't distill acetone, it's fucked; seriously, give up on that plate.

[Edited on 8-7-2010 by peach]
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[*] posted on 8-7-2010 at 18:18


I agree with peach. Up until about a year ago I could walk into Wal-mart and buy a "hotplate" for $8. It might not be as safe as yours for something like acetone but... you get my point I suppose. I bought a small hotplate/stirrer combo for ~$80 and, although it doesn't have much heat output, I know for a fact I could fractionally distill acetone, possibly without insulation on the column.

Heating mantles are best by far. I wish I had a 1 L and a 250 mL.... (if anyone is getting rid of one, let me know... and a variac)

EDIT

In practice you can even use a 500 mL mantle for down to 100 mL flasks. Maybe even smaller but I haven't tried it.

Also, I don't know about others but I try to avoid corks whenever possible. One time I tried to "distill" HBr using a cork--for those who can't guess what happened I got HBr(g) (which was condensing with the water in the air to HBr(aq) I assume because I could see it) everywhere.

[Edited on 7-9-2010 by MagicJigPipe]




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[*] posted on 8-7-2010 at 18:22


Quote: Originally posted by Crucible  
I'm finally ready to fire up my new glassware and decided to start with something simple, distillation of acetone.



Congratulations, you have successfully refluxed acetone, while not what you intended to do - it is still something... ;)




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