气相流化床聚乙烯颗粒粒径分布模型的研究

气相法流化床聚乙烯生产过程中,聚乙烯颗粒粒径分布影响聚合速率、脱挥速率、后处理工序生产成本和最终的聚乙烯物性。为预测流化床中聚乙烯的粒径分布,考察各操作变量和动力学参数对粒径分布的影响,运用了质量衡算的方法,在综合分析聚合过程中聚乙烯颗粒的生长、磨损和扬析等行为的基础上,建立了稳态操作时聚乙烯颗粒粒径分布预测模型。模型计算结果表明,当单一粒径催化剂进料时,随着催化剂粒径或是操作气速的增大,聚乙烯粒径分布向大粒径方向偏移,且分布变宽;相比于操作气速,催化剂粒径作用更为显著。同时发现,床层压力和温度对聚乙烯粒径分布的影响很小。在催化剂粒径有分布的情况下,不同粒径催化剂的质量比不但影响树脂的平均粒径,而且也影响树脂的粒径分布曲线,并在一定的配比下会出现双峰颗粒粒径分布曲线。最后,对某聚乙烯厂家的流化床反应器的聚乙烯颗粒粒径分布进行了模拟计算,计算结果与实验数据基本一致,说明该模型较好反映了气相流化床反应器的反应历程和规律,具有良好的工业应用前景。     

磷酸酯钕系催化剂合成窄分子量分布高顺式聚异戊二烯

以2-乙基己基磷酸单2-乙基己基酯钕盐(简称Nd)/氢化二异丁基铝(简称Al)/一氯二乙基铝(简称Cl)为催化剂,对异戊二烯(Ip)进行聚合,考察了催化剂配制条件和聚合温度对聚合的影响,并通过傅里叶变换红外光谱和核磁共振表征了聚合物的微观结构。结果表明,催化剂配制过程中,c(Ip)/c(Nd)越大,陈化温度越高,聚合物的分子量分布越窄;陈化温度越高,陈化时间越长,聚合物的数均分子量(M珚n)越大;c(Al)/c(Nd)越大,聚合物的M珚n越小,分子量分布越宽;聚合温度越高,聚合物的M珚n也越小,但分子量分布基本不变,其值为2.0～2.2;聚合物的顺式-1,4-结构摩尔分数基本不受反应条件的影响,为95.5%～97.1%。     

用混合配体稀土催化剂制备窄分子量分布高顺式聚丁二烯

以混合配体磷酸酯钕(简称Nd)/氢化二异丁基铝(简称Al)/二甲基二氯硅烷(简称Cl)催化体系催化丁二烯聚合,该催化剂在n(Al)/n(Nd)为10时即有高活性,所得聚合物具有窄分子量分布(分子量分布指数小于2.0)和高顺式-1,4-结构立构规整性(摩尔分数99%左右)。考察了n(Al)/n(Nd)、n(Cl)/n(Nd)、Cl种类、陈化时间及聚合温度和时间等对聚合的影响,结果表明,催化活性随着n(Al)/n(Nd)和n(Cl)/n(Nd)的增大以及陈化时间的延长而提高,同时聚合物的数均分子量普遍下降,分子量分布变宽;聚合物的顺式-1,4-结构含量基本不受反应条件的影响,均为摩尔分数99%左右,表明所形成的活性中心具有较高的稳定性。     

聚合条件对稀土顺丁橡胶分子结构的影响

研究了丁二烯在三异丁基铝-环烷酸镨钕富集物—氯二异丁基铝催化体系中的聚合。考察了各种聚合条件对聚合物分子量及其分布的影响。通过调整催化剂用量、单体浓度、聚合温度等因素,可使聚合物的特性粘度在3—10之间变化,而且发现催化剂浓度及单体浓度均与聚合物分子量呈线性关系。     

超临界CO2法制备超细HMX颗粒

考察了预膨胀压力、HMX丙酮溶液初始浓度、取样停留时间及其他因素对制备HMX超细微粒粒度和晶体性质的影响.制备的超细HMX微粒平均粒径在350 nm以下,一部分微粒粒度小于100 nm.结果表明,预膨胀压力对HMX颗粒尺寸的影响较大,压力增加,HMX平均粒度变小,粒度分布变窄;HMX丙酮溶液初始浓度对HMX的粒度和粒度分布有很大影响,初始浓度越小平均粒径就变小,粒度分布变窄.停留时间及喷嘴尺寸对颗粒粒度、粒度分布及其形貌都有不同程度的影响.     

