Sciencemadness Discussion Board

anyway to speed up distillation without vacuum?

conducter - 13-5-2007 at 03:16

i have a distillation running, and its been running for the last 10 hours. the distilling flask is a 500ml rbf, and had 250ml of an oil in it. Well it took a while before it started coming over but it seems like a few drops every minute or so.

About 50-60ml of the distillate has come over, and although it looks good, it is taking a damn long time. Is it possible that this could take more than 24 hours?

Im just looking for a way to speed this up a little, i have the distillation adapter wrapped in aluminum foil to contain the heat. The flask is submerged in a peanut oil bath and the fisher hotplate/stirrer is on 10, which is as hot as it gets. Its bubbling a whole lot just seems that its not coming over fast enough.

not_important - 13-5-2007 at 04:01

Adequate heat input is needed, reducing heat loss as you've done is part of that, a second layer of foil loosely wrapped around the first might help, the air gap is part of the insulation. Insulating the bath is another, to reduce heat loss there. More surface area is yet another, that means a larger flask, works if the heat flux is large enough.

But too fast a distillation rate will to some extent defeat the purpose of distilling - to separate various components of a mixture. You need some reflux going on to get separation of even things boiling fairly far apart pushing the distillation too fast will reduce the effectiveness of separation.

evil_lurker - 13-5-2007 at 09:26

What is the BP of the material your trying to distill and how big is your hot plate?

Anyways, I have found it very helpful to wrap a rag (double or triple that sucker up, make it thick) around the top of the flask, take off adapter, and part of the condensor (secure it with clothespins).

And if your using water in your condensor... don't. Hook it up to some sort of blower or an aquarium air pump and air cool the condensate... running water will definately cause troubles at high temps.

conducter - 13-5-2007 at 10:41

the bp is 232C i believe.

Anyways because i didnt have a thermometer, i scorched it, the distillate smelled very sour and not at all pure like the compound was suppose to smell like. which im told is like flowers.

Back to the drawing boards i guess

not_important - 13-5-2007 at 10:49

Distillation without a thermometer is like driving an automobile with the windows painted over, you'll get somewhere but it's not likely to be where you wanted to go. The only time you don't need a thermometer is with steam distillation, where you keep some water in the pot and determine end point by when the organic phase stops coming over.

On top of that, if what you are distilling is the large majority of the starting mix, or the highest boiling component except for gunk, you will want to add a chaser to avoid overheating the pot. You never want to take the still pot to dryness or even near dryness.

bio2 - 13-5-2007 at 11:04

If an immersion heater is placed in the oil bath then
1/2 or less the wattage is needed compared to heating the
bath with a hotplate. This also gives faster response

A 300-400 watt immersion heater will easily boil up
a 2-3L flask of water if everything is insulated.

A thermometer should be placed in the bath so
that the temperature can be adjusted 10-30 degrees
or so over the component you are trying to distill..
Needless to say another thermometer must be in the
still head vapor flow.

[Edited on by bio2]

evil_lurker - 13-5-2007 at 11:56

232ºC is waaaay too hot to do atmospheric distillation... you REALLY need vacuum to pull it off.

Your going to decompose the oil your distilling (as you have already discovered), the peanut oil is likely to catch on fire @250ºC+, and you have no thermometer so you have no clue what is coming over.

Simply put, you ain't got the right equipment to do the job.

Organikum - 13-5-2007 at 12:05

Why dont you read your own posts?
Quote:
Originally posted by conducter
at the hive swim found this

Chromic
(Synaptic Self-Mutilator)
11-09-03 14:18
No 469860

MDP2P

"SWIC has seen MDP2P distilled without a vacuum at 283C (made from oxone and from peracetic routes)... but don't expect the teflon on the stir bar to last for long, ensure everything is very insulated with glasswool (inc. the clamp), and your yields will be down about 10% on the recovery of the ketone...

So by comparison, 200C is rather light heating... but again, make sure you use glass wool insulating everything, including the clamp. The stir bar will be discolored... but not destroyed."

Is this really possible, swim is terrible and cannot for the life of him figure out what type of pump/aspirator to get and how to not explode his distillation setup so he wants to try to distill the ketone at atmospheric pressure.

Would a chaser liquid be a good idea? to keep the mdp2p from charring in the flask to polymerized crap.
Emphasis by me.
You simply dont follow instructions and therefor you are paying the price by decomposing your oil. What a pity, just because you are not able to get and use some glass or stonewool. Who told you that aluminiumfoil is an insulator? At >200°C? For sure not common sense.
Get some glasswool or improvise a hot-air bath by building a kind of tent around flask and head made from stron aluminium foil preferably but not necessarely insulated by something.
If you ask yourself now why aluminium foil as a tent works but not wrapped around the flask/head, then - then well that you have to figure out yourself. Its not so hard.

