hydrocarbons via oxygenates

Transcription

1 Methane conversion U to higher hydrocarbons via oxygenates Unni Olsbye GeCat, Cluny, May 14, 2014

2 Cost development fossil carbon sources IEA and EPIA: Solar photovoltaics competing in energy sector (2011) Auke Lont (Statnett): Energi og marked (2012)

3 Industrial developments

4 Methane (CH 4 ) - Dry gas Methane is a stable, symmetrical molecule Melting point: ºC Boiling point: ºC C-H bonds are strong (425 kj/mol) No functional group, magnetic moment or polar distribution to facilitate chemical attack The challenge is selectivity rather than activity

5 px Synthesis gas the preferred alternative Synthesis gas production is based on thermodynamic equilibrium H H2O C CH4 CO2 CO T/K > 800ºC

6 Direct methane conversion processes - pyrolysis (CH 4 : H 2 = 1 : 1) CH 4 C 2 H 6 + H 2 C 2 H 4 + H 2 C 2 H 2 + H 2 2 C + H 2 A. Holmen, Cat. Today 142 (2009) 2

7 Selectivity (%) Direct methane conversion processes partial oxidation k 1 k 2 A B C C2 + HC CH3OH, HCHO MeCl, gas phase or LaCl3 MeCl, Ni/LaCl3 MeBr, super acids MeX, super acids MeBr, gas phase Simulated, k1 = k CH 4 Conversion (%) U. Olsbye et al, Cat. Today 171 (2011) 211

8 Methane-to-hydrocarbons via methyl halides n CH 3 X (CH 2 ) n + n HX I. Lorkovic et al. J. Phys. Chem. A 110 (2006) 8695, I. Lorkovic et al. Chem. Comm. (2004) (5) 566

9 Selectivites (C%) MTH vs. MeXTH 350 C 50 MeOH over SAPO Conversion: 92 % MeOH over ZSM-5 Conversion: ~100 % MeCl over ZSM-5 Conversion: ~100 % methane ethene ethane propene propane MeCl over SAPO-34 Conversion: 5.2 % MeBr over SAPO-34 Conversion: 3.9 % butenes butanes C 5+ aliphatics C 5+ aromatics C. E. Taylor Stud. Surf. Sci. Catal. 130 (2000)

10 Selectivites (C%) MTH vs. MeXTH 350 C 50 MeOH over SAPO Conversion: 92 % MeOH over ZSM-5 Conversion: ~100 % MeCl over ZSM-5 Conversion: ~100 % methane ethene ethane propene propane MeCl over SAPO-34 Conversion: 31 % MeBr over SAPO-34 Conversion: 15 % butenes butanes C 5+ aliphatics C 5+ aromatics WHSV eq = 6.2 h -1 WHSV eq = 0.8 h -1 WHSV eq = 0.8 h -1 Svelle et al. J. Catal. 241 (2006)

11 Key processes, methane conversion CH 3 OH Polymers 4 * UOP Advanced Methanol to Olefins (MTO) process CO + H 2 Diesel fuel

12 The Methanol to hydrocarbons reaction - catalysed by Brønsted acidic zeolites or zeotypes 5 Å

13 Conversion (%) R&D on the MTH reaction driving forces Enhanced product selectivity Enhanced catalyst stability Fundamental insight Time on stream (min)

14 R&D on the MTH reaction driving forces Enhanced product selectivity Today: Influence of Fundamental insight Topology Acid strength Morphology on product selectivity

15 Based on: Handbook of Porous Solids, Wiley-VCH, Weinheim, 2002, Topology influence = Shape selectivity Reactant selectivity Product selectivity Restricted transition state-like selectivity

16 AFI MOR BEA Materials tested (Si/Al 20, Δ (OH) CO ads = cm -1 ) 3D 8-ring CHA 1D 10-ring SSZ-13 TON 3D 10-ring TUN IMF MEL MFI TNU-9 IM-5 ZSM-5 ZSM-11 1D/3D 12-ring

