4.42. An equimolar liquid mixture of benzene and toluene is separated into two product streams by distillation. A process flowchart and a somewhat oversimplified description of what happens in the process follow: Vapor-97% mole benzene Reflux Overhead product n(mol) CONDENSER n,(mol) Feed 100 mol DISTILLATION COLUMN 0.500 mol B/mol 0.500 mol T/mol Boilup Yu[mol B(v/mol) Bottoms product REBOILER "almol B(I/mol) Problems 189 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 Yg/(1 – yg) Хв/(1 — хв) = 2.25 where yg and xg 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) Calculate the molar amounts of the overhead and bottoms products, the mole fraction of benzene in the bottoms product, and the percentage recovery of toluene in the bottoms product (100 x moles toluene in bottoms/mole toluene in feed).
4.42. An equimolar liquid mixture of benzene and toluene is separated into two product streams by distillation. A process flowchart and a somewhat oversimplified description of what happens in the process follow: Vapor-97% mole benzene Reflux Overhead product n(mol) CONDENSER n,(mol) Feed 100 mol DISTILLATION COLUMN 0.500 mol B/mol 0.500 mol T/mol Boilup Yu[mol B(v/mol) Bottoms product REBOILER "almol B(I/mol) Problems 189 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 Yg/(1 – yg) Хв/(1 — хв) = 2.25 where yg and xg 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) Calculate the molar amounts of the overhead and bottoms products, the mole fraction of benzene in the bottoms product, and the percentage recovery of toluene in the bottoms product (100 x moles toluene in bottoms/mole toluene in feed).
Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN:9781259696527
Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Chapter1: Introduction
Section: Chapter Questions
Problem 1.1P
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Transcribed Image Text:4.42. An equimolar liquid mixture of benzene and toluene is separated into two product streams by distillation.
A process flowchart and a somewhat oversimplified description of what happens in the process follow:
Vapor-97% mole benzene
Reflux
Overhead product
n(mol)
CONDENSER
n,(mol)
Feed
100 mol
DISTILLATION
COLUMN
0.500 mol B/mol
0.500 mol T/mol
Boilup
Yu[mol B(v/mol)
Bottoms product
REBOILER "almol B(I/mol)
Problems 189
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
Yg/(1 – yg)
Хв/(1 — хв)
= 2.25
where yg and xg 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) Calculate the molar amounts of the overhead and bottoms products, the mole fraction of benzene in
the bottoms product, and the percentage recovery of toluene in the bottoms product (100 x moles
toluene in bottoms/mole toluene in feed).
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