The Vespiary

The Hive => Chemistry Discourse => Topic started by: Bubbleplate on June 15, 2002, 02:22:00 AM

Title: Nitromethane Separation
Post by: Bubbleplate on June 15, 2002, 02:22:00 AM

Is it (relatively) safe to distill off nitromethane from oil using a gently heated water bath under a non-vacuum Distillation setup? Or is it safer/better to use a vacuum setup?

Title: It's safe
Post by: Chromic on June 15, 2002, 02:51:00 AM

I've done it before without problems. Do not distill the nitromethane to dryness and you will be fine.

Title: Not a water bath
Post by: Rhodium on June 15, 2002, 03:51:00 AM

You cannot distill it without vacuum on a water bath, as the bp of nitromethane is 101°C. Either use an oil bath or a heating mantle.

Title: Azeotrope
Post by: Antoncho on June 15, 2002, 08:20:00 AM

Also note that NM forms an azeotrope w/water, which boils at around 80C - so unless you dry it w/CaCl2 (can't dry it w/Na2SO4) - AND if it contains some water (it always does when prepared from NaMeSO4) - you'll see two fractions.



Antoncho

Title: Separation
Post by: hermanroempp on June 15, 2002, 01:07:00 PM

You want to separate nitromethane from fuel for model planes, right? This fuel contains oil, nitromethane and methanol. I always get the nitromethane+oil by gently shaking the fuel with an approx. 10% solution of NaCl in a separating funnel (to dissolve most of the methanol), standing over night and drawing off the nitro/oil mix (lower phase). This goes straight into distillation, using a 30 cm Vigreux. After a small forerun of methanol/water the nitromethane distills. Dried over CaCl₂, filtered, ready for use.
Can't give you the exact ratios of 40% fuel/salt solution used, as I do this always by gusto and it just works fine.. :)

---

Quidquid agis, prudenter agas et respice finem!

Title: Thanks Rhodium!
Post by: Bubbleplate on June 15, 2002, 05:37:00 PM

OOOPS! Just realized my book lists temperatures in Centigrade, not Fahrenheit!! Duh!
And double checking my Merck Index I see that the flash point is a little too close to the boiling point for my comfort - vacuum definitely a requirement. And it does indeed mix with H2O up to 10%. Sigh.
I thought I remember reading that nitro forms explosive compounds with Calcium? True? Does that mean it's NOT a good idea to dry with Calcium containing stuff?
Also, anyone know if straight nitro is available (for automotive use) OTC? Or does one have to sign for, etc.?

Title: Flash point
Post by: moo on June 15, 2002, 06:18:00 PM

But it isn't going to burst in flames at the flash point, just become ignitable.

Title: Flash point.
Post by: terbium on June 15, 2002, 06:58:00 PM

But it isn't going to burst in flames at the flash point
NO! This seems to be a common misunderstanding of the term "flash point" given the number of times this has had to be explained. Perhaps you can UTFSE to find an explanation of the term "flash point" and then post the link here.

Edit:
And I see that I misread moo's statement. Moo said it isn't going to burst into flames; a correct statement. While I read isn't it going to burst into flames; a question implying the standard misunderstanding of the term. Sorry moo!

Title: link
Post by: metwurst on June 16, 2002, 04:01:00 PM

From LaBTop's post:

Post 306128 (https://www.thevespiary.org/talk/index.php?topic=9068.msg30612800#msg30612800)

(LaBTop: "Well2,", Methods Discourse)
"The important parameters of a flammable liquid are:

The flashpoint of a material is the lowest temperature at which sufficient vapour is given off to form an ignitable mixture with air (in the standard test apparatus employed). The lower the flashpoint, the more hazardous the material. Some extremely flammable liquids have flashpoints below --30<so>sC.

The lower and upper explosive limit ---- They are the minimum or maximum concentration of the substance in air below the mixture is too lean to burn, and above which it is too rich. For some materials, the range between these limits is 10-80%.
"

And from the Physical and Theoretical Chemistry Laboratory, Oxford University

website (http://ptcl.chem.ox.ac.uk/MSDS/glossary/autoignitiontemperature.html)

(http://ptcl.chem.ox.ac.uk/MSDS/glossary/autoignitiontemperature.html):

"Autoignition temperature: The Auto-ignition Temperature of a chemical is the lowest temperature at which a material will ignite without an external source of ignition."