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Ziegler-Natta Catalysts (ziegler-natta + catalyst)
Selected AbstractsReductive Formation of Isospecific Ti Dinuclear Species on a MgCl2 (110) Surface in Heterogeneous Ziegler-Natta CatalystsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 17 2008Toshiaki Taniike Abstract Dinucleation of TiCl4 on the MgCl2 (100) surface has been conventionally believed as the origin of the stereospecificity of heterogeneous Ziegler-Natta catalysts for propylene polymerization, while the MgCl2 (110) surface has been regarded as non-stereoselective in the absence of organic donors. Based on periodic density functional calculations, we propose a new isospecific Ti dinuclear species on the MgCl2 (110) surface, which is formed as a result of reduction of Ti from 4+ to 3+. The new species closely resembles the dinuclear species on the (100) surface, but two Ti ions are obliquely stacked along the (110) surface through Cl bridges. The results address the importance of the reduction and re-distribution of surface Ti species after contacting with cocatalysts in considering the origin of the stereospecificity. [source] A Simplified Model for Prediction of Molecular Weight Distributions in Ethylene-Hexene Copolymerization Using Ziegler-Natta CatalystsMACROMOLECULAR REACTION ENGINEERING, Issue 5 2007Duncan E. Thompson Abstract A simplified steady-state model has been developed to predict molecular weight distributions and average compositions of ethylene-hexene copolymers produced using heterogeneous Ziegler-Natta catalysts in gas-phase reactors. The model uses a simplified reaction scheme to limit the number of parameters that must be estimated. The number of parameters is further reduced by assuming that different types of active sites share common rate constants for some reactions. Estimates of kinetic parameters are obtained using deconvolution analysis of industrial copolymer samples produced using a variety of isothermal steady-state operating conditions. The parameter estimates should prove useful as initial guesses for future parameter estimation in a non-isothermal model. [source] Hybrid titanium catalyst supported on core-shell silica/poly(styrene- co -acrylic acid) carrierJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010Lijun Du Abstract Hybrid titanium catalysts supported on silica/poly(styrene- co -acrylic acid) (SiO2/PSA) core-shell carrier were prepared and studied. The resulting catalysts were characterized by Fourier transform infrared (FTIR) spectroscopy, laser scattering particle analyzer and scanning electronic microscope (SEM). The hybrid catalyst (TiCl3/MgCl2/THF/SiO2·TiCl4/MgCl2/PSA) showed core-shell structure and the thickness of the PSA layer in the two different hybrid catalysts was 2.0 ,m and 5.0 ,m, respectively. The activities of the hybrid catalysts were comparable to the conventional titanium-based Ziegler-Natta catalyst (TiCl3/MgCl2/THF/SiO2). The hybrid catalysts showed lower initial polymerization rate and longer polymerization life time compared with TiCl3/MgCl2/THF/SiO2. The activities of the hybrid catalysts were enhanced firstly and then decreased with increasing P/P. Higher molecular weight and broader molecular weight distribution (MWD) of polyethylene produced by the core-shell hybrid catalysts were obtained. Particularly, the hybrid catalyst with a PSA layer of 5.0 ,m obtained the longest polymerization life time with the highest activity (2071 kg PE mol,1 Ti h,1) and the resulting polyethylene had the broadest MWD (polydispersity index = 11.5) under our experimental conditions. The morphology of the polyethylene particles produced by the hybrid catalysts was spherical, but with irregular subparticles due to the influence of PSA layer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] In situ polymerization of polyethylene/clay nanocomposites using a novel clay-supported Ziegler-Natta catalystPOLYMER COMPOSITES, Issue 10 2009Ahmad Ramazani S.A. Polyethylene/clay nanocomposites (PECNC) were synthesized via in situ Ziegler-Natta catalyst polymerization. Activated catalyst for polymerization of ethylene monomer has been prepared at first by supporting of the cocatalyst on the montmorillonite (MMT) smectite type clay and then active complex for polymerization formed by reaction of TiCl4 and aluminum oxide compound on the clay. Acid wash treatment has been used for increasing hydroxyl group and porosity of the clay and subsequently activity of the catalyst. The nanostructure of composites was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Obtained results show that silica layers of the mineral clay in these polyethylene/nanocomposites were exfoliated, intercalated, and uniformly dispersed in the polyethylene matrix even at very high concentration of the clay. Thermogravimetric analysis (TGA) shows good thermal stability of the PECNCs. Differential scanning calorimeter (DSC) results reveal considerable decrease in the crystalline phase of the PECNC samples. Results of permeability analysis show an increase in barrier properties of PECNC films. