Selective preparation of aromatic compounds from catalytic pyrolysis polyester coating over Ni, Mo and Co metal modified ZSM-5

The chemical upgrade of the waste polyester coating on the surface of aluminum cans to value-added products can not only decrease the release of toxic substances, but also improve the quality of aluminum in the recycling process. In this study, different types of zeolite molecular sieve catalysts loaded with Ni, Mo and Co were synthesized, and utilized in the rapid catalytic pyrolysis of polyester coating. Among them, the Ni/ZSM-5 achieved the maximum aromatic compounds yield of 68.43 % at 600 ℃. A series of characterization results demonstrated that the embedding of transition metals (like Ni) could promote the cyclization and aromatization of products through deoxidation and dehydrogenation reactions by changing the pore structure and increasing total acid content (Brønsted and Lewis acids) of the ZSM-5 molecular sieve. Meanwhile, the thermodynamics of polyester coating during catalytic pyrolysis was studied by thermogravimetric method. The average activation energy of Ni/ZSM-5 catalytic pyrolysis of polyester coating is 238.65 kJ/mol. Furthermore, even after being reused for over 5 cycles, the catalyst can still maintain a relatively high yield of aromatic compounds (exceeding 60 %). Finally, the mechanism for aromatic compounds formation from Ni-modified ZSM-5 in-situ catalyzed polyester coating pyrolysis was proposed. This work provided useful ideas for the subsequent treatment of solid wastes.