(724a) Non-Thermal Plasma-Assisted Hydrogenolysis of Waste Plastics to Light Hydrocarbons

While the wide application of plastic materials has significantly improved the convenience and quality of human life, the processing and recycling of waste plastics (WPs) has become an ever-growing challenge. Accompanied by the big demand for plastic products, more and more WPs have been generated. It is reported that more than 300 million tons of WPs were generated in 2015 alone. As of date, only less than 20% of these WPs can be recycled, with the rest ending up in landfills and incineration or being directly released to the environment. The inability to recycle WP has not only caused huge pressure on the environment, but also wasted tremendous amount of carbon resource. Chemical processes including pyrolysis and gasification have been actively investigated for converting WPs to value-added synthesis gas and carbonaceous materials. However, a high operating temperature (700–1300 K) is typically required to overcome the unfavorable thermodynamics and kinetics that makes these methods cost inhibitive. More recently, there have been a few studies on plastics hydrogenolysis. However, harsh reaction conditions of high temperature (600–700 K) and pressure (10–30 bar) and relatively long reaction time (> 6 h) were still needed, suggesting low hydrogenolysis kinetics.

Herein, we report a novel non-thermal plasma-enabled method which allows efficient hydrogenolysis of pure and post-consumer plastics under ambient temperature and atmospheric pressure condition. Non-thermal H₂ plasma provides a unique medium for generating reactive hydrogen species, primarily in form of ions and radicals, which can effectively break C-C bond in the polymeric structures and drive kinetically unfavorable reactions under mild reaction conditions. Light alkanes, predominately CH₄, C₂H₆ and C₃H₈ with >95% selectivity, were obtained under ambient condition (25 °C) as result of favorable thermodynamics and fast reaction kinetics in the non-thermal plasma-assisted hydrogenolysis of high-density polyethylene. Employment of this method to polystyrene generated liquid products and C₁–C₃ hydrocarbons as major gas products. Interestingly, ethylene, an important precursor in polymer industry, can be produced at a yield as high as 38 wt.%. Moreover, this non-thermal plasma-assisted hydrogenolysis method allows direct valorization of post-consumer plastic products without a need of pretreatments and shows minimal influences by the contaminants and impurities. These findings reveal a great promise of this new method for WP valorization application.