11/12/10
Class 34 Friday, November 12th
Use
heats
of
combus.on
to
find
the
heat
of
reac.on
for:
C6H6
→
C2H4
+
H2
Heats of Combustion
Energy Balances on Reactive
Processes
(Heat of Reaction Method)
Use
heats
of
combus.on
to
find
the
heat
of
reac.on
for:
C6H6
→
C2H4
+
H2
Heat of Reaction Method Procedure
• Complete material balances as much as possible
• Choose reference states for reactants and products at
states where the specific heat of reaction, ΔHro, is
known and for any non-reactive species at any
convenient temperature
• Calculate the |extent of reaction| for each reaction
occurring in the process. Select as species A, any
reactant or product for which the feed and product flow
rates are known.
1
11/12/10
• Prepare enthalpy table
• Calculate specific enthalpy of each stream
component, ΔHi^, for the species going from its
reference state to the process state and add it to
the table
• Calculate ΔH via the following:
• ΔH=∑all j ξjΔHo^rj + ∑outniHi^ - ∑inniHi^
• substitute ΔH into energy balance and solve for
unknown
n-C4H10(g) → i-C4H10(g)
n- Butane is converted to isobutane in a
continuous isomerization reactor that
operates isothermally at 149o C. The feed
to the reactor contains 93 mole % nbutane, 5 % isobutane and 2 % HCl at
149o C, and a 40 % conversion of nbutane is achieved. What is the required
rate of heat transfer per mole of feed gas.
n-C4H10(g) → i-C4H10(g)
n- Butane is converted to isobutane in a continuous
isomerization reactor that operates isothermally at 149o C. The
feed to the reactor contains 93 mole % n-butane, 5 %
isobutane and 2 % HCl at 149o C, and a 40 % conversion of nbutane is achieved. What is the required rate of heat transfer
per mole of feed gas.
Which of the following is true?
.93 mol n
.05 mol i
.02 mol HCl
nn
ni
.02 mol HCl
149o C
a) We can ignore HCl in the material balance but not in the
energy balance.
b) We can ignore HCl in the energy balance but not in the
material balance.
c) We need to include HCl in both balances.
d) We don’t need to include HCl in either balance.
2
11/12/10
n- Butane is converted to isobutane in a continuous
isomerization reactor that operates isothermally at
149o C. The feed to the reactor contains 93 mole %
n-butane, 5 % isobutane and 2 % HCl at 149o C,
and a 40 % conversion of n-butane is achieved.
What should our reference state for n-butane be?
a) 149oC
b) 25oC
c) 0oC
Sub
d) Any temperature
you want
nin(mol)
Hin (kJ/
mol)
nout (mol)
0.93
H1
nn
H4
0.05
H2
ni
H5
HCl
0.02
H3
0.02
H6
n- Butane is converted to isobutane in a continuous isomerization
reactor that operates isothermally at 149o C. The feed to the
reactor contains 93 mole % n-butane, 5 % isobutane and 2 %
HCl at 149o C, and a 40 % conversion of n-butane is achieved.
What is ζ?
Hin (kJ/
mol)
nout (mol)
n-but
0.93
H1
nn
H4
i-but
0.05
H2
ni
H5
HCl
0.02
H3
0.02
H6
Sub
nin(mol)
Hin (kJ/
mol)
nout (mol)
Hout (kJ/
n-but
0.93
H1
nn
H4
i-but
0.05
H2
ni
H5
HCl
0.02
H3
0.02
H6
mol)
mol)
i-but
nin(mol)
Reference: n-butane, i-butane at 25oC, HCl at 149oC
Hout (kJ/
n-but
Sub
n- Butane is converted to isobutane in a continuous
isomerization reactor that operates isothermally at 149o C.
The feed to the reactor contains 93 mole % n-butane, 5 %
isobutane and 2 % HCl at 149o C, and a 40 % conversion of
n-butane is achieved. What is nn?
n- Butane is converted to isobutane in a continuous
isomerization reactor that operates isothermally at 149o C.
