Gazi University
Department of Chemical Engineering
Che 341 Chemical Reaction Engineering
2008-2009 Fall Semester
Prof.Dr. Çiğdem GÜLDÜR
Res.Asst.D.Dolunay ESLEK KOYUNCU
December 5, 2008
Problem Set-5
(Energy Balance-II)
1) The irreversible first order liquid phase reaction
AR
is to be carried out in an insulated mixed flow reactor. The feed enters in to the reactor at 25 0C.
The feed concentration of the reactant (A) is 1 kmol/m3 and the volumetric flow rate is 0.025
m3/s. The reactor is equipped with cooling system in order to keep the reactor temperature
constant and coolant fluid enters to the cooling coil, placed in to the reactor, at 15 0C and leaves at
200C. Calculate the heat transfer area required.
Data:
HR= -1.46x107 J/mol
k 298 = 0.11 s-1
U= 2280 J/(m2.s.K) (Overall heat transfer coefficient)
V= 6 m3
2) A first order liquid phase endothermic reaction A  products take place in a CSTR. The feed
concentration (CA0) is 1.25 mol/L, the feed rate (o) is 20 L s-1, and the volume of the reactor
(V) is 20 000 L. The enthalpy of the reaction (  HR) is +50 kj/mol, the specific heat of the
reacting system is 3 J /g K, and its density is 900 g/L.
(a) If the feed temperature (T0) is 300K, at what temperature (Tc) must a heating coil in
the tank be maintained to keep the temperature (T) of the reaction in the tank the
same as T0? What conversion is obtained? At 300K, the rate constant k A=4x10-3 s-1.
For the coil, assume UA= 10 kj/s K
(b) If there were no heating coil in the tank, what should be temperature (T0) be to
achieve the same result?
3) A first order gas-phase reaction, A  C, is conducted in a nonisothermal PFR, operating
isobarically. Equimolar amounts of A and an inert species are fed to the reactor at a total rate
of 8 L/min, with CA0= 0.25 mol/L. Determine the residence time required for 50% conversion
of A, if operation is (a) adiabatic; and (b) nonadiabatic, using the following data:
Data: kA= 1.3x1011 e-(10550/T) s-1 with T in K
T0= 100 0C
 HR= -15.5 kj/mol
MA=MB= 200 g/mol
2
U= 100 W/m K
Cp= 37.0 J /mol K
dt= 2cm
Ts= 80 0C
1
4) An exothermic first-order liquid-phase reaction A R is conducted in a PFR. Determine the
volume required for 90% conversion of A, if the process is adiabatic.
Data: CpA= 143.75 J /mol K
CpR= 264.1 J /mol K
CA0= 2.5 mol/L
o = 360 L/h
 HR= -19000 j/mol
 = 0.85 g/cm3
kA= 2.1x107 exp (-6500/T) min-1
T0= 325 K
5) A gas-phase reaction A + B 2C is conducted at steady state in a PFR. The reaction is first
order with respect to both A and B. the reactor, constructed of stainless steel with a surface
roughness of 0.0018 inches, has a diameter of 1.5 cm and a length of 10 m. the feed contains
60 mol % A and 40 mol % B. the following data also apply:
Data:
CpA= 0.85 J /g K
CpB= 0.95 J /g K
CpC= 1.0 J /g K
o = 5.5 L/s
T0= 410 K
P= 0.800 MPa
 = 0.022 cp (assume constant)
MA= 28 g/mol
MB= 32 g/mol
MC = 30 g/mol
kA= 106 exp (-4900/T) L/mol s
 HR= -11 kj/mol
A process fluid is available to cool the reactor. If its used, the wall temperature of the reactor is
constant at 410 K, and the overall heat transfer coefficient (U) is 125 W/m 2 K.
(a) Determine xB if the reactor is assumed to operate isothermally and isobarically.
(b) Repeat part (a), assuming the process is adiabatic.
6) A liquid-phase reaction A  B is to be conducted in a CSTR at steady-state at 163 0C. The
temperature of the feed is 20 0C and 90% conversion of A is required. Determine the
volume of a CSTR to produce 130 kg B h-1, and calculate the heat load (Q) for the process.
Does this represent addition of removal of heat from the system?
Data: Cp= 2.0 J /g K
 = 0.95 g/cm3
MA=MB= 200 g/mol
 HR= -87 kj/mol
kA= 0.80 h-1 at 163 0C
7) The reversible first-order gas phase reaction
A R
is to be carried out in two mixed flow reactors (CSTR’s) connected in series. The first reactor is
adiabatic and the second one is isothermal. Conversions of A are 0.25 and 0.40 at the exit of the
first and second reactors, respectively.
a) What should be the outlet temperature at the exit of the first reactor?
b) What is the volume of the first reactor if the feed consists of pure A?
c) What is the total heat removed from the second reactor in order to keep the second
reactor at isothermal conditions (at the inlet temperature T1)?
d) What is the volume of the second isothermal CSTR ?
2
XA1=0.25
T1=?
Pure A
To
XA2=0.50
1st CSTR Adiabatic
2nd CSTR isothermal
Data : k1=103 exp [-2416/T]
CpR = CpA = 6.2 cal /g K
Hrxn= -16 kcal /mol at 300 K
K = 10 at 300 K
Total pressure stays constant at 1 atm.
FAo=0.1 mol / s
o = 8 lt/ s
 = 1x10-3 g/cm³
To=300 K
8)
Problem 9.1, 9.2, 9.3, 9.9 from the textbook: Levenspiel O., “Chemical Reaction Engineering”,
3rd ed.(1999).
HW-5: Pr.7
3