Tailor-made microdevices for maximizing process intensification and productivity through advanced heating

For the Kolbe–Schmitt synthesis from resorcinol, large process intensification was achieved recently, using a simple continuous set-up comprising a capillary reactor. However, the productivity of such capillary is low and the design less convenient for scale-up to the pilot or even production scale. Consequently, a tailor-made electrically heated microdevice was developed and successfully tested for the pilot scale using the internal numbering-up approach and enabling external numbering-up. For the Kolbe–Schmitt synthesis in aqueous potassium hydrogen carbonate solution, a productivity of 225 kg/h at 4 s residence time and 32% yield was achieved, corresponding to a space-time yield of 38,250 kg/(m3 h). As alternative heating approach, continuous microwave heating applying both multi-mode and single-mode devices and using capillary reactors of different dimensions and shapes was investigated and revealed the benefits of a compact design with respect to microwave absorption and of small dimensions for higher space-time yields up to 32,550 kg/(m3 h). The first attempt of developing a microstructured plate reactor made of PEEK for continuous microwave heating did not lead to the expected performance. The detected reasons are discussed.