Sciencemadness Discussion Board - Improvised Hempel column packing

Improvised Hempel column packing

Maroboduus - 14-9-2016 at 18:29

Just picked up a 300mm Hempel at a garage sale for $10, but the seller, who had no idea what it was, had dumped out the glass helices it was filled with. I need packing material, but those helices are expensive! I found some 2.5mm Pyrex beads on Amazon for $5 a quarter pound (they're used in beauty shops for something called a 'bead sterilizer'), But i don't know if this size is reasonable for a 3/4 inch internal diameter column. I have 2 other options I'm considering: I found some cylindrical glass beads(not lead crystal, glass) which are 3mm long by 2mm wide with 1mm holes. these certainly LOOK like little Raschig rings, but again is this just too damn small? I imagine they'll be less prone to flooding than spheres of the same size.
The other option is stainless steel 'jump rings'. They're available various sizes and the smaller ones approximate the few glass helices that were left stuck to the old grease in the column I bought.
I know the rings in 304 stainless steel won't work for some highly corrosive chemicals, but I assume they're gonna give me the best separations.
The Pyrex spheres should have the poorest fractionating capability, but I hear they still do better than A Vigreux, and obviously they'll hold up to anything the column will survive.
The cylindrical beads ought to be intermediate between these other choices for inertness and theoretical plate height, and I must admit I have a perverse urge to buy them in several colors to brighten up the lab during distillations.
So do the sizes sound reasonable, and am I making any obvious mistakes in my reasoning? If not I'll probably opt for the stainless rings, and the cylindrical beads for when I want to go all Peter Max in the lab.

Fulmen - 15-9-2016 at 02:42

Looks like you have figured things out pretty well on your own.

Efficiency of the different types of packing can be found elsewhere, but generally it all boils down to surface vs volume. Choice of material should be irrelevant (except for chemical compatibility), but size will matter. Too small and you risk flooding, too large and your fill rate decreases. The 3mm hollow beads have the right shape, but a 1mm hole will probably be too small. Surface tension and viscosity can cause the holes to plug up with liquid, if this happens the effective surface will be similar to solid beads but with increased holdup.

Sulaiman - 15-9-2016 at 03:43

I have been thinking about this lately, http://www.sciencemadness.org/talk/viewthread.php?tid=69067#...
the reference is informative.

Probably one of the best cheap column packing materials is short pieces of glass tubing, as used by at least one member here,
but I just know I'd end up with cuts etc.
I have 3mm dia glass spheres on order for my 1" dia. column(s) as a compromise,
cheap http://www.ebay.co.uk/itm/321786631538?_trksid=p2060353.m274...
as inert as the column itself,
easy to clean / re-use ... my deciding factor.

316 stainless steel wool is cheap enough to be a consumable,
I hope to compare the two sometime as a test in my B10 kit showed some promise.

I also recently received 2-3 mm multi-coloured glass beads for my B10 kit

http://www.ebay.co.uk/itm/201639389412?_trksid=p2057872.m274...
(I think that the tiny holes will not help ... tbd)

EDIT: just to be clear, the above is based on very little personal experience ... so far

[Edited on 15-9-2016 by Sulaiman]

[Edited on 15-9-2016 by Sulaiman]

Melgar - 15-9-2016 at 07:01

Happen to have any broken glassware around? Rhetorical question, lol. And if not, it's just a matter of time. Put it in a bag, break it up into smaller pieces with a hammer, and carefully pick out the pieces that are an appropriate size. Repeat with the too-big pieces as necessary. You could torch the sharp edges to make them less sharp, or put them in a furnace if you have one, until they start to visibly deform.

Dr.Bob - 15-9-2016 at 07:42

I do have some scraps of glass tubing, all borosilicate, I believe, if you wanted some pieces. It would not too much to send them in small pieces. You could break them as fine as you wish. I don't know if I have any helical pieces left, I had some a while back in one or two columns. That was a nice buy there, when someone cleans out my basement one day (hopefully many years) they will find a pile of obscure glassware that most people cannot understand. I think I have some 3-4mm glass beads as well I would give you if you pay the shipping.

