Sciencemadness Discussion Board - Thermometer and distillation

Thermometer and distillation

Housane - 6-6-2020 at 12:43

Hi all,

I have a thermometer adaptor for my jointed distillation setup but I found that my 110c glass thermometer didn’t fit into the adaptor, is there anything I can do to fix this?

Regards

Housane

Ubya - 6-6-2020 at 13:14

the only thing you can do is change the adapter or change the thermometer.

i bet you bought a thermometer adapter from china like this one

Housane - 6-6-2020 at 13:50

No it was this one https://www.betterequipped.co.uk/science-equipment/jointed-g... what sort should I get?

Ubya - 6-6-2020 at 14:20

that's thin!
is the hole where the screw cap is the same inner diameter as the tube?
if yes you need another thermometer

Sulaiman - 6-6-2020 at 16:12

As a Chinese thermometer adapter is cheaper then a good thermometer,
I'd buy a new adaper,
the adapters with a white cap are larger than red or blue.

Your red adapter can be used with a length of glass tubing for various purposes.

you could consider a different type of thermometer adapter
https://www.ebay.co.uk/itm/14-19-24-Joint-Lab-Glass-Thermome...
Chemically resistant, suitable for thermometer or thermocouple
but slow to respond to temperature changes and you need to choose the length wisely.

Housane - 6-6-2020 at 19:12

Thanks Sulaiman, I will look into that, why would you want to suspend a glass tube in your distillation setup?

Sulaiman - 6-6-2020 at 20:08

. seal one end and insert a thermocouple

. draw one end to a fine nozzle to use as an air leak for anti-bumping during vacuum distillation

. withdraw a small sample from the flask during an experiment or distillation for analysis

. bubble gas through the flask contents (not during a distillation)

earpain - 6-6-2020 at 22:37

Quote: Originally posted by Sulaiman

. seal one end and insert a thermocouple

. draw one end to a fine nozzle to use as an air leak for anti-bumping during vacuum distillation

. withdraw a small sample from the flask during an experiment or distillation for analysis

. bubble gas through the flask contents (not during a distillation)

Good ones! Also: Port for tube coming from steam generator for proper steam distillation.
Sulaiman, BTW I have tried to insert a thermocouple into a thermometer sized glass tube, with various liquids as thermal conductors and have had no success. Glycerin, mineral oil, etc. Very long response time and the glass insulates so much of the heat away.
Maybe it's that my K type thermocouple if terminated via manual twisting....although with no glass container it works very well.

Inside of oil+glass the delay is roughly 30 minutes!
I have not tried using an actual thermometer capillary body. Could you elaborate on how you achieve this, in particular with the 'hovering near vapors' setup in a 3-way distillation adapter?

Mateo_swe - 7-6-2020 at 05:22

I have bought a thermometer adapter just like the one Sulaiman suggested.
However it was not of good length to place the end of the tube at the entrance to the condenser.
I think i will try shorten the tube with a propane torch so it will be of optimum length.
I have seen this setup, thermometer tube + K-type thermocouple and LCD display unit used in several videos on YT, chemplayer uses them all the time.
The K-type sensor and LCD display unit is very cheap on ebay, about 3,5 Euros.
The glass temperature adapter is about 4 Euros, also quite cheap.
I dont know how accurate this method is but probably enough for ordinary use.
I havent used my setup yet and the delay i see earpain write about worries me a little.
I hope to test out the setup soon.

Sulaiman - 7-6-2020 at 06:19

@earpain : I have a 24/29 100mm stem adapter that is just nice for immersion via the side neck of 3-neck 500ml RBFs.
A thermometer with some cooking oil has thermal lag of a minute or two maybe, but definitely not 30min.
(maybe because it is immersed in the liquid?)

I bought a similar shorter adapter to measure vapour temperature at the top of a column - but its too short so never actually used.
(hence the "choose length wisely" comment)

I've been using cheap Chinese thermometer adapters as pictured above for vapour temperature measurements.

