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Author: Subject: What to look for in a soxhlet extractor?
Melgar
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[*] posted on 16-7-2017 at 13:27
What to look for in a soxhlet extractor?


Lately I've been finding myself frustrated with extractions where the desired compound doesn't actually dissolve very well in the only solvent that can dissolve it at all. Even worse if the solvent is expensive. Since the apparent solution to this problem is a Soxhlet extractor, I suppose I ought to buy one.

Now, the bottom taper is always something standard, but the top one is some huge weird one most of the time. Probably so you can fit in the thimble, but the only thing that can connect to it is the Allhin condenser that's made to fit it, it seems. Well, water cooling is still too much trouble, and I'd rather just put a long vigreux column (or two) above it, plug the end with cotton to minimize vapor loss, then point a small fan at the vigreux column. And if that isn't enough, fashion a heat sink out of aluminum or something. This device is supposed to make life easier, after all, and most of the time I don't care if I lose a small amount of solvent.

Do you need to use a special thimble, or can it sometimes just be the substance in a piece of filter paper formed into the appropriate shape? Do different extractors require you to do it differently?

Of course, my plan assumes I can find an 14/20 adapter to fit that huge ground glass joint, which I probably can't. So would I just have to run it dry and do the thing with the vigreaux column above it? I may have just answered my own question, since I probably will want to use its water cooling capabilities at some point, and I shouldn't avoid buying the glass necessary to do that.

So I guess I should get both the top and bottom. What if it doesn't seem to come with a thimble though? Is that a problem? Anyone have one they're looking to get rid of? Any recommendations? I mainly use 14/20, but I have a 24/40 adapter and my larger boiling flasks are all 24/40.




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Texium (zts16)
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[*] posted on 16-7-2017 at 13:34


I have a couple Soxhlet extractors, but I don't have a real thimble. Really you just need something to keep the siphon tube from sucking in solid plant matter, so I just shove a coffee filter in there and call it good! (as seen here)

I've seen an adapter for a Soxhlet extractor that goes to 24/40, but it was a used thing, so finding one would probably be hit or miss. They do exist though. Maybe check with Dr. Bob?




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PirateDocBrown
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[*] posted on 16-7-2017 at 16:33


Yep, coffee filters.

I use a male 45/50 to female 24/40 adapter, and a 24/40 Liebig. It works.

It's a cheap Chinese adapter for less than 10 bucks.

[Edited on 7/17/17 by PirateDocBrown]
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Dr.Bob
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[*] posted on 16-7-2017 at 18:18


I will second using coffee filters, the official thimble filters are expensive and a pain. Just nmake sure it is large enough. Large whatman type filter paper circles can also work, like 150 mm or so.

What you need to remember is that unlike using a gentle reflux to keep the temperature of a reaction constant, a Soxhlet's use requires a lot of solvent to distill and condense, so using a water condenser is really required unless you plan to take a year to do it. It is all about heat treansfer, and that is why they use a larger joint and big condenser, the bigger the better.

Otherwise most Soxhlets are very similar. You can always just soak the material in solvent, filter and evaporate the solvent in batches, and recycle the solvent manually, but that is painful.

I have Soxhlets in three or four sizes, and for an item with two pieces, the prices are not that bad, listed in the main thread on glassware for adoption. I also have some adapters if people want to play around, the simple ones (24/40, 19/22, 14/20) are $8 each or 2 for $15, bigger ones are more. But finding a female 45/50 to male 24/40 is tough, ones that are larger on top are much rarer than the opposite.
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BILLBUILDS
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[*] posted on 20-7-2017 at 11:09


BUY A FUCKING THIMBLE

im on my 3rd 1L soxhlet extractor because of the discharge tube getting blocked
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BILLBUILDS
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[*] posted on 20-7-2017 at 12:28


anyone know how to unblock them? its blocked with food pressed pepper. ive tried low pressure hose and H2SO4, NaOH but it just dosent reach up high enough
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[*] posted on 20-7-2017 at 12:40


Quote: Originally posted by BILLBUILDS  
anyone know how to unblock them? its blocked with food pressed pepper. ive tried low pressure hose and H2SO4, NaOH but it just dosent reach up high enough


Try kinda fast flowing water? Make sure to use paper or cotton to prevent this.
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[*] posted on 20-7-2017 at 13:12


I do not have a soxhlet but I think that you could use some thin ptfe tubing,
e.g.<= 1mm od is common and cheap via eBay
that can be manouvered to the obstruction without scratching the glass
then you could just poke at the obstruction,
or flush with air, water, H2SO4 etc.




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[*] posted on 27-7-2017 at 00:43


I just use a wad of cotton for most things. Works great. [edit] If your chemicals don't play nice with cellulose, you can use synthetic fiber. Or really anything fluffy that won't dissolve.
If your tube is blocked with pepper, use some piranha solution. Put in a ml or two of sulfuric and a few drops of H2O2. It'll dissolve.

[Edited on 27-7-2017 by wayne_m]
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[*] posted on 27-7-2017 at 03:55


for more solvent flow at a lower heat you can pull a partial vacuum as well, I use this allot when re fluxing certain things.

As stated plenty of adapters on fley bay but you got to look care fully

No water cooling Melgal? My goat man you're a masochist! Not hard to make a simple closed loop system.

5gal bucket, MCP655 pump from swift tech, a large oil cooler or radiator from a car, mount it out side or what have you, use it to cool the lab gear and computer!
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Melgar
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[*] posted on 28-7-2017 at 00:37


Quote: Originally posted by BILLBUILDS  
anyone know how to unblock them? its blocked with food pressed pepper. ive tried low pressure hose and H2SO4, NaOH but it just dosent reach up high enough

Heat with a low flame from the outside, or in an oven, until it's all char, then dissolve the residue with piranha or bleach? That generally works pretty well on organic solids. If what's left is white rather than black, that's ash, and will typically dissolve in HCl.

I can do water cooling if I must, but it requires a container of ice water, typically. I live in Manhattan, and there isn't the sort of space you'd need for something like the setup you describe. I am, however, working on a system that uses a 100-watt thermoelectric cooler, which seems plenty powerful for anything I'd do with a 14/20 set.

I'm still probably going to want to purchase a soxhlet extractor, but definitely on the small side, since I mostly use the set I have for test reactions, not for production-level synthesis or anything like that. I guess once I make sure I have enough money to cover rent, I'll see about buying one.




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