Condenser Question

[jordehwa]

Hi I just bought my first condenser, its a Graham condenser. I did some simple distillation and It worked well.

I just was wondering what is the best way to dry out the inner coil?

 

Thanks.

 

[hypervalent_iodine]

You could wash out the water with acetone and put in an oven (doesn't need to be very hot) if you need to dry it.

[John Cuthber]

No.

Don't put flammable materials - especially volatile liquids- in an oven.

Rinse it with water and leave it to dry.

[hypervalent_iodine]

No.

Don't put flammable materials - especially volatile liquids- in an oven.

Rinse it with water and leave it to dry.

So just to clarify, since it apparently wasn't obvious, I didn't mean out something dripping in acetone into a hot oven. Usually I would rinse with acetone and let it air dry for a little bit and place it in an oven. This is not an uncommon practice. You would not do this with something like ether, but it is not really a problem with acetone provided you don't make the oven too hot (as mentioned in my previous post).

[John Cuthber]

The explosive limits for acetone in air are about 3 and 12 % by volume.

Imagine that you have an oven that's a cube 40 cm each side.

That's 0.064 cubic metres or 64 litres.

A mole of acetone is 58 grams and it has a density of 0.79 g/ml

 

OK, 3% of 64 litres is 1.92 litres

The molar volume is about 24 litres so you need 0.08 moles to fill the oven with an explosive mixture.

That's 4.64 grams or about 5.9 ml

 

It takes about a teaspoon full of acetone to blow up an oven.

The thermostat will provide the spark to initiate the explosion so there's no point worrying about what temperature it's set at .

 

You might get away with one condenser in the oven (though Graham condensers have a lot more surface area to hold up liquid than straight ones) but if you put a few bits of glassware, wet with acetone, in an oven you have made a bomb.

(I just checked- I rinsed out a 1 litre RB flask with water and it gained about 5 grams)

Heating the gas mixture will widen the explosive range so it's even easier to blow up.

It is common practice, and from time to time it blows up.

 

If you plan to oven-dry the glassware then you might as well rinse with water- it's cheap and non flammable.

 

Another approach is to put the glassware away still wet.

If it has dried by the next time you need it then there's no problem.

If it's still wet, then rinse it with acetone followed by whatever solvent you plan to use it with.

[hypervalent_iodine]

Right, except that acetone is not water and if you let the acetone evaporate outside of the oven, as it will do fairly rapidly, the amount still left in the glassware when it is transferred to an oven would be negligible (and certainly not 5 g). The spark component of the thermostat for the drying ovens used in labs I would not think would be housed inside the main body of the oven, as is the case with most electric cookers (through I guess it is probably more isolated). I'll concede that it probably wouldn't be suitable for a regular oven at home.

[John Cuthber]

A few minor points:

Nobody said that acetone was water, but I think you will still get the same order of magnitude of solvent transferred to the oven.

 

What you actually wrote was "You could wash out the water with acetone and put in an oven" without any mention of waiting, airing or whatever.

 

Here is a picture of the sort of oven I'm talking about.

The thermostat is entirely within the oven.

http://www.sciquip.co.uk/store/products/leec-drying-cabinets/

It does say that a spark free option is available- which tells you them most of them are not spark free.

 

Ovens certainly cause explosions from time to time

http://www.ilpi.com/dchas/2009/20091021e.html

 

http://stao.ca/resources/safety-info/LBA%20Index%20of%20Accidents/Solvent%20explosion%20in%20laboratory%20drying%20oven%20Nov%202004.%2010.pdf

 

So, whatever you say, by way of reply, I'd like to think that anyone reading this thread will rinse stuff with water before putting it in an oven.

[jordehwa]

Air drying for the most part should be fine for me. But lets just say for example I was distilling pure acetone, and then right after that I started to distill pure ethanol (again this is just for example) how many ml of the ethanol distillate should I let run through the condenser until it would be fully rinsed? by the way my Graham condenser is 300 mms long.

 

Thanks again.

[John Cuthber]

Unhelpfully, the theoretical answer is that you never rinse out all the acetone. It gets more and more dilute, but there's always some left.

 

It's probably better to air dry the condenser first or even to rinse it with some of the alcohol before you distil it (then throw away the mixture).