7/27/2019 The Tank Reactor
2/5
2
Batch processes why?
Legal requirements - traceability
Minimized losses at malfunctioning
process
Production on demand the process is
flexible and can run depending on market
needs.
CSTR
Processes involving gas dispersion
Fermentations
Liquid phase hydrogenations
Processes involving particle suspension
Catalytic liquid phase hydrogenations
Fed-batch processes
Strongly exothermic processes
Biotechnological processes with a growth
phase and a production phase (penicillin)
alternatively processes with substrate
inhibition or overflow metabolism
Bakers yeast production Recombinant protein production using E.
coli
Methanol-based protein production using
Pichia pastoris.
Isothermal batch processes
Questions:
How long should the process run to reach a
desired degree of conversion?
When should the process be stopped to
obtain a maximum yield of the desired
product? A typical problem for sequential reactions
What is the cooling (or heating) requirement
during the process?
The mathematics
Batch processes are initial value problems described by ordinary
differential equations(ODE)
Analytical solutions
Possible for simple cases. Can be used togive initial
estimates.
Numerical solutions
Integration of (possibly a system of) ODEs.
Methods include Euler, Runge-Kutta, Gearsa s o.
Example
AR S both reactions of first order
k1=30exp(-20000/RT)
k2=1.9exp(-15000/RT)
Temperature: 5 < T < 90 C
t < 2 h
How to maximize the yield of R?
a) in a CSTR?
b) in a batch process?
7/27/2019 The Tank Reactor
3/5
3
Reactor temperature during a
batch process
No cooling, exothermic reaction T
No cooling, endothermic reaction T
(What happens in a CSTR?)
Dynamic energy balance in
a tank reactor
Energy balance
in (flow term) out (flow term) + added heat work (done by
system) = accumulated internal energy
dt
dUWQhFhF utiiinii ..
,,
NOTE! There is no source term first law of thermodynamics
Heat balances are more common than energy balances.
Heat from cooling/heating + work done (stirrer) + reaction heat
+
latent heat = accumulated internal energy
dt
dUTTcpFTTcpFVHrWQ refut
ut
iirefin
in
iis )()()()(..
Dynamic heat balance in a
tank reactor
The heat balance has a source term heat of reaction
Reactor stability
Question: How is the reactor affected bysmall disturbances to
the process,e.g. changes in inlet concentrations orinlet
temperature? Will the reactorshow a run-away behaviour, or will
itreturn to its original steady-state?
Analysis: Split the heat balance in twoterms; generated heat and
removedheat
Cl
NO2 + 2 NH3 NO2 + NH4Cl
NH2
5109.5 H cal/mol
An example of ni troani line product ion
3NHONCBCkCrKinetics
RTE
kk aexp0where
V = 5.2 m3
Reactor temperature = 175 C
Cooling
Tw = 298 K
UA = 35.85 kcal/min K
The reaction takes place in a cooled batch reactor
