Model based operation of emulsion polymerization reactors with evaporative cooling: Application to vinyl acetate homopolymerization

This work aims at maximizing the productivity of emulsion homopolymerization processes. A dynamic model of emulsion polymerization processes is extended by the inclusion of vaporization from the liquid phases in the reactor to the gaseous phase. The multi-component gas–liquid mass transfer phenomenon is described by the Maxwell–Stefan diffusion equations, which are solved by a special algorithm. A novel operation strategy is developed for running a reactor optimally with respect to batch time. This strategy is applied first to an industrial scale reactor, which is run without using evaporative cooling. Then, based on the extended model, controlled vaporization is included by which additional heat is removed from the reaction system. This makes it possible to extend the restrictions imposed by the limited heat removal of the cooling jacket considerably. Simulation results are presented for the homopolymerization of vinyl acetate in an industrial scale reactor operated in semi-batch mode. The results show that a significant amount of heat can be removed by evaporative cooling thus leading to higher productivity.     

Control of network structure in emulsion crosslinking copolymerization

A kinetic model for network structure development during crosslinking copolymerization of vinyl and divinyl monomer is proposed. The model calculations suggest that polymer networks synthesized by free-radical copolymerization are, in general, inhomogeneous at least on a microscopic scale. By application of the same kinetic parameters as those for bulk polymerizations, it was found that the crosslinking density of the polymers formed in the earlier stages of polymerization is very high in emulsion polymerizations and polymer networks tend to be highly heterogeneous. Homogeneous networks cannot be formed even under Flory's simplifying assumptions for vinyl/divinyl copolymerization in emulsion polymerizations. The present kinetic model can be used to find semi-batch policies to control the network structure, and semi-batch policies were used to illustrate the synthesis of homogeneous polymer networks.     

半间歇聚合反应分子量分布周期操作的迭代学习控制

通过对半间歇聚合反应的引发剂进料实施周期操作,研究了这类操作方式对聚合物分子量分布的影响。研究结果显示,周期操作能改善聚合反应过程,对分子量分布有明显的加宽作用。对性能指标进行改进,以引发剂周期进料的占空比为控制变量,采用基于粒子群优化的迭代学习算法,对分子量分布进行了优化控制。仿真分析表明,在实际对象和模型存在不匹配的情况下,运用迭代粒子群算法,控制输入随着批次学习的进行而逐渐趋于最优解,聚合反应的分子量分布则不断逼近希望的分子量分布。实验结果验证了以周期操作方式对半间歇聚合过程分子量分布进行迭代优化控制的可行性。     

水溶性聚合物存在下的苯乙烯/丙烯酸丁酯乳液共聚合

以苯乙烯、丙烯酸丁酯为单体,以十二烷基硫酸钠为乳化剂,并向反应体系加入适量的水溶性苯乙烯-丙烯酸共聚物进行一次投料的间歇乳液聚合反应,详细分析了该体系的动力学规律和乳胶粒直径及分布的规律,通过乳液聚合的动力学模型探讨了水溶性聚合物及其它因素对聚合反应速率、乳液稳定性的影响.结果表明,该水溶性聚合物参与的乳液聚合反应规律与小分子乳化剂的乳液聚合基本相似,但聚合反应速率大大下降.     

BATCH-TO-BATCH OPTIMAL CONTROL OF BATCH PROCESSES BASED ON RECURSIVELY UPDATED NONLINEAR PARTIAL LEAST SQUARES MODELS

A batch-to-batch optimal control approach for batch processes based on batch-wise updated nonlinear partial least squares (NLPLS) models is presented in this article. To overcome the difficulty in developing mechanistic models for batch/semi-batch processes, a NLPLS model is developed to predict the final product quality from the batch control profile. Mismatch between the NLPLS model and the actual plant often exists due to low-quality training data or variations in process operating conditions. Thus, the optimal control profile calculated from a fixed NLPLS model may not be optimal when applied to the actual plant. To address this problem, a recursive nonlinear PLS (RNPLS) algorithm is proposed to update the NLPLS model using the information newly obtained after each batch run. The proposed algorithm is computationally efficient in that it updates the model using the current model parameters and data from the current batch. Then the new optimal control profile is recalculated from the updated model and implemented on the next batch. The procedure is repeated from batch to batch and, usually after several batches, the control profile will converge to the optimal one. The effectiveness of this method is demonstrated on a simulated batch polymerization process. Simulation results show that the proposed method achieves good performance, and the optimization with the proposed NLPLS model is more effective and stable than that with a batch-wise updated linear PLS model.     

