Sciencemadness Discussion Board - Preferred heating and stirring methods..

Preferred heating and stirring methods..

Dr.Arz - 19-10-2014 at 00:29

I have been troubling some syntheses recently. Some vacuum distillations will need substantial heating, up to 160C, since I have only aspirator that can get maximum 32mbar vacuum, but then I cannot stirr it. I have stirplate but it is way too underpowered, secondly it is not possible to heat round bottom flasks with it. I need strong stirring while vacuuming because all things will begin bumping so hard I must stop it. I was thinking bleed tube but I cannot get it into the flask anyhow because I only have very small 3 neck flask.

So I need to get much more power to the flask while still maintain stirring capability. I was thinking of constructing my own stirrer from fan or other electric motor, because I have ring gas heater that has 100mm hole in the middle and this could work well, but the heater will get even too much power and there may be too much local heating. I do fear that direct heating may cause other safety risks. The gas heater is rated 6000W power and larger distillations like ethanol purification goes very nicely but even adjusted to lowest power it is too much for vacuum distillation.

Do you have any advice or ideas how to heat and stir properly? I could buy stirplate from ebay, but I still need to get some kind of mantle, and running those plates very hot while empty may destory them, I have burned at least 3 hotplates this way.

There is another way, though. I do have a vacuum pump aside of aspirator, but it is meant for refrigerant vacuuming and it is way too powerful. secondly, I dont have a gauge to measure or adjust the vacuum. Does anyone know where to get gauges or regulators that allow measuring vacuum in 0.1-50mbar scale at sufficient precision? I thought originally the adjustment of vacuum the best option because this I could get almost all liquids boiling points below 100C which allows me to use normal water batch.

Hmm... How about casting a bottom shaped mantle from lead for specific size of rb flask? Lead thermal conductivity is 50 times the water. It could yet be insulated by casting some CaSO4 plaster around it.

http://www.engineeringtoolbox.com/thermal-conductivity-d_429...

Or even a more stupid idea. They seem to sell cast alu blocks at Sigma A. How if one does grind aluminium foil into small granules and use them as heating bath?

[Edited on 19-10-2014 by Dr.Arz]

careysub - 19-10-2014 at 07:22

Quote: Originally posted by Dr.Arz

...

Hmm... How about casting a bottom shaped mantle from lead for specific size of rb flask? Lead thermal conductivity is 50 times the water. It could yet be insulated by casting some CaSO4 plaster around it.

http://www.engineeringtoolbox.com/thermal-conductivity-d_429...

Or even a more stupid idea. They seem to sell cast alu blocks at Sigma A. How if one does grind aluminium foil into small granules and use them as heating bath?

[Edited on 19-10-2014 by Dr.Arz]

How about just casting the flask support of plaster and be done with it? Its thermal conductivity is at least as good as sand used in a sand bath (which you could also use).

Possible implementations - get a metal jar lid, perhaps tape a cardboard casting rim around it for height, and cast with plaster, using the actual flask (and plastic wrap) for the mold, push the flask all the way down to the lid for maximum conductivity.

One thing NOT to try - adding finely granulated aluminum to plaster to increase its thermal conductivity. This is how you make "plaster thermite" (I seriously doubt you could ignite it with a hot plate, but still...).

[Edited on 19-10-2014 by careysub]

Texium - 19-10-2014 at 07:29

If you want to heat an RBF using a hotplate, create a closed channel of aluminum foil between the top of the hotplate and the bottom of the flask. This creates an air bath of sorts, since a high percentage of the heat is trapped in between the hotplate and the flask without much escaping to the environment. It makes a huge difference. The only downside to it is that it makes it difficult to see the flask's contents.

