Free-radical polymerization of styrene using a split-and-recombination (SAR) and multilamination microreactors

• Continuous free-radical polymerization of St can be done in commercial microreactors.
• Polymer conversions of at least 30% are attainable.
• Overall heat transfer coefficients in the range of 2.8–3.04 kW/m2 K were obtained.
• The microreactors can equalize temperature differences of 70 °C at 97% efficiency.

The objective of this investigation was to characterize the heat transfer capabilities of two microreactors and to demonstrate their potential as chemical reactors for conducting the continuous free-radical polymerization of styrene monomer. The microreactors operate respectively with the split-and-recombination (SAR) and the multilamination mixing mechanism; and both units feature an integrated forced-convection heat exchanger. For the highest flow conditions investigated, the SAR and multilamination heat exchangers achieved maximum overall heat transfer coefficients of 3.02 and 2.8 kW/m2 K respectively reaching efficiencies of ∼0.95. Monofunctional, bifunctional, and tetrafunctional peroxide initiators were used for the polymerization runs at two reaction temperatures, e.g. 100 and 130 °C aiming at conversions of at least 30%. The functionality of the chemical initiator in combination with the right processing temperature was the main factor allowing attaining this conversion goal. It was found that only the tetrafunctional initiator was able to produce the conversion level desired at both temperatures. Low values of polydispersity indexes (PDI < 1.7) were obtained for all the reaction conditions investigated with the samples obtained in the multilamination microreactor exhibiting an overall lower value than those produced in the SAR configuration.