Fundamental aspects of heterogeneous Ziegler–Natta olefin polymerization catalysis: an experimental and computational overview

Abstract

MgCl2 supported Ziegler–Natta (Z–N) catalyst have emerged as a most exciting chemical process for polyolefin technology, which is responsible for production of ~150 million ton polyolefin (polyethylene and polypropylene) per...

Electronic Properties of Ti Sites in Ziegler–Natta Catalysts

“…The hexa-1 model in Figure 1 was used as a starting point for building up five models representative for the possible Ti species formed upon reaction with a TEAl activator, according to the most common activation paths proposed in the literature, 2,5 which include the formation of a coordination vacancy on the Ti site through the homolytic or heterolytic cleavage of a Cl ligand (dechlorination) and the exchange of another Cl ligand with an ethyl group (transalkylation or metathesis). The five structurally optimized models (whose atomic coordinates are provided in the SI) are represented in Figure S1 and are referred hereafter as (i) Ti IV For each one of the optimized models described above, the UV−vis spectra and L 2,3 -edge NEXAFS spectra were simulated to single out their spectroscopic fingerprints and to understand the sensitivity of the two techniques to small variations in the structure of the Ti sites.…”

“…The hexa-1 model in Figure was used as a starting point for building up five models representative for the possible Ti species formed upon reaction with a TEAl activator, according to the most common activation paths proposed in the literature, , which include the formation of a coordination vacancy on the Ti site through the homolytic or heterolytic cleavage of a Cl ligand (dechlorination) and the exchange of another Cl ligand with an ethyl group (transalkylation or metathesis). The five structurally optimized models (whose atomic coordinates are provided in the SI) are represented in Figure S1 and are referred hereafter as (i) Ti IV Cl 5 ⊕ , obtained from the heterolytic cleavage of a Cl ligand; (ii) Ti III Cl 5 , derived from the homolytic cleavage of a Cl; (iii) Ti IV Cl 5 R, resulting from transalkylation; (iv) Ti IV Cl 4 R ⊕ , obtained through transalkylation of model Ti IV Cl 5 ⊕ ; and (v) Ti III Cl 4 R, obtained by transalkylation of model Ti III Cl 5 .…”

“…Ziegler–Natta (ZN) catalysts are at the heart of the polyolefin production, affording at present almost 80 million tons of polypropylene per year, with a worldwide economic turnover exceeding 100 billion dollars, and their great properties are recognized as a fundamental benchmark for the whole chemical industry. Their extraordinary success in terms of activity and selectivity is due to the perfect combination of four indispensable components, namely, a titanium chloride precursor, a high surface area MgCl 2 support, organic molecules acting as Lewis bases (namely, the electron donors), and an aluminum alkyl activator. − The first three components constitute the precatalyst, which can be prepared following different routes that have been optimized in decades of industrial research , to generate multigrain and porous spherical particles as a result of aggregation of so-called primary particles. − This hierarchical structure is fundamental to guarantee controlled fragmentation during olefin polymerization and to provide a polymer with the desired morphology.…”

Mechanistic Study on Effect of Electron Donors in Propylene Polymerization Using the Ziegler–Natta Catalyst

“…The Ziegler–Natta catalyst is one of the most important catalysts for industrial polyolefin production, which mainly produces polyethylene and isotactic polypropylene . Nowadays, a typical supported Ziegler–Natta catalysis system consists of four key elements: TiCl 4 (the catalyst precursor), MgCl 2 (the support), electron donors (Lewis bases), and alkylaluminum (the catalyst activator). , The introduction of electron donors is a great breakthrough in the Ziegler–Natta catalysis system for propylene polymerization. Electron donors can be divided into two types: (i) the internal donor (added during the catalyst preparation), e.g., ethyl benzoate, phthalate, succinate, 1,3-diether, malonates, etc .…”

“…3 Nowadays, a typical supported Ziegler−Natta catalysis system consists of four key elements: TiCl 4 (the catalyst precursor), MgCl 2 (the support), electron donors (Lewis bases), and alkylaluminum (the catalyst activator). 4,5 The introduction of electron donors is a great breakthrough in the Ziegler−Natta catalysis system for propylene polymerization. Electron donors can be divided into two types: (i) the internal donor (added during the catalyst preparation), e.g., ethyl benzoate, phthalate, succinate, 1,3-diether, malonates, etc., 6−16 and (ii) the external donor (added during the olefin polymerization), e.g., silane, alkoxysilane.…”