Solvent Stills

I'm considering installing a solvent still at home. I recycle practically all my solvents, using a conventional fractionnal distn setup, after treatment of the crude solvent (washing with either conc. H2SO4 or base, K2CO3, brine, etc) and reflux over a proper dessicant.
Mostly using 19/26 glassware, these distn are very-time consuming, and do not allow partial reflux, require stopping the heating after initial reflux, attaching a dry fractionnal distn apparatus, and heating again, etc.

At work, we have turned to using continous solvent stills for each solvent, for those not familiar the solvent is constantly refluxed over a suitable dessicant, under a stream of inert gas, and collected in solvent still heads (picture ), so fresh solvent is constantly been distilled into the head, and can be withdrawn with a syringe, or drained into a schlenk.

I have no need for such stills, as i only need performing batch distillation, after a prior reflux, either in a schlenk for rigorously dry solvents, or in a simple receiver (no inert gas) for recycling regular-grade solvents (acetone, methanol, toluene, etc).

Now, at work, we used to have small stills under a hood, for batch distn of solvents. Since we now have designated rooms with a still for each solvent, nobody uses them anymore, and I just can locate the old stills. I was looking for one to bring back home if unused and ok with my boss, or at least show the model to the glassblower. I have looked all other the net for a picture or drawing on such a still, but not find any. I'm not refering to a conventional reflux head, a bit like stoechiometric_steve's impressive still displayed in the "tour my lab" thread, but of a system half-way between a perkin triangle and a dean stark trap, (poorly) represented here:







Once the tap under the reflux condenser is entirely closed, full reflux is set. If totally opened, direct distn occures. The reflux ratio can be set, ie for 4 drops falling from the condenser, one falls in the receiver, the rest falls back into the still pot.

I would like to know if anyone here posses, or uses at work, this or a similar device, and if so where he bought it and for how much, to see if it's worth asking for a custom glassware (which would be relatively expensive). I have checked aldrich and other companies catalogue, most of them only have the recent (and f$*@ing expensive) reflux heads. The glassblower from which the lab used to buy/get repaired the glassware is now retired, so i have no means of knowing if these were custom-made of commercially produced.. i could always ask the administration to check the bills, but that would be a very long process, and it's not sure anything will be mentionned... I asked a few colleagues, most of them didn't have the slightest opinion, so I figured I could ask here.

I also wanted to know what kind of setups people have installed at home, I have already seen Steve's beautifull still, and would be delighted to see other setups.

We use something similar, here's a very rough sketch.

The blue bit is the water circulator/cooler. Crosses are valves (they are quite expensive, but I prefer teflon valves) and the large black line on the left is a large diameter glass tube.

During drying the valve above the pot is open, allowing easy reflux. After the solvent has been drying for a while we close that valve, allowing the upper chamber to fill up until it reaches the level of the large diameter glass tube (the black line), where it then spills back down into the pot. We then can take small amounts through the rubber septa or larger amounts into another round bottom.

Once dry, we usually are always refluxing the solvent, but keep the valve above the pot closed, this circulates the solvent in the upper part.

As always we keep the system under a slight positive nitrogen pressure.

Good luck

Thank you for th ecomment. That system is pretty similar to the still head I linked too. Unfortunaly, this isn't what I'am seeking, as this sytem, like those at work I described, make avalible a constantly renewed amount of solvent in the head, and is refluxed all day.

I will be performing batch distn, receiving the dried solvents in schlenks that will then be stored under Ar and 3A MS, after a few hs reflux over adequate dessicant, or simply repacked into amber bottles for regular-grade solvents. At first, iw as thinking of using my Dean Stark, but agin this is a 19/26, and I have no means of connecting a schlenk to the draining of the trap. I guess I could be using it for solvents I need in small quantities and not rigorously anhydrous. After all, the system I described is very similar to a Dean Stark trap, except the the trap itself has an insgnificant volume (<1mL).

I will show the diagram to my glassblower and see if he knows if these can still be bought commercially, and if not how much it would cost to have one made in 29/32. I will surely place a vigreux between the still and the head, depending on the contamination of the recycled solvent and the purity required. With an adequate reflux ratio, the theoretic nb of plates can be significantly increased IMHO. The neck of the head (connected to the pot) could also be filled with steel wool or another garniture.
One major draw back is that it isn't possible to measure the vapor temp, no fitting for the thermometer. With pur solvents this isn't a problem, but for recycling solvents containing traces of other more volatil compounds (I have, for example, several liters of AcOET/Pet ether used as eluant for columns and distilled off the products with a vigreux, providing a very gross seperation. The pet ether-rich fraction will be washefd with conc. NaOH no problem, but the AcOET will require carefull fractionnation. Ethyl acetate is very cheap (8E 5L), but I dispose of my waste at a chemical waste company, which charges roughly 1E per liter... So I prefer keeping the amount of waste minimum.)

Well, I suppose that for general uses traces of hydrocarbon won't be problematic, and that if I need very pur AcOEt, I will start of from the commercial product.

Sorry, started thinking out loud


I'll post some pictures if/when I get it installed

We have two continuous reflux stills for diethylether and THF over Na/K alloy. I have drawn a schematic which I hope is clear enough.

