At 05:49 PM 3/26/2014, Larry Alofs wrote:
>What intrigues me about the original question is what actually
>happens when you heat a mixture (say 50-50) of water and ethylene
>glycol to its boiling point.  Does the ethylene glycol become more
>concentrated or do they vaporize together as happens when we use
>acetone for examle to dry lab glassware.

Me too.  I haven't found anything conclusive with a mild search.  A
few data point:

If you take a 70:30 glycerine:water mixture in a sprinkler system and
spray it into a domestic grease fire in Truckee, California, there
will be a big explosion that kills your wife and burns you severely,
blows window glass 85 feet, and knocks the casings of pre-cased
interior doors apart.  This seems to be the event that caught the
NFPA's attention in 2009, though similar things had happened before.

At least one 50:50 premix MSDS lists it as NFPA 704 fire 1, health 2,
reactivity 1; same as pure ethylene glycol.  It shows flash point as
N/A because >20% water, but autoignition temp 748F (quoted as pure glycol).

Ethylene glycol just makes it into NFPA 704 fire 1, as its flash
point (closed-cup method) is about 238F against a threshold of 200F for fire 2.

Autoignition point is listed variously at 748F or 770F.

Boiling point 387F.

Heat of vaporization 369 BTU/lb vs 970 BTU/lb for water.

Comparison: autoignition point of gasoline varies by composition,
range of roughly 475-535F.  Diesel about 410F.  Propane about
880F.  Paper about 425-475F.  Triethylborane -4F. <-- watch out for that stuff!

I suspect that a lot depends on the particular conditions obtaining
at the time.

Yrs,
d