Thermochemical conversion via co-pyrolysis has the potential to be an efficient route for converting biomass and coal to syngas and chemical products. However, the synergistic effect between coal and biomass influences the co-pyrolysis behaviour and needs to be comprehensively studied. This study compared the pyrolysis behaviour of coal and sugarcane bagasse and investigated their interactions under high-pressure co-pyrolysis. Using techniques such as GC, GC-MS, and elemental analysis, the effects of blending ratio and pressure on co-pyrolysis were studied. This study aimed to explore pyrolysis reaction pathways under different conditions and examine the regulatory mechanisms underlying the synergistic effect on syngas formation, especially hydrogen gas, under high pressures. The impacts of blending ratio and pressure (0.1-1.6 MPa at 0.5 MPa increments) on the yield and composition of pyrolysis products were studied at 700 °C.
Pressure was found to alter the evolution and interactions of volatile and secondary reactions to different degrees, hence influencing the pyrolysis reaction pathways. For brown coal, pressure promoted volatile formation, facilitating the generation of CH₄ rather than syngas (H₂ + CO) due to enhanced methanation reaction. In contrast, sugarcane bagasse produced fewer volatiles and gases with pressure but also formed less syngas. However, both samples produced more polyaromatic compounds with pressure.
During the co-pyrolysis, the optimum blending ratio to maximise the synergetic effect was 50%, where the formation of H₂ was promoted while that of CO was inhibited due to interactions among primary products, which indicated altered secondary reactions. The interactions were enhanced under high pressure, resulting in even higher gas yield and lower tar yield than the theoretical values. Conversely, the synergistic effect under high pressures led to the promotion of H₂ and the depression of CO, likely due to the distinct characteristics of volatiles from coal and biomass samples — namely, the favoured reactions and specific reaction pathways of volatiles evolved from different samples can differ markedly during secondary reactions. Higher pressures also promoted the formation of polyaromatic compounds in tar and hydrogen transformation from tar into gas during co-pyrolysis. The results obtained in this study imply that the co-pyrolysis of brown coal and sugarcane bagasse at elevated pressures can be an effective method for controlling the selectivity of syngas and H₂ formation.

Co-pyrolysis, high pressure, sugarcane bagasse, brown coal, hydrogen, syngas