Mixture flash point lower than two pure components: Study, is this a common effect?

[jamesbanda]

I’ve been made aware of a paper on Flash point predictions for binary mixtures. Which describes systems with mixture flash points that can be 10-15 C lower than the pure components within the mixtures. These are for non-reacting systems, I am aware of systems which react with air and then form a different compound it is explainable that the flash point is lower. But I’d like to understand if this is an industry wide phenomenon or only related to certain chemicals with non-ideal properties. I've been working in a certain industry for some time and never heard of this before..

For example the paper presents octane and methanol as having individual flash points of 9 and 11C, but the mixture flash point is shown going down to 1C. A similar trend is seen heptanes and ethanol

The paper is by MIGVIA DEL C VIDAL VAZQUEZ, “BINARY MIXTURE FLAMMABILITY CHARACTERISTCS FOR HAZARD ASSESSMENT”, Written in 2005 at the Texas university.

I’d like to see if members of the group are aware of this issue / effect and is it widely understood. This is the first time I’ve been aware of this effect.

 

[sshep]

Hey James,

Interesting. I don't know much about flashpoints of mixtures as a subject itself, but I do know that alcohols and paraffin systems that you have stated form minimum boiling azeotropes- i.e. the vapor pressure of the mixture is higher than the pure component vapor pressures. I propose that the flash point may be a consequence of the azeotrope phenonmonen.

best wishes,
Sean

 

[Compositepro]

The flash point is where the concentration of flammable vapors reaches the lower flammable limit in air. There are many liquid mixtures where the vapor pressure of each component is not directly proportional its liquid concentration. For example two immiscible liquids will each exert their full vapor pressures.