Presentation on theme: "Ziegler-Natta Catalysis"— Presentation transcript:
1Ziegler-Natta Catalysis Presented by:Mehrban ashiqSaad afzalPresented To:M.phil Inorganic- Analytical Chemistry 3rd SemesterDepartment of Chemistry, University of Gujrat, Pakistan.Course Title: Organo -Transition ChemistryCourse code: CHEM-529Instructor: Dr. Muhammad Ali Mohsin
2Ziegler-Natta Catalysis Outline:IntroductionCatalysisActivation EnergyZiegler-Natta Olefin PolymerizationZiegler's DiscoveryMechanismNatta's DiscoveryPP StereochemistryDifferent Catalyst system and % yieldConclusion
3Branched/low-density = (LDPE) Ziegler-Natta Catalystmost popular plastic.Grocery bags, shampoo bottles, toys, etc.Simple structure than all polymers.Branched/low-density = (LDPE)Easier to makeLinear/high-density = (HDPE)
4CatalysisCatalysts increase reaction rate without themselves being changedCan accelerate a reaction in both directionsDo not affect the state of equilibrium of reactionsimply allow equilibrium to be reached faster
5Activation energyMolecules must be activated before they can undergo a reactionReactants must absorb enough energy from surroundings to destabilize chemical bonds (energy of activation)Transition stateIntermediate stage in reaction where the reactant molecule is strained or distorted but the reaction has not yet occurred
6Ziegler’s Discovery 1953 K. Ziegler, E. Holzkamp, H. Breil & H. Martin Angew. Chem. 67, 426, 541 (1955); 76, 545 (1964).ProblemIdea:
7Ziegler-Natta Catalysts Combination of a transition metal compound of an element from groups IV to VIII, and an organometallic compound of a metal from groups I to III.Catalyst – Transition metalCo-catalyst – Organometallic Compound, mainly alkyl or alkylhalides of aluminium and boron, or methylaluminoxane.
8Ziegler-Natta Catalysis of Alkene Polymerization Ziegler-Natta CatalystA typical Ziegler-Natta catalyst is a combination ofTiCl4 and (CH3CH2)2AlCl,orTiCl3 and (CH3CH2)3Al.
9Polymerization Steps Replacement of one Cl by alkyl group of Al alkyl Bonding of Propylene to a vacant siteInsertion of propylene into Metal-alkyl bond- InitiationCreation of vacant site for propylene adsorptionRepetition of steps 2,3 & 4 leading to chain growth/propagationCatalyst configuration decides the configuration of added propyleneTermination of polymer chain with hydrogen- Termination
10Conventional Ziegler-Natta Catalyst Catalyst components TiCl4 & AlEt3Organo aluminium compound reduces TiCl4 to generate TiCl3Active phase TiCl3Different crystalline forms- α , β, γ , & δβ Chain structure; α , γ , & δ have layer structureActivity & Isotacticity differsα – Hexagonal Close packed – hcp of Cl ionsγ - Cubic close packed –ccp of Cl ionsTi ions occupy Octahedral holes of Cl- matrix
11Mechanism of Coordination Polymerization InitiationAl(CH2CH3)3+TiCl4ClAl(CH2CH3)2+CH3CH2TiCl3
12Mechanism of Coordination Polymerization InitiationAl(CH2CH3)3+TiCl4ClAl(CH2CH3)2+CH3CH2TiCl3CH3CH2TiCl3+H2CCH2CH3CH2TiCl3H2CCH2
13Mechanism of Coordination Polymerization InitiationTiCl3CH3CH2CH2CH2CH3CH2TiCl3H2CCH2
14Mechanism of Coordination Polymerization propagationTiCl3CH3CH2CH2CH2H2CCH2TiCl3CH3CH2CH2CH2
15Mechanism of Coordination Polymerization propagationTiCl3CH3CH2CH2CH2CH2CH2H2CCH2TiCl3CH3CH2CH2CH2
16Mechanism of Coordination Polymerization propagationTiCl3CH3CH2CH2CH2CH2CH2H2CCH2etc.
18Catalytic cycle for polymerization of ethylene - Cossee-Arlman mechanism - Direct insertion of olefin across M-alkyl bond
19Natta’s Discovery Isotactic Syndiotactic 1954 Giulio Natta, P. Pino, P. Corradini, and F. DanussoJ. Am. Chem. Soc. 77, 1708 (1955) Crystallographic Data on PPJ. Polym. Sci. 16, 143 (1955) Polymerization described in FrenchIsotacticSyndiotacticZiegler and Natta won Nobel Prize in 1963
20Automobile and appliance Polypropylene tacticityAutomobile and applianceparts, rope, carpetingSoft n’ sticky…not very good for anything
21Zieglar-Natta Catalyst - Before Z-N Catalyst invention, PP composites were only atactic form- After that, isotactic PP composites of extraordinary MW(>106) is synthesizedLDPEHDPEPPThis has less hardness, stiffness and strength compared to HDPE, but better ductility, Free radical10 billion lb/yrUse chromium compounds.Zieglar-Natta process is recent application.A few number of branchesAlR3, AlHR2Natta4 billion lb/yr
28Z-N catalysts- Generations catalyst FirstTiCl3 and AlEt2ClSecondTiCl3 + AlEt2Cl + Mono/Di ethers, Mono/Di estersThirdTiCl4 supported on MgCl2 + Al-Alkyl + Phthalate esters -3rd componentMgCl2 has layered structure; Ionic radii of Mg2+ & Ti3+ similarStructural compatibilityPolymer yield > 30 Kg/g ; Isotacticity index %FourthMorphology controlled catalystsSpherical polymer product-No extrusion
29General Composition of Catalyst System and % Yield Main Group Metal alkylTransition Metals Compounds% Yield of PolymerAl2Et6TiCl448AlBu360TiCl*380-92VCl478VCl373CrCl336TiCl340-50[Et2Be] n94-96[Et2Mg] n78-85Et2Zn30-40[AlClMe2] 296-98R.C.MEHROTRA,. A.SINGH. “Organometallic Chemistry” Revised Second Edition page(464)
30Limitationswe can't make poly(vinyl chloride) by Ziegler-Natta polymerization. When the catalyst and cocatalyst come together to form the initiating complex, radicals are produced during intermediate steps of the reaction. These can initiate free radical polymerization of the vinyl chloride monomer.Acrylates are out, too, because Ziegler-Natta catalysts often initiate anionic vinyl polymerization in those monomers.