Fyndium
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Vacuum vs steam distillation?
For achieving similar outcome, to purify through distillation, a non-water soluble compound, what are the differences and benefits or downsides of
these two methods? I have performed a lot of vacuum processes, but I have never performed a single steam distillation.
I am not quite familiar with steam distillation, but I did read somewhere that essentially you could just straight boil water (and add more with
dropper as necessary) with the compound to yield a steam distilled result in a similar way as to directing steam from an external boiler into the
distillation vessel. Is this correct, or is it necessary to use external steam source? Does strong overhead stirring benefit or hinder this process?
Using external steam generator vessel is not an issue, and I suspect that it is the case, as all diagrams depict an assembly with separate boiler unit
with tube inlet, but if it's not necessary, I prefer to follow the KISS principle. It appears to me that external steam is used as booster to reduce
the vapor pressure of the desired compound.
One question remains, if there are significant fractions of impurities that are only less volatile than the compound, is steam distillation effective
at separating them at all, or does it leave only very heavy non-volatiles behind?
Few potential benefits I see in steam, if it conceptually works as I think, is that it is somewhat self-regulating so it does not need constant,
intimate babysitting but can be ran parallel more easily, much safer in terms of not having high vacuum reaction vessels running at high temps and
having issues with multiple cold traps protecting the vacuum pump from inevitable contamination of volatiles and water vapor, and also the fact that
in case vacuum appliances are not available, no need to acquire them in the first place.
[Edited on 30-11-2022 by Fyndium]
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Tsjerk
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Steam distillation is easy and lovely, but the question is; how well does your compound come over with steam? Some do well, some a bit, and others
not at all. It depends on vapor pressure at 100 degrees, but you have to check for your compound.
I've never used externally generated steam. And yes, as long as you make sure your distillation doesn't run dry, no baby sitting required.
[Edited on 30-11-2022 by Tsjerk]
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DraconicAcid
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From what I can tell, steam distillation will leave behind things that are completely non-volatile, and things that are soluble in hot water. I've
rarely done steam distillation, but it's just been with water boiling in the flask, not externally generated steam. Externally generated steam was
handy in the old days, when every lab was heated with a boiler system, so the lab could draw off steam for steam baths and steam distillation with a
minimum of fuss or additional plumbing.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Pumukli
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I like this "coincidental wave" I'm living through nowadays. 
Believe it or not, on this (very) afternoon I dug up a file from my archived chemistry jewels which was saved years ago. I'm contemplating calling a
local (in-country) glass-blower and request a quote for this thing:
Attachment: steamdist.pdf (2.8MB)
This file has been downloaded 259 times
The article is about a continuous steam distillation apparatus which was used at a DuPont research laboratory in the fifties. I think it would nicely
fit in any amateur's laboratory today. 
If it wasn't enough for the public about me and my coincidences then take these two as well:
Attachment: steam.distillation.phenolics.pdf (432kB)
This file has been downloaded 236 times
I came across this article in those days when I was trying a method to optimize the 4-MeO-Phe synthesis I mentioned earlier.
According to this article, my luck seems to fall a bit short, 4-MeO-Phe is not easily volatile by steam... On the plus side it seems that hydroquinone
is not volatile by steam at all, so there might be a way to exploit this...
A few days later I came across this one:
Attachment: steam.distillation.phenolics.nacl.pdf (249kB)
This file has been downloaded 226 times
Wow, the continuation of the previous one. Actually a clever trick to increase the volatility of "not really steam volatile compounds" - while leaving
hydroquinone still in the dirt (at least in the reaction mixture).
I hope someone someday may experience the same "Ahh"-s what I had been experiencing when I first read them! 
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Fyndium
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Excellent, it appears that steam distillation has it's place along with vacuum distillation, however it looks that it's limitation is the inability to
separate any fractions - it's just merely an assisted normal distillation. Many reactants to be purified can contain impurities that have volatility
close enough they will smear over along with impurities, but for removing heavy molecules, polymerized gunk and other crap it seems like a great tool.
It is interesting to see that the steam-distillability is not directly related to boiling point of the substance. I have to do a few test runs with it
to see how it works out.
It also does not appear to be slow(er than ordinary distillation), looking at the collection rates given in the attached documents.
What I like about is the ability to do parallel work. When you got a stable setup you only need to check every once in a while, depending on it's
nature, it can save a lot of time.
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