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Homogeneous Catalysis HMC-7- 2016

Homogeneous Catalysis HMC-7- 2016. Dr. K.R.Krishnamurthy National Centre for Catalysis Research Indian Institute of Technology,Madras Chennai-600036. Polymerization Ethylene & Propylene polymerization Ziegler –Natta catalysts Metallocene catalysts. Chemical Industry-The Fact Sheet.

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Homogeneous Catalysis HMC-7- 2016

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  1. Homogeneous CatalysisHMC-7- 2016 Dr. K.R.Krishnamurthy National Centre for Catalysis Research Indian Institute of Technology,Madras Chennai-600036

  2. Polymerization • Ethylene & Propylene polymerization • Ziegler –Natta catalysts • Metallocene catalysts

  3. Chemical Industry-The Fact Sheet • 70000 products • 10 Million direct employees • 50 Million indirect employees • Wide range of products/processes / feed-stocks • Enabling better quality of life • Annual growth rate 2.4 % Global enterprise valued at $2.2 Trillion …… and growing

  4. Chemical Industry- Products pattern Polymers constitute 20 % of Mega Chemical Industry

  5. Polymers -Types Single Polymer chains as seen by AFM

  6. Polymerization-Types Mode of formation • Addition Polymerization - Polyethylene, Polypropylene Grafting, cross-linking • Condensation Polymerization - PET, Nylon 66 Mechanism of formation • Free radical - LDPE, PVC • Co-ordination - PP,PBR • Ionic - Cationic, Anionic- Poly acrylonitrile

  7. Addition Polymers-Types

  8. Block Random • ABS- Acrylonitrile-Butadiene-Styrene co-polymer • PAN-Strong fibre character • PBR- Rubber-Elasticity-shock absorber • PS - Tough & hard • The co-polymer has very high strength & toughness Graft

  9. Polymers- Finger prints Catalyst & Process controlledReflected in Regioselectivity Melting point Cis/Trans Isomerism Crystallization temp. Stereoselectivity Glass Transition temp. Mol. Wt distributuion Modulus Polydispersity Crystallinity Viscosity Morpohology Hardness Stiffness Transparency Catalysts & process dictate the property of polymer

  10. Polymers-The journey Monomer Co-monomer(s) Type of polymerization Co-catalysts Donors etc. Type of catalyst Type of process/reactor Type of Processing, Processing aids, Machinery Reaction conditions Processing Polymer resin End Product

  11. History of PE & PP (1933) (1955) • Propylene polymerization on similar catalysts by Natta (1956) • - 3 generations of catalysts • Silica supported chromia catalyst for ethylene polymerization • Banks & Hogan- Phillips (1958)- Low pressure/Temp process • Metallocene catalysts- Kaminsky (1989) • Post metallocene catalysts Ziegler & Natta awarded Nobel prize in 1963 Global consumption- PP - 45 Mill.MT; Value- $65 Billn. (2007) PE - 65 Mill.MT (2008)

  12. Free radical ploymerization- Ethylene Ethylene (C2H4) forms polyethylene (PE) in the presence offree radical R• (catalyst or initiator) monomer initiation propagation

  13. Ploy ethylene – Types Vs Properties • PE by free radical route • Extensive branching • Long and short branches • Lower crystallinity 30-60% • Density 0.91-0.925 • Vary P, T during synthesis PE MW Density Tensile strength Branching Mill. g/cc MPa HDPE 0.2-0.5 > 0.941 43 Low LDPE 0.1 0.91-0.940 24 Med & Short LLDPE 0.1 0.91-0.925 37 Short UHMWPE – MW- 3-6 Million Co-monomers for LLDPE → 1-Butene/1-Hexene/1-Octene

  14. Surface structure of Chromium based PE catalysts 1.CrO3/ Silica- Phillips • Choice of silica (~300 m2/g), Cr loading (1%), promoters & pretreatment • (calcination, pre-reduction) of the catalysts are crucial • 30-40 % of PE is produced by Phillips process 2.Chromocene/Silica- Union Carbide

  15. Z-N- Polymerization of ethylene

  16. Catalytic cycle for polymerization of ethylene - Cossee-Arlman mechanism - Direct insertion of olefin across M-alkyl bond

  17. High Pressure Autoclave Tubular Low Pressure Slurry phase Gas phase Solution phase Processes for PE production

  18. PE TechnologiesHigh Pressure Processes • Employs free radical catalyst for polymerization • Energy intensive process • Product with easy processability Tubular Tubular- More of Long chain branching (LCB) & less Short chain branching (SCB) Autoclave- More SCB & less LCB Autoclave

  19. Low Pressure PE Processes Polyolefin (PE/PP) Process Technologies Slurry Phase Gas Phase Solution Phase (PE Only) CSTR Stirred bed Heavy Diluent Light Diluent FBD

