丁二烯气相聚合研究进展

介绍了目前国外丁二烯气相聚合的研究情况,包括丁二烯气相聚合用催化剂,聚合颗粒增长及模型化,聚合动力学等方面的最新进展。     

球形TiCl4/MgCl2催化剂引发丙烯气相聚合动力学

采用微机在线控制的半连续烯烃聚合反应器,在加压条件下进行了球形TiCl₄/MgC_l2催化剂催化的丙烯气相聚合,测定了单体瞬时聚合速率等重要的动力学数据,考察了不同聚合条件对聚合动力学的影响,并用Flory-Huggins方程估算了聚合物非晶区中的单体浓度C_m.研究表明聚合速率与C_m成正比;丙烯聚合速率在反应一开始就迅速衰减,之后是缓慢的衰减.提出了一个n级衰减的丙烯气相聚合动力学模型,根据实验数据拟合得到了模型的各个参数,其中活性中心的衰减级数为2.5,气相聚合的表观增长活化能为77.1 kJ•mol^-1.用该模型可以较好地模拟加压条件下的丙烯气相聚合动力学行为.     

稀土钕催化剂上丁二烯气相聚合过程研究

在２升的卧式双轴自清洁型搅拌床反应器对负载型稀土催化剂催化的丁二烯气相聚合过程进行了实验研究。考察反应温度和压力等因素对聚合速率和分子量及其分布的影响。确定了合适的反应条件并获得了有关的动力学参数。     

丁二烯气相聚合过程中的单体吸附效应和本征动力学模型

采用负载型稀土催化剂 ,在搅拌床反应器内进行丁二烯气相聚合动力学的研究 .考察了单体在聚合物小粒子中的吸附效应和单体压力与温度对聚合速率影响 ,在此基础上 ,提出了本体系的本征动力学模型     

球型催化剂用于乙烯聚合性能的研究

考察了不同Al/Fi和聚合温度下的催化剂聚合动力学行为.Al/Ti 对聚合速率的影响用keii提出的Langmiur-Hinshelwood模型进行关联,活性中心的衰减为一级衰减.不同温度对动力学的影响符合Arrhenius方程.     

镍催化体系丁二烯溶液聚合行为

以镍系催化丁二烯溶液聚合制得顺式－１，４－聚丁二烯的小试及工业生产为基础，对丁二烯溶液聚合的宏观动力学行为及工业生产中出现的问题进行了研究。结果表明，当单体转化率大于３０％时，聚合偏离动力学一级反应；终止釜胶样辊压干燥是导致门尼值升高的主要原因。     

硅胶负载型烯烃聚合催化剂的研究 Ⅴ 化学活化对催化剂相结构和聚合动力学的影响

用ＸＲＤ手段对硅胶负载型气相聚乙烯催化剂的相结构受化学活化的影响进行了研究,在一定范围内三乙基铝的加入量对热活化硅胶载体相结构影响很小,所制备的催化剂仍为非晶型,当三乙基铝的加入量超过脱除热活化硅胶表面剩余羟基所需量较大时,催化剂表面会形成微量的络合结晶物,这些微量结晶物使催化剂的聚合效率明显降低。聚合动力学实验表明,没有经过化学活化的催化剂聚合动力学为快速衰减型且聚合活性很低,只有通过使用适当三乙基铝配比的化学活化后才能获得动力学平稳的高效催化剂     

硅胶负载型烯烃聚合催化剂的研究V 化学活化对催化剂相结构和聚合动力学的影响

用XRD手段对硅胶负载型气相聚乙烯催化剂的相结构受化学活化的影响进行了研究,在一定范围内三乙基铝的加入量对热活化硅胶载体相结构影响很小,所制备的催化剂仍为非晶型,当三乙基铝的加入量超过脱除热活化硅胶表面剩余羟基所需量较大时,催化剂表面会形成微量的络合结晶物,这些微量结晶物使催化剂的聚合效率明显降低.聚合动力学实验表明,没有经过化学活化的催化剂聚合动力学为快速衰减型且聚合活性很低,只有通过使用适当三乙基铝配比的化学活化后才能获得动力学平稳的高效催化剂.     

