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Kinetic and Mechanism Studies on Pyrolysis of Printed Circuit Boards in the Absence and Presence of Copper

2018; American Chemical Society; Volume: 7; Issue: 2 Linguagem: Inglês

10.1021/acssuschemeng.8b03382

2168-0485

Wei Liu, Jiaqi Xu, Junwei Han, Fen Jiao, Wenqing Qin, Zhuzhang Li,

Microplastics and Plastic Pollution

The kinetic and mechanism of pyrolysis for Cu-free printed circuit board (CFPCB) and Cu-coated printed circuit board (CCPCB) were studied using nonisothermal thermo-gravimetry (TG) analysis coupled with Fourier-transform infrared (FTIR) spectrometry. TG and DTG (differential thermo-gravimetry) analyses were performed to study the mass loss characteristics. Kinetic analysis adopted the Ozawa–Flynn–Wall (OFW) model to confirm the reaction series by the variation pattern of activation energy. The real-time detection technique was used into three-dimensional (3D) FTIR analysis for providing the composition of evolved gases. The results indicated that the pyrolysis reaction of CFPCB can be divided into four separate stages. Stage I (α < 0.075) was ascribed by the breakage of N-containing cross-linkages with low boiling volatiles formed. The irregular cleavage of chemical bonds occurred in Stage II (0.075 < α < 0.85) with the decomposition of both brominated and nonbrominated compounds. In Stage III (0.85 < α < 0.9), the decomposition of nonbrominated compounds was proceeded with the small molecules continuously released. The pyrolysis reaction was almost completed in Stage IV (α > 0.9) with chars formed and few small molecules released. For the CCPCB pyrolysis, only two reaction stages were observed. Complex reactions with the decomposition of both brominated and nonbrominated compounds were observed in Stage I (α < 0.85), with various organic and inorganic components formed. In Stage II (α > 0.85), chars were formed and few small molecules were released. The presence of copper affected the reaction rate and product components during the pyrolysis of PCBs, resulting in shorter reaction time, lower activation energy and fewer brominated pollutants. However, the presence of copper also posed a difficulty for the efficient separation of evolved components and cleaning treatment of tail gases.