Partial pressure claculations

[koshyeng]

Can someone please guide me on partial pressure calculation for this applicaion.

I have a tank filled with acetone-polymer mixture(for simplicity I assume 100% acetone) and pressurized to 500 psig with hydrogen. What would be the partial pressure of hydrogen in the tank when the temperature is raised to 150 deg F. Pressure is maintained at 500 psig with a control valve.

Appreciate your help.

 

[speco]

Koshyeng,

The total pressure is the sum of the two partial pressures of hydrogen and acetone vapor. If you know the saturation pressure of acetone at 150 F, that is its partial pressure. The remaining partial pressure is that of the hydrogen.

 

[sshep]

It is literally as simple as speco says. If the vapor pressure of acetone at 150F is 20psia, the partial pressure of H2 will be (500 + 14.7) - 20 = 494.7 psi. The H2 mol% will be (494.7/514.7).

best wishes,
sshep

 

[25362]

You have assumed "for simplicity" 100% acetone probably because the polymer has negligible vapor pressure. But if you have a solution of acetone and polymer, then the mol fraction in the liquid assuming an activity coefficient of 1.0 (which is not sure, I have encountered activity coefficients of 1.25 for acetone in non-electrolyte solutions at this level of temperatures) would have to be multiplied by the tabulated pressure to get the acetone contribution to the total pressure. Simply adding Raoult's law to the Dalton law for ideal solutions.

 

[koshyeng]

Thanks Guys.

You are right 25362. Vapor presuure of NBR rubber dissolved in acetone has no significant vapor pressure.Pressure control valve maintains 500 psi in the reactor as Hydrogen is being consumed.(hydrogenation on NBR rubber)

 

[Latexman]

In my experience, equilibria in a system with a fluid, either gas or liquid or both, and a solid can be much more complicated than vapor-liquid or liquid-liquid equilibria. Not only does the equilibria depend on the usual temperature, pressure and concentrations of components; it also depends on the physical form (amorphous or crystalline), method of preparation, and previous history of the solid. That said, I do not know your system nor the risk being taken from the outcome of your calculations. Your system may behave ideally; it may not. The risk may be small; it may jeopardize your career. If you don't know how your system behaves (why else would you be asking us) or the risk is too large, I recommend researching your system in the literature and/or the lab until you are comfortable.

Good luck,
Latexman

 

[koshyeng]

Latexman,

Appreciate your comments.
Lab data on Vapor phase compostion is 98.5% in agreement with the calculated molar composition of Acetone and Hydrogen based on partial pressures. This clearly indicates that atleast in this process, NBR has no significant contribution to vapor pressure. 1.5% difference could be due to monomers in the NBR rubber that vaporizes.

 

[koshyeng]

I am trying to get a good grip on this subject.

If I have acetone and water mixture(unknown composition from different sources) fed continuously to a tank at 4 psig( maintained by a PCV) and 201 deg F. What will be th e partial pressure of acetone?

Vapor pressure of acetone at 201 deg F is 46 psi.

Appreciate for educating me.

 

[Latexman]

I know acetone and water form an azeotrope, so you will probably need a liquid activity coefficient model to come up with reasonable answers. I believe we used the Wilson equation for acetone/water.

Good luck,
Latexman