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Author: Subject: What size beads to use in a Hempel column?
evil_lurker
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What size beads to use in a Hempel column?

So I'm having a brain fart...

What size beads to I need to run in my hempel column?

I'm thinking 4mm is a bit too small and might cause some flooding issues, 5mm would be about right, 6mm would definately be OK but I would lose some efficiancy.

Oh yeah, I.D. is about 24mm if that makes a difference... I think my next column is going to be a 29/42 so I can run it a bit faster.

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evil_lurker
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Sweet.. found em, soda-lime, non-perforated, $26lb. Beats the hell out of Kimax brand at$136lb.

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Sauron
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Beads are a very poor packing medium. Raschig rings are better, berl saddles (porcelein not glass) are even better.

The sole virtue of glass beads is that they are cheap. But their surface to volume ratio sucks, and therefore they have a large HETP. They also have a low % free volume so your boilup rate will have to be very low in order to avoid flooding column and ruining seperation.

Like I said, they suck. You will not have a happy fractionation with glass beads.

Fractionations under the best conditions are tedious, fiddly, and demanding of skilled attention to get best results so it does not pay to shoot yourself in the foot before you start..

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MagicJigPipe
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I've been curious. I purchased a used 300mm column a few months ago that came packed with "steel wool". It's not normal steel wool that you would buy at the grocery store. The strands are thicker and "woven" in a regular pattern (it looks "professional" and I know it came from a "pro" lab). Also, it's stainless steel.

What are the advantages (if any) of this? Why would a professional lab use it if there are better alternatives?

P.S. I'm almost certain it is for distilling some sort of petroleum type solvent (as in, something that SS would be inert to).

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evil_lurker
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I wonder how some PTFE tubing cut into raschig rings would work out...

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Goodloe packing?

Semi-loose SS mesh packing used to be common in the USA. I have it in all of my Hempels and it works well. Flooding is never even close to being an issue, you'd have to overpack it quite tightly. Get the column heated, set your reflux ratio and that's that. Beads would be the last form of packing that I'd want to use.
Magpie
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I have found that SS mesh (a scrub pad, not steel wool) works very well. Check your hardware store. The only problem is that it is not as chemically resistant as glass.
Sauron
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The scrubbing pad as packing is popular with home alcohol distillers but the chemical resistance is marginal; if they made such mesh out of tantalum that would be better. Apart from that issue, it is difficult to get truly consistent column packing with this approach. Professional stainless mesh packing (Goodloe, manufactured by Gltsch in Dallas for the petrochemical industry, is knitted not woven mesh compressed into cylindrical sections with a very consistent density/free volume, and within the chemical limits of the material, is a nearly ideal packing. I used to do business with these guys when they were Metex in Metuchen NJ before they sold out to Glitsch. Almost 30 years ago. But my application was different.

There's a home-alcohol supplier in Malmo, Sweden trading as www.partyman.se, who sells Raschig rings at reasonable prices, for still column packing. His name is Gert, tell him the guy in Bangkok sent you.

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smuv
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Local supermarkets also carry copper scrubbing pads which I used to use as a packing material; they seem to be pretty inert as I am using the same pads that I bought 3 years ago. Although after I got my vigreux column I seem to be able to cut cleaner fractions...so I make no claims for the efficiency of this packing material.
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For me, copper scrubbers (be sure that a magnet won't pick them up) is all that I will use with ethanol. Stainless scrubbers work well for almost everything else, provided of course you can get somewhat of a uniform packing density when you have to shove them thru a 24/40 joint. IMO, certain halogenated compounds and acidic natured compounds need something more inert such as beads or raschig rings, hence the reasoning behind this thread.

I've used the ceramic rings from brewhaus, the USA distributor of Gert's stuff. They are OK, but not the most inert stuff or the most efficiant for small diameter columns found in the lab... if they were a mm or two smaller they would be awesome.

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Magpie
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Evil, have you tried broken glass? That's what I use when concerned about corrosion. I really don't know how efficient it is compared to other options such as a Vigreux column. But I always thought that a Vigreux was equivalent to only 3 or 4 theoretical stages.
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For me, glass beads always yeilded a much better purity than a vigreux column... though there is the issue of holdup...

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evil_lurker
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Today I did some what of an expiriment to evaluate how much PTFE tubing it would take to fill up my Hempel column.

Since PTFE tubing is expensive and not readily available, I decided to use something cheaper, polyethylene tubing 1/4" (6.35mm) OD and cut to approximate 1/4" lengths using a sharp kitchen knife. Based on my "hands on" research, 3 feet (90mm) of tubing is enough to fill approx 40-50mm of column length with an ID of about 26mm.

After some digging, I found the company below which has some "oddball" 0.210 (5.33mm) sized PTFE tubing with 1/8" (3.18mm) centers for .96¢ per foot, which ain't too bad of a price.

http://www.rotaloc.com/PTFE-Tube-Rod.html

I also did some measuring of the ceramic raschig rings as Sauron mentioned. Most fell somewhere between 5.95mm to 6.35mm OD with 1.5-2mm ID center holes.

How this would affect a real life column is somewhat up in the air, but I bet the PTFE rings would result in about a 25% jump in efficiancy.

Not all chemicals are bad. Without chemicals such as hydrogen and oxygen, for example, there would be no way to make water, a vital ingredient in beer.
Magpie
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Evil_ says:
 Quote: I also did some measuring of the ceramic raschig rings as Sauron mentioned. Most fell somewhere between 5.95mm to 6.35mm OD with 1.5-2mm ID center holes.

