Kaminsky catalysts

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Under Kaminsky catalysts are mixtures of a metallocene -dihalogenids with methylaluminoxane (MAO). These catalysts allow the polymerization of olefins. The catalyst systems were developed in the 1980s by Walter Kaminsky and Hansjörg Sinn at the University of Hamburg .

The catalysts are both academic research and for industrial production of polyolefin - plastics is of great importance, since by varying the ligand and the catalyst symmetry, the activity and selectivity of the catalysts in terms of tacticity and molecular weight distribution of the polymers obtained in wide limits can be varied.

history

Shortly after the Ziegler-Natta process was discovered, metallocenes were also tested as transition metal components for these, but the activity of these mixtures was only very low. In 1973 Karl-Heinz Reichert and David S. Breslow independently found that adding a small amount of water to the titanocene / alkylaluminum chloride system markedly increases the activity. By chance in 1975 Walter Kaminsky’s Hamburg laboratory found out that adding a large amount of water (Al: H 2 O = 1: 2) to a mixture of biscyclopentadienyldimethyltitanium and trimethylaluminum produced a very active polymerization catalyst for ethylene. Further investigations in 1977 showed that the active cocatalyst is methylaluminoxane (MAO). The targeted production and combination of MAO, especially with zirconocenes, polymerizes olefins 10 to 100 times faster than the Ziegler-Natta catalysts used until then.

presentation

The metallocenes used by Kaminsky and Sinn are complexes of transition metals of the titanium group of type 1 . The compounds are generally light from the element chlorides and cyclopentadienyl - sodium accessible or its derivatives.

Kaminsky catalysts

Reactions

Polyethylene

The Kaminsky catalyst systems produce polyethylene with a high catalytic activity from ethene at room temperature and atmospheric pressure . At higher ethene pressure, the activity increases further so that, for. B. at temperatures around 95 ° C and pressures of about 8 bar ethene per gram of zirconium a yield of about 40,000 kg of polyethylene is obtained. Due to the low catalyst concentration, it can remain in the finished product and does not affect the processing behavior or the stability of the products. The obtained molar mass distribution is narrower than with conventional Ziegler catalysts.

Polypropylene

By using C 2 -chiral metallocenes of the Brintzinger type ( 2 ) in which two indenyl ligands are bridged, it was possible to produce highly stereoselectively polymerized α-olefins. If the metallocene 1 ( zirconocene dichloride , hafnocene dichloride ) is used for the polymerization of propylene , atactic polypropylene is obtained , while the catalyst 2 with C 2 symmetry leads to isotactic polypropylene and the complex 3 with C s symmetry leads to syndiotactic polypropylene.

Co-polymerisation

By modifying the metallocene complexes, catalysts for the targeted copolymerization of various olefins can also be produced. The properties of ethylene-propylene, ethylene-1-octene or copolymers based on ethylene- norbornene can be varied over a wide range.

Heterogenization

The homogeneous Kaminsky catalysts can be heterogenized with the aim of replacing them as a replacement for conventional Ziegler-Natta catalysts in existing production plants. The heterogenization also allows the MAO / metallocene ratio to be reduced by several orders of magnitude.

Various methods can be used to heterogenize the catalyst system. The fixation can take place from the suspension as well as from the gas phase. The complex can be covalently bound to the carrier material via the ligand or it can only be present in a physisorbed form. As carriers are aluminum oxides , magnesium chloride , silica gels , zeolites and polymers such as polystyrene or silicones used.

Web links

literature

Individual evidence

  1. ^ Walter Kaminsky : Metallocenes . In: Ullmann's Encyclopedia of Industrial Chemistry . Wiley, June 15, 2006, pp. 685–691 , doi : 10.1002 / 14356007.b16_b36.pub2 (English).
  2. ↑ KH Reichert, KR Meyer: On the kinetics of the low-pressure polymerization of ethylene with soluble ZIEGLER catalysts . In: The Macromolecular Chemistry . tape 169 , no. 1 , 1973, p. 163–176 , doi : 10.1002 / macp.1973.021690116 .
  3. ↑ Wendell P. Long, David S. Breslow: The influence of water on the catalytic activity of bis (π-cyclopentadienyl) titanium dichloride-dimethylaluminum chloride for the polymerization of ethylene . In: Justus Liebig's Annals of Chemistry . tape 1975 , no. 3 , May 15, 1975, p. 463-469 , doi : 10.1002 / jlac.197519750310 .
  4. ^ Walter Kaminsky : New polymers by metallocene catalysis . In: Macromolecular Chemistry and Physics . tape 197 , no. 12 , 1996, pp. 3907-3945 , doi : 10.1002 / macp.1996.021971201 (English).
  5. ↑ Walter Kaminsky: “Increasing the efficiency of polymerization catalysts”. In: Aktuell-wochenschau.de. GdCh , accessed June 8, 2018 .
  6. ^ Report in the 2003 yearbook of the Max Planck Institute for Coal Research.
  7. ↑ John R. Severn, John C. Chadwick, Robbert Duchateau, Nic Friederichs: “Bound but Not Gagged” Immobilizing Single-Site α-Olefin Polymerization Catalysts . In: Chemical Reviews . tape 105 , no. 11 , November 2005, p. 4073-4147 , doi : 10.1021 / cr040670d .