The Ideal Gas Lawyer
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Testing the efficacy of a fractionating column?
Is there an easy way to do it without an FTIR or similar to analyze your product? I'm actually a professional chemist working my first job in R&D
at a plastics company but the place is brand spanking new and therefore is light on a lot of chemistry basics you'd find at an average lab (I had to
buy RC car fuel and distill out the nitromethane when I needed methanol). Anyway, the glassware kit we bought had this addition funnel with ground
glass joints top and bottom that I'd like to try and use for fractional distillation. I bought some 1cm glass beads at the craft store and used them
to fill the column which I think will make for a good fractionating media. Of the non-chlorinated solvents we have available (ethyl acetate, IPA, THF,
acetone and xylene) I think the best pairing for a test would be acetone/THF (BPs 10°C apart ). I have it handled up to that point, what I'm
struggling with is how I can confirm the purity of my final product without the spectroscopy I took for granted back in undergrad.
This is my first post so if its in the wrong place, let me know.
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leu
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Do you understand how to measure the boiling point of the components There's some
useful information in the forum library if you don't The end results from the
effort applied
Chemistry is our Covalent Bond
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forgottenpassword
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You might want to use something more efficient than 1cm glass beads! Most things would be more efficient. Even bread!
Use thin layer chromatography to compare your isolated substance to a known sample. If the two substances behave identically on the same plate then
there is a high probability that they are the same substance. If they behave identically on two different plates then they are certainly the same
substance. Silica and alumina plates will allow you to categorically identify most substances, so long as you have reference standards, which I assume
that you do.
[Edited on 28-1-2014 by forgottenpassword]
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The Ideal Gas Lawyer
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Quote: Originally posted by leu | Do you understand how to measure the boiling point of the components There's some
useful information in the forum library if you don't The end results from the
effort applied |
The method I was taught was to read off a thermometer with the bulb placed right at the opening in the distillation head that leads to the condenser.
Thats what I used when I was distilling the methanol but I was hoping for something more precise.
Quote: Originally posted by forgottenpassword | You might want to use something more efficient than 1cm glass beads! Most things would be more efficient. Even bread!
Use thin layer chromatography to compare your isolated substance to a known sample. If the two substances behave identically on the same plate then
there is a high probability that they are the same substance. If they behave identically on two different plates then they are certainly the same
substance. Silica and alumina plates will allow you to categorically identify most substances, so long as you have reference standards, which I assume
that you do.
[Edited on 28-1-2014 by forgottenpassword] |
This right here is what I was looking for. I somehow managed to forget that TLC was a thing. I don't have plates right now but they're quite a bit
easier/faster to get than an FTIR
Whats ineffective about beads? I was planning on having the purchasing coordinator add some Raschig rings to the next order of lab equipment (which
will now also include some silica gel plates), but in the meantime, can you recommend another material I should pack the column with?
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forgottenpassword
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My mistake. I thought that you were going to do column chromatography rather than a distillation. Beads are fine.
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blogfast25
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Quote: Originally posted by The Ideal Gas Lawyer | [Whats ineffective about beads? I was planning on having the purchasing coordinator add some Raschig rings to the next order of lab equipment (which
will now also include some silica gel plates), but in the meantime, can you recommend another material I should pack the column with?
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The ratio of surface area to bulk volume for beads is lousy. The fact that they take up some much volume (for a given surface area) can lead to
'column flooding'. Raschig rings are much better. I think they probably represent the best cost/effectiveness ratio, compared to some more exotic
column packings like saddle shapes.
[Edited on 28-1-2014 by blogfast25]
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The Ideal Gas Lawyer
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Reread the OP and realized I didn't make that as clear as I should have. My bad.
Quote: Originally posted by blogfast25 | Quote: Originally posted by The Ideal Gas Lawyer | [Whats ineffective about beads? I was planning on having the purchasing coordinator add some Raschig rings to the next order of lab equipment (which
will now also include some silica gel plates), but in the meantime, can you recommend another material I should pack the column with?
|
The ratio of surface area to bulk volume for beads is lousy. The fact that they take up some much volume (for a given surface area) can lead to
'column flooding'. Raschig rings are much better. I think they probably represent the best cost/effectiveness ratio, compared to some more exotic
column packings like saddle shapes.
[Edited on 28-1-2014 by blogfast25] |
That's my understanding as well. I think the glass should work OK while I wait out the requisition process though. Until the real rings come in, I
wonder how well 1/4" stainless steel nuts would work, assuming I'm not trying to separate anything super corrosive.
