Impact of plastic type on synergistic effects during co-pyrolysis of rice husk and plastics

Pyrolysis of varied type of plastic waste generates distinct reaction intermediates, which affect their co-pyrolysis with biomass feedstock in different ways. This was investigated herein in co-pyrolysis of specific plastic types, including polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), and polycarbonate (PC), as well as rice husk (RH) at 600–800 °C. The experimental results demonstrated that synergistic mechanisms in the co-pyrolysis were dependent on plastic type. PP provided small hydrogen radicals to pyrolyzates derived from RH, leading to an increase in aromatic production up to 69.5% at 600 °C. PS melted and acted as an insulator, inhibiting oil formation while increasing char yield. Organic acids derived from PET enhanced the char formation and dehydration of RH, resulting in increased levels of char and water. The interaction between RH/PET resulted in a reduction of aromatics by 53.2% at 800 °C because of the synergistic promotion of water formation. In contrast, aromatic structures in PC interfered with degradation of oxygen-containing functional groups in RH, enhancing oil, with aromatics increasing by 35.7% at 700 °C, as well as increased gas yields through promoting decomposition of RH. Furthermore, when all the feedstocks were mixed together, accelerated pyrolytic interactions enhanced the cracking of each individual polymer.