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The solutions to midterm #2 for a chemical engineering 140 course, including calculations for molar compositions, recycle ratios, conversions, and final compositions of streams. It also discusses the annual production rate of acetic acid and potential uses for the vapor stream.
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Midterm #2 Solutions
AVERAGE: 80/205 (39%) S.D.: 35 HIGH: 182/205 (89%)
Grade Disribtution:
CHE 140 Midterm 2 Grade Distribution
0
5
10
15
20
0-30 31-50 51-70 71-90 91-110 111-130 131+
Regrade Policy: DO NOT WRITE ON YOUR EXAMS Please make a photocopy. Write on the photocopy anything that we may have missed. Hand in the original and the photocopy to your TA by Friday, November 18.
Midterm #2 Solutions
( 205 ) 1. The problem is simplified below with labeled streams, their components and compositions as given in the problem statement.
Component A = salicylic acid Component B = acetic anhydride Component C = acetylsalicylic acid (Aspirin) (Product) Component D = acetic acid
A + B → C + D MW = 138 MW = 102 MW = 180 MW = 60
Choose 100 mol basis for Stream E (reactor feed).
E = 13.93 * 1.18 =^ 16.44 mol^ +
Stream E 100 mol basis A 13.93 mol B 16.44 mol D
Stream F A B
Stream G B D
Stream H A B C D
Stream I A B ( 1.724 mol%) C D
Stream J W
Stream K A B C D W
Stream L B D W
Stream M A (11.86 wt%) C W (0.44 wt%)
(
B
Reactor Centrifuge
Dryer Wash Tank
Stream E 100 mol basis A 13.93 mol B 16.44 mol D 69.63 mol
Stream F A B
Stream G B D
Stream H 100 mol A 2.09 mol B 4.63 mol C 11.84 mol D 81.47 mol
Stream I A B ( 1.724 mol%) C D
Stream J W
Stream K A B C D W
Stream L B D W
Stream M A (11.86 wt%) C W (0.44 wt%)
ol +
DE = 100 – 13.93 – 16.44 = 69.63 m AH = 13.93 – (0.85)13.93 = 2.09 mol BH = 16.44 – (0.85)13.93 = 4.59 mol + C (^) H = 0 + (0.85)13.93 = 11.84 mol + DH = 69.63 + (0.85)13.93 = 81.47 mol +
for Stream H:
H = 100 mol Mole fractions A: 0.0209 +2. B: 0.0459 +2. C: 0.1184 +2. D: 0.8147 +2.
No slightly off; text above is correct
te: Numbers in diagram may be
Midterm #2 Solutions
(40) v. Determine the final composition (in wt %) of the vapor stream leaving the dryer. Based on e annual production rate, how many pounds of acetic acid are produced by this process per year?
illing in Stream K should be straight forward.
38 g / mol] = 288 g 6 ⇒ M = 2428 g
l ol
g L = 11.84 mol [ 60 g / mol ] =^ 710.4 g .8 g
th
J = 5.8 * 26.22 = 152.07 mol F BL = 0.45 mol
Reactor Centrifuge
Dryer Wash Tank
Stream E 100 mol basis A 13.93 mol B 16.44 mol D 69.63 mol
B D
Stream H 100 mol A 2.09 mol B 4.63 mol C 11.84 mol D 81.47 mol
Stream I 26.22 mol A 2.09 mol B 0.45 mol C 11.84 mol D 11.84 mol
Stream J 152.08 mol W 152.08 mol
Stream K 178. A 2.09 mol B 0.45 mol C 11.84 mol D 11.84 mol W 152.08 mol
Stream L 3483.1 g B 0.45 mol, 45.9 g D 11.84 mol, 710.4 g W 151.49 mol, 2726.8 g
Stream M A 2.09 mol, 288 g C W 0.593 mol, 10.68 g
Stream F 25.89 mol A 13.93 mol 11.96 mol
Stream G 74.11 mol B 4.18 mol 69.63 mol
DL = 11.84 mol AM = 2.09 mol AM = 2.09 mol [ AM = M * 0. WM = 0.0044 * 2428 = 10.68 g WM 10.68 / [18 g / mol] = 0.593 mo WL = 152.08 – 0.593 = 151.49 m
BL = 0.45 mol [ 102 g / mol ] = 45. D WL = 151.49 mol [ 18 g / mol ] = 2726 L = 45.9 + 710.4 + 2726.82 = 3483.1 g Mass fractions for Stream L: B: 45.9 / 3483.1 = 0. D: 710.4 / 3483. L: 2726.8 / 3483.1 = 0.
+ Pro y w to Stream M. 5
perl orking with component A + Calculating the amount of W in Stream M (mass or mols). +5 Calculating the amound of B, D, and W in Stream L (mass or mols). +5 Determing the wt% of B, D, and W in Stream L.
The annual production rate of acetic acid can be found before completing part (v). This was graded similar to part iv.
35,
tonC yr
1 tonmolC 180 tonC
11.84 tonmolD ⎠ 11.84 tonmolC
60 tonD ⎠ 1 tonmolD
2000 lbs ⎠ 1 ton
⎟ =^ 23,300,000 lbsD ⎠
(15) vi. Given that acetic acid is an important industrial chemical, what might we do with this vapor ream?
some reasonable separation process that could be applied to the stream: + uggest either selling the acetic acid or applying it to another process: +
ords: + cid into the process given in the problem. Since
g costs?
st
Mention S Suggest recycling it into the same process: - Mention collecting it, but without saying what should be done with it afterw Some students suggested recycling the acetic a acetic acid is a byproduct (and we already have enough solvent), this is inappropriate.
(15) vii. How might we take advantage of process streams to reduce heating and coolin
Midterm #2 Solutions
Use term heat exchange reasonably: + Describe where the heat exchanger should be placed: + t less useful: + ial heating is possible: -
Other creative ideas that are possible, bu Stream H and K chosen, but did not mention that only part
