4 replies to this topic

[AKsrey]

I have a solid that sublimes in an organic solution. I need some help estimating the amount of the solid that enters the vapor space.

[MrShorty]

I'm not sure if this will be helpful, and there isn't much information to go on, but here are a couple of ideas:

1) If there's a solid phase present (solid vapor equilibrium SVE or solid liquid vapor equilibrium SLVE), I'd probably simply assume the partial pressure of the solid is equal to the sublimation pressure of the pure solid. Of course, I'm assuming you have an expression or tabulated data for the sublimation pressure.

2) If there's no solid phase present, but the solid is dissolved in the organic liquid (vapor liquid equilibrium VLE), then I might start by using Raoult's law to calculate the partial pressure of the solid. If you have information for activity coefficients, you could use that to improve the estimate.

Does that help any?

[AKsrey]

I'm not sure if this will be helpful, and there isn't much information to go on, but here are a couple of ideas:

1) If there's a solid phase present (solid vapor equilibrium SVE or solid liquid vapor equilibrium SLVE), I'd probably simply assume the partial pressure of the solid is equal to the sublimation pressure of the pure solid. Of course, I'm assuming you have an expression or tabulated data for the sublimation pressure.

2) If there's no solid phase present, but the solid is dissolved in the organic liquid (vapor liquid equilibrium VLE), then I might start by using Raoult's law to calculate the partial pressure of the solid. If you have information for activity coefficients, you could use that to improve the estimate.

Does that help any?

[AKsrey]

Yes As you suggest the real problem is data. The solid is tetramethylsuccinonitrile which is a decomposition product of the polymerization initiator AIBN ( Vazo 64 ). I can find only a small amount of data, but so far none that relates to vapor pressure.

Thanks

[MrShorty]

It seems that in most phase equilibrium problems for mixtures we use pure component properties to define the standard state or ideal state. In my experience it is, as you note, difficult to calculate the phase equilibria if you can't calculate the standard or ideal state.

It depends on how crucial this calculation is, but I see there is some data available for succinonitrile. I haven't thought through what the effect of the four methyl groups would be, but I might use the data for succinonitrile to come up with some estimate for the properties of tetramethylsuccinonitrile. Downside to that is that, at some point, you start estimating based on estimates (based on estimates based on estimates...). How many layers of estimates before you decide it's not any better than drawing numbers out of a hat?