Multiple active site Monte Carlo model for heterogeneous Ziegler‐Natta propylene polymerization

In this study, the kinetics of propylene polymerization catalyzed with the fourth heterogeneous Ziegler‐Natta catalyst is studied. More than one type of active site is present in the propylene polymerization based on an analysis of the GPC curves. A multiple active site kinetic model (MSmodel) is proposed by using Monte Carlo technique. Good agreements in the polymerization kinetics are achieved for fitting the kinetic profiles with the MSmodel. In addition, the MSmodel is used to describe the dynamic evolutions of the active sites and their effects on the propylene polymerization. The simulated results indicate that different types of active sites have different polymerization kinetics and the site type can affect the propylene polymerization kinetics. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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     

丁二烯气相聚合产物分子量分布和粒径分布模型研究

对非均相催化的丁二烯气相聚合,基于聚合物多层模型,考虑催化剂颗粒间活性位初始浓度和粒径分布对聚合物分子量分布和粒径分布的影响,建立了聚合物分子量分布和粒径分布的数学模型。模拟了反应温度、催化剂颗粒间活性位初始浓度和粒径分布等因素的影响,结果表明。随着温度升高,聚合物颗粒平均粒径变小,粒径分布变窄,聚合物分子量变小,分子量分布变宽;催化剂颗粒间的活性组分负载越均匀,聚合物分子量越大,分子量分布和粒径分布越窄;随着催化剂平均粒径变大,聚合物分子量变小,分子量分布变宽,不存在催化剂颗粒粒径分布和聚合物颗粒粒径分布间的复制现象。模型模拟结果与实验结果吻合较好,可用于预测丁二烯气相聚合产物的分子量、分子量分布和粒径分布。     

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     

POLYMERIZATION KINETICS AND MODELING OF SLURRY ETHYLENE POLYMERIZATION PROCESS WITH METALLOCENE/MAO CATALYSTS

Polymerization methods of ethylene include the slurry, solution, and gas-phase processes. This study investigates polymerization conditions and kinetics under slurry process. Typical metallocene catalyst/cocatalyst Cp₂ZrCl₂/MAO system was used for ethylene polymerization. Two kinds of polymerization kinetics were compared in this study, multiple active-site model and transfer-effect model. The kinetic studies used metallocene-type polymerization kinetics, including catalyst activation, initiation, chain propagation, chain transfer, and termination steps. In addition, kinetic constants of polymerization reaction model were calculated. Calculation results of catalyst activity and molecular weight were compared with experimental results, indicating their good correlation. Moreover, the conventional polymerization was modified to accurately predict the molecular weight behaviors under various reaction conditions with the proposed transfer-effect model. Exactly, how reaction time, pressure, catalyst concentration, and cocatalyst ratio affect catalyst activity and molecular weight of the polymer were also discussed.     

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     

离子液体与树脂催化合成醋酸正丁酯的动力学比较

以阳离子交换树脂AMBERLYST15和各种离子液体为催化剂,研究了醋酸和正丁醇反应生成醋酸正丁酯的动力学。实验测定了催化剂种类、反应温度和催化剂量对反应速率的影响,并用拟均相模型对实验数据拟合。在实验条件下,发现AMBERLYST15和己内酰胺四氟硼酸盐催化效率很高,表观活化能分别为36.69,37.06kJ/g,指前因子分别为120.0,61.50m3/(g.h)。结果表明,树脂AMBERLYST15和己内酰胺四氟硼酸盐离子液体二类催化反应的活化能相近,指前因子却相差很大,2种催化剂在相同的催化机理下有不同的催化效率。     

丁二烯气相聚合动力学模型研究

以搅拌床反应器中负载型催化剂催化的丁二烯气相聚合动力学实验为基础,用失活行为不同的两种活性位组合失活模型模拟了丁二烯气相聚合的衰减型动力学行为。研究结果表明,用活性位的1级失活和1．5级失活的组合失活模型可以满意地描述聚合速率的衰减行为。     

