Continuous synthesis of tert-butyl peroxypivalate using a single-channel microreactor equipped with orifices as emulsification units

Abstract

The two-step synthesis of tert-butyl peroxypivalate is performed in a single-channel microreactor. The first step, the deprotonation of tert-butyl hydroperoxide, is done in a simple mixer tube setup. The residence time section for the second reaction step is equipped with orifices for interfacial area renewal, needed for ensuring mass transfer between the two immiscible phases. The strong dependence of the reaction performance on the size of the interfacial area is demonstrated by using a setup with 4 orifices (distance of 52 cm), giving a HPLC yield of 71% at a residence time of 8 s and a reaction temperature of 23 °C. A further shortening of orifice distances helped to shorten the residence time down to 1.5 s and 0.5 s (using 9 orifices and 3 orifices with a distance of 5 cm). When using these setups, the produced heat could not be removed from the system sufficiently quickly (ΔT=38 K). The achieved yields (ca. 70% by HPLC) are close to the state of the art (cascaded batch processing) and provide an indication that the tert-butyl peroxypivalate synthesis can be performed at higher temperatures or at least, a more flexible process control can be allowed compared to high-volume batch reactors. Processing at higher reaction temperatures up to 70 °C shows a slight optimum at reaction temperatures between 40 °C to 50 °C, depending on the setup used. Knowing this novel process window as well as the optimum orifice geometry and distance will allow for tailored design of the microreactor. For the processing in the single-channel microreactor setup using 9 orifices (distance of 5 cm) and a reaction temperature of 40 °C a space-time-yield of 420,000 g L(-1) h(-1) was reached which is higher than the space-time-yield for the industrial 3 cascaded batch reactor process (190 g L(-1) h(-1)).