(354e) Microwave Catalysis Technology Application in Plastic Upcycling

The chemical upcycling of plastic represents an attractive approach of using plastic waste as feedstock in promoting the circular economy and decarbonizing the chemical industry. Currently, the majority of plastic ends up in landfills or the environment, harming the ecosystem and affecting the natural environment. Thermochemical pathways (e.g., pyrolysis, gasification) and high pressure hydrogenolysis enable depolymerization films to produce small molecules that could be used as fuel or integrated into chemical refineries. However, these thermochemical processes suffer from severe challenges which include inevitably higher energy input leading to higher greenhouse gas (GHG) emission (i.e., ∼12 kgCO₂/1 kg H₂ production in gasification); poor product selectivity; low value of products, thus requiring significant upgrading for converting to valuable products.

In this work, we reported the application of microwave catalysis technology application in plastic upcycling. Microwave heating has many advantages over conventional heating, including non-contact, selective and rapid heating, and quick start-up and shutdown. This fundamental difference results in important advantages in using microwave to initiate the catalytic depolymerization of plastics, particularly, the microwave irradiation’s selectivity, as the microwave almost exclusively interact with the absorbing catalyst particles whilst the plastic substrate remains cold; thus, the self-decomposition of plastic polymers and many side reactions that occur at high temperatures are effectively limited.

The microwave catalysis technology demonstrated several advantages in plastic upcycling: (1) lower energy consumption leading to lower GHG emission, < 300 °C under atmospheric pressure; (2) higher selectivity of target product; (3) higher value of products (e.g., BTX aromatics (benzene, toluene, and xylene), ethylene, carbon nanofibers, and H₂, etc.); (4) moreover, the product can be adjusted based market requirement. For example, a high BTX aromatics (benzene, toluene, and xylene) yield of 44.7 % from low-density polyethylene (LDPE) was achieved using ZSM-5 catalyst at a low temperature of 300 °C under atmospheric pressure. Also, as shown in Figure 1, the high-quality separated CNFs can be generated from LDPE by microwave catalysis, meanwhile, the high purity H₂ (>93%) generated.

This proof-of-concept heralds an exciting new era of applications for the responsible and sustainable recycling of waste plastic, in which plastic are efficiently converted back to high-value petrochemical products.