(154aa) Thermal Oxo-Degradation of Post-Consumer Waste Plastics to Increased Yields of Desirable Products Using Less Energy

Lack of attention to the end-of-life disposal of plastics has resulted in their relentless accumulation in the environment or in landfills, motivating research on upcycling, largely defined as depolymerizing plastics into chemical building blocks for new products. One such method is pyrolysis of plastics to commodity fuels and chemicals. However, commercialization of conventional pyrolysis of plastic in an inert atmosphere has been hampered by large thermal requirements stemming from long reaction rates. The rate of thermal depolymerization of waste plastics can be accelerated by the addition of oxygen in a process known as thermal oxo-degradation (TOD). This study offers the prospect of TOD to upcycle post-consumer waste plastics rapidly and efficiently. Thermal oxo-degradation proceeds through a multi-step free-radical chain reaction in which oxygen has a catalytic effect on chain breaking reactions. Using moderate temperatures and small amounts of air in a fluidized bed reactor, we have shown that high density polyethylene and polypropylene are rapidly deconstructed to more than 80 wt.% condensable products while using up to 84% less energy due to exothermic energy release from partial oxidation reactions. Compositional analysis of TOD product oil shows 61 wt.% olefins and 19 wt.% di-olefins, which can be upgraded to value-added products. Similarly, polystyrene can be depolymerized through TOD to high yield (69 wt.%) of the monomer styrene, comparable to the 65 wt.% styrene achieved during pyrolysis. Through TOD, the depolymerization of polystyrene can become a self-sustained reaction, eliminating the need for external provisioning of thermal energy to the process. Comparable yields of the monomer styrene have been produced through this process. Thermal oxo-degradation has proved to be a successful pathway to a plastics circular economy through the reduction of energy while maintaining desirable yields, making it a commercially viable process.