I tie a string to the thermometer and a stand clamp just in case the thermometer slips, so far not needed but better safe than sorry.
_______
I've been having a new problem,
near the end of a distillation in my 5l flask in a heating mantle,
the mantle heats the exposed glass so much that the thermometer in a side neck of the rbf gets overheated,
So overheated that just a few days ago I popped the bulb of the thermometer!
I don't know how to overcome this problem yet.
=====
@Mateo_swe : unless you spend quite a lot of money,
thermometers and thermocouple temperature meters can be inaccurate by quite a few degrees.
Use a liquid with a known boiling point (e. g. water) to calibrate your thermometer in the position that it will be used in during distillations.

P. S. My 100mm stem adapter was poorly ground so did not fit well,
a couple of turns of plumbers ptfe tape fixes this problem.

[Edited on 7-6-2020 by Sulaiman]

XeonTheMGPony - 7-6-2020 at 07:20

http://alchemylabsupply.3dcartstores.com/Thermometer-Adapter...

Sulaiman - 7-6-2020 at 07:37

Excellent!
I was considering using ptfe in the form of an overhead stirring bearing (I use one for my stirrer at home in UK)
but the eBay versions are only for 7mm diameter, and the clamping is marginal.
I'll look around for similar in 19/26
Thanks!

[Edited on 7-6-2020 by Sulaiman]

Housane - 7-6-2020 at 09:00

Thanks for all the help, I will look into getting the correct length probe style one

earpain - 8-6-2020 at 07:08

Quote: Originally posted by Sulaiman

@earpain : I have a 24/29 100mm stem adapter that is just nice for immersion via the side neck of 3-neck 500ml RBFs.
A thermometer with some cooking oil has thermal lag of a minute or two maybe, but definitely not 30min.
(maybe because it is immersed in the liquid?)

I bought a similar shorter adapter to measure vapour temperature at the top of a column - but its too short so never actually used.
(hence the "choose length wisely" comment)

I've been using cheap Chinese thermometer adapters as pictured above for vapour temperature measurements.

I tie a string to the thermometer and a stand clamp just in case the thermometer slips, so far not needed but better safe than sorry.
_______
I've been having a new problem,
near the end of a distillation in my 5l flask in a heating mantle,
the mantle heats the exposed glass so much that the thermometer in a side neck of the rbf gets overheated,
So overheated that just a few days ago I popped the bulb of the thermometer!
I don't know how to overcome this problem yet.
=====
@Mateo_swe : unless you spend quite a lot of money,
thermometers and thermocouple temperature meters can be inaccurate by quite a few degrees.
Use a liquid with a known boiling point (e. g. water) to calibrate your thermometer in the position that it will be used in during distillations.

P. S. My 100mm stem adapter was poorly ground so did not fit well,
a couple of turns of plumbers ptfe tape fixes this problem.

[Edited on 7-6-2020 by Sulaiman]

I found an old thread I believe you were a part of. It was a bit of a fierce argument regarding the question: Can an electrically conductive material be used instead of cooking oil in such a set up:
e.g. Hg, solder(tin, Pb, silver, all that)Galllium, or simply thermal paste.

It seemd the consensus was that it would not matter. When you set up an immersion probe for your 3-necked flask, do you make the glass tube yourself? Or do you use a broken thermometer capillary?

Also: Technically, according to the spec sheets I believe you linked me to, a thermometer cannot possibly rupture from too much heat. There is an overflow resorvoir on top that's measued specifically to make sure of this. Of course, this would be a NIST type-A or similar.

Thanks for your advice

Sulaiman - 8-6-2020 at 08:14

I would not use mercury as it can form amalgams with some of the constituents of the thermocouple alloys.

Thermocouples do not generate a voltage across the junction,
the voltage is due to temperature gradients along the wires (Seebeck effect)
so in theory you can have any number of dissimilar metals in series at the measurement temperature with no change in performance.
Some members with more direct experience than me reported that this may not be so simple so I bow to their experience.
I have had erroneous readings from bare-wire Thermocouples in water - not sure why
(I suspect electrolysis is involved)

Although pastes such as heatsink compound have good thermal conductivity,
liquids can transfer heat by convection currents.
I've not tried heatsink compound as it is messy stuff.

My immersion probe is just a commercial borosilicate thermometer adapter / pocket, with a thermometer and cooking oil as I described above.