BATCH-TO-BATCH OPTIMAL CONTROL OF BATCH PROCESSES BASED ON RECURSIVELY UPDATED NONLINEAR PARTIAL LEAST SQUARES MODELS

A batch-to-batch optimal control approach for batch processes based on batch-wise updated nonlinear partial least squares (NLPLS) models is presented in this article. To overcome the difficulty in developing mechanistic models for batch/semi-batch processes, a NLPLS model is developed to predict the final product quality from the batch control profile. Mismatch between the NLPLS model and the actual plant often exists due to low-quality training data or variations in process operating conditions. Thus, the optimal control profile calculated from a fixed NLPLS model may not be optimal when applied to the actual plant. To address this problem, a recursive nonlinear PLS (RNPLS) algorithm is proposed to update the NLPLS model using the information newly obtained after each batch run. The proposed algorithm is computationally efficient in that it updates the model using the current model parameters and data from the current batch. Then the new optimal control profile is recalculated from the updated model and implemented on the next batch. The procedure is repeated from batch to batch and, usually after several batches, the control profile will converge to the optimal one. The effectiveness of this method is demonstrated on a simulated batch polymerization process. Simulation results show that the proposed method achieves good performance, and the optimization with the proposed NLPLS model is more effective and stable than that with a batch-wise updated linear PLS model.     

Open-loop control of particle size distribution in semi-batch emulsion copolymerization using a genetic algorithm

The open-loop generation of an optimal feed profile to attain a target particle size distribution (PSD) in the semi-batch emulsion co-polymerization of vinyl acetate and butyl acrylate is described. A nominal model of the process based on population balancing is utilized for this purpose. A Genetic Algorithm is employed as the optimization strategy. The optimal recipes generated in these studies are implemented on an experimental emulsion polymerization reactor. The end-point PSD obtained in these experiments closely matches the target in spite of the model uncertainties and process disturbances. Examination of the evolution of the PSD up to the end point provides useful information for feedback control strategies.     

Online polymer molecular weight and conversion monitoring via calorimetric measurements in RAFT emulsion polymerization

BACKGROUND: Online measurements of key emulsion polymerization attributes, such as conversion and molar mass distribution, are unavailable. Costly offline measurements at low sampling frequencies with time delays usually lead to insurmountable challenges in real‐time product quality monitoring and process/product control. RESULTS: We developed an online calorimetric method monitoring the evolution of conversion and molecular weight in complex polymerization reactors. Our experiments were carried out in a 1 L reactor to produce polystyrene homopolymer. Monomer conversion was obtained in real time from polymerization rate, which was estimated from temperature measurements using platinum thermal transducers. The calorimetric model was validated offline for batch and semi‐batch emulsion polymerization of styrene with and without transfer agents. The conversion was validated using offline gravimetry. The molecular weights measured offline via size exclusion chromatography with multiple detectors compared well with those estimated online using the calorimetric method. CONCLUSION: We found that a semi‐batch emulsion polymerization process can be controlled online to approach living polymerization involving transfer agents. Thus our model is suitable as a ‘soft‐sensor’ for real‐time control applications. Copyright © 2009 Society of Chemical Industry     

Inferential Conversion and Composition Monitoring via Microcalorimetric Measurements in Emulsion Terpolymerization

Online calorimetry was used to estimate the conversion and the cumulative terpolymer composition in free radical emulsion polymerization of styrene/methyl methacrylate (MMA)/methyl acrylate (MA) within batch and semi-batch stirred tank reactors. The model includes the mass and energy balance equations over the reactor and its peripherals. Energy balance equations include the heat of reaction, internal and external heat transfer effects, as well as external heat losses. Experiments were conducted in conjunction with a reactor instrumented with platinum resistance thermal transducers and gravimetric conversion measurement devices. The experiments were conducted at variable operational conditions of feed rate, temperature and monomer feed ratios. The estimated values of conversion and terpolymer composition obtained from calorimetric data were compared with measurements of conversion and cumulative terpolymer composition by gravimetry and NMR techniques. Good agreement was observed between the inferential calorimetric estimation and corresponding process measurements. We established that online calorimetry is suitable for use as a soft sensor for the prediction of the rate of reaction, conversion and terpolymer composition.     