17 Kinetic diameter of largest product (Å) AFI *BEA MOR TON CHA Product shape selectivity : product cut-off (> 4 % selectivity) at 350 C, 13 kpa MeOH 8,0 7,5 7,0 6,5 6,0 TUN IMF MFI MEL 1,2,4-TriMB HexaMB 5,5 Dibranched alkanes 5,0 4,5 4,0 Linear Alkanes Cross section of largest pore (Å) S. Teketel et al. Catalysis 26 (2014)179

18 Methanol to Hydrocarbons : An autocatalytic reaction ZSM-5 A A + B k 1 B k 2 B k 2 >> k 1 Chen and Reagan, J. Catal. 59 (1979) 123 Olsbye et al Angew. Chemie Int. Ed. 51 (2012) 5810

19 Mechanistic studies :The hydrocarbon pool concept I. M. Dahl, S. Kolboe, Catal. Lett. 20 (1993) 329 I. M. Dahl, S. Kolboe, J. Catal. 149 (1994) 458

20 Main mechanistic pathway : The dual cycle mechanism H 2 O n CH 3 OH CH 3 OH H 2 O CH 3 OH n H 2 O H 2 O CH 3 OH Higher alkenes Alkanes CH 3 OH H 2 O S. Svelle et al. J. Am. Chem. Soc. 128 (2006) M. Bjørgen et al. J. Catal. 249 (2007) 195

21 Aromatics yield (%) Transition state shape selectivity : product distribution at 350 C, 13 kpa MeOH TON MEL MFI IMF TUN MOR *BEA Aromatics AFI yield vs. conversion Increasing 50 pore size C%) TUN MFI 10 IMF MEL 5 CHA TON AFI Conversion (C%) MOR BEA 12-ring structures 3D 10-ring structures 1D 10-ring structure 3D 8-ring structure S. Teketel et al. Catalysis 26 (2014)179

22 C 3 Yield (%) C 5+ Aliphatics yield (%) Transition state shape selectivity : product distribution at 350 C, 13 kpa MeOH e.g. C 4 H 8 + C 3 H 6 C 7 H C 3 aliphatics CHA TON MEL MFI IMF TUN MOR *BEA AFI Conversion (C%) C 5+ aliphatics Conversion (C%) 3D10-ring structures 1D 10-ring structure 12-ring structures 8-ring structure S. Teketel et al. Catalysis 26 (2014)179

23 General conclusion, shape selectivity Individual classes of reactions are sterically suppressed in the following order: Intermolecular hydride transfer reactions Cracking reactions Methylation reactions

24 C 3 C 4 MTG Aromatics normalized C 2 C 4 C 5+ MFI (ZSM-5) 3D 10-rings C 3 MTH ZSM-5 C 5+ ZSM-22 C 2 TON (ZSM-22) 1D 10-rings C 4 Propene Propane Aromatics SAPO-34 CHA (SAPO-34) 3D 8-rings C 2 Propene Propane Retention time /min C 3 MTO C 5+ 5 C Retention time /min Aromatics Retention time /min SAPO-34

25 Acid strength influence CH 3 OH SSZ-13 Si/Al = m crystals O-H (CO) = 340 cm -1 SAPO-34 (Al+P)/Si = m crystals O-H (CO) = 270 cm -1 F. Bleken et al., Top. Catal., 52 (2009) 218. ; B.P.C. Hereijgers et al., J. Catal., 264 (2009) 77

26 Acid strength influence H-SSZ-13 H-SAPO-34 Opt temp 350 C Opt temp 400 C

27 H-SAPO-5 as model catalyst CHA H-SAPO-34 AFI H-SAPO-5 AFI: Wide (12-ring) tubular channels ~7.3 Å

28 H-SAPO-5 versus H-SSZ-24 Selectivity (C%) IR response in O-H stretch region Product selectivity at 18.5 % conversion (350 C, 4 kpa CH 3 OH) H-SAPO-5 (Si/(Al+P) = 20-80) H-SSZ-24 H-SAPO H-SSZ-24 (Si/Al = 35) 0 C1 C2 C3 C4 C5 C6+ Arom H-SSZ-24 favors aromatic products M. Westgård Erichsen et al. J. Catal. 298 (2013) 94; Cat. Today 215 (2013) 216

29 H-SAPO-5 versus H-SSZ-24 : Co-reaction of 12 C benzene and 13 CH 3 OH (250 C) 13 CH 3 H 3 13 C 13 CH CH 3 OH H 3 13 C 13 CH 3 13 CH 3 OH H 3 13 C + 13 CH 3 *CH 3 OH H-Zeolite H 3 13 C 6H 2 O 13 CH 3 13 CH 3 H-Zeolite H 3 13 C H 2 O 13 CH 3 13 CH 3 Zeolite - M. Bjørgen et al. J. Catal. 221 (2004) 1.

