E. Toukoniitty, J. Wärnå, D. Yu. Murzin and T. Salmi. Common in fine chemicals production: Three-phase applications, reactant, solvent (l) -

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1 Transient methods in three-phase catalysis E. Toukoniitty, J. Wärnå, D. Yu. Murzin and T. Salmi Three-phase systems Common in fine chemicals production: Three-phase applications, H 2, 2 (g) - reactant, solvent (l) - catalyst (s) Batch- / Semi-batch reactors utilized typically Complex reactions where regio-, diastereo- and enantioselectivity can be involved High selectivity crucial 1

2 Typical reaction scheme H H (I) H (E) H (B) (A) H H H (F) (D) Complex reaction scheme (parallel and consecutive) Pt/Al 2 3 catalyst Toluene solvent 2 C, 1 bar H 2 Main product used for the synthesis of several pharmaceuticals e.g. ephedrine... H H H H H (H) (C) (G) Hydrogenation of 1-phenylpropane-1,2-dione over a Pt/Al 2 3 catalyst Examples of three-phase reactions for fine chemicals production Substrate Catalyst Reference Citral Ni/Si 2 (fibrous) T. Salmi et al. Appl. Catal. A. Gen. 196 (2) 193. Glucose Ru/C (pellets) P. Gallezot et al. J. Catal. 18 (1998) 51 Ethyl pyruvate Pt/Al 2 3 (powder) + CD N. Kunzle et al. J. Catal. 186 (1999) 239 Ketopantolactone 1-Phenyl-1,2- propanedione Pt/ Si 2 (fibrous) E. Toukoniitty et al. 216 (2) 73 2

3 Transient methods Well established tools in mechanistic studies of two-phase reactions (gas-solid) e.g. Temporal Analysis of Products (TAP), Steady State Isotopic Transient Kinetic Analysis (SSITKA) TAP reactor set up (1%D 2 )/Ar (1%H 2 )/Ar Rahkamaa-Tolonen, J. Catal. 21 (22) 17 Transient methods Transient methods are seldom used in three-phase reactions Experimentation and analysis is demanding Transients are introduced into a system by varying e.g. pressure, temperature, concentration etc. Typically step and pulse change experiments ee (%) Time-on-stream (min) 3

4 Setup in transient experiments - batch reactor Required for transient experiments Setup in transient experiments fixed bed reactor 6-way injection valve Pulse or Step change H 2 HPLC pump H 2 d i = 9 mm Catalyst bed H 2,Ar, 2 or liquid MS (gas phase) GC (Liquid phase) H 2, Ar or 2 saturation 4

5 Setup in transient experiments - product analysis n-line methods (MS, IR, UV-VIS, etc.) In the presence of liquid-phase and complex product mixtures containing e.g. mixtures of enantiomers conventional on-line methods cannot be utilized Practical solution Small liquid-phase samples are collected and analyzed off-line with e.g. GC, HPLC, etc. Analysis can be a bottle neck and a rate limiting factor in threephase transient experiments Transient experiments in a batch reactor Step change in modifier concentration/composition during reaction Successfully applied in investigations of nonlinear behavior of binary modifier mixtures Practical limitations due to slow transient responses and short reaction times V L changes, however, often ΔV L is small and has insignificant influence on the results 5

6 Transient experiments in a fixed bed reactor Step change and pulse experiments More versatile compared to batch reactor: Reaction time does not limit the experiments in case of slow responses Change of solvent, reactant, concentration, etc. possible More demanding experimentation compared to batch reactor (kinetic regime, flow conditions) Enantiomers Mirror plane H H (R)-enantiomer H H (S)-enantiomer Non-superimposible mirror image structures e.g. left and right hands 6

7 Enantiomers (R)- and (S)- enantiomers behave differently in the human body (chiral environment) Enantiopure chemicals play a central role in the areas of Pharmaceuticals Agrochemicals Fragrances Living organisms Asymmetric heterogeneous catalysis The demand for enantiopure chemicals is increasing and technically simple and inexpensive production methods are needed. Chirally modified metals (Ni, Pt, Pd ) easy catalyst separation and handling continuous operation inexpensive Research aims to increased mechanistic understanding 7

