聚合反应周期进料对分子量分布可控性分析

对聚合产品的分子量分布实现在线控制是保证高分子产品质量的重要任务。以实验室规模的乙烯基丁基醚管式阳离子聚合反应为研究对象,验证了单体、引发剂周期进料对分子量分布有加宽效应,并从混合平均分布的角度研究了周期进料对分子量分布的影响,从而分析了实现分子量分布控制的可行性。     

利用温度分布控制管式聚合反应的分子量分布

阐述了如何利用管式反应器内的温度分布控制聚合反应的分子量分布(MWD)这样一个新课题。文章包括这个基本思想的可行性研究,即温度分布与终端产品的分子量分布的关系及可控性问题;系统的控制变量(进料流量和反应物比率)和输出变量(温度分布及分子量分布)之间的灵敏度分析;控制策略包括模式识别和专家系统的应用等,还介绍了基于这种思想的计算机仿真结果及分析讨论意见。     

基于间歇反映器的迭代学习控制

根据间歇反应的特性,提出改进型的PID迭代学习算法。用这种方法实现的PID控制器结果简单,作用于系统中可以得到较强的鲁棒性和较好的动态特性。通过仿真结果可以看出这种方法具有很好的可行性和实用性。     

水性体系用颜料分散剂的分子量及分子量分布的控制

采用自由基聚合和稳定自由基聚合,可合成水性体系用的颜料分散剂。介绍了低聚合度、窄分子量分布的聚合物分散剂的控制方法。引发剂、链转移剂、单体的浓度、溶剂种类、反应方式、温度等诸因素对分散剂的分子量和分子量分布有很大影响。讨论了诸因素对分散剂分散性的影响。     

基于无约束迭代学习的间歇生产过程优化控制

针对基于迭代学习控制的间歇过程优化控制算法难以进行收敛性分析的难题,本文基于数据驱动的神经模糊模型提出一种新颖的间歇过程无约束迭代学习控制方法,通过调节因子的变化去除了约束条件,使控制轨迹在批次轴上收敛,并创新性地对优化问题的收敛性给出了严格的数学证明。在理论研究的基础上,将本文提出的算法用于间歇连续反应釜的终点质量控制研究,仿真结果验证了本文算法的有效性和实用价值,为间歇过程的优化控制提供了一条新途径。     

一种计算间歇过滤机最佳操作周期的新方法

通过引入当量非过滤时间的概念,导出了间歇过滤机最佳操作周期的计算公式,可以快速准确地计算间歇过滤机的最佳操作周期和最大生产能力,附有计算举例。     

一种计算间歇过滤机最佳操作周期的新方法

本文通过引入当量非恒压过滤时间的概念,导出了间歇过滤机最佳操作周期的计算公式,可以快速准确地计算间歇过滤机的最佳操作周期和最大生产能力,附有计算举例。     

一类间歇生产过程的迭代学习控制算法及其收敛性分析

针对基于迭代学习控制的间歇过程产品质量优化控制算法难以进行收敛性分析的难题,并且考虑到实际生产中存在外部干扰和不确定因素的影响,本文对间歇过程模型参数动态更新问题进行了分析,建立了间歇生产过程产品质量的神经模糊(NF)预测模型,提出了一种新颖的批次轴参数自适应调节算法。在此基础上,构造了一种基于数据驱动的间歇生产过程产品质量迭代学习控制算法,并对优化问题的收敛性给出了严格的数学证明。最后,将本文提出的算法用于一类典型的间歇过程终点质量控制研究,仿真结果验证了本文算法的有效性和实用价值,为间歇过程的优化控制提供了一条新途径。     

利用B样条神经网络实现聚合反应分子量分布的建模与控制

介绍了以B样条函数作为基函数的神经网络的基本结构和特性,提出了利用B样条神经网络建立聚合物分子量分布（MWD）模型的方法和拓扑结构,以及基于模型预估的控制MWD的新方法.根据预估的分子量分布数据和事先确定的性能指标,使用最优化方法,计算出控制序列,使过程输出达到给定的理想分布.以某实验室规模的苯乙烯聚合反应为仿真对象,研究了此方法的建模与控制实现,证明了方法的可行性.     

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     

乙烯淤浆聚合动态分子量分布模拟计算

以乙烯淤浆聚合反应过程为研究对象,提出动态分子量分布的严格模型的数值计算方法。将动态分子量分布的大规模微分代数混合模型解耦为小规模微分代数方程组动态矩模型与大规模常微分方程组粒数衡算模型,然后通过变量解耦的方法进一步将大规模粒数衡算方程组转换为序贯差分方程组,实现了乙烯动态分子量分布严格模型的数值模拟计算。动态模拟乙烯聚合反应从一个稳态切换到另一个稳态,通过在切换后稳态的分子量分布计算结果与Flory分布计算方法进行比较,两者得到的分子量分布曲线吻合很好,证实了本文提出的动态模拟计算方法的精度和准确度都获得良好的保障。     

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。     

Control of molecular weight distribution and tensile strength in a free radical styrene polymerization process