The 1.5-2mm ID center holes may be OK for the ethanol-water system but this seems pretty small to me. If the liquid/vapor can't move through the holes due to surface tension then that inner surface area is wasted.

I would also like to find berl saddles of the right size for my Hempel column (ID=15mm). In the mean time I use broken, thin-walled glass of high curvature, as I think it most closely simulates saddles. Its disadvantage is that it is not regular and there is bound to be some channeling and short-circuiting.
evil_lurker
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Quote:
Originally posted by Magpie
Evil_ says:
 Quote: I also did some measuring of the ceramic raschig rings as Sauron mentioned. Most fell somewhere between 5.95mm to 6.35mm OD with 1.5-2mm ID center holes.

The 1.5-2mm ID center holes may be OK for the ethanol-water system but this seems pretty small to me. If the liquid/vapor can't move through the holes due to surface tension then that inner surface area is wasted.

I would also like to find berl saddles of the right size for my Hempel column (ID=15mm). In the mean time I use broken, thin-walled glass of high curvature, as I think it most closely simulates saddles. Its disadvantage is that it is not regular and there is bound to be some channeling and short-circuiting.

I can get 6mm berl saddles from Chemglass but they are quite expensive at around 10 cents each. I don't know if they are glazed or unglazed.

6mm raschig rings would set me back \$86 per lb.

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By Evil_Lurker:
 Quote: I can get 6mm berl saddles from Chemglass but they are quite expensive at around 10 cents each. I don't know if they are glazed or unglazed.

I don't think that is too bad a deal. At least you can buy them in lots as small as 250. I suspect (but don't know) that they are glazed as I would think that unglazed would be hard to keep clean. That 6mm size is probably right for a column that has the 24/40 end fittings as that is most common. They are probably a little large for my 19/22 column, but still might be the best alternative.

But I'm just talking out of my ass here. I don't know any of this from experience.
Sauron
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6mm is actually better for larger diameter columns. Like 40-50mm ID.

Aldrich I believe also sells berl saddles and sized smaller than 6mm but I have not looked lately. - I went and looked. Aldrich only sells 6mm and in pack of 250 which they say is c. 2 liters packing volume. I would bet their price is higher than Chemglass, too.

As they are reusable, the expense is not so onerous.

[Edited on 28-4-2008 by Sauron]

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MagicJigPipe
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"Goodloe, manufactured by Gltsch in Dallas for the petrochemical industry, is knitted not woven mesh compressed into cylindrical sections"

That's what is in my column. I just didn't know how to describe it.

I found a picture I took a while back. If you look closely you can see the "spiral" pattern it makes.

[Edited on 4-27-2008 by MagicJigPipe]

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That looks a little more random and less knitted than Goodloe and similar products used in large scale processes.

Note that the Fieser and Williamson text recommends using either copper or steel kitchen scubbers and mentions "Chore Boy" by name. The stuff that I've seen isn't from scrubbers but damned if I can find out who supplied it. Nobody seems to sell it anymore, for sure.

What about just using plain Miyuki, Toho, etc. seed beads? These are just (commonly) 2-4 mm Raschig rings sold at a lower price. They'd have to be better than solid beads.
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Hardware suppliers often carry heavier gauge steel wool in with supplies for stripping paint from wood, and I've seen still heavier stuff intended for doing the same for painted metal. although that seems to have disappeared as small blasters using softer materials have become common.

Beads do work, but make sure to avoid beads with fancy finishes; look for clear or at least some monochromatic colour. Art beads may cost a lot more than plain solid glass beads, shop around to avoid paying too much. You might be able to find 6 mm beads as well as 4, 2 mm is getting a bit small I believe.
Sauron
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The packing in photo above is not at all what I was talking about. The compressed knitted mesh packing inserts are very structured and consistent and not at all random. They look and feel solid but free volume is as high as 85-95%.

Am I wrong to call this Goodloe packing? If so correct me please.

Glitsch makes related products for shock absorption and EMI shields.

S.C., 4mm Raschig rings would be super. I think 2mm is just too small, even for 10mm ID columns. Eternal distillations would result. But 4mm ought to be perfect for columns in the 10, 19, 25mm ID range. Above than 6mm takes over. I have no particular preference in 6mm between Raschig rings and berl salles. I'd use either. A little arithmetic would tell which has more surface area vs free volume (the latter probably needs to be measured rather than calc'd) but they ought to be both worthwhile and the choice is probably one of cost and availability.

[Edited on 28-4-2008 by Sauron]

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MagicJigPipe
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Okay. It's not random, though. The pattern repeats itself all the way down the column. It seems a little random close up because the "threads" have been mangled and pushed around but it is definitely in a pattern.

It was obviously made for the column because it is the perfect diameter and cannot be "picked apart". It's so compressed and almost feels solid when removed.

If you could look at it from a distance you would notice the regular repeating pattern (even close up it repeats, just not as obvious).

Has anyone seen something like this before? I haven't.

"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think, free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
Sauron
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Seed beads = crafts supplies. Mostly these are colored, but some appear to be clear glass. Sizes vary. Raschig rings have OD = length. So I have a friend in the (antique) bead business, he attends the big bead shows, so I asked him to source 4mm OD 4mm long clear glass beads, priced by the Kg. I told him 2mm ID, I dunno if they even spec beads that way.

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evil_lurker , in the USA, check Harrington Industrial Plastics for PTFE, PFA & FEP tubing in stock in all sizes and most any other plastic pipe or tubing.

The FEP tubing is the way to go, for all around versatility and price.
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