CatalyticReaction Engineering
Yongdan Li
Nov-Dec, 2018
Professor of Industrial ChemistryDepartment of Chemical and Metallurgical EngineeringSchool of Chemical TechnologyAalto UniversityEmail: [email protected] 1, E404
1
Kinetics of Homogeneously Catalyzed Reactions
LEC 3
2
Part 2-1 Homogeneously Catalyzed Reactions
Homogeneous catalysis
Types:
Acid/base catalysis by homogeneous acids/bases
Organometallic catalysis (transition metal complexes)
Significant applications:
Alkylation
Polymerization
Fine and specialty chemical synthesis
Hydroformylation
3
Part 2-1 Homogeneously Catalyzed Reactions
The reactant molecules directly contact with the catalyst molecules
reactant molecule catalyst molecule product molecule
External diffusion
Internal diffusion
In the homogeneous catalytic process,
there are not external and internal
diffusions
4
Part 2-1 Homogeneously Catalyzed Reactions
Molecular diffusion
Forced convection
Diffusion and convection allows the molecules to mix
5
Part 2-2 Kinetics of Reactions
Elementary reaction – Mass interaction law
The reactants are converted directly into the products in one step
aA + bB cC + dD CAa=R CB
bk
is the order of the reactiona+b is the rate constantk
A I1 P
A I1 could be an elementary reaction
I1 P could be an elementary reaction
According to the reaction mechanism
Non-elementary reactions
6
Part 2-2 Kinetics of Reactions
Pseudo-steady state hypothesis
How to simplify rate equations?
PIA 211
0r1I 1/RR 11
Quasi-equilibrium hypothesis
7
Part 2-2 Kinetics of Reactions
Some reaction steps are assumed to be slow and some others fast
Slow steps determine reaction rate and fast steps are assumed to be
in equilibrium
Quasi-equilibrium hypothesis
8
Part 2-2 Kinetics of Reactions
Quasi-equilibrium hypothesis
CPBI2.
PICA1.
21
11
2
CP
BI22CP2BI22
1
PI
CA11PI1CA11
K
cccckRcckcckR
K
cccckRcckcckR
2
121
11
11
1. Reaction steps are elementary reactions:
First step is assumed fast and second one is slow
9
Part 2-2 Kinetics of Reactions
3. This is substituted in the rate equation of second reaction step:
21
PP
BA
P
C12
2
CP
P
CBA122
KK
cccc
c
cKk
K
cc
c
cccKkR 21
1
2
2. Fast step in equilibrium
1
1
11
P
CA1I
CA
PI
1c
ccKc
cc
ccK
According to Quasi-equilibrium hypothesis
4. Slow steps determine reaction rate R=R210
Part 2-2 Kinetics of Reactions
Pseudo-steady state hypothesis
CPBI2.
PICA1.
21
11
1. Generation rates of instable intermediates are assumed to be 0
B2P1
PC2CA1
I
PC2BI2PI1CA1I
ckck
cckcckc
0cck1cck1cck1cck1r
1
2
1
21111
11
Part 2-2 Kinetics of Reactions
2. This is substituted in the rate equation of second or first reaction step
3. Equation is simplified:
2
1
2
PC2
B2P1
P2A1
CB22 cckckck
ckckcckR
R=R1=R1=R2
B2P1
21
PP
BAC21
B2P1
PPC21CBA21
2ckck
KK
ccccckk
ckck
ccckkccckkR
1
21
1
21
R=R1=
12
Part 2-2 Kinetics of Reactions
4. Assuming k-1cP1>>k2cB the same equation is obtained as using quasi-
equilibrium hypothesis
21
PP
BA
P
C122
KK
cccc
c
cKkRR 21
1
B2P1
21
PP
BAC21
B2P1
PPC21CBA21
2ckck
KK
ccccckk
ckck
ccckkccckkR
1
21
1
21
13
HPBAH2.
AHHA1.
OHPHOHP3.
PBA2.
OHAOHAH1.
