Generation Ziegler-Natta Catalyst Research Articles

Impact of Process Poisons on the Performance of Post‐Phthalate Supported Ziegler–Natta Catalysts in Gas Phase Propylene Polymerization

AbstractThe impact of common process catalyst poisons on the performance of a 6th generation Ziegler–Natta catalysts during the gas phase polymerization of propylene are examined using two approaches: introducing propylene without purification, or with one or two sets of purification columns, and by introducing carbon dioxide (CO2), oxygen (O2), water (H2O), methanol (CH3OH), ethyl acetate (C4H8O2) and dimethyl sulfoxide (C2H6SO) during the polymerization. As expected, purification columns increases the catalyst activity significantly, slightly reduce catalyst decay. Injecting TiBA during the reaction leads to an activity increase. The addition of two full sets of columns substantially increased the repeatability of polymerization reactions. The power of deactivation of poisons injected during the polymerization reaction is: O2 > CO2 > CH3OH > C2H6SO > C4H8O2 > H2O. Adding CO2, O2, and CH3OH resulted in a progressive decrease in molecular weight while almost no effect is observed with H2O. However, C4H8O2, and C2H6SO resulted in a mild increase in molecular weight. Additionally, the effects on crystallinity and stereoregularity are similar where CO2, O2, H2O and CH3OH caused a progressive decrease while C4H8O2 and C2H6SO resulted in a mild increase, indicating some isotacticity control by these two poisons.

Sensitivity analysis and multi-objective optimization of gas-phase polymerization of propylene using Ziegler-Natta catalysts

Gas-phase polymerization of propylene via 4th generation Ziegler-Natta (ZN) catalysts was studied and optimized using intelligent data-based methods. The effect of co-catalyst (triethylaluminium (TEA)) and external donor (ED) compositions on the activity and PP-isotacticity for two commercial MgCl2/TiCl4/phthalate(ID)/TEA/silane(ED) catalyst systems with different Ti-contents were investigated using design-of-experiment (DOE) combined with response-surface-methodology (RSM). Sobol’s sensitivity analysis was employed to determine the quantitative impact of catalyst compositions on the target variables. Both catalysts performance was optimized via multi-objective genetic algorithm (GA) to maximize the activity and PP-isotacticity. Results revealed that the activity and PP-isotacticity for both catalysts will be enhanced at low co-catalyst and high ED amounts, respectively. Increasing the ED improved the activity of low-Ti catalyst, whereas it reduced the activity of high-Ti one. Sensitivity results for both catalysts depicted the comparable influence of co-catalyst and ED on the activity and the strong influence of ED on PP-isotacticity. GA optimization offered the activity of 3.7 – 4.65 gPP/mgCat and PP-isotacticity of 95.8 – 97.5 % for low-Ti catalyst at the optimal TEA/Catalyst = 7 – 7.2 and TEA/ED = 6.0 – 7.2 and the activity of 3.9 – 4.7 gPP/mgCat and PP-isotacticity of 93 % for the high-Ti one at the optimal TEA/Catalyst = 7 – 11.2 and TEA/ED = 12.

Quality control for Ziegler-Natta catalysis via spectroscopic fingerprinting

Commercial olefin polymerization catalysts are typically produced at a manufacturing site before transport to production facilities for storage and eventual use. During transport and storage, catalysts can deteriorate resulting in decreased catalytic performance due to contact with environmental factors. In this work, a spectroscopic toolbox was developed for quality assurance purposes of a third generation Ziegler-Natta catalyst for ethylene polymerization. A pre-activated, industrial Ziegler-Natta catalyst was exposed singly to heat, dry air, and moisture to study the specific environmental factors. Activity tests were performed with the polymer morphology inspected by SEM and image analysis. Catalyst characterization was conducted using Fourier Transform Infrared spectroscopy with CO and Diffuse Reflectance UV–Vis spectroscopy to relate unique spectroscopic fingerprints to different environmental effects. Reactivity towards gas-phase ethylene polymerization was tested using Diffuse Reflectance Infrared Fourier Transform spectroscopy. This work demonstrates the development of a new spectroscopic methodology useful for quality control in Ziegler-Natta catalysis.

