Synergistic effects from fast co-pyrolysis of lignin with low-rank coal: On-line analysis of products distribution and fractal analysis on co-pyrolysis char

Synergistic effects from fast co-pyrolysis of low-rank coal with lignin via on-line mass spectrometry were explored. Iso-conversional method was used to obtain frequency factor and activation energy of main gaseous products. The morphology evolution of both individual and co-pyrolysis char was analyzed via fractal theory quantificationally. The results indicated that various synergistic effects were found from the distribution and composition of products. CO and CO₂ were the main content of the gaseous products, and the content of CO from lignin increased with the temperature. Lignin promoted the generation of tar and inhibited the formation of gaseous products during fast co-pyrolysis, which reflected different synergistic effects, respectively. Positive synergistic effects were observed from the component proportion of CH₄ as the temperature increasing higher than 600 °C. Kinetic analysis indicated that activation energy for H₂ from lignin and low-rank coal was 32.21 and 59.90 kJ/mol, and higher temperature would be beneficial for H₂ formation. Fractal analysis indicated that lignin promoted the surface morphology of co-pyrolysis char to become more complicated, with the fractal dimension of individual char less than those of co-pyrolysis char.