Mass transport and kinetics in the heterophasic copolymerization of propylene

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The PhD work focuses on an experimental and modeling study of reaction and mass transfer kinetics in the polymerization of high impact polypropylene (hiPP) under industrial conditions. This polymerization occurs in two stages: first, a semicrystalline, isotactic homo-PP matrix is produced, followed by the formation of an amorphous, elastomeric ethylene-propylene copolymer, which is immiscible with the homo-PP matrix. Speculations suggest that changes in particle morphology, such as pore clogging and reduced porosity, may lead to diffusion limitations in the second polymerization stage. The objective is to develop an experimentally justified reaction-transport model to analyze the balance between reaction and diffusion during the process. Gas-phase polymerization experiments were conducted in a 5-liter horizontal stirred tank reactor in semi-batch mode, allowing for the monitoring of individual monomer consumption rates through gas composition analysis. Additionally, high-pressure sorption measurements in a non-reacting system were performed to assess solubility and transport properties independently of reaction kinetics. These measurements, conducted on both copolymer powders and pressed polymer films, enable the derivation of effective diffusion coefficients for the heterophasic material. Insights into the morphological developments of the polymer powders can be drawn from these experiments. A proposed mass transport model de