Kinetics of ethylene polymerization at high temperature with Ziegler–Natta catalysts

A kinetic technique is developed for the study of ethylene polymerization reaction at high temperature with Ziegler–Natta catalysts. The technique is based on the calculation of polymerization rate parameters from the data on ethylene consumption vs. time. It takes into account increase of reaction temperature at the beginning of the reaction. Kinetic data in coordinates “polymerization rate–time” are presented for several pseudohomogeneous catalysts (TiCl₄? AlEt₂Cl, Ti(OiC₃H₇)₄? AlEt₂Cl), heterogeneous catalysts (δ-TiCl₃? AlEt₃, δ-TiCl₃? AlEt₂Cl, TiCl₄/MgCl₂? AlEt₃, TiCl₄/MgCl₂? AlEt₂Cl) and solubilized catalysts (δ-TiCl₃? poly-1-hexene? AlEt₂Cl) at 180°C and reaction pressure 14.6 atm for first 10 min of the reaction. These data are useful for the selection of Ziegler–Natta catalysts for testing in ethylene polymerization reaction in continuous high pressure reactors at short residence times.     

High activity mixed metal alkyl cocatalysts for α-olefin polymerization

High activity α-olefin polymerization catalysts are generally obtained by mixing MgCl₂-supported TiCl₄ (MgCl₂/TiCl₄) with an aluminum trialkyl cocatalyst. Surprisingly, AlEt₂Cl, which is the preferred cocatalyst in polymerizations employing nonsupported Ti compounds, is a poor cocatalyst when used with MgCl₂/TiCl₄. It was found that in propylene and 1-butene polymerizations, using different MgCl₂/TiCl₄ catalysts, the cocatalyst activity of AlEt₂Cl can be greatly improved by the addition of a magnesium or lithium alkyl. The mixed metal alkyl obtained from AlEt₂Cl and MgBu₂ is a particularly effective cocatalyst always yielding more polymer, of about the same stereospecificity, than the conventional aluminum trialkyls. The exact nature of the mixed metal alkyl cocatalysts is not known, but the available evidence argues against in situ aluminum trialkyl formation resulting from the alkylation of AlEt₂Cl by the second metal alkyl.     

A stacked neural network approach for yield prediction of propylene polymerization

Prediction of reaction yield as the most important characteristic process of a slurry polymerization industrial process of propylene has been carried out. Stacked neural network as an effective method for modeling of inherently complex and nonlinear systems–especially a system with a limited number of experimental data points–was chosen for yield prediction. Also, effect of operational parameters on propylene polymerization yield was modeled by the use of this method. The catalyst system was Mg(OEt)₂/DIBP/TiCl₄/PTES/AlEt₃, where Mg(OEt)₂, DIBP (diisobutyl phthalate), TiCl₄, PTES (phenyl triethoxy silane), and triethyl aluminum (AlEt₃) (TEAl) were employed as support, internal electron donor (ID), catalyst precursor, external electron donor (ED), and co‐catalyst, respectively. The experimental results confirmed the validity of the proposed model. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Microstructure of isotactic polypropylene obtained using Ziegler–Natta catalyst at high polymerization temperature

The microstructure of the isotactic polypropylene obtained with various MgCl₂‐supported catalyst systems at high polymerization temperature of 70–100°C is investigated by discussing the intrinsic relation between the different types of active centers and the polymerization temperatures via gel permeation chromatography, temperature rising elution fractionation, and ¹³C NMR. For the MgCl₂/TiCl₄/di‐n‐butyl phathalate‐AlEt₃/external donor and MgCl₂/TiCl₄/2,2‐diisobutyl‐1,3‐dimethoxypropane‐AlEt₃ catalyst systems, the differences in the isotactic productivity of polymers obtained at different polymerization temperatures mainly result from the variation of both the activity of the different isospecific active centers and the stability constants of the complex of catalyst/donor. The reaction rate of high isotactic active centers reaches maximum at 85–90°C, and this effect contributes to both the highest isotacticity and the narrowest molecular weight distribution. For the MgCl₂/TiCl₄/phthalate ester‐AlEt₃ catalyst system, the isotacticity of polypropylene remains approximately constant in the temperature range of experiments, which could be ascribed to elution of phthalate ester after the activation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42487.     

