Modelling and simulation of polymerisation processes

In order to model the effects of uneven spatial distribution of components and temperature a computational fluid dynamics (CFD) model has been developed for a living polymerisation reaction in a tubular reactor. The low moments of the molecular weight distribution (MWD) and the dispersiry index of the product as well as the more usual spatial concentration of species and temperature have been calculated. The modelling and simulation work was carried out using the CFD code PHOENICS version 2.1 on Pentium PCs. Additionally, a novel algorithm is described which makes the design of reactor control strategies more tractable by providing a very rapid route to a qualitative approximation of the MWD of products from living polymerisation processes. Numerically simulated data generated using this new procedure are compared with slower but more rigorous approaches to the same problem. The examples cover living polymerisations in an isothermal batch reactor, a steady-state continuous stirred tank reactor (CSTR) and feed-perturbed CSTR. It is demonstrated that, although the novel algorithm comprises only four differential equations, it provides the essential information concerning the position and relative intensity of the peak(s) in a MWD plot needed for the design of reactor control strategies for the production of tailored MWDs.     

A continuous tubular reactor for core–shell latex particles

High solids content poly(butyl acrylate)/poly(methyl methacrylate) core–shell latex particles were produced using miniemulsion polymerisation in a continuous linear tubular reactor. The resulting products were and shown to be comparable to a batch process. Final solids contents of 41 and 48 wt.% were shown to be possible in a simple tubular reactor. Differential scanning calorimeter analysis indicated that core–shell particles were formed under these conditions. © 2011 Canadian Society for Chemical Engineering     

Batch-to-batch optimal control of a batch polymerisation process based on stacked neural network models

A neural network based batch-to-batch optimal control strategy is proposed in this paper. In order to overcome the difficulty in developing mechanistic models for batch processes, stacked neural network models are developed from process operational data. Stacked neural networks have enhanced model generalisation capability and can also provide model prediction confidence bounds. However, the optimal control policy calculated based on a neural network model may not be optimal when applied to the true process due to model plant mismatches and the presence of unknown disturbances. Due to the repetitive nature of batch processes, it is possible to improve the operation of the next batch using the information of the current and previous batch runs. A batch-to-batch optimal control strategy based on the linearisation of stacked neural network model is proposed in this paper. Applications to a simulated batch polymerisation reactor demonstrate that the proposed method can improve process performance from batch to batch in the presence of model plant mismatches and unknown disturbances.     

In situ mass-suspension polymerisation

In situ mass-suspension polymerisation of MMA was carried out in a single reactor. The mass polymerisation was carried out in a gently agitated monomer layer of a two stratified layers of monomer and water in the reactor. The degree of conversion at which mass polymerisation changed to suspension polymerisation, by increasing the rate of agitation, was altered systematically. The polymer content of the monomer/polymer solution, formed during the mass polymerisation stage, significantly affected the evolution of the particle size distribution. Mass-suspension polymerisation was found to be more vulnerable to drop coalescence and process failure than conventional suspension polymerisation. The results indicate the importance of the transition stage in a typical suspension polymerisation during which the rate of polymerisation is very low and the adsorption of stabiliser on the surface of drops is completed. The polymer beads from the mass-suspension polymerisation had a very broad size distribution with a large contribution from satellite particles.     

MULTILEVEL PCA AND INDUCTIVE LEARNING FOR KNOWLEDGE EXTRACTION FROM OPERATIONAL DATA OF BATCH PROCESSES

A new methodology for monitoring batch processes is presented which is based on analysis of historical operational data using both principal component analysis (PCA) and inductive learning. Historical data of batch operations are analysed according to stages. For each stage, PCA is employed to analyse the trajectories of each variable over all batch runs and groups the trajectories into clusters. The first one or two PCs for all variables at a stage are then used in further PCA analysis to project the operation of the stage onto operational spaces. Production rules are generated to summarise the operational routes to produce product recipes, and to describe variables' contributions to stage-wise state spaces. A method for automatic identification of stages using wavelet multi-scale analysis is also described. The methodology is illustrated by reference to a case study of a semi-batch polymerisation reactor.     

Calorimetric determination of polymerisation conversion in a large laboratory reactor

A calorimetric measuring system for continuous recording of rate of reaction and conversion in a 14 1 polymerisation reactor has been developed. The reactor was jacketed and thermostated with circulating water. The measuring signals to the calculating unit represented the temperature difference between inlet and outlet water, the water flow and the heat losse from reactor to the environment. The measuring system was constructed to calculate correctly the conversion even if the heat losses to the environment changes during the reaction. The applicability of the reactor system was demonstrated by its use in suspension polymerisation of vinyl chloride.     

Aspects of Vinyl Chloride Suspension Polymerisation

Some observations on the formation and growth of PVC granules during polymerisation are described, particularly with reference to granule morphology. The physical structure of the final granule is very dependent on polymerisation variables and of these, the influence of reactor agitation, temperature of polymerisation and protective colloid are briefly discussed.     

