Experimental Study of the Conversion of Polyethylene and Polypropylene to Non-Condensable Gases using a Lab-scale Bubble Column Reactor with Molten Metal Catalysis

Abstract Sustainable solutions for recycling waste plastics are necessary to replace conventional processing techniques. Plastic pyrolysis is a promising technology for converting waste plastic into useful chemicals. This study aims to selectively separate and produce hydrogen (H2) via plastic pyrolysis using a molten metal catalyst. The characteristics of plastic conversion to non-condensable gas under various operating conditions, such as the number of reactors, reaction temperature, and type of molten metal catalyst used, were investigated. Nitrogen (N2) was introduced into a molten metal bubble column reactor containing a metal catalyst, and plastic was then uniformly mixed inside the catalyst through the formed rotating flow. Polyethylene and polypropylene were pyrolyzed at 700–900 ℃. In the single reactor, the fraction of H2 was similar to that reported in previous studies; however, the fraction of light hydrocarbons increased. As the number of reactors increased in the multi-stage reactor, the fraction of CH4 increased to 58%. At elevated reactor temperatures, the fraction of H2 increased to 40% as the decomposition of light hydrocarbons increased. The dominant influence on H2 production was C2H4 decomposition. The present study derived the optimal operating conditions for increasing H2 production during plastic pyrolysis with molten metal catalysts.