THE CHEMISTRY OF SCAVENGER ON THE PERFORMANCE OF THE SUPPORTED METALLOCENE CATALYST

Abstract

In this study, the effect of the various types and concentrations of alkylaluminum acting as scavenge impurities which contaminate in materials commonly used in polyolefin processes was studied on catalytic activity of supported metallocene catalyst and product properties. Alkylaluminum was divided into 2 types including triethylaluminum (TEA) and triisobutylaluminum (TiBA) used to investigate. The addition of alkylaluminum as scavenger is important and necessary in this polymerization process because without alkylaluminum to scavenge impurities rapid deactivation occurs. The concentration which reached maximum catalytic activity was found at 0.7, 1.2 mmol/L in hexane and 6.027, 8.603 kg.PE/g Cat.*h of TEA and TiBA, respectively in ethylene homopolymerization. Nevertheless, with excess concentration of scavenger, the catalytic activity is depressed. This is due to heterodinuclear complexes form which may inhibit or lower the catalytic efficiency. TEA can be presumed that facile the formation of heterodinuclear complexes than TiBA due to steric effect (or hindrance). Furthermore, TEA is a stronger reducing agent than TiBA to reduce Zr(IV) to Zi(III) states, which is inactive for ethylene polymerization. The melting temperature and the crystallinities of the polymers are, therefore, unaffected by the concentration of scavenger. For ethylene and 1-hexene copolymerization, the 1-hexene incorporation was not a function of the trialkylaluminum concentration. The effects of hydrogen have shown a decrease catalytic activity due to metal hydride complex formed leading to a lower propagation rate.