Slurry Polymerization Of Ethylene Research Articles

Reduction of Chain Entanglement of Ethylene Polymerization Endowed by the Dormancy Effect of Fluorosilicone Microdroplets

The refined fluorosilicone microdroplets were introduced during the ethylene slurry polymerization to reduce the chain entanglement of ultra-high-molecular-weight polyethylene (UHMWPE) through the intermittent dormancy of living polymer chains. The dormancy effect is endowed by the highly frequent collisions between microdroplets and growing PE particles to block the transfer channel of reactants on the particle surface. The dwell time of microdroplets on the particle surface is an order of magnitude higher than that of the microbubbles, and the increase rate of the chain entanglement degree with the polymerization activity controlled by microdroplets is 2 orders of magnitude smaller than that of the microbubbles, indicating that fluorosilicone microdroplets have a better effect on the reduction of the chain entanglement. Compared with commercial products, the UHMWPE prepared in this work shows a lower chain entanglement degree and better mechanical properties, indicating that reducing the entanglement degree is one of the important means to improve the mechanical properties of UHMWPE.

Simple and Strong Dative Attachment of α-Diimine Nickel (II) Catalysts on Supports for Ethylene Polymerization with Controlled Morphology

In this article, preparation of novel spherical MgCl2 supported α-diimine nickel (II) catalysts for ethylene polymerization in slurry phase is reported. α-Diimine ligands were synthesized by condensation reaction of 2, 6-disubstituted alkyls or aryls anilines and Ace naphthoquinone Which have hydroxyl functionality in their para-position. Hydroxyl functionalized α-diimine attached strongly on to the spherical MgCl2 support surface by dative bonding. No linker was needed to attach the complexes onto the support surface and the amount of loaded Nickel was controllable to improve morphology and especially bulk density of polymer powder. A significant reduction in catalysts activity has happened when homogeneous catalysts were supported onto silica but this reduction was decreased when they were supported onto thermally treated spherical MgCl2. As homogeneous bis(N,N′-(4-(3-hydroxyl-propyl)-2,6-di[(4-tert-butyl-phenyl)-phenyl) amino] Ace naphthoquinone Nickel dibromide(d) showed the highest activity among other evaluated homogeneous catalysts, its MgCl2 supported catalyst (d/S-MgCl2) has shown the highest activity among MgCl2 supported catalysts too. These MgCl2 supported catalysts were pre-polymerized in presence of ethylene monomer in the mild polymerization condition to yield a pre-polymerized catalyst with polymer/catalyst weight ratio equal to six. Ethylene polymerization was carried out to make spherical particles of polyethylene without reactor fouling by these pre-polymerized catalysts. Clearly, it is shown in SEM images that the spherical morphology of MgCl2 support is replicated in the produced polymer. The molecular weight and molecular weight distribution of produced polymer with MgCl2 supported catalysts were higher than those produced by homogeneous catalysts. α–Diimine nickel (II) complexes have hydroxy functionality where produce strong dative bonding onto spherical MgCl2. This bonding is strong enough that these catalysts are suitable for slurry polymerization of ethylene without reactor fouling due to catalyst leaching from support. The chemical structure of MgCl2 leads to high active supported catalysts. The molecular weight and polydispersity index of produced polymrers using these supported catalysts are higher than those produced by equivalent homogeneous catalysts and are controllable by selection of appropriate ligand for used α–diimine nickel (II) complex or hydrogen concentration in ethylene polymerization.

Effect of supported MAO cocatalysts in ethylene polymerization and ethylene/1-hexene copolymerization using Cp*TiCl2(O-2,6-iPr2C6H3) catalyst

Ethylene slurry polymerization using Cp*TiCl2(O-2,6-iPr2C6H3) in the presence of supported solid MAO cocatalysts proceeded without decreasing in the activity compared to the homogeneous system, affording polymers with controlled shape replicated from the original support. Unique characteristics by 1 in the ethylene/1-hexene copolymerization observed in the homogeneous system (high catalytic activity, efficient 1-hexene incorporation, temperature dependence) have also been preserved in this catalysis, affording high molecular weight poly(ethylene-co-1-hexene)s with unimodal molecular weight distributions as well as with high 1-hexene contents.

