Decoupling of interphase reactions and gas-gas interactions in co-gasification of sugarcane bagasse and waste plastic

Steam co-gasification of sugarcane bagasse and polyethylene can significantly improve hydrogen production and syngas quality. Nevertheless, the underlying synergistic mechanisms governing this co-gasification process remain incompletely understood and underdeveloped. In this work, a phase-decoupling strategy for evaluating synergistic performance was first proposed based on interphase reactions, and its effectiveness was quantified using dimensionless synergy indices. The results showed that for the steam gasification of bagasse at 900°C, nearly 61% of the hydrogen derived from char gasification; additionally, the water-gas shift reaction, a slightly exothermic process, proceeded extensively at this high temperature and made a considerable contribution to hydrogen yield. For the co-gasification of bagasse and polyethylene, homogeneous synergy exerted a dominant advantage on hydrogen yield, accounting for approximately 73%; and while heterogeneous synergy exhibited an absolute advantage in regulating the H 2 /CO ratio of syngas, with a contribution ratio of about 85%. Furthermore, deashed bagasse, microcrystalline cellulose, xylan, and vanillin—used as surrogates for oxygen-containing components in biomass—all exhibited varying degrees of positive synergies when co-gasified with polyethylene. Among these surrogates, vanillin and deashed bagasse showed the most remarkable synergistic performance, achieving synergistic indices of 0.39 and 0.49 respectively for hydrogen yield; these values exceeded the synergistic index of 0.32 obtained from the co-gasification of bagasse and polyethylene. This finding confirms that the interactions between organic compounds are a key factor responsible for the positive synergy in the co-gasification of biomass and waste plastics. Simultaneously, the interaction between lignin-derived compounds and plastic volatiles acts as the primary driver of gas-phase homogeneous synergy.