Influence of the particle size of the MgCl₂ support on the performance of Ziegler catalysts in the polymerization of ethylene to ultra‐high molecular weight polyethylene and the resulting polymer properties

Abstract

A highly systematic size series of Ziegler catalysts with similar porosities and surface textures are synthesized by varying the stirring speed during the MgCl 2 support synthesis. Besides the mean particle size, the only substantial difference observed between the various catalysts is the size and number of nodules per particle. Varying the mean diameter of the catalyst particles between 1.5 and 11.9 mm, leads to a pronounced impact on the activity in ultra-high molecular weight polyethylene (UHMWPE) polymerization, while the M w capabilities are only affected to a limited extend. In addition, it is observed that both the M w s as the polymer bulk density (BD) increases during the course of the polymerization. This particularity allows to optimize the M w and/or BD at a set polymer size, by tuning the catalyst particle size. This is particularly interesting in UHMWPE production, as control of the morphological and structural properties of the UHMWPE reactor powders are critical for efficient processing as well as the performance of the final product.

Tailored bimodal ultra‐high molecular weight polyethylene particles

“…are presented in Supporting Information. For the monomodal samples, a correlation between M w and the first melting temperature (MT) is observed (Figure ), which is similar to previous reported data using Ziegler catalysts on these supports . The bimodal PE reactor blend particles do not follow this M w correlation.…”

“…In addition, it has previously been demonstrated that highly active postmetallocene catalysts, including the titanium phosphinimide family, can be obtained on MgCl 2 supports . The MgCl 2 support that was employed was based on previously published UHMWPE Ziegler catalyst preparation, where catalyst particle size could be varied from 1.5 to 12 µm …”

“…< 300 µm) and are typically produced in small “fed batch” or continuous slurry CSTR processes by heterogeneous multisite Ziegler catalysts, as mentioned earlier. In these processes, ideally one single catalyst particle produces one single UHMWPE reactor particle via replication and the final UHMWPE reactor particle size is a function of the initial catalyst particle size and the catalyst yield (CY), expressed as grams of polymer produced per gram of catalyst used and the porosity difference between the catalyst and polymer particle (eq ) …”

“…Phenylmagnesium chloride (PhMgCl) was prepared via the interaction of metallic magnesium (Mg) with chlorobenzene (PhCl) in the presence of dibutylether (DBE) . A home‐made 2 L glass reactor with various inlets, equipped with a mechanically driven stirrer, glass baffles, and a thermostat is used for the support preparation.…”

“…The MgCl 2 support was obtained via the interaction of the above organomagnesium compound with PhSiCl 3 in PhCl . 130 milliliter of the above product (PhMgCl in DBE) was transferred into an inert 1 L glass reactor equipped with a thermostat, internal temperature control, and a mechanical stirrer.…”