Green Photochemical Processes and Technologies for Research & Development, Scale-up and Chemical Production

Photochemistry is often viewed as a green chemical method since photons are regarded as a 'clean and traceless reagent'. Despite this, photochemical transformations generally suffer from a variety of 'non-green' drawbacks that have prevented their widespread adaptation in chemical manufacturing. These include the necessity for hazardous solvents, low quantum yields of photochemical transformations, high energy demands of traditional lamps and the need for high dilution due to the low penetration of light into the reaction mixture. As a result, photochemical operations generate large volumes of hazardous solvent waste, demand prolonged irradiation times and require high energy inputs. This highlight article shows recent examples of green photochemical processes and technologies that overcome these limitations. These include photodecarboxylations in water matrices with high quantum yields in an advanced 308-nm excimer falling film reactor, solar photooxygenations utilizing concentrated sunlight generated in a parabolic trough loop and photosensitized additions in resource-efficient microreactors under continuous flow conditions. The results show that photochemistry can be implemented as a truly green methodology across the entire chemical process spectrum from early R&D to scale-up and subsequently production.