cyphazard
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distilation/vaccum apparatus
I see that a heating mantle /w stir bar or a hotplate /w stir bar is kinda expensive. vaccum systems are also expensive (I hear of using water
aspirators but I am unsure of their effeciency and cost)
I also see that rotary evaporators are expensive.
a good distillation apparatus with a hotplate/heating mantle is about $500.00 while a rotary evaporator is $2600.00
is it worth the extra $ to purchase a rotary evaporator?
I hear of higher yields and better purity but just how better?
your personal opinions are greatly appreaciated
Stein Um Stein
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bahamuth
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I wouldn't use a rotary evaporator to distill solvents with the intention to purify them, as it is made to quickly remove solvents from a
reaction/exctraction mixture leaving the higher boiling substances in the evaporation flask. The solvent is condensed and left in the recovery flask.
A rotavap can be modified to distill solvents with good recovery of the solvent but for the purity I have no idea, may be to mych carry-over with the
great speed of distillation a rotavap is known for, though this may be regulated also. IMO rotavaps have way too big solvent losses unmodified to be
used to distill with the intent of recovering the solvent. IIRC recovery ratios on a unmodified rotavapor is about 80%.
A regular distilling/reaction kit may be found on ebay for as little as 200 USD without a heating mantle. A vacuum may be applied to any standard
org. chem distilling kit if an adapter is present. Recovery ratios varies but are generally high compared to a rotavap.
Size is a big issue, as a standard rotavap won't do well with a bigger flask than 2 L, with an optimum of about 1 L.
A regular kit, say 24/40 may be used with a much bigger distilling flask if one chose to do so.
If large scale solvent distillation, say 10 L at a time you may want to buy a larger glassware setup which in turn increases exponentially price-wise
with size.
Do you need a vacuum? Usually a vacuum is not needed for the distilling of most solvents but speeds things up which incidently isn't always a good
thing when one distills something.
Any sufficiently advanced technology is indistinguishable from magic.
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cyphazard
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I am unsure if I need a vacuum or not. I plan on performing fractional distillations on pulverized plant material. one chemical boils off at 450 F
while another at 488 F. I am unsure if an oil bath can reach these temperatures. which I believe gives me no choice to use a vacuum.
rotary evaporators look very appealing to me. From what I read I beleive that no solvent-vapor escapes correct? (it all ends up in the receiving
flask?) so assuming I was using a flammable solvent to extract plant constituents I wouldn't be filling my house with flammable vapors right? which
means that A_ a great + on safety, and B_ a great + on convenience (compared to wasting solvent, and having my house smell like some pungent solvent)
in theory shouldent a typical distillation apparatus do the same thing? shouldn't 100% of the distilate end up in the receving flask?
Time is not an issue for me at all. Its just getting necessary plant constituents out.
I plan on doing 1kg batches of pulverized plant material (dried, consistency of powder sugar) which I beleive would fit in a 1 liter, or 2 liter
round-bottom flask. I will be testing a whole bunch of plants in my area for random chemical constituents. But I dont plan on doing large batches.
their shouldent be a difference in yield right?
for example if I had 100 grams of plant material that contained 5% pinene. and threw it inside of a rotovap and alembic/retort and set the tempature
to 313 F should I (with both the rotovap and alembic/retort) end up with 5 grams of pinene in the receiving flask?
thanks for your reply
Stein Um Stein
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Arthur Dent
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@ cyphazard :
Reading your post, I see that your intent is more an extraction than a distillation. In that case, perhaps in addition to your distillation apparatus,
you should consider getting a soxhlet apparartus. This would probably be more efficient than plain boiling your plant material in a flask filled with
solvent.
It would also be much less expensive than a Rotovap. A complete soxhlet apparatus can be had between $60 and $200 on ebay!
Robert
--- Art is making something out of nothing and selling it. - Frank Zappa ---
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Magpie
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Have you considered a steam distillation?
The single most important condition for a successful synthesis is good mixing - Nicodem
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bahamuth
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Usually the losses on a rotavap comes from incomplete condensation of the distillate and the fact that one is pulling a vacuum on the whole system
often bringing the condensed solvent to boil in the receiver flask and passing through the vacuum pump/aspirator. A rotavap would be a perfect thing
if any of the constituents in the extracted material is heat sensitive, or oxygen sensitive. If not you should probably look into steam distilling it,
which is also a semi-gently extraction, though only for hydrophobic molecules if I got it right. Anyone care to correct me if I'm wrong here?
A soxlet is a very versatile tool for extraction but it tends to destroy alot of product if the product reacts withitself or is heat-sensitive, since
it will be drained into the boiling flask at the end of each cycle (soxhlet is a continuous extraction, siphon based) and thus be boiled for a
prolonged period. A wide range of solvents may be tested in a relativly short time to make out the perfect solvent/product match to extract just the
things you want extracted.
Usually one does extraction and purifying in several distinct steps usually not dependent on each other. You mention high boiling products, at
~230-250 degrees Celsius. If you plan on separating them from the other constituents of your extract you will need to fractional distill it as you
said, which method/apparatus also depends if the products can handle high temp over short or prolonged periods or if it is heat sensitive and also on
volume. But since you plan on doing different plant substrates and thus different compounds it really depends, and also finished product purity play a
big part in what to aquire...
To dry distill e.g. pinene (at atm. pressure) out from dry plant material would be a pain in terms of time and impurities from thermal degradation of
the plant material. My guess it would yield a sticky tar hard to clean up, if at all. Highly doubt reduced pressure would help either...
Give us more examples/details and I might be able to give more concrete suggestions..
PS. 1kg batches is quite the size of dry plant material, in the 10 L area or so i believe...
Any sufficiently advanced technology is indistinguishable from magic.
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Dr.Bob
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"I am unsure if I need a vacuum or not. I plan on performing fractional distillations on pulverized plant material. one chemical boils off at 450 F
while another at 488 F. I am unsure if an oil bath can reach these temperatures. which I believe gives me no choice to use a vacuum."
A rotovap is fine for low vacuum removal of solvent. It would be very rare to try to run a high vacuum distillation on a rotovap, however. It is
hard to get the rotary seal to hold a good enough vacuum, and they usually only heat to 80-100 C at best via a water bath. This is not a very
practical thing for something with a BP of 450 F.
The standard way to extract plant materials is to soak or heat the material in a large volume of the appropriate solvent, then remove most of the
solvent (this is where a rotovap is useful) to provide a crude extract. If the desired material can then be distilled away, then a vacuum
distillation system would be practical, along with a cow or similar system to allow the collection of fractions while under vacuum. If you have not
done this on a small scale yet, then I would try it on a much smaller scale first to see if it is practical first, before spending $2600 on a rotovap.
Many plant extracts are destroyed by heat or oxygen, so that may or may not work well for your materials.
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