The thermometer that popped recently was a red liquid (presumably alcohol) in glass type from a Chinese distillation kit.
It had a bubble at the top but it still exploded!

I doubt that wires would fit through the very fine capillary bore of a thermometer.

earpain - 8-6-2020 at 13:01

Quote: Originally posted by Sulaiman

I would not use mercury as it can form amalgams with some of the constituents of the thermocouple alloys.

Thermocouples do not generate a voltage across the junction,
the voltage is due to temperature gradients along the wires (Seebeck effect)
so in theory you can have any number of dissimilar metals in series at the measurement temperature with no change in performance.
Some members with more direct experience than me reported that this may not be so simple so I bow to their experience.
I have had erroneous readings from bare-wire Thermocouples in water - not sure why
(I suspect electrolysis is involved)

Although pastes such as heatsink compound have good thermal conductivity,
liquids can transfer heat by convection currents.
I've not tried heatsink compound as it is messy stuff.

My immersion probe is just a commercial borosilicate thermometer adapter / pocket, with a thermometer and cooking oil as I described above.

The thermometer that popped recently was a red liquid (presumably alcohol) in glass type from a Chinese distillation kit.
It had a bubble at the top but it still exploded!

I doubt that wires would fit through the very fine capillary bore of a thermometer.

Sorry I wrote that reply out of order, cooking oil, understood =D

Your response here is clearly a meta-distillation of years of thinking/re-thinking. Very valuable.

Amusing to imagine myself trying to thread a single strand or two of wire into the barely visible capillary column of a thermometer.
-but-
I recently read about the method used for filling such thermometers with Hg circa 1900. Heat the bulb, as it's cooling it sucks in the Hg, repeat, seal off.
Perhaps i'll try that with electronic solder! And then that would conduct thermally, and electrically with a K type twist at the very top.
Cheers

Sulaiman - 10-6-2020 at 22:49

@ XeonTheMGPony ... I found a temporary fix for the overheating thermometer problem,
a few turns of silicone rubber tubing, carrying water from the condenser, wrapped around the thermometer adapter.

The lower thermometer now reads 100.6
which is what I got when I calibrated it in boiling water - so the fix works really well,
shown here (see the red arrow) distilling some water
and calibrating my new/replacement thermometer (top of column) (photo on right hand side)
100.8 ... not bad for a RM17 (USD4) 76mm immersion mercury thermometer.

Click on photo to enlarge it.

P.S. I was impatient with this setup and did not attach the 'safety strings' to the thermometers.

[Edited on 11-6-2020 by Sulaiman]

Refinery - 13-6-2020 at 07:33

This is an amateur question, but:

When distilling for ex acetone, it boils at around 56 NTP, but when distilling proceeds, the temp can raise up to 70-80C. Is this because the heating device heats up the claisen head, because what I'm getting is still pure acetone which does not form clumps when dried with CaSO4. The other components are water (100C) and stuff that boils at 150 and 200C approx and they do not form azeotropes.

Naturally I'm pushing the distillation to about as much as my condenser can handle, because pulling over even smaller volumes of acetone would take an entire day and contamination is not an issue with wide BP gaps.

wg48temp9 - 13-6-2020 at 12:17

Quote: Originally posted by Sulaiman

I

Thermocouples do not generate a voltage across the junction,
the voltage is due to temperature gradients along the wires (Seebeck effect)
so in theory you can have any number of dissimilar metals in series at the measurement temperature with no change in performance.
Some members with more direct experience than me reported that this may not be so simple so I bow to their experience.

Contact between different metals does generate a potential difference between them. Its even possible to measure the potential electrostaticaly by charging a metal plate capacitor. Then separating the plates to increase the voltage to make it measurable with a sensitive electroscope. (from memory of an old electrostatics book I read).

Its also true as you suggest that the temperature difference along a wire also produces a potential difference along the wire.

I don't know which or if both are responsible for the measured voltage in thermocouple temperature gauge. I suspect the voltages along the wires even composed of different metals cancel but I was unable to find a good/reliable reference confirming that.

Here is a hyperphysics link explaning the contact(junction) potential. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/tcoup.ht...