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blogfast25
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Quote: Originally posted by The Ideal Gas Lawyer |
That's my understanding as well. I think the glass should work OK while I wait out the requisition process though. Until the real rings come in, I
wonder how well 1/4" stainless steel nuts would work, assuming I'm not trying to separate anything super corrosive. |
For extracting acetone from nail polish remover I once actually used a stainless steel scouring pad (the very coarse ones) to pack a short column. It
worked very well. But for obvious reasons glass as packing is preferred.
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Magpie
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In your original post you show a picture of a piece of glassware. What is it and how do you intend to use it in this case?
The single most important condition for a successful synthesis is good mixing - Nicodem
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Metacelsus
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It is an addition funnel. However, he intends to use it as a fractionating column. I think it's worth a try, but is unlikely to be as good as the real
thing.
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bfesser
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Don't bother trying to use that addition funnel as a <a href="https://en.wikipedia.org/wiki/Fractionating_column" target="_blank">fractionating
column</a> <img src="../scipics/_wiki.png" />. Just buy a real column off of eBay, or from a lab supplier—they're relatively
cheap. There's too much of a constriction in the stopcock bore for your plan to be successful. Also, stainless steel, copper, and bronze scouring
pads ('wool') should all be available at a local hardware store, and make great column packing.
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bfesser
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Thread Moved 28-1-2014 at 19:33 |
Magpie
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I agree. The bore on that stopcock plug is likely no more than 3mm. It will severely restrict your boilup rate.
Separating two liquids with a bp difference of only 10°C is going to be a challenge. My guess is that you will need a column of length no less than
600mm. You might also need a still head that will provide reflux control.
Packing diameter should be ideally be no more than 1/4 or 1/5 the diameter of your column. And almost anything will be better than spheres. Broken
glass is not bad and a SS scrub pad can be quite good.
What liquids do you intend to separate and what efficiency do you require?
The next time you need methanol, and don't want to order it from a chemical supply house, use gasoline de-icer "Heet" or "Drygas."
The single most important condition for a successful synthesis is good mixing - Nicodem
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Oscilllator
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If you somehow managed to connect the addition funnel upside down it should work fine. Just a thought.
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The Ideal Gas Lawyer
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Quote: Originally posted by Cheddite Cheese | It is an addition funnel. However, he intends to use it as a fractionating column. I think it's worth a try, but is unlikely to be as good as the real
thing. | Quote: Originally posted by bfesser | Don't bother trying to use that addition funnel as a <a href="https://en.wikipedia.org/wiki/Fractionating_column" target="_blank">fractionating
column</a> <img src="../scipics/_wiki.png" />. Just buy a real column off of eBay, or from a lab supplier—they're relatively
cheap. There's too much of a constriction in the stopcock bore for your plan to be successful. Also, stainless steel, copper, and bronze scouring
pads ('wool') should all be available at a local hardware store, and make great column packing. | Quote: Originally posted by Magpie | I agree. The bore on that stopcock plug is likely no more than 3mm. It will severely restrict your boilup rate. |
I agree it's far from ideal but I thought I'd give it a try just to see. I obviously won't get great throughput but I'm curious if it will work at
all. I might also try removing the stopcock and sealing the sides so that the vapor can pass through the bore with less restriction. Teflon tape and
parafilm perhaps? I hadn't considered using a scouring pad as a packing material, definitely worth a try. Are glass beads really *that* bad?
Quote: Originally posted by Magpie | ...
Separating two liquids with a bp difference of only 10°C is going to be a challenge. My guess is that you will need a column of length no less than
600mm. You might also need a still head that will provide reflux control.
...
What liquids do you intend to separate and what efficiency do you require?
.... |
In that case I'll probably try an easier combination first. maybe IPA and THF (16°C) or Acetone/EA (21°C) I'm unfamiliar with the sort of still
head you're talking about can you explain some more? I don't have a specific use in mind right now, I just want to refamiliarize myself with the
technique and find a setup that work for when I actually do need it.
Quote: Originally posted by Magpie | ...
The next time you need methanol, and don't want to order it from a chemical supply house, use gasoline de-icer "Heet" or "Drygas."
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That was what I was looking for at first but I couldn't find the specific product refered to on http://en.wikipedia.org/wiki/List_of_commonly_available_chem... Without a way to confirm the contents I didn't want to risk it.
Thanks for all of you guy's help btw
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Magpie
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Quote: Originally posted by The Ideal Gas Lawyer |
In that case I'll probably try an easier combination first. maybe IPA and THF (16°C) or Acetone/EA (21°C) I'm unfamiliar with the sort of still
head you're talking about can you explain some more? |
Here's some stillheads w/adjustable reflux for sale by Dr.Bob:
http://www.sciencemadness.org/talk/viewthread.php?tid=15667&...
But I would get a good column ($30-40) and try that first.
[Edited on 29-1-2014 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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