Multiscale modelling: from surface chemistry to reactors

Transcription

1 Multiscale modelling: from surface chemistry to reactors T.Salmi, E. Toukoniitty, J. Wärnå, A. Taskinen, D. Yu. Murzin Laboratory of Industrial Chemistry and Reaction Engineering, Johan Gadolin Process Chemistry Centre Åbo Akademi

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3 Åbo Akademi Teknisk kemi och reaktionsteknik

4 Competence Edges Kinetics Catalysis Reactor modelling

5 Business idea From reaction mechanism to reactor design From green chemistry to green process technology

6 Three-phase systems Common in fine chemicals production: Three-phase applications, H 2, O 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

7 Examples of three-phase reactions for fine chemicals production Substrate Catalyst Reference Citral Ni/SiO 2 (fibrous) T. Salmi et al. Appl. Catal. A. Gen. 196 (2000) 193. Glucose Ru/C (pellets) P. Gallezot et al. J. Catal. 180 (1998) 51 Ethyl pyruvate Pt/Al 2 O 3 (powder) + CD N. Kunzle et al. J. Catal. 186 (1999) 239 Ketopantolactone 1-Phenyl-1,2- propanedione Pt/ SiO 2 (fibrous) E. Toukoniitty et al. 216 (2000) 73

8 Enantioselective hydrogenation HO HO (I) (E) OH O O O OH (B) O (A) HO OH HO (F) (D) O Complex reaction scheme (parallel and consecutive) Pt/Al 2 O 3 catalyst Toluene solvent 20 0 C, 10 bar H 2 Main product used for the synthesis of several pharmaceuticals e.g. ephedrine... HO O HO OH OH OH (H) (C) (G) Hydrogenation of 1-phenylpropane-1,2-dione over a Pt/Al 2 O 3 catalyst

9 Modified catalyst Omodifierad katalysator 50 % S 50 % R Interaktion Överskott av den ena enantiomeren Reaktant Modifikator CD Reaktant H H H H H H H Pt Pt Pt Pt Pt Pt Pt Pt Bärarmaterial

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 m particles 4 nm D = 40% d Pt = 2.5 nm SEM image of the 5 wt.% Pt/SiO 2 fiber catalyst TEM image of the 5 wt.% Pt/Al 2 O 3 (Strem Chemicals) catalyst

11 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. 210 (2002) 17

12 ee (%) 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 Time-on-stream (min)

13 Setup in transient experiments - batch reactor Required for transient experiments

14 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, O 2 or liquid MS (gas phase) GC (Liquid phase) H 2, Ar or O 2 saturation

15 Setup in transient experiments - product analysis On-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

16 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 V L is small and has insignificant influence on the results

17 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)

18 Enantiomers Mirror plane O O OH (R)-enantiomer H H OH (S)-enantiomer Non-superimposible mirror image structures e.g. left and right hands

19 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

20 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

21 Asymmetric heterogeneous catalysis over cinchona alkaloid modified Pt catalysts Cinchona alkaloid modified Pt catalyst were discovered by Orito et al for hydrogenation of a-keto esters Trace amounts of modifier (monolayer) can induce high enantioselectivity (ee=98%) and up to 100-fold rate acceleration Extensively studied in batch reactors N H OH N Cinchonidine (CD)

22 Catalyst modifier anchoring part quinuclidine N atom N chirality N H OH Cinchonidine (CD)

23 Principle of a chirally modified catalyst Unmodified catalyst: 50% (R) and 50% (S) (R)-enantiomer product (S)-enantiomer product + H 2 + H 2 ee Reactant pro-r Pt particle R S R S 100% 0% Reactant pro-s

24 Principle of a chirally modified catalyst Modified catalyst: (R)- enantiomer product 90% (R) and 10% (S) 1-to-1 reactantmodifier interaction (S)-enantiomer product Modifier Modifier ee Reactant R S R S 100% Pt particle 80% Reactant

25 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?

26 ee Hydrogen uptake (mol dm -3 ) Step change: c(modifier) Appl. Catal. 235 (2002) E E E E-02 No rate acceleration Slow decrease of ee 0.2 CD stop CD on 5.0E Time-on-stream (min) 0.0E+00 5%Pt/SiO 2 fiber, T=25 o C, Toluene, c DIONE =0.025M

27 Enantiomeric excess (%) Change of solvent toluene -> acetic acid acetic acid -> toluene Toluene Change of solvent during reaction 60 Toluene Acetic acid Acetic acid c(modifier inlet) liquid flow rate Time-on-stream (min) Instantaneous drop of ee (R)-1

28 Pulse of O 2 Catal. Lett. 93 (2004) 171 Increase of ee and rate Pulse of O 2 at 40 and 80 min CO (Ads) +½O 2 -> CO 2

29 Conversion of EP O Transient experiment O O M M 0.05 M Racemic Enantioselective Time-on-stream (min) Fixed bed reactor, 10 bar H 2 15C The deactivation rate proportional to reactant inlet concentration Modifier restores initial activity and prevents deactivation Steady-state and transient experiments revealed that ligand acceleration originates from reduced catalyst deactivation!!! Journal of Catalysis 241 (2006) 9

30 c (mmol l -1 ) Catalyst deactivation confirmed by continuous experiments in a fixed bed B R C S A Time-on-stream (min)

31 Kinetic modeling Journal of Catalysis. 213 (2003) 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). T Tilted Parallel P