The feed to the reactor contains 93 mole % n-butane, 5 %
isobutane and 2 % HCl at 149o C, and a 40 % conversion of
n-butane is achieved. What is ni?
Hout (kJ/
mol)
Sub
nin(mol)
Hin (kJ/
mol)
nout (mol)
n-but
0.93
H1
.56
Hout (kJ/
H4
i-but
0.05
H2
ni
H5
HCl
0.02
H3
0.02
H6
mol)
3
11/12/10
n- Butane is converted to isobutane in a continuous
isomerization reactor that operates isothermally at 149o C.
The feed to the reactor contains 93 mole % n-butane, 5 %
isobutane and 2 % HCl at 149o C, and a 40 % conversion of
n-butane is achieved. What is H1 ?
Sub
nin(mo
l)
Hin
(kJ/
nout
(mol)
(kJ/mol)
n- Butane is converted to isobutane in a continuous
isomerization reactor that operates isothermally at 149o C.
The feed to the reactor contains 93 mole % n-butane, 5 %
isobutane and 2 % HCl at 149o C, and a 40 % conversion of
n-butane is achieved. What is H2 ?
Sub
Hout
nin
Hin
(mol) (kJ/mol)
nout
(mol)
(kJ/mol)
Hout
mol)
n-but
0.93
H1
0.56
H4
n-but
0.93
14.287
0.56
H4
i-but
0.05
H2
0.42
H5
i-but
0.05
H2
0.42
H5
H6
HCl
0.02
H3
0.02
H6
HCl
0.02
H3
0.02
n- Butane is converted to isobutane in a continuous
isomerization reactor that operates isothermally at
149o C. The feed to the reactor contains 93 mole %
n-butane, 5 % isobutane and 2 % HCl at 149o C,
and a 40 % conversion of n-butane is achieved.
What is H3 ?
a) 10.36
b) 11.45 c) 14.14
Sub
nin
Hin
(mol) (kJ/mol)
nout
(mol)
(kJ/mol)
n-but
0.93
14.287
0.56
H4
i-but
0.05
12.86
0.42
H5
HCl
0.02
H3
0.02
H6
Hout
n- Butane is converted to isobutane in a continuous
isomerization reactor that operates isothermally at
149o C. The feed to the reactor contains 93 mole %
n-butane, 5 % isobutane and 2 % HCl at 149o C,
and a 40 % conversion of n-butane is achieved.
What is H4 ?
d) it doesn’t matter
Sub
nin(mol)
Hin (kJ/
mol)
nout (mol)
Hout (kJ/
mol)
n-but
0.93
14.287
0.56
H4
i-but
0.05
12.86
0.42
H5
4
11/12/10
n- Butane is converted to isobutane in a continuous
isomerization reactor that operates isothermally at
149o C. The feed to the reactor contains 93 mole %
n-butane, 5 % isobutane and 2 % HCl at 149o C,
and a 40 % conversion of n-butane is achieved.
Sub
n-but
i-but
nin(mol)
Hin (kJ/
nout (mol)
Hout (kJ/
0.93
14.287
0.56
14.287
0.05
mol)
n- Butane is converted to isobutane in a continuous
isomerization reactor that operates isothermally at
149o C. The feed to the reactor contains 93 mole %
n-butane, 5 % isobutane and 2 % HCl at 149o C,
and a 40 % conversion of n-butane is achieved.
What is ΔHrxn in kJ/mol?
mol)
12.86
0.42
12.86
Sub
nin(mol)
Hin (kJ/ nout (mol)
mol)
Hout (kJ/
mol)
n-but
0.93
14.287
0.56
14.287
i-but
0.05
12.86
0.42
12.86
n- Butane is converted to isobutane in a continuous
isomerization reactor that operates isothermally at 149o C.
The feed to the reactor contains 93 mole % n-butane, 5 %
isobutane and 2 % HCl at 149o C, and a 40 % conversion of
n-butane is achieved. What is Q in kJ?
Sub
nin(mol)
Hin (kJ/ nout (mol)
mol)
Hout (kJ/
mol)
n-but
0.93
14.287
0.56
14.287
i-but
0.05
12.86
0.42
12.86
5