2
2
General mechanism
Part 2-3 Catalysis by Acid or Base
14
Several reactions in organic chemistry catalyzed by acid or base
Part 2-3 Catalysis by Acid or Base
Electrophilic substitution
Alkylation of aromatics Halogenation of aromatics Sulphonation of aromatics
Nitrification of aromatics
Overall reaction
15
Part 2-3 Catalysis by Acid or Base
Ethyl
carbonium
Aromatic
carbonium
Ethyl
benzene
First step : Carbonium formation
Second step : Electrophilic substitution
16
Part 2-3 Catalysis by Acid or Base
Nucleophilic substitution
Haloalkanes produce alcohols
Overall reaction
Reaction mechanism
17
Part 2-3 Catalysis by Acid or Base
Electrophilic addition
Alkenes produce haloalkanes, esters and alcohols
Bromonium ion
Overall reaction
Reaction mechanism
18
Part 2-3 Catalysis by Acid or Base
Nucleophilic addition
Alkynes produce alkyl ethers or alkyl esters
Methyl vinyl ether
Methoxy negative ion
Methyl vinyl ether carbanion
Overall reaction
First step : Methoxy negative ion formation
Second step : Nucleophilic addition
19
Part 2-3 Catalysis by Acid or Base
Carboniums
Several types of intermediates
Formation steps
Intermediates of the electrophilic attacking
Ethyl carboniumAromatic carbonium Benzyl carbonium
20
Part 2-3 Catalysis by Acid or Base
Carbanions
Several types of intermediates
Strong base
Strong base
Formation steps
Intermediates of the nucleophilic attacking
Acetylenyl carbanion Ethyl acetate carbanion Methyl vinyl ether carbanion
Strong base
21
Kinetics of reactions catalyzed by acid or base
CR
H
R'
CO
H+ OH - C C
O -
H
R
R'C - C
O
H
R
R'+ H2O
C CO -
H
R
R'C
H R''
O
+CR
R'
CO
H
CH
R''
O -
CR
R'
CO
H
CH
R''
O -
O
H H+
CR
R'
CO
H
CH
R''
OH+ OH -
A I1 W
I1 B I2
I2 W C
OH
OH
Part 2-3 Catalysis by Acid or Base
Aldol condensations 22
Reaction steps as elementary reactions
3
OHPWI33OHP3WI33
2
I
BI22I2BI22
1
WI
OHA11WI1OHA11
K
cccckRcckcckR
K
ccckRckcckR
K
cccckRcckcckR
22
2
121
1
1
Part 2-3 Catalysis by Acid or Base
K1=k1/k-1 K2=k2/k-2 K3=k3/k-3
A+OH- I1+W (1) I1+B I2 (2) I2+W C+OH- (3)
23
Let’s assume
0RRr
0RRr
32I
21I
2
1
1cKk
kc
k
KKk
K
ccccKKk
R
W2
2
3B
1
213
PBAOH213
Part 2-3 Catalysis by Acid or Base
R1=R2=R3
= =
(K=K1K2K3)R=R1=R2=R3
Get cI1and cI2
cI1and cI2
24
Let’s assume
First step and third step is assumed to be fast
Second reaction step is slow
2
I
BI2I2BI22K
ccckRckcckRR 2
121
W
OHA1I
OHA
WI
1c
ccKc
cc
ccK
1
1 W3
OHPI
WI
OHP3
cK
ccc
cc
ccK
2
2
After substitution in the rate equation of the second step
K
ccc
c
cKkR PBA
W
OH12 K=k2K1K2K3
Part 2-3 Catalysis by Acid or Base
R=R2
cI1and cI2
25
QE vs. PSS hypothesis
If k1 and k3 are large (2. step RDS), second term of denominator prevails in
the PSS rate equation (the same equation is obtained as with QE hypothesis):
K
ccc
c
cKkR
cKk
k
K
ccccKKk
R
1cKk
kc
k
KKk
K
ccccKKk
R
PBA
W
OH12
W2
2
3
PBAOH213
W2
2
3B
1
213
PBAOH213
PSS hypothesis
QE hypothesis
Part 2-3 Catalysis by Acid or Base
26
If k1 and k2 are large (3. step RDS), third term of denominator (+1) prevails
in the PSS rate equation (the same equation is obtained as with QE
hypothesis):
K
ccccKKkR
1cKk
kc
k
KKk
K
ccccKKk
R PBAOH213
W2
2
3B
1
213
PBAOH213
PSS hypothesis QE hypothesis
Part 2-3 Catalysis by Acid or Base
27
Part 2-4 Catalysis by Transition Metal Complex
Metal atom(s) or ion(s) : d-block transition elements
A neutral molecule with one ormore electron pairs
Ligands :
Metal complexes contain metal atom(s) or ion(s) and ligands that are bundled
into one entity through coordination bond(s), and the entity can be identified as
a unit.
