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One hundred mol/s of a feed mixture containing 60.0 mol% n-pentane and 40.0 mol% n-hexane are separated in the distillation column shown below. The overhead vapor is essentially pure n-pentane and is saturated at 13.6 atm (200 psi) absolute pressure. The liquid stream leaving the bottom of the column is sent to a reboiler where a portion of it is vaporized and recycled to the column. The remaining liquid is taken out as the bottoms product and leaves the reboiler at 177 degree C (350 degree F). A sample of the bottoms product is analyzed and found to contain 67.0 mol% n-hexane. Determine: The molar flow rate of the overhead vapor and of the bottoms product. The temperature of the overhead vapor. The absolute pressure in the reboiler. The composition of the vapor leaving the reboiler.

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Trinidad TremblayLv2

24 Apr 2019

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Anequimolarliquidmixtureofbenzeneandtolueneisseparatedintotwoproductstreamsbydistillation. A process flowchart and a somewhat oversimplified description of what happens in the process follow:
Feed
100 mol 0.500 mol B/mol 0.500 mol T/mol
n1(mol) n1(mol) CONDENSER
DISTILLATION COLUMN
Boilup yB[mol B(v)/mol]
Vaporâ97% mole benzene
Reflux
Overhead product
Bottoms product
REBOILER xB[mol B(l)/mol]

Inside the column a liquid stream flows downward and a vapor stream rises. At each point in the column some of the liquid vaporizes and some of the vapor condenses. The vapor leaving the top of the column, which contains 97 mole% benzene, is completely condensed and split into two equal fractions: one is taken off as the overhead product stream, and the other (the reflux) is recycled to the top of the column. The overhead product stream contains 89.2% of the benzene fed to the column. The liquid leaving the bottom of the column is fed to a partial reboiler in which 45% of it is vaporized. The vapor generated in the reboiler (the boilup) is recycled to become the rising vapor stream in the column, and the residual reboiler liquid is taken off as the bottom product stream. The compositions of the streams leaving the reboiler are governed by the relation
yB/1 â£ yB 2:25 xB/1â£xB
where yB and xB are the mole fractions of benzene in the vapor and liquid streams, respectively. (a) Take a basis of 100 mol fed to the column. Draw and completely label a flowchart, and for each of four systems (overall process, column, condenser, and reboiler), do the degree-of-freedom analysis and identify a system with which the process analysis might appropriately begin (one with zero
degrees of freedom). (b) Write in order the equations you would solve to determine all unknown variables on the flowchart,
circling the variable for which you would solve in each equation. Do not do the calculations in this part. (c) Calculatethemolaramountsoftheoverheadandbottomsproducts,themolefractionofbenzenein the bottoms product, and the percentage recovery of toluene in the bottoms product (100 Ã moles
toluene in bottoms/mole toluene in feed).

A liquid mixture of 50% benzene (B), 45% toluene (T) and 5% non-volatile (S) is separated into two product streams by distillation. The process is continuous, non-reactive and steady state.

Inside the column a liquid stream flows downward and a vapor stream rises. The vapor leaving the top of the column contains 95 mole% benzene and balanced toluene. The vapor does not contain the non-volatile component (S). The vapor is completely condensed and split into two fractions: 60% is taken off as the overhead product stream, and 40% (the reflux) is recycled to the top of the column. The overhead product stream contains 90% of the benzene fed to the column.

The liquid leaving the bottom of the column, containing all three components, is fed into a partial reboiler in which 45% of it is vaporized. The vapor generated in the reboiler (the boilup) is recycled to become the rising vapor stream in the column, and the residual reboiler liquid is taken off as the bottom product stream. The recycled vapor (boilup) contain only benzene and toluene. The composition of the streams leaving the reboiler are governed by the relation:

(y_B/(1-y_B)) / (x_B/(1-x_B)) = 2.25

Where y_B and x_B are the mole fraction of benzene in the boilup vapor and liquid streams leaving the reboiler, respectively.

Choose a basis of 100 mole/h overhead product. Draw and completely label the flow chart with known and unknown information. Minimize the number of unknowns on the flowchart by using the information and relations provided.

Do degrees of freedom analysis for all individual units and the overall system. Identify a system with which the process analysis might appropriately begin.