NiBR分子量及其分布的调节

对影响NiBR分子量及其分布的主要因素的研究表明，采用Al-Ni二元陈化稀B单加方式时，改变进料丁二烯－汽油的温度，可在一定范围内有效地调节聚合物的分子量分布；提高聚合反应温度，聚合物分子量有所3降低；而改变体系中两组催化剂的摩尔比，是在较大范围内灵活调节聚合物分子量的最有效方法。     

Synthesis of high cis-1,4 polyisoprene having narrow molecular weight distribution with Nd ( P507 ) 3/AIH (i-Bu) 2/AIEt2 Cl catalyst

以2-乙基己基磷酸单2-乙基乙基酯钕盐(简称Nd)/氢化二异丁基铝(简称Al)/一氯二乙基铝(简称Cl)为催化剂,对异戊二烯(Ip)进行聚合,考察了催化剂配制条件和聚合温度对聚合的影响,并通过傅里叶变换红外光谱和核磁共振表征了聚合物的微观结构.结果表明,催化剂配制过程中,c(Ip)/c(Nd)越大,陈化温度越高,聚合物的分子量分布越窄;陈化温度越高,陈化时间越长,聚合物的数均分子量((-M)n)越大;c(Al)/c(Nd)越大,聚合物的(M-)n越小,分子量分布越宽;聚合温度越高,聚合物的(M-)n也越小,但分子量分布基本不变,其值为2.0～2.2;聚合物的顺式-1,4-结构摩尔分数基本不受反应条件的影响,为95.5％ ～97.1％.     

气相法聚乙烯BCG-Ⅱ型催化剂的开发和应用

对气相法聚乙烯BCG-Ⅱ型催化剂的组成、粒径分布及催化剂的淤浆聚合性能进行了研究。研究结果表明，BCG—Ⅱ型催化剂的活性较高，聚合物堆密度适中，应用在Unipol乙烯气相聚合工艺装置上操作良好，所生产的树脂颗粒均匀。干爽且流动性好，产品质量合格、稳定。     

从分子量分布探討均相及非均相丁二烯顺式-1,4聚合的机理

本工作以逐步沉淀法测定了在均相（Et_2AlCl-CoCl_2·4C_5H_5N）及非均相（i-Bu_3Al-TiI_4）Ziegler型催化剂的作用下,丁二烯在各种条件下进行顺式-1,4聚合的分子量分布。结果指出,不论均相或非均相催化聚合得到的分子量分布都比较窄。对于均相体系,升高聚合温度、降低单体浓度、添加链转移剂（如乙硫醚、N-苯基-β-萘胺、庚烷）、减少催化剂钴的浓度和增加Al/Co比,均能使聚合物的分子量分布变窄;而对于非均相体系,则降低聚合温度和减少Al/Ti比均能增加分子量的均一性;单体浓度和催化剂老化对分子量分布无显著影响。 非均相聚合的分子量分布比均相聚合的更窄,前者的微分分布曲线的高峰偏于高分子量部分,而后者的偏于低分子量部分。这可能是由于非均相聚合的链终止速度依赖于链长,而均相聚合的链终止速度与链长无关。     

磷酸酯钕催化体系对异戊二烯聚合的影响

以Nd（P204）3（简称Nd）/Al（i-Bu）2H（简称Al）/Al（i-Bu）2Cl（简称Cl）为催化剂,对异戊二烯（Ip）进行聚合,考察了Ip聚合的影响因素,并通过傅里叶变换红外光谱表征了聚合物的微观结构。结果表明,随着Al/Nd（摩尔比）的增大,聚合收率增大,聚合物的数均分子量减小,分子量分布变宽,顺式-1,4-结构摩尔分数下降,但均在98%以上;随着Cl/Nd（摩尔比）的增大,聚合收率先增大后减小,聚合物的重均分子量（珚Mw）减小,分子量分布变宽,顺式-1,4-结构摩尔分数略有下降,但均超过96%;随着三元陈化时间的延长,聚合收率减小,聚合物的珚Mw增大,分子量分布变窄,顺式结构无明显变化;随着聚合温度的升高,聚合收率先增大后减小,聚合物的珚Mw减小,分子量分布变宽,顺式-1,4-结构含量下降;在Al/Nd为5,Cl/Nd为2.5,三元陈化时间为60 min,聚合温度为30℃的最佳反应条件下所得聚合物的顺式-1,4-结构摩尔分数达到98.74%。     

