复合载体负载型催化剂制备UHMWPE动力学行为

研究了采用氯化镁和硅胶复合载体负载Mg-Ti型催化剂催化乙烯聚合的性能和动力学行为,考察了聚合温度、时间、压力、助催化剂对催化剂性能的影响,以及链转移反应在其中所起到的作用。结果表明,温度对聚乙烯的相对分子质量影响最大,乙烯分压和聚合温度对催化剂的活性有明显影响,存在一个使催化剂高活性的最适宜铝钛物质的量之比。     

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     

Kinetic study of olefin polymerization with a supported metallocene catalyst. III. Ethylene homopolymerization in slurry

A kinetic study of ethylene homopolymerization is conducted with a supported unbridged metallocene catalyst in a slurry reactor. The effects of operational parameters such as the reaction temperature and pressure on kinetics are investigated. The kinetic parameters which have been determined for this particular catalyst from previous gas phase studies are used in a slurry reactor model to predict the polymerization behavior under various reaction conditions. The experimental data compare favorably with the predictions from this model. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2901–2917, 2001     

Late Transition Metal Catalyst Based on Cobalt for Polymerization of Ethylene

The late transition metal catalyst of [2,6-diacethylpyridinebis(2,6-diisopropylphenylimine)]cobalt(II) dichloride was prepared under controlled conditions and used for polymerization of ethylene. Methylaluminoxane (MAO) and triisobuthylaluminum (TIBA) were used as a cocatalyst and a scavenger, respectively. The highest activity of the catalyst was obtained at about 30°C; the activity decreased with increasing temperature. At polymerization temperatures higher than 50°C not only was a sharp decrease in the activity observed but also low molecular weight polyethylene product that was oily in appearance was obtained. The polymerization activity increased with increasing both of the monomer pressure and [MAO]:[Co] ratio. However, fouling of the reactor was strongly increased with increasing both of the monomer pressure and the amount of MAO used for the homogeneous polymerization. Hydrogen was used as the chain transfer. The activity of the catalyst and the viscosity average molecular weight (M_v) of the polymer obtained were not sensitive to hydrogen concentration. However, the viscosity average molecular weight of the polymer decreased with the monomer pressure. The (M_v), the melting point, and the crystallinity of the resulting polymer at the monomer pressure of 1 bar and polymerization temperature of 20°C were 1.2 × 10⁵, 133°C, and 67%, respectively. Heterogeneous polymerization of ethylene using the catalyst and the MAO/SiO₂ improved morphology of the resulting polymer; however, the activity of the catalyst was also decreased. Fouling of the reactor was eliminated using the supported catalyst system.     

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

The 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     

The influence of aluminum alkyls on the polymerization of ethylene with SiO2/MgCl2-supported TiCl4 catalysts

The influence of different aluminum alkyls (diethylaluminum chloride, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum and isoprenylaluminum) on the ethylene polymerization activity of a laboratory prepared high-activity SiO₂/MgCl₂-supported TiCl₄ catalyst has been investigated. A slurry reactor (decane diluent) was used for measuring rates of polymerization. The average molar mass, the breadth of the molar mass distribution, the polymerization activity, and the shapes of the activity-time profiles, were strongly dependent on the nature of the aluminum alkyl. For several of the cocatalysts used, the catalytic activity approached a constant value after a certain amount of time under reaction conditions. In this constant activity region, a first-order dependence of the polymerization rate on the monomer concentration was found for all of the systems examined. However, the activation energy of the polymerization reaction was found to depend strongly on the type of cocatalyst which was used.     

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.     