CS-1型聚丙烯催化剂的聚合动力学行为

采用聚合实验并结合理论模拟技术对CS-1型高效聚丙烯催化剂的聚合动力学进行了研究。对通过聚合实验所获取的聚丙烯凝胶渗透色谱(GPC)进行解析,得到CS-1型聚丙烯催化剂的最可几活性中心数目。以此为基础,通过理论模型耦合实验结果确定了各活性中心的聚合动力学方程及各自动力学参数取值。此外,采用扩充的实验结果对模型进行了考核。结果表明,文中所建立的多活性中心动力学方程可以用来表征CS-1型聚丙烯催化剂的聚合动力学行为。     

在微量水存在下一步法合成羟基聚硅氧烷的动力学特征

以八甲基环四硅氧烷为单体,四甲基氢氧化铵为催化剂,水作封端剂,在较高温度、排氧加压密闭的条件下,一步合成羟基聚硅氧烷。采用重量法测定转化率,根据聚合机理,导得动力学模型:ee[]ln{1}1[]1[]bkBtAA-=---。在此基础上,探讨温度、催化剂、水量等条件对聚合速率及聚合物特性粘数的影响,得到聚合活化能为91.4kJ穖ol-1。研究还发现,反应混合物粘度和聚合物特性粘数随转化率单调递增,这为连续法一步合成羟基硅氧烷创造了条件。     

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。     

苯乙烯和四氯化碳加成反应动力学的研究

以负载氯化亚铜为催化剂,研究了苯乙烯和四氯化碳加成反应的动力学,为工业反应过程的开发和操作提供了理论依据.在本实验条件下,催化剂的粒径为10-8～10-7m,内扩散影响可以忽略.当搅拌速度大于210 r·min-1时,外扩散影响基本消除,反应进入动力学控制区.系统地测定了65～75℃下的反应动力学数据.依据自由基加成反应机理和单活性位吸附的假设,建立了动力学模型,-rA=K[CA] [CB]+k1[CB].对实验数据进行非线性拟合,得到反应动力学模型参数.计算得到其控制步骤—解离吸附的反应活化能为1.11×103kJ·mol-1.动力学模型与实验数据吻合较好,在实验范围内可信度较高.     

Study of the effect of BDMA catalyst in the epoxy novolac curing process by isothermal DSC

Epoxy novolac/anhydride cure kinetics has been studied by differential scanning calorimetry under isothermal conditions. The system used in this study was an epoxy novolac resin (DEN431), with nadic methyl anhydride as hardener and benzyldimethylamine as accelerator. Kinetic parameters including the reaction order, activation energy and kinetic rate constants, were investigated. The cure reaction was described with the catalyst concentration, and a normalized kinetic model developed for it. It is shown that the cure reaction is dependent on the cure temperature and catalyst concentration, and that it proceeds through an autocatalytic kinetic mechanism. The curing kinetic constants and the cure activation energies were obtained using the Arrhenius kinetic model. A suggested kinetic model with a diffusion term was successfully used to describe and predict the cure kinetics of epoxy novolac resin compositions as a function of the catalyst content and temperature. Copyright © 2003 Society of Chemical Industry     

离子液体中裂解C_5馏分二烯烃聚合反应动力学

用离子液体1-丁基-3-甲基咪唑六氟磷酸盐作为裂解C5馏分中混合二烯烃的反应介质和催化剂,考察了其对混合二烯烃二聚反应的影响。在温度303.15—343.15 K、离子液体质量分数0.3—0.8范围内,采用封管实验方法测定了C5混合二烯烃的动力学数据。在相同温度范围内,测定了离子液体介质中环戊二烯无限稀释状态下的动力学数据。将催化剂影响因数引入Arrhen ius方程,确定了离子液体介质中二烯烃聚合反应动力学模型。用墨森数值积分和非线性最小二乘法拟合求取了各反应速率常数,得到了模型参数和各聚合反应对于催化剂质量分数的反应级数,动力学模型预测值与实验值吻合良好。     