Metal complexes
H2O NH3 CO
Negatively charged ions (anions)
A molecule or multi-atomic ionwith π bonding electrons
OH- Cl- CN-
PPh3
28
Part 2-4 Catalysis by Transition Metal Complexes
Metal complexes
Ligands can have one or more donor atoms and can coordinate through either
one or more of those donor atoms
Examples:nitrite (NO2-)
Cyanide (CN-), cyanate (CNO-) and thiocyanate (NCS-) ions
[ ]- [ ]- [ ]-
29
Part 2-4 Catalysis by Transition Metal Complexes
Metal complexes
Coordination number : The number of ligands binding with one metal atom
or ion
23)Ag(NH
Coordination number 2
Coordination number 3
3HgI
Pt(PPh3)3
lower oxidation state ions such as Pt(0), Ag(I) and Hg(I) complexes exhibit a
lower coordination number
Plane triangle
Linear
30
Part 2-4 Catalysis by Transition Metal Complexes
Metal complexes
Coordination number 4
2
4NiCl
[AuBr4]-
[Zn(NH3)4]2+
Coordination number 5
[Cu(H2O)5]2+
2
5SbCl
Fe(CO)5
[Ni(CN)5]2-
Tetrahedron Plane square
Square pyramidal Trigonal bipyramidal 31
Part 2-4 Catalysis by Transition Metal Complexes
Metal complexes
Coordination number 6
3
6Fe(CN)
Coordination number 7, 8 and 9 ……
These coordination numbers are mainly observed in lanthanide and actinide
(with f electrons) complexes
Octahedron
32
Part 2-4 Catalysis by Transition Metal Complexes
Metal complexes
3 4 3 3 3[Pt(PPh ) ] [Pt(PPh ) ] PPh
The coordination number can change.
33
Part 2-4 Catalysis by Transition Metal Complexes
Insert reaction
Ln—M—R Ln—M—C—C—R
—— CC
Several key reactions in coordination catalysis
Bonds that can be inserted by a molecule : M-C, M-H, M-X, M-N
Molecules : CO, CO2, SO2 , H
Insert directly
First coordinate and then insert
34
Part 2-4 Catalysis by Transition Metal Complexes
Addition reaction and elimination reaction
The difficulty of addition and the reaction rate are related to the type of the
central atom and ligand.
Rh
CO
PPh3
PPh3
Cl
+ CH3I Rh
CO
PPh3
PPh3
Cl
CH3
I
M=Ir(I) The reaction is irreversibleM=Rh(I) The reaction is reversible
IrCO
PPh3
PPh3
Cl
+ CH3I Ir
CO
PPh3
PPh3
Cl
CH3
I
35
Part 2-4 Catalysis by Transition Metal Complexes
a
b
The higher the positive charge density of the central atom, the easier the
formation of the M-H bond.