A new method is presented for modeling and controlling polymer molecular weight distribution (MWD) and tensile strength in a batch suspension polymerization of styrene. The molecular weight distribution is modeled by computing the weight fraction of the polymer in different chain length intervals. Tensile strength is then related to the modeled molecular weight distribution using a correlation available in the literature and based on the concept of a threshold molecular weight. This method enables the design of operating conditions for a batch suspension polymerization reactor, which will theoretically yield amorphous polystyrene with a desired tensile strength. Two numerical examples are presented to illustrate the feasibility of the proposed method. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1017–1026, 1998     

Molecular weight distribution broadening of polypropylene by periodic switching of hydrogen and catalyst additions

This study presents a feasibility study of the broadening of the polypropylene molecular weight distribution produced using a multisite Ziegler‐Natta catalyst in a continuous liquid‐pool polymerization reactor. The broadening is achieved by operating the reactor under periodic forcing of both hydrogen and catalyst feed flows. Model‐based dynamic optimization is used to determine the cycle period and peak width for these inputs. Through simulation it is shown that limited widening (～ 30%) of the molecular weight distribution can be achieved in case of a limited removal of hydrogen from the reactor. The results also show that the forced removal of hydrogen from the reactor could potentially double the polydispersity index of the produced polymer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

基于分布函数矩的聚合物分子量分布预测控制

聚合物分子量分布（molecular weight distribution,MWD）是聚合产物重要的质量指标,由于无法在线测量,使得直接质量控制至今难以实现。在利用Legendre正交多项式组合神经网络建立聚合反应分子量分布灰箱模型的基础上,把MWD这个三维空间控制问题解构为以其矩向量为特征的二维时间域的控制问题,提出了通过控制分布的矩值实现分子量分布的预测控制方法。目标函数以矩值误差平方和为基础,考虑控制变量的约束条件,同时引入可测低阶矩的修正项,使得分子量分布的部分闭环反馈控制得以实现。该方法以实验室规模的苯乙烯聚合过程为对象进行了仿真建模与控制研究,获得良好的控制效果,证明了方法的有效性。     

高转化率乳聚丁苯橡胶聚合过程中乳液相对分子质量分布与粒径分布考察

采用中石油吉化分公司乳聚丁苯橡胶高转化率大生产配方,考察了实验室聚合反应釜聚合反应单体转化率随反应时间的变化,采用激光粒度分析仪和凝胶渗透色谱仪测定了聚合反应不同单体转化率的胶乳的粒径分布与分子质量分布,结果表明：胶乳粒径呈正态分布,粒径主要集中分布在0.1μm附近,胶乳的平均粒径随反应时间的延长逐渐增大,但是增加的幅度越来越小;聚合反应时间在11 h前（即转化率小于72%）,胶乳的重均分子质量、Z均分子质量一直增大,而数均分子质量变化无明显规律;而分子质量分布宽度指数随反应的进行变小,表明调整的高转化率配方合成的丁苯橡胶可有效改善聚合生成的胶乳粒径分布。     

Calculating molecular weight distributions in emulsion polymerization under conditions of diffusion limited chain transfer

When highly reactive chain transfer agents with low water solubilities (e.g., long chain thiols) are used in emulsion polymerizations, transport of the chain transfer agent (CTA) from the monomer droplets to the polymer particles can become diffusion limited. Consequently, the concentration of CTA in the particles is lower than expected, resulting in apparent transfer constants that can be much lower than the actual transfer constants obtained from studies with homogeneous systems such as bulk or solution. Furthermore, molecular weights will be greater than those obtained in homogeneous systems with the same overall concentration of CTA. There are currently no techniques or methodologies available for predicting molecular weight distributions when the transport of CTA is diffusion limited. Apparent transfer constants may be used but they are typically restricted to a given system and operating conditions. In this work, we describe how the actual CTA concentration in the polymer particles can be estimated through analysis of instantaneous molecular weight distributions. This information is then used to calculate the cumulative molecular weight distribution during the polymerization. Comparisons with experimental molecular weight distributions validate the essential correctness of the approach, but also highlight potential problems. The extension of the approach to online applications is discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 217–227, 2000     

On the molecular weight distribution polydispersity of continuous living‐radical polymerization

Batch living‐radical polymerization techniques were used to produce polymers with molecular weight distributions approaching the narrowness of truly living (ionic) systems. Continuous reactors may offer some advantages for living polymerization in copolymer morphology, but continuous polymerization with any level of backmixing will broaden the molecular weight distribution. This study used simple moment techniques to demonstrate that idealized living‐radical polymerization in a single stirred tank reactor will have a polydispersity of 2. This is also the theoretical minimum polydispersity for a truly living polymerization. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 539–542, 2004     

Calculation method of molecular weight averages in polymerization with chain-length-dependent termination

A systematic method for calculating the molecular weight distribution moments in free radical polymerization where termination rate depends on the size of the participating radicals, is presented. The central part of the method is the evaluation of the distribution of termination rates in the balance equations. From an adopted functional form of the termination rate constant, the moment equations are derived. For evaluating the moments of the termination rate distribution an approximate reconstruction of the radical chain length distribution using Laguerre polynomials is proposed. The calculation method can handle termination by disproportionation and combination simultaneously and allows easily to take into account diffusioncontrolled initiation, propagation and chain transfer reactions. The usefulness of the method is illustrated by simulating the bulk polymerization of methyl methacrylate and styrene. The calculated results of conversion, molecular weight averages (M _n,M _w,M _z and M _z+1) and polydispersity are in good agreement with the reported experimental data.