Correlated X-ray Ptychography and Fluorescence Nano-Tomography on the Fragmentation Behavior of an Individual Catalyst Particle during the Early Stages of Olefin Polymerization

摘要

A combination of X-ray ptychography and X-ray fluorescence tomography (XRF) has been used to study the fragmentation behavior of an individual Ziegler-Natta catalyst particle, ～40 μm in diameter, in the early stages of propylene polymerization with submicron spatial resolution. The electron density signal obtained from X-ray ptychography gives the composite phases of the Ziegler—Natta catalyst particle fragments and isotactic polypropylene, while 3-D XRF visualizes multiple isolated clusters, rich in Ti, of several microns in size. The radial distribution of Ti species throughout the polymer—catalyst composite particle shows that the continuous bisection fragmentation model is the main contributor to the fragmentation pathway of the catalyst particle as a whole. Furthermore, within the largest Ti clusters the fragmentation pathway was found to occur through both the continuous bisection and layer-by-layer models. The fragmentation behavior of polyolefin catalysts was for the first time visualized in 3-D by directly imaging and correlating the distribution of the Ti species to the polymer—catalyst composite phase.