Control of polymerization processes using an inhibitor

In this work the behaviour of two substances (inhibitors or retarders) has been studied in a series of methylmethacrylate polymerization experiments by using calorimetric techniques. The substances used were: hydroquinone and 1,4-benzoquinone. In order to identify situations that can lead to a runaway reaction, an Early Warning Detection System (EWDS) has been used. The detection criterion for runaway is based on the calculation of the divergence of the reactor. When the EWDS signals an alarm, small amounts of inhibitor or retarder have been added to the reaction mixture. The use of substances that can destroy the free radicals during polymerization processes is a good method to stop the reaction if a runaway phenomenon occurs. In this work the behaviour of hydroquinone and 1,4-benzoquinone was investigated in methylmethacrylate polymerization processes. The first behaved as an inhibitor, the second as a retarder. In order to control an emulsion polymerization process benzoquinone is preferred because, if added during the reaction, it does not completely stop the process but diminishes the polymerization rate giving a higher final conversion. An Early Warning Detection System (EWDS) has been used to identify anomalous process conditions that can lead to runaway reactions. The EWDS performance has been satisfactory: in fact anomalous temperature behaviours have been early detected without producing false alarms.