Digital Distillation Thermometer

DrugPhreak · Working Bee

Does anyone know of a company that makes digital distillation thermometers? I need one that would go up to ~350C. I’m tired of this analog crap and the scale on my thermometer starts too low so the boiling point of any substance below 100C cannot be determined because the adapter is blocking it. I’m sure this is not the case with better thermometers, but it’s time to go digital. It seems like a major part of chemistry is still in the dark ages. Confused

loki · guinea pig

I don't think it is wise do do atmospheric distillations above 150 degrees, a lot of substances will decompose at this temperature (I may be assuming incorrectly that you are referring to distillation). thermometers that measure up to 200 degrees are cheap and common (us$5), the ones i have the scale starts about 100mm up from the bulb and thus are perfectly fine when used in a distillation apparatus. Another option is an ir temperature sensor which a friend of mine says is ok for sensing temperatures through pyrex. For distillation the thermometer only needs to be just below the point the side port goes. For doing temps in a rbf, usually that would entail a two neck rbf, there are also ones which have a kind of socket which goes deep enough to sense the tempratures inside (i'm not sure but i think the port has to be filled with oil or something to ensure heat is conducted properly). If you have the money, there is the option of a thermocouple which reads the temperature on an external digital display.

DrugPhreak · Working Bee

In a field where precision is so important it's mind-boggling why no company has made a distillation thermometer that is just like the analog kind, but digital. Confused

methyl_ethyl · Riedel De Haen

Many companies make what you are in search of. I will be honest I have used digital thermo-regulators, in line with a heating mantle and a thermo-coupled temperature probe, and find no advantages over a proper Hg thermometer and vari-ac mantle or oil bath.

Set up:

Distillation apparatus, with a thermocoupled temperature probe in place of a thermometer, that is connected to a digital thermo-regulating device. A heating mantle is plugged directly into the thermo-regulating device. In theory you should be able to set a temperature and the thermo-regulation device will regulate the temperature of the mantle in order to maintain the temperature you specified. This may work for some constant temperature liquid phase applications, however with distillations where temperatures at the probe (vapour phase) are dependant upon the boiling point of the fraction that is coming over, this causes many problems.

Problem 1:
The thermo-coupled temperature probe is quite a bit smaller in diameter than a standard thermometer. Thus the standard thermometer adapter must be modified in order to achieve a leak free atmosphere under high vacuum. I have never been able to modify a standard thermometer adapter in order to house a thermo-coupled probe to my standards.

Problem 2:
I found at first that there was an extreme over or under shooting of temperatures that were dialed in on the thermo-regulator. This is most probably due to the "lag time" between the condensation forming on the probe, and the + or - "feedback" that informs the mantle to turn on or off. I thought I should be able to "set it and forget it" (i.e. dial in what ever temperature you expect you fraction of interest ot come over at, and walk away). In doing so one would come back to a Leuckhart ala negra. I found that in order to not over shoot temperatures one would have to start at the lowest boiling fraction and slowly increase the temperature a few degrees at at time.

Problem 3:
All of the extra work and decreased vacuum efficiency lead me to believe that this digital thermo-regulating, thermo-coupled bullshite, was not half as efficient as a proper Hg thermometer and vari-ac mantle or oil bath set up, in regards to distillations.

I encourage you to experiment with such equipment that perhaps could make life much easier when dealing with liquid phase temperature regulation and the like. But as far as distillations go, the set up I described does not work well as I described it. I am sure there are many that can make it work flawlessly, however I can only tell you what I know, and after what I have experienced, I have never gone back to the digital probes since my early work with Leuckharts. Perhaps I tried to get too precise before I had any type of understanding as to what is actually going on, who knows.

much_love

methyl_ethyl

loki · guinea pig

yeah, thermal lag makes it much simpler to just use variable heat settings, temps up top can take quite a while to adjust to temps in the flask.

I kinda got the impression that the initiator of this thread must have been referring to sensing the temperature in the boiling chamber though, because most lab thermometers are plenty long enough before the bulb to read right down to at least zero.

DrugPhreak · Working Bee

Thanks for all the info Methyl_Ethyl. One of my digital hotplate/stirrers has a connector for an immersion probe and temperature probe etc, but they are $600 each and I will never pay that. How much did all that cost you? Do you know where I can get just a digital distillation thermometer? Just like this, but digital so it fits into a thermometer adapter/still head just the same...

methyl_ethyl · Riedel De Haen

bio · Working Bee

To replace a regular thermometer just get an electronic thermoneter that will measure standard thermocouples and RTD's. For readout only these are fairly reasonable or if you have a DMM then modules are available that plug right in to the voltage jacks, many types available.

Then get an Inconel or similar chemical resistant metal sheathed probe of the length and diameter to fit your thermometer adapter. The teflon ones with the o rings are nice but a standard works OK unless under about 1mm. If distilling strong acid then glass or teflon sheathed is required. Check Omega, they have good tech info also in their catalog and a huge range of items for this application.

As methyl ethyl said there is no advantage in these things especially when Hg thermometers are cheaply available in all possible lenghts and ranges. About three thermometers are needed to have the readout above the adaptor if you want to cover say 30-200deg. Actually I found that the disadvantage is that I tended to rely on the damn thing too much looking at it across the room and trust me they DO drift and require calibration. A mercury unit is much more reliable.

If wanting some type of temperature control then the only thing that will come close to working properly is the PID type and they require programing to each particular
procedure which is way too much trouble if only doing this as a once in a while thing.

DrugPhreak · Working Bee

I guess I'll stick with the Hg thermometers then. I have two 18" 0-330C Hg thermometers, but if I stack one on top of the other the temperature on the top one will be accurate?

bio · Working Bee

Standard distillation/thermometer adaptors are made for 76mm immersion thermometers. A correction needs to be applied if using a total immersion. A 0-150deg one is all that's needed for almost anything and is much easier to read than a 260 deg for example.

DrugPhreak · Working Bee

I probably shouldn't have purchased such long range thermometers then, but I thought they would come in handy since I plan to distill many essential oils with high boiling points. It sucks how 0-100C is blocked by the adapter though because I also need to boil many low boiling solvents too… time to get some more thermometers.