CHIMIA (Mar 2001)
New Method for Online Observation of Growing Polyolefin Particles
Abstract
In classical experimental research work on catalytic olefin polymerization, kinetics and powder properties are always determined as an average value over a large number of polymer particles. When studying the properties of the polymer, the powder has to be evacuated from the reactor system. This evacuation step will often change the properties to be measured.Here, a method for direct observation of growing polymer particles is shown. To allow individual observation of a number of growing polymer particles in a catalytic gas phase polymerization, a polymerization cell was built with a transparent lid. The cell was placed in a microscopic video system in such a way that the particles could be observed during reaction and pictures of the particles were stored with a preset time interval.Using a 4th generation Ziegler-Natta catalyst at 40 °C and a propylene pressure of 8 bar, polymerizations were carried out in the presence of hydrogen. It was shown that reaction kinetics can be derived from these experiments, not only average values for larger number of particles, but also kinetics for individual particles. It is shown that kinetic results can be obtained in a reproducible way, and thus it is well possible to kinetically characterize a catalyst in gas phase polymerization using this method.As the current lid is not only transparent to visible light, but also to infrared light, an infrared camera can be applied to measure surface temperatures of the growing polymer particles. This can be of large help in development of single particle models. One can also think about different applications and extensions. New analysis method could be applied to the same principle, for example Raman spectroscopy or X-ray tomography. Next to that, currently a stirrer is being implemented to introduce convective cooling of the particles and one can also think about application of other media than gas phase, like the slurry phase.