A highly non-stereospecific catalyst for propene polymerization

Summary The MgCl₂-supported TiCl₃ catalyst containing a small amount of Ti(about 0.1 wt.%) was prepared by treating the mixture of MgCl₂ and TiCl₃ 3py with an excess amount of AlEt₂Cl. Propene polymerization was conducted at 40°C by using AlEt₃ as cocatalyst. The catalyst system was found to be highly active, which gave atactic polypropylene     

Copolymerization of ethylene with propylene by MgCl2-containing highly active Ti catalysts

Summary In the ethylene-propylene copolymerization, two catalyst systems were examined. The one(cat-[a]) was the solid MgCl₂-containing Ti treated with ethyl benzoate together with AlEt₃, and the other(cat-[c]) was based on a homogeneous mixture of MgCl₂ dissolved in 2-ethylhexanol/n-decane and TiCl₄, which was treated with AlEt₂Cl. Both catalyst systems exhibited very high activity in comparison with the conventional catalysts of TiCl₃-AlEt₂Cl and VOCl₃-AlEt₂Cl. These two new systems, however, are different from each other in micro structure of the product copolymer,i.e., the latter(cat-[c]) brings about more random distribution of the monomeric units and also the decreased regiospecificity concerning the arrangement of propylene unit.     

Kinetic study of a highly active MgCl2‐supported Ziegler–Natta catalyst in liquid pool propylene polymerization. II. The influence of alkyl aluminum and alkoxysilane on catalyst activation and deactivation

The influence of alkyl aluminum and alkoxysilane on the kinetics in liquid pool propylene batch polymerization was investigated with a highly active Ziegler–Natta catalyst system that consisted of MgCl₂/TiCl₄/diester–alkoxysilane/AlR₃. In this study, diethyl phthalate and t‐BuEtSi(OMe)₂ were used as a diester and an alkoxysilane, respectively. The catalyst activity depended on the concentration of the alkyl aluminum when it came into contact with the catalyst. In addition, alkoxysilane as an external donor had a role in activating the catalyst. With respect to activity decay, the overreduction of Ti did not seem to be the cause. Instead, the decay rate decreased with an increasing alkoxysilane/catalyst ratio. This implied that activity decay was caused by the formation of dormant sites after 2,1‐misinsertion of propylene. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2669–2679, 2002     

Ethylene and propylene polymerization catalyzed by a model Ziegler-Natta catalyst prepared by gas phase deposition of magnesium chloride and titanium chloride thin films

Model Ziegler-Natta catalysts are prepared by gas phase deposition of ultra-thin TiCl₄/ MgCl₂ films in UHV conditions. A monolayer of TiCl₄ chemisorbed on a solid solution of titanium and magnesium chloride is formed in this way. The reduction and alkylation of TiCl₄ by its reaction with a liquid layer of AlEt₃ condensed on the halide film is monitored by XPS. Most of the TiCl₄ is reduced by AlEt₃ and is incorporated in the mixed titanium /magnesium chloride. The model catalyst is active in the polymerization of ethylene and propylene at 300 K, both in the absence and in the presence of AlEt₃ in the reaction cell. The polymers that form over the catalyst film have been characterized by Raman spectroscopy. The weak signals from methyl end groups and unsaturations suggest high molecular weight for both polymers. The polypropylene film has a high degree of isotacticity even without the use of any electron donor. For the propylene polymerization reaction the overall turnover frequency is in the range between 0.1 and 1 molecule/(site s).     

Effects of residual and external alkylaluminum on the synthesis of syndiotactic polystyrene with cyclopentadienyltitanium tribenzyloxide–methylaluminoxane catalyst

The effects of residual trimethylaluminum (TMA) in methylaluminoxane (MAO) and external alkylaluminum (AlR₃) on styrene syndiotactic polymerization with CpTi(OBz)₃ as a catalyst precursor have been investigated by comparison of the polymerizations using a series of MAOs containing various amounts of residual TMA. The results indicated that the residual TMA plays a deciding role in the reduction of Ti and promotes formation of the active centers for styrene polymerization. The variations in the catalytic activity and molecular weight of the polymer caused by additions of external AlR₃, AlMe₃, AlEt₃, Al(i-Bu)₃, and AlEt₂Cl, into the catalyst systems are quite different, depending the properties of MAO used and the type of the external AlR₃. It was found that there is an optimum range of concentration ratio of the free AlR₃, including the residual TMA and external AlR₃, to the total Al compounds, 25–35 mol %, for maximum catalytic activities. The catalytic activities decrease at the ratios either above or below the range. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 765–770, 1998     