Modeling of molecular weight distribution of gas‐phase polymerization of butadiene

A mathematical model of the molecular weight distribution (MWD) based on a multilayer model and an improved intrinsic kinetics model was proposed to simulate the MWD of the gas‐phase polymerization of butadiene with a heterogeneous catalyst. Intrinsic kinetics and heat and mass‐transfer resistances based on the multilayer model of a polymeric particle were considered in the modeling of the MWD. The effects of the reaction conditions, catalyst particle size, mass‐transfer resistance, deactivation of active sites, and transfer of the polymer chain on the molecular weight and MWD were simulated. The results show that the effects of the deactivation of active sites and transfer of the polymer chain on the average molecular weight are significant and that the effect of the catalyst particle size on the MWD is not significant. The simulation results of the molecular weight and MWD are compared with the experimental results. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 88–103, 2003     

Modeling and analysis of a slurry reactor system for heterogeneous olefin polymerization: The effects of hydrogen concentration and initial catalyst size

This article deals with the development of a model for the polymerization process using a Ziegler‐Natta catalyst in a slurry reactor system. Employed here is the hierarchical model describing the entire reactor system that is subcategoried by the gas bubble phase, the continuous gas phase, the liquid phase, the solid polymer particle, and the surface of catalyst where chemical reaction occurs. The concept of the multigrain model (MGM) is introduced to describe the growth of polymer particle from the original catalyst particle. We also adopt the concept of multiple active sites to elucidate the broad molecular weight distribution (MWD). The major concern here is the effects of the hydrogen concentration and the size of the initial catalyst on the performance of the polymerization reactor. It is demonstrated that the hydrogen gas can be used for the purpose of controlling not only the molecular weight but the molecular weight distribution (MWD) of the polymer. In addition, the relationship between the molecular weight and the concentration of hydrogen gas is investigated. The size of the initial catalyst is found to exercise a significant influence on the morphology of the resultant polymer particle. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2480–2493, 2001     

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     

Development of a multi-scale, multi-phase, multi-zone dynamic model for the prediction of particle segregation in catalytic olefin polymerization FBRs

A comprehensive multi-scale, multi-phase, multi-compartment dynamic model is developed to analyze the extent of particle segregation in catalytic, gas-phase ethylene-propylene copolymerization fluidized bed reactors (FBRs). From the numerical solution of the proposed integrated model, the temporal-spatial evolution of the morphological (i.e., particle size distribution, PSD) and molecular (i.e., molecular weight distribution, MWD) polymer properties in a catalytic polymerization FBR can be predicted. In particular, the polymer molecular properties are determined by employing a generalized multi-site, Ziegler-Natta kinetic scheme. To determine the growth of a single catalyst/polymer particle, the random pore polymeric flow model (RPPFM) is utilized. The RPPFM is solved together with a dynamic discretized particle population balance equation (PBE) to calculate the dynamic evolution of PSD in the various compartments of the FBR. Moreover, overall dynamic mass and energy balances are derived in order to assess the dynamic behavior of catalytic gas-phase FBRs. The effects of various fluidized bed operating conditions (e.g., fluidization gas velocity, temperature and catalyst feed rate) on the morphological and molecular distributed polymer properties are thoroughly analyzed.     

丙烯聚合建模研究:扩散作用的影响

提出了均匀分布多粒模型 (UMGM) ,用于研究单个聚丙烯粒子的增长过程。在不考虑催化剂多活性中心和失活的情况下 ,扩散作用能够在较大范围内解释丙烯聚合过程中分子量分布以及反应速率的变化。分析了扩散系数、催化剂的活性以及催化剂颗粒大小对反应的影响。仿真结果表明 ,扩散作用对高活性催化剂的影响更加显著 ,并且与催化剂粒子的大小有密切关系。本模型能够方便地扩展到多活性中心以及采用更加复杂的微观反应动力学方程 .与其他单粒子模型相比 ,UMGM模型参数物理意义明确 ,计算速度快 ,为工业反应器的建模和优化奠定了基础。     

Population balance modeling for a continuous gas phase olefin polymerization reactor

