Photocatalytic reactor design is a challenge which inherits the existing mass transfer issues of conventional catalysis with the addition of photon transfer issues. For more than three decades, many research teams have taken the challenge and various new design concepts have emerged to overcome the limitations. The majority of the research on photocatalytic reactor design was put to use on reactors with environmental applications, namely, wastewater treatment. This work is a review on the most important design concepts which had a high impact on the photocatalytic reactor designs. Another aspect covered in this work is the methods for comparing the wastewater treatment reactors. Several benchmarks have been considered and the new photocatalytic space–time yield benchmark measure has been demonstrated by comparing three different designs. With the aid of the new benchmark measure and the extensive state of the art, a new direction in the research on photocatalytic wastewater treatment is indicated, namely, lighting design instead of new geometries.

This research investigates heating in microreactors by application of microwave fields. Problems encountered with microwave heating equipment currently used in microwave enhanced chemistry research are: hardto-predict electromagnetic field patterns, the lack of controllability and optimizabillity of heat generation, and low utilization efficiency. This conflicts with the highly optimized processing conditions that are characteristic for microreactor systems. These issues are related to the resonant nature of microwave fields. To avoid these problems a novel coaxial traveling microwave field applicator is proposed here and a method to optimize it is demonstrated.