Ziegler-Natta (ZN) catalysts are among the most important catalysts for the industrial production of plastics. The main components of ZN catalysts are TiCl4 in combination with an organic aluminum component as a cocatalyst, whereas a wide range of additional components exists which influence the catalyst behavior. In this work the focus is on modifications of ZN systems both during the synthesis of the titanium component and on the interactions of the final catalyst with the cocatalyst. All polymerization experiments are carried out in a 0.5 L multipurpose reactor system.
Among the various modifications during the synthesis, the heat treatment during titanation shows the largest effect. Increasing the temperature during the heat treatment increases the polymerization activity and, more importantly, affects the incorporation of 1-butene. This allows a more homogeneous 1-butene distribution to be achieved. Hitherto this behavior is only known for metallocene based polyethylene and indicates a more homogeneous distribution of the active centers. In the next step, the influence of pretreatment, in particular the catalyst/cocatalyst relationship, is investigated. Various aluminum alkyls (i.e., triethylaluminum (TEA), triisobutylaluminum (TIBA), tridodecylaluminum (TDDA)) are used in these studies. One aspect is the effect of the catalyst/cocatalyst precontacting time. The influence of the precontacting time is examined under well mixed and non-mixing conditions. In addition, the effect of several key parameters such as ethylene-, hydrogen-, and comonomer-concentration on the ideal precontacting time is analyzed. Moreover, a comprehensive mass transfer model is employed. The study reveals that there is an optimum precontacting time before and after which the catalyst activity decreases, while the optimum time depends on the precontacting conditions. In addition to the contact time, the type and amount of the aluminum alkyl used, is one of the decisive factors for the polymerization with ZN systems. The polymerization activity varies for each aluminum alkyl, with TDDA achieving the highest polymerization rate. The steric differences shift the ideal cocatalyst concentration individually for each aluminum alkyl. From the data obtained, a model is created to simulate the effect of the aluminum alkyl on the polymerization activity.