30 H-SAPO-5 versus H-SSZ-24 : Co-reaction of 12 C benzene and 13 CH 3 OH (250 C) H-SAPO-5 H-SSZ-24 M. Westgård Erichsen et al. J. Catal. 298 (2013) 94; Cat. Today 215 (2013) 216

31 Morphology influence ZSM-5 nanosheets H-ZSM-5 nanosheets of 4 nm thickness (~2 unit cells). About 20 % of T-sites at the surface How about shape selectivity? B.-T. L. Bleken. et al Top Catal. 56 (2013) 558

32 Surface properties of H-ZSM-5 nanosheets 3745 cm cm cm -1 B.-T. L. Bleken. et al., Phys. Chem. Chem. Phys. 15 (2013)

33 product yield [%] Product distribution: nano vs. bulk WHSV: NS-ZSM-5 = 2.7 h -1 C-ZSM-5 = 5.4 h -1 The shape selectivity is still present! Activity is lower Conversion [%] B.-T. L. Bleken. et al., Top. Catal. 56 (2013) 558.

34 Fundamental studies Kinetic studies of individual reaction steps

35 Theoretical approach Light alkene methylation reactions Apparent activation energy (kj/mol) c a ethene propene butene Experiment T cluster model Periodic model S. Svelle, S. Kolboe et al, J. Phys. Chem. B 107 (2003) 9281 S. Svelle, J. Sauer et al. JACS 131 (2009) 816

36 Theoretical approach Light alkene methylation reactions Experimental methylation rate constants (100 C/140 C) H-FER H-MFI H-MOR H-BEA Ethene Propene Theoretical methylation rate constants (350 C) I.M. Hill, A. Bhan et al. J. Catal. 291 (2012) 155 J. Van der Mynsbrugge Chem. Eur. J. 19 (2013) 11568

37 What is the influence of topology? ZSM-5 Beta Three dimensional 10- and 12-ring systems Identical density of acid sites» ICP-MS ~ 45

38 ln(rate of methylation) ln(rate of methylation) Condition dependency 3,0 H-ZSM-5 2,5 2,0 1,5 Reaction is first order in benzene and zero order in methanol Linear Arrhenius plots Apparent barriers:» 59 kj/mol for H-ZSM-5» 58 kj/mol for H-beta Compare well to literature values from global kinetic modeling» kj/mol for toluene Y. S. Bhat et al. Ind. Eng. Chem. Res. 28 (1989) 890. R. Mantha et al. Ind. Eng. Chem. Res. 30 (1991) 281. J. L. Sotelo et al. Ind. Eng. Chem. Res 32 ( S. Al-Khattaf et al. Chem. Eng. J. 139 (2008) 622. S. Rabiu, S. Al-Khattaf, Ind. Eng. Chem. Res. 47 (2008) 39. H. Vinek, J. A. Lercher, J. Mol. Catal. 64 (1991) 23. 1,0 0,5 0,0 0,0015 0,0016 0,0017 0,0018 0,0019 1/T (K -1 ) 2,5 H-beta 2,0 1,5 1,0 0,5 0,0-0,5 0,0015 0,0016 0,0017 0,0018 0,0019 1/T (K -1 )

39 What is the influence of topology? Identical reaction orders and identical activation energies Suggest that the reaction mechanism is the same What causes the threefold difference in the methylation rate?

