Study on kinetics of spent FCC catalyst applied to the living waste plastics

The thermochemical method is one of the most potential ways to treat waste plastics. In order to reduce the energy consumption of pyrolysis, this study selected spent fluid catalytic cracking (FCC) catalyst as a catalyst for pyrolysis of waste plastics to explore the pyrolysis process of mixed waste plastics (polypropylene (PP)/polyethylene (PE)/polystyrene (PS)). The kinetic calculations show that there was a positive synergistic effect in the co-pyrolysis of mixed plastics, which was beneficial to the reduction of activation energy. However, the participation of spent FCC catalysts can further reduce the pyrolysis temperature and activation energy of plastics, and increase the thermal degradation rate. Compared with non-catalytic pyrolysis, the pyrolysis temperature corresponding to the maximum weight loss rate during catalytic pyrolysis was about 12 K earlier, the maximum degradation rate was about 41% higher, and the average activation energy decreased by about 22 kJ/mol. In order to further improve the catalytic efficiency of spent FCC catalysts, the spent FCC catalysts were modified by ball milling or ultrasonic method and then used for plastic pyrolysis. It was found that the modification effect of ball milling method was better than that of the ultrasonic method. Through thermodynamic analysis, it was found that the endothermic reaction occurred in the process of plastic pyrolysis and could not proceed spontaneously. The formed pyrolysis products reduced the disorder of a microscopic system. Combined with the experimental results of this paper, it can provide theoretical support for the catalytic pyrolysis of spent FCC catalysts for mixed waste plastics.