Einfluß des stofftransportes bei der polymerisation von äthylen und 1-okten mit Ziegler-Katalysatoren

The polymerization of ethylene and 1-octene with supported Ziegler-catalysts was investigated with regard to the influence of mass transport of monomers on the kinetics, molecular weight and molecular weight distribution. In the case of the polymerization of ethylene, it was found that for certain conditions of reaction the mass transport of ethylene can influence the kinetics of polymerization respectively the catalyst efficiency strongly. The molecular weight and molecular weight distribution of the polyethylene formed are practically not affected by the conversion as well as particle size of catalyst and polymer. The molecular weight distribution however is affected by the concentration of the catalyst. The polymerization process of ethylene in suspension is distinguished by chemical and physical processes. A continuous chain initiation, for example, is based on the continuous reduction of the catalyst particles to small pieces during the course of polymerization. An apparent chain termination respectively catalyst deactivation can occur when catalyst particles are encapsulated within the growing polymer particles. The polymerization of 1 -octene for similar conditions of reaction gave polymers which were solved completely in the system used. The molecular weight distribution of the polymer formed nevertheless was very broad. This indicates that the mass transport of the monomers through the solid phase of polymer cannot be the main reason for the broad molecular weight distribution of the polymers which are produced by heterogeneous Ziegler-catalysts in suspension.     

铬钒双金属催化剂乙烯聚合反应动力学模型化

双金属催化剂可催化乙烯聚合在单个反应器内制备双峰聚乙烯。考察了新型Cr-iV双金属催化剂及相应的单金属S-2和iV催化剂在不同实验条件下的乙烯均聚反应动力学。通过对Cr-iV催化剂聚合产物分子量分布曲线的解析发现铬钒活性中心之间存在相互作用,铬中心活性受到抑制,钒中心活性得到增强;聚合温度基本不改变铬钒活性中心生成的聚合物的质量分数。采用简化的单中心乙烯均聚动力学模型分别描述铬钒双活性中心的动力学行为,结合双金属催化剂的聚合实验结果确定了各个活性中心的动力学参数。相比单金属催化剂,Cr-iV催化剂中铬活性中心链增长速率常数降低,说明其聚合活性降低;而钒活性中心链失活速率常数减小,稳定性增强,活性提高。     

Poly(1‐octene) synthesis using high performance supported titanium catalysts

Poly(1‐octene) was synthesized by polymerization of 1‐octene using high performance MgCl₂‐supported TiCl₄ in combination with triethyl aluminum (TEAl) as cocatalyst in n‐hexane for 2 h. Two catalysts, C₁ (diester catalyst) having di‐isobutyl phthalate as internal donor and C₂ (monoester catalyst) having ethyl benzoate as internal donor were utilized for the atmospheric polymerizations to evaluate the influence of structurally different internal donors on the productivity, rate of polymerization and molecular weight profiles. The kinetic profile assessed in terms of variation of reaction parameters like temperature, cocatalyst to catalyst molar ratio and monomer concentration was found to be dependent on them. From these kinetic analyses, optimize conditions for polymerizations of 1‐octene using diester as well as monoester catalyst were elucidated. The difference in the performance of diester and monoester catalyst system can be explained in terms of stability of active titanium species and chain transfer process. NMR spectroscopy of synthesized poly(1‐octene) indicate predominantly isotactic nature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Ethylene polymerization with iron‐based diimine catalyst supported on MCM‐41

A mesoporous molecular sieve MCM‐41 supported iron‐based diimine catalyst ( MC ) was prepared for the first time. The kinetic behavior of ethylene polymerization with MC was studied. The effects of Al/Fe molar ratio and various cocatalysts on the catalytic activity and properties of the polyethylene obtained were investigated. The results showed that good catalytic activities can be reached with cocatalyst methylaluminoxane (MAO) and triethylaluminium (TEA). Ethylene polymerization with MC gave polymers with higher molecular weight, melting temperature and onset temperatures of decomposition (T_onset) and better morphology than those obtained with the corresponding homogeneous catalyst. Copyright © 2004 Society of Chemical Industry     

Geometrically Constrained Polymerization of Styrene Over Heterogeneous Catalyst Layer in Silica Nanotube Reactors

