(183b) Catalytic Depolymerization of Waste Polyolefins By Induction Heating: Selective Alkane/Alkene Production

The global production of plastics, 400 mmt in 2015, is rising at >4%/yr. Nevertheless, the recycling rate of waste plastics is unsustainably low, <10% in the U.S. The current approaches to recycling plastics have many limitations. For example, plastics pyrolysis is limited by an unwieldly product distribution and high operating temperatures. In this work, we depolymerized polyethylene (LDPE, HDPE) to useful products by utilizing efficient energy input from RF induction heating, coupled with a heterogenous catalyst.

We have selectively depolymerized, without added H₂, low- and high-density polyethylene to C2-C20+ alkanes/alkenes by utilizing efficient energy (lower fluid temperature) RF induction heating, coupled with dual-functional heterogenous catalysts consisting of Fe₃O₄ nanoparticles and Ni-based catalysts. The Fe₃O₄ was used to locally generate heat when exposed to the RF field (<65 mT). Initial results indicate that nickel-exchanged zeolite catalysts are more selective to light olefins with fewer aromatics and minimal coke formation, while nickel supported on CeO₂-ZrO₂ or CeO₂ is more selective to C7-C18 alkanes/alkenes, but with some coke formation. LDPE conversions up to 95% was obtained with Ni supported on Fe₃O₄ at 600 A, 2 h, with minimal aromatics, coke and light gas formation. The difference in selectivities is associated with two possible depolymerization mechanisms, a reverse Cossee-Arlman mechanism or a random cleavage process. The depolymerization process was also tested on commercial LDPE (grocery bags) using the Ni on Fe₃O₄ catalyst, resulting in similar conversion to liquids and gases (~48%) as for virgin LDPE but reduced coking under the same reaction conditions.