Polymer degradation to fuels over microporous catalysts as a novel tertiary plastic recycling method

Abstract

The catalytic degradation of polyethylene over various microporous materials—zeolites, zeolite-based commercial cracking catalysts as well as clays and their pillared analogues—was studied in a semi-batch reactor. Over all catalysts the liquid products formed had a boiling point distribution in the range of motor engine fuels, which increases considerably the viability of the method as a commercial recycling process. From the zeolites, ZSM-5 resulted mostly in gaseous products and almost no coking due to its shape selectivity properties. Commercial cracking catalysts fully degraded the polymer resulting in higher liquid yield and lower coke content than their parent ultrastable Y zeolite. This confirmed the suitability of such catalysts for a polymer recycling process and its commercialisation potential, as it confirmed the potential of plastic waste being co-fed into a refinery cracking unit. Clays, saponite and Zenith-N, a montmorillonite, and their pillared analogues were less active than zeolites, but could fully degrade the polymer. They showed enhanced liquid formation, due to their mild acidity, and lower coke formation. Regenerated pillared clays offered practically the same performance as fresh samples, but their original clays' performance deteriorated after removal of the formed coke. Although performance of the regenerated saponite was satisfactory, with the regenerated Zenith the structural damage was so extensive that plastic was only partly degraded.