Industrial polymerization reactors, control

H. Seki, M. Ogawa, S. Ooyama, K. Akamatsu, M. Ohshima, and W. Yang. Industrial application of a nonlinear model predictive control to polymerization reactors. Control Engineering... 

Modeling and Control of Continuous Industrial Polymerization Reactors... 

Control of industrial polymerization reactors is a challenging task because, in general, control engineers lack rigorous polymerization process knowledge, process model, and rapid online or inline sensors to measure polymer properties. Exothermic polymerization processes often exhibit strongly nonlinear dynamic behaviors (e.g., multiple steady states, autonomous oscillations, limit cycles, parametric sensitivity, and thermal runaway), particularly when continuous stirred tank... 

Most industrial polymerization reactors are operated at constant tanperature and constant pressure, and sometimes controlled using computer data acquisition and sensors. So, Equation (12.6) may be well applicable for these systems. Combining Equation (12.6) with Equation (12.5) ... 

Ratio control is a form of feedforward control which is widely used in the chemical industry and has proven very useful in polymerization reactor control. As is evident from its name, its purpose is to keep the ratio of two process variables at a... 

In many industrial polymerization processes, pressure is applied to control the thermodynamic state in the reactor as well as to effect downstream separations of products... 

Industrially, polymerizations are carried out to over 99% conversion and thus there is no need to reduce the unreacted monomer unless very low levels are required to meet regulatory. product, or workplace requirements. Most poly(vinyl acetate) emulsions contain less than 0.5 wt % unreacted vinyl acetate. All of the processes are operated in conventional glass-lined or stainless steel kettles or reactors. Control of the process is important to ensure reproducibility of the product. 

Another reason for taking control action only when the process is out of control is because there is assumed to be a cost associated with control action. This is often true in the discrete manufacturing industries where it may be necessary to shut down the assembly line in order to make adjustments to equipment. Often this is not true in the chemical process industries where corrective action may be free , as in the adjustment of the temperature of a polymerization reactor. 

Lewin, D.R., 1996. Modelling and Control of an Industrial PVC Suspension Polymerization Reactor. Computers Chem Engng 20 S865-S870. 

PVA is produced on an industrial scale by hydrolysis (methanolysis) of PVAc, often in a one-pot reactor. Different grades of PVA are obtained depending upon the degree of hydrolysis (HD). Polymerization reactions can be carried out in batch or in continuous processes, the latter being used mostly for large-scale production. In the continuous industrial process, the free-radical polymerization of vir l acetate is followed by alkaline alcoholysis of PVAc. The molecular weight of PVAc is usually controlled by estabhshing the appropriate residence time in the polymerization reactor, vir l acetate feed rate, solvent (methanol) amount, radical initiator concentration, and polymerization temperature. 

In this section, the proposed process-control design approach is illustrated with a representative starved emulsion semibatch polymerization and numerical simulations, with a model that emulates and industrial size reactor [11], Moreover, the simulation example corresponds to a scaled-up version of the theoretical-experimental calorimetrie estimation study presented before with a laboratory scale reactor [15]. 

Polymerization - that is, polycondensation and polyaddition - performed on an industrial scale presents a number of specific reaction and process engineering aspects which differentiates these processes from reactions of low molecular weight molecules. This is also true for aspects of the dynamic control of polymerization reactors. Therefore the concepts developed for low-molecular-weight chemistry must be adapted to the specific problems of polymerization reactions. The scope of the present chapter is the assessment of risks linked with the performance of polymerization reactions on an industrial scale. Moreover, the focus is on the control of the course of reaction by means of chemical reaction engineering [1]. Risks linked with handling of raw material or products are not treated in this chapter. Part of the chapter is based on a comprehensive text by Moritz [2], who is acknowledged for his authorization to use it here. 

The polymerization reactor is usually at the heart of the manufacturing process, impacting both downstream processing and final customer-related polymer properties. The following factors have contributed to the industrial significance of polymer reactor control ... 

J. P. CoNGALiDis, J. R. Richards, Process control of polymerization reactors an industrial perspective , Polym. Reaction Eng., 1998, 6, 71. 

Hvalaa N, Aller F, Mitevaa T, Kukanjab D. Modelling, simulation and control of an industrial, semi-batch, emulsion-polymerization reactor. Comp Chem Eng 2011 35 2066-2080. 

The approach to the steady state is important in industry because it controls the rate at which product grade crossovers occur in continuous reactors. For the HCSTR, Equations indicate how c,(0, cjt), and c(f) vary as functions of time for different combinations of flow, polymerization, and concentration conditions. 

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