Praxichys - 15-9-2016 at 08:39

I use these in my column:

http://www.ebay.com/itm/Ceramic-Raschig-Rings-for-Moonshine-...

$22 for a liter of porcelain rings with 6mm OD and about 6mm length. They fit perfectly into a 25mm ID column. The volume they give you is enough to fill my 400mm Hempel column about twice.

[Edited on 15-9-2016 by Praxichys]

wg48 - 15-9-2016 at 09:14

Quote: Originally posted by Melgar

Happen to have any broken glassware around? Rhetorical question, lol. And if not, it's just a matter of time. Put it in a bag, break it up into smaller pieces with a hammer, and carefully pick out the pieces that are an appropriate size. Repeat with the too-big pieces as necessary. You could torch the sharp edges to make them less sharp, or put them in a furnace if you have one, until they start to visibly deform.

I have tried broken up glass bottles with hammer thing. Unless you break the glass up so the pieces are about as wide as they are thick they tend to stack like plates. The flats tend to line up and the range of sizes tend pack very tightly in parts. I would guess that the poor packing at least halves the effective length of the column. and increases the hold up.

If I had to do it again I would use steel bar roller on a hard rubber or wood surface and then tumble them to round them off to some extent.

However given the low cost off glass balls (about 10£/$ a liter of 3mm dia) and how well they will pack I would go for that option if you possible can. Of cause it depends on how good a column you need.

Melgar - 15-9-2016 at 09:46

Quote: Originally posted by wg48

Quote: Originally posted by Melgar

Ah. The one time I did it, I just happened to have a few pieces of especially thick glass and some short pieces of glass tubing that I couldn't use to break up. Actually, I wonder if you could use the quartz tubes from old HID lamps? Probably more trouble than it's worth, but I've been meaning to find a use for those things for a while now, since every so often I'll see a whole bunch of those lights discarded as part of a renovation project or something.

Maroboduus - 15-9-2016 at 19:24

Thanks for the information and advice. It hadn't occurred to me that if the holes in your packing material are too small they might increase the holdup more than the efficiency. I tried broken glass years ago but had channeling and packing distribution problems. Maybe I would of had better luck with those little glass cubes you get when you smash tempered glass.

Guess I'll try those glass spheres for now. From that reference on column efficiency it looks like they'll be a nice improvement over my old Vigreux column. I think I've got some tubing and a tubing cutter around somewhere, so maybe I'll try that too when I get inspired enough to do all that cutting and fire polishing.

Frankly, I'm still hunting around for my the rest of my old labware. It's been years since I last did any amateur chemistry, but finding that column, and a liquid extractor body, at that garage sale sort of inspired me to start monkeying around again.

And anyway this site makes for some damned interesting reading. Seems a lot more reality based than some of those primarily drugs and explosives oriented sites I found at first.

j_sum1 - 15-9-2016 at 19:32

Quote: Originally posted by Maroboduus

And anyway this site makes for some damned interesting reading. Seems a lot more reality based than some of those primarily drugs and explosives oriented sites I found at first.

Agree wholeheartedly. Good to have you here. Have fun.

careysub - 16-9-2016 at 05:36

Would it useful to make a column packing out of 316 stainless tubing, foil or thin sheet?

Stainless steel scrubbers or wool have been cited, but you can get tubing in all diameters, which are easier to segment than glass. With foil for thin sheets you could make structured shapes, stamping them out in a DIY mold, or twisting into a helix etc.

Praxichys - 16-9-2016 at 06:18

Stainless packing is rather limited. Where I work, we have some columns with coarse stainless wool packing because it's cheap and efficient. The problem is that these stills are strictly for hydrocarbons only. Any acid contamination of the vapors degrades the steel, contaminates the pot, and the metals in the pot can catalyze all sorts of nasty side reactions. There are surprisingly few practical applications of SS packing, and in the amateur laboratory you'll end up wanting a glass column eventually.

