A sustainable way of recycling polyamides: dissolution and ammonolysis of polyamides to diamines and diamides using ammonia and biosourced glycerol

Abstract

In order to make recycling a viable strategy for post-consumer plastics, economically feasible revalorization processes must be developed. The ammonolysis of polyamides can be such a cutting-edge recycling technology; however, due to the rigid structure of these polyamide plastics, operating conditions of current ammonolysis processes are harsh, including high temperatures (>300 °C) and high NH₃ pressures. Here, we report a very green and elegant ammonolysis process of the widely abundant polyamide 66 by using a hard Lewis acid catalyst and 1 bar of NH₃ in a simple glycol solvent at 200 °C. Computational studies revealed that especially the vicinal diol moiety of these glycol solvents plays a key role in activation of the ammonia nucleophile, with glycerol being the most effective solvent, reaching the depolymerization equilibrium after 20 h even without a catalyst. To our delight, a biosourced glycerol (obtained from the saponification of triglycerides) could also directly serve as a suitable solvent, even outperforming the ammonolysis process in highly purified glycerol.