Molecular weight distribution of living polymers in a semi-batch reactor

For anionic polymerization with slow initiation and rapid propagation step analytical expressions are presented to calculate average molecular weights and molecular weight distributions for a semi-batch process, in which a monomer solution contaminated by impurities is fed to an initiator solution in the reactor. The validity of the model was checked for the case of the polymerization of isoprene by n-butyllithium in n-heptane. The differences observed between theoretical and experimental values are explained by the changes in the rate constants of the initiation and the propagation step caused by the change in the polarity of the reaction solution by the continuously fed impurities. Furthermore it is shown that polymers with bimodal molecular weight distributions are formed if the semi-batch procedure is followed by a batch one to increase the monomer conversion.     

TMPTMA交联改性聚丙烯酸酯乳液的合成与性能

以三羟甲基丙烷三甲基丙烯酸酯（ TMPTMA ）为内交联单体,苯乙烯（ St ）、甲基丙烯酸甲酯（ MMA）、丙烯酸丁酯（ BA）和甲基丙烯酸（ MAA）为共聚单体,采用半连续核壳乳液聚合工艺合成了自交联聚丙烯酸酯乳液（ T-PAE）。考查了TMPTMA添加量与添加方式对乳液聚合稳定性以及涂膜性能的影响。研究发现：随着TMPTMA含量的增加,T-PAE乳液聚合的稳定性降低,聚合凝胶率增大,乳胶粒的平均粒径下降；涂膜的耐介质性能和交联密度相应提高,合适的TMPTMA加入量为总单体质量的0．5%~1．0%。     

Semibatch styrene suspension polymerization processes

Emulsion and suspension polymerization processes have widely been studied for more than 40 years. Although both polymerization processes are performed in heterogeneous media, each one presents its own typical characteristics, such as the particle size distribution, molecular weight distribution, polymer particle nucleation rate, and polymerization rate. In this study, semibatch styrene suspension polymerizations were carried out with feed compositions typical of emulsion processes. The initial reactor charge resembled the recipe of standard styrene suspension polymerizations, and the emulsion polymerization constituents were added during the batch. The influence of the moment at which the emulsion feed was started on the course of the polymerization and the effects of the feed on the polymer properties were analyzed. The polymer particle morphology and the average molecular weights changed very significantly with the emulsion feed time, and the changes could lead to the production of broad molecular weight distributions. Core–shell polymer particles could also be obtained, with the core being formed of polymer particles originating from the suspension polymerization process and the shell being formed of polymer particles originating from the emulsion polymerization. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3021–3038, 2003     

Online inferential product attribute estimation for optimal operation of emulsion terpolymerisation: Application to styrene/MMA/MA

An advanced model for process design and control of emulsion terpolymerisation was developed. A test case of emulsion terpolymerisation of styrene (Sty), methyl methacrylate (MMA) and methyl acrylate (MA) was investigated on state of the art facilities for predicting, optimising and control end-use product properties including global and individual conversions, terpolymer composition, the average particle diameter and concentration, glass transition temperature, molecular weight distribution, the number- and weight-average molecular weights and particle size distribution.The model equations include diffusion-controlled kinetics at high monomer conversions, where transition from a ‘zero-one’ to a ‘pseudo-bulk’ regime occurs. Transport equations are used to describe the system transients for batch and semi-batch processes. The particle evolution is described by population balance equations which comprised a set of integro-partial differential and nonlinear algebraic equations. Backward finite difference approximation method is used to discretise the population equation and converts them from partial differential equations to ordinary differential equations. The model predictions were experimentally validated in the laboratory and were found to be in excellent agreement, thus paving the way for further application of the model.     

Mechanistic study of the formation of amphiphilic core-shell particles by grafting methyl methacrylate from polyethylenimine through emulsion polymerization

The mechanism for the formation of amphiphilic core-shell particles in water is elucidated via a kinetic study of semi-batch polymerization of methyl methacrylate (MMA) grafted from polyethylenimine (PEI) initiated with tert-butyl hydroperoxide in an emulsion polymerization. The monomer conversion, the polymerization kinetics, the particle size, the particle number density, the poly(methyl methacrylate) (PMMA) core diameter, the percentage of unbound PEI, and the grafting efficiency of PMMA were determined at various times during the polymerization. The particle number density and the percentage of unbound PEI were almost independent of the controllable variables. The particle sizes and the core diameters increased with each consecutive batch of monomer addition, while the grafting efficiency of PMMA decreased. These data supported the hypothesis that the PEI-g-PMMA graft copolymers were formed early in the polymerization and later self-assembled to a new phase, micellar microdomains. These microdomains act as loci for subsequent MMA polymerization as the monomer is fed into the reaction, without subsequent formation of new particles. The size of the resulting highly uniform core-shell particles (99-147 nm) can be controlled by choosing the amount of monomer charged. Thus, this polymerization method is viable for a large scale production of core-shell particles with high solids content.     

