MicrokineticModeling of BioalcoholDehydration in H-FAU, H ... · MicrokineticModeling of...

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Microkinetic Modeling of Bioalcohol Dehydration in H-FAU, H-MOR, H-ZSM-5 and H-ZSM-22

Zeolites

Methusalem, Advisory Board Meeting, June 24, 2013

1http://www.lct.ugent.be

LaboratoryLaboratoryLaboratoryLaboratory forforforfor

Chemical Chemical Chemical Chemical TechnologyTechnologyTechnologyTechnology

C.M. Nguyen, K. Alexopoulos, M.-F. Reyniers, G.B. Marin

Overview

• Introduction

• Alcohol adsorption

• Alcohol dehydration

• Conclusions

Bioalcohols to hydrocarbons as a green route

van der Borght et al.,i–SUP, Bruges, Belgium, May 6, 2012.

Different temperatures = different product distributions

Ethanol

dehydration

Taarning et al.,Energy Environ. Sci., 4 (2011) 793

H-ZSM-5

Different zeolites = different product distributions

H-SAPO-34

H-ZSM-5

Olefins

Gasoline

Haw et al., Acc. Chem. Res. 36 (2003) 317

Zeolite Models: 1 acid site per unit cell

10-MR 10-MR

Si/Al = 47 Si/Al = 95

Si/Al = 95 Si/Al = 35

Process optimization utilizes microkinetic modeling

Marin and Yablonsky, Kinetics of Chemical Reactions: Decoding Complexity, Wiley-VCH, 2011

C1-C4 alcohol adsorption thermodynamics

Nguyen et al., Europacat X, Glasgow, August 28, 2011

Nature of ROH-ZeOH complexes

PHYSISORPTION PHYSISORPTIONCHEMISORPTION

�Nature of ROH-ZeOH has remained unclear fromexp. data [1&2].�Molecular dynamics (MD) simulations for CH3OH-Zeolite [3]:

�Hzeolite strongly fluctuates midway between BAS and CH3OH.�Chemisorbed fraction increases with decreasing zeolite pore size.

[1] Mirth et al. J. Chem. Soc. Faraday Trans. 86, 3039 (1990). [2]Zamaraev andThomas, Advanced inCatalysis 41, 335 (1996). [3]Payneet al.J. Am. Chem. Soc. 121, 3292 (1999).

0 50 100 150 200 250 300

distance, r (pm)

Ab initio MD simulation: NVT, 500K

1 2 3 4 5 6

time (ps)

2000 2500 3000 3500

frequency (cm-1)

IR spectrum

ν(O-H) / ZeOH

ν(C-H)

ν(O-H)

Bonn et al. Chem. Phys. Letts. 278 (1997) 213 Nguyen et al. Phys. Chem. Chem. Phys. 12 (2010) 9481

3100 3300 3500 3700

frequency (cm-1)

Rotation along O…H bond

ν(O-H)

Bonn et al. Chem. Phys. Letts. 1997 (278) 213

Eads: theory vs experiment

experimenttheory

H-ZSM-5

Nguyen et al. Phys. Chem. Chem. Phys. 12 (2010) 9481 Lee et al. J. Phys. Chem. B 101 (1997) 381

Influence of carbon number

Nguyen et al. Phys. Chem. Chem. Phys. 12, 9481 (2010)

∆H0ads = αNC + β

α = -12 kJ mol-1 per C

1 2 3 4

Carbon number

β = -100 kJ mol-1 per C

Phys. (H-ZSM-5, Straight)

Chem. (H-ZSM-5, Straight)

Influence of zeolite topology

1 2 3 4

Carbon number

H-MOR (12-MR)

H-ZSM-5 (Straight)

H-ZSM-5 (Zigzag)

H-ZSM-22

Influence of branching level

Nguyenet al. J. Phys. Chem. C 115 (2011) 8658.

1-BuOH i-BuOH

2-BuOH t-BuOH

Zeolite-catalyzed alcohol conversion to fuels and chemicals

Alcohols

Ethers

Olefins

Aromatics

ValidationGoal: Simulate the influence

of reaction conditions and zeolite framework on product distribution

H-FAU H-ZSM-5

H-MOR H-ZSM-22

Method:

T, P, W/F, %H2OReactor

simulation

Reaction network

Thermo-dynamics

Ab-initio based microkinetic modeling

Validation

Reactor simulation

Reaction network

Thermo-dynamics

Reactor simulation

Reaction network

Thermo-dynamics

Validation

Desorption profile of adsorbed ethanol in H-MOR

Kondo et al. J. Phys. Chem. C 114 (2010) 20107

H-MORStatic IR cell reactorNo DEE is observed

Ethanol dehydration in a flow reactor at 368 – 398 K

[1] Chiang & Bhan, J. Catal. 271(2010) 251

yDifferential flow reactor

0.05 bar ethanol

Ethene is observed only in 8-MR side pocket of H-MOR [1].8-MR side pockets prevent formation of bulky ethanol dimers [1].

