Author Topic: Differences in temperatures???  (Read 1218 times)

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Just4Fun

  • Guest
Differences in temperatures???
« on: December 18, 2003, 05:42:00 AM »
SWIM who is new to chemistry recently performed a distillation of an essential oil in a dream and in that dream he keep notes of all the temperatures, times.  One of the confusing parts of that dream was determining what temperature they were looking for that is commonly referred to by other bees.

SWIM noticed that using a 29" vacuum their essential oil came over at and showed a thermometer reading of 61C.  The oil bath had a range of 109C - 120C with no change on the thermometer temperature.  SWIM now believes after this experiment that the temperature other bee are referring to is the thermometer temperature when they are referring to the temperature their distillation came over at.  If SWIM is wrong please advise.  SWIM has a question though, is it normal for the oil bath temperature to be able to fluctuate 10-15C without affecting the distillation temperature.

Second, When performing an Rxn and one is to hold the temperature to 104C, what temperature is watched?  Is it the internal temperature of the mixture?  If so what is the best way to measure that temperature?  Can a thermometer be used and left in the Rxn?  Also, Is the internal temperature hotter than the oil bath temperature?

SWIM has searched TFSE extensively and has learned allot but really needs someone to clarify these silly question.

Thanks

Antibody2

  • Guest
what you are measuring is the temperature of...
« Reply #1 on: December 18, 2003, 09:04:00 PM »
what you are measuring is the temperature of the vapour during a distillation. Think of it like this: water boils at 100C (at atomospheric pressure) regardless of the temperature of the heating element. Your oil will also have a fixed vapour pressure (temp at which it boils) for a given amount of vacuum.

out of curiosity what oil is coming over at 61C with only 29" vacuum? That BP strikes me as being way low for any the oils that bees commonly distill.

If the other question regarding a reaction temp of 104C is refering to methylamine production from ammonia chloride and formaldehyde, then they are refering to the actual liquid temperature (not the vapour) and your thermometer needs to extend all the way into the reactants.


Just4Fun

  • Guest
Thanks for the response :) The oil SWIM was...
« Reply #2 on: December 19, 2003, 01:58:00 AM »
Thanks for the response :)

The oil SWIM was distilling was sas.  I heard he hooked up a vacuum gauge to a brand new Robinair 15600 and the gauge was reading @ 29 in.  He though that the 15600 could pull a > 29 in vacuum so maybe the gauge from a auto parts store is in accurate. To test the oil distillation he put the final product in the freezer and only got a small substance the size of the tip of a felt marker to freeze. the rest is still liquid.

What do you think about his situation?

homeslice

  • Guest
I'll just try to answer the simple questions...
« Reply #3 on: December 19, 2003, 08:38:00 AM »
I'll just try to answer the simple questions heh.
On the chart on the page from rhodiums site it says that 29 inches of hg should distill safrole at about 125, correct?

https://www.thevespiary.org/rhodium/Rhodium/chemistry/safrole.distillation.html


Swim gets confused himself by this chart as he has read about safrole coming over at 60ish?
Also swims read on some post along his journeys at the hive that the oil bath is about 15-20 degrees hotter than the inside of the distillation flask, which is about right as swims safrole came over at 108c and his bath was about 120, but when his bath dropped to like 117 it stopped coming over. Also the bath temp can be very high and still have a low distillation temp but this isnt the best way to distill.


FlaskGenie

  • Guest
Two Cents
« Reply #4 on: December 20, 2003, 09:33:00 AM »
Swim has been dreaming while waiting for a new vac pump.  He is dreaming of fractional dist of nitromethane from RC Fuel.  Swim is measureing 3 temps.  OIl bath, in flask liquid and Temp at 3way.  Just throwing this out there so yall can see how these temps vary in swims dream.
Firs fraction is Meoh.  Bath is water and is kept at 60-74c. vapor is ~64, Flas liquid is 66c.  I increase bath to ~90 and flask stays constant 66c w/ vapor vairing little.  When bring over nitro fraction there is more variables.  First switch to oil bath.  When doing nitro oil bath varies from 104c to 140c.  During this range of oil bath temps, flask temp stays @ 104 to 107 w/ vapor gen @101.  There was a little azatrope fraction along the way but my point is the oil bath tem varied over 30 degrees w/o greatly effecting the flask temp.  The only reason I bothered reasing oil bath temp was to start the nitro coming over when it slowed.  And increasing the oil bath temp did kick it back in.  Hope these notes help