Dynamic behaviour of a continuous-flow polymerisation reactor

The polymerisation of a vinyl monomer, which is promoted by an added free-radical generator, is considered. When the polymerisation occurs in a continuous-flow reactor, the dynamic behavior of the reactor is shown to depend on the generator concentration. Reactor stability can depend on the start-up procedure. In the case of styrene polymerisation, start-up procedures which are safe when initiation is purely thermal may be unsafe when a generator is present. The importance of small changes in physical properties of the reaction fluid is demonstrated and the behavior of monomers other than styrene is discussed.     

Calorimetric estimation for a batch-loop emulsion polymerisation reactor

To facilitate the online monitoring and control of a pilot-scale polymerisation reactor, state estimation techniques are investigated. Specifically, a batch-loop reactor is employed for the emulsion polymerisation of methyl methacrylate. The reactor consists of jacketed tubular sections fitted with in-line static mixers, thus providing mixing homogeneity and improved temperature control. A direct estimation of the reaction rate is attained through measurements of process and jacket side temperatures, and thus a calorimetric method of estimation. This is compared with a Kalman filter based calorimetric approach, in which there is compensation for model uncertainties and measurement noise. For both estimation methods, no knowledge of the kinetic model for polymerisation is needed. Experimental results indicate that with an accurate model of the process energy balance, in which, for example, the recycle pump energy input is described, the Kalman filter approach is found to provide excellent prediction of conversion, for both high and low conversions, for this pilot-plant reactor system. The approach does not require any (approximate) kinetic knowledge, and is thus considerably easier in implementation than the extended Kalman filter approaches.     

乳液聚合数学模型

本文报导了在50℃下苯乙烯乳液聚合和悬浮聚合的试验研究。对在无挡板搅拌釜中的间歇乳液聚合提出了一个数学模型。这个模型不仅考虑了吸附在单体珠滴表面上的乳化剂的影响,而且考虑到凝胶效应。模型所需要的终止速度常数与转化率之间的依赖关系是从悬浮聚合的试验数据整理而成的。结果表明,本模型可以在相当宽的转化率范围内成功地预计转化速率和胶乳中的颗粒尺寸及数目。     

Precipitation polymerisation of vinylidene fluoride in supercritical CO2 and real-time calorimetric monitoring

Vinylidene fluoride was polymerised in supercritical carbon dioxide. Power compensation calorimetry was used to monitor the polymerisation process on-line. The polymer product was found to have a low apparent-density, leading to an observed high solid content in the autoclave at low yields. In situ calorimetry showed a sharp transition of the heat transfer in the reactor, leading to a useful parameter for monitoring the polymerisation process. The stirring rate was found to have no effect on the molecular weight, but did modify the calorimetric traces and the morphology of the polymer. The polymerisation at a lower pressure resulted in a lower molecular weight product and a lower polymerisation rate.     

Surfactant-free emulsion polymerisation of methyl methacrylate and methyl acrylate using intensified processing methods

The feasibility of enhancing the latex yield and colloid characteristics in the surfactant-free emulsion polymerisation (SFEP) of methyl methacrylate (MMA) and methyl acrylate (MA) through the use of intensified processing technologies is reported in this paper. The effects of high power ultrasonic energy as a well-established technique for mixing and mass transfer enhancements were compared with thermal initiation in a conventional mechanically agitated reactor. Although increases in ultrasonic power input resulted in higher rates of reaction and larger particles in the MMA polymerisation, reaction yields were nevertheless found to be low compared with the thermally initiated stirred tank reactor experiments. This was attributed to the low frequency ultrasound used (24 kHz) that was observed to provide excellent emulsification but was ineffective in terms of radical generation. The results for a thermally initiated SFEP of MA in a narrow channel reactor as an example of a continuous flow reactor technology showed that reaction rates were comparable with those achieved in the stirred tank reactor but at only a fraction of the specific power input whilst smaller particles with a tighter distribution are generated. These effects highlight the process intensification characteristics of the narrow channel reactor for the SFEP of MA.     

Polymerisation of methyl methacrylate in a pilot-scale tubular reactor: modelling and experimental studies

A pilot-scale tubular reactor fitted with in-line static mixers is experimentally and theoretically evaluated for the polymerisation of methyl methacrylate (MMA). A non-isothermal and non-adiabatic axially dispersed plug-flow model is used to describe the flow characteristics of the reactor. The model is applied to the polymerisation of a concentrated MMA solution (up to 72% (v/v)). Key model parameters were attained through independent bench and pilot-scale experiments. Measured monomer conversions and polymer molecular weight were accurately predicted by model simulation. The presence of static mixers is shown to give near-ideal plug-flow operation for the experimental conditions of this study. Furthermore, an approximately four-fold increase in overall heat transfer coefficient is indicated due to the radial mixing incited by the mixers. Studies also demonstrated the importance of inhibitor kinetics on the dynamic and steady-state performance of the reactor.     

