Mechanistic study on comonomer effect in ethylene/1-hexene copolymerization with TiCl4/MgCl2 model Ziegler-Natta catalysts

Recent progress in preparation of branched polyethylene with nickel, titanium, vanadium and chromium catalytic systems and EPR study of related catalytic systems

A SiO2/MgCl2-bisupported Ziegler–Natta-type catalyst is studied in gas-phase ethylene/1-butene copolymerization. With a minimal amount of alkylaluminum required to activate the catalyst, polymeriza...

/pdf/engineering-poly-ethylene-co-1-butene-through-modulating-the-21pjcnf2yo.pdf

Engineering Poly(ethylene- co -1-butene)through Modulating the Active Species by Alkylaluminum

In this study, the simultaneous effect of cyclohexyl chloride (CHC) as a high-performance promoter and different electron donors (ED) on ethylene polymerization was studied. The polymerization reactions were carried out using Mg (OEt)2/ TiCl4/ TEAl Ziegler-Natta catalyst system. The results showed that CHC and ED, like methanol and diethyl ether (DEE), had a high impact on ethylene polymerization and copolymerization with 1-hexene. The catalyst activity was increased in the optimum ratio of CHC and ED up to 40% and 212.5% for methanol and DEE, respectively, than the donor-free system. The synthesized catalysts and polyethylene powder were characterized by scanning electron microscopy (SEM). The results exhibited the positive effects of EDs on catalysts morphology in the presence of CHC and ED. Through using methanol, an increase in the catalyst's porosity led to increased activity, while DEE creates cracks on the surface catalyst particles and incremented the catalyst activity by increasing fragmentation phenomena. The EDs had direct effects on melt flow index (MFI) as well as flow rate ratio (FRR) and also improved wax and fine (<63µm) content in produced polyethylene. The particle size distribution (PSD) results indicated that polyethylene powder had a larger particle size and favorable operating properties in the presence of DEE and methanol. Thermal analysis of different synthesized polyethylene demonstrated that polyethylene's crystallinity and melting point did not change with EDs and CHC.

Synthesis of novel Ziegler Natta catalyst in the presence of internal promoter and electron donors for ethylene and ethylene/ 1-hexene polymerization

Many researchers have studied the effects of donors, promoters and alkyl aluminum compounds on the polymerization catalysts, the polymerization process and the final properties of polymers. Neverth...

Investigation of the effects of heat treatment parameters during synthesis of titanium-magnesium-based Ziegler-Natta catalysts

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.

/pdf/optimal-catalyst-and-cocatalyst-precontacting-in-industrial-3edpmy491g.pdf

Optimal Catalyst and Cocatalyst Precontacting in Industrial Ethylene Copolymerization Processes

Extended Abstract Ziegler-Natta (ZN) catalysts are among the most significant types of catalyst for the industrial production of plastics. The main components of ZN catalysts are TiCl4 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 MgCl2 or SiO2 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.

/pdf/influence-of-different-aluminium-alkyls-on-the-ziegler-natta-3848pf2gl1.pdf

Influence of Different Aluminium Alkyls on the Ziegler-Natta Polymerization

Various MgCl2-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.

Effects of Alterations to Ziegler–Natta Catalysts on Kinetics and Comonomer (1-Butene) Incorporation

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Papers

Optimal Catalyst and Cocatalyst Precontacting in Industrial Ethylene Copolymerization Processes

Influence of Different Aluminium Alkyls on the Ziegler-Natta Polymerization

Effects of Alterations to Ziegler–Natta Catalysts on Kinetics and Comonomer (1-Butene) Incorporation