OH5C2 H

H5C2 O

Ethene*

(2)(5)

Ethoxide

+ H2O(g)

- H2O(g)

+ H2O(g)

- H2O(g)

+ C2H4(g)- C2H4(g)

+ DEE(g) - DEE(g)

+ C2H5OH(g)

- C2H5OH(g)

- C2H5OH(g)+ C2H5OH(g)

+ C2H4(g)

- C2H4(g)

H 5OH (g

Reaction network of ethanol dehydration

Reactor simulation

Reaction network

Thermo-dynamics

Validation

Dispersion – corrected pbc[DFT-D]

( )∑ ∑=∈

−−

−=L Lji

D LrfLr

DDFTDDFT EEE +=−

� VASP 4.6

� Plane wave basis set & Projector Augmented Wave method

� GGA PBE-D2 implementation for zeolites [1,2].

� Brillouin zone sampling restricted to the Γ point.

� Convergence criteria: Ecutoff = 600 eV, ∆ESCF = 10-6 eV,Max force = 0.02 eV/Å

� CI-NEB for transition state location [3]

� Statistical thermodynamics & PHVA – MBH [4][1] Grimme J. Comput. Chem. 27 (2006) 1787 [2] Kresse et al. J. Phys. Rev. B 48 (1993) 13115[3] Henkelman et al. J. Chem. Phys. 13 (2000) 9978 [4] De Moor et al. J. Chem. Theory Comput. 7 (2011) 1090

Monomolecular pathway (300 K)

Bimolecular pathway (300 K)

Reactor simulation

Reaction network

Thermo-dynamics

Validation

(1) C2H5OH(g) + * ↔ M1

(2) M1 ↔ M2

(3) M2 ↔ Ethoxy + H2O(g)

(4) Ethoxy ↔ Ethene*

(5) Ethene* ↔ Ethene(g) + *

(6) M1 + C2H5OH(g) ↔ D1

(7) D1 ↔ D2

(8) D2 ↔ DEE* + H2O(g)

(9) DEE* ↔ DEE(g) + *

(10) DEE* ↔ C1

(11) C1 ↔ M1 + Ethene(g)

(12) C1 ↔ Ethene*+ C2H5OH(g)

Reactor simulation

qqwhere

∆−=

expexp‡0

‡‡

immobile surface species

where, F molar flow (mol/s),

W catalyst weight (kg) , Ct acid site concentration (mol H+/kg),

R turnover frequency, r reaction rate (molecules/site/s = mol/mol H+/s),

νji the stoichiometric coefficient of component i in the elementary step j

��∗ ��∗��

Plug flow reactor equations for each gas-phase

component i with QSSA for the surface species i*:

��

TST for reaction rate coefficients:

(apart from Ethene* where a 2D translation

and 1D rotation is assumed)

Reactor simulation

Reaction network

Thermo-dynamics

Validation

Experimental validation

0 10 20 30 40 50 60

Ethanol pressure (kPa)

X (%) S-DEE (%) S-C2H4 (%)

T= 503 K

Wcat/FEtOH,0 = 6.5 kg s / mol

� Good agreement between theory (full lines) and experiment (points)

0 10 20 30 40 50 60

X (%) S-DEE (%) S-C2H4 (%)

T= 503 K

� Better agreement between theory (full lines) and experiment (points),

if the activation energy for ethoxy formation is slightly increased (+2 kJ/mol)

(3) M2 ↔ Ethoxy + H2O(g)

Influence of reaction conditionsC2H4 yield (%)

450 460 470 480 490 500Temperature (K)

14H-ZSM-5

More ethene at higher T and lower pEtOH

Is DEE a primary product?

