Reduced pressure distillation question and smoke?

So, I went onto distilling an essential oil for the first time. Oil of wintergreen. It BP is 220 C and my current vacuum, while my chemglass is in the shop for overheating, looks to be pulling about 100 torr. Not all that good, but its what im working with at the moment. Everything seemed to be sealed up nicely at all the joints, and from the nomograph in zubricks manual it should have been coming over around 140ish C.

I started to get something around 100C and just kept climbing to 110C then 120 C and then to 13o C and 140C and going up to 150ish C. All the while, I had distillate coming over. I did not have a pause in-between temp ranges. I figured all the early temps were foreruns, but it just kept climbing and carrying over distillate.

So, I cut it off. Then I cut the hotplate off and removed it from the oil and then a couple minutes later cut the vacuum off.

I got a light, white smoke or steam in the boiling flask right after I cut off the vac. Ive never seen that before...any explanation?

I feel it was sealed up nicely. It held the vacuum constant after I turned the vac off before starting up the distillation confirming I had tightly greased seals. The gauge did not budge after 5-10 minutes after pump was cut off.

Should my temp constantly rise like 40 degree C and dropping distillate the whole time as its climbing? That would be new to me, but I am aways learning something new. It was on a slow drip, so I wasn't cooking the heck out of it. It was like a drop every 1-2 seconds.

Thanks

I am in no way defending my guess, just offering ideas;
your bourdon gauge may not indicate pulsing pressure variations due to its time constant,
since its only a guess, one way that I can imagine testing for this potential problem could be;
add a funnel with the large end covered in Al or PE kitchen foil/film to your vacuum system
(small end of funnel connects to vacuum line)

pulsing at audio frequencies will make the funnel act like a loudspeaker, so pulsing can be heard.
pulsing at lower frequencies can be checked for by touching the foil or film and feeling for vibrations.

...................................................

Without adding a reflux condenser, and using a packed (Hempel) column or similar complications.
I guess that the best fractionation will be achieved by your setup when the boiling rate is maximum
(provided that there is stirring there should be no hot spots)
and the insulation is adjusted to give just enough reflux in the column to allow some product to come over.
As this is exactly what you seem to have done, I can't think of any improvement.

................................................

One other possibility - a miscible impurity, possibly forming an azeotrope ?

Quote: Originally posted by Dr.Bob

You should allow the apparatus to cool before releasing the vacuum. The smoke was possibility from the oil vapors reacting with the air that leaks in once the vacuum is turned off or released. In the case of air reactive materials, this can start a fire in the rbf or condenser. So best to turn off the heat, let the apparatus cool some under vacuum, then bleed inert gas in, if possible, as the vacuum is released, or at least make sure that the flask has cooled. A friend had a co-worker injured when they opened a large distillation from vacuum to air while very hot, and the material in side violently reacted. Not a common problem, but one to be aware of. This is especially true of many essential oils, flavors, and any material with aldehydes, double bonds, or other oxidizable materials.

Quote: Originally posted by Sulaiman

I am in no way defending my guess, just offering ideas; your bourdon gauge may not indicate pulsing pressure variations due to its time constant, since its only a guess, one way that I can imagine testing for this potential problem could be; add a funnel with the large end covered in Al or PE kitchen foil/film to your vacuum system (small end of funnel connects to vacuum line) pulsing at audio frequencies will make the funnel act like a loudspeaker, so pulsing can be heard. pulsing at lower frequencies can be checked for by touching the foil or film and feeling for vibrations. ................................................... Without adding a reflux condenser, and using a packed (Hempel) column or similar complications. I guess that the best fractionation will be achieved by your setup when the boiling rate is maximum (provided that there is stirring there should be no hot spots) and the insulation is adjusted to give just enough reflux in the column to allow some product to come over. As this is exactly what you seem to have done, I can't think of any improvement. ................................................ One other possibility - a miscible impurity, possibly forming an azeotrope ?

Quote: Originally posted by Sulaiman

I just had a terrible thought of the foil failing under maximum vacuum I don't have (and don't want) experience of sudden catastrophic vacuum failure with hot glassware and reactants, but I bet its not funny, so maybe try with just the pump, trap (if any) and funnel ?

I just tried Al foil over a 100mm dia glass funnel attached by a short length of tubing to my little piston vacuum pump,
usually this pump gives -75 to -80 kPag, 20 to 25 kPa (150 to 190 mm Hg) absolute pressure.

The foil held up ok,
I could not hear or feel any diaphragm/foil vibrations other than those that I attributed to the pump,
so it is certainly not a sensitive test

EDIT: Now that I think about it, I will not be surprised if you have a negative result,
even if the pressure fluctuates by say +/- 10%, or even multiplied or divided by two,
the absolute pressure change will be negligible compared to atmospheric pressure,
so very little diaphragm movement is expected.
(seems like just one more of my dumb 'brilliant' ideas


[Edited on 1-11-2017 by Sulaiman]