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers [source] Effect of Comonomer Ethylene on Plateau Modulus of Crystal-line Ethylene-propylene Random Copolymer with Broad Molecular Weight DistributionCHINESE JOURNAL OF CHEMISTRY, Issue 6 2005Ding Jian Abstract Ethylene-propylene random copolymer with ultra-high molecular weight (UHPPR) and broad molecular weight distribution (MWD) was prepared with Ziegler-Natta catalyst. The viscoelastic behavior of UHPPR has been investigated by means of oscillatory rheometer at 180, 200 and 220 °C. The loss modulus (G, curves of 180 and 200 °C present a pronounced maximum at 38.10 and 84.70 r/s, respectively. For the first time, this makes it possible to directly determine the plateau modulus () of crystalline ethylene-propylene random copolymer with broad MWD in a certain experimental temperature G,(,) curve. The plateau modulus of UHPPR is 4.51×105 and 3.67×105 Pa at 180 and 200 °C respectively, increasing with random incorporation of comonomer ethylene into the molecular chains and being independent of molecular weight. [source] Effects of external donors and hydrogen concentration on oligomer formation and chain end distribution in propylene polymerization with Ziegler-Natta catalystsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2010Torvald Vestberg Abstract The effect of type and concentration of external donor and hydrogen concentration on oligomer formation and chain end distribution were studied. Bulk polymerization of propylene was carried out with two different Ziegler-Natta catalysts at 70 °C, one a novel self-supported catalyst (A) and the other a conventional MgCl2 -supported catalyst (B) with triethyl aluminum as cocatalyst. The external donors used were dicyclopentyl dimethoxy silane (DCP) and cyclohexylmethyl dimethoxy silane (CHM). The oligomer amount was shown to be strongly dependent on the molecular weight of the polymer. Catalyst A gave approximately 50 % lower oligomer content than catalyst B due to narrower molecular weight distribution in case of catalyst A. More n -Bu-terminated chain ends were found for catalyst A indicating more frequent 2,1 insertions. Catalyst A also gave more vinylidene-terminated oligomers, suggesting that chain transfer to monomer, responsible for the vinylidene chain ends, was a more important chain termination mechanism for this catalyst, especially at low hydrogen concentration. Low site selectivity, due to low external donor concentration or use of a weak external donor (CHM), was also found to increase formation of vinylidene-terminated oligomers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 351,358, 2010 [source] Reductive Formation of Isospecific Ti Dinuclear Species on a MgCl2 (110) Surface in Heterogeneous Ziegler-Natta CatalystsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 17 2008Toshiaki Taniike Abstract Dinucleation of TiCl4 on the MgCl2 (100) surface has been conventionally believed as the origin of the stereospecificity of heterogeneous Ziegler-Natta catalysts for propylene polymerization, while the MgCl2 (110) surface has been regarded as non-stereoselective in the absence of organic donors. Based on periodic density functional calculations, we propose a new isospecific Ti dinuclear species on the MgCl2 (110) surface, which is formed as a result of reduction of Ti from 4+ to 3+. The new species closely resembles the dinuclear species on the (100) surface, but two Ti ions are obliquely stacked along the (110) surface through Cl bridges. The results address the importance of the reduction and re-distribution of surface Ti species after contacting with cocatalysts in considering the origin of the stereospecificity. [source] Continuous Soluble Ziegler-Natta Ethylene Polymerizations in Reactor Trains, 2 , Estimation of Kinetic Parameters from Industrial DataMACROMOLECULAR REACTION ENGINEERING, Issue 2 2008Marcelo Embiruçu Abstract We show that it is possible to estimate kinetic parameters for complex mechanistic polymerization models from