Sciencemadness Discussion Board
Not logged in [Login - Register]
Go To Bottom

Printable Version  
 Pages:  1  2
Author: Subject: Fire & Explosion risk vs. scale
LearnedAmateur
National Hazard
****




Posts: 436
Registered: 30-3-2017
Location: Somewhere in the UK
Member Is Offline

Mood: Free Radical

[*] posted on 13-1-2018 at 05:00


I assume this is common knowledge but I’ll add it anyway since it hasn’t been mentioned - never use water to extinguish a solvent fire. Dumping water onto an immiscible solvent will just cause it to float and keep burning, riding the water and going where it flows, and spraying with a hose will likely end in the fire becoming even more widespread. Not so much a problem with ethanol and such (mist setting), but kerosene, DCM, toluene etc. is the real issue. An even bigger danger is if the solvent has a higher boiling point than water, as is a common cause of housefires - for example if you have an oil fire, attempting to extinguish with water will lead to it sinking and instantaneously boil, launching hot, firey droplets everywhere and making the issue impossible to contain.

I only work with <100mL at a time so I’ve never had a fire myself, even when boiling 10-20 mL of solvents in a boiling tube using a blowtorch flame which I can do quite comfortably.

As for boiling chips, I use rough marble chips about 5-10mm in size that have been treated with dilute H2SO4 to form an inert and insoluble coating of CaSO4. These work pretty great for most applications and I’ve never had them interfere with a reaction. From personal experience, I too have attempted to use glass shards as chips but I’ve found that they cause the boiling to be more violent and tend to jump around a lot - mineral based chips produce more consistent nucleation with smaller bubbles leading to a gentle simmer/rolling boil.

[Edited on 13-1-2018 by LearnedAmateur]




In chemistry, sometimes the solution is the problem.

I am now training to manufacture contact lenses for a living. Time to join the lab community!
View user's profile View All Posts By User
NEMO-Chemistry
International Hazard
*****




Posts: 1547
Registered: 29-5-2016
Location: UK
Member Is Offline

Mood: No Mood

[*] posted on 13-1-2018 at 08:07


Quote: Originally posted by LearnedAmateur  
I assume this is common knowledge but I’ll add it anyway since it hasn’t been mentioned - never use water to extinguish a solvent fire. Dumping water onto an immiscible solvent will just cause it to float and keep burning, riding the water and going where it flows, and spraying with a hose will likely end in the fire becoming even more widespread. Not so much a problem with ethanol and such (mist setting), but kerosene, DCM, toluene etc. is the real issue. An even bigger danger is if the solvent has a higher boiling point than water, as is a common cause of housefires - for example if you have an oil fire, attempting to extinguish with water will lead to it sinking and instantaneously boil, launching hot, firey droplets everywhere and making the issue impossible to contain.

I only work with <100mL at a time so I’ve never had a fire myself, even when boiling 10-20 mL of solvents in a boiling tube using a blowtorch flame which I can do quite comfortably.

As for boiling chips, I use rough marble chips about 5-10mm in size that have been treated with dilute H2SO4 to form an inert and insoluble coating of CaSO4. These work pretty great for most applications and I’ve never had them interfere with a reaction. From personal experience, I too have attempted to use glass shards as chips but I’ve found that they cause the boiling to be more violent and tend to jump around a lot - mineral based chips produce more consistent nucleation with smaller bubbles leading to a gentle simmer/rolling boil.

[Edited on 13-1-2018 by LearnedAmateur]


Boiling chips i use bits of broken coffee mugs, i have a regular and ample supply of these. they are normally heavily glazed and pretty inert IMHE.
View user's profile View All Posts By User
LearnedAmateur
National Hazard
****




Posts: 436
Registered: 30-3-2017
Location: Somewhere in the UK
Member Is Offline

Mood: Free Radical

[*] posted on 13-1-2018 at 09:07


I’ve heard that anything ceramic/porcelain based is fine for less stringent applications, plus it has some natural porosity to them. I have quite a collection of marble chips so I prefer those, plus they’re reusable with a small wash between uses - the only thing that turns me off of broken mugs is that the glazing does decrease surface area which is where the marble excels. Albeit, I’ve never used them, and since they’re recommended I don’t have anything to say against it, especially since mugs can be found in just about any home whereas marble may not.



In chemistry, sometimes the solution is the problem.

I am now training to manufacture contact lenses for a living. Time to join the lab community!
View user's profile View All Posts By User
NEMO-Chemistry
International Hazard
*****




Posts: 1547
Registered: 29-5-2016
Location: UK
Member Is Offline

Mood: No Mood

[*] posted on 14-1-2018 at 03:46


Quote: Originally posted by LearnedAmateur  
I’ve heard that anything ceramic/porcelain based is fine for less stringent applications, plus it has some natural porosity to them. I have quite a collection of marble chips so I prefer those, plus they’re reusable with a small wash between uses - the only thing that turns me off of broken mugs is that the glazing does decrease surface area which is where the marble excels. Albeit, I’ve never used them, and since they’re recommended I don’t have anything to say against it, especially since mugs can be found in just about any home whereas marble may not.

My lab has a fresh broken mug most days :D, actually its the handles I break, if you want more surface area then an angle grinder does a fine job taking the glaze off.
View user's profile View All Posts By User
tommy claisen
Harmless
*




Posts: 13
Registered: 27-9-2015
Member Is Offline

Mood: No Mood

[*] posted on 25-2-2018 at 07:03


if it's an option, i would recommend distilling solvents using a slight vacuum (650mm Hg, CO2 trap) so that a bubbler w/ inert gas can be used. no chips needed.
View user's profile View All Posts By User
Sulaiman
International Hazard
*****




Posts: 1715
Registered: 8-2-2015
Location: England
Member Is Offline

Mood: No Mood

[*] posted on 25-2-2018 at 10:06


Dry ice is tooexpensive for me so almost all distillations are at atmospheric pressure.
I do intend to use reduced pressure for kerosene distillation.
The thought of a superheated solvent fire still terrifies me - way beyond just respect,
but I guess that's a good thing.

I've modified my diy 500ml heating mantle to incorporate a 2l pyrex bowl around/under the mantle/insulation,
above the magnets, to catch liquids - to give me get away time at least ;)

P.S. Even though I've never used boiling chips I believe that I do understand why and how they work.
superheated liquids cannot easily vapourize other than at a liquid/gas boundary, which is normally at the surface, or an existing submerged bubble, in a porous material, capillary tube, or simply added via an air leak.
Once a bubble is available to evaporate into, the bubble grows rapidly.
Without a nucleation site it is very difficult to start a new bubble due to surface tension.

[Edited on 25-2-2018 by Sulaiman]




When doing chemistry, don't forget basic physics.
View user's profile View All Posts By User
BaFuxa
Harmless
*




Posts: 24
Registered: 18-9-2017
Location: Mars
Member Is Offline

Mood: Buzzing

[*] posted on 26-2-2018 at 06:14


In my experience, boiling chips are not perfect to prevent bumping. I have had bumping occur even with glass chunks and sand. What works very well is a rotating stir bar.

If you plan vacuum distillation then you should set up a cold trap otherwise your pump will get ruined.

But you can do it without vacuum, I have distilled some gasoline in a 500 ml rbf without vacuum two times and nothing spectacular happened. It just stinks. Just monitor the temperature to stay clear of the autoignition points of the most volatile compounds and you are fine. I never pushed it above 68°C. Ventilate well or do that in a fumehood. The smell is horrendous and sticks everywhere.





C
View user's profile View All Posts By User
 Pages:  1  2

  Go To Top