[tcmbrendan]

Hi guys,

I'm about to attempt an extraction of some herbs with ethanol and I have my soxhlet apparatus rigged up with everything. One problem that I have, and pardon my lack of understanding, is that the top of the condenser is open to the air. I'm assuming that this open area of the condenser is meant for a rubber stopper as to keep any ethanol from escaping.

My question is:  By placing a rubber stopper at the top of the condenser and making this a closed system would this build up a lot of pressure and perhaps crack the glass or damage the soxhlet apparatus?

Also, If I left the top open to the elements would the condenser cool the ethanol solution before it reached the top(the opening of the condenser) and escaped?

Basically.. Do I need to buy a rubber stopper to close the top of the condenser from leaking ethanol?

Thanks,

B

[Arkcon]

Briefly, yes, the top of the heating flask, before the condensor, is meant to have a rubber stopper.  Often, it has a thermometer, because that's how we monitor the temperature.  However, after the condensor, where distillate drips out, the system should be open.  So there's no problem of over-pressure.  Unless you've set up your system totally wrong, in which case, any disaster could happen at any time.   Its hard to be sure from your description, a diagram or picture might help.  But you should be able to see, at a glance, if a stopper would completely seal the system

[tcmbrendan]

My apparatus is exactly as shown here, It wasn't clear to me if that was a rubber stopper at the VERY Top of the condenser or just the outlet of the glass.

The entire system is "closed" up until the point of outlet at the top, which to my knowledge allows pressure to escape?

My question is: Wouldn't an opening at the top of the condenser allow solvent to escape out the top or does the condenser prevent any and all of this from happening?

[Corribus]

That depends a lot on what solvent you are condensing and what kind of condenser you are using (and how cool the water is that's flowing through it, if you're using a water condenser).  In general you only need to seal the condenser if you're trying to do a process under inert atmosphere.  If solvent is escaping the top of the (unsealed) condenser, you will be able to see this.  You will be able to see how high up solvent vapors are making by where condensation is happening.  If they are making it to the top (if you smell solvent), use a longer (or different type of) condenser, use colder water or a higher flow rate, or use a more gentle heating, etc. 

Sealing the condenser will cause the pressure to rise - although likely not high enough to crack the glass (the stopper will likely pop off first).  This will raise the boiling temperature and may change the characteristics of the extraction, although probably not with this type of extraction.

[tcmbrendan]

Thank you for the helpful replies =)

[billnotgatez]

I looked at this setup and have a question

It appears to me that the heated gases rise up via the side channel 3

Then they are cooled in condenser 9

Some falls as liquid back into area 4 and 5

while some escapes out of the top of condenser 9 (assumed unwanted or displaced air due to heating)

but the stuff collected in area 4 and 5 is eventually allowed to return to the flask 2 and 1 via an overflow 6 and 7

Am I seeing this correctly

[Arkcon]

Oops ... I misunderstood a  soxhlet extraction as a distillation.  Sorry.  My bad.  Corribus:'s comments are the ones to go with, not mine.

[curiouscat]

If they are making it to the top (if you smell solvent), use a longer (or different type of) condenser, use colder water or a higher flow rate, or use a more gentle heating, etc. 

Sealing the condenser will cause the pressure to rise - although likely not high enough to crack the glass (the stopper will likely pop off first).  This will raise the boiling temperature and may change the characteristics of the extraction, although probably not with this type of extraction.

I like all the ideas (colder water etc.) except sealing the condenser. I'd be wary of creating a closed heated system unless you know exactly what you are doing.

[Corribus]

Especially at a home environment where you don't have a proper fume hood. 

Honestly I wouldn't do any kind of reflux of a solvent outside of a fume hood, and certainly not in my home.  I don't know what you're using for your heating source, but if it's an open flame, any ethanol leaking out the top of the condenser could lead to a disaster.  There's a reason (other than the fact that it's illegal) that bootleggers do their distilling in shacks far away from the house.

[DrCMS]

I looked at this setup and have a question

It appears to me that the heated gases rise up via the side channel 3

Then they are cooled in condenser 9

Some falls as liquid back into area 4 and 5

while some escapes out of the top of condenser 9 (assumed unwanted or displaced air due to heating)

but the stuff collected in area 4 and 5 is eventually allowed to return to the flask 2 and 1 via an overflow 6 and 7

Am I seeing this correctly

Yes that is how it works but the outflow 6 and 7 works like a syphon and empties the liquid collected in 4 and 5 in one go.

[tcmbrendan]

Especially at a home environment where you don't have a proper fume hood. 

Honestly I wouldn't do any kind of reflux of a solvent outside of a fume hood, and certainly not in my home.  I don't know what you're using for your heating source, but if it's an open flame, any ethanol leaking out the top of the condenser could lead to a disaster.  There's a reason (other than the fact that it's illegal) that bootleggers do their distilling in shacks far away from the house.

Do you think a fume hood is necessary with this setup and a heating mantle? I know you are better safe than sorry but given that the condenser is moderately sized and that I would be able to smell fumes( i think) do I still run the risk of ethanol vapors gathering and posing a threat?

[Corribus]

In a properly equipped chemistry lab, people do refluxes on the benchtop all the time.  This does not necessarily mean it is safest way to do it; on the other hand, most people in a properly equipped chemistry lab are trained chemists who know what they are doing.  Or at least, that's the hope.  University labs are a mixed bag, to say the least.  I don't know what your training is, of course, so judge your own skill as you see fit.

If you choose to do it at home, I would certainly recommend you have proper PPE (safety goggles, lab coat, and so forth) as well as a fire extinguisher handy that is rated for that the kind fire.  Do it in a well-ventilated space.  Even a floor fan in the area would help disperse ethanol fumes.  While I assume you will be handling a small volume of ethanol, it doesn't take much to start a serious fire.  Never leave it unattended and keep sources of ignition away.