Sciencemadness Discussion Board

Distillation of Flammable substances with an open flame

xSJF1414 - 17-2-2021 at 12:18

I'm just getting into amateur chemistry and have got a load of new glassware. However I do not have a heating mantle and I am planning on using a camping gas burner. I am planning on distillations, some flammables (benzene, alcohols) would this be too dangerous?

DraconicAcid - 17-2-2021 at 12:24

It might be okay as long as you keep your receiving flask well below the flash point of the liquid you are distilling- keep your benzene on ice, keep the glassware sealed, and don't go near ether. But I don't recommend it. A hot plate and a bot water/oil bath would be much safer, if you can't get a heating mantle.

xSJF1414 - 17-2-2021 at 12:36

Quote: Originally posted by DraconicAcid  
It might be okay as long as you keep your receiving flask well below the flash point of the liquid you are distilling- keep your benzene on ice, keep the glassware sealed, and don't go near ether. But I don't recommend it. A hot plate and a bot water/oil bath would be much safer, if you can't get a heating mantle.

Thanks, I forgot about hot water/oil baths that is much better. I also remember hearing that sand could be used to get to high temperatures if needed.

Fyndium - 17-2-2021 at 12:39

Get a pot, fill it with CaCl2:water about 50-70:balance ratio w/w so you can get it up to 140-150C without boiling, and heat that pot with your gas burner. Stable, non-flammable, cheap and safe heating without hotspots, works like a charm. Safer method will be hotplate, like said. I use induction plate, it's more efficient, faster and surface temp remains relatively cool. Direct flame heating is a last resort, although used much more commonly than should be. Many of the more ancient labs use a lot of bunsen burners without wire mesh heat shields to heat flasks, and cracking one is a rare occasion, but when it happens, you don't want it to happen. It can make an ordinary day into full-scale lab fire in seconds.

Receiver flask: immerse in cold water, ice might not be necessary. More important, lead the takeoff vacuum adapter with tube away from the setup, so any minor vapors escaping won't float in vicinity of fire.

If you don't live in very hot climate, evaporation of solvents, except for ethers and similar is not a major issue, if common sense is used, eg. do not keep anything volatile and flammable in open, large mouthed vessels like beakers, etc. I heat ether only by administering boiling water into a bath which is heated separately from the setup.

Heating mantle is absolutely not a necessity, although it offers stirring which must be done with overhead solutions when using baths with other heating methods. Major downside of heating mantle appears to be easy charring when boiling down solutions, when the mantle heats the exposed surface of the glass.

I recommend sand only for very high heat jobs(+250C) and a lot of patience. It is probably the slowest method to heat anything, difficult to adjust flask immersion and it tends to scratch glass. Up to about 80C water will suffice, for -30 to +150C CaCl2 bath is my go-to, 150 to 200+ an oil bath (canola oil smoke point is 220C, silicone oil works also up to 250C max) and above 250 sand, or in special circumstances, direct flame heat. Heating mantle is good for everything up to ~250. Too high will likely reduce it's lifespan so I recommend moving to sand thereforth.

[Edited on 17-2-2021 by Fyndium]

xSJF1414 - 17-2-2021 at 13:59

Thanks a lot!

Aloesci - 17-2-2021 at 14:59

Its definitely way safer to get a hotplate when dealing with easily flammable substances.
It just makes everything a lot easier. If you use it right (eg baths for round bottom flasks) you will probably end up saving money because your glassware wont break nearly as often as when using flame.

I sometimes use a hotplate which was marketed for heating food and for some reason whoever designed it made it capable of reaching 400 C! It easily boils conc. sulfuric if on a high setting, and it only cost about £20.

woelen - 17-2-2021 at 23:58

Another very good safety measure is to do things outside in a somewhat open space, or in a space, surrounded by concrete, bricks, etc. In such an area I take more risks (e.g. distilling red P to make white P with a propane torch), than when inside in my lab. If you have the space outside, use it.

Corrosive Joeseph - 18-2-2021 at 00:18

Only a crazy person heats flammables with a naked flame.

Do yourself a favour and research the Berme REX-C100 PID Temperature Controller


....and then wire it into an old deep fat fat fryer.... Zero to 400 degrees C temperature controlled oil bath for the price of a packet of cigarettes.


Fyndium - 18-2-2021 at 01:49

Then yet to find an oil that withstands 400C. ;)

Issue with buying lab hotplate stirrers and mantles tends to be the challenge of finding a good and reliable one. I've bought two hotplates, which first was absolute garbage for both heating and stirring, and the second one is always a bit exciting how does the heating work. Good quality brand stuff then costs so much that an amateur starts to go into extreme lengths for not having to pay 800$ for the smallest model. Many hotplates also have very low power, such that you can expect it to heat 200mL beaker of water into simmering in about an hour, but you might never get it to boil. I'd rather have 2kW food grade hotplate that has full range of adjustability from zero to cherry red.

Also, with big hotplate or mantle you can heat smaller vessels or multiple smaller vessels, but with small one you can only do small stuff. I bought myself 2000mL sitr-mantle from AliExpress branded JoanLab and so far it has been good. The price was 200$ with shipping and the smaller versions from 250 to 1000 cost only 10-30$ less so I got the biggest model and I'm glad I did.

outer_limits - 18-2-2021 at 02:01

I've bought once 1000ml stirring mantle but the stirring was not so strong. Then I bought another mantle without any fancy features - simple mantle that must be connected through a transformer and has a rod which makes it attachable to a lab stand. I can use that with my hotplate which is strong enough to stir almost everything I want in my scale. Now I have quite good stirring and heating

draculic acid69 - 18-2-2021 at 05:28

I'm just gonna say no.bad idea.flames and flammable substrates are a solid bad idea.

Corrosive Joeseph - 18-2-2021 at 20:12

Quote: Originally posted by Fyndium  
Then yet to find an oil that withstands 400C. ;)

Brake fluid.... ;)


Vomaturge - 18-2-2021 at 22:19

At least according to Wikipedia, the highest rated brake fluids are around 260C boiling point. If I recall correctly, 400C (750F) is about the temperature where you can just see a glow in the dark. Zinc melts at 420C. I suppose if I were feeling even more contrary, I'd try to melt a penny in brake fluid.

As far as the OP's question, distilling flammable substances on a flame is a triple threat: increased risk of cracking the glassware, risk of escaping vapors flashing back and igniting/bursting the glassware, and increased risk of fire from spills and breakages that can happen in any distillation. An electric cooking hot plate might be a better option

[Edited on 19-2-2021 by Vomaturge]

Fyndium - 19-2-2021 at 02:28

The color temperature chart.

3f9a0932eb444db1337b07c7cc83da63.jpg - 80kB