Sciencemadness Discussion Board - odorless heating baths?

odorless heating baths?

Funkerman23 - 4-5-2014 at 17:03

I don't know how many of you have a copy( or use) the Concise encyclopedia Chemistry ( Degruyter publishes it) but in the textr I was looking for alternatives to the standard oil bath. On the heating bath section is mentions a cold saturated solution of calcium chloride. The text says it should work up to 180 but at standard pressure I can't get it to go above 120 C. Does anyone out there have experience with that bath liquid? Does silicone oil have any odor on heating? Advice, comments and suggestions are always appreciated.

violet sin - 4-5-2014 at 17:10

whats wrong with good 'ole mineral oil? what temps are you trying to achieve?

Dr.Bob - 4-5-2014 at 17:21

Silicone oil does not produce any odors that I have noticed up to over 200 C. Even mineral oil works up to pretty high temps. You can use sand if you are careful, or other inert materials like BBs or SiC pellets. Look up dry baths or for previous threads here on Sci Mad. Any water based bath will be a problem, as water requires more energy to heat up to temp than almost any other substance, so it would be very slow to heat and cool.

forgottenpassword - 5-5-2014 at 00:16

Sand.

Funkerman23 - 5-5-2014 at 04:37

And roach another hot plate? No thank you.Bad enough I have to use a Mini fryer for my largest flasks but sand is a pita all around.

Quote: Originally posted by forgottenpassword

Sand.

Varmint - 5-5-2014 at 05:14

Not really in the bath category, but I want to try a section of one of the new silicone baking sheets on my hotplate for the flat bottom stuff (beakers/erlenmayer).

Sand works well for the most part, but I'd prefer something with higher thermal conductivity.

Ever needed to evaporate lots of water? With sand, the instant you get what would be a rolling boil, the boil carries away all the heat it can from the sand (cooling it), so the boil stops, sand heats up, and you get into a cycle that is limited by the thermal conductivity.

What we need is the equivalent of a beanbag chair for glassware. A tough, inert, highly flexible yet puncture resistant "bag", filled with fine metal shot (aluminum beads 0.020" or smaller?). That would be ideal.

DAS

Praxichys - 5-5-2014 at 07:19

Try DOT 5 brake fluid. It's silicone based and has a minimum dry boiling point of 260C. Unlike other oils, it has a really high flash point (like 360C), and it's inert enough to resist a lot of accidental chemical spills without significant degradation. It's also available worldwide.

NeonPulse - 8-5-2014 at 02:41

Quote: Originally posted by Praxichys

Try DOT 5 brake fluid. It's silicone based and has a minimum dry boiling point of 260C. Unlike other oils, it has a really high flash point (like 360C), and it's inert enough to resist a lot of accidental chemical spills without significant degradation. It's also available worldwide.

that would most certainly smell terrible, brake fluids reek pretty badly without heating. clean sand has worked well for me in the past.

taffy - 20-5-2014 at 13:22

I've used sand baths for years without problems...the only downside is slow heat conduction obviously but it's not too bad...

I also really enjoy aluminum foil baths...just rip the stuff up and stuff it in a big aluminum/steel pot enough to cover about halfway up the sides of the flask.

Burner - 20-5-2014 at 16:19

I have used sand baths (which as taffy has said are slow to heat) but I have also used aluminum pie weights (looks like mis-shaped aluminum shot [http://www.amazon.com/MATFER-BOURGEAT-340001-Baking-Weights/dp/B001U1725Y/ref=sr_1_7?ie=UTF8&qid=1400631124&sr=8-7&keywords=pie+weights+a luminum]) when rapid heating was required and the flask contents permitted (definitely no strong bases!

).

[Edited on 21-5-2014 by Burner]

BromicAcid - 20-5-2014 at 16:24

Eucetic metal baths are all the rage in old-school days. Check out Woods Metal, the wiki article is even so kind as to link to other metal baths. Also I have seen and used eucetic salt baths, usually with potassium nitrate as the main component. Either one of these will furnish you with an odorless bath as you requested. Could have sworn this is come up before quite a bit so searching the forum should help too.

Burner - 20-5-2014 at 18:19

^^^ I had stopped using some of these eutectic metal baths since many of the more common compositions included cadmium. In spite of good laboratory safety practice I have had too many unfortunate cadmium exposures so I tend to avoid it when I can. Guess I am getting a bit more cautious in my "old age"!

Burner - 20-5-2014 at 18:22

Now that I think about it, if cost were a "secondary" concern (though it rarely is!) perhaps a gallium metal bath would be an option (for those with SUBSTANTIAL disposable income)!

macckone - 20-5-2014 at 18:23

Granular Magnesium Oxide or Alumina.
They are both good heat conductors.
Alumina will scratch glass though.
Alumina is available as blasting media in 200 grit.

