Control of monomer conversion and polymer production

A second classical control problem is the control of the residual monomer content (monomer conversion) of the polymer material that is withdrawn from the reactor and of the polymer productivity. Maximum monomer conversion and polymer production are limited by short reaction batch times (or residence times in continuous reactors), by the existence of diffusional limitations in the reaction medium (glass effect 

Reduction of the final monomer content of the produced polymer is of fundamental importance for many practical reasons. First, increase of monomer conversion usually leads to increase of polymer productivity (unless significant increases of batch times and/or residence times are implemented simultaneously), which may cause a significant impact on the process economics. Besides, monomer (and other volatile organic compounds (VOCs)) content of the final polymer product is limited by law and market preferences. This limiting concentration is usually much lower than the one achieved during polymerization, which means that additional post-polymerization treatments are required. As these are costly operations, it is interesting to minimize the amount of monomer at the end of polymerization (maximize monomer conversion). 

Reduction of residual monomer (increase of monomer conversion) and increase of polymer productivity can be obtained through manipulation of reaction times [29], of reactor temperatures (which may be allowed to increase at the end of the polymerization to promote the conversion of the residual monomer) [30], of monomer feed rates [31] and of mixtures of initiators (or of bifunctional initiators) and catalysts with different decay characteristics [32]. 

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