Enhanced co-pyrolysis synergies between cedar and Naomaohu coal volatiles for tar production

Tar production from co-pyrolysis is highly dependent on synergies between coal and biomass volatiles. Therefore, enhancing their interactions during co-pyrolysis is crucial. In this study, three mixing modes, including mechanical mixing (M-type) and two layered loading modes (the U-type with upper Naomaohu coal (NMH) and lower cedar sawdust (CS) and the L-type with upper CS and lower NMH), were specially designed to explore the synergies between NMH and CS volatiles based on the analyses of products distribution, tar fractions and compositions, and stable radicals in char. The results show that sufficient void space is required for the co-pyrolysis synergies between CS and NMH volatiles. With the M-type mode, the CS volatiles preferably formed char on the NMH surface in a limited void space, inhibiting coal pyrolysis. The layered L-type and U-type modes enhanced the co-pyrolysis synergies, and the CS volatiles acted as hydrogen donors to enhance tar production. Compared with the L-type mode, the U-type mode resulted in better synergies between NMH and CS volatiles, contributing to higher tar yield of 44.68 wt%. In addition, the volatile synergies were conductive to the formation of aliphatic chain radicals in char, methyl-containing compounds, and 3–4 ring aromatic compounds in tar. This research will guide the optimization of tar production and co-pyrolysis technique exploitation.