Microwaves assisted deconstruction of HDPE waste into structured carbon and hydrogen fuel using Al2O3-(Ni, Zn, Mg)Fe2O4 composite catalysts

Abstract

Plastic waste management is becoming an issue of global concern due to the excessive consumption of plastics with one-time use. The decomposition of plastic into valuable products by catalytic pyrolysis has gained significant attention as a promising method of valorizing plastic waste. This paper demonstrates the microwave-assisted decomposition of plastic waste materials for carbon nanotubes (CNTs) and high H2 production using magnetic-based catalysts via in-situ exsolution. Magnetic-based catalysts, namely Al2O3-NiFe2O4, Al2O3-ZnFe2O4, and Al2O3-MgFe2O4 were prepared using aluminum oxide, iron nitrate, zinc nitrate, and magnesium nitrate. CNTs and H2 were produced from the decomposition of wasted HDPE using the prepared catalysts. The Al2O3-NiFe2O4 catalyst showed better formation of CNTs and gas due to its low dielectric loss factor. The high surface area and magnetic-support interaction also promoted the catalytic activity of the catalyst. The oil byproduct mainly contained C8-C16 compounds, showing better selectivity for small molecules in the tested process. Conclusively, Al2O3-NiFe2O4 produced CNTs with good structural properties and fewer impurities than Al2O3-ZnFe2O4 and Al2O3-MgFe2O4 composites. The Al2O3-NiFe2O4 catalyst showed 90% hydrogen composition in evolved gases. In all cases, almost 90% of the hydrogen evolved from the feedstock within the first 2 min of the processing time.