system. Ziegler-Natta (ZN) catalysts generally dominate in PE and PP production, but they have their limitations when higher α-olefins are used for copolymerization. The disadvantages of ZN systems in this case are uneven and limited comonomer incorporation. The comonomer is incorporated randomly along the polymer chain, with a tendency to higher comonomer concentrations in the low-molecular weight fractions and less in the high molecular weight part. Further, ZN catalysts lead to broad molecular weight distributions (MWDs), which may be problematic with respect to the amount of extractable material.Higher-branched low molecular weight parts lead to a faster degradation which reduces the durability of the polymer material. Therefore, polyolefines with a homogeneous comonomer incorporation show beneficial properties concerning tensile strength, film transparency, and environmental stress cracking, which results in advantages for many applications, such as films and pipes. Metallocenes can tackle these requirements, as they can polymerize longer α-olefins (up to C26), yield narrow and homogeneous MWDs, and support comonomer incorporation of up to 20%. The demand for metallocene-based polyolefins, especially PE, is increasing significantly. The Various MgCl 2 -supported Ziegler-Natta (ZN) catalysts are synthesized with the intention to influence polymerization performance and 1-butene incorporation in an ethylene copolymer. Modifications are introduced during different steps in the synthesis process, namely support preparation, titanation, and catalyst workup. While multiple different effects are observed upon modification, heat treatment during titanation shows the greatest impact. Increasing the heat-treatment temperature increases polymerization activity. More importantly, the 1-butene distribution can be shifted toward a more homogeneous profile. The amount of 1-butene incorporated is similar to both for short-and for very long-chain molecules. This behavior has so far been known only from metallocene-based polyethylene and suggests that active sites are distributed more homogeneously in the ZN catalyst.
In industrial-scale catalytic olefin copolymerization processes, catalyst and cocatalyst precontacting before being introduced in the polymerization reactor is of profound significance in terms of catalyst kinetics and morphology control. The precontacting process takes place under either well-mixing (e.g., static mixers) or plug-flow (e.g., pipes) conditions. The scope of this work is to study the influence of mixing on catalyst/cocatalyst precontacting for a heterogeneous Ziegler-Natta catalyst system under different polymerization conditions. Slurry ethylene homopolymerization and ethylene copolymerization experiments with 1-butene are performed in a 0.5 L reactor. In addition, the effect of several key parameters (e.g., precontacting time, and ethylene/hydrogen concentration) on catalyst activity is analyzed. Moreover, a comprehensive mass transfer model is employed to provide insight on the mass transfer process and support the experimental findings. The model is capable of assessing the external and internal mass transfer limitations during catalyst/cocatalyst precontacting process. It is shown that catalyst/cocatalyst precontacting is very important for the catalyst activation as well as for the overall catalyst kinetic behavior. The study reveals that there is an optimum precontacting time before and after which the catalyst activity decreases, while this optimum time depends on the precontacting mixing conditions.
An efficient, safe and scalable continuous flow process for the synthesis of amine oxides with hydrogen peroxide is described.
Extended AbstractZiegler-Natta (ZN) catalysts are among the most significant types of catalyst for the industrial production of plastics. The main components of ZN catalysts are TiCl 4 in combination with an organic aluminium component as a cocatalyst. In addition, there are a variety of chemicals that improve or alter the catalyst behaviour. Various carrier materials such as MgCl 2 or SiO 2 are used to influence catalyst activity and particle shape. In addition, there is a large group of electron donors for influencing the catalyst behaviour and the final polymer [1,2].Nevertheless, the aluminium compound as a so called "cocatalyst" is one of the most decisive factors in the polymerization with ZN catalyst systems [3]. Therefore, a systematic study was carried out to determine the influence of different aluminium alkyls on the homo-polymerization of ethylene with a ZN catalyst system. For the experiments triethylaluminium (TEA), triisobutylaluminium (TIBA) and tridodecylaluminium (TDDA) were used in different concentrations. The three components were selected for their different properties and industrial importance. TEA is the most commonly used aluminium alkyl with little to no steric hindrance. TIBA is a, more complex aluminium alkyl mainly used as scavenger agent, while TDDA is generally unknown. A 0.5 l multi-purpose reactor system with liquid propane as solvent and a commercially available ZN catalyst of the 4 th generation were used to carry out the polymerizations. The data obtained was used to model the polymerization activity based on kind and amount of the aluminium alkyl used.The polymerization activity was different for each aluminium alkyl. While the polymerization activity increased to a plateau for the more complex aluminium alkyls TIBA and TDDA, TEA behaved differently. With TEA as a cocatalyst, the polymerization activity increased to a peak value at a concentration of 3 mmol l -1 and decreased for higher concentrations. In general, the polymerization activity achieved, increased with the size of the aluminium alkyl molecule. TDDA exhibited the highest polymerization activity at 4.5 mmol l -1 , which was 25% above the activity level for TEA and 20%, respectively, over that of TIBA. In conclusion, the steric differences of the used aluminium compound have a great influence on the polymerization activity. Based on the experimental data, a model was created to simulate all cases for the concentration of the three different aluminium alkyls. For this, the model postulated by Alshaiban and Soares [4] was extended to additionally represent the influence of aluminium alkyl and its concentration.
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