Question

For this problem, you are separating ethanol (more volatile) from water in three flash separators. The feed solution contains 100 mol/s with 30% ethanol by mole.The first flash unit is operated at 87 °F. The mole fractions of ethanol in the vapor phase and liquid phase are 0.42 and 0.09, respectively. The vapor stream leaving the first flash is then fed to a 2nd flash and the temperature is decreased to 83 °F.The mole fractions of the ethanol in the vapor stream and liquid stream out of this 2nd flash are 0.55 and 0.20, respectively. Finally, the vapor stream of the 2nd flash enters a 3rd flash where the temperature is dropped to 81 °F. The mole fractions of the ethanol in the vapor stream and liquid stream out of this 3 rd flash are 0.61 and 0.40.

a. Draw and label the diagram. Circle the unknowns. Determine the degrees of freedom.

b. Solve for each of the unknowns.

c. Now imagine that all the liquid streams from all three flash units are combined together in a mixer. Calculate the total molar flow rate and the mole fraction of ethanol exiting this mixer.

d. Calculate the total number of moles of ethanol leaving the 3rd flash unit as a vapor. What is the fraction of ethanol in the feed that is recovered in this stream?

e. What could you do to improve the fraction of ethanol that is recovered?

Answer 1

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DATE jaquar.conm (B) Impte balance F=D + B' = 0.33 DI and 36.36 me S0 aquar GROUP

jaquar.com 七 охо.IS. о.GI D3 + o.4 B 6 0.21 GROUP Motei

jaquar.com DATE.. Molk fra cluon は, 57-0 . 176 flash unit as