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Author: Subject: large capacity soxhlet issue
chemrox
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[*] posted on 6-7-2012 at 10:01
large capacity soxhlet issue


I have a large capacity soxhlet. The side mounted extractor barrel holds 2 L. (This is different than the 5L one I mentioned previously). Anyway, I'm extracting Reed Canary Grass with ether. The issue is the siphon tube doesn't drain the extractor. It drains slowly enough to maintain the extractor at always full. This is great for extraction but makes emptying the apparatus a pain. I wonder if the drain tube is too large or too short? Anyway I solved the problem once by some vigorous finger tapping. That's one cycle down-many more to go...3L is too small a flask for this. 5L would be appropriate.



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Zan Divine
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[*] posted on 6-7-2012 at 12:38


It sounds like the drain tube is a little too tall. The Soxhlet must be able to fill to a point higher than the top of the bend in the drain.

An inelegant solution is to incline the extractor slightly to bring the bend a little lower. The elegant solution, with a torch, is not simple but it can be done...flatten the curve in the drain tube to lower it a few mm.

[Edited on 6-7-2012 by Zan Divine]




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[*] posted on 8-7-2012 at 05:53


The other thing that you want to make sure of is that the solvent in the body has free and easy access to the base of the drain tube. A layer of glass wool (or similar) a quarter or half inch high should be placed at the bottom. You probably already did this, but in case you haven't, you should. Of course, if you actually have the real soxhlet filter tubes, this isn't a concern.

Sometimes just increasing the reflux rate can change the dynamics of starting the siphoning process. I realize that you are using Et2O and that you make not have a lot of headroom in this area.

[Edited on 8-7-2012 by Zan Divine]




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Arthur Dent
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[*] posted on 9-7-2012 at 15:41


A trick I do when I use my sohxlet is to wet the extractor area with the solvent before assembling the apparatus. That way when I put on the heat and the solvent begins to flow, the cotton plugs at the bottom and at the top have already settled and don't expand too much and disturb the threshold of the drain tube.

As for the real soxhlet thimbles... never used them, this is truly the hardest-to-find chemistry consumable imaginable. The only time I found some was in Sigma Aldrich's catalog... eer... nevermind!

Robert




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chemrox
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[*] posted on 9-5-2014 at 16:35


Back again with a different plant and same solvent, ether. There's no issue with flow through the system. This extractor is way big for thimbles and I have left the plants in a crumbled but not powdered condition so a grate at the bottom hold nearly everything back. The bend in the tube is still below the max height of the liquid in the vessel. Zan's answer intrigued me at first because the motion in leaning the apparatus slightly always makes the liquid fill the siphon just past the overflow point. However, in principle there can't be siphoning until the height of the liquid in the vessel is higher than the bend in the tube. I.e. the condensed solvent fills the vessel up the siphon bend and then it's supposed to siphon. Instead it pours over in a much slower stream ~ the rate of condensation. Maybe I should add excess heat to the flask and try to make the liquid in the extractor exceed the leak down rate. Also I have allowed the extractor to be a little cooler than the rising vapor. I try to keep just below the vp of the ether. What do you guys think of higher heat? (With ether this means shutting down at night).



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chemrox
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[*] posted on 13-5-2014 at 12:51


Interesting addendum. I decided having it stay full wasn't such a bad idea. A mistake I made was overheating the holding vessel and almost evaporated 2 L of ether. I lowered the heat. I left the vessel full and after an hour (or less) it siphoned anyway. The vessel needs to fill to a certain height above the bend and over she goes. Adding heat to the flask and lowering heat in the vessel seemed to cure the issue. Tricky little bastard. Zan is right on.



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feacetech
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[*] posted on 15-5-2014 at 19:58


Quote: Originally posted by Arthur Dent  

As for the real soxhlet thimbles... never used them, this is truly the hardest-to-find chemistry consumable imaginable. The only time I found some was in Sigma Aldrich's catalog... eer... nevermind!

Robert


Whatman make extraction thimbles but they aint cheap

I like the soxhlets that have a the side arm as opposed to the siphon bend

like the diagram here http://www.techknow.org.uk/wiki/index.php?title=Soxhlet_Extr...

I hope you werent extracting a mono amine from that grass :p

big extactors you have bet they cost a bit?
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quantumchromodynamics
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[*] posted on 16-5-2014 at 15:01
extraction question


When done chuck the solvent and keep the goods? Would petroleum either maybe work even better?
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Mildronate
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[*] posted on 17-5-2014 at 11:07


Chemrox can you post picture of your soxlet?
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[*] posted on 29-5-2014 at 20:53


When I was in highschool, I had an acquaintance who built a cigarette smoking machine. Used a vacuum pump to provide low grade suction, and a condensor fashioned from couple of glass flasks, to catch the tar and nicotine. He accumulated an impressive quantity of crud, pretty quickly. Just lit up the cigarettes, and let the machine convert them to CO2, H2O, and the Alkaloids of interest.

Seems to me, Canary Reed grass, might be amenable to the same method of extraction. Either giant "spliffs" or a tube furnace type arrangement, might be used to "smoke" the alkaloids out, while a vacuum would pull the vapors into a chamber set up for condensation.

[Edited on 30-5-2014 by zed]
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