What a shame, now somebody has gone the long way to some precious oil and fucks it up in the almost last step just for not doing the obvious, simple, cheap and logical.

Ozone - 13-5-2007 at 20:01

I have found that sparging or "blow-down" technique can be quite helpful. Here, a stream of gas (N2 is very good) is either delivered below the liquid volume with something like an "aquarium rock--glass frit" or delivered just over the surface of the medium.

It is not as clean, but it is faster. Watch out for azeotropes and possible liquid entrainment.

Chasers work well for removing the last small amounts of solvent or reactant (think SOCl2). Just be careful with the boiling points--with care your solvent can be removed, without care, you can easily blow your stuff out of the condenser (when your chaser flash-boils), etc.

Aluminum foil works well for insulating your apparatus, and it's cheap.

Either way, be careful.

Cheers,

O3

Sauron - 14-5-2007 at 06:36

There's simply no substitute for the 5-P Principle in fractionation.

Proper Planning Prevents Piss-poor Performance.

Matching the heat source to the size of pot to the column and lagging the column well, packing it right, understanding the nature of the mixture and its components, how many TPs are called for and what RR, and allowing adequate time for equilibration before taking ANYTHING off (that is, before reducing from 100% reflux). Muck up any of that and you might as well be doing a simple distillation.

Inadequate heat, or too much column, or poor packing design, or too high a RR than is called for, and your distillation will take forever.

All that being said, a proper fractionation is always slow and it is simply very bad thinking to try to speed up a distillation.

Vacuum does not speed up a distillation. VAcuum lowers the bp. Vacuum or no vacuum, upping the surface of the evaporating liquid as in a rotary evaporator or kugelrohr, does speed things up but these are very rarely used for anything but simple distillations, although Buchi showed off a fractionating glassware set not too long ago more or less as a stunt.

What are the boiling points of your components? If they are far enough apart you can get away with simple distillation or a short inefficient column like a Vigreaux. If they are very close you will have a challenging time seperating them at all, without a spinning band still and you want to talk about slow? Those 200 tp stills have a throughput of a coupls ml an hour. But they can seperate components that are only a few degrees apart in bp.

Most practical columns of say 50-200 cm will have 5-20 theoretical plates (that is, they have a 10 cm HETP) and are run at about a 5-15:1 reflux ratio. They need hours to equilibrate. Fractionation is an art within the art and a science within the science.

DrP - 14-5-2007 at 07:31

sometimes warming the column with a hair drier can help. However, I suspect vacuum is needed here.

Sauron - 14-5-2007 at 10:17

Warming the column, simply turns a fractionatin into a simple distillation. You want to INSULATE (LAG) thermally isolating the column so that the system of mantle/pot/column and still head can come to equilibrium. The best columns are vacuum jacketed and silvered for exactly that reason. Only an observation strip is left unsilvered so you can visually confirm that the column is not flooding - a condition indicative of too high a boilup rate, or too low a percentage of free volume (due to poor choice of packing or inappropriately small ID or combination of these.)

Warming the column will move everything over and negate the seperation that is the whole point of the procedure. It may get the distillation done, but it doesn't get the seperation done, and the whole sheebang will have to be done over. Bad show.

evil_lurker - 14-5-2007 at 10:48

Hey Sauron, what type of column would you recommend for separation of mononitrotoluene isomers?

Sauron - 14-5-2007 at 20:16

First of all I'd want to be damned sure no possibility of dinitrotoluene present if I were doing this at atmospheric pressure. That's a must. If not sure use a pump.

Secondly, the o-ester is a liquid and comes over first, and is the predominant product. You need a good column, and good technique, and stop distilling when temperature rises enough to indicate the p-isomer is starting to come.

There's so little m-isomer that there is very little point in trying to seperate it by distillation and bp's are too close (m- and p-) anyway. Take your mostly p-isomer from the pot, and recrystallize it till the mp of the dried product is the literature value.

The m-isomer is in the mother liquor and can be recovered from there but why bother?

I'd use a Hempel column packed with Raschig rings or berl saddles, the dimensions depend on how much MNT you are distilling.

DrP - 14-5-2007 at 23:59

Quote:
Originally posted by Sauron
Warming the column, simply turns a fractionatin into a simple distillation.


He doesn't mention that he is using a fractional column - he just says distilation. He is not getting ANYTHING coming over at all.


Quote:

Warming the column will move everything over and negate the seperation that is the whole point of the procedure. It may get the distillation done, but it doesn't get the seperation done, and the whole sheebang will have to be done over. Bad show.



