Effects of melt-state shear homogenization on catalytic pyrolysis of mixed plastic waste for feedstock recycling

Abstract

Although significant effort has been made to develop separation and sorting strategies for recycling mixed plastic waste in recent decades, these processes are often complex, time-consuming, and labor-intensive, and may not be efficient when scaled up. This research aims to evaluate the potential of a homogenization and dechlorination algorithm based on a remelting-restabilization technique to improve the homogeneity of heterogeneous mixed plastic waste through high-shear pulverization. The effectiveness of this method for chemical recycling in the presence of a synthesized clay catalyst was evaluated and modeled using pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and kinetic studies. The results showed a significant increase in the homogeneity level of mixed plastic in terms of physical, thermal, and rheological behavior after two runs of extrusions. Additionally, the amount of chlorine in the mixed waste samples was reduced from 18.3 mg/kg to 1.45 mg/kg after thermal treatment at 300 °C for 2 hours. The inclusion of a modified clay catalyst resulted in a reduction in activation energy and initial degradation temperature by approximately 13% and 31%, respectively. The modeled kinetics results showed that the reaction rate in the presence of the catalyst increased at both low and high conversions over a wide range of temperatures. However, an increase in the number of extrusions only increased the degradation rate at high temperatures due to induced thermal history. Py-GC-MS test results revealed that the use of clay catalyst in homogenized samples enhanced the amount of low carbon atom products (C5 to C12) by 7.5% and 27% at 450 °C and 550 °C, respectively. Furthermore, the amount of aromatic product increased after the inclusion of the clay catalyst for both pyrolysis temperatures, including 450 °C and 550 °C.