Influence of supported vanadium catalyst on ethylene polymerization reactions

BACKGROUND: In the research area of homogeneous Ziegler–Natta olefin polymerization, classic vanadium catalyst systems have shown a number of favourable performances. These catalysts are useful for (i) the preparation of high molecular weight polymers with narrow molecular weight distributions, (ii) the preparation of ethylene/R‐olefin copolymers with high R‐olefin incorporation and (iii) the preparation of syndiotactic polypropylenes. In view of the above merits of vanadium‐based catalysts for polymerization reactions, the development of well‐defined single‐site vanadium catalysts for polymerization reactions is presently an extremely important industrial goal. The main aim of this work was the synthesis and characterization of a heterogeneous low‐coordinate non‐metallocene (phenyl)imido vanadium catalyst, V(NAr)Cl₃, and its utility for ethylene polymerization. RESULTS: Imido vanadium complex V(NAr)Cl₃ was synthesized and immobilized onto a series of inorganic supports: SiO₂, methylaluminoxane (MAO)‐modified SiO₂ (4.5 and 23 wt% Al/SiO₂), SiO₂? Al₂O₃, MgCl₂, MCM‐41 and MgO. Metal contents on the supported catalysts determined by X‐ray fluorescence spectroscopy remained between 0.050 and 0.100 mmol V g^?1 support. Thermal stability of the catalysts was determined by differential scanning calorimetry (DSC). Characterization of polyethylene was done by gel permeation chromatography and DSC. All catalyst systems were found to be active in ethylene polymerization in the presence of MAO or triisobutylaluminium/MAO mixture (Al/V = 1000). Catalyst activity was found to depend on the support nature, being between 7.5 and 80.0 kg PE (mol V)^?1 h^?1. Finally, all catalyst systems were found to be reusable for up to three cycles. CONCLUSION: Best results were observed in the case of silica as support. Acid or basic supports afforded less active systems. In situ immobilization led to higher catalyst activity. The resulting polyethylenes in all experiments had ultrahigh molecular weight. Finally, this work explains the synthesis and characterization of reusable supported novel vanadium catalysts, which are useful in the synthesis of very high molecular weight ethylene polymers. Copyright © 2007 Society of Chemical Industry     

基于聚合物分子量分布的乙烯淤浆聚合工艺优化

分子量及分布是聚合物生产过程中极其重要的质量指标,但目前的技术水平并不能实现分子量及其分布的实时测量,基于反应机理的动态建模是实现其软测量的重要方法。以乙烯淤浆聚合工艺为研究对象,基于聚合机理,分别以聚合物的平均分子量和分子量分布为目标,以循环气中氢气乙烯比为决定变量,采用稳态优化方法求取聚合物生产的工艺条件。结果表明:以平均分子量为优化目标所得的结果与分析值的偏差较大,虽然聚合物的平均分子量符合要求,但聚合物的分子量分布曲线与所需产品的分子量分布曲线之间的最大误差可达0.092;而以分子量分布曲线为目标所得的最大误差只有0.069。因此,以分子量分布曲线作为目标的优化方法明显比常规的以平均分子量为目标的优化方法优越。     

Nano‐sized silica supported Me2Si(Ind)2ZrCl2/MAO catalyst for ethylene polymerization

Nano‐sized and micro‐sized silica particles were used to support a zirconocene catalyst [racemic‐dimethylsilbis(1‐indenyl)zirconium dichloride], with methylaluminoxane as a cocatalyst. The resulting catalyst was used to catalyze the polymerization of ethylene in the temperature range of 40–70°C. Polyethylene samples produced were characterized with scanning electron microscopy (SEM), X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). Nano‐sized catalyst exhibited better ethylene polymerization activity than micro‐sized catalyst. At the optimum temperature of 60°C, nano‐sized catalyst's activity was two times the micro‐sized catalyst's activity. Polymers obtained with nano‐sized catalyst had higher molecular weight (based on GPC measurements) and higher crystallinity (based on XRD and DSC measurements) than those obtained with micro‐sized catalyst. The better performances of nano‐sized catalyst were attributed to its large external surface area and its absence of internal diffusion resistance. SEM indicated that polymer morphology contained discrete tiny particles with thin long fiberous interlamellar links. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Ethylene polymerization with a silica‐supported iron‐based diimine catalyst

