The global production of plastics, 400 mmt in 2015, is rising at &gt;4%/yr. Nevertheless, the recycling rate of waste plastics is unsustainably low, &lt;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. 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 (ZSM-5)-based Ni catalysts are more selective to light olefins, while Ni supported on ceria catalysts are more selective to C7−C14 alkanes/alkenes. The morphology of the zeolite support influences product selectivity as Pt on different zeolite types give a different range of product. Whiles MFI are selective towards light products, zeolite LTL are geared towards bigger hydrocarbons. LDPE conversions up to 95% 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.

Catalytic depolymerization of waste polyolefins by induction heating:  Selective alkane/alkene production

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.