LECTURE 9. Solving Material Balance Problems Involving Non-Reactive Processes Prof. Manolito E Bambase Jr. Department of Chemical Engineering. University of the Philippines Los Baños SLIDE 1 Example 9–5. Distillation of Benzene, Toluene, and Xylene A liquid mixture containing 30.0 mole% benzene (B), 25.0% toluene (T), and the balance xylene (X) is fed to a distillation column. The bottom product contains 98.0 mole% X and no B, and 96.0% of the X in the feed is recovered in this stream. The overhead product is fed to a second distillation column. The overhead product from the second column contains 97.0% of the B in the feed to this column. The composition of this stream is 94.0 mole% B and the balance T.
Transcript
LECTURE 9. Solving Material Balance Problems Involving Non-Reactive Processes
Prof. Manolito E Bambase Jr. Department of Chemical Engineering. University of the Philippines Los Baños SLIDE
1
Example 9–5. Distillation of Benzene, Toluene, and Xylene
A liquid mixture containing 30.0 mole% benzene (B), 25.0% toluene (T), and the balance xylene (X) is fed to a distillation column.
The bottom product contains 98.0 mole% X and no B, and 96.0% of the X in the feed is recovered in this stream. The overhead product is fed to a second distillation column.
The overhead product from the second column contains 97.0% of the B in the feed to this column. The composition of this stream is 94.0 mole% B and the balance T.
LECTURE 9. Solving Material Balance Problems Involving Non-Reactive Processes
Prof. Manolito E Bambase Jr. Department of Chemical Engineering. University of the Philippines Los Baños SLIDE
2
Example 9–5. Distillation of Benzene, Toluene, and Xylene
Calculate
a. the percentage of the benzene in the process feed (i.e. the feed to the first column) that emerges in the overhead product from the second column.
b. the percentage of toluene in the process feed that emerges in the bottom product from the second column.
LECTURE 9. Solving Material Balance Problems Involving Non-Reactive Processes
Prof. Manolito E Bambase Jr. Department of Chemical Engineering. University of the Philippines Los Baños SLIDE
3
Example 9–5. Distillation of Benzene, Toluene, and Xylene
LECTURE 9. Solving Material Balance Problems Involving Non-Reactive Processes
Prof. Manolito E Bambase Jr. Department of Chemical Engineering. University of the Philippines Los Baños SLIDE
4
Example 9–5. Distillation of Benzene, Toluene, and Xylene
DEGREES OF FREEDOM ANALYSIS
Unit: Column 1
unknowns (n2,n3,xB2,xT2)
+4
material balances –3
% recovery for X –1
Degrees of freedom 0
Unit: Column 2
unknowns (n2,n4,n5,xB2,xT2,xB5,xT5)
+7
material balances –3
% recovery for B –1
Degrees of freedom +3
LECTURE 9. Solving Material Balance Problems Involving Non-Reactive Processes
Prof. Manolito E Bambase Jr. Department of Chemical Engineering. University of the Philippines Los Baños SLIDE
5
Example 9–5. Distillation of Benzene, Toluene, and Xylene
LECTURE 9. Solving Material Balance Problems Involving Non-Reactive Processes
Prof. Manolito E Bambase Jr. Department of Chemical Engineering. University of the Philippines Los Baños SLIDE
6
Example 9–5. Distillation of Benzene, Toluene, and Xylene
DEGREES OF FREEDOM ANALYSIS on Entire Process
Unit: Entire Process
unknowns (n3,n4,n5,xB5,xT5) +5
material balances –3
% recovery for X –1
Degrees of freedom +1
LECTURE 9. Solving Material Balance Problems Involving Non-Reactive Processes
Prof. Manolito E Bambase Jr. Department of Chemical Engineering. University of the Philippines Los Baños SLIDE
7
Example 9–5. Distillation of Benzene, Toluene, and Xylene
Column 1 Calculations:
1. 96% recovery of X =====> n3 = 44.1 mol/h
2. Total Balance =====> n2 = 55.9 mol/h
3. Benzene Balance =====> xB2 = 0.536 mol B/mol
4. Toulene Balance =====> xT2 = 0.431 mol T/mol
Column 2 Calculations:
1. 97% recovery of B =====> n4 = 31.0 mol/h
2. Total Balance =====> n5 = 24.9 mol/h
LECTURE 9. Solving Material Balance Problems Involving Non-Reactive Processes
Prof. Manolito E Bambase Jr. Department of Chemical Engineering. University of the Philippines Los Baños SLIDE
8
Example 9–5. Distillation of Benzene, Toluene, and Xylene
Column 2 Calculations (cont.):
3. Benzene Balance =====> xB5 = 0.036 mol B/mol
4. Toulene Balance =====> xT5 = 0.892 mol T/mol
Additional Calculations:
4 B4
5 T5
n xamountinfinaloverhead%RecoveryB x100 97%
amountinfeed (100)(0.300)
n xamountinfinal bottom%RecoveryT x100 89%
amountinfeed (100)(0.250)
LECTURE 9. Solving Material Balance Problems Involving Non-Reactive Processes
Prof. Manolito E Bambase Jr. Department of Chemical Engineering. University of the Philippines Los Baños SLIDE
9
Example 9–6. Separation of Benzene and Toluene by Distillation
An equimolar liquid mixture of benzene and toluene is separated into two product streams by distillation.
