Synergistic effects during co-pyrolysis of milled wood lignin and polyolefins at the gas phase and liquid/solid phase contacting modes

Co-pyrolysis of biomass and waste plastics is the preferred technology for enhancing the production of fuels and valuable chemicals. Here, we studied the co-pyrolysis of milled wood lignin (MWL) with polyethylene (PE) and polypropylene (PP) at various weight ratios by thermogravimetry (TG), evolved gas analysis–mass spectrometry (EGA–MS), and product recovery tests using a fixed-bed reactor. Two reaction modes, liquid/solid phase (LSP) and gas phase (GP) contacting modes, were applied to investigate the physical prevention of melted polymers on the interactions between the vapored intermediates. The TG results showed that the weight losses were slightly altered in the MWL/PE and the decomposition was delayed in MWL/PP blends, whereas the EGA-MS analysis indicated that more vaporized products from the blends were detected by MS. The fixed-bed experiments showed that the yield of liquid was largely enhanced by the higher proportion of PE or PP in the blends, primarily due to the formation of lower oligomeric hydrocarbons from polyolefins. The yields of gasoline and kerosene were significantly increased in the GP mode from the co-pyrolysis of MWL with PE and PP, respectively. These results suggest that the MWL pyrolysates could enhance the cracking of PE intermediates in the GP reaction mode, whereas the rearrangement reactions of PP intermediates may be inhibited in the LSP reaction mode, converting more wax products into liquid. This paper provides a better understanding of the detailed synergistic effects during biomass and plastics co-pyrolysis.