Interaction of α-TiCl3 with organoaluminium compounds and its correlation with propylene polymerization

Summary The kinetics of the interaction between the catalyst components of a Ziegler-Natta sterospecific system formed by TiCl₃ and AlEt₃ in heptane was studied. The experimental results show that the rate of propylene polymerization is influenced by the rate of the interaction, activation energy, and the efficiency of interaction.     

Control of molecular weight distribution for polypropylene obtained by a commercial Ziegler–Natta catalyst: Effect of a cocatalyst and hydrogen

The polymerization of propylene was carried out with an MgCl₂‐supported TiCl₄ catalyst (with diisobutyl phthalate as an internal donor) in the absence and presence of hydrogen (H₂) as a chain‐transfer agent. Different structures of alkylaluminum were used as cocatalysts. The effects of the alkyl group size of the cocatalyst, H₂ feed, and feed time on the propylene polymerization behaviors were investigated. The catalyst activity significantly decreased with increasing alkyl group size in the cocatalyst. The molecular weight and polydispersity index (PDI) increased with increasing alkyl group size. With the introduction of H₂, the catalyst activity increased significantly, whereas the molecular weight and PDI of polypropylene (PP) decreased. Additionally, the effect of the polymerization time in the presence of H₂ on the propylene polymerization was studied. The molecular weight distribution curve was bimodal at short polymerization times in the presence of H₂, and we could control the molecular weight distribution of PP by changing the polymerization time in the presence of H₂. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of ethylene-propylene-diene terpolymers with supported Ziegler-Natta catalyst

Terpolymerizations of ethylene, propylene and diene (1,3-butadiene, 1,5-hexadiene or 1,7-octadiene) by MgH₂/TiCl₄–AlEt₃ catalyst system were carried out. The compositions of the obtained terpolymers were evaluated. The effect of diene concentration in the reaction medium for each polymerization system on the terpolymer composition was observed. The structure of the diene repeat units was also investigated.     

Catalytic activity and control of the nascent morphology of polyethylenes obtained with first and second generation of Ziegler–Natta catalysts

The morphologies of the as-produced polyethylenes obtained by slurry polymerization process of ethylene in n-heptane, using heterogeneous conventional and supported Ziegler–Natta catalysts, were investigated. The ability of four different catalytic systems in controlling the size and shape of the nascent polymer particles were tested. The catalytic systems employed were: the original Ziegler type catalyst produced by reduction of TiCl₄ with Et₂AlCl, the Natta type catalyst TiCl₃–AA, the reduced TiCl₄ with the metal carbonyls [Mo(CO)₆ and Mn₂(CO)₁₀], and the supported TiCl₄ on three commercial silicas having different surface areas: Davison 951, 952, and also the Dart 1000. It was found that the carriers affect the catalytic activity of the final catalyst and also its kinetic behavior. The supported Ziegler–Natta catalysts control more easily the nascent polymer particles (size, shape, and porosity) than the conventional ones. In addition the morphology of the catalysts and the subsequent polymer particles are closely related to the parent morphology of the silicas used as carriers. Furthermore, the nascent morphology of the polyethylenes obtained with the conventional TiCl₄–Et₂AlCl catalytic system can be modified by using different |Al|/|Ti| ratios, resulting in more dense, spherical, and bigger polymer particles by increasing this ratio. On the other hand, detailed studies on the texture or arrangement of the polymer particles reveal the existence of mainly two fine morphologies (globular and wormlike), which are the result of the order of the primary or elementary catalyst particles (microspheres and platelets), the force linking them together, and the activity of the polymerization centers placed on their surface.     