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。     

ROLE OF WATER IN THE KINETIC MODELING OF METHANOL TRANSFORMATION INTO HYDROCARBONS ON HZSM-5 ZEOLITE

The attenuating effect of reaction-medium water (feed and/or reaction product) on the kinetics of the steps of methanol transformation into hydrocarbons on a HZSM-5 zeolite catalyst was studied by means of a kinetic model. In this model, the effect of water was quantified in all the steps of the kinetic scheme by means of a kinetic parameter, which is constant with temperature under the conditions of the MTG process. At low temperature, under conditions in which only methanol dehydration occurs, the kinetics of this reaction is attenuated by the presence of water, and the coefficient that quantifies the attenuation decreases as temperature is increased. In addition to considering the effect of water content in the reaction medium, another innovation of the kinetic model proposed, compared to those proposed in the literature consisting of lumps, is the fact that the higher reactivity of dimethyl ether over methanol is taken into account. A step of cracking of gasoline lump hydrocarbons to produce light olefins (ethene and propene) was also taken into account. The kinetic model proposed was verified by using the results obtained in an integral isothermal fixed bed reactor, in the 573-723 K range, for an ample range of space time values. The results revealed that the effect of water is due to its adsorption on the active sites by competition with the intermediate compounds of the kinetic scheme.     

ROLE OF WATER IN THE KINETIC MODELING OF METHANOL TRANSFORMATION INTO HYDROCARBONS ON HZSM-5 ZEOLITE

The attenuating effect of reaction-medium water (feed and/or reaction product) on the kinetics of the steps of methanol transformation into hydrocarbons on a HZSM-5 zeolite catalyst was studied by means of a kinetic model. In this model, the effect of water was quantified in all the steps of the kinetic scheme by means of a kinetic parameter, which is constant with temperature under the conditions of the MTG process. At low temperature, under conditions in which only methanol dehydration occurs, the kinetics of this reaction is attenuated by the presence of water, and the coefficient that quantifies the attenuation decreases as temperature is increased. In addition to considering the effect of water content in the reaction medium, another innovation of the kinetic model proposed, compared to those proposed in the literature consisting of lumps, is the fact that the higher reactivity of dimethyl ether over methanol is taken into account. A step of cracking of gasoline lump hydrocarbons to produce light olefins (ethene and propene) was also taken into account. The kinetic model proposed was verified by using the results obtained in an integral isothermal fixed bed reactor, in the 573–723 K range, for an ample range of space time values. The results revealed that the effect of water is due to its adsorption on the active sites by competition with the intermediate compounds of the kinetic scheme.     

Anchovy oil thermal polymerization kinetics

The thermal polymerization reaction kinetics of anchovy oil was investigated with and without catalyst. In order to make a comparison, linseed oil was included in the study. Reactions were carried out 260, 270, and 280°C, and a kinetic model was determined for each case. The reactions for linseed oil with and without catalyst at all temperatures followed the first-order kinetics. In the case of anchovy oil, the best-fitted straight line is obtained by plotting viscosity values against time, and the reaction proceeds in two stages at 280°C without catalyst. The use of catalyst lowered the temperature to 270°C for the appearance of two different rates. Additionally, some mathematical equations were derived between iodine value, refractive index, viscosity, and reaction time.     

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     

Synthesis,Characterization and Application of a Multi-Site Phase Transfer Catalyst in Radical Polymerization of n-Butyl Methacrylate—A Kinetic Study

The multi-site phase transfer catalyzed radical polymerization of n-butyl methacrylate (n-BMA) using newly synthesized and characterized 1,1,2,2-tetramethyl-1-benzyl-2-n-propylethylene-1,2-diammonium bromide chloride (TMBPEDBC) as a multi-site phase transfer catalyst was investigated in an aqueous-organic two-phase system at 60 ± 1°C under nitrogen circumstances. The kinetics and effects of various operating variables (monomer, initiator, catalyst, temperature, acid, and ionic strength) on the rate of polymerization (Rp) were examined in detail. The order with respect to monomer, initiator and multi-site phase transfer catalyst was found to be 0.50. A suitable kinetic reaction scheme has been proposed to account for experimental observations, and its significance is discussed.