Process intensification of a photochemical oxidation reaction using a Rotor-Stator Spinning Disk Reactor: A strategy for scale up

Photochemical transformations have witnessed a remarkable growth of attention in the past decade due to the popularity of photoredox catalysis and the technological progress in energy-efficient light sources. However, the scaling of these photon-induced processes remains a daunting challenge for chemists and engineers in the industry, often discouraging their implementation in the production of fine chemicals and pharmaceuticals. To address this key issue, we report herein the development of a conceptually new photochemical reactor, called photo Rotor-Stator Spinning Disk Reactor. The photocatalyzed gas–liquid oxidation of α-terpinene to the drug ascaridole with Rose Bengal as photocatalyst was achieved with throughputs of over 1 kg·day−1 (270 mmol·h−1) under visible light irradiation. The performance of the reactor is correlated to various process parameters such as rotation speed, liquid flowrate, and catalyst concentration, among others. The conversion and selectivity increase from 37% to 97% and 75% to 90% respectively with an increase of rotation speed from 100 to 2000 RPM. The reactor operates with negligible pressure drop and allows for facile fine-tuning of the mixing efficiency. In this paper, we have also compared the performance of this reactor to other reactors such as the batch, micro, thin-film, and the vortex reactor, among others, and have found the photo-Rotor-Stator Spinning Disk Reactor to have superior productivity as well as higher productivity per volume (2.8 mol ·s−1 ·m−3). The findings of this study can be used to study, design, optimize and scale photochemical processes using the rotor–stator spinning disk reactor.