Production of polyolefins by metallocene catalysts and their recycling by pyrolysis
May 10-15, 2015
Polyolefins and their product engineering by organometallic catalysts have grown to the largest industrial application in the field of polymers. In 2014 about 150 million tons of polyethylene, polypropylene, and polyolefin copolymers were produced worldwide. Polyolefins are sustainable polymers since they show a wide variety of properties, consist of only carbon and hydrogen atoms, efficiently produced from easy available monomers and can be recycled. Beside Ziegler-Natta and Phillips catalysts metallocenes and other transition metal complexes, activated by methylaluminoxane allow to tailor the structure, the tacticity, and the stereoregularity of polyolefins in a way which has not been reached before[1,2]. Isotactic, syndiotactic, and isoblock polypropylenes can be obtained with high impact strength, elasticity, and transparency. Metallocene catalysts are also able to copolymerize ethene or propene with cyclic olefins such as cyclopentene or norbornene as well as with macromers to form polymer glass or long chain branched polymers with new properties. Exceptionally strong polymer composites can be synthesized by in-situ polymerization in a two step process. First, the soluble metallocene/methylaluminoxane catalyst is absorbed on the surface of fillers, then by addition of ethene or propene, a polyolefin film is formed, covering the particles, layered silicates, or fibers. A new water resistant paper is obtained by starch and cellulose fiber filled polyethylene, Polyolefin nanocomposites produced by in-situ generation show better mechanical properties than material produced by mechanical blending such as improved stiffness, high gas barrier properties, significant flame retardancy, and high crystallization rates Exciting advantages - just starting - are the synthesis of defined copolymers with three and more monomers, short and long chain branched polyolefins, block copolymers by chain shuttling, living polymerization. Highly filled polyolefin nanocomposites cause a tremendous boost of physical and chemical properties. Polyolefin wastes can easily be recycled by extrusion moulding or by pyrolysis to gas and oil. While for extrusion moulding pure polymers have to be used the pyrolysis can take mixed and contaminated polyolefins. In a fluidized bed process, indirect heated by fire tubes, different products are obtained in dependence of the pyrolysis temperature. By 500°C about 90 % aliphatic waxes are formed, by 700°C mainly olefins and aromatics . By addition of Lewis acids such as titanium or aluminum chlorides to the fluidized bed it is possible to decreasing the pyrolysis temperature at 100 °C.
 W. Kaminsky, Discovery of Methylaluminoxane as cocatalyst for Olefin Polymerization Macromolecules 45 (2012) 3289-3297.  W. Kaminsky, A. Funck, C. Klinke, In-situ Polymerization of Olefins on Nanoparticles or Fibers by Metallocene Catalysts, Top Catal 48 /2008) 84-90  P.J.Pawel, W. Kaminsky, F. Buzeto, W. Yang, Pyrolysis of polyolefins for increasing the yield of monomers recovery, Waste Management Oxford 32 (2012) 840-846