Development of Supported Single-Site Catalysts and Produced Polyethylene

Following the development of conventional multi-site Ziegler-Natta catalysts during the 60–80s, large academic and industrial efforts are been devoted to the design and synthesis of well defined new family of single-site olefin polymerization catalysts, with the group 4 metallocene class of compounds receiving the most attention. Recently, there is also a growing interest in the late transition metal catalysts based on nickel, palladium, iron and cobalt compounds.The new generation of single-site catalysts can really impact the polyolefin industry if they can be used as dropped into large capacity production plants and produced resins that can be processed in the existing equipment without major modifications. Both requirements should be achieved at a favorable cost/performance balance respect to conventional polyolefin technologies. The main objectives of the present contribution is to address two of the most important issues the single-site catalysts technology is currently facing, namely, development of methods for supporting the new single-site catalysts suitable for dropping into slurry and gas-phase processes and the development of polyethylene with better properties and good processability. Firstly, after describing existing procedures for the preparation of supported metallocene catalysts, the method developed by Repsol is then followed. Repsol proprietary technology is based on functionalized metallocene that can react with appropriate carriers producing supports catalysts exhibiting: high activities (while retaining the essential characteristics of their homogeneous analogs), high stability, no reactor fouling or sheeting, good morphology (polymers replicate the catalyst morphology) and bulk densities of the resulting polymers. This method is also very suitable for the design of well defined multi-site catalysts that produce tailor-made bimodal or multimodal resins (either polymer molecular weight and/or chemical composition distributions) with controlled polymer architectures and showing good processability.Finally, the advantages and disadvantages of supporting nickel α-diimine and iron pyridine bis-imine catalysts will be discussed together with the produced polyethylene.