Holistic utilization of waste plastics through a tandem process

In this study, a tandem process that combines catalytic pyrolysis with catalytic chemical vapor deposition (CVD) was performed to investigate the conversion of waste plastics to carbon nanomaterials, oil, and for hydrogen production. This study primarily explored the effects of plastic types and the plastic feeding rate on the pyrolysis products and the quality and morphology of carbon nanomaterials. High-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET) were used as carbon precursors for the growth of carbon nanomaterials on nickel foams. Results showed that PS produced the highest liquid oil with just 2 % of predominantly amorphous structured carbon nanomaterials. PET had the lowest hydrogen yield and approximately 42 % amorphous carbon due to the formation of more CO₂ and CO. Most importantly, since HDPE, LDPE, and PP produced more graphitic carbon nanomaterial with fewer structural defects compared to PET and PS, they are more favorable for the production of hydrogen and carbon nanomaterials. Additionally, HDPE loading significantly affected the quality of the produced carbon nanomaterial, particularly higher or lower feedstock loading resulting in more defects. This proposed tandem process shows great potential for upcycling waste plastics for secondary use.