T= 495 K, H-ZSM-5

0 1 2 3 4

site time (mol H+ s / mol EtOH0 )

H-ZSM-22

H-ZSM-5

Influence of zeolite topology

10-MR zeolites more reactive than 12-MR zeolites

10 kPa EtOH,

T= 473 K

Factors governing zeolite reactivity

Ea,D1 AD1 kD1/368 KH–FAU 154 5.1 1013 6.3 10–9 H–MOR (12–MR) 161 1.2 1015 1.6 10–8 H–ZSM–5 136 6.2 1013 3.1 10–6 H–ZSM–22 122 1.1 1014 5.2 10–4

TS stabilization: Hydrogen bonds

TS stabilization: Electrostatic interactions

H-FAU H-MOR

H-ZSM-5 H-ZSM-22

tial /

Electrostatic: H-FAU < H-MOR < H-ZSM-5 < H-ZSM-22

Stabilization factor, α

ΔΔΔΔEEEETSIITSIITSIITSII

TSII (H-FAU)

TSII (ZeOH)

D1 (H-FAU)

D1 (ZeOH)

ΔΔΔΔ((((ΔΔΔΔEEEEads,D1ads,D1ads,D1ads,D1))))

)( 1,Dads

∆∆∆=ααααα

H-FAU 0.0

H-MOR 0.4

H-ZSM-5 1.9

H-ZSM-22 3.1

H-FAU is the reference

Conclusions

• First principles microkinetic modeling provides predictive

guidance for the influence of catalyst’s characteristics and reaction

conditions on reactivity and product selectivity.

• Alcohol adsorption strength increases with decreasing zeolite pore

size (indicative of primary driving vdW forces).

• Entropy-enthalpy compensation governs the shape-selectivity

effect of H-ZSM-5 on adsorption of butanol isomers.

• 10-MR zeolites are more reactive than 12-MR zeolites (more effectively stabilized TS by HB/Electrostatic interactions)

• Long Term Structural Methusalem Funding by the

Flemish Government – grant number BOF09/01M00409

• European Community’s Sixth Framework Programme

(contract nr 011730)

• Fund for Scientific Research (FWO) – Flanders

• Stevin Supercomputer Infrastructure of Ghent University

• Experimental data (H-MOR): Kristof Van der Borght

• Ab initio MD: Roger Rousseau, Mal-Soon Lee

Acknowledgements

Glossary

• Alcohol chemisorption: Upon chemisorption over the Brønsted acid site, the acid proton is completely transferred to the alcohol, leading to formation of a positively charged oxonium ion.

• Alcohol physisorption: An alcohol is physisorbed over the Brønsted acid site and is stabilized by strong hydrogen bonds with the zeolite. The acid proton is still attached to the zeolite.

• Electrostatic potential: evaluated from the interaction between a negative unit charge and the local charge density. This factor is critical in stabilizing positively charged adsorbed complexes and especially transition states in the zeolite.

Zeolites are promising catalysts for biorefinery processes

Fluidic Catalytic Cracking & Hydrocracking are based on Zeolites

Huber andCorma, Angew. Chem. Int. Ed. 46 (2007) 7184.Taarning et al., Energy Environ. Scie. 4 (2011) 793.

Influence of temperature

10 kPa EtOH, H-MOR

More ethene formation at higher T

0 2 4 6 8

space time ( kg s / mol )

453 K0

0 2 4 6 8

space time ( kg s / mol )

0 2 4 6 8 10 12

Conversion (%)

10 kPa EtOH 50 kPa EtOH

0 2 4 6 8 10 12

Conversion (%)

10 kPa EtOH 50 kPa EtOH

Is DEE a primary product?

T= 495 K, H-MOR

0 10 20 30 40 50 60

X-sim (%)

S-DEE-sim (%)

S-E-sim (%)

X-exp (%)

S-DEE-exp (%)

S-E-exp (%)

T= 503 K

� Good agreement between theoretical (full lines) and experimental

(points) conversion

H-ZSM-5

0 10 20 30 40 50 60

X-sim (%)

S-DEE-sim (%)

S-E-sim (%)

X-exp (%)

S-DEE-exp (%)

S-E-exp (%)

T= 503 K

� Better agreement between theory (full lines) and experiment (points)

by modifying the kinetics of reaction 10, i.e. k10-mod=10 k10, K10-mod=K10

H-ZSM-5

(10) DEE* ↔ C1

Experimental results

T= 503 K

Wcat/FEtOH,0 = 6.5 kg s / molH-ZSM-5

Kristof van der Borght , personal communication

Experimental results

Kristof van der Borght , personal communication

Ethanol

DEEEthylene

Higher hydrocarbons

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