  20. Block diagram of a typical slurry polymerization process

  21. Typical process flow diagram for gas phase polymerization

  22. Processes for Polyethylene

  23. Conventional Ziegler-Natta Catalyst • Catalyst components TiCl4 & AlEt3 –co-catalyst • Organo aluminium compound reduces TiCl4 to generate TiCl3 • Active phaseTiCl3 • Different crystalline forms- α , β, γ , & δ • β Chain structure; α , γ , & δ have layer structure • Layer structure ensures vacant co-ordination sites • Activity & Isotacticity differs • α – Hexagonal Close packed – hcp of Cl ions • γ - Cubic close packed –ccp of Cl ions • Ti ions occupy Octahedral holes of Cl- matrix • α , γ & δ yield high isotacticity while β- gives low isotacticity • DEAC is a better co-catalyst than TEAC since over reduction of TiCl4 • beyond Ti3+ (to Ti2+) is avoided

  24. Ball-milling of the catalysts decreases the particle size and hence increases Surface area by forming smaller TiCl3 crystallites. Such treatment increases polymerization activity Use of electron donors increases the stereoselectivity Isotacticity Index DEAC- 90-95% TEAC- 70-85 % EADC is converted to DEAC Type of co-catalyst influences Isotacticity Index

  25. Stereochemistry of PP- a) Three different orientation of methyl groups in PP backbone b) Stereo chemical relationship between two adjacent methyl groups

  26. Z-N Polymerization-Stereochemistry

  27. PP- Streochemistry Vs Properties PP Elastic Hardness MP Mech.props Modulus-Gpa Mpa ° C Isotactic 1.09 125 160-170 Stiff/Brittle Syndiotactic 125-131 Robust, transparent Atactic 0.15 1.4 < 0

  28. Polymerization of propylene- Reaction scheme

  29. Polymerization of propylene- Steps • Replacement of one Cl by alkyl group of Al alkyl • Bonding of Propylene to a vacant site • Insertion of propylene into Metal-alkyl bond- Initiation • Creation of vacant site for propylene adsorption • Repetition of steps 2,3 & 4 leading to chain growth/propagation • Catalyst configuration decides the configuration of added propylene • Termination of polymer chain with hydrogen- Termination

  30. Streochemistry of active site P ----------- CH3 Cl ------------ ----------- Ti Cl Cl CH3 1.501Å ----------- H C  124.3° Cl 1.336Å 4 Bridging Cl 1Terminal Cl replaced by alkyl 1 Vacant site for propylene adsorption ---------- C H H

  31. Polypropylene- Stereoregulation Methyl group of the incoming propylene prefers a trans position vis-à-vis the polymer chain-p – Right ; cis orientation as shown on left is not favoured

  32. PP Stereochemistry- Effect of metal & ligand

  33. Possible insertion modes for Propylene across Metal-Alkyl bond- Different orientations of methyl group 1 2 P 3 1,2 Insertion M 2 M P + 3 1 3 2,1 Insertion P 2 M 1 1 3 M 3,1 Insertion P 2

  34. Z-N catalysts- Generations catalyst First • TiCl3 and AlEt2Cl Second • TiCl3 + AlEt2Cl + Mono/Di ethers, Mono/Di esters –Effect of TiCl3 • Crystallite size, ball-milling & increase in surface area Third • TiCl4 supported on MgCl2 + Al-Alkyl + Phthalate esters -3rd component • MgCl2 has layered structure; Ionic radii of Mg2+ & Ti3+ 0.066 & 068 nm • Structural compatibility MgCl2 & TiCl4 • Polymer yield > 30 Kg/g ; Isotacticity index -96-99% Fourth • Morphology controlled catalysts • Spherical polymer product-No extrusion Removal of Atactic PP and catalyst residue Catalyst residue removed by washing with alcohols & water-Deashing High activity catalyst → Elimination of catalyst removal deashing & extrusion

  35. Removal of catalyst residue and atactic PP are the two critical steps

  36. Polymerization Propylene recovery Degassing Centrifugation and Catalyst deactivation Solvent recovery Deashing Drying Extrusion PP PP- First Generation Process • Large plant size • High capital and operating cost • Large number of equipments • Large inventory of solvent • Energy intensive • Solvent purification • APP removal • Catalyst deashing Total process steps: 8

  37. Polymerization Propylene recovery Degassing Centrifugation and Catalyst deactivation Solvent recovery Drying Extrusion PP PP-Second Generation ProcessHexane Slurry • Plant size small • Reduced capital and operating cost as compared to first generation process • No catalyst deashing • Large inventory of solvent • Energy intensive due to solvent purification step • Still involved removal of APP Total process steps: 7

  38. Polymerization Propylene recovery Degassing And Steaming Extrusion PP PP-Second Generation ProcessLiquid Pool (Bulk Loop) Spheripol • Plant size further reduced • Capital and operating cost reduced considerably as compared to Hx slurry process • Very simple to operate • Energy efficient • Removal of APP not required Total process steps: 5

  39. Polymerization Propylene recovery Degassing & deactivation Extrusion Polypropylene PP-Third Generation Process Gas Phase • Plant size reduced • Capital cost high (10-15%) but operating cost reduced considerably • Very simple to operate • Energy intensive – Extrusion step required • Removal of APP not required Total process steps: 5

  40. Polymerization Propylene recovery Degassing and deactivation No Extrusion Polypropylene Spheribeads PP-Third Generation ProcessLiquid Pool (Spheripol + Adipol) • Plant size reduced • Capital cost and operating cost reduced considerably vs. Hx slurry • Very simple to operate • Energy intensive–Extrusion not required • Removal of APP not required Total process steps: 4

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