I dont suggest sitting there and heat the the kit until it ALL boils over - that would be F.ing Stupid. Just warming the bottom of the column to help the stuff on the way. Any way - you right - it's not ideal, but if the guy is waiting days and nothing is happening then hey it's worth a try. - the guy needs a vacuum to do it properly - that much is obvious.

Sauron - 15-5-2007 at 00:40

He hasn't divulged the boiling points involved or the identity of the components of the mixture he is trying to fractionate. That makes it just about impossible to comment. If his column was selected properly and lagged properly there would be no need to "help anything along", assuming adequate heat input in the first place. There's more than a dozen variables involved in any fractionation, all interrelated, and the trick is not to screw up on too many of them or this is the kind of goat-fuck that ensues.

DrP - 15-5-2007 at 00:52

232 Degrees C acording to the origional poster.

[Edited on by DrP]

Sauron - 15-5-2007 at 02:07

That's a single bp. What else is in there and how far away are the other bp's?

Aluminum foil is not an insulator, it's a very good conductor of heat. Cotton wool would be better. The oil bath ought to be at least 20-40 C hotter than the bp. If that hot plate won't hack it, then indeed the only choices are a hotter heat source or a vacuum to lower the bp.

Even an aspirator ought to do the job.

Organikum - 15-5-2007 at 02:24

Quote:
Originally posted by conducter
Its bubbling a whole lot just seems that its not coming over fast enough.
So obviously you are loosing the temperature uphill and that can only come from lousy insulation.

If the compound you distill is what I think it is - this can be steamdistilled btw. Forced steam is preferred, a easy setup with an old pressure cooker, Cyclo Knight posted some nice pictures of such a setup in the Toluene -> Benzaldehyde thread.

/ORG

evil_lurker - 15-5-2007 at 07:24

Usually I like to run in the 1-5 mole range, with a 1L flask as my boiler... all my joints are 24/40.

I'm definatly going to run any nitrotoluene under vacuum first to reduce risk of explosion... not to mention that 220ºC would be pushing my hot plate and oil bath to a much higher temp than I would prefer. Unfortunately I'm going to have to wait till I get my digital vacuum regulator factory recalibrated or until I get off my lazy butt and boil some distilled water under vacuum and record the actual boiling temp vs what is read on the meter.

It also doesn't help my distillation technique that my hot plate is a hunk of crap... I prefer to use it with an oil bath and magnetic stir bar running as my heat source because it does a great job of preventing bumping. However, every time the heat cycles the stir bar slows down... when the heat kicks off the bar picks up speed and the column "surges" so its basically impossible to achieve any decent sort of equilibrium in a fractionating column.

I still manage to get some fractionation... I'm guessing based on prior distillation runs that I'm able to achieve an approximate total reflux ratio of 3:1 on a 300mm hempel column packed with 6mm raschig rings if I take things pretty slow (the pot is a freebie and adds 1). I figure if it was properly lagged and I had a better heat control I could hit 4:1.

bio2 - 15-5-2007 at 18:40

........ However, every time the heat cycles the stir bar slows down... when the heat kicks off the bar picks up speed and the column "surges" so its basically impossible to achieve any decent sort of equilibrium in a fractionating column.................

A triac based dimmer will prevent the cycling problem, if
tuned to the heat requirement, stays on even at low heat settings.

conducter - 16-5-2007 at 22:45

if one is distilling dichloromethane from a mixture of gelling thickener and methanol, if one applied aspirator vacuum. Would the DCM distill without even adding heat? Because it will boil at around 30C at atmospheric, so im wondering if vacuum was applied, would that eliminate the need for heat?

Edit:

Also there is a aspirator ivebeen wanting to buy and wanted to know if you guys think this is strong enough for most purposes...


Specifications:
Vacuum Inlet:
10 mm / .385"

Water Outlet:
10 mm / .385"



Length:
137 mm / 5 3/8"

Vacuum generated @ 30 psi
29.5" Hg



[Edited on 17-5-2007 by conducter]

DrP - 16-5-2007 at 23:25

Quote:
Originally posted by conducter
if one is distilling dichloromethane from a mixture of gelling thickener and methanol, if one applied aspirator vacuum. Would the DCM distill without even adding heat? Because it will boil at around 30C at atmospheric, so im wondering if vacuum was applied, would that eliminate the need for heat?



Yes - if you get the pressure right - you can look it up on a chart to find what pressure you would need to vac down to to allow the DCM to evap off at room temp.

not_important - 17-5-2007 at 01:20

DCM boils at ~40 C at atmospheric, 20 C at very roughly 300 mmHg. The methanol would be coming over as well, it's vapour pressure is about 100 mm at the same temperature.

You'll just about need a dry ice condenser to recover the DMC, though; it's VP will be in the range of 125 to 150 mm at zero C. At least under standard pressure you can get away with tap or ice water for cooling.