Creating column packing from glass tube is easy. Use a permanent marker to draw lines that divide the tube into lengths about equal to its diameter. Follow up with a triangle file to lightly score the glass on each mark. Place the tube on a table so that only one segment hangs over the edge with the score line facing the ceiling. Use a rubber or rawhide mallet to strike the piece off, then move the tube so the next segment hangs off and repeat until the whole tube has been broken into even segments, which fall into a waiting container. The trick to this is having a hard table with a clean, sharp corner.

A hook with a long handle is made from a coat hanger, and a single segment is threaded onto this. This is placed in a flame to fire polish the edges. Each segment only take a few seconds, and the finished segments can be allowed to cool on a tile surface. A column only needs a handful of packing, so you can fill a 300mm Hempel column with about 1.5m of 6mm tube, which would take an hour or so to finish.

In my experience, I would not recommend spherical glass beads. In a column, the goal is to maximize the surface area. A sphere has the lowest surface area to volume ratio of all the 3D shapes. It also has a lot of thermal mass which means that establishing a good thermal gradient to tune the reflux ratio takes forever. Also, any bead size smaller than about 6mm has problems with flooding unless you're separating some extremely low-BP substances. Glass spheres do have unique applications but fail to deliver as a good all-around packed column for the amateur laboratory, IMO.

careysub - 16-9-2016 at 07:15

Possibly a mix of glass beads and broken glassware would be better than either alone? The beads preventing the flat-ish pieces from stacking together and channeling?

Maroboduus - 17-9-2016 at 08:18

Yeah, the flooding potential with small beads was something I wondered about. I can see where the rings have a lot more empty space in there, and lower heat capacity for the area.

Fortunately, I've got considerable distilling of solvents to do, so I'll have ample opportunity to see which options give good results with my equipment and the way I work. I suppose different situations and materials will favor different packings to some extent.

I like getting my solvents from non chemical supply house sources ( if anyone knows how that's supposed to be hyphenated, my hat's off to you!) whenever I can, so better fractionation should be a real boon, even before I get around to purifying my own products.

Magpie - 17-10-2016 at 18:07

My fractionating columns are 200mm and 600mm in length, both Hempel type, 13mm ID. I like these small diameter columns as they have low holdup. However it has been a challenge to find a suitable glass packing.

For years I have been using broken glass made from a used food jar. I wasn't too careful about what glass I selected as I was in a hurry. This glass has always been subject to flooding and channeling due to overly large, thick pieces. I have wanted to buy some helices but they are too expensive.

I'm happy to say that I think I have found an acceptable source. I made this packing from 6 feet of borosilicate glass tube, 6mm x 4mm. I cut the tubing into 6ea 1 foot sections and placed them in a large ZipLock bag. Then using a hammer I broke these tubes into small pieces, trying not to overly pulverize them. I then screened these broken pieces through a 1/8" x 1/8" screen, discarding the fines. The accepts just fill my 200mm Hempel. I place a few of my old oversize glass pieces in the bottom as a support. The packed column is shown below.

I have used this column twice now, once to recover acetyl chloride, and once to recover acetic acid. It has performed well in both cases with no channeling or flooding. I did have to go slow with the acetic acid, however: a distillate recovery rate of ~0.7d/s. Reflux falling out of the column bottom was about 2.4d/s.

[Edited on 18-10-2016 by Magpie]

Maroboduus - 23-10-2016 at 10:12

That's a good idea.
My Hempel is pretty narrow too (13 mm), and I didn't think that cut lengths of tubing would pack very well in a space like that. Those curved broken pieces should be a better fit. I've still got some beads to try out too.

I'm still waiting on a 24/40 Claisen adaptor so I can use my 24/40 cold finger to return condensate to the column.

Most of my glass is 19/22, but I've accumulated a few bits of 24/40 here and there (like the 300mm Hempel)when it was cheap, and I've finally decided to Fill out my 24/40 equipment so I can do reagent purification on a larger scale.

Distilling solvents will be a lot less hassle with the larger still.