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Effect of prepolymerization on polymerization rate of propene

Presentation held at 4th Blue Sky Conference on Catalytic Olefin Polymerization, 27.6-01.07.2016, Sorrento / Italy
Einfluss von Prepolymerisation auf die Polymerisationsgeschwindigkeit von Propen
: Bartke, Michael

2016, 24 Folien
Conference on Catalytic Olefin Polymerization <4, 2016, Sorrento>
Fraunhofer IAP ()
polymerization; Catalysts; prepolymerization; rate
Anfrage beim Institut / Available on request from the institute

Effect of Prepolymerization on polymerization rate of propene Michael Bartke, Martin-Luther-University Halle-Wittenberg and Fraunhofer Polymer Pilot Plant Center In olefin polymerization with supported catalysts, catalyst activities and productivities are continuously improving. In terms of heat removal, the most critical stage during polymerization is directly after injection of the catalyst to the reactor: the active sites of the catalyst are concentrated on a relative small catalyst particle with only limited heat removal area to the continuous phase. Many authors have observed or predicted severe particle overheating up to polymer melting. One established mean to overcome this particle overheating challenge is to use a prepolymerization step prior to main polymerization. By applying mild conditions, the polymerization rate during prepolymerization is reduced in such a way, that particle overheating is avoided. Due to particle growth, heat transfer area is generated, which improves heat removal conditions in the subsequent main polymerization step significantly. In addition, catalyst fragmentation occurs in a more controlled manner and typically improved particle morphology is obtained. Prepolymerization is used commercially in a number or processes and is described in many patents and publications[1,2,3], mostly focusing on morphology development. Also increased productivities due to prepolymerization have been reported, but not many quantitative modelling studies to account for the role of prepolymerization on reaction rate are known in open literature. In lab-scale, prepolymerization is experimentally mostly studied as an in-situ prepolymerization: the reaction is started at mild conditions and then the reactor is heated up to main polymerization temperature. The heating-up period typically takes 10 to 15 minutes, during which the conditions do change. Hence, in-situ prepolymerization is a bit undefined. Another approach is to carry out prepolymerization as an external prepolymerization in a separate reactor under constant conditions and then to inject the prepolymerized catalyst to main polymerization under reaction conditions. This approach allows more defined and controlled prepolymerization and main polymerization conditions. However possible effects of storage-times of the prepolymerized catalyst have to be considered. In the presentation, experimental results for the impact of prepolymerization on reaction rate in both bulk- and gas-phase polymerization of propene for different Ziegler-Natta and also a supported metallocene catalyst applying both in-situ and external prepolymerization methods will be presented and discussed. In addition, a simplified modelling approach to account for the impact of prepolymerization on polymerization rate will be presented. The model is based on calculation the actual polymer particle temperature during course of the polymerization under consideration of a highly temperature dependent deactivation reaction.