available industrial data. A methodology is developed for efficient handling and reconciliation of industrial data and is then applied to allow estimation of kinetic parameters for industrial ethylene polymerizations performed in reactor trains using soluble Ziegler-Natta catalysts. The parameter estimation procedure is formulated as a nonlinear optimization procedure subject to hard and soft model and process constraints. Parameter estimates obtained for the catalyst system allow a very good description of actual industrial data used during the estimation process and also allow very good prediction of process performance when completely new operating conditions are considered. It is concluded that complex phenomenological models can be successfully fitted to actual industrial processes without the need to carry out extensive experimental tests in the laboratory. [source] Continuous Soluble Ziegler-Natta Ethylene Polymerizations in Reactor Trains, 3 , Influence of Operating Conditions upon Process PerformanceMACROMOLECULAR REACTION ENGINEERING, Issue 2 2008Marcelo Embiruçu Abstract The behavior of continuous solution ethylene/but-1-ene polymerizations through Ziegler-Natta catalysts is analyzed, based on a previously developed mathematical model. In order to do that, dynamic simulations are carried out and process responses are analyzed as functions of process operating policies and flowsheet configuration, at conditions that resemble the actual operation of industrial sites. It is shown that system responses are highly nonlinear and very sensitive to disturbances of the operating conditions and that catalyst decay is of fundamental importance for proper understanding of process behavior. Results indicate that mixing conditions inside the reactor vessels exert a significant impact upon the final polymer quality and can be manipulated for in-line control of final resin properties. Finally, it is shown that the development of feed policies, based on the use of lateral feed streams, allows the simultaneous control of melt flow index, stress exponent and polymer density of the final polymer resin. [source] A Simplified Model for Prediction of Molecular Weight Distributions in Ethylene-Hexene Copolymerization Using Ziegler-Natta CatalystsMACROMOLECULAR REACTION ENGINEERING, Issue 5 2007Duncan E. Thompson Abstract A simplified steady-state model has been developed to predict molecular weight distributions and average compositions of ethylene-hexene copolymers produced using heterogeneous Ziegler-Natta catalysts in gas-phase reactors. The model uses a simplified reaction scheme to limit the number of parameters that must be estimated. The number of parameters is further reduced by assuming that different types of active sites share common rate constants for some reactions. Estimates of kinetic parameters are obtained using deconvolution analysis of industrial copolymer samples produced using a variety of isothermal steady-state operating conditions. The parameter estimates should prove useful as initial guesses for future parameter estimation in a non-isothermal model. [source] Precise arguments on the distribution of stereospecific active sites on MgCl2 -supported ziegler-natta catalystsMACROMOLECULAR SYMPOSIA, Issue 1 2004Boping Liu Abstract The stereospecific nature of active sites on various MgCl2 -supported Ziegler-Natta catalysts was investigated by stopped-flow technique combined with temperature rising elution fractionation (TREF) method. A modified three-sites model with precise description of the stereospecific nature of various types of active sites stemmed from surface titanium species, Al-alkyl compounds, Mg-compounds and electron donors has been proposed. It was demonstrated that the isospecificity of active sites strongly depends on the bulkiness of the ligands situated at the two most important ligand positions for construction of asymmetry and chirality of the active sites with steric hindrance. In general, there may exist both monometallic and bimetallic sites in heterogeneous Ziegler-Natta catalyst system. The kinds of active titanium species with different chemical structures on this catalyst system should be limited, whereas, the non-discrete distribution of isospecificity of active sites could be considered to generate from the numerous types of steric and electronic effects from the surroundings of active titanium species as well as large number of reversible and dynamic transformation reactions simultaneously occurred on the heterogeneous catalyst surface. [source] | ||||||||||