Basically THF vapor rises through the sidearm until it reaches the condensor, where it drips into the collection flask. This flask is equipped with a 3-way valve which can be used for taking THF from the flask or to flush it back into the heating flask (in cases where it has been standing overnight without continous reflux for example).It also has a protrusion from beneath with a hole, through which THF flows back into the heating flask once it reaches a certain level. Schlenk line is not necessary, flushing the apparatus before use and equipping it with an Ar balloon is sufficient. This will supply you with dry THF that is suitable for anionic polymerizations.

IMO Chemglass makes the finest solvent stills sold. I really like their design. They have both the 2500ml and the 1000ml resevoir heads... my price is around $280ml for the 1000 and $353 for the 2500ml.



The whole setup looks like this:



Like vulture said, the stills can be used for both storage and distillation, and they have septums from which to draw solvent off.

Yes, those are the kinds of stills I mentionned I didn't want to have rather than have one still per solvent, and roughly 250-500ml disponible at all times, I prefer using the same still batchwise for any solvent, and collect 500-1L in the respectives schlenks/bottles to store (enough to use in a month for solvents in schlenks/under argon)
But it's interesting to see each ones' opinion on these. I suppose their implantation is now worldwide

I have a message from a colleague telling me he located one of the old stills, so I might take a pic or borrow it to show it to the glassblower. I will post the picture here, so than people can see what I'm talking about.

El, have you installed such a still in your home-lab? Or do you use your regular distn set for solvents?

Well, at work we always used to keep these sealed schlensk for up to 1 months, some other MS or CaH2. When stored, we use glass stoppers with minimum grease, with parafilm, and swap to septums when needed. Obviosuly degassed and purged at each handling. Never had any problems this way, even with pretty sensible reactions.

But now I guess fresh solvents are even better, even though having "public" stills is somethime frightening when you see how some people redraw from them... I always felt more confident when i had distilled the solvent myself in a schlenk only me and my labmates handled.. But you don't stop progress

EDIT: anyway, for my personal use, I don't need extra pur solvents. The most "extrem" would be for random grignards and LiAlH4 reductions.

[Edited on 6-7-2008 by Klute]

I spent an hour yesterday playing with glassware, trying to compose a somehow reasonable solvent still with a resevoir as seen on the previous posts. I have a few ordinary variable reflux heads but the receiver seems to be problematic, almost having to consult a glassblower It would be a nice feature to have some distilled dry solvent waiting in the receiver, but it also should be possible to let the solvent flow back to the flask if having been stored for too long. This feature seems to demand a receiver with a three-way valve.

Considering the cost of waste disposal, and purchasing new solvents I have always been the type to recycle all of my solvents. The system I use is pretty simple it consists of a fractioning column mounted on whatever size RB flask is necessary for the volume of solvent being recycled on top of that is a 500ml solvent recovery flask with an Allihn condenser. I simply allow the solvent to reflux over a suitable drying agent in an argon atmosphere for approximately 24hrs at which point I drain the solvent off into its appropriate container with a constant flow of argon running over it (depending on solvent volume this can take several times). This setup works great and I have never had a problem with the purity of my solvents using it (Confirmed with GC/MS).

Here is a picture of the setup that I just put up today to recycle some DCM I had been storing for awhile. I first pre-dried the DCM over magnesium sulfate then filtered it into the 2 liter flask where it is now refluxing over P2O5. I will collect the purified solvent tomorrow over either fresh P2O5, or I am considering using 4A molecular sieves.

Thanks for the pic! I am definitavily getting more and more jelous of you guys

can you store your DCM over P2O5 without any discoloring? I guess it will contain some acidic impurities though?

Yes you can store the DCM over P2O5 without any discoloration of your solvent. The reason there is discoloration in the refluxing flask is due to the fact that even with pre-drying over MgSO4 there was still an excess of water, and I have a sneaking suspicion that there was a little bit of MeOH in the DCM as well thankfully the P2O5 took care of that for me .

I don’t think that there would be any acidic impurities in the DCM so long as it was completely anhydrous; although the possibility does exist hence I will be storing the DCM over 4A molecular sieves. I was personally surprised that DCM even had an azeotrope with water; I thought that it was far too non-polar to absorb any appreciable amount of water.

This entire procedure can be found on page 7 of the attached document. I of course made a few modifications to accommodate my situation.

Attachment: purification of solvents for electroanalysis page 7 DCM.pdf (213kB)
This file has been downloaded 2886 times

I have mounted a small solvent still with my Dean Stark. It works without any problems, i am currently using it to recycle some acetone. Actually I realized the sytem I was looking for is very similar to this, so I might consider getting a 29/32 dean stark and athermometer adaptor.

I attached a 600mm vigreux on a l three nack RBF, the dean starl on top, mounted with a short alhin condenser protected by a CaCl2 guard (not really necessay here). The exit from the tap was fitted in a thermometer adaptor, with the adequate joint (the same one I use when placing a gas admission tube for example), itself connected to a 500mL three nack RBF. The only inconvienment in that the receiver isn't pressure equilized, so it needs some optimization for distillations under argon (with a schlenk I suppose).

