Synergistic effect of co-pyrolysis between Naomaohu coal and waste plastics

Understanding the synergistic effect of co-pyrolysis between coal and different plastics is very important to reveal the matching between coal and waste plastics, and the influence of plastics with different structures and properties on the synergistic effect can be recognized based on the composition and distribution of co-pyrolysis products. In this study, the co-pyrolysis of low-rank Naomaohu coal (NMH) with thermoplastic polyethylene (PE), polypropylene (PP), polystyrene (PS), and thermosetting phenol-formaldehyde resin (PF) were carried out in a fixed-bed reactor to investigate the synergistic effect of co-pyrolysis between NMH with different plastics. The results showed that the product distribution of NMH co-pyrolysis with different thermoplastics are similar, showing the highest tar yield, while co-pyrolysis with thermoset PF showed the highest solid yield. The addition of PE and PF to NMH had a positive synergistic effect on the tar yield, with an added value of 3.2 wt% and 2.9 wt%, respectively, which was related to the large overlap interval of the weight-loss temperatures of NMH with PE and PF as exhibited by the TG results. In addition, the co-pyrolysis of NMH with polyolefin plastics PE and PP increased the content of aliphatic hydrocarbons such as alkanes and alkenes in the tar, while the co-pyrolysis with polyaromatic plastics PS and PF significantly increased the aromatic compounds such as aromatics and phenols of the tar. Therefore, suitable plastics can be selected for co-pyrolysis with coal to improve tar yield and tar quality.