I'm having problem distilling, and not sure whats going on?
So charged the smallest flask I have, (100ml) with 20ml of oil and started up my plate/stirrer, got my oil bath going.
When I had done a B.P. test the oil in the test tube didn't start to reflux till after 200c and didn't start to boil till almost 230c at which time it
started darkening. When I tried to distille it was already darkening prior to reflux.
The oil was in a constant stated of reflux in the pot unable to make its way to the condenser. it wasn't till the temp on the bath was over the 230c
mark that it stared coming over, however the thermometer was reading 150c. I was having a hard time holding the temp.
Why was it Refluxing like that and did I just scorch what I was trying to distille?
Is there a setting the stir bar should be set at in relation to how hot your distilling?
some help would be so appreciated as I want to understand and correct things before I try my hand at separating mixtures of volatile's.
I was using pipe insulator at the still head and this time it melted as well as oil dripped out the pan screws onto part of the plates surface, could
of been bad. I'm guessing it got way to hot.bbartlog - 10-9-2014 at 15:51
You don't say what your oil was, but a lot of organic compounds will start to decompose at such temperatures. This is why people do vacuum
distillation (and/or steam distillation).
It's not surprising that the oil bath would be higher temperature than the flask and/or still head, after all, a lot of heat has to flow and keep
flowing through the glass (which is a lousy conductor) in to the oil and from there pass up in to the still head / adapter, before everything is
holding enough heat for something to pass over at such an elevated temperature.
I have also melted pipe insulator (which is OK for 100C or lower distillation, but not for this); I did it while distilling ethylene glycol. You can
wrap the still head in a combination of cloth and/or foil, which should be good up to 250C, but in general I would suggest using a vacuum and lower
temperatures instead. Your setup sounds kind of risky. Actinium - 10-9-2014 at 16:03
thanks for the reply.
I have a very basic setup, no point to going out and spending big bucks on all the bells and whistles if you can't even use basic tools properly.
As far as the oil I'm still trying to figure out exactly the contents.
I'm very reluctant on using the aspirator I have seems unreliable for myself.
Should stirring be hard over a certain temp or volatility?
Would insulation be a good Idea?
What would you recommend for high temps to hold the bath?
idk, I like steam distillation as it's mild and easy but hate letting problems keeping me from learning.forgottenpassword - 10-9-2014 at 23:58
Put petroleum jelly on all of the joints and wrap a lot of aluminium foil around the joint of the flask, the entire still head and thermometer joint,
and the joint to the condenser. Immerse the flask deeply in your heating bath so that almost the whole of the flask is heated.
There shouldn't be such a large difference in temperature between the heating bath and temperature in the flask. It suggests that you are heating it
too quickly. Try a more gradual heating with strong stirring of the flask contents at higher temperatures.
Even if you only distill a few ml of each component, and char the rest, at least you will have accurate information as to the boiling points.
I assume that you are not using a fractionating column. If you are, don't.
[Edited on 11-9-2014 by forgottenpassword]forgottenpassword - 11-9-2014 at 03:56
He is trying to determine the boiling points as a means to identify the fractions. Distilling at an unknown pressure would not be helpful in this
instance.aga - 11-9-2014 at 04:50
I found Petroleum jelly (vasolene) to be a bad thing with distilling oils etc.
The trick seems to be to use a very tiny amount, so as to get an extremely thin film of the stuff on the glass joint.
Mine's kept in a 2ml syringe.
Almost a year now and there's at least 1ml left.Praxichys - 11-9-2014 at 11:13
Vaseline is useless. It melts completely just above room temperature and will contaminate everything. Even distilling water with Vaseline in the
joints leaves dH2O with an oil slick on top. Not good!
Yes, any joint grease is only applied in very tiny amounts, just enough to wet a 5-10mm band (24/40) of ground glass near the outside of the joint
when it is put together and gently rotated to ensure no paths to the outside exist. Such a tiny amount is used, a $20 tube of real fluoro grease is a
good investment and will last many years.
You don't really need joint grease for anything but air sensitive, vacuum, or quantitative distillations. Usually the material you are distilling gets
into the joints and seals it anyway. Unless I am are working with something super nasty, I usually don't even bother. There IS a higher propensity for
the joints to freeze, but I have been doing this for years and never had problems getting anything apart with the clever application of heat.
Check out my YouTube channel. I distilled about 30ml of chromyl chloride in a 24/40 setup with no joint grease. It fumed a bit at the joints until
they self-sealed with CrO3. I also distill halogenated solvents without grease to avoid contamination, since many will dissolve fluoro grease. Joint
grease is hell to remove from some extracted organics. Just make sure you have good ventilation because a very small but detectable amount escapes
through the joints.
Removing vaseline is easy. It dissolves in basically everything nonpolar. Wash your glass with mineral spirits, naphtha, lighter fluid, "white gas",
laquer thinner, etc. It will come right off. If there is a lot in there, use a hair dryer to melt the bulk of it out first.
Removing real joint grease is more challenging since it retains viscosity at high temperatures and does not dissolve in many solvents. However, I have
found that the Dow stuff slowly dissolves in nonpolar solvents like toluene, naphtha, chloroform, trichloroethylene, etc. If soaking is not an option,
pulling a rag soaked in solvent through the apparatus with a wire is usually enough to do the trick.
Between distillations, I just wipe it off the joints with a clean rag after rinsing the glassware.
[Edited on 11-9-2014 by Praxichys]Actinium - 12-9-2014 at 14:58
thank you for all the replies and helpful tips.
Need to get another deep pan since I scorched the last one. I have the pots neck, thermometer adapter and condenser joints, wrapped in cloth and
insulated with foil. seems to help alot.
I'm planning on using the claisen packed with glass wool on the next run to try and further purify/separate the fractions.
As far as steam distillation, is there a way to identify fractions based on how much below or over 100c the distillate comes over? or do you have to
know before hand. I find it truly fascinating and awesome that you can do so much with water in such a simple and gentle manner.forgottenpassword - 13-9-2014 at 10:00
I am not having much luck with TLC, the main problem being seeing the spots after development.
You need a jar with a few crystals of iodine in the bottom. Place your dry plate in the jar, close the lid and wait until the spots have developed.
Iodine is the easiest, cheapest, and most general stain for TLC. Actinium - 13-9-2014 at 15:49
that will make two fun projects, as Iodine is Regulated with no threshold in the U.S. so Guess I would have to make a trip to the Pharmacy and extract
it. Or Synthesize it.Amos - 13-9-2014 at 18:03
Depending on how much you want, and if you mind going on record for buying it, you can buy pretty large quantities of potassium iodide online for a
reasonable price.
