(708c) Multiphase Photoreactor Intensification Via Wireless LED Packed Beds

Photochemical and photocatalytic reactions are a powerful emerging tool in the green synthesis of organic molecules. In contrast to thermochemical reactions, they promise greater energy efficiency, milder reaction conditions, and a decrease in the number of synthesis steps. Unfortunately, conventional batch photochemical systems are not inherently scalable, making translation to industrial applications challenging. Fundamentally, this is most clearly attributed to the penetration depth of light, as described by Beer-Lamber relationship: as the size of the reactor is increased, the depth of light penetration into liquid medium decreases exponentially. Small-diameter plug flow reactors with external illumination have been employed industrially by Merck, AbbVie, and others to 1) transition photochemistry from batch to continuous flow, and 2) overcome light penetration challenges by employing millimeter-scale optical paths. In this work, a fixed bed reactor is packed with wireless µLEDs (µLED-PBR) and engineered to scale the oxidation of alpha-terpinene. Unlike tubular PFRs, the µLED-PBR design is infinitely volumetrically scalable. During the oxidation of alpha-terpinene, a co-current trickle flow regime was established with a 29 µm liquid film flowing over the μLEDs. In stark contrast to small channel tubular flow reactors, the packed bed experienced negligible hydrodynamic pressure drop penalties. In a stirred batch reactor, with 250 μLEDs shinning into the reactor, 12% conversion was achieved in 60 min, as compared to the 250 μLED PBR 11% conversion was achieved in a 1.4 min residence time. The space time yield of the reactor normalized to the power consumption for the µLED-PBR were orders of magnitude greater than other thin film flow reactors. The designed reactor has the potential facilitate the scale-up of other chemistries such as and metallophotoredox cross-electrophile coupling reaction.