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[Berkeley04]

Hello everyone,

new to this.. it's been a while since I've brushed up on my chem e thermo! sorry if this is such a basic question for some.

I am heating a closed steel vessel (1 Liter) containing Hexane/Water at about 13/1 mass ratio. I purge the system with Nitrogen to remove any oxygen. The system is then heated anywhere from 100 - 200C.

I'd like to calculate the pressure as a function of temperature.

Somethings other things I know I have to consider in my calculations (that are throwing me off) are:
Head space volume.
Nitrogen vapor fraction.


First pass I ran the system at 120C, and obtained a pressure of 60psi.

I have access to perry's handbook and chem Cad thermo.. maybe someone can point me in the right direction using these tools.

Please help!

[djack77494]

Berkeley,
I would view the closed vessel as containing two parts. You have the liquid filled portion and the vapor space. Though a small part of the liquid may vaporize, the liquid volume is pretty near constant. The pressure in the head consists of the partial pressure exerted by the liquid constituents plus the trapped gas (nitrogen). As you heat the vessel, the partial pressure of your haxane/water mixture increases. You can estimate this by adding the partial pressures of the hexane and water, suitably adjusted for concentrations of each. (This assumes an ideal mixture.) Refer to the GPSA Handbooks or any thermo book for details, if needed.) In the vapor space, you have a known quantity of nitrogen. Its pressure will increase in response to a temperature increase. At your conditions, you can approximate the P-T relationship using the ideal gas law PV=nRT. Now simply add the haxane, water, and nitrogen partial pressures to get the total. Repeat as needed to get plot.