BromicAcid - 20-5-2014 at 18:49

Burner, check out Rose's Metal, 98C melting point, 50% Bismuth, 25% Lead, 25% Tin.

Zyklon-A - 20-5-2014 at 19:20

There's quite a few alloys with even lower MP's:
[% by weight]
Field's Metal: Bi 32.5, In 51.0, Sn 16.5 MP=60.5°C
Bi 40.63, Pb 22.1, In 18.1, Sn 10.65, Cd 8.2 MP=46.5°C
Bi 50.0, Pb 25.0, Sn 12.5, Cd 12.5 MP=71°C
Bi 50.0, Pb 31.2, Sn 18.8 MP= 97°C
Bi 50.0, Pb 28.0, Sn 22.0 MP=109°C

Most of these where found on this Wikipedia page.
BTW, Bromicacid, in the page linked above, it says Roes's metal melts 109°C, and has the percent composition as listed in the last alloy I posted. Of course the alloy you mentioned probably does melt at what you said it does, but it seems strange that there would be two alloys with the same name, but different compositions, and different MP's.

[Edited on 21-5-2014 by Zyklonb]

Refinery - 24-5-2020 at 08:43

My experience on heating baths:

- Direct heating with propane: very fast, very adjustable, very dangerous
- Air bath, w/ or wo/ foil mantle: slower, but works well for stuff under 80C
- Water bath: works well under 80C
- Sand bath: sssllloowww..... And as an insulator, thermal conductivity is buffered so much that anything done with it will get done very slowly, as the reaction takes energy away from the reaction flask's surface, the sand will cool down and the conductivity is too slow to keep it up. The bottom of the vessel glowed yellow (~800C+) when the top of the sand was easily touchable.
- Salt bath: does not differ from sand, but does not scratch glass
- Oil bath: works quite well for up to 150-200C, but is an imminent fire hazard. I have to admit I lit up one bath years ago, and it was PITA to put out, because of the glassware immersed in it. Have used it only once.
- Brake oil: That smoke and reek.. My workspace filled up with thick, stenchy smoke and the bath kept smoking forever even after heating was stopped. Perhaps heating it very slowly, or with indirect heating, it could be minimized. I even thought making a cover on top of the bath and putting a fan duct on it to suck out all the smoke, but probably just skip it.
- Paraffin wax: odorless, flash point 220C, BP 360C. Haven't tested, but sounds good. Granules cost about 5 bucks per kg.
- CaCl2 bath: I stopped my last test at 155C, but sources cite it should go up to 160-180C until it starts to turn solid. When kept sub boiling, water vapor is negligible, and naturally it has zero odor. Glass will have CaCl2 coating, but it is rinsed off very easily. I'm gonna make boil-saturation-test soon, because I have a reflux reaction I need to run at 160C for few hours. I will boil the solution, and gradually add more CaCl2 and monitor the temp and see when it either doesn't wanna dissolve anymore or it turns into thick gunk. When let to cool, the salt starts to crystallize out immediately. I used the bath to distill off some solvents, and the bath was basically still, with a thick layer of white crystal ice layer on top of it, even though it was 130C.

CaCl2 bath is my favorite so far. It is totally inert, odorless, cheap as dirt (25kg bag of road salt costs 15 bucks). The bath can be heated with high powered propane burner because the salt liquid does not take on itself on the extreme surface temperature, but it heats up the bath very quickly.

I like to use propane to heat, because it is very fast, powerful and easily adjustable, but the surface temp increases dramatically, which causes oils and fluids to smoke easily. This could possibly be reduced by heating either slowly, or using buffer plate. I'm gonna try a 5kg dumbbell plate plasma cut from 20mm steel plate, which would heat up in a controlled manner and transfer the heat more slowly to the container itself.

What I'd like to test is a metal shot bath. Steel shots for shotguns are available cheaply in bulk from 1mm upwards, 5kg costs about 30 bucks and it has got more than 1L volume. Al shots could be better, and copper perhaps best, but the cost can be prohibitive.

Someone mentioned al foil bath. The concept here is to rip al foil, blend it in a blender into small shreds, and use then like metal shots. I wonder though if the air volume insulates the bath more than the al conducts heat because the foil shreds are so lightweight. A liter of them weights few hundred grams.