Effect of multi-ethers and conventional alkoxysilanes as external donors on the 4th generation Ziegler-Natta catalysts for propylene polymerization

The multi-ether compounds with different numbers of methoxy groups containing 1,3-dimethoxy-2,2-bis(methoxymethyl)propane and 1-methoxy-2,2-bis(methoxymethyl)butane were synthesized using the Williamson reaction from pentaerythritol and 1,1,1-tris(hydroxymethyl)propane, respectively, in the presence of sodium hydride and methyl iodide in tetrahydrofuran and they were characterized by 1H NMR, 13C NMR, and FTIR spectroscopy. These compounds were employed as external donors in the polymerization of propylene using the industrial Ziegler-Natta catalyst. A commercial spherical MgCl2-supported Ziegler-Natta catalyst containing diisobutyl phthalate as the internal donor was used for the polymerization of propylene. The role of ether compounds and industrial alkoxysilanes on the properties of polypropylene were studied using the xylene solubility method, melt flow index, gel permeation chromatography, scanning electron microscopy, and differential scanning calorimetry. The addition of the electron donors has led to improvements in the activity and selectivity of the Ziegler-Natta catalyst system.

The effect of mixed and individual silane external donors on the stereo-defect distribution, active sites and properties of polypropylene synthesized with fourth generation Ziegler—Natta catalyst

Polypropylene was synthesized with a fourth generation of Ziegler—Natta catalyst and in the presence of mixed and individual external donors, namely cyclohexyl dimethoxymethylsilane and dicyclopenthyl dimethoxysilane. A synergic effect on molecular weight and polydispersity index and changes in crystallinity and crystallization peak temperature with change in molar ratio of donor C to D were observed. The SSA results and related statistical parameters showed that in spite of close average stereo-regularity, the stereodefect distribution differences among the samples obtained with mixed external donors were so vast. The influence of mixed and individual external donors on active site distribution was studied and the results are discussed. The relationship between the crystallinity, molecular weight, stereo-defect distribution and dynamic and mechanical properties of samples was investigated.

Probing the coordinative unsaturation and local environment of Ti³⁺ sites in an activated high-yield Ziegler-Natta catalyst.

The typical activation of a fourth generation Ziegler-Natta catalyst TiCl4/MgCl2/phthalate with triethyl aluminum generates Ti(3+) centers that are investigated by multi-frequency continuous wave and pulse EPR methods. Two families of isolated, molecule-like Ti(3+) species have been identified. A comparison of the experimentally derived g tensors and (35,37)Cl hyperfine and nuclear-quadrupole tensors with DFT-computed values suggests that the dominant EPR-active Ti(3+) species is located on MgCl2(110) surfaces (or equivalent MgCl2 terminations with tetra-coordinated Mg). O2 reactivity tests show that a fraction of these Ti sites is chemically accessible, an important result in view of the search for the true catalyst active site in olefin polymerization.

Effect of Varying Hydrogen Concentration, External Donor Concentration, and Temperature on Propylene Polymerization Kinetics and Microstructure of Polypropylene Made with a 4th Generation Ziegler-Natta Catalyst

This paper presents the results of a detailed investigation on propylene polymerization kinetics and microstructural characterization of polypropylene samples made with a 4th generation Ziegler–Natta catalyst under varying hydrogen pressures, external donor concentrations, and polymerization temperatures. Hydrogen had a positive effect on the mmmm pentad fraction at low donor concentrations, in agreement with our previous Monte Carlo model. Estimated activation energies for activation, propagation, and deactivation were very close to the values previously reported by our group for a narrower set of experiments with the same catalyst.

Light‐Induced Catalyst and Solvent‐Free High Pressure Synthesis of High Density Polyethylene at Ambient Temperature

The combined effect of high pressure and electronic photo-excitation has been proven to be very efficient in activating extremely selective polymerisations of small unsaturated hydrocarbons in diamond anvil cells (DAC). Here we report an ambient temperature, large volume synthesis of high density polyethylene based only on high pressure (0.4-0.5 GPa) and photo-excitation (~350 nm), without any solvent, catalyst or radical initiator. The reaction conditions are accessible to the current industrial technology and the laboratory scale pilot reactor can be scaled up to much larger dimensions for practical applications. FTIR and Raman spectroscopy, and X-ray diffraction, indicate that the synthesised material is of comparable quality with respect to the outstanding crystalline material obtained in the DAC. The polydispersity index is comparable to that of IV generation Ziegler-Natta catalysts. Moreover the crystalline quality of the synthesised material can be further enhanced by a thermal annealing at 373 K and ambient pressure.

