Experimental investigation on mechanisms of fine particles generation for the Borealis Borstar multistage olefin polymerization process

Abstract

Simultaneous production of large amount of undesired fine particles is a big trouble in the Borstar multistage olefin polymerization process. Aiming at reducing the fine particles, the formation mechanism and formation location of the fine particles were thus studied. First, the influence of catalyst nature was considered. Second, the ash content, bulk density, morphology, and molecular weight distribution of polyethylene with different particle sizes from the small‐scale loop prepolymerization reactor, supercritical loop reactor, and gas phase fluidized bed reactor were studied, respectively. In combination with particle growth model, scanning electron microscope, gel permeation chromatography, and laser particle size analyzer, the particle morphology and growth kinetics were investigated. The results showed that fine particles were mostly generated in the supercritical loop reactor, and were significantly affected by the particle size distribution, residence time distribution, and particle fragmentation of the catalyst. Furthermore, scanning electron microscope images showed the catalysts with low activity tended to generate more fine particles. Based on these results, several strategies for reducing the amount of fine particles were proposed, which could be applied in the industrial process. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46589.

A Multipore Model for Heterogeneous Catalytic Polymerization: Structure–Performance Relationships

“…One of the main solutions to overcome this problem is using a prepolymerization step at milder reaction conditions and hence at modest reaction rates. [20] However, for some systems, prepolymerization may not be necessary to prevent fulling, provided that the necessary conditions for the occurrence of continuous bisection are met.…”

“…The "shrinking core" or "layer-bylayer" mechanism with the fragmentation starting from surface and gradually advancing to the center of the particle, and the "continuous bisection" with the fragmentation of whole particle into couple of big subparticles at once and then successive fragmentations of the subparticles into finer and finer ones. [20] Some researchers believe that the two mechanisms simultaneously take part in fragmentation process. [21][22][23] For instance, Bossers et al [23] used a combination of X-ray ptychography and X-ray fluorescence to investigate the fragmentation behavior of a single Ziegler-Natta catalyst particle in the early stages of propylene polymerization.…”

A combined experimental and molecular simulation study on stress generation phenomena during the Ziegler–Natta polyethylene catalyst fragmentation process

“…A deep understanding of that phenomena would lead to further optimization of the process. [5][6][7][8][9][10] Indeed, even smaller variation of the properties of the fragmented particles in the early stages of polymerisation can be amplified during the successive polymerization steps and lead to very different morphologies. In practice, the control of the initial fragmentation in the plants is mainly handled based on experience and best practices.…”

Experimental Evaluation of a Catalyst Fragmentation Model for Olefin Polymerization

“…In order to provide information about particle shape and size distribution after polymerization, Jiang et al. [ 11 ] calcined the reaction product to retrieve the catalyst particles after polymerization. Lee and Choi [ 12 ] calcined the polymer produced and analyzed the ashes by SEM evaluating shape and size stability of nanoparticles of silica used as catalyst support.…”

“…Emami et al [8] Kissin et al [9] and Yang et al [10] opted for carrying the polymerization reaction out under low temperature, pressure or monomer concentration in order to allow scanning electron microscopy (SEM) analysis at intermediate steps of the fragmentation process. In order to provide information about particle shape and size distribution after polymerization, Jiang et al [11] calcined the reaction product to retrieve the catalyst Fragmentation of supported catalysts plays an important role on olefin polymerization, which has motivated several studies on this topic in recent years. This work aims to obtain experimental data to compare with the predictions of a theoretical model previously developed in the research group, which uses only kinetic constants and the catalyst physical properties as input parameters.…”