I've used baths with 2L and 4L flasks, and the volume of liquid needed depends a bit on the vessel, but my CaCl2 solution volume is 3 liters and it is well enough for 2L flask. I use stainless steel bowl, originally made for kitchen stuff, diameter of 260mm and it is half-sphere shaped so it minimizes waste volume. Bigger bath is better though for more stable temp control if it comes to that.

[Edited on 24-5-2020 by Refinery]

Refinery - 25-5-2020 at 09:58

Candles should be a good and cheap source of paraffin wax.

[Edited on 25-5-2020 by Refinery]

Mateo_swe - 25-5-2020 at 14:09

Nobody uses oil baths?
There must be oils that have quite high temperature limits.
What about motor oils used in cars, do they smell or smoke?.
Or are oil baths dangerous as someone said earlier?
The flash point dont mean they autoignite at that temp and if using an electric heat source shouldn't it be OK up to at least say 200°C with a good oil?

I tried reflux some isopropanol in a big 3L flask on my hotplate stirrer a few days ago and it took really long time getting up to temp.
I tried insulate with some aluminium foil that made it little better but next time i must use some oil bath or other alternative to try speed it up.

Refinery - 26-5-2020 at 00:37

I have found that hotplates are insufficient for any NTP distillations above ~100C if their volume much exceeds 500 mL.

I strongly prefer CaCl2 bath for anything up to 150C, probably 160-170C, haven't yet tested how far it can go without getting solid, I took it only up to 155C. It is inert, cheap, stable, reuseable and when I was refluxing at 130C it did not release any noticeable steam.

Mateo_swe - 2-6-2020 at 11:56

Are you sure?
Well, i dont doubt your word, if you say its good its probably good.
What made me unsure is that if looking up Calcium chloride and its melting point it says:

772–775 °C anhydrous
260 °C monohydrate, decomposes
175 °C dihydrate, decomposes
45.5 °C tetrahydrate, decomposes
30 °C hexahydrate, decomposes

So you must have anhydrous calcium chloride or maybe the monohydrate variant.
What is the most common one?
The hexa or tetrahydrate seem to decompose on heating.
Doesnt that mean it will not form the next lower hydrate like for example epsom salt do when heated?
Im quite new at chemistry so i dont know these things, i might be wrong about this.

earpain - 6-6-2020 at 06:25

I use to have a ceramic hot plate. NaCl bath actually worked pretty well. Now I have a cast aluminum body stirrer/hotplate. In a pinch, I've used Al foil, molding it around the shape of the flask. Not sure why people say this insulates the heat, I think of it more as dissipating, but in a shape conforming to the flask.

Recently I completely took an old hotplate apart, and found plenty of white glass wool insulation. Now I wrap an RBF first in the insulation, then in aluminum foil. This seems to really improve performance as well as max temp. Also it helps a LOT for vacuum distillations. Counting pennies in my piggy bank to buy a few mantle elements or something funky like silicone tape.

My issue with oil baths is the simple fact that there is a very hot liquid, heating up something that is often aquieous and 'interesting'. Not to mention a water cooled condensor very near by.

Refinery - 6-6-2020 at 06:45

Quote: Originally posted by Mateo_swe

Are you sure?

I used it again, so I'm somewhat sure I used CaCl2.

I prepared it by heating water and adding CaCl2 as it dissolved, and temp got up to 155C if I remember right and I though it will be fine and I stopped adding. I used the bath to distill acetone, ethanol, etc and when heated, it remains crystal clear, but crystals form a film on the surface, and when heating is stopped, it begins to crystallize pretty quickly. When I stopped my work and cooled down the CaCl2, it turned into a sludge which I poured into a can.

Now when I returned my lab, the sludge was turned into a rock solid chunk, and I decided to just gut the can than wait for it to melt when I attempted to boil it. I dumped it in my bath vat and heated it, and it melted quickly at around 40-50C to form a sludge, and then it cleared up. I added a bit water to hasten the melting process though, since I did not need super high temps.

I successfully ran a 8-hour distillation of ethanol with the bath, and the surface went down by about one centimeter during that time. It never boiled at all, did not even form bubbles. So it evaporates slowly, and allows keeping steady temps probably up to 140-160C range without issue for hours. It just sits there, with a film of crystals on the surface and does nothing, except for the heat.

Now when I was done, I just left it in the vat and wrapped it with plastic wrap, so it solidifies in there and I can just melt it by putting it on top of my heater till I can immerse a flask in it.

I'm very happy with the results I got with CaCl2 and I must recommend it to everything at least below 150C. It has thermal conductivity like water bath, it is inert(unless you spill mineral acids in it), does not steam or smoke, does not smell and is dirt cheap.