β-H transfer reaction
36
Part 2-4 Catalysis by Transition Metal Complexes
Rearrange reaction
Ln-M-CH2-CH=CH2 Ln-M-
σ bond π bond
Substitution reaction
[Fe(CN)6]4-(aq) + H2O (aq) [Fe(CN)5(H2O)]
4-(aq) + CN-(aq)
37
Part 2-4 Catalysis by Transition Metal Complexes
The oldest (Otto Roehlen, 1938) and most significant (largest production
volumes) homogeneously catalysed process.
normal butyraldehyde
Hydroformylation
iso butyraldehyde
main product
38
Part 2-4 Catalysis by Transition Metal Complexes
Hydroformylation
Depending on the environment (pressure, temperature), different forms of
the complex with different properties can exist
Most common catalyst:
rhodium - tri-phenyl phosphine
complex (Rh-TPP)
Rh-TPP complexe
39
Part 2-4 Catalysis by Transition Metal Complexes
Rh
T P P
H
O C
T P P
Rh
T P P
H
O C
T P P
Rh
H
C ( O ) C H 2 C H 2 R
T P P
T P P H
C O
7 RCH 2 CH 2 CHO
8
CO CO
1
D
2 R
Rh
H
T P P
T P P
R
3
Rh
T P P
C H 2 C H 2 R
O C
T P P
CO 4
Rh
T P P
T P P H
C O
C O
5
Rh
C O
C ( O ) C H 2 C H 2 R
T P P
T P P
R A
Rh
C O T P P
T P P H
C O
R
Rh
T P P
T P P C H 2 C H 2 R
C O
C O
H 2 6
O C
Mechanistic model for kinetics of propene hydroformylation with Rh catalyst. AIChE J., 58: 2192–2201. 40
Part 2-4 Catalysis by Transition Metal Complexes
Ethylene oxidation
C2H4 + O2[PdCl4]
2-
CH3CHO
Pd (II) and ethylene form complexes
1K2
4 2 4 3 2 4[PdCl ] C H [PdCl (C H )] Cl fast
2
1 4 2 4K [[PdCl ] ][C H ][A][Cl ]
1 2
4 2 4
[A][Cl ]K
[[PdCl ] ][C H ]
A
CuCl2 HCl
Step 1
41
Part 2-4 Catalysis by Transition Metal Complexes
2K
3 2 4 2 2 2 2 4[PdCl (C H )] H O trans [PdCl (H O)(C H )] Cl
Cl- and H+ fall off
fast
fast3K
2 2 2 4 2 2 4(trans )[PdCl (H O)(C H )] (trans )[PdCl (OH)(C H )] H
2K [A][B][Cl ]
2
[B][Cl ]K
[A]
A B
3
[C][H ]K
[B]
B C
3K [B][C][H ]
Step 2
Step 3
42
Part 2-4 Catalysis by Transition Metal Complexes
2
4 2 41 2 3 2
[[PdCl ] ][C H ]C=K K K
[H ][Cl ]
2
1 4 2 4K [[PdCl ] ][C H ][A][Cl ]
2K [A][B][Cl ]
3K [B][C][H ]
43
Part 2-4 Catalysis by Transition Metal Complexes
Change structure
slow
fast
4k
2 2 4 2 2 2slow(trans )[PdCl (OH)(C H )] (cis )[Cl Pd(CH CH )(OH)]
fast
2 2 2 3(cis )[Cl Pd(CH CH )(OH)] CH CHO Pd(0) H 2Cl
C D
D
Catalysis regeneration
2 2CuCl 0.5O 2HCl 2CuCl H O k6
2
2 4Pd 2CuCl 2Cl [PdCl ] 2CuCl
k5 fast
fast
Step 4
Step 5
Step 6
Step 7
44
Part 2-4 Catalysis by Transition Metal Complexes
2
4 2 44 1 2 3 2
[[PdCl ] ][C H ]R k K K K
[H ][Cl ]
4 4R R k [C]
Slowest step (step 4) determines the reaction rate
2
4 2 41 2 3 2
[[PdCl ] ][C H ]C=K K K
[H ][Cl ]
2
4 2 41 2 3 2
[[PdCl ] ][C H ]C=K K K
[H ][Cl ]
2
1 4 2 4K [[PdCl ] ][C H ][A][Cl ]
2K [A][B][Cl ]
