The Technology

Worldwide production of plastics is currently more than 330 million tons per year with production of plastic waste anticipated to increase at an estimated 3.9% per year. It is estimated that approximately 12 trillion tons of plastic waste will require disposal by 2050. Currently, the majority of plastics are landfilled or incinerated with only a small proportion recycled, as plastic recycling is only available for some thermoplastics. Due to these limitations, plastic upcycling technologies, such as thermochemical degradation of pyrolysis and gasification are being explored. Pyrolysis and gasification, however, yield a mix of hydrocarbons and require tremendous energy, and gasification also generates carbon dioxide (CO₂). As such, a clean (low emission), energy-efficient process, directly producing defined valuable products is needed to improve the valorization of plastic waste.

NETL has developed a thermochemical decomposition method that employs a fluidized bed microwave (MW) reactor with inert gas for fluidization, an abundant magnetite catalyst (e.g., iron, alumina, metal oxides), co-fed into the reactor with mixed plastic waste. The reactor system enables the catalyst to be heated at a higher temperature than the plastic/porous media mixture, preventing the melting of the plastic before the catalyst reaches the reactive temperature, and minimizing liquid yields. This design removes the need for two separate reactors, reducing capital expenditures and operating costs. It also increases the residence time of the plastic in the reactor to completely decompose the plastics, tars, and hydrocarbons into H₂ and carbon and controls the rate of plastic breakdown. A solid/gas separator adjoining the reactor removes the resultant carbon and H₂ from the catalyst which is reduced in-situ and recirculated through the reactor bed for reuse. In lab tests, the MW-based process demonstrated an efficiency of over 70% in H₂ recovery from plastic waste and efficiency of more than 60%, superior to that of conventional pyrolysis-based plastic conversions. Only negligible amounts of CO₂ and carbon monoxide (CO) were produced.