SWIM - 13-6-2020 at 12:42

Quote: Originally posted by Refinery

This is an amateur question, but:

When distilling for ex acetone, it boils at around 56 NTP, but when distilling proceeds, the temp can raise up to 70-80C. Is this because the heating device heats up the claisen head, because what I'm getting is still pure acetone which does not form clumps when dried with CaSO4. The other components are water (100C) and stuff that boils at 150 and 200C approx and they do not form azeotropes.

Naturally I'm pushing the distillation to about as much as my condenser can handle, because pulling over even smaller volumes of acetone would take an entire day and contamination is not an issue with wide BP gaps.

Sounds about right. When the heat is way up the acetone vapors get superheated before they get to the condenser.

For close separations there ought to be a bit of distillate suspended on the thermometer.
This little drop indicates you haven't superheated the vapors and the thermometer reading is accurate.

But of course in your case you know whats in there and the separation is an easy one, so an accurate temperature is not all that important.

Sticking a distillation column or bump trap between the flask and the Claisen would probably reduce the superheating, but probably wouldn't make the separation much better, just slower.

Refinery - 13-6-2020 at 12:59

Indeed, if I were to do a separation distillation, I would use column, slower speed and even apply reflux. This is a case sensitive matter.

Just had to clear out this thing. Obviously the boiling point of acetone is only the minimum temp of vapor temperature until it turns into a liquid. I guess the upper limit is where it decomposes into other molecules.

Abromination - 13-6-2020 at 15:12

@earpain: I have ruptured 2 thermometers before, they are most certainly capable. Both popped while measuring the temp of an oil bath.

Eddie Current - 13-6-2020 at 18:19

Quote: Originally posted by Ubya

the only thing you can do is change the adapter or change the thermometer.

i bet you bought a thermometer adapter from china like this one

I suspect that slight diameter variation can be made in these things by changing the O rings to facilitate the correct diameter.

It all depends on the purpose of the set up that you are utilising.

earpain - 26-6-2020 at 06:59

Quote: Originally posted by Refinery

Nope, no way. Something is very wrong with your setup.
Can you post a pic or give more details on the size of the vessels?

Acetone has always been the absolute easiest and most rewarding chemical to distill.

Consider this: What is used as the coolant for fission reaction power plants? H2O.
Sometimes sure steam can be super-heated but it's very very difficult to achieve.

I think I saw something on a science show as a kid that showed a container of water next to an active fission reactor. The water just kept refluxing, condensing, over and over.Maintaining a nice even 100C.

I've distilled acetone a lot of times. The stillhead thermometer will read your room temperature even as the acetone begins to throw a tantrum. Then one drop condenses on the bulb(theoretical plate), and within seconds acetone is pouring across the condenser, and the temp jumps up to 56C. Even if it's half water and half acetone, 56C until the acetone is all gone, then swooosh right up to 100C.

Azeotropes happen. H2SO4 and H2O is the infamous exception to this, and there will be a sloping gradient. But either you have an entirely different chemical(s), a totally warped thermometer, or...something else.

Will shortly post pics of how I solved my problem finally. It's a culmination of this entire thread, including that exact thermometer adapter.

Refinery - 27-6-2020 at 07:24

Probe on still head.

4L flask in a 300mm diameter CaCl2 bath heated to temp not measured (usually between 100 and 130C). I would call it more of a stripping than distilling. I pushed it as fast as my condenser can handle to reduce time since there was only acetone, minor amount of water and compound that boils at 200C. As long as condensate appear on still head, the temp sits nicely at its BP, and this is also the case when using fractionating column. The same probe was used on boka still head with very accurate and constant readings corrected with barometer for azeotropic alcohol fractionation.

I was under impression compounds can exist in gas phase at almost any given temp below their decomp if they have room to expand. Air you breathe would be superheated gas if you compare it to their boiling temps. Gas-liquid equilibrium buffer happens under active reflux. So I see no reason acetone vapors couldn't heat to much higher temps, especially when they hover on a large 130C molten salt water bath. This only means the still head structural temp is as hot too so no condensation happens.

[Edited on 27-6-2020 by Refinery]