# Optimal Conditions for CO2/n-Hexane Flash Separation

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A liquid stream, composed of carbon dioxide () and -hexane (-), has a flow rate of 100 kg/hr and a pressure of 100 bar. This stream is fed to a flash distillation vessel operating at a lower pressure and a user-set value of the temperature . The phi-phi approach is used with the Peng–Robinson equation of state (PR EoS) to compute the mass flow rates of in the exiting vapor stream (), as well as the mass flow rate of -hexane in the exiting liquid stream (). This Demonstration determines the pressure at which a profit function reaches its maximum value (indicated in the plot by a green dot). It is assumed that this objective function (expressed in $/hr) is equal to . The arc-length continuation technique is employed to generate in one single calculation the red curve (i.e. the profit curve versus pressure). The values of the optimal pressure and maximum profit are both reported in green on the plot.

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Contributed by: Housam Binous and Ahmed Bellagi (January 2017)

Open content licensed under CC BY-NC-SA

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References

[1] M. Morales. *Aspen Plus V8.0 Tutorial–Sensitivity Analysis* [Video]. (Dec 30, 2016) www.youtube.com/watch?v=L8inROJ10Jw.

[2] Aspentech. "Aspen Plus." (Dec 30, 2016) www.aspentech.com/products/engineering/aspen-plus.

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