Flash Distillation of a Mixture of Four Hydrocarbons

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Consider a liquid feed composed of ‐butane, ‐pentane, ‐heptane, and ‐octane at 50 °C and 1000 kPa. The feed has a flow rate of 10 kmol/hr and contains mole% for each of the four hydrocarbons.


The Demonstration calculates the composition of the liquid and vapor leaving the flash vessel for user-selected values of the flash pressure, , and the added heat rate, , expressed in kJ/hr. The adiabatic flash distillation case is recovered if one sets . Values of the flash pressure (in kPa) and temperature (in Kelvin) are also displayed.


Contributed by: Housam Binous, Naim Faqir, and Brian G. Higgins (November 2012)
Open content licensed under CC BY-NC-SA



Fugacity coefficients as well as enthalpy correction functions are calculated using the Peng–Robinson equation of state [1, 2].

Expressions for ideal-gas constant-pressure heat capacities were obtained from Aspen-HYSYS.


[1] E. J. Henley and J. D. Seader, Equilibrium-Stage Separation Operations in Chemical Engineering, New York: Wiley, 1981.

[2] D-Y. Peng and D. B. Robinson, "A New Two-Constant Equation of State," Industrial and Engineering Chemistry Fundamentals, 15(1), 1976 pp. 59–64. DOI: 10.1021/i160057a011

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