A supported iron‐based diimine catalyst (SC) was prepared by immobilization of 2,6‐bis[1‐(2,6‐diisopropylphenylimino)ethyl]pyridine iron chloride (I) on silica and employed in ethylene polymerization. The kinetic behavior of ethylene polymerization with SC was studied. The effects of the Al/Fe molar ratio, reaction temperature, and cocatalyst on the catalytic activity as well as the melting temperature, molecular weight, and morphology of the polymers obtained were also investigated. The results showed that good catalytic activities can be obtained even with a small amount of the cocatalyst methylaluminoxane (MAO) or triethylaluminum (AlEt₃). The polyethylenes obtained with a supported catalyst had higher molecular weight, higher melting temperature, and better morphology than those obtained with a homogeneous catalyst. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 466–469, 2003     

Gas‐phase ethylene polymerization using zirconocene supported on mesoporous molecular sieves

Mesoporous molecular sieves, with pore diameters of 2.6–25 nm, were impregnated with methylaluminoxane and bis(butylcyclopentadienyl)zirconium dichloride and tested as catalysts for the gas‐phase homopolymerization of ethylene at ethylene pressures of 200 psi and temperatures of 50–100°C and for 1‐hexene/ethylene copolymerization at 70°C. The activities and activity profiles, at constant Zr and Al contents, depended on the pore size of the supports and the polymerization temperature. Maximum activities for both the homopolymerizations and copolymerizations were observed for catalysts made with supports having pore diameters of 2.6 and 5.8 nm. Homopolymerization activities were highest at temperatures of 70–80°C; average homopolymerization and copolymerization activities up to 9000 kg of polyethylene/(mol of Zr h) were obtained. The weight‐average molecular weights (M_w's) were not a function of the support pore size but decreased with increasing reaction temperatures, from about 260,000 at 50°C to about 165,000 at 100°C. The polydispersities were essentially constant at 2.5 ± 0.2 for the homopolymers. M_w's for the 1‐hexene/ethylene copolymers had an average value of 117,000 with an average polydispersity of 2.8. The amount of triisobutyl aluminum added to the reactor significantly affected the activity and activity profiles. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1161–1177, 2003     

Effect of cocatalysts on ethylene polymerization with fluorinated bisphenoxyimine titanium as a catalyst

In this study, we examined various alkylaluminums, including triethylaluminum (TEA), triisobutylaluminum (TIBA), and diethylaluminum chloride (DEAC), as cocatalysts for the activation of ethylene polymerizations in the presence of a fluorinated Fujita group invented titanium (FI‐Ti) catalyst, bis[N‐(3‐tert‐butylsalicylidene)‐2,3,4,5,6‐pentafluoroanilinato] titanium(IV) dichloride (complex 1 ). DEAC, because of the strong Lewis acidity, was an efficient cocatalyst for activating complex 1 for the ethylene polymerizations, whereas TEA and TIBA as cocatalysts could hardly polymerize ethylene. The effects of the polymerization temperature and Al/Ti molar ratio on the formation of active species, properties, and molecular weight of the resulting polyethylene were investigated. In the complex 1 /DEAC catalyst system, the oxidation states of Ti active species were determined by electron paramagnetic resonance. The results demonstrated that Ti(IV) active species were inclined to polymerize ethylene and yielded high‐molecular‐weight polyethylene. Comparatively, Ti(III) active species resulted from the reduction of Ti(IV) by DEAC and afforded oligomers. Moreover, the bigger steric bulk for the cocatalysts was necessary to achieve ethylene living polymerization with the fluorinated FI‐Ti catalyst. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Bis(imino)pyridyl Co(II) and Fe(II) catalysts immobilized on SBA-15 mesoporous material: new highly active supported catalysts for the polymerization of ethylene

A series of bis(imino)pyridyl Co(II) and Fe(II) complexes containing allyloxy group on the pyridine ring were prepared. These metal complexes were heterogenized covalently immobilizing on modified SBA-15 mesoporous material in the presence of Karstedt catalyst. This immobilization technique was demonstrated to be an ideal one since the resulting supported catalysts resembled closely their homogeneous counterparts, mirroring the feature of active sites.     