Highly Tunable Catalyst Supports for Single-Site Ethylene Polymerization

A new class of tunable crystalline solid supports for metal complexes has been synthesized and used for ethylene polymerization. We developed a family of high surface area, highly dispersible layered double hydroxides (AMO–LDHs) which, on treatment with alkyl aluminum activators, are able to support metallocene and nonmetallocene complexes to make active catalyst systems for the slurry polymerization of ethylene. We show that the chemical composition of the AMO–LDH support can dramatically affect catalyst activity, polymer morphology, and polymer microstructure. A Zr K-edge EXAFS study of these active catalysts has enabled us to observe a metallocene-derived single-center catalytic species in close proximity to the support.

Ethylene Polymerization via Metallocenes: An Experimental Study

ABSTRACTAn experimental study oriented to gather kinetic modelling data in the ethylene polymerization via metallocenes is reported. Also is illustrated the employment of two methods for determination of kinetic behavior and the instantaneous activity of Ziegler-Natta catalysts in the slurry polymerization of ethylene. The theoretical basis for both methods is described as well as the required instrumentation for its implantation at a laboratory level. An experimental program of polymerization with two different metallocenic systems was executed, showing that the direct (measurement of ethylene flow) as well as the calorimetric method (based on energy balances) give equivalent high quality information on the kinetic performance of the catalyst.

Modeling and Simulation of Ethylene Polymerization in Industrial Slurry Reactor Series

A five-site comprehensive mathematical model was developed to simulate the steady-state behavior of industrial slurry polymerization of ethylene in multistage continuous stirred tank reactors. More specifically, the effects of various operating conditions (i.e., inflow rates of catalyst, hydrogen and comonomer) on the molecular structure and properties of polyethylene (i.e., Mw, Mn, polydispersity index (IPD), melt index, density, etc.) are fully assessed. It is shown that the proposed comprehensive model is capable of simulating the steady-state operation of an industrial slurry stirred tank reactor series. It is demonstrated that changing the catalyst flow rate, changes simultaneously the mean residence-time in both reactors, which plays a significant role on the establishment of polyethylene architecture properties such as molecular mass and IPD. The melt index and density of polyethylene are mainly controlled by hydrogen and comonomer concentration, respectively.

Simulation and Analysis of an Ethylene Slurry Polymerization System Using Supercritical Propane

In this paper, a model for an ethylene slurry polymerization system using supercritical propane as a solvent is developed by adopting a set of thermodynamic and kinetic parameters using fundamental chemical engineering principles and Polymers Plus software. The Ziegler–Natta catalyst is characterized by assuming the existence of multiple types of catalyst sites and deconvolution data from gel permeation chromatography to determine the most probable chain-length distribution and relative amounts of polymer produced at each site type. A set of suitable reaction subclasses and kinetic constants for different site types that fit plant conditions is developed, validating our model. The values calculated for production rate, ethylene conversion, residence time, H2/C2H4 molar ratio in the reactor, number-average molecular weight, and polydispersity index are all close to actual values, verifying that our model accurately describes plant conditions.

Thermodynamic Data of Ethylene–Propane Mixtures in Condensed and Supercritical State

AbstractThermodynamic data of ethylene/propane mixtures is technically relevant, since propane is one of the diluents used in commercial slurry polymerization of ethylene. Despite this commercial importance, there is almost no information on thermodynamic data of ethylene/propane mixtures available in open literature. In this study, thermodynamic data for the binary system ethylene/propane has been measured in the range relevant for slurry polymerization of ethylene, both in sub‐ and supercritical conditions. Phase equilibrium measurements have been carried out in the range of 40–80 °C with ethylene partial pressures up to 10 bar. Thermodynamic properties of supercritical mixtures have been measured in the range of 90–105 °C and ethylene fractions of up to 20 mol‐%. The measured data can be described in good agreement with the Peng–Robinson equation of state, modified by the Rackett model for density calculation. Missing parameters such as the interaction parameters as well as Rackett model parameters have been determined by parameter estimation based on our experimental results. The parameterized model can be used for further application in engineering sciences, e.g., calculation of properties not directly measurable such as densities and concentrations in liquid phase.magnified image

