I've been using a soxhlet extractor recently, i'm using 95% ethanol and have been extracting lemon from dried peel.
I typically keep the ethanol in the flask and replace the spent lemon peel multiple times. I notice my final solution is very dark and red/brown in
colour.
Is it likely I am degrading/burning the lemon extract or is it just dark due to the concentration?
Is it normally better to just do a single extraction and then replace with fresh solvent for the next run or is my approach acceptable?Texium - 13-11-2022 at 09:26
What are you trying to get out of it? If you’re after limonene or other volatiles, then Soxhlet extraction is just the wrong approach, and you
should use steam distillation instead.Rainwater - 13-11-2022 at 11:01
Quote:
Is it likely I am degrading/burning the lemon extract or is it just dark due to the concentration?
It could be sugar, but deffenetly side reactions
Small amounts of acid can react with ethanol.
If you leave it you will end up with sweet-smelling tar and some very low bp compounds.
Sugars are a pain to remove.
You may want to pick a solvent that your target and sugar differ greatly in solubility. Chemgineer - 13-11-2022 at 11:35
Is it likely I am degrading/burning the lemon extract or is it just dark due to the concentration?
It could be sugar, but deffenetly side reactions
Small amounts of acid can react with ethanol.
If you leave it you will end up with sweet-smelling tar and some very low bp compounds.
Sugars are a pain to remove.
You may want to pick a solvent that your target and sugar differ greatly in solubility.
Thanks, that's useful information, whilst recovering limonene would be good, I am more trying to teach myself how to do extractions and when and where
to use different approaches.Tsjerk - 13-11-2022 at 11:43
Peels are full of all kinds of organics, and many decompose/react upon prolonged heatingChemgineer - 13-11-2022 at 12:32
What are you trying to get out of it? If you’re after limonene or other volatiles, then Soxhlet extraction is just the wrong approach, and you
should use steam distillation instead.
The last steam distillation I tried ended up with a product that seemed to be a suspension of oil in water and wouldn't easily separate into layers.
[Edited on 13-11-2022 by Chemgineer]Tsjerk - 13-11-2022 at 13:05
That often happens after steam distillation, you can extract with a solvent with a different bp and distill it again.
[Edited on 13-11-2022 by Tsjerk]Rainwater - 14-11-2022 at 05:33
For an amateur like me,
rather than getting a soxhlet kit,
why not just use a large excess of solvent,
then distill off most of it (for later re-use)
then filter out any solids
leaving a solution similar to what a soxhlet would have produced? Bedlasky - 14-11-2022 at 18:22
I notice my final solution is very dark and red/brown in colour.
Methyl ethyl ketone from denaturated EtOH + acids from lemon --> aldol condensation products. Ethanolic solutions of KOH are usually yellow because
of this.Texium - 15-11-2022 at 10:22
For an amateur like me,
rather than getting a soxhlet kit,
why not just use a large excess of solvent,
then distill off most of it (for later re-use)
then filter out any solids
leaving a solution similar to what a soxhlet would have produced?
Multiple extractions with smaller amounts
of solvent is much more efficient than a single extraction with a large amount of solvent. Also, if I was extracting volatiles into the solvent, I
wouldn't trust it for reuse, even if it was distilled, unless I used a very efficient column, but at that point, it's probably not even worth it.
