Influences of carbon structure on the reactivities of lignite char reacting with CO2 and NO

Raw and demineralized lignite samples were pyrolyzed from 773 to 1673 K to generate chars. The chars were characterized with Raman spectroscopy for the structure evolution. The reactivities of the chars reacting with CO₂ and NO were measured with thermogravimetric analysis. The derived reactivity indexes were correlated with the treatment temperature and the Raman structural parameters to demonstrate the applicability of Raman spectroscopy for evaluation of the reactivities of char CO₂ gasification and char-NO reaction. It was found that char microstructure evolution with the treatment temperature could be represented by Raman band area ratios. I_D1/I_G and I_G/I_ALL represented the evolution of the ordered carbon structure while the combination of I_D3/(I_G + I_D2 + I_D3) reflected the evolution of the amorphous carbon structure of the lignite chars with increasing the treatment temperature from 773 to 1673 K. Reactivity indexes of the demineralized chars reacting with both CO₂ and NO were found to increase with increasing the treatment temperature, implying that the structure ordering did result in the losses of the reactivities. Higher reactivities of the non-demineralized chars indicated the catalytic role of inorganic matter in the reactions with both gases. I_D1/I_G and I_G/I_ALL had good linear correlations with the reactivities particularly of the demineralized chars if considering the structure evolution behaviors at lower and higher temperatures, respectively. I_D3/(I_G + I_D2 + I_D3) was found to have fairly good linear correlations with the reactivity indexes of the lignite chars generated over the whole temperature range.