Semi batch reactor presentation for chemical engineering

Semi batch reactor

1. Chemical Reaction Engineering
Asynchronous Video Series
Chapter 4, Part 5:
Selectivity
Semibatch Reactors
H. Scott Fogler, Ph.D.

2. Selectivity and Yield
Instantaneous Overall
Selectivity:

3. Selectivity and Yield
Instantaneous Overall
Selectivity:
Yield:

4. Selectivity and Yield
Instantaneous Overall
Selectivity:
Yield:
Example: desired product ,
undesired product ,

€
r
D
=k
1
C
A
2
C
B

€
r
U
=k
2
C
A
C
B
2

5. Selectivity and Yield
Instantaneous Overall
Selectivity:
Yield:
Example: desired product ,
undesired product ,
To keep the selectivity of the desired products high with respect to the undesired
products carry out the reaction at high concentrations of A and low
concentrations of B. If the reactor is liquid phase, a high selectivity can easily
be achieved using a semibatch reactor in which B is few slowly to A.

€
r
D
=k
1
C
A
2
C
B

€
r
U
=k
2
C
A
C
B
2

6. Semibatch Reactors
Semibatch reactors can be very effective in maximizing selectivity in liquid phase reactions.
The reactant that starts in the reactor is always the limiting reactant.

7. Semibatch Reactors
Semibatch reactors can be very effective in maximizing selectivity in liquid phase reactions.
The reactant that starts in the reactor is always the limiting reactant.
Three Forms of the Mole Balance Applied to Semibatch Reactors:
1.Molar Basis:

8. Semibatch Reactors
Semibatch reactors can be very effective in maximizing selectivity in liquid phase reactions.
The reactant that starts in the reactor is always the limiting reactant.
Three Forms of the Mole Balance Applied to Semibatch Reactors:
1.Molar Basis:
2.Concentration Basis:
dN
A
dt
=
dC
A
V( )
dt
=V
dC
A
dt
+C
A
dV
dt
=V
dC
A
dt
+υ
0
C
A
=r
A
V

9. Semibatch Reactors
Semibatch reactors can be very effective in maximizing selectivity in liquid phase reactions.
The reactant that starts in the reactor is always the limiting reactant.
Three Forms of the Mole Balance Applied to Semibatch Reactors:
1.Molar Basis:
2.Concentration Basis:
3.Conversion:
dN
A
dt
=
dC
A
V( )
dt
=V
dC
A
dt
+C
A
dV
dt
=V
dC
A
dt
+υ
0
C
A
=r
A
V

10. Semibatch Reactors
Semibatch reactors can be very effective in maximizing selectivity in liquid phase reactions.
The reactant that starts in the reactor is always the limiting reactant.
Three Forms of the Mole Balance Applied to Semibatch Reactors:
1.Molar Basis:
2.Concentration Basis:
3.Conversion:
dN
A
dt
=
dC
A
V( )
dt
=V
dC
A
dt
+C
A
dV
dt
=V
dC
A
dt
+υ
0
C
A
=r
A
V
For constant molar feed:
For constant density:

11. Semibatch Reactors
The combined mole balance, rate law, and stoichiometry may be written in terms of number of moles,
conversion, and/or concentration:

12. Semibatch Reactors
The combined mole balance, rate law, and stoichiometry may be written in terms of number of moles,
conversion, and/or concentration:
Conversion Concentration Number of Moles

€
dX
dV
=
−r
A
N
A0
V

€
=
k
N
A
V
N
B
V
V
N
A0
=
kN
A01−X( )N
B()
VN
A0

13. Semibatch Reactors
Polymath Equations:
Conversion Concentration Moles
d(X)/d(t) = -ra*V/Nao d(Ca)/d(t) = ra - (Ca*vo)/V d(Na)/d(t) = ra*V
ra = -k*Ca*Cb d(Cb)/d(t) = rb + ((Cbo-Cb)*vo)/V d(Nb)/d(t) = rb*V + Fbo
Ca = Nao*(1 - X)/V ra = -k*Ca*Cb ra = -k*Ca*Cb
Cb = (Nbi + Fbo*t - Nao*X)/V rb = ra rb = ra
V = Vo + vo*t V = Vo + vo*t V = Vo + vo*t
Vo = 100 Vo = 100 Vo = 100
vo = 2 vo = 2 vo = 2
Nao = 100 Fbo = 5 Fbo = 5
Fbo = 5 Nao = 100 Ca = Na/V
Nbi = 0 Cbo = Fbo/vo Cb = Nb/V
k = 0.1 k = 0.01 k = 0.01
Na = Ca*V 
X = (Nao-Na)/Nao

14. Semibatch Reactors
⎥
⎦
⎤
⎢
⎣
⎡
−=−
C
DC
BAA
K
CC
CCkr

15. Semibatch Reactors
⎥
⎦
⎤
⎢
⎣
⎡
−=−
C
DC
BAA
K
CC
CCkr
At equilibrium, -r
A
=0, then

16. Semibatch Reactors
⎥
⎦
⎤
⎢
⎣
⎡
−=−
C
DC
BAA
K
CC
CCkr
At equilibrium, -r
A
=0, then
X
t
X
e
X