Funkerman23
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Snyder as a Fractionating column: valid idea?
Hello
Over the years here I have seen a few threads that mention a Snyder column, and maybe one somewhat talking about it being a good column to use for
fractional.
To get a definite answer, I am asking you good folks out right: would Snyder column be a good column for Fractional distillations. Would it give more
plates than a vigreaux? Or is it not a good choice for fractionating.
I understand that they are used in the Kuderna Danish concentrating apparatus and their intent is to only allow the carrier solvent vapor out of the
apparatus and keep the sample in but somehow there seems to be doubt that this would make for a good fractionating column.
Thank you for your time and thank you for helping me finally put this one to bed.
[Edited on 7-7-2019 by Funkerman23]
" the Modern Chemist is inundated with literature"-Unknown
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happyfooddance
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How could you put to bed such a broad question when you haven't even suggested what you would be distilling or WHY you would be distilling it?
I remember once seeing a thread where a guy was asking about vigreux columns, asking what size of column people were using these days. Without even
mentioning what he was distilling, nor what volume, nor why, and of course never specifies joint size or column width... This post is kinda like that
post.
Edit: basically, not every "fractional distillation" is even remotely similar to any other fractional distillation, and no column (or packing, still
head, thermometer, heating element, stirring mechanism, anti-foaming agent, or ambient condition) is going to be ideal in anything close to a majority
of circumstances.
[Edited on 7-7-2019 by happyfooddance]
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Sulaiman
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I can't help you put this one to bed as I have neither a Vigreux nor a Snyder colum,
so until a member with hands-on experience replies :
I would expect each stage of a Snyder column to be approximately equivalent to one theoretical plate,
a good physical representation of both theory and large-scale bubble-tray columns,
so it is probably an ideal teaching/learning column.
In general, the efficiency of a fractionating column is proportional to the area of liquid in contact with vapour,
so at typical amateur scale (NS24) I'd expect the HETP of ;
. a plain tube to be >=100mm at low throughput
. a Vigreux column >= 50mm at similarly low throughput
. a Hempel column packed with spherical glass beads >=25mm
. a Hempel column packed with s/s wool >=20mm
The Snyder column has a very small cross-sectional area for gas flow,
so you would need to operate it at a low flow rate.
I'd expect one benefit of a Snyder column to be low hold up relative to a Hempel column,
so if you have small quantities to handle then I'd expect a Snyder column to be useful.
I can imagine a Snyder column being difficult to clean compared to all other column types.
CAUTION : Hobby Chemist, not Professional or even Amateur
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BromicAcid
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Snyder column is my favorite column of all. Separation is better than a Vig and much less than a packed. But for atmospheric distillations it
usually gets the job done well enough.
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Funkerman23
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Both Sulaiman and happyfooddance make points that are both prudent. and unanswerable by me. I don't know the details of the prior threads nor what
separations they where trying to achieve. I do not own a Snyder column. The idea that it could be used as a fractionating column didn't make sense but
enough support was there that I second guessed myself. A plate per chamber sounds right and at the time I posted the OP I hadn't though of it. Suffice
it to say I am glad to be corrected. In my defense, my idea of a column is more like a Dufton or a raschig ring packed Hemple than a Snyder. But each
separation is ,indeed, vastly different.
[Edited on 7-7-2019 by Funkerman23]
" the Modern Chemist is inundated with literature"-Unknown
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happyfooddance
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The air between one's feet and one's knees is a type of effective column, constantly operating.
I have seen this type of column produce some quite remarkable (and profitable) separations.
Not quite related but on the same scale as "Sun as variac".
I can't see that you were corrected about anything as you just asked a question, however a "definitive answer" requires in this case a more well
defined question
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Sulaiman
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"Sun as variac"... please elaborate as Google failed me.
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S.C. Wack
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From what I've read, Snyders do not perform well in tests against other columns.
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j_sum1
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From what I understand, (which might not be much) a column is a column. Critical factors are number of theoretical plates, surface area, heat
transfer rate, ability to maintain the required thermal gradient and volumetric flow rate. Of course these are interdependent. Within these
parameters are a number of design possibilities and some are obviously more space efficient than others. The bottom line is that if you can achieve
your desired separation at a reasonable rate without flooding then there is no particular reason to prefer one design over another. The different
designs are merely different ways of achieving the same goal: generally by increasing surface area and number of plates.
That said, there is one very good reason to use a Snyder column -- few bits of glassware look and sound as cool.
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Panache
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Quote: Originally posted by BromicAcid  | | Snyder column is my favorite column of all. Separation is better than a Vig and much less than a packed. But for atmospheric distillations it
usually gets the job done well enough. |
I concur and they're fucking cool, they make a lovely sound, kinda like having a friend chat away at you without you needing to listen or respond.
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