Probably even higher temps can be obtained, if monohydrate decomposes at 260C, it could be useable in a liquid/sludge form even up to that temperature, but letting it cool a bit will solidify it, so preparing over 150C baths must be done in situ so that a lower concentration is first made, flask immersed and more CaCl is gradually added so that it remains liquid and temp rises to desired range. I remember seeing a chart though where CaCl melting point and hydrate decomp point crosses so the decomp is lower than melting, so it will remain solid and water just evaporates away, and it's likely that temps above 160-170C may remain questionable until proven otherwise.

Mateo_swe - 7-6-2020 at 04:23

It seems CaCl2 is quite usable as a bath media then.
As long as the temps are under 230-250°C.

I looked up the Epsom salt (MgSO4) that i dry in the oven to use for removing water from chemicals.
It says the same text as the CaCl2, ie. the different hydrates decompose at different temps:
MgSO4 Melting points:
anhydrous decomposes at 1,124°C
monohydrate decomposes at 200°C
heptahydrate decomposes at 150°C
undecahydrate decomposes at 2°C

So what happens (i think) is when the MgSO4 comes to 150°C it breaks the heptahydrate and releases water that evaporates and the remaining forms the monohydrate.
When it comes to 200°C the monohydrate breaks, releasing water that evaporates and forms the anhydrous, water free form.
I thought the "decomposes" meant the whole molecule breaks apart.
Maybe it does mean that, but the lower hydrate form of MgSO4 is produced as no other compounds or molecules is present to interfere with the formation of MgSO4.
Maybe the same will be the result if heating CaCl2 so it changes to a lower hydrate form and release water.
Can someone explain if this is what will happen if heating CaCl2 beyond 260°C when the monohydrate "decomposes"?
Will it just evaporate the water and form the anhydrous form of CaCl2 or does something else happen?

Sulaiman - 7-6-2020 at 07:10

I had been using cooking oil in a pot for quite some time with no problem, mostly for ethanol distillations,
The oil was 50 to 100 Celcius higher temperature than the rbf contents due to the poor thermal conductivity of glass,
recently in another thread somewhere here on SM the danger of the rbf breaking and depositing its contents into the very hot oil was discussed.
Since then I've only used heating mantles.

Sand and/or salt baths work on a hotplate but to get a reasonable heating rate the hotplate had to be very hot,
Some members have damaged expensive hotplates this way.

P. S. When hydrates decomposing are mentioned it normally refers to dehydration.

[Edited on 7-6-2020 by Sulaiman]

Refinery - 7-7-2020 at 10:12

I committed a small test with CaCl2 due to having a kg of it right on hand. I mixed about 500mL of water into 1kg of anhydrite and boiled it until all granulates were dissolved.

I managed to initially get it up to 175C, but a large amount of solids were present, but it would be very usable as a heating bath anyway. At 165C a crust keeps forming on top, but the liquor is in fully liquid form beneath it. Less heating will make it still, and little to no evaporation occurs, hence it could be kept as such for hours to go. I used my CaCl2 bath to distill ethanol for 8 hours straight, and it only lost few mm of depth due to evaporation.

A preparation for high temp bath would be best done in such way that first a fully liquid solution is made, and then more CaCl2 is gradually added while boiling, until desired temp is achieved.

The downside with high temp CaCl2 bath appears to be that it turns into porridge while still way above 100C and it solidifies probably before cooling below that, so high temp bath should be either produced from ground CaCl2 hydrate into which the reaction vessel is immersed and gradually heated, or as above, preparing first a less concentrated bath up to ~50% that remains liquid at safe temps to immerse a flask, and then add more CaCl2 to bring the temp up. For lower temp baths a lower concentration solution can be used as such.

CaCl2 works as dual-use material because it remains liquid with good viscosity down to -35C(tested) and all the way to -50C in +30% concentrations. The viscosity resembles cooking oil. It appears to be an excellent coolant for it's temp range.

It is practically odorless, but it has a very mild, sharp odor within its immediate vicinity, probably owing due to it's extreme hygroscopicity, which irritates membranes, hence breathing in it's dust feels quite uncomfortable.

I would consider twice using this type of bath to heat sulfuric acid or other acids or substances that could react readily with chloride. A flask full of concentrated sulfuric acid breaking at 180C while being immersed in concentrated CaCl2 liquid would cause instant release of huge, most likely lethal amount of HCl gas, and probably also splattering of burning hot, corrosive and toxic mixture of chloride, acid and HCl.

A major benefit of CaCl2 is it's very low price, being sold as road salt, usually in 77% hydrate granular form. A 25kg bag tends to cost between 10 and 20 bucks, depending on vendor.

[Edited on 7-7-2020 by Refinery]