Page 548 - Elements of Chemical Reaction Engineering Ebook

51 8 Steady-State Nonisothermal Reactor Design Chap. 8

P8-13A The reaction
A+B a C+D
is carried out abiabatically in a series of stagedpacked-bed reactors with inter-
stage cooling. The lowest temperature to which the reactant stream may be
cooled is 27°C. The feed is equal molar in A and B and the catalyst weight in
each reactor is sufficient to achieve 99.9% of the equilibrium conversion. The
feed enters at 27°C and the reaction is carried out adiabatically. If four reactors
and three coolers are available, what conversion may be achieved?

Additional information:
AH,, = -30,000 callmol A CpA=CpB=Cpc=CpD 25 cal/g mol-K
=
K, (50°C) = 500,000 FAo = 10 mol A/min

First prepare a plot of equilibrium conversion as a function of temperature.
[Partial a&: T = 360 K, X, = 0.984; T = 520 K, X, = 0.09; T = 540 K,
X, = 0.0571
P8-14, Figure 8-8 shows the temperature-conversion trajectory for a train of reactors
with interstage heating. Now consider replacing the interstage heating with
injection of the feed stream in three equal portions as shown below:

520'
520'
XecO.3 1 1
XecO.3
450'
450'

Sketch the temperature-conversion trajectories for (a) an endothermic reaction
with entering temperatures as shown, and (b) an exothermic reaction with the
temperatures to and from the first reactor reversed.
PS-15 Exothermic reversible reaction with a variable coolant temperature. The
elementary reaction
A+B a 2C
is carried in a PBR that has a heat exchanger surrounding the reactor. The feed
is equal molar in A and B with FA0 = 5 mol/& The coolant surrounding the
PBR flows in the same direction as the reactant. The feed enters at a tempera-
ture of 330K. Plot X, Xe and T as a function of catalyst weight up to W = 4500
kg, for the base case given below
Additional Znfonnation (Base Case)
E = 25 kcdmol CpA = CpB = CPc = 2Ocdmol/K
AHm = -20 kcdmol C,, = 40 caVmoyK

Ua
k= 0*004dm6 @310K - 0.5- Cal
=
mol e kg s pB kg*s-K
K, = 1000@303 Ta = 320 K
a = 0.0002 kg m, =1OOOg/s
F, = 5 molls c, = 18 CaIJgiK
C, = 0.3 mol/dm3 8, =I