Rate of the activated anionic polymerisation of ε-caprolactam onto an isocyanate bearing polypropylene in the melt

This paper concerns the rate of the activated anionic polymerisation of ε-caprolactam (CL) onto 3-isopropenyl-α,α-dimethylbenzyl isocyanate bearing PP (PP-g-TMI) in the melt to form a graft copolymer with PP as backbone and PA6 as grafts. The polymerisation was catalysed by sodium ε-caprolactam (NaCL). The PP-g-TMI/NaCL/CL polymerisation system being heterogeneous, the polymerisation was carried out in a batch mixer. Emphasis was placed on the effects of temperature and the concentrations of NaCL and the isocyanate group in the form of PP-g-TMI on the polymerisation rate. Results suggested that if the polymerisation is to be carried out by a reactive extrusion process whose mean residence time is less than a few minutes, it is recommended that the polymerisation temperature be higher than 220 °C. Moreover, the molar ratio between NaCL and CL should be higher than 0.5 and at the same time that between the isocyanate group in the form of PP-g-TMI and NaCL, should be smaller than 4.     

A simple model of hyperbranched polymerisation involving AB<Subscript>2</Subscript> and B<Subscript><Emphasis Type="Italic">f</Emphasis></Subscript> core monomers and methods of narrowing the molecular size distribution

Summary A simple kinetic model of modelling hyperbranched polymerisation involving AB₂ and B_f core monomers is developed and analytical solutions of the model are presented. The number- and weight- average polymerisation degrees can be calculated using the model as functions of polymerisation time or conversion degree. Application of the model is tested for predicting the broadness of molecular size distribution of the hyperbranched polymers obtained by varying the procedures of feeding AB₂ monomer to polymerisation reactor.     

提高单级SBR系统总氮去除率方法的探讨

针对单级SBR系统在脱氮过程中的碳源矛盾,从几个方面对如何提高单级SBR系统的总氮去除率进行了探讨,提出了单级SBR系统中混合液内循环比的概念,并在分析TN去除率和内循环比关系的基础上得出了单级SBR反应器TN去除率的计算公式。另外,介绍了一种提高SBR工艺TN去除率的改进运行方式,并对如何将SBR和目前新兴的几种脱氮工艺相结合以提高反应器的TN去除率进行了探讨。     

Step polymerisation with unequal reactivities in a CSTR

A mathematical model for step polymerisation of BB with AA in a CSTR where the functional groups of AA are not equally reactive has been developed. Unequal reactivity can be due to either asymmetry or induced asymmetry. The polydispersity index (PDI) of the product of a CSTR was calculated and was found to be always greater than that of a batch reactor. Calculations show that, when compared with situations where unequal reactivity is absent, the presence of induced asymmetry can cause either an increase or a decrease in PDI while the presence of asymmetry can only cause a decrease in PDI. However where BB is in excess of AA in the feed, the limit of the calculated PDI as residence time tends to infinity was unaffected by unequal reactivity.     

Galacto-oligosaccharide production with immobilized β-galactosidase in a packed-bed reactor vs. free β-galactosidase in a batch reactor

We report here that the usage of immobilized enzyme in a continuous packed bed reactor (PBR) can be a good alternative for GOS production instead of the traditional use of free enzyme in a batch reactor. The carbohydrate composition of the product of the PBR with immobilized enzyme was comparable to that of the batch reactor with free enzyme. The stability of the immobilized enzyme at a lactose concentration of 38% (w/v) and at 50 °C was very high: the half-life time of the immobilized enzyme was approximately 90 days. The enzymatic productivity of GOS production using immobilized enzyme in a PBR can be more than six times higher than that of GOS production with free enzyme in a batch reactor. Besides, when aiming for an equal volumetric productivity to the batch process in designing a PBR, the volume of the PBR can be much smaller than that of the batch reactor, depending on the enzyme dosage and the run time of a single batch.     

Experimental studies on parametric sensitivity of a batch reactor

Runaway behaviour of exothermic reactions in a batch reactor has been studied experimentally on the example of acetic anhydride hydrolysis catalyzed by sulphuric acid, in a 700 ml batch reactor. High parametric senstivities of peak reactor temperature with respect to initial reactor temperature and catalyst concentration were obtained.     

Study on the enzymatic hydrolysis of racemic methyl ibuprofen ester

The hydrolysis of racemic methyl ibuprofen ester in the presence of lipase from Candida rugosa was investigated in shake flasks. Experiments were performed to study the effect of temperature, pH and shaking speed on the reaction rate. Different hydrophobic co‐solvents were screened for the highest reaction rate and the presence of enzyme inhibition by substrate and products was examined. A kinetic expression was then proposed to describe the reaction. Kinetic parameters were determined for the optimum operating conditions and the proposed model was verified with the experimental results. Next, this reaction was scaled up to a fed batch stirred tank reactor. Batch reactor and fed batch reactor configurations were compared for better conversions. The effects of aqueous phase hold‐up, substrate concentration and feed flow rate on the conversion of the reaction were also studied. Higher conversions were obtained in a fed batch reactor when compared with the batch reactor. In the fed batch reactor, increased conversions were observed with lower feed flowrates and high aqueous phase hold‐up. © 2001 Society of Chemical Industry