3K [B][C][H ]
4 4R R k [C]
45
Part 2-5 Free Radical Reaction
Containing one or more single electron species called free radicals
Free radical
(Alkyl radicals) (Aryl radicals)
(Derivative radicals) (Halogen radicals )
46
Homolytic cleavage of bond
Formation of free radicals
C6H5 C
O
-O-O- O2C
O
C6H5C
070-80
C6H5C
O
. 2CO2C6H52 +.heart
heatingheart
hearthν
The ease of cleavage is directly related to the bond dissociation energy
The bonds with easy homolytic cleavage, such as :
Part 2-5 Free Radical Reaction
C-N O-O C-I
benzoyl peroxide
47
Oxidation or reduction of single electron
Fe2+ + H2O2 Fe3+ HO+ ● + HO-
Part 2-5 Free Radical Reaction
e-
48
Typical reactions of free radicals
Addition reaction
Transfer reaction R· + R'H R-H + R'·
R·+ R'· R-R'
heart
Termination reaction
Part 2-5 Free Radical Reaction
Coupling
Disproportionation
49
The halogenation of hydrocarbons
The hydrogen atom in the saturated hydrocarbon molecule is replaced by a
halogen atom.
heartCH4 + Cl2 CH3Cl + HClhv, ( )
CH3Cl + Cl2 CH2Cl2 + HClhv
heartHCl
CH2Cl2 + Cl2 CHCl3 + HClhv heartHCl
hvCHCl3 + Cl2 CCl4 + HClheartHCl
heartHCl
Part 2-5 Free Radical Reaction
50
Cl : Clhv
Cl. .Cl+
+ ..Cl CH4 HCl + CH3
..CH3 + Cl2 CH3Cl + Cl
+ Cl ..Cl Cl2
+CH3. CH3
. CH3CH3
+ .ClCH3. CH3Cl
Chain initiation
Chain propagation
Chain termination
Part 2-5 Free Radical Reaction
51
Radical addition of alkene
Electrophilic addition
Radical addition
Part 2-5 Free Radical Reaction
52
Chain initiation
Chain propagation
Initiator
More stable
Part 2-5 Free Radical Reaction
53
Chain termination
Part 2-5 Free Radical Reaction
54
Kinetics of free radical reaction
H2 + Br2 = 2HBr
1 Br2 2 Br ●k1
HBr + H 2 Br + H2
k2● ●
Part 2-5 Free Radical Reaction
5 Br2k5
2Br ●
HBr + Br 3 H + Br2k3
● ●
4 H + HBr H2 + Br ● ●
k4
55
Part 2-5 Free Radical Reaction
0C2kCCkCCkCCkC2kdt
dC 2Br.5
2HBr.2HBrH.4
2BrH.3
2Br1
Br.
0CCkCCkCCkdt
dCHBrH.4
2BrH.3
2HBr.2
.H
2Br
5
1Br. C
k
kC
HBr42
Br3
2Br
5
1
2H2
H.CkCk
Ck
kCk
C
Get and
56
Part 2-5 Free Radical Reaction
The rate of reaction, in terms of the disappearance of H2
0CCkCCkCCkdt
dCHBrH.4
2BrH.3
2HBr.2
.H Because of
RH2 =RHBr=2RH2
We get =RHBr=2RH2
RHBr=2RH2=
HBr42
Br3
2Br
5
1
2H2
H.CkCk
Ck
kCk
C
HBrH.42
HBr.2 CCkCCk
2BrH.3 CCk
2Br
HBr
3
1
21
2Br
2H
21
5
12
C
C
k
k1
CCk
k2k
57
References
• Chemistry of Catalytic Processes
– Bruce Gates
• Kinetics of Gas Phase Reactions
– Guy-Marie Côme
58
Catalytic Reaction Engineering
Yongdan Li
Nov-Dec, 2018
Professor of Industrial ChemistryDepartment of Chemical and Metallurgical EngineeringSchool of Chemical TechnologyAalto UniversityEmail: [email protected] 1, E404
59