Styrene has been polymerized to syndiotactic polystyrene (sPS) over a layer of heterogeneous Cp*Ti(OCH₃)₃/MAO catalyst immobilized onto the surfaces of silica nanotube reactor (SNTR) arrays of 60–200 nm in diameter. The polymer produced in the SNTR arrays has been found to have the molecular weights much larger than the polymers synthesized by a liquid slurry polymerization over silica-supported catalysts. A dynamic reactor model that consists of diffusion and reaction terms has been derived and solved to quantify the kinetics of styrene polymerization in a single nanotube reactor. The two-site kinetic model applied to the silica nanotube reactor model shows that the experimentally observed high polymer molecular weight can be fitted if the chain transfer rate constants for monomer and β-hydride elimination are reduced significantly. The simulation results suggest that the presence of dense crystalline sPS nanofibrils filling the nanotubes constrain the molecular movements of polymer chain ends in the proximity of catalyst sites to limit the chain transfer reactions. POLYM. ENG. SCI., 60:700–709, 2020. © 2020 Society of Plastics Engineers     

Indirect Synthesis of Bis(2‐PhInd)ZrCl2 Metallocene Catalyst,Kinetic Study and Modeling of Ethylene Polymerization

Bis(2‐phenylindenyl)zirconium dichloride (bis(2‐PhInd)ZrCl₂) catalyst was synthesized via the preparation of bis(2‐phenylindenyl)zirconium dimethyl (bis(2‐PhInd)ZrMe₂) followed by chlorination to obtain the catalyst. Performance of the catalyst for ethylene polymerization and its kinetic behavior were investigated. Activity of the catalyst increased as the [Al]:[Zr] molar ratio increased to 2333:1, followed by reduction at higher ratios. The maximum activity of the catalyst was obtained at a polymerization temperature of 60 °C. The rate‐time profile of the reaction was of a decay type under all conditions. A general kinetic scheme was modified by considering a reversible reaction of latent site formation, and used to predict dynamic polymerization rate and viscosity average molecular weight of the resulting polymer. Kinetic constants were estimated by the Nelder‐Mead numerical optimization algorithm. It was shown that any deviation from the general kinetic behavior can be captured by the addition of the reversible reaction of latent site formation. Simulation results were in satisfactory agreement with experimental data.     

Poly(propylene‐co‐ethylene) produced with a conventional and a self‐supported ziegler–natta catalyst: Effect of ethylene and hydrogen concentration on activity and polymer structure

A novel self‐supported emulsion‐based catalyst and a conventional MgCl₂‐supported Ziegler–Natta catalyst were used in the copolymerization of propylene and ethylene under industrial conditions using triethyl aluminium as cocatalyst and dicyclopentyl dimethoxy silane as external donor. The effects of the concentration of ethylene and hydrogen on the polymerization behaviors and polymer properties were investigated. The combined effect of both ethylene and hydrogen increased the relative activity of the novel catalyst more than for the conventional catalyst. This trend was consistent with our earlier observed higher degree of dormancy, due to 2,1 insertions, found with the novel catalyst. More importantly, the work has uncovered that the self‐supported catalyst incorporates ethylene in a more random fashion and produces copolymers with relatively narrow molecular weight distribution (MWD). These results in combination with polymer microstructure studies using Fourier transform infrared spectroscopy, ¹³C‐NMR spectroscopy, and differential scanning calorimetry all indicated that the novel catalyst has a narrower distribution of active site types than the conventional reference catalyst. The narrow composition of active site structures, the narrow MWD, and the random incorporation of ethylene into the polymer chain indicated that the emulsion‐based catalyst possesses features that to a certain degree tend to be more indicative for a single‐site‐like catalyst structure and behavior. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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     

Polymerization of ethylene by (α‐Diimine) nickel catalyst and statistical analysis of the effects of reaction conditions