8 Asymmetric heterogeneous catalysis over cinchona alkaloid modified Pt catalysts Cinchona alkaloid modified Pt catalyst were discovered by rito et al for hydrogenation of α-keto esters Trace amounts of modifier (monolayer) can induce high enantioselectivity (ee=98%) and up to 1-fold rate acceleration Extensively studied in batch reactors N H H N Cinchonidine (CD) Catalyst modifier anchoring part quinuclidine N atom chirality N H H N Cinchonidine (CD) 8

9 Principle of a chirally modified catalyst Unmodified catalyst: 5% (R) and 5% (S) (R)-enantiomer product (S)-enantiomer product + H 2 + H 2 ee = Reactant pro-r Pt particle [ R] [ S] [ R] + [ S] 1 % = % Reactant pro-s Principle of a chirally modified catalyst (R)- enantiomer product Modified catalyst: 9% (R) and 1% (S) 1-to-11 reactant- modifier interaction (S)-enantiomer product Modifier Modifier ee = Reactant [ R] [ S] [ R] + [ S] 1 % = 8% Pt particle Reactant 9

10 Catalysts D = 27% d Pt = 4 nm Structure sensitive reactions Relatively large metal particles are needed for optimum selectivity and reaction rate (~ 4 nm) 1 mm μm particles 4 nm D = 4% d Pt = 2.5 nm SEM image of the 5 wt.% Pt/Si 2 fiber catalyst TEM image of the 5 wt.% Pt/Al 2 3 (Strem Chemicals) catalyst Mechanistic questions Is there any deactivation? Catalyst regeneration and prevention of deactivation? Mechanism of nonlinear behavior of binary modifier mixtures? Mechanism of ligand acceleration? Can one increase selectivity under transient conditions? 1

11 Catalyst deactivation.3.25 M (racemic) 1 Possible catalyst deactivation difficult to distinguish.25 8 Ethyl pyruvate c (mol/l) EP (R )-EL (S )-EL 6 4 ee(%) 2.5 ee Time (min) + H 2 Typical batch reactor kinetics. H Conditions: c (EP).25 mol L -1, c (CD)= mol L -1, 5 mg 5 wt.% Pt/Al 2 catalyst, toluene, 15 o C, 1 bar H 2 (R)-Ethyl lactate Catalyst deactivation 1 ee or conversion (%) 8 Conversion Enantiomeric excess (ee) Time-on-stream (min) Identical conditions as in batch reactor => Relatively rapid catalyst deactivation noticeable Conditions: c (EP).25 mol L -1, c (CD)= mol L -1, 25 mg 5 wt.% Pt/Al 2 3 catalyst, toluene, 15 o C, 1 bar H 2, V L 3. ml min -1, V H ml min -1 11

12 Step change: c(modifier) Appl. Catal. 235 (22) 125 ee CD stop CD on 2.5E-2 2.E-2 1.5E-2 1.E-2 5.E-3 Hydrogen uptake (mol dm -3 ) No rate acceleration Slow decrease of ee Time-on-stream (min).e+ 5%Pt/Si 2 fiber, T=25 o C, Toluene, c DINE =.25M Pulse of 2 Catal. Lett. 93 (24) 171 Increase of ee and rate Pulse of 2 at 4 and 8 min C (Ads) +½ 2 -> C 2 12

13 Change of solvent toluene -> acetic acid acetic acid -> toluene 1 Enantiomeric excess (%) Toluene Acetic acid Change of solvent during reaction Toluene Acetic acid Time-on-stream (min) c(modifier inlet) liquid flow rate Instantaneous drop of ee (R)-1 Increased selectivity under transient operation ee increased under transient operation conversion decreased 13

