Effect of hydrogen partioning on homo-propylene polymerization kinetics

Despite the intense amount of research to improve the performance, efficiency and costs of polypropylene production, scale up of the scientific results from laboratory scale batch reactors to industrial scale continuous production plants remains still a challenge. In order to illustrate effects of scale-up in terms of kinetics, bulk phase syntheses of homo-polypropylene are presented for two grades with different melt flow rate (MFR) targets (50, 7.5 g/10mins) in different reactor sizes (0.25 and 5l) with calorimetric monitoring of the heat of reaction. In coordinative polymerization of propylene, molecular weight is mainly controlled by addition of hydrogen as chain transfer agent [1]. In laboratory scale, bulk phase polymerization reactions are typically carried out in partially filled reactors. In such partially filled reactors, partitioning of hydrogen between gas phase and liquid phase takes place. In the used 5 liter reactor, for all MFR grades studied, uni-modal molecular weight distributions have been observed. In contrast in the 0.25 liters reactor, it was surprisingly observed, that high MFR grades show a bi-modality in molecular weight. In order to study this phenomenon, hydrogen concentration in liquid phase ( ) has been investigated before and during the polymerization reaction by a combination of gas chromatography measurements and mass balance calculations. It could be shown, that in the 0.25 liter reactor, a drift in hydrogen concentration in the liquid phase is responsible for the observed bimodalities in molecular weight. Due to consumption of propylene, the hydrogen concentration is increasing during the course of reaction. A two-step feeding procedure for the 0.25 liter reactor has been developed in order to minimize these drifts in concentration. The developed procedure allows to produce unimodal product also at high MFR grades. In addition, a correlation between the composition of materials in the reactor ( ) and the concentration of hydrogen in the liquid phase has been established. This correlation has been used to design bimodal reactions in the 5 liter reactor. The experimental MFR results were in agreement with the targeted values. Please click Additional Files below to see the full abstract

Kinetic study of bulk propylene homo-polymerization and propylene/ethylene gas-phase copolymerization under industrially relevant conditions

Polypropylene is one of the most widely manufactured polymers and is produced via coordinative polymerization with metal-organic catalysts in different polymerization processes. Catalysts are continually developed and optimized, hence there is a constant need for kinetic studies of polymerization catalysts. Scope of this work is a kinetic study of two different Ziegler-Natta catalysts in a multi-step polymerization of propylene, consisting of a bulk-phase homo-polymerization and a subsequent gas-phase copolymerization of propylene and ethylene. For studying kinetics, an existing polymerization reactor has been equipped with a compensation heater to realize a calorimetric method for measurement of reaction kinetics in bulk polymerization conditions. The experimental results have been compiled in a phenomenological kinetic model. The purpose of the model is to describe polymerization kinetics and the resulting polymers with respect to the corresponding reaction conditions.Polypropylen ist eines der meistgenutzten Polymere und wird über koordinative Polymerisation mit metall-organischen Katalysatoren in verschiedenen Verfahren hergestellt. Bei der koordinativen Polymerisation hängt die Kinetik der Reaktion von den verwendeten Katalysatoren ab, die stetig weiterentwickelt werden. Ziel dieser Arbeit ist eine kinetische Studie von zwei unterschiedlichen Ziegler-Natta Katalysatoren in mehrstufigen Polymerisationen Verfahren, das aus einer Homopolymerisation von Propylen in Masse und einer nachgeschalteten Copolymerisation von Propylen und Ethylen aus der Gasphase besteht. Zunächst wurde ein existierender Versuchsaufbau um eine Kompensations-heizung erweitert, um die Kinetik der Massepolymerisation mit Kalorimetrie untersuchen zu können. Abschließend ist basierend auf den Ergebnissen ein Modell entwickelt worden, mit dem die Kinetik der Polymerisation und die resultierenden Polymere in Abhängigkeit der Reaktionsbedingungen beschrieben werden kann

Reaction calorimetry for studying kinetics in bulk phase polymerization of propene

Polypropylene is one of the commercially most important polymers and is produced via coordinative polymerization with supported metal-organic catalysts in different processes. While kinetic measurements for slurry and gas-phase polymerization of propene are well-established, for bulk phase polymerization of propene, often the only kinetic information obtained from an experiment is the yield. In this paper, two calorimetric methods and their application for measurement of kinetics of bulk phase polymerization of propene are discussed. On the one hand a special calibration-free heat flow calorimeter and on the other hand power compensation calorimetry coupled with a software sensor for online baseline correction.Publikationsfonds ML

Diffusivity of multicomponent gas mixtures in polyethylene

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