This article regards the ethylene polymerization catalyzed by a nickel catalyst and activated by ethylaluminum sesquichloride (EASC). The effects of the reaction conditions [polymerization temperature, cocatalyst (EASC) concentration, and ethylene concentration] on the average molecular weights of the final polymers and reaction yields were evaluated with the help of empirical statistical models. It is shown that reaction temperature and cocatalyst (EASC) concentration exert the most important effects on average molecular weights and catalyst activity. The polydispersities of the obtained polyethylenes are larger than the polydispersities of polyethylenes obtained with typical Brookhart catalysts. The analysis of polymer branching frequencies shows new types of short branching and significant amounts of long branches, which may explain the relatively large polydispersities of the obtained polymer samples. POLYM. ENG. SCI., 50:1797–1808, 2010. © 2010 Society of Plastics Engineers     

Copolymers of ethylene with butene-1 and long chain α-olefins. II. Dodecene-1 as long chain α-olefin

Ethylene/dodecene-1 and ethylene/butene-1/dodecene-1 copolymers were prepared and their polymerization reaction in heptane slurry was studied. The Ziegler–Natta catalyst was aluminium-activated TiCl₃, and the cocatalyst was triethylaluminium. The dodecene-1 contents in the ethylene/dodecene-1 copolymers were less than 3 wt %. The dodecene-1 contents in terpolymers of ethylene, butene-1, and dodecene-1 ranged up to 10 wt %. The dependence of basic properties on composition of terpolymers was investigated.     

Polymerization of olefins through heterogeneous catalysis. XVII. Experimental study and model interpretation of some aspects of olefin polymerization over a TiCl4/MgCl2 catalyst

Using a high-activity MgCl₂-supported TiCl₄ catalyst, kinetic studies of ethylene and propylene polymerization are conducted in a semi-batch gas phase stirred-bed reactor system. Based on the experimental observations obtained from this study and others in the literature, simple kinetic mechanisms are proposed to explain the data. This model considers both the site formation from the interaction of catalyst and cocatalyst as well as the participation of monomers during site activation. By using this model together with parameters estimated from various sources, some aspects of kinetic behavior have been successfully predicted. These include the rate enhancement introduced by α-olefins, the effect of the Al/Ti ratio on kinetic features such as catalyst activity and decay rate, as well as the different reaction orders observed for various monomers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1037–1052, 1997     

FI Zr-type catalysts for ethylene polymerization

Two FI-type catalysts of Bis[N-(3,5-dicumylsalicylidene)-naphthylaminato]zirconium(IV) dichloride (catalyst (a)) and Bis[N-(3,5-dicumylsalicylidene)-anthracylaminato]zirconium(IV) dichloride (catalyst (b)) were prepared and used for ethylene polymerization comparatively. Methylaluminoxane (MAO) was used as cocatalyst. Polymerization reactions of ethylene using the prepared catalysts at the different conditions of polymerization were carried out. Plurality of the fused aromatic rings on the N atom of the imine in the catalyst structure affected the polymerization activity and molecular weight of the resulting polymer as well. Productivity of the prepared catalysts increased with the addition of [Al]/[Zr] molar ratio. The highest activity was observed at about 35–40 °C for the catalysts. The catalyst (b) produced higher viscosity average molecular weight (M_v) of the obtained polyethylene, while generally the activity of the catalyst (a) was higher than the catalyst (b). Similar behavior was observed for the polymerization carried out at the monomer pressure of 2 to 6 bars using the catalysts. The higher the pressure the more activity of the catalysts obtained, in the range studied. Crystallinity and melting point of the obtained polymer were between 55–65% and 120–135 °C respectively. Higher pressure increased both the crystallinity and the M_v values of the resulting polymer. The polymerization was carried out using different amounts of hydrogen. Higher amount of hydrogen could increase the activity of the catalysts. A linear dependence between the polymerization time and the molar weight was observed, however the polydispersity was broadened with the time.