Effect of the mixing modes on the integrated process of co-pyrolysis of coal and biomass with CO2 reforming of methane to improve tar yield

To investigate the influence of mixing modes on the integrated process of co-pyrolysis of coal and biomass with CO2 reforming of methane (CP-CRM), in this paper, Naomaohu coal (NMH) and elm (ELM) were chosen and three mixing modes (NMH/ELM, ELM/NMH and Blends) were examined over Ni-based reforming catalysts prepared by ball milling, and compared with the co-pyrolysis under N2 atmosphere (CP-N2). The results showed that the products distribution was significantly affected by the mixing mode. Tar yield during CP-CRM under Blends model was higher than those of NMH/ELM and ELM/NMH, increasing by 35.29% compared with CP-N2. Meanwhile, light oil content in the tar was higher than those of NMH/ELM and ELM/NMH, and the pitch content was lower than those of NMH/ELM and ELM/NMH. The phenols content in tar from Blends model was 19.52% higher than that of CP-N2, along with more free radicals in tar than that of CP-N2, which was mainly ascribed to the enhanced heat and mass transfer between raw material particles by mechanical mixing, making the co-pyrolysis process more complete. At the same time, the mechanical mixing was conducive to more efficient action of hydrogen-rich free radicals (such as •H, •CHx) on pyrolysis products, suppressing the secondary cracking and polymerization. The results provide a good guidance for regulating tar yield and compositions of the co-pyrolysis process.