The pre-dried over K2CO3 acetone (600mL) is been refluxed over K2CO3 (~5g) for an hour to get close to equilibrium in the vigreux, then the dean stark stopcock will be slightly opened to give a low reflux ratio (no special volatil compounds here).


The whole setup:


The Dean Stark:


Reflux:


The pot:

Okay it is getting a little bit more clear now, if I understand correctly you have recycled solvent which you would like to dry in first place and that's why you're using this system.
Second thing is your recycled solvent might still contain another solvent and because of that it is better to gradually collect it?
I mean now you're telling that at your work they have a still on every floor for a different solvent.
Or do you mean you would like to add a mixture of solvents in the still and distill them batch wise and also dry at once.

My dean&stark is like below:



[Edited on 2-9-2008 by DNA]

No, no, not to that extent

But I keep all the solvents I use for extarctions and chromatography, once distilled off, in seperate bottle according to the main constituant: one mainly toluene, one mainly DCM, one mainly AcOET, etc

then, depending on the solvent, I do a couple washes (to remove most esters and alcohols off toluene or DCM for example), acids and alcohols from ethyl acetate, ex, then distill them int he still, with a little dessicant sometimes (mostly NaOH/KOH to destroy any ketones, K2CO3 fro acetone, etc). So the solvents are often of technical grade, containing <5% impurities, but sometimes even purer than before (toluene). All these can be used for chromatography (large consumption), extractions, or reactions that only require regular grade solvents.

What can be annoying are mixture forming azeotropes, or have very clsoe bp's, and that can't be seperated using washes or chemical means (methanol and acetone). These I keep for cleaning purposes mostly.


It's a bit of work, I've got dozens of used solvents bottles, but I only generate under 5l of organic waste every 2-3 months, compared to every day at work and it saves me alot of expense solvent-wise.


One day I'm thinking of setting up a larger still, a bit like Stoichiometric_Steve's one, that would turn 12/24H so that I ca ncatch up all my "to recycle'" work

[Edited on 2-9-2008 by Klute]

Storing DCM over P2O5

Ok, I've finally upgraded to the new fancy still heads like everyone now days




Hopefull this beauty is going to be up and distilling in a few days! The much larger volume will help me recycle all the used solvents that have been accumulating, and I will be able to prepare some rigorously dried solvents much more easily.

I'm going to figure out a way of connecting a schlenk or a RBF to the lower exit, to be able to distill the solvent in a receiver batch-wise aswell as having a constant supply of freshly distilled solvent.

Good point is I will also be able to use the Dean Stark to prepare "technical" solvents from the used ones at the same time. i will need to upgrade the cooling system though, as even after distilling acetone for a few hours the water heats up to over 30-35°C (roughly 15L in a cooler, with a small aquarium pump).

And the best thing is that I got for 25E

Who's a lucky boy then!!

I wasn't going to reopen this thread after getting these on the weekend, however given it has been, i'm going to gloat.
$20 for both!!!!, sometimes things are perfect, they are as new, even the rubber on the septum is unperished, i also got the reservoir for the top of the one on the left.

$20?

That's what John calls a better than stolen price; e.g. the bus fair to the guys house to break in and take it would cost more.

I believe the type of still head Steve has is called a Perkin's.

Here's the QuickFit site with a picture of their's and a description

I think items like these, the still heads, a Markham apparatus and pistol drying tubes fall into the "I'm turning into a glasswhore" catagory, which is great as far as this whore is concerned.

They're not using the stills at work? I have $20 here that will take them all! And all those nasty health hazard solvents in them.

Don't know if it's been mentioned, but CurlyArrow has a great section on anhydrous solvents and recycling

The comments are worth reading.

They're all talking about using solvent purification systems, which are essentially a stainless tube packed with alumina, and then maybe Q5 catalyst in another to deoxygenate the solvent. I've seen photos of these in labs whilst google searching, some labs now have a big bank of them all lined up with colourful taps to drawn off the solvents, through a spout or septum.

When it comes down it to, they're just metal chromatography columns with no detector and far lower pressures (~10 - 15psi); flash columns under a blanket of argon. I'd be willing to bet they could be put together at home well below the $30k price tag of the commercial options (albeit, that's for arrays). With the pressure being that low, perhaps borosillicate tube could be used; e.g. old flash columns. I think the pressure is simply applied by running some of the inert blanket into the resevoir.

Also working in our favour, when considering a home brew variation, is that we don't have 30 students and members of staff continually pouring solvent off, everyday. So everything gets smaller. A roll of spooled, thin stainless packed with alumina for each solvent?

These columns are getting ppm's of water very close to distillation from sodium, without the fireballs and explosions.

He also discusses using 3 / 4A molecular sieves for similar work.

I too have seen a number of pages describing CaH as the preferred drying agent for DCM. If anyone has some, shoot me a PM, because my supplier doesn't, and I could use a bit.

With regards to stolen deals, I just picked up an item that costs $20k to have serviced, new, for two beers.

[Edited on 25-8-2010 by peach]