Little_Ghost_again - 19-10-2014 at 07:32

a small ball bearing placed inside a glass rod (i used a broken pipette I had ), I hated untll the glass melted around the ball then when cold I cut each side 3-4mm from the ball so it had wings.
this works well in a RBF for stiring and seems to be fairly powerful, on my stirrers I have found sometimes slower speeds work better.
Depending on temperature I cheat with heat, if its low enough I put the sodium chloride out of my desiccators in the pan instead of sand (I figure I might as well use the heat to dry my salt).
Dont use normal plaster use herculite2 even better if you find herculite2 on ebay there is often another sold by the same people, its much much harder and not much more money.
Tinfoil wrapped around everything keeps the heat in AND stops the government spying on you at the same time.
I often use tin foil but only when I feel its safe to take my hat off

macckone - 19-10-2014 at 08:47

160C(320F) is well within the range of an oil bath.
Common cooking oil (peanut oil) is good to about 440F(227C).
Smoke points of cooking oils vary and peanut is one of the best.

http://www.goodeatsfanpage.com/collectedinfo/oilsmokepoints....

a bleed tube is preferred to stirring in most cases
but overhead stirring is the way to go.

Little_Ghost_again - 19-10-2014 at 09:47

I tried overhead stirring but it made my eyes sting like fuck

zenosx - 19-10-2014 at 17:51

Professional stir bars aren't that expensive. Just hit up e-bay. When I first started I did the same thing by enclosing a mag in a sealed glass tube. Using the teflon pro versions won't scratch up your glassware, and if you are doing vacuum distillations, scratches = weakness / possible implosion = no eyes... don't skimp on something so cheap.

Also, I have an ancient hotplate from the 60's that is literally exposed nichrome wire, and it will run on high all day without burning up. I have heard of sandbaths, etc, ruining hotplates. Maybe go with the oil baths for a change?

Dr.Arz - 19-10-2014 at 20:55

I think i will make insulated nichrome loop for low voltage high amp heater and place it into steel shot bath. Copper would be better but it costs 7 times more. Yesterday I digged up my old transformers and find the thickest nichrome wire I could find which was 2mm and a 500mm long loop heated to white hot almost instantly, but with dimmer it works perfectly from very low temperatures. This allows me to submerge it into the steel shot batch and I can use my cheap mag stirrer to stir the liquid. I think i have to place ceramic insulator on top of the plate just in case the heat loop heats it too much. I burned many cook plates with sand and air baths before, they just get too hot and burn off. Probably made from some cheap b-grade stuff. First one stood over a year but second one didn't last for more than few months. After that I used gas heater but Im afraid heating with open flame.

Overhead vacuum stirring sounds too professional and expensive thing to to. I already have teflon coated stirbars. Only way to get bleed tube all way down is to put it where thermometer normally goes and when I do vacuum fractioning it would have to be something like 600-700mm long. I said already I have only very small 3-neck flask and I would have to distill some larger volumes multiple times to get it all done.

Dr.Arz - 20-10-2014 at 06:22

Has anyone think of using hot air gun to aid heating? Idk if one can adjust the power by attaching dimmer between gun plug and wall but one could build a ceramic or insulating box similar to mantle around the flask and make loop around it for air to circulate, so not to blow it directly to flask but around it. There one could put mag stirrer underneath. Most hut guns have adjustable power and speed but they can give heat from 50 to even over 650 which is more than enough to heat anything. Air conductivity is such low that no hot spots should form as easily as with flame.

Little_Ghost_again - 20-10-2014 at 08:05

Quote: Originally posted by Dr.Arz

Has anyone think of using hot air gun to aid heating? Idk if one can adjust the power by attaching dimmer between gun plug and wall but one could build a ceramic or insulating box similar to mantle around the flask and make loop around it for air to circulate, so not to blow it directly to flask but around it. There one could put mag stirrer underneath. Most hut guns have adjustable power and speed but they can give heat from 50 to even over 650 which is more than enough to heat anything. Air conductivity is such low that no hot spots should form as easily as with flame.

