Sciencemadness Discussion Board

Azeotrope/Steam Distillation

CamelWithoutAmmo! - 26-7-2006 at 10:02

Hey this is my first post on this site and im putting it under this category because I am truly a beginner in the world of chemistry!

Anyways, my question is basically about the theory behind one of these types of distillations. An external steam distillation is pretty much out of the question, so im looking to do an internal steam distillation. One setup is the typical distillation setup, the 3 neck distilling flask connected to a 3 way adapter, which is connected to a condenser and then the vacuum adapter and receiving flask. To one of the necks on the 3 neck adapter a funnel is attached which can introduce hot water to the distilling flask.

My goal is to extract the essential oils from various herbs and plants, and this includes steam distilling things such as bark, leaves, other solid parts of the plant, etc. I understand that in a steam distillation, the steam forms an azeotrope with the oils in the plant and comes over into the receiving flask.

I am unsure of several things:
1) Should the stuff im distilling (bark, leaves) be put into the distilling flask with water in it, and then heat up the flask to produce steam? Will this form the azeotrope I want that will end up in the receiving flask?

2) Is the funnel even necessary? If a heating mantle or other heating source was heating up the distilling flask, and water ran out, couldn't it simply be disconnected from the 3 way adapter and more water added? Was the funnel in that setup purely for convenience?

Thanks for your help! :D

pantone159 - 26-7-2006 at 10:17

Quote:
Originally posted by CamelWithoutAmmo!
1) Should the stuff im distilling (bark, leaves) be put into the distilling flask with water in it, and then heat up the flask to produce steam? Will this form the azeotrope I want that will end up in the receiving flask?


It's not an azeotrope, which is a mixture of things that boil at a constant temp. In steam distillation, you have immisible substances (water, oil) that boil when there combined vapor pressure = 1 atm, and what comes over is a mix of the two things, which are easily separable.

Your procedure should work, though.
Quote:
Originally posted by CamelWithoutAmmo!
2) Is the funnel even necessary? If a heating mantle or other heating source was heating up the distilling flask, and water ran out, couldn't it simply be disconnected from the 3 way adapter and more water added? Was the funnel in that setup purely for convenience?


The funnel is just for convenience, to save you the trouble, when the water runs out, of shutting everything down, adding more water, and starting over.

CamelWithoutAmmo! - 26-7-2006 at 16:40

So it is not necessary for the bark or leaves to be separate from the water in the distilling flask, they can simply be floating on top of the water that is boiling?

pantone159 - 26-7-2006 at 17:39

The stuff should be in the water, yes. You might want to grind them up, though.

CamelWithoutAmmo! - 26-7-2006 at 19:05

Thanks for the help pantone! :D

Tacho - 27-7-2006 at 09:32

The reason for the funnel is because, more often than not, you need to distill a large quantity of water to yield a small quantity of product, so, being able to add more water without cooling and dismantling the whole setup is very desirable.

I posted a question sometime ago about how to increase the yield of steam distillation. I got many interesting suggestions. The one I found most interesting was to use ethylene glycol to raise the vapour pressure of water. I made a test, and the water boiled way above 100°C, but, since I did not know if what I was trying to distill was steam distillable at all, I ended up with inconclusive results.

Misanthropy - 30-8-2006 at 14:51

One has PEG 3350 which should be fine for this. Will it come over with the steam at all though?

not_important - 30-8-2006 at 15:30

Adding NaCl to the still pot is often helpful in speeding up steam distillations. It's not the rise in boiling point, but the salting out effect.

Adding sugar or glycols has been used to raise the boiling point, and thus speed things up. If the stuff in the pot is oxidising or acid, it's better not to put such materials in - especially sugar. Otherwise, as the polyols/polyethers (PEG/PEO) strongly associate with the water and have high boiling points, they won't come over.

You do want to stick to short chain PEG, though. Longer chains can increase the viscosity of the water layer, which can interfer with the distillation and cause bumping. Di- or tri- ethylene glycol have been used, that's like PEG100 or 150, P2 or P3.

The glycol does increase the solubility of many organics in the aqueous layer, this can reduce the effectiveness of the steam distillation. Check the solubility of your product in the water-glycol mix. Put a few ml of water+glycol in a test tube with a couple drops of product and heat to boiling; see if the product noticably dissolves.