Molten salt-assisted Co-pyrolysis of biomass and waste plastics: Analysis of product characteristics

Co-pyrolysis is an effective way to achieve high-value utilization of biomass and waste plastics. To overcome the limitations of asynchronous heat transfer in traditional co-pyrolysis processes, a ternary molten carbonate system (Li₂CO₃-Na₂CO₃-K₂CO₃) was used as the reaction medium to study the effects of temperature (450-550 °C) and feedstock ratio (CS:PE = 3:1-1:3) on the co-pyrolysis products of corn stover (CS) and polyethylene (PE) plastic. The molten-salt environment facilitated synchronized decomposition of CS and PE plastic, effectively suppressing polycondensation and coking reactions while promoting hydrodeoxygenation of functional groups and C-O bond cleavage. Moreover, alkaline sites provided by alkali-metal cations catalyzed more complete secondary cracking and reforming of volatiles, resulting in an increase in gas production and a decrease in bio-oil and biochar production. Meanwhile, the fractions of H₂ and CO in the syngas were enriched, the hydrocarbon content in the pyrolysis bio-oil increased, and oxygenated compounds such as alcohols, aldehydes, and ketones were markedly reduced. Additionally, the templating and etching effects of the molten salt improved the structural ordering of the biochar, lowered its O/C ratio, and promoted a transition from microporous to mesoporous architecture. Notably, the synergistic effect between CS and PE was most pronounced at 550 °C with a 1:1 blending ratio, where the H₂ content reached 29.26 vol% (108.11 mL g−1) and the hydrocarbon fraction in the bio-oil increased to 62.52%. Overall, molten salt-assisted co-pyrolysis provides a promising strategy for the targeted production of H₂/CO-rich syngas, low-oxygen bio-oil, and structurally optimized biochar from biomass and waste plastics.