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Evaluation of kinetic data From simple plots to advanced computations
Evaluation of kinetic data
From simple plots to advanced
computations
Intrinsic kinetics
What is intrinsic kinetics ?
Real kinetics, free from mass and heat transfer effects
Kinetics of universal value, independent of equipment, laboratory, experimentalist
The goal of fundamental research
The sound basis of applied research
Great responsibility in reporting kinetic data!
Turnover number
(TON) & turnover frequency
(TOF)
What they are? TON in enzymatic catalysis: maximum number of
molecules of substrate (=reactant) that an enzyme can convert to product per catalytic site per time
TON in organometallic catalysis: number of moles of reactant that a mole of catalyst can convert before becoming deactivated – TOF is turnover per time
Initial rate
What is initial rate and how to determine it in a reliable
way ? What we dear to publish?
The rate at t=0
Example: Glucose hydrogenation (A.Aho) Best performing catalysts
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
time*mcat (min*g)
Rela
tive c
on
cen
trati
on
glucose (Catalyst A)
sorbitol (Catalyst A)
glucose (RuO2/NCNT)
sorbitol (RuO2/NCNT)
glucose (Ru/NCNT small NP)
sorbitol (Ru/NCNT small NP)
glucose (Ru/NCNT-PVP)
sorbitol (Ru/NCNT-PVP)
glucose (Olga DP non-reduced)
sorbitol (Olga DP non-reduced)
Example:Hydrolysis of
hemicelluloses
O-Acetylgalactoglucomannane – our molecule
-a branched hemicellulose (GGM)
Hydrolysed with the aid of homogeneous and
heterogeneous catalysts
Heterogeneous catalysts
Smopex-101
Fibrous and non-porous: d=0.01 mm I=4 mm
Polymer, polyethene-graft-polystyrene with sulfonic
acid functional group
Capacity 3.6 mmoleq/g
20 μm
Autocatalysis detected- initial rate? –
TOF ? – very difficult!
0 500 1000 1500 2000 2500 3000 3500 4000 45000
50
100
150
200
250
300
350
400
450 data set 1
time/s
c/(mg/l)
mannose
galactose
and glucose
Initial rate – how to determine
Which is a good method to determine the initial rate?
The rate at t=0
Model the kinetics properly, then calculate the initial rate from the model
Model the kinetic curve empirically (e.g. by polynomial), calculate the initial rate from the model
Make a test plot (logarithmic or other), extrapolate to zero
Take a difference between to first experimental points (terrible!) – the accuracy is questionable and depends on the reaction order ! Avoid this method!
Best performing catalysts
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
time*mcat (min*g)
Rela
tive c
on
cen
trati
on
glucose (Catalyst A)
sorbitol (Catalyst A)
glucose (RuO2/NCNT)
sorbitol (RuO2/NCNT)
glucose (Ru/NCNT small NP)
sorbitol (Ru/NCNT small NP)
glucose (Ru/NCNT-PVP)
sorbitol (Ru/NCNT-PVP)
glucose (Olga DP non-reduced)
sorbitol (Olga DP non-reduced)
Reaction order
What is apparent reaction order – is it old-
fashioned?
Definition: the exponent or sum of exponents above the concentrations/activities appearing in the rate equation
(Apparent) reaction order is good to be determined as one of the first diagnosis of kinetic data
Example: Lactose hydrogenation
A
B
C
D
The reaction scheme is complicated Detailed
kinetic analysis is needed
Effect of catalyst amount
Effect of hydrogen pressure
Linear plots obtained
Reaction is of first order with respect to lactose (on Ni and Ru catalysts),
the apparent reaction order with respect to hydrogen is 0.73
- SUGGEST a mechanism and rate equation!
Parallel reactions – kinetic
analysis
Two products are formed, P1 and P2 from A (and other
reactants) – is the reaction scheme parallel? If yes, what
is the ratio between rate constants ?
Procedure: Plot P1 vs time and P2 vs time; then plot P1
vs P2 is the plot linear, is the plot dependent on
temperature
QUESTION: if the plot P1-P2 plot is linear, how does
the selectivity vs conversion plot look?
Example: Selectivity vs conversion
Influence of ligand mass on (a) conversion and (b) selectivity
in hydroformylation of propene on Rh/CHDPP (100°C, 10 bar,
250 ppm Rh) (A.Bernas).
0
0.2
0.4
0.6
0.8
1
0 30 60 90 120 150 180
time (min)
co
nvers
ion 0.5 wt-%
1 wt-%
2 wt-%
3.34 wt-%
10 wt-%
(a)
10 wt-% CHDPP
0.5 wt-% CHDPP
0
0.1
0.2
0.3
0.4
0.5
0 0.2 0.4 0.6 0.8 1
conversion
iso
sele
cti
vit
y
0.5 wt-%
1 wt-%
2 wt-%
3.34 wt-%
10 wt-%
(b)
10 wt-% CHDPP
0.5 wt-% CHDPP
Simultaneous reactions – kinetic
analysis
A typical case when a mixture of similar type of molecules
react in a mixture (e.g. hydrogenation of a mixture of
molecules)
A typical question: Do they follow a similar type of reaction
kinetics?
PROPOSE A PROCEDURE TO CHECK THIS!
Example: Hydrogenation of A
& G mixtures (V. Sifontes)
Mixture hydrogenation - Molar ratio 1, 40 bar.
Modeling principles
Langmuir-Hinshelwood model
Non-competitive hydrogen adsorption
Simple reaction networks
Parameter estimation and simulation
carried out with numerical software
(ModEst)
Modeling results at 105°C and
40 bar pressure. Ratio 3.6:1.
■ L-arabinose, □ L-arabitol,
● D-galactose, ○ D-galactitol.
Lines denote regression values.
Modeling results at 105°C and
50 bar pressure. Ratio 3.6:1. .
■ L-arabinose, □ L-arabitol,
● D-galactose, ○ D-galactitol.
Lines denote regression values..
Modeling – mixtures (A&G)
Sensitivity analysis for D-galactose
activation energy.
Sensitivity analysis for L-
arabinose activation energy.
(
31)
Sensitivity analysis
Product distribution analysis
A double logarithmic plot should give
a straight line!
(
32)
Hydrogenation of (D-gal:L-ara=0.5)
solution at 120°C and 40 bar
Hydrogenation of (D-gal:L-ara=5)
solution at 120°C and 40 bar
Product distribution analysis
Final message
Remember the big responsibility in reporting initial rate,
TOF, TON...
Determine apparent reaction orders as the first step
Make a simple preliminary analysis of complex systems,
before throwing everything to regression analysis
The best way to do industrially relevant kinetics is to
perform experiments under industrially irrelevant
conditions! – broad experimental domain needed to
make reliable kinetics
Here we are!
