HW # 11-CHEN 354-Spring 10
Due Monday, April 12, 2010
Problem 1. Estimate the pressure and vapor-phase composition in equilibrium with a liquid whose
overall composition is 50 mol % furfural and 50 mol% isobutene at 37.8oC.
Data:
Saturation pressures at 37.8oC : Pisosat =4.909 bar; Pfurfsat = 4.93x10-3 bar.
Isobutane and furfural are only partially miscible in the liquid phase. At 37.8oC the two coexisting liquid
phases contain 11.8 and 92.5 mol % isobutene respectively, iso(at xiso = 0.925) =1.019, and furf(at xfurf
=0.882) =1.033.
Problem 2. Ethyl alcohol and n-hexane are put into an evacuated, isothermal container. After
equilibrium is established at 75oC, it is observed that two liquid phases and a vapor phase are in
equilibrium. One of the liquid phases contains 9.02 mol% of n-hexane. Activity coefficients for nhexane-ethyl alcohol liquid mixtures can be represented by
RT ln i = 8.163 xj2 kJ/mol
a. Compute the equilibrium composition of the coexisting liquid phase.
b. Compute the equilibrium pressure and vapor phase mole fractions
Data: Vapor pressure equations (T in K, P in bar)
ln Phexanesat = -3570.58/T + 10.4575
In PEOHsat = -4728.98/T + 13.4643
Problem 3. Ethanol and n-hexane form two liquid phases at many temperatures. Assuming that the
activity coefficients of n-hexane/ethyl alcohol mixtures can be represented by the equation RT ln gi
=8.163 xj2 kJ/mol and that the vapor pressures of the pure components are as in Problem 2, compute
the T-x-y diagram at pressures P= 0.1013 bar, P= 1.013 bar, and 10.13 bar.
Problem 4. At 25oC, a binary system is in a state of 3-phase VLLE. Analysis of the two equilibrium liquid
phases ( and ) yields the following compositions:
x2 =0.05;
x1 = 0.01
Vapor pressures for the two pure components at 25oC are:
P1sat = 0.7 bar; P2sat = 0.1 bar
Stating your assumptions, determine reasonable estimates of:
(a) the activity coefficients 1 and 2
(b) the equilibrium 3-phase pressure
(c) the equilibrium vapor compositions y1 and y2
(d) the activity coefficients 2 and 1
(e) Sketch the P-x1 diagram at 25oC.