Batch polymerization control strategies

Continuous Polymerization Control Strategies hi continuous polymerizations, temperature and pressure are controlled in much the same way as in batch systems. 

Polymer production technology involves a diversity of products produced from even a single monomer. Polymerizations are carried out in a variety of reactor types batch, semi-batch and continuous flow stirred tank or tubular reactors. However, very few commercial or fundamental polymer or latex properties can be measured on-line. Therefore, if one aims to develop and apply control strategies to achieve desired polymer (or latex) property trajectories under such a variety of conditions, it is important to have a valid mechanistic model capable of predicting at least the major effects of the process variables. 

Obviously, temperature trajectories are not anployed in continuous reactors. Instead, the various vessels in a series of polymerization reactors may operate at different tanperatures. Then, the polymerizing mixture will see diffeoit tanpera-tures as it passes from one vessel to the next Likewise, monomer trajectories are replaced in continuous systans with intermediate injection of a more reactive monomer between polymerization vessels. This strategy can be exploited to adjust the CCD. Monomer conversion can be adjusted by manipulating the feed rate of initiator or catalyst. If online MWD is available, initiator flow rate or reactor temperature can be manipulated to adjust MWD. Polymer quality and end-use property control are hampered as in batch polymerization case by infrequenL ofif-Une measurements, hi addition, online measurements may be severely delayed due to the constraints of the process flow sheet. For example, even if online viscometry (via melt index) is available every 1-5 min, the viscometer may be situated at the outlet of an extruder downstream of the polymerization reactor. The transportation delay between the reactor where the develops and the viscometer where the is measured (or inferred) may be several hours. Thus, even with frequent sampling, the data are old. 

In continuous polymerizations, temperature and pressure are controlled in much the same way as in batch systems. Obviously temperature trajectories are not employed in continuous reactors. Instead, the various vessels in a series of polymerization reactors may operate at different temperatures. The polymerizing mixture, then, will see different temperatures as it passes from one vessel to the next. Likewise, monomer trajectories are replaced, in continuous systems, with intermediate injection of a more reactive monomer between polymerization vessels. This strategy can be exploited to adjust the copolymer composition distribution. 

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