14 rigin ligand acceleration (LA) 5-5 fold higher TF over modified site due to reactantmodifier interactions => ligand acceleration ver 1 articles state that LA is an intrinsic kinetic feature The LA concept is included in all previous kinetic models rate (mol L -1 min -1 g -1 ) LA c(ep) / mol L ee (%) Batch reactor, 1 bar H 2 15 C Journal of Catalysis 241 (26) 96 rigin of ligand acceleration Increased activity Reduced deactivation LA requires a times higher TF which is induced by reactant-modifier modifier- interactions Modifier prevents deactivation and maintains high initial activity Journal of Catalysis 241 (26) 96 14

15 rigin of ligand acceleration Increased activity Reduced deactivation LA requires a times higher TF which is induced by reactant-modifier modifier- interactions Modifier prevents deactivation and maintains initial activity Journal of Catalysis 241 (26) 96 Transient experiment 1. Conversion of EP M.25 M.5 M Racemic Enantioselective The deactivation rate proportional to reactant inlet concentration Modifier restores initial activity and prevents deactivation Time-on-stream (min) Fixed bed reactor, 1 bar H 2 15 C Steady-state and transient experiments revealed that ligand acceleration originates from reduced catalyst deactivation!!! Journal of Catalysis 241 (26) 96 15

16 Kinetic modeling Journal of Catalysis. 213 (23) 7 Non-steady state and steady state kinetic models were tested Parallel and tilted adsorption modes for modifier Different number of adsorption sites for reactant (two adsorption modes) and modifier (two adsorption modes). θ T Tilted Parallel θ P Mechanism 16

17 Mechanism steps 1 and 2 : adsorption of the reactant (A) A1m and A2n : the adsorption modes of 1- and 2- carbonyls n, m the number of sites required for adsorption of them CH 3 Mechanism steps 3 and 4: adsorption of the modifier Mp : the parallel adsorption mode of the cinchonidine,, interacts with An or Am. Mq : the tilted adsorption mode; a spectator. 17

18 Mechanism Racemic hydrogenation on unmodified sites Enantioselective hydrogenation to (R) Some hydrogenation to (S) may take place on the modified sites Kinetic model Impossible to obtain explicit rate expressions, but fractional coverages are solved numerically by Newton s method c A (mk 1 (1+ k 7 /k 8 )c (m-1) Θ m + nk 2 (1+ k 9 /k 8 )c (n-1) Θ n ) + c M (pk 3 c (p-1) Θ p + qk 4 c (q-1) Θ q ) + (m+p+f)k 1 K 3 K 5 (1+k 11 /k 12 )c A c M c (m+p+f-1) + (n+p+l)k 2 K 3 K 6 (1+ k 13 /k 14 )c A c M c (n+p+l-1) + Θ = 1 18

19 Rates Mass balances Kinetic modelling :slurry mod_1.txt.1 c (mol dm -3 ) A B time Time (min) C D + E Response simulation (Dump file) 19

20 Kinetic modelling: parameters E.Toukoniitty, B. Sevcikova, P. Mäki-Arvela, J. Wärnå, T.Salmi, D.Yu. Murzin, Journal of Catalysis, 23, 213, 7 Reactor modeling dc r Dynamic axial dispersion model for i dt continuous fixed bed reactor Peclet number from impulse experiments with an inert tracer 2 1 d cli = ρ B + ( PeLε Lτ L ) ( ε Lτ L ) 2 dz Li 1 Injection 2 μl (H 2 + NaCl) H 2 dcli dz H 2 response 2

21 Transient modelling :dione kinetic parameters from batch non-steady adsorption (dynamics) C B. B time. C Catalysis Today 79-8 (23) time Problems with by- porducts description More recent modelling x C C c (mol/l) c (mol/l) time (min) 5 x C time (min) 3 C c (mol/l) c (mol/l) time (min) time (min) 21

22 Conclusions Three-phase pulse and step change experiments are technically possible and give reproducible results Continuous operation and transient experiments give valuable mechanistic information about catalyst regeneration and deactivation mechanisms Suitable for investigation of solvent effects Ideal for studying competitive adsorption Transient operation can also increase selectivity Conclusions Transient three-phase experiments give valuable information about reaction mechanisms and catalyst deactivation, which cannot be obtained from steady state experiments 22