Catalytic Pyrolysis of Polyethylene with Microporous and Mesoporous Materials: Assessing Performance and Mechanistic Understanding.

Abstract

Testing the performance for the catalytic pyrolysis of plastic waste is hampered by mass transfer limitations induced by a size mismatch between the catalyst's pores and the bulky polymer molecules. To investigate this aspect, the behavior of a series of microporous and mesoporous materials was assessed in the catalytic pyrolysis of polyethylene (PE). More specifically, a mesoporous material, namely sulfated zirconia (Zr(SO4)2) on SBA-15, was synthesized to increase the pore accessibility, which reduces mass transfer limitations and thereby enables to better assess the effect of active site density. To demonstrate this approach, mesoporous SBA-15 wascompared to microporous zeolite Y. Using the degradation temperature during thermogravimetric analysis as a measure of activity, no correlation between acidity and activity was observed for microporous zeolite Y. However, depending on the Mw of PE, the reactivity of the mesoporous catalysts increased with increasing Zr(SO4)2 weight loading, showing that utilizing a mesoporous catalyst can overcome the accessibility limitations at least partially, which was further confirmed by polymer melt infiltration and in situ X-ray diffraction. Product analysis revealed that more aromatics and coke were produced with zeolite Y. The mesoporous material remained active and structurally intact and catalyses PE degradation via acid- and radical-based pathways.