Correlation of Arrhenius parameters for UHMWPE synthesis with ethylene solubility characteristics in different polymerization media

AbstractThe effect of different polymerization media like n‐hexane, cyclohexane, isooctane, n‐decane, toluene, varsol, and light normal paraffin (LNP) on the kinetics of the slurry polymerization of ethylene using a highly active Ziegler Natta (ZN) catalyst for synthesizing UHMWPE was studied. Attempts have been made to determine the solubility of ethylene in the above polymerization media in a very basic manner and to correlate same with the process activation energy based on the Arrhenius plots. The ethylene solubility seemed to depend on the number of carbon atoms in the media, besides other parameters like geometry, dipole moment, etc. It is obvious and well understood that the monomer (ethylene) concentration has a direct bearing on the polymerization kinetics, which influenced the activation energy (Ea) besides other parameters like catalyst/cocatalyst concentration, temperature, etc which were kept constant during the study. The role of the catalyst system in controlling the activation energy was also further exemplified by employing a different ZN catalyst system wherein higher activation energy was observed. This was ascribed to restricted activation pathways for the catalyst under the comparable experimental conditions employed. As soon as better activation pathways for the catalyst were enabled the activation energy dropped down remarkably. The Ea for the synthesis of ultra‐high molecular weight polyethylene (UHMWPE) using traditional MgCl2 supported Ti catalyst was found to be 5–12 kcal/mol which compared well with the values obtained by other researchers using other similar catalyst systems for different ethylene polymerization processes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Supported hybrid early and late transition metal catalysts for the synthesis of polyethylene with tailored molecular weight and chemical composition distributions

Supported hybrid catalysts using metallocenes and a nickel diimine catalyst were synthesized and used for ethylene slurry polymerization and ethylene/1-hexene copolymerization. Two types of metallocenes, together with a nickel diimine catalyst were supported onto SiO2 through chemical bonding, and a borate compound was physisorbed for the activation of the catalysts. These supported hybrid catalysts had high catalyst activities and made free-flowing polymer particles. The chemical composition distribution, molecular weight averages and distributions of resultant polymers were controlled by catalyst structure and polymerization conditions such as reaction temperature and the use of α-olefin. According to GPC-IR, 13C NMR and CEF characterization results of some polymers, more 1-hexene was incorporated in the high molecular weight region, short chain branches were generated by the chain walking mechanism in low molecular weight region. The morphologies of the resulting particles were investigated by SEM.

Studying the effects of SiO2 specifications and properties of (SiO2/MgCl2/TEOS/TiCl4/AlEt3) catalyst system on kinetic behavior and hydrogen responsibility of ethylene slurry polymerization

AbstractA series of silica gels with different physico‐chemical properties such as average pore size diameter, pore volume, attrition quality index, and bulk density were prepared, characterized, and subjected to treatment in special thermal program. Catalyst precursors were prepared by reaction of these silica gels with dibutyl magnesium (MgBu2) at 50°C and then addition of tetraethoxy ortho silicate and subsequent impregnation with titanium tetrachloride (TiCl4). Polymerization of ethylene by these catalysts at comparable conditions and also at different PH2/PC2 ratio was carried out; the results showed that support properties have significant influence on polymerization behaviors such as activity profile, productivity, and hydrogen responsibility. To quantitative analysis of the results, a new kinetic relation for rate‐time profiles was derived, and these kinetic parameters were used to study and calculate of the effects of support specification. It was observed that trends of activity profiles were mainly affected by support properties and as well as PH2/PC2 ratio. Interestingly enough, catalysts with different pore volume diameter show different behavior with variation of PH2/PC2 ratio. Increasing in pore size diameter from 60 to 200 Å give raises catalyst activity by two times. Finally, mentioned variables were attributed to different particle growth and mechanism of fragmentation during polymerization. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Ethylene slurry polymerization using nickel diimine catalysts covalently-attached onto MgCl2-based supports

