Study on pyrolysis behavior and kinetics of waste plastics with spent FCC catalyst

Abstract

Pyrolysis is the most promising method for treating plastic waste since it can convert waste plastics into high value‐added products, which have significant application potential. In this study, kinetic and thermodynamic analyses of spent fluid catalytic cracking (FCC) catalysts were performed for testing their applicability in catalytic cracking of mixed plastics. Thermogravimetric analysis data were obtained at different heating rates under an inert atmosphere, and the synergistic effect between the mixed plastics and activation energy reduction before and after pretreatment of the spent FCC catalysts was discussed. Through a variety of model‐free methods (Flynn‐Wall‐Ozawa, Kissinger‐Akahira‐Sunose, Starink, and Kissinger methods), it is proved that the spent FCC catalyst facilitates the reduction in activation energy required for the pyrolysis of plastics, which is reduced by approximately 13% from 278 to 242 kJ/mol. The catalytic performance of spent FCC catalyst was improved after pretreatment, while its activation energy decreased by approximately 21% from 278 to 220 kJ/mol. The Friedman‐Reich‐Levi method was used to fit the curve, and the number of mechanism functions in plastic pyrolysis was determined according to the slope of the fitting curve. The C‐R method was used in combination with the Malek method to determine the optimal mechanism function. Moreover, kinetic parameters of the spent FCC catalyst for catalytic cracking of plastics were obtained via kinetic studies on the pyrolysis of mixed plastics, which provided theoretical guidance for industrialization of plastic pyrolysis.

Simulation of the Two-Stage Pyrolysis Process of Mixed Waste Plastics

“…It can be seen from Figure that there is only one severe weight loss stage in the pyrolysis process of PP, LDPE, PS, and PET, indicating that the pyrolysis process of these four plastics is completed in one step . Among them, the conversion rates of PP, LDPE, and PS are close to 100%, indicating that the three plastics are almost completely converted into pyrolysis oil and pyrolysis gas during the pyrolysis process, resulting in almost no formation of pyrolysis residues.…”

Thermal degradation of virgin and waste plastics: Estimation of kinetic and thermodynamic parameters using model‐free iso‐conversional methods

“…A comparison of the experimental and model-predicted data showed a good agreement except at the high conversions (Figure 7). Shan et al (2023) 57 also found Avrami-Erofeev equation to satisfactorily fit the catalytic degradation data of HDPE, PP and PS. Das and Tiwari (2017) 7 and Zhang et al (2022) 46 reported a two-dimensional contractingcylinder model for the degradation of HDPE and LDPE and a three-dimensional contracting-sphere model for PP.…”