Assignment Solution 8
Chemical Engineering 2800 (Summer 2008)
Fundamentals of Process Engineering
University of Utah
Dr.Mataz Alcoutlabi
Problem 1
19.23, p. 587
Calculate the bubble point of a liquid mixture of 80 mole% nhexane and 20 mole% n
pentane at 200 psia.
Solution
Find BP for nhexane, npentane at 200 psia with x
p
= 0.20
Data:
*
*
10
log (
)
,
,
B
p
A
p
bar T
K
T
C
=

=
=
+
A
B
C
pentane
3.9892
1070.6
2
40.454
Hexane
4.0026
6
1171.5
3
48784
Total pressure by Raoults’ law is
*
*
(
)
p
h
tot
p
h
p
h
tot
p
h
p
p
p
x p
x p
p
y
y
=
+
=
+
=
+
Or
*
*
1
p
h
p
h
i
tot
tot
p
p
x
x
y
p
p
=
+
=
Solve using Goal Seek in Excel
Total pressure is
200
1.01325 13.79
14.696
tot
p
x
bar
=
=
447
345
BP
T
K
F
=
=
Extra credit:
*
0.330,
1
0.670
p
p
p
h
p
tot
p
y
x
y
y
p
=
=
= 
=
Problem 2
19.26, p. 587
A liquid mixture of npentane and nhexane containing 40 mole percent npentane is fed
continuously to a flash separator operating at 250
°
F and 80 psia. Determine:
a)
The quantity of vapor and liquid obtained from the separator per mole of feed.
b) The composition of both the vapor and the liquid leaving the separator.
Solution
Flash separator at T = 250
°
F, p
tot
= 80 psia
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View Full DocumentUse p* from the previous problem
•
Overall balance: F – V – L = 0
•
Balance on pentane:
0
Fp
p
p
Fx
Vy
Lx


=
Assume ideal solution:
*
i
i
tot
i
y p
x p
=
Then
*
*
*
h
h
tot
p
p
p
p
x
p
p

=

and
*
p
p
p
tot
p
y
x
p
=
And
,
1
p
Fp
p
p
y
x
L
V
L
F
y
x
F
F

=
= 

No iteration is required. Calculation performed in Excel
)
0.645,
0.355
)
0.466,
0.280
0.534,
0.720
p
p
h
h
V
L
a
F
F
b y
x
y
x
=
=
=
=
=
=
Problem 3
19.30, p. 588
Late in the evening of 21 Aug1986 a large volume of toxic gas was released from beneath
and with Lake Nyos in the Northwest Province of Cameroon. An aerosol of
water mixed
with toxic gases swept down the valleys to the north of Lake Nyos, leaving more than
1700 dead and dying people in its wake. The lake had a surface area of 1.48 km2 and a
depth of 200250 m. It took 4 days to refill the lake, hence it was estimated to have lost
about 200000 tons of water during the gas emission. To the south of the lake and in the
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 Summer '08
 process
 OC, mm Hg, Lake Nyos, exit air

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