Catalytic pyrolysis and kinetic study of real-world waste plastics: multi-layered and mixed resin types of plastics

Multi-layered and mixed resin types of plastics are a great challenge for the waste recycling industry. The majority consist of two or more types of polymers, making it difficult to recycle mechanically, which leads to landfill or incineration plant. As a way of thermochemical recycling, pyrolysis is a promising cleaner technology that could use this plastics waste stream potential and convert it into valuable products like fuels. The hypotheses of this research are that the average apparent activation energy of multi-layered and mixed resin plastic real-world waste samples can be decreased with the addition of selected iron-modified zeolite catalyst and that catalytic pyrolysis in fixed bed reactor will give products that show good potential for use as an energy vector. To evaluate activation energy, kinetic analysis was conducted using the isoconversional model-free Friedman model in conjunction with the multivariate nonlinear regression method. Pyrolysis products were analysed using nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy and calorimetry. The catalyst significantly reduced the activation energy of the flexible plastic film sample, which means that the process with catalyst requires less energy consumption. In the case of rigid plastics, the activation energy was lower at the beginning of the process with the catalyst. The catalyst reduced pyrolytic condensates’ viscosity of both samples. Analyses revealed how catalyst promoted the formation of aliphatic compounds in flexible plastics film oil, monoaromatic compounds in rigid plastics oil, and a significant decrease in polyaromatic compounds that degrade the quality of the fuel. The values of higher heating value were high (36–42 MJ/kg). Finally, the pyrolytic oil composition revealed satisfying quality and good potential for further use as an energy vector due to the high higher heating value. Graphic abstract