32 Chiral modifier Parallel mode (actor) Tilted mode (spectator) M + q* Mq* M + p* Mp* H Different size requirement p* q* E.Toukoniitty, B. Sevcikova, P. Mäki-Arvela, J. Wärnå, T.Salmi, D.Yu. Murzin, Journal of Catalysis, 2003, 213, 7 N 8 9 N 1 OH H H

33 Coverage dependent adsorption modes A + m* A1m* A + n* A2n* Different size requirement m* n* E.Toukoniitty, B. Sevcikova, P. Mäki-Arvela, J. Wärnå, T.Salmi, D.Yu. Murzin, Kinetics and modeling of 1-phenyl-1,2-propanedione hydrogenation, Journal of Catalysis, 2003, 213, 7

34 DFT energy profiles DFT Energy profile Antti Taskinen

35 Modelling principles 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) Dynamic axial disperion model for continuous fixed bed reactor Peclet number from impulse experiments with inert tracer Simplex-Levenberg-Marquardt method for parameter estimation

36 Batch reactor modelling Liquid phase mass balance dc dt i N a i p N GLi a GL Liquid-solid flux N i k Li c i c i R Gas-liquid flux Hydrogen in gas phase K H p N GLi b cgi Kic Ki 1 k k Li Gi b Li where c 2 * TOT,L = L /M L x c RT H 2 H 2 TOT, L

37 c (mol dm -3 ) Kinetics in batch mod_10.txt A B time Time (min) C D + E Respo nse simu lation (Dump file) Enantioselektiv hydrering av 1-fenyl-1,2-propandion A. Simulerade resultat (linje) jämförs med experimentella (cirklar).

38 c (mol/l) c (mol/l) Kinetics in batch Kinetics in batch B E A C D A US No US time (min) Concentration of 1-phenyl-1,2-propanedione (A) in presence and absence of ultrasound (solid line represents the model fit) B time (min) Concentrations of all components (A: 1- Phenyl-1,2-propanedione, B: (R)-1-hydrxy- 1-phenylpropanone, C: (S)-1-hydroxy-1- phenylpropanone, D+E: (R)+(S)-2-hydroxy- 1-phenylpropanone, solid line represents the model fit). C D+E

39 Axial dispersion Dynamic axial dispersion model for continuous fixed bed reactor Peclet number from impulse experiments with an inert tracer H 2 O H 2

40 E(t/) t/ The fit of the model to the RTD tracer experiment

41 Reaction and mass transfer again Bulk Film Bulk Film Solid

42 Dynamic column model Liquid phase Gas-liquid masstransfer dc dt Li = 1 w L L dc dl Li + L D L d 2 dl c Li 2 + N b Li a v N s Li a P Gas phase dc dt Gi = 1 G dc dl Gi w G dw + a 1 dl G c Gi a 2 c Gi d dt G + G D G 2 d c dl Gi 2 N b Li a v Liquid-solid flux from the particle model N s Li a p Masstransfer Through the net

43 Particle model Reaction, diffusion and catalyst deactivation in porous particles Particle model dc dt i S d Nir 1 p ri p r dr S

44 Fluxes Gas-liquid mass transfer N b Li a v = k 1 Li c K a v b Gi i + c k Gi b Li 1 a v K i Liquid-particle mass transfer from the particle model

45 Numerical approach PDEs discretizied with finite difference formulae The ODEs created solved with a stiff algorithm (BD, Hindmarsh) Parameters estimated with a hybrid Simplex-Levenberg-Marquardt method

46 c mol/dm 3 20 C A B 0 C time(min) 30 C A c mol/dm x C B C time(min) C. Modelling results at different temperatures (20, 30 and 40 C). Experimental data points, curves- modeling results. c mol/dm c mol/dm B B 0 C time(min) 40 C A C time(min) 40 C c mol/dm B C time(min) c mol/dm B C time(min)

47 c (mol/dm 3 ) Pe=5 Pe= Pe=1 Pe= time (min) Concentrations of B (-) (upper curves) and C (--) (lower curves) as a function of time (min) for different Peclet numbers.

48 ee Pe= Pe=5 0.7 Pe= Pe= time (min) Enantiomeric excess as a function of time (min) for different Peclet numbers

49 c, mmol/dm CM= CM= 5* 10 CM= 2* 10 CM= time (min) Concentrations of components B (-) (upper curves) and C (--) (lower curves) as a function of time for different modifier concentrations

50 ee CM= 10-3 CM= 5 * CM= 2* CM= time (min) Enantiomeric excess as a function of time for different modifier (CM) concentrations.

51 c (mol/dm 3 ) c0= c0= 0.05 c0= time (min) Concentrations of components B (-) (upper curves) and C (--) (lower curves) as a function of time for different initial concentrations of reactant A (c0).

52 ee c0= 0.1 c0= c0= time (min) Enantiomeric excess as a function of time for different initial concentrations of the reactant A.

53 coverage c * A coverage c M p* position in reactor position in reactor coverage c M q* position in reactor Coverages of c*a, cp*m (active form) and cq*m (spectator) at different positions in the reactor (1 inlet, 9 outlet) and for different times (the times are marked in the figures).

54 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

55 Conclusions Transient three-phase experiments give valuable information about reaction mechanisms and catalyst deactivation, which cannot be obtained from steady state experiments Detailed mathematical modelling is possible and successful Without theoretical chemistry, the model would have been wrong!

56 Further reading