Catalytic Depolymerization of Waste Polyolefins by Induction Heating: Selective Alkane/Alkene Production

Low- and high-density polyethylene (LDPE/HDPE) have been selectively depolymerized, without added H₂, to C2-C20 + alkanes/alkenes via energy-efficient radio frequency induction heating, coupled with dual-functional heterogeneous Fe₃O₄ and Ni- or Pt-based catalysts. Fe₃O₄ was used to locally generate heat when exposed to magnetic fields. Initial results indicate that zeolite-based Ni catalysts are more selective to light olefins, while Ni supported on ceria catalysts are more selective to C7-C14 alkanes/alkenes. LDPE conversions up to 94% were obtained with minimal aromatic, coke, or methane formation which are typically observed with thermal heating. Two depolymerization mechanisms, a reverse Cossee-Arlman mechanism or a random cleavage process, were proposed to account for the different selectivities. The depolymerization process was also tested on commercial LDPE (grocery bags), polystyrene, and virgin HDPE using the Ni on Fe₃O₄ catalyst, with the LDPE resulting in similar product conversion (∼48%) and selectivity as for virgin LDPE.