Alkali Metal Doped SiC Foam Microwave Fast Response Catalyst for Selective Production of Monocyclic Aromatic Hydrocarbons from Polyethylene Pyrolysis

Microwave catalytic pyrolysis offers an efficient route to converting low-density polyethylene (LDPE) into monocyclic aromatic hydrocarbons (MAHs) but is limited by poor heat and mass transfer. Herein, alkali metal doped SiC foams are designed as advanced catalyst supports with superior microwave absorption, high surface roughness, and low pressure drop. K@SiC foam is heated using microwave, which rapidly heats to 600 °C in 40 s, at the heating rate of 14.5 °C/s, over 2.45 times that of commercial SiC spheres. In contrast, undoped SiC foam only reached 150 °C after 10 min. When using K@SiC foam loaded with ZSM-5 and pseudoboehmite as the catalyst for LDPE pyrolysis at a pyrolysis temperature of 500 °C and a catalytic temperature of 450 °C, with a bed height of 109 mm and a feeding rate of 60 g/h, the resulting bio-oil contained average aromatics and MAHs contents of 86.34% and 81.98%, respectively. After wet-air regeneration, the regenerated catalyst achieved 86.04% MAHs selectivity, even significantly outperforming the fresh catalyst, and the catalyst maintained stable performance over two cycles. The characterization results show that regeneration under wet air yields a higher specific surface area of 90.39 m2/g. This suggests that water vapor etching enlarges the catalyst pores, reducing pressure drop and offering guidance for industrial application.