Gas phase polymerization of 1,3‐butadiene with supported neodymium‐based catalyst: Investigation of molecular weight

The gas phase polymerization of 1,3‐butadiene (Bd), with supported catalyst Nd(naph)₃/Al₂Et₃Cl₃/Al(i‐Bu)₃ or/and Al(i‐Bu)₂H, was investigated. The polymerization of Bd with neodymium‐based catalysts yielded cis‐1,4 (97.2–98.9%) polybutadiene with controllable molecular weight (MW varying from 40 to 80 × 10⁴ g mol^?1). The effects of reaction temperature, reaction time, Nd(naph)₃/Al(i‐Bu)₃ molar ratio, and cocatalyst component on the catalytic activity and molecular weight of polymers were examined. It was found that there are two kinds of active sites in the catalyst system, which mainly influenced the MW and molecular weight distribution of polybutadiene. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1945–1949, 2004     

The influence of the preparing conditions of SiO2 supported Cp2ZrCl2 catalyst on ethylene polymerization

In this work, ethylene was polymerized by using Cp₂ZrCl₂ supported on silica pretreated with methylaluminoxane (MAO) as the catalyst system. The influence of the conditions for the preparation of the heterogeneous catalyst, such as temperature, washing method of the catalytic solid, MAO and metallocene concentration in the support treatment, time of MAO, and metallocene immobilization on the support, type of alkylaluminum used in the support pretreatment, and calcination temperature of the support were investigated. Aluminum and zirconium content fixed on the silica surface were determined by inductively coupled plasma emission spectroscopy. Polymer characteristics were determined by gel permeation chromatography and differential scanning calorimetry. According to the results, the activity of some supported catalysts were far higher than with the homogeneous system. Moreover, polyethylene with very high molecular weights were also obtained and with molecular weight distribution larger than those produced with the homogeneous precursor. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2054–2061, 2002     

Ethylene polymerization over supported titanium‐magnesium catalysts: Effect of polymerization parameters on the molecular weight distribution of polyethylene

The data on the effects of polymerization duration, cocatalyst, and monomer concentrations upon ethylene polymerization in the absence of hydrogen, and the effect of an additional chain transfer agent (hydrogen) on the molecular weight (MW), molecular weight distribution (MWD), and content of vinyl terminal groups for polyethylene (PE) produced over the supported titanium‐magnesium catalyst (TMC) are obtained. The effects of these parameters on nonuniformity of active sites for different chain transfer reactions are analyzed by deconvolution of the experimental MWD curves into Flory components. It has been shown that the polymer MW grows, the MWD becomes narrower and the content of vinyl terminal groups in PE increases with increasing polymerization duration. It is assumed to occur due to the reduction of the rate of chain transfer with AlEt₃ with increasing polymerization duration. The polydispersity of PE is found to rise with increasing AlEt₃ concentration and decreasing monomer concentration due to the emergence of additional low molecular weight Flory components. The ratios of the individual rate constants of chain transfer with AlEt₃, monomer and hydrogen to the propagation rate constant have been calculated. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Butyl chloride as promoter in ethylene polymerization by magnesium ethoxide‐supported catalyst

The effects of butyl chloride as a promoter in the ethylene polymerization were studied using a Mg(OEt)₂/TiCl₄/triethyl aluminum (TEA) Ziegler–Natta catalyst system, where Mg(OEt)₂, TiCl₄, TEA were used as support, catalyst, and activator, respectively. The influence of BC on the catalyst performance, polymerization rate, and polymer properties were investigated. This study strongly indicates that BC could act as a promoter with high performance in the ethylene polymerization. There was a remarkable increase in the catalyst yield and polymerization rate, in particularly, in the presence of hydrogen which was used for controlling the molecular weight. A reduction in the polymer molecular weight was observed in the presence of BC and hydrogen. The morphology of the polymers was evaluated through scanning electron microscopy and particle size distribution. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40189.     