工业聚合反应装置 Ⅳ．乳液聚合反应器（上）

比较了乳液聚合用间歇聚合釜和连续搅拌釜式反应器操作中的反应工程特性，并根据这些特性介绍了间歇式和连续式乳液聚合反应器，除釜式外还有环管式和脉冲填料塔等新型反应器，同时还相应讨论了乳液聚合过程反应热的撤除以及传热设备。     

核壳型硅丙复合乳液的合成及其性能研究

用单体预乳化法和半连续种子乳液聚合法合成了核壳型硅丙复合乳液,研究了壬基酚聚氧乙烯醚-2-磺酸基琥珀酸单酯二钠盐(MS-1)与十二烷基硫酸钠(SDS)复配比例、核层聚合乳化剂补加速率及壳层聚合乳化剂补加速率对乳液性能和乳胶粒粒径及其分布的影响。考察了复配乳化剂用量对单体转化率、涂膜耐水性的影响规律。结果表明,所合成的系列乳液中,复配乳化剂所合成乳液的乳胶粒粒径小,粒径最小为72.99nm,乳液黏度大,其最大值为60.0mPa.s;而采用MS-1单一乳化剂所合成乳液的乳胶粒粒径分布最窄,其多分散性指数(PDI)为0.01,乳液黏度最小,其值为37.78mPa.s。当核层和壳层聚合乳化剂持续补加时间分别为120min和210min时,聚合体系乳胶粒数目基本保持不变,后续加入的单体在种子乳胶粒表面进行聚合,形成"核壳"结构。此外,随着乳化剂用量增加,单体的转化率提高但涂膜的耐水性下降。并用红外、透射电镜分别对聚合物分子链结构和乳胶粒形貌结构进行了表征。     

Emulsification in batch‐emulsion polymerization of styrene and vinyl acetate: A reaction calorimetric study

Dispersion of liquid–liquid systems is commonly applied in industrial processes such as extraction, suspension, and emulsion polymerization. This article describes the influence of the quality of emulsification on the course and outcome of a batch‐emulsion polymerization of styrene and vinyl acetate. From visualization experiments and polymerizations in combination with reaction calorimetric studies, a critical impeller speed, N*, can accurately be determined for a particular reactor setup and a given recipe. The results show that styrene–water emulsions are more difficult to emulsify than vinyl acetate–water emulsions. In general, a large turbine impeller appears to be more effective in emulsifying monomer–water dispersions than a pitched‐blade impeller. In addition, for vinyl acetate emulsion polymerization, the possibility of premixing the reaction mixture has been investigated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 944–957, 2001     

Nonlinear adaptive temperature control of multi-product, semi-batch polymerization reactors

This paper considers the temperature control of semi-batch polymerization reactors in which some of the following issues must be considered: (i) production of multiple products in the same reactor; (ii) changing heat transfer characteristics, during a batch and from batch to batch; (iii) time varying and nonlinear reaction rate due to changing monomer concentration and diffusion controlled termination reactions (gel effect); (iv) the absence of detailed kinetic models for the reactors. The industrial challenge problem published by Chylla and Haase [Chylla, R. W. and Haase, D. R. (1993) Temperature control of semi-batch polymerization reactors (with corrected updates). Comput. Chem. Eng. 17, 257–264) is used as the simulation basis for evaluating these problems.

A nonlinear adaptive controller consisting of a nonlinear controller (based on differential geometric concepts) coupled with an extended Kalman filter (which uses only readily available data and knowledge) is shown to provide excellent control in all the above situations. In particular, the on-line estimation is critical for the strong performance of the nonlinear controller over a broad range of conditions. PID controllers with feedforward terms can perform well at one set of conditions, however, they require retuning as conditions and products change.     

The modeling of batch and continuous emulsion polymerization reactors. Part I: Model formulation and sensitivity to parameters

A detailed model for the prediction of the behavior of batch or continuous emulsion polymerization reactors has been formulated, and an efficient numerical scheme for simulation developed. The model makes use of population balance equations and detailed mechanisms for chemical and physical rate processes. The numerical procedure chosen for its solution is orthogonal collocation on finite elements. In this paper, a few comparisons with experimental data are presented to demonstrate the model validity. Finally, a parametric sensitivity study is carried out to identify the most important kinetic and physical parameters. In the sequel, a comprehensive comparison of model predictions with a wide variety of experimental data will be presented.