A MgCl 2 -based Ziegler–Natta catalyst was characterized using X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and IR spectra. We focused on the XRD reflection at 2θ = 50° to determine the thickness of MgCl 2 crystals, and validated these results with TEM pictures. SEM pictures were taken in order to measure the size of the nanoparticles formed by the MgCl 2 crystals. Several compounds were synthesized for comparison and to aid interpretation of the infrared (IR) spectra. The catalysts were prepared by precipitating MgCl 2 , which was used as support material and subsequently treated with TiCl 4 . The thickness of the catalyst crystals was calculated from the XRD reflection at 2θ = 50°. Changing the precipitation temperature within a range from 40 to 90 °C altered the thickness of the MgCl 2 crystal plates. The maximum thickness of 7 nm was achieved at a precipitation temperature of 60 °C. The SEM pictures showed that the nanoparticles had a diameter of ~200 nm. A crystal base unit had a volume that corresponded to that of a sphere of 3.5 nm radius. Thus, we estimated that a typical catalyst particle with a diameter of 20 μm contained about one million nanoparticles, each of which consisted of about 25,000 MgCl 2 crystal units.

The presented micro gas-phase reactor is a very suitable tool for the investigation of polymerizations. To achieve conditions which are closer to industry an overflow is installed in the microreactor. With this setup it is now possible to have a distinct exchange of ethene during the polymerization. CFD calculations have been performed to evaluate the reactor setup and according to these results the reactor has been modified to allow an exchange of the reactor volume two times per minute. The overflow leads to a better heat removal from the growing polymer particles and supplies the active centers with preheated ethylene. The performed overflow-polymerizations are compared with polymerizations in static conditions and the results allow deeper understanding of the polymerization kinetics on particle level in gas phase conditions.

The concept of using a micro-reactor tool for studying single particle polymerization is demonstrated in the present study. The micro-reactor is equipped with a video microscope for capturing the growth of polyethylene-particles during polymerization. The gas-phase polymerizations are done in conditions very close to industrial set points. As catalyst a standard 4th generation Ziegler–Natta system has been used. From the obtained particle growth curves the rate of polymerization is calculated and related with SEM pictures to allow better understanding of the gas-phase polymerization of ethylene. Different Al/Ti ratios and reaction temperatures are examined and explain the behavior of growing polyethylene-particles in a satisfying way.