Study on the kinetics of catalytic pyrolysis of single and mixed waste plastics by spent FCC catalyst

Plastic products are an indispensable part of life and are widely used in different fields. However, plastic products have the characteristics of short average service life and not easy to degrade naturally, which are prone to cause serious environmental pollution by long-term accumulation in the environment. The use of low-cost catalysts is the goal pursued by enterprises. In this paper, polypropylene (PP), low-density polyethylene (LDPE), polystyrene (PS), mixed waste plastics (WPs) and spent FCC catalyst (a solid waste produced by oil refining enterprises) were used as research objects to simulate the pyrolysis and catalytic pyrolysis of waste plastics in real life. The results showed that compared with the direct pyrolysis of plastics, the addition of spent FCC catalysts could significantly reduce the initial pyrolysis temperature of PP, LDPE and WPs, with the largest decrease in the initial pyrolysis temperature of PP (about 59 K). The average activation energy of PP, LDPE and WPs decreased with the participation of spent FCC catalyst compared with the direct pyrolysis. Among them, the activation energy of LDPE decreased most significantly (about 22 mass%), followed by PP, and WPs decreased the least. However, the results of thermogravimetric analysis and kinetic calculations showed that the spent FCC catalyst was not suitable for catalytic pyrolysis of PS. The purpose of this experiment is to promote "circular economy". The solid waste products produced by oil refining enterprises are applied to the catalytic pyrolysis of waste plastics, which provides theoretical support and data reference for reducing the energy consumption of plastic pyrolysis and realizing the diversified application of spent FCC catalysts.