Quantifying the sources of synergistic effects in co-pyrolysis of pinewood and polystyrene

Co-processing of biomass and plastic wastes via pyrolysis and gasification for feed-flexibility revealed the presence of synergistic enhancement of H2 and syngas yield and lowering of char and tar yields. However, an understanding of the source of these interactions and their quantification is lacking. To address this, we investigated the co-pyrolysis of pinewood (PW) and polystyrene (PS) blends at 900 °C using uniquely arranged sample-loading configurations in a fixed-bed reactor with online product gas and energy consumption analysis. Quantification of interactions such as volatiles-volatiles, volatiles-feedstock, and volatiles-char interactions in comparison with weighted results from individual pyrolysis of PW and PS provided deconvoluted information on the synergistic effects. Volatiles-volatiles interaction accounted for a 33% increase in H2, while PS volatiles-PW intermediates interaction accounted for 17% increase, and inhibitive PW volatiles-PS intermediates interaction led to 8% decrease. This deconvolution also revealed another 20% increase associated with the evenly mixed co-pyrolysis of PW and PS that was not accounted for from the volatiles-feedstocks interaction. The co-pyrolysis of PS with PW char also revealed the catalytic activity of PW char on plastics decomposition which was found to be restricted by the capacity of PS melt to block the char’s active sites during their direct contact. Cracking of PS volatiles on these catalytic active sites led to the increased yields of CH4 and H2. These results provide quantified insight into the sources of interaction between biomass and plastics to enhance synergy, develop component compatibility, and gain prediction capability for sustainable and feed-flexible gasifier development.