Fragmentation of Ziegler‐Natta Catalyst Particles During Propylene Polymerization

Abstract

Summary: Analyzing polymer particles by microscopy technique at different polymerization times provided information regarding the catalyst support break‐up rate and degree of fragmentation during polymerization. Polymer samples were prepared at different polymerization times and melted under a video microscope to track the progress of fragmentation. Studies focused on effect of the catalyst support on the process and degree of catalyst fragmentation. Fragmentation behaviors of both a catalyst without an external support and a silica supported Ziegler‐Natta catalyst were compared. Fragmentation of catalyst was observed to occur in the whole catalyst matrix at the very beginning of polymerization. In the case of the catalyst without an external support, fragmentation was faster and more uniform than that of the silica supported catalyst. Results corresponded to the activity distribution of single catalyst particles as determined by video microscopy. The catalyst without an external support having particles of similar activities showed similar degrees of fragmentation. Conversely, silica supported catalyst having particles of different growth behavior produced particles having different degrees of fragmentation. The rate of increase in the number of catalyst fragments and their surface area with time during polymerization was investigated. Results correlated the catalyst activation period during the initial stage of polymerization to catalyst fragmentation.Poly(propylene) particles produced with silica supported (upper image) and non‐supported (lower image) Ziegler‐Natta catalysts.magnified imagePoly(propylene) particles produced with silica supported (upper image) and non‐supported (lower image) Ziegler‐Natta catalysts.

Evaluation of the Initial Stages of Gas‐Phase Ethylene Polymerizations with a SiO2‐Supported Ziegler–Natta Catalyst

“…A proprietary SiO 2 -supported Ziegler-Natta catalyst with a titanium content of 2.0 wt.-% was used for ethylene polymerization. This catalyst system is similar to the one used by Aboudd et al [35,36] and the reader is referred to those works for more information about the catalysts. Gas-phase ethylene polymerizations were carried out in a 1 cm 3 fixed-bed microreactor at different temperatures and partial pressures of ethylene and hydrogen.…”

“…Microscopy has been used by several research groups for in situ monitoring of homopolymerizations and copolymerizations reactions in the gas phase, mainly because of the non-destructive feature of this technique. [33] Recently, Abboud et al [34][35][36] employed videomicroscopy to follow the polymer particles melting obtained from heterogeneous catalysts. Laser scanning confocal fluorescence microscopy is also available for online monitoring of olefin polymerization.…”

Dynamics of fragmentation of catalyst carriers in catalytic polymerization of olefins

“…According to their and other studies there is a sudden increase in the catalyst activity at the beginning of the polymerization followed by a rapid or slow decrease of activity caused by the clogging of pores by polymer and slowing down the monomer transport to catalyst sites (Di Martino et al, 2005). Another reason causing the decrease of catalyst activity is the possible overheating of catalyst/polymer particle in the early stages of particle growth and the catalyst deactivation (Fink et al, 2001;Abboud et al, 2005;Kumkaew et al, 2003).…”

“…MgCl 2 carriers break typically faster than silica supports and the distribution of fragments within the polymer phase as well as the fragment size distribution are uniform (Abboud et al, 2005). The fragmentation of silica-supported catalysts often does not proceed completely and resulting fragments have a broader size distribution.…”

Uma revisão sobre polimerização de olefinas usando catalisadores Ziegler-Natta heterogêneos

“…novo método para observação em linha das partículas poliméricas em crescimento, baseado na combinação de imagens de infravermelho e microscopia ótica, com a finalidade de acompanhar in situ a evolução da temperatura da superfície da partícula. Dada a sua natureza não destrutiva, técnicas de acompanhamento in situ baseadas em imagens tomadas com auxílio de um microscópio ótico são hoje empregadas por diversos grupos de pesquisa para acompanhamento de reações de homopolimerização e copolimerização em fase gasosa [84][85][86][87] . Recentemente, Xalter [88] e Xalter and Mülhaupt [89] empregaram uma técnica de espalhamento de luz (Focused Beam Reflectance Measurement -FBRM) acoplada à microscopia ótica para o monitoramento em linha do crescimento de partículas de polietileno, permitindo a determinação da distribuição do tamanho de partículas em polimerizações em lama conduzidas com catalisadores heterogêneos suportados em sílica e cloreto de magnésio.…”