Or buy a cheap smd solddering gun, you can control temp and air flow

TheAlchemistPirate - 21-10-2014 at 08:39

I recently have decided that I need a bath of some kind to evenly heat RBFs and other glassware. I have a nice hot plate/stirrer from homesciencetools that can get up to 200 degrees C, which I bought before I knew what a heating mantle or bath was. My question is, what would be the best media to put in a basin of some sort that would surround any glassware I put in? These are the medias I've considered.
Oil- This is what I first considered, I would probably use peanut oil as it apparently works up to 227 degrees C? The problem is that I heard it can stain glassware, which is enough of a turn-off for me. It also might be messy to clean up and wont appreciate any chemicals I accidentally spill into it.
Sand- I don't know much about this, it might scratch my glassware and not be very controllable as far as temperature.
Small metal bearings- This is what I'm going for. I would buy aluminum ones, as they have many advantages over other metals. First, aluminum won't screw up the magnetic fields in my stirbar setup. Second, it is very heat-conductive. Third,it is very resistant to the types of chemicals I will be heating. The only disadvantages are cost, and the fact I'm not sure if I could accurately measure the temperature of the bath itself.
For a basin to put the media in, I was thinking about metal (probably aluminum too) or glass.

[Edited on 21-10-2014 by TheAlchemistPirate]

Metacelsus - 21-10-2014 at 11:43

What about mineral oil? That's the standard bath liquid.

Little_Ghost_again - 21-10-2014 at 11:49

I use cheap cooking oil for deep fat fryers, it has done me to over 320c fish and chips cook at 270c.
Vegetable oil cheap as you can get, its not fit to eat but makes a great oil bath oil

aga - 21-10-2014 at 15:20

What exactly is 'Mineral Oil' ?

Baby lotion ?

Specifically, what do i go and buy ?

jamit - 21-10-2014 at 17:58

I don't like heating oil bath, although depending on the reaction, something this is only reliable method. But for most lab uses, a heating mantle is great. I just purchased a whole bunch of different size.

If anyone's interested in purchasing a used 250ml, 500ml, 1000ml, 2000ml or 3000ml heating mantle w/cord, let me know. I have a friend who is selling it and I've purchased from him. The prices ranges from 50.00 - 200.00 depending on the size. I think the 250ml is 50.00, 500ml is 75.00, 1000ml is 100.00, the 2000ml is 150.00, and the 3000ml is 175.00 and the 5000ml is 200.00.

Loptr - 22-10-2014 at 06:27

Quote: Originally posted by aga

What exactly is 'Mineral Oil' ?

Baby lotion ?

Specifically, what do i go and buy ?

You can find it in the pharmacy area of grocery stores. It's sold as a mild laxative and skin protector.

http://www.amazon.com/Vi-Jon-Inc-S0883-Mineral-Oil/dp/B001B2...

Dr.Arz - 22-10-2014 at 06:49

Anyone have experience on vacuum overhead stirrers?

http://www.thomassci.com/Equipment/Overhead-Stirrers/_/GLASS...

It states that there is a vacuum seal using viton O-ring which may leak a very little to none, but sufficient to keep vacuum well up.

So one should be able to turn a plug from ptfe and make another plug to the stirrer bar and turn a small smooth groove for O-ring?

Overhead vacuum stirring would permit using normal cheap hotplates that can put over 2000watt of thermal power by using air bath.

TheAlchemistPirate - 22-10-2014 at 18:11

This may belong more in the reagents/apparatus acquisition section, but I need this for heating. Could anyone cite a source of a small basin, made of aluminum or glass, as I mentioned above? It needs to be around 6 by 6 inches and around 4 inches high. It will sit on a hot plate/stirrer and be used for oil baths.. I seriously have searched every site I could think of to find something like this I need, so please forgive me for posting this.

[Edited on 23-10-2014 by TheAlchemistPirate]

Oxirane - 23-10-2014 at 04:42

Use cookware. They have thick bottoms that stay flat during heating, which is very important because conducting heat by aluminium is hundreds of times more efficient than by radiating through air, even the gap is small.

Dr.Arz - 1-11-2014 at 10:49

Anyone used digital hot air guns to heat? The more expensive models have very accurate temp adjustment from low 50C up to over 600C with adjustable air flow. They could be used to heat all kinds of stuff including caltaytic tubes.