The vapor stream leaving at the top of the column, which contains 97 mole% benzene, is fed to a condenser to undergo complete condensation.
The condensed liquid is split into two equal fractions: one is taken off as the final overhead product stream and the other (the reflux) is recycled to the top of the column.
The final overhead product contains 89.2% of the benzene fed to the column.
LECTURE 9. Solving Material Balance Problems Involving Non-Reactive Processes
Prof. Manolito E Bambase Jr. Department of Chemical Engineering. University of the Philippines Los Baños SLIDE10
Example 9–6. Separation of Benzene and Toluene by Distillation
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 the column, and the residual reboiler liquid is taken as the final bottom product stream.
The compositions of the streams leaving the reboiler are governed by the relation:
B B
B B
y /(1-y ) = 2.25x /(1-x )
LECTURE 9. Solving Material Balance Problems Involving Non-Reactive Processes
Prof. Manolito E Bambase Jr. Department of Chemical Engineering. University of the Philippines Los Baños SLIDE11
Example 9–6. Separation of Benzene and Toluene by Distillation
where yB and xB are the mole fractions of benzene in the vapor and liquid streams, respectively.
Using 100 mol of feed as a basis, calculate
a. the molar amounts of the overhead and bottoms products
b. the mole fraction of benzene in the bottoms product
c. and the percentage recovery of toluene in the bottoms product.
LECTURE 9. Solving Material Balance Problems Involving Non-Reactive Processes
Prof. Manolito E Bambase Jr. Department of Chemical Engineering. University of the Philippines Los Baños SLIDE12
Example 9–6. Separation of Benzene and Toluene by Distillation
LECTURE 9. Solving Material Balance Problems Involving Non-Reactive Processes
Prof. Manolito E Bambase Jr. Department of Chemical Engineering. University of the Philippines Los Baños SLIDE13
Example 9–5. Distillation of Benzene, Toluene, and Xylene
DEGREES OF FREEDOM ANALYSIS
Unit: Entire Process
unknowns (n3,n5,yB3)
+3
material balances –2
% recovery for B –1
Degrees of freedom 0
Unit: Dist. Column
unknowns (n2,n4,n5,yB2,yB4)
+5
material balances –2
Degrees of freedom +3
LECTURE 9. Solving Material Balance Problems Involving Non-Reactive Processes
Prof. Manolito E Bambase Jr. Department of Chemical Engineering. University of the Philippines Los Baños SLIDE14
Example 9–5. Distillation of Benzene, Toluene, and Xylene
DEGREES OF FREEDOM ANALYSIS
Unit: Reboiler
unknowns (n2,n3,n4,yB2,yB3,yB4)
+6
material balances –2
45 % vaporization –1
mole fraction relationship –1
Degrees of freedom +2
LECTURE 9. Solving Material Balance Problems Involving Non-Reactive Processes
Prof. Manolito E Bambase Jr. Department of Chemical Engineering. University of the Philippines Los Baños SLIDE15
Example 9–5. Distillation of Benzene, Toluene, and Xylene
