I wish to calculate the boiling point of the following solution.

78.8% Glycerol, 11.6% Propylene Glycol, 8.3% Water, 1.2% Nicotine
(molar fraction)
0.5790 Glycerol, 0.1037 Propylene Glycol, 0.3121 Water, 0.0052 Nicotine

I am trying to use Raoults law, after ruling out Boiling point elevation (due to the number of solutes), but I'm stuck with getting the vapor pressure values for each solute since I don't yet know the temperature.

So as I understand it, at some temperature, the sum of each component's vapor pressure will equal 1atm. This temp is what I wish to calculate. Am I on the right track? Any advice appreciated.

EDIT: - Additional;

I've found Antoine's equation.
Also found Antoine values for all ingredients from webbook.nist.gov
Note: Antoine values used for Glycerol (57% mol.frac) are only valid over 456°K, a full 48° more than my calculated BP.

Have made a spreadsheet and got a result of 135°C, which is considerably lower than what I had expected.

View/Edit spreadsheet here

Have I used a sensible method to calculate BP for this solution?

Obviously, this is for my DIY e-cig juice, not commercial, just read something that piqued my interest and needed to investigate.

EDIT 2: Additional.

Thank you Ivan, porphyrin and airhuff for your comments, they were helpful to my understanding. I wish I had some equipment to actually experiment instead of calculate. But in saying that I would have been happy with a +-10°C result.

Also thank you user44840, I had not heard of bubble point or known the difference from boiling point.

So now as i understand it (please forgive me for being persistent, and correct wherever I'm wrong) Dew point is used (as a upper limit) due to the changing molar fraction of the mixtures components as it evaporates, which in this case increases the boiling point as glycerine concentration increases.

So (looking at user44840's diagram, and over simplifying) if I put the solution into a beaker and apply heat I would see the first bubbles at approx 150°C and the last of the solution would remain until ~290°C? (Ignoring PG, Nic and Glycerine decomposition at 280°C)

I am having a problem reconciling this information with my actual experience using an e-cig. I have never noticed a viscosity difference between the start and end of a tank, which would be easily noticeable even if only 50% of the water was removed. (Water is used as a thinner since glycerine is far too viscous). However I quickly found on google people claiming to experience this exact thing. I guess also glycerine being hygroscopic may also account for my experience above.

It is now obvious my question is of limited theoretical use, and reality has far too many variables for such a simple analysis.

As Ivan suggested "Chemistry is an experimental science, after all." Anyone want to let me in their lab for a day?

Thanks once again folks.

  • 3
    $\begingroup$ You'd rather not put too much trust in the calculations. Chemistry is an experimental science, after all. I would expect a mixture like this to be markedly non-ideal and hence deviate from Raoult's law in an unpredictable way. $\endgroup$ – Ivan Neretin May 3 '17 at 10:10
  • 1
    $\begingroup$ I agree with @Ivan Neretin, calculation will not be that helpful as alcohol water mixtures show considerable deviations from Raoult's law. A good place to start might be to look for glycerol water boiling temperatures at different compositions, some data is here engineeringtoolbox.com/… $\endgroup$ – porphyrin May 3 '17 at 10:35
  • $\begingroup$ I agree with porphyrin that the link he gave is a good place to start. The only comment I would make is to not waste your time and efforts accounting for the effect of nicotine. Whatever BP estimate you come up with will be in the +/- 10's of degrees arena anyway, and compensating for the effect of that small amount of nicotine will not improve this at all. Your spreadsheet kind of validates this too. Anyway, good luck! $\endgroup$ – airhuff May 5 '17 at 2:33
  • $\begingroup$ You may want to contact the team to merge your accounts. $\endgroup$ – Martin - マーチン May 8 '17 at 10:53

Raouls law is a good method to estimate about what the "boiling point" will be. The bubble point is the lowest temperature that a mixture will be in vapor liquid equilibrium. What you actually want is the dew point. Mixtures don't have a boiling point like pure water. Instead, mixtures have a range at which they will be in a state of VLE or vapor liquid equilibrium. So you need to find the temperature that no liquid exists i.e. The dew point Phase diagram glycerol and water


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