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  • 1
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 28 (1988), S. 121-135 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The control of polymerization reactors is particularly arduous for several reasons; (a) difficulty in specification of the control objectives; (b) high exothermicities and viscosities involved: (c) complicated process dynamics: and (d) problems with measurement of the polymer structure. Computer control has now simplified many tasks such as sequential operations of batch reactors; but no less important, it has made feasible the implementation of elaborate state estimation and control algorithms. The tendency in the polymerization industry and in current research centers is centered on producing ‘tailor-made’ polymers from the view of its microscopic and/or macroscopic structures. To this end, several solutions have been proposed. For example, in the ‘chemical approach’, open loop methods have been developed based on the detailed dynamic models of the processes. Any control technique requires a knowledge of the process to be controlled through mathematical models. These models may be developed either from detailed mass and energy balances, or through empirical input-output or “black-box” techniques. The most promising control techniques are probably optimal control, adaptive control, and their combinations. Optimal control is powerful because it utilizes directly the detailed non-linear plant model. Adaptive control developed for linear plants has already proven satisfactory, in spite of the highly nonlinear nature of the polymerizations. Undoubtedly, improved solutions will be obtained when this technique is extended to non-linear systems.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 33 (1987), S. 2165-2177 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: In a previous publication1, a suboptimal technique was developed to solve the problem of producing polymers with prespecified values of the number-average chain length and the polydispersity, through “living” anionic polymerizations carried out in continuous stirred-tank reactors. The solution of that problem involved the periodic operation of the monomer solution feed and of the initiator solution feed, as well as readjustments in their feedstock concentrations. The present work solves the problem directly, without resorting to laborious “optimization-rescaling” procedures. The objective functional considers not only the polymer quality, but also the required polymer production. Compared with the previous results1, the present solutions are better and obtained with less computational effort. The proposed technique may be applicable to other optimal periodic control problems with nonconventional objective functionals.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 31 (1986), S. 1019-1039 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Within certain limitations, this work shows that the production of polymers with any prespecified number average chain length and polydispersity is theoretically feasible when “living” anionic polymerizations are carried out in continuous stirred tank reactors (CSTRs) which are under optimal periodic forcing of the feed flows. The optimal periodic control problem was solved adopting a suboptimal objective function and a novel iterative numerical procedure. When the objective function is minimized in order to reduce the time average polydispersity, then the operation tends to become a sequential semibatch process. Conversely, if the objective is to maximize these variables, then the reagent concentrations inside the reactor tend to be 180° out of phase. Different periods of oscillation must be selected depending on whether the required average polydispersities are above or below the steady state value of 2. The greatest flexibility in the MWD control is obtained with fast kinetics, and, in this case, average polydispersities between 1.06 and 9.2 may be required.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 374-382 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: This work proposes a cascade model reference adaptive algorithm to control a continuous polymerization reactor, which is operated under forced oscillations of its feeds. The objective is to produce a polymer with desired average values of the average chain length, of the average polydispersity and of the average polymer production; in spite of the fact that some of the model parameters may be unknown and/or may vary slowly with time. This objective is achieved by imposing the first two moments of the number chain length distribution (NCLD) to follow predetermined periodic trajectories. The proposed control scheme is an extension of that by Eliçabe, et al., when the number of independent controls is less than the number of system states. Computer simulations have shown the feasibility of the proposed technique, provided continuous state measurements are available.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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