Today, I went into lab to run a distillation. As I was looking around for a “pig,” (you know, one of these guys:
or “cow-tail,” or “spider,” or some other member of the animal kingdom. I’ll consider helping the push for “Lady GaGa Claw” to be a commonly associated name with this thing, but I’m going to need some help… )
and, whilst rummaging, I came across a little borosilicate riddle:
Of course, I hadn’t seen a distill head like this, but upon later inspection of the Aldrich catalog, it’s nothin’ fancy. Indeed, my lab is new enough, and decently stocked, thus I’ve yet to see anything truly esoteric or crazy old. Anyway, if you want to play the guessing game, give it a shot. Who’d put a jacket over a vigreux column, anyway…
If you don’t know and would like to find out, or, if you’d like to find why this arbitrary guessing game is a little more relevant to today’s post, check below the jump
Well, it took a minute of me pondering in lab, and for a split second I contemplated breaking the damn thing to test my hypothesis, but, I figured that the vigreux column was under a vacuum, held by the outer, “extra” layer of glass. Why, you ask?
Well, if you’re unfamiliar with distillation, general setups look like this:
Hot vapor rises, the vapor cools and returns to liquid in the condenser, and then drips into a collection flask or container at the bottom. The addition of the spiky looking Vigreux column adds additional surface area and generally helps with separating compounds with similar boiling points. However, what this little graphic doesn’t tell you is that the temperature difference between the top of the head, where the thermometer reads, and the temperature of the heatsource at the base can be pretty big.
So, to combat the temperature difference, it’s not uncommon to insulate the distill head with layers of aluminum foil, and maybe sandwiching paper towel or cotton between the layers, thereby giving a more even heating from base to the beginning of the condenser, and furthermore, eliminating the problem of scorching your product before it even makes its way over. Permanent, solid insulation is great for reproducability and smooth temp. increase, and insulation by vacuum is pretty much the best/easiest way to go about it (same way your Dewar, double-walled mug, or Thermos works). Nifty, right?
Here is where my problems from yesterday start. Despite ample insulation of a short-path head via the cotton-aluminum method, progress was slow going. The temperature would rise, some distillate would come over, and then the temperature would dip back down. By wrapping my hand around the head or ever so slightly repositioning the foil closures, the temperature would spike again, and drop again. This is no good for business of any kind, especially distillation.
As dinner was fast approaching last night, I pulled the plug on the rollercoaster distillation, with hopes of trying again with the lovey glass posted above. All the better: today I’m poised to distill more, better, and looking much less like 1960’s era NASA