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CPMD: perspectives and industrial applications

CPMD: perspectives and industrial applications. Mauro Boero

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CPMD: perspectives and industrial applications

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  1. CPMD: perspectives and industrial applications Mauro Boero Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504 CNRS-UDS, 23 rue du Loess, BP 43, F-67034 Strasbourg, France and CREST, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan, and JAIST, Hokuriku, Ishikawa, Japan Work done in collaboration with BASF A.G. and Sumitomo Co.

  2. Outline • Main interests and computational details • MgCl2active surfaces • TiCl4 and Ti2Cl6 catalytic species • Active centers and complex formation: stability problems under real reaction conditions • a-Olefins polymerization: ethylene and propylene • The role of a donorphthalate (few notes) • Conclusions and perspectives (?)

  3. Main interests • Ziegler-Natta (ZN) catalysis is by far the most important industrial process in the production of polyolefins with high degree ofstereoselectivity • The reaction occurs at room temperature with a very high reaction rate and low amount of catalyst • Experimental probes fail in recovering the microscopic picture due to the very fast reaction and the low percentage of active sites • Quantum dynamical simulations can be a viable tool to study in an unbiased way and on affordable time scale active sites and the reaction pathway

  4. Annual Worldwide Production (2008)1 : 45 million tons • Share of consumption by region (2007)2 : China — 23% North America — 18% Western Europe — 18% Asia/Pacific — 16% Middle East/Africa — 9% Japan — 11% Central/South America — 5% • Key Products: Packaging, textiles, fibers, automotive components, cups, cutlery, housewares, appliances, electronic components, carpeting, photo and graphic arts products. • Top 10 world producers by 2008 market share (in descending order)3 : LyondellBasell, Sinopec Group, Saudi Basic Industries Corp. (SABIC), PetroChina Group, Reliance Industries, ExxonMobil, Borealis, Total PC, Ineos, Formosa Plastics 1 Source: ChemSystems2 Source: Townsend Solutions3 Source: Chemical Market Associates, Inc. (CMAI)

  5. Polyolefins items produced routinely in industries and laboratories

  6. MgCl2 simulation cells: • Surface (100), orthorombic, 32 formula units, 17.673 x 14.560 x 28.000 Ǻ 3 • Surface (110), monoclinic, 30 formula units, 19.095 x 12.522 x 28.000 Ǻ 3 ab = 70.2o • Surface (104), orthorombic, 48 formula units, 14.560 x 21.711 x 28.000 Ǻ 3

  7. MgCl2 bulk crystal structure Space group: R3m, a = 3.640 Ǻ, b = 17.673 Ǻ

  8. MgCl2 (110) surface • Unrelaxed: Mg-Cl = 2.526 Ǻ ClMgCl = 180o • Relaxed: Mg-Cl = 2.322 Ǻ 2.403 Ǻ ClMgCl = 154o DE = 3.4 kcal/mol Mg

  9. Deposition of the TiCl4 catalyst

  10. Mononuclear Ti centers Octahedral Ti 6-fold on MgCl2 (110) surface as proposed by Corradini and co-workers. Ebind= 40.3 kcal/mol 5-fold Ti site on MgCl2 (110) surface obtained from CPMD Ebind= 29.4 kcal/mol [JACS120, 2746 (1998)]

  11. Active mononuclear centers Active Corradini center: Active 5-fold center: removal of 1dangling Cl substitution of a Cl with + substitution of a Cl with a methyl group. a methyl group.

  12. Free energy calculation • Select the reaction coordinate x to be monitored. Our choice: x=|C1-Ca| (olefin-chain distance) • Add to the Car-Parrinello lagrangean LCP the constraint x: LCPa LCP+ lx(x-x0) • Compute the ensemble average < lx > according to the Blue Moon prescription • Integrate the constraint force along the sampled path see M. Sprik, G. Ciccotti, J. Chem. Phys. 109, 7737 (1998)

  13. First insertion of ethylene

  14. Main phases of the insertion • The p-complex (left), the transition state (center) and the final product (right) • Reaction coordinate: x = |C1-Ca| • The reaction is a-agostic assisted

  15. Ethylene polymerization from mononuclear Ti • ELF of the main steps of the ethylene insertion: the p-complex (right), the transition state (center) and the final product (right). ELF=0: blue, ELF=1: red • ELF is projected on the plane containing the C1 and C2 carbon atoms (grey) of the ethylene and Ti (purple).

  16. Catalysis of polyethylene: energetics Experiment: Barrier = 6-12 kcal/mol Product = -22 kcal/mol Corradini 6-fold site 5-fold site

  17. Second insertion of ethylene

  18. Second insertion of ethylene • p-complex (left), transition state (center) and final product (right) in a single snapshot • Reaction is b-agostic assisted

  19. Isotacticity:regular polymer where each unit has the same orientation Propylene molecule Isotactic (stereoregular) polypropylene Q.: How can the Ziegler-Natta Ti catalyst produce isotactic polypropylene ?

  20. Possible olefin orientations for propagation 4 possible insertions, but only (a) can give a barrierless complex and a transition state lower by ~7-8 kcal/ mol with respect to (b), (c) and (d). This propylene enantioface has the minimum steric hindrance

  21. Propene polymerization from mononuclear Ti The computed propene 1,2 insertion is Isotactic. The barrier is 10.5 kcal/mol (exp.9.5-12) with a final gain of 16.7 kcal/mol below the p-complex. Cldangling-Mg = 3.03-3.22 Ǻ

  22. Complexation and insertion energies for ethylene and propene a = Corradini site, b = 5-fold site

  23. Donor di-n-butyl phthalate • Ability to coordinate to the support also in presence of Ti. O1-O2 = 2.7-3.9 Ǻ (phthalates, diethers) • Absence of secondary reactions with the catalyst • Absence of secondary reactions with the Metal-C bond and the growing polymer

  24. Interaction of a donor with the support

  25. Interaction of the donor with the active Corradini center • Ti-Mg1= 3.781 Ǻ, close to Mg-Mg distance on (100) • Mg1-O1= 2.203 Ǻ Ti-O2 = 1.942 Ǻ • Binding energy = 20.1 kcal/mol • The center is poisoned by the donor • No interaction with 5-fold

  26. Conclusions (and perspectives) • The role and the relative importance of various MgCl2active surfaces has been investigated • Interaction of Ti species with the support has been studied • The polymerization reaction has been investigated and the reaction pathway elucidated • The problem of the stability of the active sites in a realistic system has been inspected • The possible role of a donor phthalate has been addressed at a dynamical first principles level

  27. Acknowledgements • Hors Weiss, BASF AG • Stephan Hueffer, BASF AG • John Lynch, BASF-TARGOR • Akinobu Shiga, Sumitomo Co. • Shinichiro Nakamura, Mitsubishi Co. • Minoru Terano, JAIST • Hans-Joachim Freund, Fritz-Haber-Institut MPG Related publications: J. Am. Chem. Soc. 120, 2746 (1998) Surf. Sci. 438, 1 (1999) J. Am. Chem. Soc. 122, 501 (2000) J. Phys. Chem. A 105, 5096 (2001) Macromol. Symposia 173, 137-147 (2001) Mol. Phys. 100, 2935 (2002)

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