Ethylene polymerization by phenylenedimethylene‐bridged homobinuclear zirconocene/methylaluminoxane systems

In the presence of methylaluminoxane (MAO), ethylene polymerization was successfully performed with homobinuclear zirconocene complexes {[(C₅H₅)ZrCl₂](C₅H₄CH₂ C₆H₄CH₂C₅H₄)[(C₅H₅)ZrCl₂]; 3o , 4m , and 5p }, which were prepared conveniently by the reaction of disodium(phenylenedimethylene)dicyclopentadienide [C₆H₄(CH₂C₅H₄Na)₂] with 2 equiv of (N⁵‐Cyclopentadienyl)trichlorozirconium dimethoxyethane (CpZrCl₃(DME)) in tetrahydrofuran and characterized by ¹H‐NMR and elemental analysis. The effects of the polymerization parameters, such as the temperature, time, concentration of the catalyst, MAO/catalyst molar ratio, and isomeric difference of the homobinuclear metallocene complexes 3o , 4m , and 5p were studied in detail. The results showed that all three catalytic systems had moderate activities in ethylene polymerization and afforded polyethylene with relatively broad polydispersities. The catalytic activity of 4m was somewhat higher than that of 3o and 5p but lower than that of 4,4′‐bis(methylene)biphenylene‐bridged zirconocene catalysts; this indicated that the distance between the two metal centers was too short in comparison with a 4,4′‐bis(methylene)biphenylene bridge to increase the catalytic activity. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Preparation,characterization, and polymerization of chromium complexes‐grafted Al/SBA‐15 and Ti/SBA‐15 nanosupports

Ethylene polymerization catalysts have been prepared by grafting chromium (III) nitrate onto Al/SBA‐15 and Ti/SBA‐15 mesoporous materials. A combination of XRD, nitrogen adsorption, TEM, and inductively coupled plasma‐atomic emission spectroscopy (ICP‐AES), were used to characterize the catalysts. Polymerization activity of Cr/SBA‐15 catalyst is significantly improved by Al or Ti insertion to the supports. Particularly, the chromium catalyst prepared with Ti/SBA‐15 support is more active than Al/SBA‐15 catalyst. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Optimal operation of ethylene polymerization reactors for tailored molecular weight distribution

This work presents a comprehensive steady‐state model of the high‐pressure ethylene polymerization in a tubular reactor able to calculate the complete molecular weight distribution (MWD). For this purpose, the probability generating function technique is employed. The model is included in an optimization framework, which is used to determine optimal reactor designs and operating conditions for producing a polymer with tailored MWD. Two application examples are presented. The first one involves maximization of conversion to obtain a given MWD, typical of industrial operation. Excellent agreement between the resulting MWD and the target one is achieved with a conversion about 5% higher than the ones commonly reported for this type of reactor. The second example consists in finding the design and operating conditions necessary to produce a polymer with a bimodal MWD. The optimal design for this case involves a split of the initiator, monomer, and modifier feeds between the main stream and two lateral injections. To the best of our knowledge, this is the first work dealing with the optimization of this process in which a tailored shape for the MWD is included. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

TH-1L高效气相法浆液催化剂催化乙烯聚合

开发了一种新型高效气相法浆液聚合催化剂TH-1L,研究了该催化剂的制备工艺及其在气相法中试装置上的催化聚合。TH-1L不仅催化性能优良,而且聚合过程中避免使用复杂昂贵的在线还原系统,可降低生产成本,适于工业化生产。     

Polyaniline‐supported acid catalyst: Esterification of cinnamic acid with alcohols