MgCl 2 /alcohol adducts were recrystallized with alkyl aluminums and used as catalysts supports for nickel diimine complexes functionalized with amine groups. These supported catalysts were used to polymerize ethylene in a slurry reactor. The MgCl 2 -based supported nickel diimine catalysts had higher activities than the equivalent SiO 2 -supported nickel diimine catalysts, even without the use of activators. These catalysts made polyethylene with melting temperatures and molecular weights higher than those made with the equivalent homogeneous catalysts. Interestingly, the catalyst activity and polymer molecular weight could be controlled by changing the support composition. In addition, covalent chemical bonds between the functionalized nickel diimine complex and the MgCl 2 -based supports avoided catalyst leaching during polymerization, leading to the production of polymer particles with good morphology. The mechanical strength of the resulting polymer particles, however, was lower than those made with SiO 2 -supported nickel diimine catalysts.

Synthesis of Supported Nickel Diimine Catalysts for Ethylene Slurry Polymerization

AbstractEthylene slurry polymerizations were performed using supported nickel diimine catalysts. The effects of catalyst structure and polymerization conditions on catalyst activity, polymer particle morphology, and polymer properties were investigated. Covalently attached supported nickel diimine catalysts activated with ethyl aluminum sesquichloride (EASC) have high activities and made polymers with spherical morphology. Compared with the equivalent homogeneous catalysts, the covalently attached supported catalysts produced polyethylene with higher melting temperatures, higher molecular weights, and broader molecular weight distributions. Borates used as internal activator during the synthesis of these supported catalysts successfully activated the nickel diimine complexes.magnified image

Novel High Performance Ziegler-Natta Catalyst for Ethylene Slurry Polymerization

A novel high performance MgCl 2/TiCl 4 catalyst with tetrabutyloxsilicane as electron donor was prepared for ethylene slurry polymerization process. The properties of the catalyst such as particle size distribution, catalytic activity, hydrogen responsibility and copolymerization performance were investigated and compared with commercial catalyst (imported catalyst). Copolymerization of ethylene and 1-butylene using the catalyst was studied in a pilot plant. The composition, structure and property of the copolymer were characterized by 13C nuclear magnetic resonance ( 13C NMR) and gel permeation chromatography-Infrared (GPC-IR), and compared with those of the copolymer obtained from a commercial catalyst. In comparison with the commercial catalyst, the novel catalyst had a higher activity (up to 34.6 kg·g −1) and a better particle size distribution (PSD), and produced polymers having higher bulk density (up to 0.37 g·cm −3) with less fine resin. Meanwhile, the novel catalyst showed a higher hydrogen responsibility and better copolymerization performance. The results indicated that the copolymer obtained from the novel catalyst has a higher branch in the high molecular weight fraction and lower branch in the low molecular weight fraction.

Catalytic Behavior of Bis(imino)pyridineiron(II) Complex Supported on Clay Minerals during Slurry Polymerization of Ethylene

Abstract Supported catalysts prepared by an impregnation method using the bis(imino)pyridineiron(II) complex and clay minerals (montmorillonite, fluorotetrasilicic mica, and saponite) were used for ethylene polymerization. The activities of the montmorillonite- and saponite-based catalysts were much higher than that of the mica-based one.

Simulation of Slurry Polymerization of Ethylene

A model of slurry polymerization of ethylene in a multistage continuous stirred-tank reactor (CSTR) was developed in order to find the effect of stagewise variation of parameters on polymer polydispersity and rate of polymerization. Higbie's penetration theory has been used to calculate monomer absorption rate in the presence of micron-sized single site type catalyst in slurry phase. The residence time distribution of the growing polymer particles in an ideal CSTR was modelled by a relaxation-type unsteady state approach. The effect of gas-liquid mass transfer limitations on polymer properties is predicted for various reactor configurations. An analysis of various possible configurations of two-stage CSTR with stagewise variation of the partial pressures of ethylene and/or hydrogen has been made.