Effect of Hydrogen and External Donor on the Microstructure of Polypropylene Made with a 4th Generation Ziegler–Natta Catalyst

AbstractThe effect of adding hydrogen and/or electron donor on the microstructure of polypropylene polymerized with a 4th generation Ziegler–Natta catalysts at two temperatures on the molecular weight distribution, tacticity, and crystallinity of polypropylene is thoroughly investigated in this article. Polypropylene tacticity and crystallinity increases not only when external donors are added, but also when hydrogen is used as a chain transfer agent. The molecular weight distribution of the resins is deconvoluted into several Flory's most probable distributions to show how different active site types respond to the presence of electron donor and hydrogen. magnified image

Solid state 13C NMR characterisation study on fourth generation Ziegler–Natta catalysts

In this study, solid state 13C NMR spectroscopy was utilised to characterize and identify the metal–ester coordination in active fourth generation (phthalate) Ziegler–Natta catalysts. It is known that different donors affect the active species in ZN catalysts. However, there is still limited data available of detailed molecular information how the donors and the active species are interplaying. One of the main goals of this work was to get better insight into the interactions of donor and active species. Based on the anisotropy tensor values (δ11, δ22, δ33) from low magic-angle spinning (MAS) 13C NMR spectra in combination with chemical shift anisotropy (CSA) calculations (δaniso and η), both the coordinative metal (Mg/Ti) and the symmetry of this interaction between metal and the internal donor in the active catalyst (MgCl2/TiCl4/electron donor) system could be identified.

Investigation of Effective Factors on the 4th Generation Ziegler-NattaCatalyst Activity by Design of Experiments

cocatalyst, cyclohexylmethyldimethoxysilane as external electron donor, and interaction between these two factors on catalyst activity in propylene polymerization with a 4th generation Ziegler-Natta catalyst. The experiments were performed by a two factor factorial design (concentration of triethylaluminium and cyclohexylmethyldimethoxysilane) and the analysis of variance was used to evaluate the results by Minitab14 software. This experimental design enabled us to investigate the main effects or individual effects of each factor and determine whether the factors had interaction or not. It was found that triethylaluminium had significant effect on catalyst activity but cyclohexylmethyldimethoxysilane donor was not individually effective on catalyst activity.

Polymerization of liquid propylene with a 4th generation Ziegler–Natta catalyst—influence of temperature, hydrogen and monomer concentration and prepolymerization method on polymerization kinetics

In a batch-wise operated autoclave reactor, liquid propylene was polymerized using a 4th generation, TiCl 4/MgCl 2/phthalate ester–AlEt 3–R 2Si(OMe) 2, Ziegler–Natta catalyst system. By using a calorimetric principle it was possible to measure full reaction rate versus time curves for obtaining data on polymerization kinetics, under industrially relevant conditions. The influence of polymerization temperature, the hydrogen and monomer concentration, and the prepolymerization method on reaction kinetics were investigated. A new method for prepolymerization, the so-called non-isothermal prepolymerization, is described. In this short prepolymerization procedure featuring an increasing polymerization temperature the thermal runaway on particle scale was avoided. It was shown that this prepolymerization method can relatively easily be applied to an industrial process, with the introduction of a continuous plug flow reactor, giving a narrow residence time distribution, acceptable yield-in-prepolymerization and a method for monitoring catalyst activity. Using different methods for calculating the monomer concentration at the active site of the catalyst, the influence of polymerization temperature was determined. It was shown that at high polymerization temperatures, the reaction rate is barely influenced by polymerization temperature, when no prepolymerization is used. This is ascribed to thermal runaway on particle scale of a fraction of the catalyst particles. When a prepolymerization is used, this effect disappears and thermal runaway is avoided. When systematically reducing the monomer concentration ( C m,bulk ) in the bulk by replacing part of the liquid propylene by hexane, the reaction rate proved to be remarkably independent of the monomer concentration. With reducing C m,bulk , reaction rate decreased very slowly until C m, bulk =150 g/ l . When further decreasing C m,bulk , reaction rate dropped rapidly. The hydrogen concentration was varied over a wide range at 60°C and 70°C. For both temperatures it was shown that reaction rates increased rapidly with increasing hydrogen concentration at low hydrogen concentrations. At higher hydrogen amounts, this effect disappeared and a maximum reaction rate was found.

