Sciencemadness Discussion Board

How useful is this piece of glassware ?

Sulaiman - 27-12-2016 at 03:33

Just because it is (relatively) cheap (£12.79) I am considering one of these
in anticipation of higher m.w. vacuum distillations. :P
Untitled.jpg - 70kB

I recently saw a photo or video by a member here (forgot who) using one
- any comments on the usefulness of this piece
(compared to a typical kit of separate pieces) ?

j_sum1 - 27-12-2016 at 04:02

Yeah baby. A short path condenser. I want one.

Good for low volume stuff where you don't want you product spread over a large surface. Good for things like phenol that tend to solidify in the condenser. Good for when you need a phase change but don't need a lot of heat transfer.

And that is a great price too.

[Edited on 28-12-2016 by j_sum1]

Sulaiman - 27-12-2016 at 07:07

thank you, that was all the self-justification that i needed,
I ordered it because of the price, similar pieces, even on smaller neck sizes, cost a few times more.

P.S. I've changed my mind about EtOH, as I'm typing the first rough distillation is comming over at 90 - 91 C, 60 - 65 %
Aiming for 250 mL final product.
Gotta start somewhere (cheap) with lots of data available for comparisons.

Dr.Bob - 27-12-2016 at 07:27

Short path condensers are great for simple distillations, fewer joints to leak, small holdup, and the heat fast, as stated above. And that is a great price, as new quality made ones are well over $100 new, and even cheap Chinese ones can be $50-70. Several distillations of ethanol can provide a decent purity, but hard to get much better then 80-90% without a real distillation column, from what I have seen.

Sulaiman - 27-12-2016 at 07:52

I'm expecting (hoping for) about 250ml 50% after this first batch,
with a reasonably good column I'm expecting 90% easily doable,
but from 90% to near Azeotropic will take mny theoretical plates,
but 95% is half the water of 90% so saves on chemical drying.
Anyway, that's my direction at the moment.

Chemetix - 27-12-2016 at 09:38

Looks like they've got the ground drip tip upside down

aga - 27-12-2016 at 09:47

Distilling ethanol is pretty straightforward and has been written about a lot.

First just do a quick/rough distillation aka a 'stripping run' to get rid of most of the water.
You'll get about 70% EtOH without any special care.

If you have a vigreux column, do a slower (less fierce heat) second distillation with that, carefully watching the temperature and collect only the ethanol fraction +/- 1 C, depending on the accuracy of the thermometer.

That'll be azeotropic more-or-less.

If you have no vigreux, a 'thumper' also works pretty well.
Just watch the temperature at the exit of the 'thumper'.

Stick at near-azeo or treat for a few days with 3A molecular sieves (oven dried for 2 hours).

Alternatively add some tripotassium phosphate and immediately redistill to get near 100% EtOH.

250ml of product is quite a lot of distilling.

I got about the same and now wish i'd gone for 500ml instead to really fill the bottle : it's now starting to get a bit empty again.

Sulaiman - 27-12-2016 at 12:24

Quote: Originally posted by Chemetix  
Looks like they've got the ground drip tip upside down

well spotted!

if you had pointed that out before I committed to buy
I would still have bought it :) maybe this is why it is cheap ?
not that it matters to me.

aga - 27-12-2016 at 13:05

It looks odd, but basically OK.


Got it all backwards.

The input is the ground glass on the top left.

Thermometer top right.

Right-top and down = condenser out, condenser in, vacuum.

Output the 6mm pipe at the bottom, with a nice ground glass male conector to correctly mate with the receiver flask.


[Edited on 27-12-2016 by aga]

Sulaiman - 27-12-2016 at 13:52

although it can be used as a 'normal' still
I believe that the value is in it's smallness and (almost) straight paths

at the published (unable to check so far) limit of my 2-stage rotary the mean free path in air is up to 100mm
so molecules fly through the low pressure air in straight lines,
bouncing off walls like snooker balls off cushions,
as opposed to diffusion, jostling through the crowded atmosphere.
(why this helps I'm not quite sure yet)
The very low pressure allows higher m.w. substances to vapourise at lower temperatures, minimising decomposition of delicate molecules.
I think :P

I do not know if I'll ever use it as intended, depends how deep into organics I get.

j_sum1 - 3-1-2017 at 03:28

Here is UC235 recommending a short path condenser. Watch for a minute or so from this point.

As for the backwards drip tip, if you find that it does not drip satisfactorily in use you could probably use some emery paper to grind it back a bit so that it is anged the other way. It would take ten minutes or so of careful sanding. But I would not bother unless it was affecting things somehow.

PirateDocBrown - 3-1-2017 at 04:17

That IS a good price!

I use SP for reagent purification, when a quick distill is what's needed to get rid of the great bulk of impurities. Far easier than setting up to whole still.

It's also good for high-boiling distillations, to render these products.

It's good at vacuum or ambient.

alking - 4-1-2017 at 10:43

As others have said I'd grab that based on the price alone, that's super cheap for a short path rig. I'd try to get the ethanol to ~80% or so and then use a drying agent. Using an extra 50g of MgSO4 or w/e is cheap, cheaper and more time saving to me than an extra distillation to get 90%+.

Ime a vigreux alone is not going to give you enough separation to even get 95%. When distilling 40% I only aim for 75-85% purity because it takes 3-10x longer to get a better separation with that, I'm talking ~20hrs to distill ~700ml worth of 90%. It's far easier for me to spend 2-3 hours to get 75%, dry it, and then redistill to get it anhydrous. If you can pack your column well it might be worth it though.

Sulaiman - 4-1-2017 at 12:38

I'm not doing distillation to make ethanol, (although I shall of course keep it as a reagent/solvent)
I brewed ethanol to learn distillation cheaply,
I expect to spend several days trying different distillation setups,
from a simple distillation up to maybe 11 effective plates,