高效乙烯聚合催化剂的制备Ⅱ.催化剂的聚合性能

研究了以微球硅胶负载新型含镁络合物为载体制备的乙烯聚合催化剂的动力学行为及共聚性能,考察了聚乙烯颗粒的微观结构,结果表明:该聚合反应动力学行为呈“上升-衰减”型,聚乙烯颗粒呈微球状,复现了催化剂的形貌,该催化剂具有良好的共聚性能。     

铬/钒双金属催化剂催化乙烯气相聚合

在实验室小试气相聚合釜中对铬/钒双金属催化剂进行乙烯聚合评价,考察了不同聚合温度和压力时催化剂的性能,研究了不同条件下催化剂的动力学行为,并将其聚合动力学曲线与用工业铬系催化剂的进行了比较。结果表明:随着聚合温度升高,用铬/钒双金属催化剂制备的聚乙烯的相对分子质量减小,熔体流动速率增大,在所研究聚合温度范围内铬/钒双金属催化剂对温度更敏感;随着聚合压力增大,催化剂活性显著提高,聚乙烯相对分子质量增加;聚合动力学曲线与铬系催化剂不同,聚合反应速率先增大再降低最后逐渐达到平稳。     

Studies on Macro-kinetics of Gas Phase Polymerization of Butadiene with Rare-earth Catalyst

The study of the kinetics of gas phase polymerization of butadiene with heterogeneous catalyst based on neodymium (Nd) was carried out. The effects of reaction temperature, reaction pressure, dispersing medium, and types of catalyst on kinetics of polymerization were investigated. A kinetic model with two kinds of active sites was proposed. The results show that the effects of the reaction temperature and the types of dispersing medium and catalyst on the kinetic performance of polymerization are significant, and that the combined model of first and second order decay of active site of catalyst can be used to describe the phenomena.     

Studies on the polymerization of propylene using high activity ziegler-natta catalysts. 1: Kinetic models for rate decay in ziegler-natta polymerization

Kinetic models for describing the time dependence of the polymerization rate and active centre concentration for high activity Ziegler-Natta catalyst systems are discussed. It is demonstrated that the decay in the rate of polymerization and in the concentration of active centres with time for the polymerization of propylene with the heterogeneous catalyst system MgCl₂/EB/TiCl₄? Al(i-Bu)₃/EB can be represented better by a modified multi-centre first order decay model than by the other models which are considered.     

The role of diffusion in the Ziegler polymerization of ethylene

A theoretical and experimental study has been made of the polymerization of ethylene in a slurry reactor using a highly active Ziegler catalyst in the presence of hydrogen. A model of the polymerization system has been set up in which polymerization is assumed to proceed with encapsulation of catalyst subparticles. Allowance is made for an experimentally observed first-order decay in intrinsic catalyst activity. The theoretical prediction of the model for the monomer absorption rate behavior and the molecular weight characteristics of the polymers formed are in agreement with experimental findings. Experimental evidence is presented that in the earliest moments of a polymerization significant amounts of polymer are formed with molecular weights 100 times those in the balance of the polymerization. It is concluded that in this system the polymerization is diffusion controlled throughout the major part of the catalyst lifetime. This diffusion phenomenon, together with the gradual loss of active sites, is of vital importance in determining the molecular weight and molecular weight distribution of the polyethylene product.     

Kinetics of slurry phase polymerization of styrene to syndiotactic polystyrene with pentamethyl cyclopentadienyl titanium trimethoxide and methyl aluminoxane. I. Reaction rate analysis

