Greetings fellow nerds.
In previous videos i've shown the dean stark apparatus.
A very useful piece of equipment that lets you take advantage of azeotropes that phase separate to remove one of them from a mixture.
This is especially useful for removing water from solvents like toluene or xylene.
For a complete review, you can check my original video which i've linked in the video description.
Briefly, the dean stark apparatus is installed onto the boiling flask containing your mixture and a condenser connected on top.
Vapors travel through the apparatus and condense where they phase seperate into a lighter and heavier phase.
The lighter phase overflows flows back into the boiling flask where it will boil out with more of the heavier phase, usually water.
The water collects in the trap as the distillation runs.
This is the traditional dean stark apparatus and this mode of operation is also known as light return mode
since we're returning the lighter phase while keeping the heavy phase.
Sometimes though we want heavy return mode, where the heavy phase is returned.
For example, in purifying very high boiling organic substances using steam distillation.
I did this when i was purifying 7-hexyl-7-tridecanol.
A lot of herbalists also use this to extract essential oils.
But a traditional dean stark apparatus doesn't actually have this functionality.
So to do this i had to improvise my own heavy return dean stark apparatus from various pieces of lab equipment.
I didn't buy a specialized apparatus because i didn't think i was going to need it enough.
Well, now that i'm doing a bit more organic chemistry
i've decided that improvising my own apparatus everytime was too cumbersome as well as detrimental to the chemistry
since there is a huge amount of deadspace in the apparatus where i could lose product.
My apparatus also needs to be prefilled with carrier solvent and this also adds to the waste and contamination of our reactions.
Now a perfectly specialized unit is rather costly, and i was never going to buy that.
But there is a much cheaper type that sacrifices a bit of effectiveness but still offers a powerful tool for the amateur.
It's called the clevenger apparatus.
That name always makes me laugh, it sounds like a superhero pornstar.
Anyway, let's have a look at the design.
The clevenger apparatus has a stopcock to conveniently drain the trap contents.
The boiling flask is attached to this arm and the vapors travel up the arm
and to the condenser column where they condense back into a liquid and fall into the trap.
All of this is just like a traditional dean stark apparatus.
The interesting part is this arm that connects the lower part of the trap to the vapor carrying arm.
Rather than overflowing from the top like a traditional dean stark apparatus, the condensate overflows through this arm.
You'll also notice that rather than connecting as close as possible to the bottom, the arm is connected to the middle of the trap.
This actually allows us to use this as both a light return or heavy return dean stark apparatus depending on how we process the condensate.
Now i know this is almost impossible to understand without some visual examples so let me show it in use.
So here is a boiling flask containing some organic solvents and water and i've connected up the clevenger apparatus.
On top is the condenser column.
Now we just boil the mixture and start condensing.
Looks like i got a bit of foam over but i'm not worried, this is just a demonstration.
Now the trap will fill and as said before, the lower arm channels the distillate back into the boiling flask.
As you can see here the lighter phase is flowing back while the heavier phase collects in the bottom below the return arm.
If you drain the heavier phase then this operates exactly like a traditional dean stark apparatus in light return mode.
So you conveniently have a dean stark apparatus when you need it.
But of course, you can already use a traditional dean stark apparatus for that.
What if we want heavy return mode, how do we collect the lighter phase?
Let me reset the apparatus this time using lots and lots of water so it's easier to demonstrate.
I've also prefilled the trap with water but this is optional, you can run the trap empty and this will still work,
a big advantage over my improvised apparatus.
Now let me start the boiling.
And there we go.
As you can see the distillate is collecting in the trap and phase separating.
The lighter phase is filling the trap while the heavier phase is channeled up the return arm and overflows over.
The lighter phase cannot overflow until it fills enough to reach the lower return arm.
This is an important point about how the clevenger apparatus works.
Eventually if you have enough of both phases, they'll reach equilibrium at the return arm.
At this point both phases overflow and return to the boiling flask.
If either of them distills more, then it's returned more and the cycle reaches equilibrium.
It doesn't matter where you start or what ratio of either phase distills.
Anyway, collecting the lighter phase is a bit unwieldy.
You first drain the heavier phase, then quickly swap out the collection container and drain the lighter phase.
You then take the heavier phase and pour it back into the apparatus through the condenser column.
At which point you can continue the distillation as usual.
Not exactly elegant, but at the same time, miles better than my improvised apparatus which actually didn't have a means of collecting as it ran.
You had to actually shut down everything, collect, and then restart or use very large collecting traps.
This clevenger apparatus does a much better job.
So overall the clevenger apparatus is a very convenient dual mode form of the dean stark apparatus.
You can use it exactly like a dean stark apparatus in light return mode by draining away the heavy phase as it collects.
And with a bit of manual labor, you can use it in heavy return mode by draining both phases,
manually returning the heavy phase, and keeping the lighter phase.
A special note if you're buying this.
A lot of clevenger apparatuses have the return arm connected near the bottom of the trap.
These such apparatuses can only be used in heavy return mode.
The upside is that without a bottom half to fill, it's easier to collect the lighter phase without having to manually return the heavy phase.
But if you want to a dual use apparatus, you need to find one that connects the return arm above the bottom like this one.
On the other hand, if you're an herbalist or otherwise don't need light return mode then such an apparatus will probably be desirable
since it saves on the labor of monitoring the apparatus and returning the heavy phase.
But for the amateur chemist, i recommend getting a dual use apparatus like this one to access the broad range of experiments you'll encounter.
Anyway, there you have it, the clevenger apparatus.
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