40 Cluster calculations, benzene methylation ZSM-5 Beta Experiment ZSM-5 Beta A (m 3 /mol s) E a (kj/mol) k(350 C) Theory ZSM-5 Beta A (m 3 /mol s) E a (kj/mol) k(350 C) J. Van Mynsbrugge et al. J. Catal. 292 (2012) 201

41 Isolation of single reactions Considered mechanisms: Stepwise mechanism Concerted mechanism S. Svelle et al., Top Catal, 54 (2011) 897

42 Isolation of single reactions: Alkene methylation in a TAP reactor Studied catalyst: H-ZSM-22 ZSM-22 ZSM-22 1D,10-ring zeolite Si/Al = 45, pore diameter 5.7 Å ZSM-22 TAP reactor ZSM-23 ZSM-23 EU-1 Vacuum conditions 0.25 ms pulses, giving < 1/100 molar amount of gas compared to active sites on catalyst Knutsen diffusion Catalytic tests at 320, 350, 370 and 400 C with ethylene, propene or iso-butene ZSM-2 Pulse valves QMS EU-1 ZSM-22 SiC ZSM-22 SiC ZSM-48 ZSM-23

43 Pulse intensity Alkene methylation in a TAP reactor Reactant feed procedure: Pretreatment with O 2 pulses at 550 C Alternate pulsing of methanol and alkene 1/ Argon + 13 C-methanol 2/ Argon + alkene 0.5 s Time Detection of the methylation product by following the 13 CH 2 -C n H 2n MS peak 320 pulse pairs used to produce each data point

44 Intensity Alkene methylation in a TAP reactor Example of experimental response curve: Argon Argon Argon Water Calculate conversion by curve fitting and mass balance (MS signal area) 4 2 Methanol Ethylene Propene Time (ms) 13 C methanol Ethylene pulse pulse Estimate adsorption and rate constants by the following model: O n (g) = O n (ads) (1) O n (ads) + X O n+1 (ads) (2) O n+1 (ads) = O n+1 (g) (3) X is assumed constant

45 Alkene methylation in a TAP reactor Alkene conversion (%) at 400 C Ethene Propene Iso-butene Curve fitting MS areas Isobutene methylation seems sterically hindered, and ethene methylation sterically promoted, in ZSM-22 compared to ZSM-5

46 Intrinsic methylation kinetics from first principles Periodic DFT with BEEF-vdW functional and GPAW code Reaction between alkenes and methoxy groups Alkene Activation Energy (kjmol -1 ) Apparent rate Constant (sec -1 ) Intrinsic rate Constant (sec -1 ) ethene x 10 6 propene x x 10 8 isobutene x x 10 8 Wellendorff, Nørskov et al., Phys. Rev. B 85 (2012)

47 molar flow (a.u.) Correlation between experimental and modelled data Using adsorption constants derived from theory, and the rate constant as only variable, excellent agreement between experimental and simulated data was obtained: ethene, exp. ethene, model propene, exp. propene, model iso-butene, exp. iso-butene, model Alkene Activation Energy theoretical (kjmol -1 ) Activation Energy Experimental (kjmol -1 ) propene ± time, s R. Brogaard, Y. Schuurmann, U. Olsbye et al J. Catal. (2014) accepted

48 Overall Conclusions Some main trends in shape selectivity of MTH in zeolites have been outlined Higher acid strength favors reactions with delocalised transition states Shape selectivity can survive in nanosheets Combined experimental and computational efforts are required to develop leads for catalyst reaction tailoring TAP studies are a promising tool for studying the kinetics of single reaction steps.

49 Outlook Open questions remain Effect of defects Effect of surface sites Effect of pore-mouth versus internal sites SSZ-24 Zeolite synthesis and detailed characterisation, in combination with kinetic studies, remain key to further progress in the field of zeolite- / zeotype-catalysed reactions

50 Acknowledgements Karl-Petter Lillerud Stian Svelle David Wragg Francesca Bleken Wegard Skistad Shewangizaw Teketel Marius W. Erichsen Reynald Henry Rasmus Brogaard Ivar Martin Dahl Bjørnar Arstad Ole Swang Pablo Beato Ton V. W. Janssens Finn Joensen Yves Schuurmann Silvia Bordiga Carlo Lamberti Financial support from: Bert M. Weckhuysen Bart Hereijgers Davide Mores Luis Arramburo