LCA as a Tool to Detect Environmental "Hot Spots" in Early-Stage Mechanochemical Synthesis of Organic Dyes

Reducing environmentalimpacts through mechanochemical processing:life cycle assessment is performed to evaluate the environmental impactof organic dyes, valuable chemicals used in multiple industrial applications,via mechanochemical twin screw extrusion. Life cycle environmentalimpact results are significant for producing the dyes through twinscrew extrusion compared to those from a solvent-batch process. Mechanochemical methods are currently under investigationas alternativeapproaches to conventional solvent-batch synthetic chemistry. Environmentallife cycle assessment (LCA) is needed to evaluate and compare chemicalproducts made through mechanochemical processes with those from conventionalproduction routes, using "cradle-to-gate" system boundaries.However, chemical supply chains involved in product manufacturingare often unknown, and synthesis tracing of these chemicals is neededto create life cycle environmental profiles. Herein, we trace thesynthesis of the chemicals required to produce Pigment Black 31, aperylene diimide (PDI) organic dye, based on two main principles:maximum reaction yield and minimum synthetic steps. This approachfacilitates comparing the environmental life cycle impact of producingPigment Black 31 via twin-screw extrusion (TSE) with a conventionalsolvent-batch process, wherein similar reactants are used in bothsystems. The production of Pigment Black 31 via the TSE process affordsa roughly order-of-magnitude reduction across global warming and humanand ecological health life cycle environmental impacts following ReCiPe2016 methods, mainly due to solvent reduction and elimination comparedwith production via the solvent-batch process. Interestingly, thisreduction is found despite the need for a methanol extraction stepin the purification of Pigment Black 31 made by TSE. We conclude thatwhile LCA data sets may not be available for other organic dyes producedsimilarly through TSE processes, the life cycle environmental impactsfor Pigment Black 31 can be used to approximate those of similar organicdyes, such as Pigment Black 32.