Polyaniline‐supported acid salts such as polyaniline‐hydrochloride, polyaniline‐sulfate, and polyaniline‐nitrate were prepared by oxidation of aniline using benzoyl peroxide and ammonium persulfate as oxidizing agents. Polyaniline salts were used as catalysts in the esterification of cinnamic acid with alcohols. Polyaniline‐sulfate salt was found to be the best catalyst for the esterification of cinnamic acid. The reusability, handling, and recovery of the catalyst were found to be good. The yield of the ester depended on the type of the polyaniline salt, amount of the catalyst, amount of alcohol, and both the time and the temperature of the reaction. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1584–1590, 2005     

Heterogeneous catalyst mixtures for the polymerization of ethylene

Heterogeneous cocatalysts, catalysts, and catalyst mixtures for the polymerization of ethylene were prepared applying “fumed silica” and mesoporous MCM-41 support materials and zirconocene dichloride, titanocene dichloride, and a bis(arylimino)pyridine iron complex as catalyst precursors. The catalyst mixtures produced polyethylenes which exhibit the properties of two single polymers. Polyethylenes with the desired bimodal molecular weight distributions could be obtained with a series of ternary Zr/Ti/Fe catalysts. The ability of the zirconium and titanium species to copolymerize short-chain 1-olefins produced by the iron centers (“in situ” copolymerization) is useful for the production of copolymers from only one monomer (ethylene).     

尤尼帕工艺用钒系催化剂的开发

钒系催化剂是尤尼帕 PE 工艺第三代催化剂,在钒系催化剂作用下,可以生产出具有宽分子量分布及双峰分子量分布的聚乙烯树脂。当加入分子量调节剂,如含氧、含硅或含磷化合物时,树脂的分子量可以由宽变窄,密度也可在一广阔的范围内变化。本文综述了联合碳化物公司钒系催化剂的最新发展,其配方及在烯烃聚合中的应用.     

Dimethylsilylbis(1‐indenyl) zirconium dichloride/methylaluminoxane catalyst supported on nanosized silica for propylene polymerization

A dimethylsilylene‐bridged metallocene complex, (CH₃)₂Si(Ind)₂ZrCl₂, was supported on a nanosized silica particle, whose surface area was mostly external. The resulting catalyst was used to catalyze the polymerization of propylene to polypropylene. Under identical reaction conditions, a nanosized catalyst exhibited much better polymerization activity than a microsized catalyst. At the optimum polymerization temperature of 55°C, the former had 80% higher activity than the latter. In addition, the nanosized catalyst produced a polymer with a greater molecular weight, a narrower molecular weight distribution, and a higher melting point in comparison with the microsized catalyst. The nanosized catalyst's superiority was ascribed to the higher monomer concentration at its external active sites (which were free from internal diffusion resistance) and was also attributed to its much larger surface area. Electron microscopy results showed that the nanosized catalyst produced polymer particles of similar sizes and shapes, indicating that each nanosized catalyst particle had uniform polymerization activity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

茂锆金属催化剂催化乙烯聚合研究

主要考察了含锆的茂金属催化剂中催化乙烯反应条件优化研究,在最优条件下催化聚合反应所得的产物与吉林石化公司聚乙烯厂聚乙烯产品进行分析对比.对茂锆金属催化剂催化乙烯聚合反应条件研究表明,适宜的助催化剂[Al]与主催化剂[Cat]的摩尔比在1 500左右,适宜的主催化剂浓度在1.5×10-4 mol/L左右,最佳聚合温度60℃,此时催化剂的活性可达到106 gPE/(molCat·h).从物理性能、热性能、相对支化度、相对分子质量及其分布分析可知,制备出的负载茂锆金属催化剂在最优反应条件下催化乙烯聚合所得的产物与吉林石化公司聚乙烯产品性质基本一致,符合产品的指标,支链分布均匀,分子量分布更窄.同时对茂锆金属催化剂主、助催化剂催化乙烯聚合的作用和机理进行了探讨.