Steady-state population balance models have been developed for a continuous flow gas phase olefin polymerization process with both uniform sized and log-normally size distributed high activity catalyst feeds. For the calculation of polymer properties such as molecular weight averages and weight fraction of comonomers in the copolymer, a multigrain solid core model was used with an assumption that intraparticle monomer mass transfer resistance is negligibly small. The multigrain solid core model was incorporated into the population balance model and the effects of feed catalyst particle size distribution and catalyst deactivation parameters on the polymer production rate, polymer particle size distribution, and polymer properties were investigated. It is observed for deactivating catalyst that the polymer particle size distribution tends to be narrower with a reduced amount of large polymer particles. For the catalyst with nonuniform site deactivation, polymer particles of different sizes exhibit different molecular weight and copolymer composition. © 1994 John Wiley & Sons, Inc.     

Particle size distribution in olefin continuous stirred-bed polymerization reactors

The control of polymer particle size and PSD is of industrial importance. Very fine particles pack poorly, thereby limiting reactor capacity, and present a dust explosion hazard. In olefin polymerization, a particle size distribution (PSD) in the polymerization reactor has been derived using population balances. Three reasonable reaction mechanisms for Ziegler-Natta catalysts, i.e., a simple reaction model, an active site reduction model, and a two sites model, have been used to derive the average number of active sites. It was observed that the PSD depends not only on residence time, but also on the reaction mechanism. It was also found that multiple active sites change the PSD slightly. The PSD, however, does not depend on initial catalyst volume.     

Modeling and simulation of polypropylene particle size distribution in industrial horizontal stirred bed reactors

This work aims at developing a steady-state particle size distribution (PSD) model for predicting the size distribution of polypropylene particles in the outflow streams of propylene gas-phase horizontal stirred bed reactors (HSBR), on the one hand and investigating the effect of the catalyst residence time distribution (RTD) on the polymer PSD, on the other hand. The polymer multilayer model (PMLM) is used to describe the growth of a single particle. Knowing the PSD and RTD of a Ziegler–Natta type of catalyst and polymerization kinetics, this model allows calculating the polymer PSD of propylene polymerization in the HSBRs. The calculated polypropylene PSDs agree well with those obtained from the industrial reactors. The results reveal that both the PSD and the RTD of the catalyst affect the polymer PSD but in different manners. The effect of RTD on the PSD is less significant in the case of a nonuniform size catalyst feed. This model also allows investigating the effects of other process parameters on the polymer PSD under steady-state conditions, including intraparticle mass- and heat-transfer limitations, initial catalyst size, and polymer crystallinity. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Gas‐phase polymerization of butadiene. Data acquisition using minireactor technology and particle modeling

Minireactor technology has been used for kinetic studies on polymerization kinetics, phase equilibrium, and mass transfer on a very small scale. There is a nonlinear influence of temperature and pressure on the polymerization rate. The phase equilibrium can be described by a Flory–Huggins approach, with a temperature‐dependent interaction parameter. The diffusion coefficient seems to be slightly pressure dependent, and the temperature dependence can be described with an Arrhenius equation. A simple formal kinetic scheme with formation of active sites, chain propagation, chain transfer to cocatalyst, and deactivation of active sites has been applied. This kinetic scheme was implemented in two different models; they are, a particle model taking into account mass transfer and a simple chemical model with no mass transfer. In principle, both models describe the experimental results for rate and molecular weight distribution equally well, with rate constants of the same magnitude. Molecular weight distributions calculated by the chemical model are narrower. However, the chemical model gives no explanation for the experimental observed rate dependence on catalyst particle size. With increasing catalyst activity, the differences between both models become more significant and the particle model becomes more and more important. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 270–279, 2003     

Modeling of molecular weight distribution of propylene slurry phase polymerization on supported metallocene catalysts

A mathematical model of the molecular weight distribution (MWD) based on a particle growth model and the kinetic scheme is developed to simulate the MWD of the slurry phase propylene polymerization on a silica-supported metallocene catalyst by means of the equations of moments. The model is used to predict molecular weight distribution, including the number-average molecular weight, the weight-average molecular weight, and the polydispersity index. The results show that the mass transfer has great influence on the polymerization reaction, and it can broaden the MWD especially; moreover, the MWD can be evaluated by simulation; the average molecular weight increases as pressure or temperature, and MWD shifts to long chain lengths as the effective diffusion coefficient increasing thought the influence is not remarkable; furthermore, the MWD's simulation results are calculated, which fit greatly with the experimental data.