Polypropylene Decomposition in Hydrocarbon Solvents: Zeolite-Catalyzed Chemical Recycling

Abstract

Chemical recycling of waste plastics into valuable chemical feedstocks, specifically targeting C₃–C₄ gas products and naphtha fraction ranging from C₅–C₉ products, was explored in this study. Our approach involves melting/dispersing polypropylene in a hydrocarbon solvent and decomposing it using a zeolite catalyst. This technique effectively reduces the viscosity of molten plastics, enhances heat transfer, and allows the easy separation of inorganic fillers via filtration. Comprehensive analytical methods are used to identify and differentiate various decomposition products, including aliphatic hydrocarbons, monocyclic and polycyclic aromatics, and heavier hydrocarbons, distinguishing them from those derived from the solvent. The product distribution was thoroughly analyzed using a suite of techniques, including gas chromatography, two-dimensional gas chromatography, distillation gas chromatography, gel permeation chromatography, and thermogravimetric-differential thermal analysis. Our results highlight the effectiveness of using n-hexadecane and zeolite beta, achieving a remarkable 60 wt % yield of naphtha fraction (C₅–C₉) from polypropylene decomposition at 400 °C.

This paper discusses analytical methods adhering to the mass balance approach for the products of plastic decomposition in hydrocarbon solvents.