Scale-up of visible light organo-photocatalytic synthesis reactions in a spinning disc reactor

Visible light photocatalysis uses sunlight or low energy lighting; and recently a range of chemical transformations using organic dye catalysts have been discovered, which can replace toxic and expensive metal catalysts. A great challenge faced is that of finding innovative ways to scale-up visible light photocatalytic reactors, as they require large surface area to volume ratios due to light penetration being reduced with solution depth. This challenge suggests the use of a high surface area reactor, like a spinning disc reactor (SDR). This article reports the first in-depth study that compares the performance of a visible light SDR to a batch reactor, with the aim of establishing the key scale-up parameters. Two oxidation reactions using a cheap organic dye catalyst were studied (mass-transfer-limited & photon-flux-limited) using a specifically designed solar simulator. The key variables influencing the rate constant (s ⁻¹) and productivity (mmol h ⁻¹) were disc surface area, light intensity and flowrate. Light uptake was 900% higher for the mass-transfer-limited reaction and 400% higher for the photon-transfer-limited reaction in the SDR compared to the batch reactor and a disc pattern study identified optimal flow patternsThese findings were further confirmed by outdoor experiments, which showed similar results. This study offers a new way to scale-up visible light photocatalytic reactions, thereby reducing energy demand and moving industrial chemistry away from fossil fuels.