Conversion of Polyethylene Terephthalate Based Waste Carpet to Benzene-Rich Oils through Thermal, Catalytic, and Catalytic Steam Pyrolysis

Management of carpet wastes has become a substantial environmental issue in the United States. Specifically, reutilization of polyethylene terephthalate (PET) from waste carpet is increasingly problematic because of the steadily growing market share of PET-based carpets and the very low value of their wastes. In this work, we investigate pyrolysis as an option for repurposing PET carpet wastes. In particular, slow and fast, thermal and catalytic pyrolyses, with and without the co-feeding of steam, are investigated in terms of their selectivity to monoaromatic products. It is seen that higher temperatures increase the conversion of PET to aromatic hydrocarbons. Pyrolysis at slow heating rates is very selective to benzene production. Thermal pyrolysis of waste carpet produces significant amounts of benzoic acid and acetylbenzoic acid as liquid products, whereas catalytic pyrolysis enhances the decarboxylation of these acids, producing aromatic hydrocarbons. ZSM-5 and CaO are effective catalysts for enhancing deoxygenation reactions during catalytic pyrolysis of waste carpet but with significantly different selectivities. Catalytic steam pyrolysis is seen to accomplish the highest selectivity to benzene among all the pyrolysis options studied, due to the enhancement of hydrolysis reactions. The essentially pure benzene organic liquid product from steam pyrolysis of carpet-originated PET presents a unique opportunity for the reutilization of this unsustainable waste.