Novel spherical Ziegler–Natta catalyst for polymerization and copolymerization. I. Spherical MgCl2 support

AbstractSpherical MgCl2 adducts used as supports for a Ziegler–Natta catalyst for olefin polymerization were prepared by the general precipitation method. The influence of MgCl2/EtOH (mol/mol) and the dispersion speeds on the particle size (PS) and particle size distribution (PSD) were investigated. It was found that the former played a trivial role in controlling the PS and PSD, and the latter was the key factor. In particular, the influence of ethanol on the crystal structure was further examined, with consideration given to the performance of the supported Ziegler–Natta catalyst. It was believed that the reactions between MgCl2 and ethanol had a controlling effect on the destruction of the original anhydrous MgCl2, which was the key point in the preparation of suitable supports for the latest generation Ziegler–Natta catalyst. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3112–3119, 2002

High precision prepolymerization of propylene at extremely low reaction rates—kinetics and morphology

A one-liter slurry phase polymerization reactor was set-up to carry out catalytic polymerizations of propylene at low reaction rates. The catalyst system used in this work was a fourth generation Ziegler–Natta catalyst, with tri-ethyl aluminum as cocatalyst and di-cyclopentyl dimethoxy silane as external electron donor. The low reaction rates allowed us to systematically study the formed particles. Polymer powder was produced with a yield of prepolymerization (YPP) varying from 0.3 g of polypropylene (PP) per gram catalyst to 50 g PP per gram catalyst. Because of the well-defined polymerization conditions, the intra- and inter-particle morphologies can be studied in order to investigate the fragmentation of the catalyst. Cross-sectional SEM pictures show a decreasing size of fragments with increasing YPP. The fragmentation does not proceed as sometimes described in literature in layers, starting from the outer layer and advancing to the center of the particle, rather the fragments are initially well distributed throughout the particle. At higher values for YPP—above 2– 4 g PP per gram the size of the fragments continues to decrease with increasing YPP, but the fragments ‘drift’ to the outer portions of the particles. In addition to the morphological aspects, a precise study of the ‘early-stage’-polymerization kinetics was carried out using measurements of monomer pressure as a function of time. Up to a YPP of about 2– 4 g PP per gram catalyst, the reaction rate decreases strongly with increasing YPP, but above this value, reaction rate remains constant with increasing YPP. This effect is ascribed to a phase transition in the growing particle. Initially, the catalyst forms the continuous phase, within which the polymer is distributed. After the phase transition, the polymer forms the continuous phase in which catalyst fragments are distributed. This change causes a change in monomer concentration at the active sites, resulting in lower reaction rates.

New Method for Online Observation of Growing Polyolefin Particles

In classical experimental research work on catalytic olefin polymerization, kinetics and powder properties are always determined as an average value over a large number of polymer particles. When studying the properties of the polymer, the powder has to be evacuated from the reactor system. This evacuation step will often change the properties to be measured.Here, a method for direct observation of growing polymer particles is shown. To allow individual observation of a number of growing polymer particles in a catalytic gas phase polymerization, a polymerization cell was built with a transparent lid. The cell was placed in a microscopic video system in such a way that the particles could be observed during reaction and pictures of the particles were stored with a preset time interval.Using a 4th generation Ziegler-Natta catalyst at 40 °C and a propylene pressure of 8 bar, polymerizations were carried out in the presence of hydrogen. It was shown that reaction kinetics can be derived from these experiments, not only average values for larger number of particles, but also kinetics for individual particles. It is shown that kinetic results can be obtained in a reproducible way, and thus it is well possible to kinetically characterize a catalyst in gas phase polymerization using this method.As the current lid is not only transparent to visible light, but also to infrared light, an infrared camera can be applied to measure surface temperatures of the growing polymer particles. This can be of large help in development of single particle models. One can also think about different applications and extensions. New analysis method could be applied to the same principle, for example Raman spectroscopy or X-ray tomography. Next to that, currently a stirrer is being implemented to introduce convective cooling of the particles and one can also think about application of other media than gas phase, like the slurry phase.

Studies on the effects of external electron donor in propylene polymerization

In order to investigate effects of an electron donor in propylene polymerization (in gas and slurry phase reactions each) by using a 3rd generation Ziegler-Natta catalyst, the catalytic activities were measured before and after the addition of an electron donor. And physical properties of produced polymer were estimated. Polymerization rate was decreased with increasing EB/A1 mole ratio because atactic sites on catalyst were selectively poisoned by the addition of the electron donor, and consequently total number of active sites were diminished. It was found that the overall reaction order was the 2nd order, and a reaction rate form was suggested by using a CO inhibition technique. Catalyst deactivation was due to the formation of dense isotactic polypropylene on the catalyst at the beginning of polymerization so that monomers had the difficulties in diffusion into catalyst surface through the dense polymer. From the measurements of polymer physical properties, probability of active site transitions from atactic→low isotactic→high isotactic sites could be considered, which may be due to the formation of a complex between co-catalyst and electron donor.