The kinetics of syndiospecific slurry polymerization of styrene in heptane has been investigated with pentamethyl cyclopentadienyl titanium trimethoxide [Cp??Ti(OMe)₃] catalyst with methylalmuninoxane. The experimental studies at different styrene/heptane ratios indicate that no global gelation occurs at low styrene/heptane ratios even at high styrene conversion. The effective propagation rate constant tends to decrease as polymerization rate is increased at higher initial styrene concentrations. To analyze the effect of catalyst deactivation, a novel three‐stage polymerization experiment has been designed and carried out where monomer is added during the polymerization. The experimental results show that the catalyst activity is very high at the beginning of polymerization but it decreases significantly as catalyst sites are occluded in the solid phase. We also observe that the catalyst remains active for more than 3 h and the rate decay is not solely due to intrinsic catalyst deactivation. Our experimental data suggests that physical transport effects cause the decay in the polymerization rate. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2132–2137, 2003     

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。     

Interaction of α-TiCl3 with organoaluminium compounds and its correlation with propylene polymerization

Summary The characterization of polymer system by means of interaction reaction between the catalyst components of a Ziegler-Natta stereospecific system formed by TiCl₃ and AlEt₃ in heptane was carried out. The experimental results show that the formation and decay of the active centers are interdependent. The interaction of the catalyst components, which causes a destruction of the solid phase, influences the rate of polymerization.     

Catalyst fragmentation during propylene polymerization: Part I. The effects of grain size and structure

Fragmentation of support/catalyst particles during propylene polymerization in the gas phase is analyzed via a mathematical model including energy and mass transfer with chemical reaction processes. The rupture phenomenon is considered specifically by the model, and evaluated as it proceeds in time, Two different regions are recognized in the polymerizing particle at fragmentation time: an inner core resembling the original solid support/catalyst structure, and an external set of layers where most of the polymerization occurs. Model predictions concerning the effects of fragmentation on polymerization are discussed. The influence of different degrees of fragmentation on thermal runaways and monomer availability at active sites located inside the support/catalyst/polymer complex is shown. Monomer concentration profiles inside the growing particles are explained in terms of the combined fragmentation-polymerization interaction. Results show a strong influence of catalyst structure on critical phenomena during early polymerization stages, and suggest the possibility of controlling critical parameters via the definition of fragment structure at catalyst preparation time.     

Modeling of the propylene polymerization catalyzed by single‐/multi‐active site catalyst: A Monte Carlo study

In the present study, a model is established to describe the propylene polymerization kinetics catalyzed by the typical catalysts with single‐/multi‐active site type in a liquid phase stirred‐tank reactor using the Monte Carlo simulation method, regardless of the mass and heat diffusion effects within the polymer particles. Many kinetic data, including polypropylene yield, concentration transformation of catalyst active sites, number–average molecular weight, etc., are obtained by the model. The simulated kinetic results are found to be in agreement with the reference ones obtained in a population balance model. Furthermore, the comparisons of the kinetic data between the polymerization catalyzed by the catalyst with single‐active site type (typically silica‐supported metallocene) and the catalyst with multi‐active site type (typically MgCl₂‐supported Ziegler‐Natta catalyst) have been studied using the model. Especially, the effects of hydrogen on the polymerization are studied using the model. The studied results show that the theory of catalyst active site can be used to explain the different propylene polymerization kinetics catalyzed by the typical catalyst with single‐/multi‐active site type. In addition, the role of hydrogen in the propylene polymerization needs to be emphasized. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Kinetic study of a highly active MgCl2‐supported Ziegler–Natta catalyst in liquid pool propylene polymerization. II. The influence of alkyl aluminum and alkoxysilane on catalyst activation and deactivation

The influence of alkyl aluminum and alkoxysilane on the kinetics in liquid pool propylene batch polymerization was investigated with a highly active Ziegler–Natta catalyst system that consisted of MgCl₂/TiCl₄/diester–alkoxysilane/AlR₃. In this study, diethyl phthalate and t‐BuEtSi(OMe)₂ were used as a diester and an alkoxysilane, respectively. The catalyst activity depended on the concentration of the alkyl aluminum when it came into contact with the catalyst. In addition, alkoxysilane as an external donor had a role in activating the catalyst. With respect to activity decay, the overreduction of Ti did not seem to be the cause. Instead, the decay rate decreased with an increasing alkoxysilane/catalyst ratio. This implied that activity decay was caused by the formation of dormant sites after 2,1‐misinsertion of propylene. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2669–2679, 2002