Sciencemadness Discussion Board

Fractional Distillation takes too long

Amy Winehouse - 4-5-2012 at 20:10

>:o

Feel free to flame me for being ignorant

But on the real, is there any way to make this go faster? I tried to turn up the heat juice(tech. term) on my hotplate while distilling the legal cap (75.5%) of OTC ethanol in CA to the azeotrope and, as the theory suggests, i got like 87% using a vigreux column. I am now watching it drip 1 drop/2 seconds and falling asleep. I'm slowly dying and I have to wait for this rubbish (not from England just like the word). There's gotta be a better way...Use two or three columns?

This thread is about possibilities don't hate on it's dissimilarity to reality.

Endimion17 - 5-5-2012 at 06:38

No, that's pretty much the optimal speed for laboratory distillations.

bbartlog - 5-5-2012 at 06:50

A bigger (wider, that is, not taller...) column will speed things up some; more volume and surface area. But in general, yes: fractional distillation is slow. Although it is not really wise to leave distillations unattended I have sometimes done so, just because I didn't want to stand around for four hours. Best I guess would be if you have something else to entertain you (other lab work, book, ipod...) while you keep one eye on your still.

watson.fawkes - 5-5-2012 at 07:07

Quote: Originally posted by Amy Winehouse  
But on the real, is there any way to make this go faster?
Learn the concept of a theoretical plate in the analysis of fractional distillation. That Wikipedia link will get you started, but that article is only an overview. There's a trade-off between the number of theoretical plates in your column, take-off rate, and product separation. By heating faster, you've traded take-off rate for separation. If you want to have a higher take-off rate with the separation you're getting now, you need a better column.

BromicAcid - 5-5-2012 at 07:55

As bbartlog said a wider column will allow more throughput and allow for a faster takeoff while still returning at a fairly decent rate. Also a taller column will allow for a faster takeoff because you are putting more theoretical plates in place however you can not take off so much that you are not returning anything and a tall thin column is not better than a short fat column in my opinion because you risk flooding.

Different packings will also affect your takeoff rate. A Vigreux column is obviously not doing it for you in one pass, invest in a packed column, you'll be able to achieve the same takeoff but you'll be able to get your desired proof in one pass.

Although not theoretically sound I have used a packed column without a fractional head in instances where a Vigreux with a fractional head was not enough and been able to get my desired product with total takeoff (I.e., no return) though that's not proper technique.

turd - 5-5-2012 at 11:40

If you're impatient, your best bet is to switch hobby to something with a higher instant-gratification potential. Chemistry needs patience and amateur chemistry in a chemophobic society even more so.

Alternative: Synthesize some Ritalin or (meth)amphetamine. Two birds with one stone! :D

simba - 9-5-2012 at 19:52

Just set it up and watch some tv. I know this is kinda difficult for a beginner, you feel like you've got a bomb planted in your house, you just can't sit back and wait whole process, but you will eventually get used to it.