Overcoming mass and photon transfer limitations in a scalable reactor: Oxidation in an aerosol photoreactor

Abstract

The use of microflow reactors enabled dramatic improvements in the apparent rates of photochemical reactions. However, scaling-up of photomicroreactors remains a challenge due to the difficulties of distributing light and flow to all units of photomicroreactors. In this work, the mass and photon transfer limitations of an easily scalable micro-structured reactor, an aerosol photoreactor, was studied. In this reactor concept, each droplet works as a microreactor. The nature of aerosol light interaction enables good light distribution to all the droplets. A singlet oxygen mediated photosulfoxidation reaction was utilized as a model reaction to assess the reactor performance. The light transfer limitations were proven to be overcome in the aerosol photoreactor. The reaction rate constant was calculated as 0.12 s−1. A simple solution of the convection–diffusion equation for a droplet was presented to check for the mass transfer limitations in aerosol reactors. The Sauter mean diameters of the droplets at different pressures varied between 7 and 8 µm. The aerosol photoreactor was proven to overcome the mass transfer limitations at these droplet diameters. In addition, the highest volumetric mass transfer coefficient (kLa) was calculated as 1.2 s−1, which was at the same order of magnitude compared to other intensified photoreactors such as Corning Advanced Flow ReactorsTM or a gas–liquid microreactor. A discussion on increasing the throughput of aerosol photoreactors further is presented. This work paves the way for efficient and scalable photoreactors for industrial use.