Heterogeneous catalysts immobilizing α-diimine nickel complexes into fluorotetrasilicic mica interlayers to prepare branched polyethylene from only ethylene

Abstract The α-diimine nickel (II) complexes immobilized into the clay mineral interlayer were prepared by the reaction of the Ni2+ ion-exchanged fluorotetrasilicic mica and the α-diimine ligand. These procatalysts showed a high catalytic activity for the slurry polymerization of ethylene in the presence of methylalumoxane, triethylaluminum or triisobutylaluminum. The activity was strongly affected by the solvent used in the preparation and the steric bulk of the ligand. A high activity (2313 kg-PE mol-Ni−1 h−1) was obtained by the polymerization at 50 °C in the presence of triisobutylaluminum using the procatalyst prepared with the [Ar–N C(CH3)C(CH3) N–Ar (Ar = 2,6-C6H3(CH3)2)] ligand in acetonitrile.

Effect of fatty amine and perfluorocarbon as anti‐fouling agent on the catalyst activity and titanium oxidation state in slurry polymerization of ethylene

AbstractIn this work, the effect of two antifouling materials on the activity of catalyst used to produce polyethylene in a 1‐L slurry reactor and on the titanium oxidation state of the catalyst was investigated. Armostat 300 with the formula alkyl C14‐C18 bis(2‐hydroxyethyl)amine is an antistatic agent that reduces static electricity of the polymer particles. It was found that within the concentration of 0.16–1.32 g/mmol Ti, Armostat 300 helps to increase the catalyst activity to 1.3–2 times. The variation of the titanium oxidation state of the catalyst in the presence of Armostat 300 at 80°C with Al/Ti molar ratio of 100 showed that Ti (III) species increased. The effect of Armostat 300 on Tm, % Xc, density, bulk density, and MFI of polymer was insignificant. In this work, Zonyl FSN‐100 with the formula Rf(CH2CH2O)xH, Rf = F(CF2CF2)y, y = 1–9, x = 1–26 was used as antifouling agent in copolymerization of ethylene with 1‐butene. It was found that Zonyl FSN‐100 at the concentration range of 5–20 ppm reduces the catalyst activity to 1.11–1.9 times. It was also shown that Ti (III) species in the presence of Zonyl FSN 100 decreased. This antifouling agent slightly decreased the properties of polymer including % Xc, density, and Mw. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 257–260, 2006

Immobilization of a zirconium complex bearing bis(phenoxyketimine) ligand on MCM-41 for ethylene polymerization

A novel zirconium complex bearing bis(phenoxyketimine) ligand ( 1) bis((3,5-di-tert-butyl-C 6H 2-2-O)PhC N(2,4-di-fluoro-C 6H 3))ZrCl 2 ( 2) was prepared and successfully immobilized on a mesoporous molecular sieve MCM-41 in chemical method. Results of slurry polymerization of ethylene with MCM-41-supported catalyst ( MC) indicated that the morphologies of polyethylene obtained differed greatly in heptane and toluene. Homogeneous catalyst 2 exhibited a very high initial activity in ethylene polymerization at room temperature resulting in great viscosity of the system. When immobilized on MCM-41, MC showed a smooth yet highly active kinetic behavior. With MAO as the cocatalyst, the effects of Al/Zr molar ratio and polymerization temperature on catalytic activity and properties of polyethylene obtained were investigated. The results showed that polyethylene obtained with MC possessed higher molecular weight ( M n) and broader molecular weight distribution ( M w/ M n) than those formed with its homogeneous counterpart.

Silica powder obtained by sol-gel method as a support of organometallic vanadium catalyst for ethylene polymerization

Sol-gel technique was employed to obtain the silica-type powder, which after modification procedure was applied as a support of organometallic catalytic system for ethylene polymerization. The powder product was synthesized using hydrolysis and condensation of TEOS, catalyzed by ammonia. Obtained material and a reference support (commercial silica Davisil) were characterized to determine their particle size distributions, BET surface area, pore volume and diameter. Gas-phase adsorption of vanadium catalyst on analyzed support materials as well as adsorption from the solution in hexane were carried out. Both carrier materials were thermally pretreated prior catalytic systems syntheses and the influence of modification method applied on resulting organometallic catalyst character was estimated in low-pressure slurry polymerization of ethylene. Obtained results prove that sol-gel material, due to its advantageous morphology with wide and shallow pores, allows to obtain catalytic systems of higher activity in low-pressure ethylene polymerization, in comparison with commercial silica Davisil.