Calculating Flashpoint 2

[wmills]

Does anyone know how to calculate the theoretical flashpoint for organic solvents?

 

[Compositepro]

The flashpoint is the temperature where the vapor pressure of the solvent is equal to the lower flamable limit. You can look-up this data but it is probably easier to look-up the flaspoint.

 

[wmills]

Thanks. I understand what you've explained for a single solvent. I would like to calculate the flashpoint for a mixture of solvents. So, after I calculate the vapor pressure of the mixture, do I then compare that to the lowest "lower flammability limit" of the solvents in the mixture?

 

[Latexman]

"The flashpoint is the temperature where the vapor pressure of the solvent is equal to the lower flamable limit" is only an approximation. Things like molecular structure and contained oxygen, to name a few, probably put some variation into it. Look up the flashpoint. It's on most MSDS.


Good luck,
Latexman

 

[wmills]

If I create a new mixture of solvents, and I look up the flashpoint on each individual solvent from its respective MSDS, what can I predict about the flashpoint of the mixture without actually testing the flashpoint?

 

[phex]

try this link, perhaps this text will give you the neccessary hints as to how to calculate (predict) the flashpoint of a mixture.

http://www.galcit.caltech.edu/EDL/publications/reprints/flash.pdf

 

[Flareman]

To determine the lower flammability of a mixture of gases, use le Chatelier's principle such that

[100%/final mixture LEL] = SUM[ component%/component LEL]
You can get the LELs from tables.
Bear in mind that tables give values for 25degC. All LELs reduce as temperature increases and increase as temperature decreases.

Then you need a graph with temperature and % as axes.

If you can calculate the adiabatic flame temperature at the published LEL it will give you one reference point on a line of LEL vs %, for LEL = 0%. Another reference point is the LEL at 25 degC which you have. Project this line back to intercept the vapor pressure curve drawn on the same curve and that's the flash point.

Oh yes! It's an estimate so use carefully.

Try to get yourself a copy of an old Bureau of Mines publication No 627 which has section on this and plenty of references.


David

 

[TD2K]

http://www.hpiconsultants.com/blending/blendguide.htm

Is a reference I have and I'm been quite happy with it. I got it for viscosity blending calculations but they have a section on flashpoint blending calculations also. Not sure if they handle organic solvents rather than straight HC and my copy isn't right at hand, drop them an email. I've found them to be very responsive.

 

[phex]

TD2K:

i do realize this is not really good practice, but is it possible to get a copy of that blending guide from you? i've been mulling over it if i should buy it or not. have heard quite some about, and already needed this particular reference once (blending RVP), but never quite made the decision. also a problem is shipping to germany...

chris

 

[lubes]

If you want to play it safe, you could say that Flash Point of the blend equals Flash Point of the most volatile blend component. Conservative, but better than nothing.

For petroleum products, might want to correlate Flash Point to T5% of each component. Then blend distillation curves (process simulators such as HYSYS can do this) and obtain T5% of blend. Back calculate Flash Point of the blend using correlation & T5% of blend.