I am using Soxhlet apparatus quite often for making plant extracts.
My 250 ml Soxhlet body became too small for low yielding plants and hot swapping thimbles was too cumbersome so I decided to purchase a 1000 ml
Soxhlet body (see picture).
Unfortunately, it has the drainage tube U turn levelled almost at the half of the body (marked by red line in the picture), meaning that the solvent
will drain before even getting to the top.
This means I cannot actually load the Soxhlet to its full capacity and I am still left with almost the same usable volume as with my older 250 ml
Soxhlet.
Can you please explain me why the drainage tube is positioned so low, rendering most of the Soxhlet volume pratically unusable?
Vosoryx - 8-8-2018 at 22:28
I have wondered the same thing often. It seems to make no sense, unless for using less solvent.
But if that were the case, then it seems like that would be a specialty item. (with the regular item being the one with the siphon tube going to the
top) Usually, the solvent is what you have in abundance and the solute is not.
I have no idea but i'm curious if anyone knows.
Great question!Deathunter88 - 9-8-2018 at 01:11
I would assume it's because most of the efficiency of a Soxhlet comes from the hot vapors that wash over whatever you're extracting and condensing
onto them. Therefore, even if your plants are not soaking in liquid solvent, they are still being extracted. After all, the point of a Soxhlet is not
to soak leaves in solvent (you could just dump them into a beaker for that), but rather to circulate fresh solvent, and in that regard the siphon tube
height has little effect on efficiency.
Again, this is speculations, but I believe it to be truthful. Vosoryx - 9-8-2018 at 07:44
I thought about that explanation, but it doesn't make sense to me.
If hot vapour were what did the extraction, why bother with a siphon tube at all? Seems like a way to make it very complicated for no reason.
Maybe. I just don't see why.Fulmen - 9-8-2018 at 10:29
No, it does not work like that. The hot vapors will not be in much contact with the sample, and with a water cooler the condensate will probably be
fairly cold.
It works by having a constant stream of pure solvent running through the sample. So the sample doesn't have to be fully submerged as long as the
condensate drips down into the thimble.
In fact allowing the thimble to be (almost) fully submerged could be risky. If it clogs up you risk washing particulates over the top, contaminating
the extract or even clogging the siphon. Abromination - 9-8-2018 at 20:28
Vosoryx, how expensive was your soxhlet?
Im considering buying one.Vosoryx - 10-8-2018 at 12:13
Vosoryx, how expensive was your soxhlet?
Im considering buying one.
Don't remember to be honest.
I got it on eBay, from deschem. They're pretty cheap and the quality is good.
Amazing customer service too.CharlieA - 10-8-2018 at 16:28
I'm inclined to agree with Fulmen.
I would think the top of the siphon tube could be a little higher. A plug of cotton or glass wool at the top of the thimble might also prevent the
solids from getting "loose" and plugging up the siphon.
Other than time or a low content of the desired material in the raw material, I would think that the smaller Soxhlet would work as well as the larger.
If solubility of the product in the solvent/receiver flask were an issue, could this be solved by going to (and thereby using more solvent)?Mr. Rogers - 11-8-2018 at 02:58
If the siphon tube is lower down in the body the solvent will recirculate faster = You need to use less. That's all it is.
[Edited on 11-8-2018 by Mr. Rogers]unionised - 11-8-2018 at 03:32
The sample in the thimble has a constant stream of clean hot solvent dripping onto it.
That's going to do the extraction slightly better than sitting in a thimble full of solvent.Yamato71 - 18-8-2018 at 08:10
You have to remember that the extraction chamber has more than solvent in it. There is also the thimble and its contents, which displaces solvent.
You don't want the solvent level to rise above the mid point of the thimble for two very good reasons. First, you want the refluxed solvent to travel
through as much of the column being extracted as possible. if the liquid level is allowed to rise to the upper part of the thimble, the portion below
the liquid level isn't being efficiently extracted because it's steeping in stagnant solvent. Once the solvent permeating the column reaches the
liquid level, it stops flowing downward. By discharging pregnant solvent early and often, almost all of the column material is extracted by flowing
solvent.
The second issue created by a high solvent level is contamination. Should the solvent level top the thimble, bits of plant matter will float out of
the thimble and find their way into the stillpot. Even worse, plant matter can clog the thin delicate siphon tube, trapping solvent in the upper
regions of the setup and allowing the boiling flask to boil dry.