Kinetic study on propylene polymerization with MgCl2/TiCl4-AlEt3/PhCO2Et System — the role of ethyl benzoate

Summary A kinetic study on propylene polymerization with the catalyst system of MgCl₂-supported TiCl₄ catalyst(MgCl₂/TiCl₄) in conjunction with AlEt₃ and PhCO₂Et (EB) has been made to elucidate the role of ethyl benzoate (EB) which is known to increase stereospecificity of produced polypropylene. It has been found that a part of added EB was fixed on the supported Ti catalyst and that EB modified the isotactic specific centers to increase the k_p (iso) value. Thus the productivity of isotactic polymer and the molecular weight of the isotactic polymer(2·10⁴(¯Mn) to 6·10⁴ at 60°C) were increased.     

Preparation of highly active supported catalysts for producing polypropylene with less content of chloride

Summary Highly active supported catalysts for propylene polymerization have been prepared by treating the complexes of TiCl₃· 3C₅H₅N and MgCl₂·(THF) with AlEt₂Cl in the presence of MgO, Mg(OH) ₂ ^x or SiO₂. Polypropylene with less content or chloride was produced over these catalysts combined with AlEt₃.     

Propylene polymerization with δ-TiCl3/AlClEt2 and δ-TiCl3/AlEt3 catalyst systems

Summary Some parameters of propylene polymerization using -TiCl₃/AlClEt₂ and -TiCl₃/AlEt₃ catalyst systems were evaluated. The catalyst was prepared through the reduction of TiCl₄ complexed with di-n-butyl ether (DBE) (mole ratio DBE/TiCl₄=0.67) by AlClEt₂. Propylene polymerizations were carried out at different Al/Ti ratios, using AlEt₃ or AlClEt₂ as cocatalysts and different polymerization temperatures. The effects of these parameters on catalyst activity, stereo-specificity and polymer molecular weight were investigated. The results indicate that these parameters strongly affect catalyst performance.     

Copolymerization of ethylene with propylene over the thermally-reduced γ-Al2O3-supported TiCl4 catalyst

Summary Copolymerization of ethylene with propylene was conducted over the thermally-reduced -Al₂O₃-supported TiCl₄ catalyst both in the absence or presence of AlEt₃ (or AlEt₂Cl). It was found that the structure of the polymer drastically changed from a random copolymer to polyethylene with an increase in the concentration of AlEt₃. A plausible mechanism was proposed for the copolymerization.     

Kinetic and morphological study of a magnesium ethoxide‐based Ziegler–Natta catalyst for propylene polymerization

BACKGROUND: Kinetic and morphological aspects of slurry propylene polymerization using a MgCl₂‐supported Ziegler–Natta catalyst synthesized from a Mg(OEt)₂ precursor are investigated in comparison with a ball‐milled Ziegler–Natta catalyst. RESULTS: The two types of catalyst show completely different polymerization profiles: mild activation and long‐standing activity with good replication of the catalyst particles for the Mg(OEt)₂‐based catalyst, and rapid activation and deactivation with severe fragmentation of the catalyst particles for the ball‐milled catalyst. The observed differences are discussed in relation to spatial distribution of TiCl₄ on the outermost part and inside of the catalyst particles. CONCLUSION: The Mg(OEt)₂‐based Ziegler–Natta catalyst is believed to show highly stable polymerization activity and good replication because of the uniform titanium distribution all over the catalyst particles. Copyright © 2008 Society of Chemical Industry     

Polymerization of propylene by highly active catalysts synthesized with Mg(OEt)2/benzoyl chloride/TiCl4

Summary Active centers have been studied in the polymerization of propylene using highly active Mg(OEt)₂/Benzoyl chloride/TiCl₄ catalysts activated with AlEt₃. The method for the measurement of active centers is based on the inhibiting effect of CO on polymerization. The activity of the present catalysts, which is higher than that of TiCl₃ or MgCl₂-supported catalyst, is mainly due to the higher concentration of active centers by one order of magnitude. In order to investigate the stability of active centers during polymerization the number of active centers are compared at various polymerization times.     

Kinetic study on propylene polymerization by a high activity catalyst system: MgCl2/TiCl4/PhCO2Et-AlEt3/PhCO2Et

Summary Kinetic study was performed in short time propylene polymerization with a high activity-high stereospecificity catalyst system composed of MgCl₂/TiCl₄/PhCO₂Et with AlEt₃/PhCO₂Et. The concentration of the active centers, [C ^*], the propagation rate constant, k _p, and the chain transfer rate, r _tr, were determined. The change of these values by the change of polymerization conditions, the concentration of monomer, AlEt₃, and the temperature, were studied.