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.