Tandem pyrolysis-catalytic upgrading of plastic waste towards kerosene-range products using Si-pillared vermiculite with transition metal modification

The transformation of waste plastics to fuel products is an appealing strategy to address plastic-associated environmental and energy issues. In this study, a tandem pyrolysis–catalytic upgrading approach, using a series of mono-/bitransition-metal-modified Si-pillared vermiculite catalysts, was adopted to transform disposable grocery bags (i.e., a polyethylene-based material) to kerosene-range fuels. The results revealed that the silicon pillars contributed to the catalyst’s excellent thermal stability to withstand temperatures of up to 1000 °C, while the transition-metallic species (e.g., Co/Ni/Fe) contributed to the fine-tuning of the catalyst’s acidity and porosity. Specifically, Co–Fe/Si-pillared vermiculite (SPV) (5:5) produced the highest yield of oil products (75.7 wt%), with alkane and aromatic selectivities of 57.5% and 27.8%, respectively, resembling the composition of kerosene. The catalyst’s high selectivities for the targeted products were attributed to the controllable acidity and porosity, enabling a balance to be achieved between these two properties. Pathways were proposed for the tandem pyrolysis in the presence of Co–Fe/SPV. The vermiculite-based catalysts showed satisfactory reusability following regeneration. Beyond polyethylene-based plastics, these catalysts are also applicable to the pyrolysis of other plastic feedstocks. Because vermiculite is a low-cost material, the developed catalyst has good commercialization potential for a wide spectrum of waste-to-energy conversions.