Slide 1

CPMD: perspectives and industrial applications Mauro Boero Institut de Physique et Chimie des Matriaux 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. Slide 2 Outline Main interests and computational details MgCl 2 active surfaces TiCl 4 and Ti 2 Cl 6 catalytic species Active centers and complex formation: stability problems under real reaction conditions -Olefins polymerization: ethylene and propylene The role of a donor phthalate (few notes) Conclusions and perspectives (?) Slide 3 Main interests Ziegler-Natta (ZN) catalysis is by far the most important industrial process in the production of polyolefins with high degree of stereoselectivity 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 Slide 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: ChemSystems 2 Source: Townsend Solutions 3 Source: Chemical Market Associates, Inc. (CMAI) Slide 5 Polyolefins items produced routinely in industries and laboratories Slide 6 MgCl 2 simulation cells: Surface (100), orthorombic, 32 formula units, 17.673 x 14.560 x 28.000 3 Surface (110), monoclinic, 30 formula units, 19.095 x 12.522 x 28.000 3 a b = 70.2 o Surface (104), orthorombic, 48 formula units, 14.560 x 21.711 x 28.000 3 Slide 7 MgCl 2 bulk crystal structure Space group: R3m, a = 3.640 , b = 17.673 Slide 8 MgCl 2 (110) surface Unrelaxed: Mg-Cl = 2.526 ClMgCl = 180 o Relaxed: Mg-Cl = 2.322 2.403 ClMgCl = 154 o E = 3.4 kcal/mol Mg Slide 9 Deposition of the TiCl 4 catalyst Slide 10 Mononuclear Ti centers Octahedral Ti 6-fold on MgCl 2 (110) surface as proposed by Corradini and co-workers. E bind = 40.3 kcal/mol 5-fold Ti site on MgCl 2 (110) surface obtained from CPMD E bind = 29.4 kcal/mol [JACS 120, 2746 (1998)] Slide 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. Slide 12 Free energy calculation Select the reaction coordinate to be monitored. Our choice: =|C 1 -C | (olefin-chain distance) Add to the Car-Parrinello lagrangean L CP the constraint : L CP L CP + ( - 0 ) Compute the ensemble average 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) Slide 13 First insertion of ethylene Slide 14 Main phases of the insertion The -complex (left), the transition state (center) and the final product (right) Reaction coordinate: = |C 1 -C | The reaction is -agostic assisted Slide 15 Ethylene polymerization from mononuclear Ti ELF of the main steps of the ethylene insertion: the - 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 C 1 and C 2 carbon atoms (grey) of the ethylene and Ti (purple). Slide 16 Catalysis of polyethylene: energetics Experiment: Barrier = 6-12 kcal/mol Product = -22 kcal/mol Corradini 6-fold site 5-fold site Slide 17 Second insertion of ethylene Slide 18 -complex (left), transition state (center) and final product (right) in a single snapshot Reaction is -agostic assisted Slide 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 ? Slide 20 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 Possible olefin orientations for propagation Slide 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 -complex. Cl dangling -Mg = 3.03-3.22 Slide 22 Complexation and insertion energies for ethylene and propene -complex (kcal/mol) Insertion (kcal/mol) Product (kcal/mol) Ethylene-8.4 a,-6.5 b +12.7 a,+6.7 b -5.8 a,-23.3 b Propene (1,2) -3.6 b +10.5 b -16.7 b Propene (2,1) +5.6 b +16.2 b (-1.0) b a = Corradini site, b = 5-fold site Slide 23 Donor di-n-butyl phthalate Ability to coordinate to the support also in presence of Ti. O 1 -O 2 = 2.7-3.9 (phthalates, diethers) Absence of secondary reactions with the catalyst Absence of secondary reactions with the Metal-C bond and the growing polymer Slide 24 Interaction of a donor with the support Mg 1 -Mg 2 () Mg 1 -O 1 () Mg 2 -O 2 () E bind (kcal/mol) (100)3.6742.1502.24621.9 (110)6.360> 4.02.0858.5 Slide 25 Interaction of the donor with the active Corradini center Ti-Mg 1 = 3.781 , close to Mg-Mg distance on (100) Mg 1 -O 1 = 2.203 Ti-O 2 = 1.942 Binding energy = 20.1 kcal/mol The center is poisoned by the donor No interaction with 5-fold Slide 26 Conclusions (and perspectives) The role and the relative importance of various MgCl 2 active 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 Slide 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)