(737g) Propylene Polymerization with Metallocene/Methylaluminoxane Catalysts: Mechanisms, Modeling and Simulation

Authors: 
Prakash, N., Birla institute of Technology and Science (BITS) - Pilani

AIChE-2014

Abstract

Polymers and co-polymers of propylene find extensive industrial and commercial  applications like engineering plastics, elastomers and synthetic rubbers. Transition metal compounds are generally used as catalysts in polymerization of propylene, Ziegler Natta catalyst being the first successful kind among them. These catalysts are the derivatives of transition metals such as titanium (TiCl4, TiCl3), vanadium (VCl4, VOCl3), etc. and are generally employed with co-catalysts which are organometallic compounds, such as Al(CH3)3, Al(C2H5)3, etc.

Ziegler-Natta catalysts are heterogeneous catalysts with multiple sites. Metallocene/methylaluminoxane complexes are the catalysts used next to Ziegler Natta catalysts in the polymer industry recently. Metallocene catalyzed propylene polymerization has recently attracted research interest since these catalysts allow the production of tailored macromolecules with properties those can be accurately designed. A broad spectrum of properties and applications of the polypropylene can be attained with metallocenes due to their single types of sites.

Two major types of metallocene catalysts are used in propylene polymerization –first type being bis-metallocene complexes of transition metals, (Cp2MtCl2) and the second type based on complexes containing one cyclopentadienyl group like [C5H4-SiMe2-(tert-Bu)N]TiCl2-MAO and [C5Me4-SiMe2-(tert-Bu)N]TiCl2-MAO, etc.

Homogeneity and single site characteristics of metallocenes enable to correlate metallocene structures with polymer properties such as molecular weight, stereochemical microstructure, behavior and mechanical properties. Understanding reaction mechanisms and kinetics of metallocene catalyzed polymerization reactions is very important to design/identify a catalyst for promising product properties or to modify the existing Ziegler-Natta based technology with metallocenes.

This article deals with the presents state of the art on the reaction mechanisms and kinetics involved in Ziegler-Natta and metallocene catalyzed propylene polymerization. Further, an approach of microscopic modeling and simulation of propylene polymerization through different metallocene catalyst systems is presented and discussed using a novel Natural Logarithmic Differential Evolution optimization algorithm.

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