Effect of sodium on three-phase nitrogen transformation during coal pyrolysis: A qualitative and semi-quantitative investigation

Abstract Alkali metals have a significant effect on the transformation of three-phase nitrogen during coal pyrolysis, but there is a lack of understanding about this mechanism of action. In this work, the effects of inorganic sodium (NaCl) and organic sodium (CH3COONa) on the mutual transformation of three-phase nitrogen in coal pyrolysis were studied by TGA-MS/FTIR, XPS and Py-GC/MS. Results shown that more nitrogen remained in char, the conversion of heterocyclic nitrogen in coal to tar-N was inhibited with most of CH3COONa and lower addition NaCl, including the transformations of N-5 to pyrrole-N and amine-N, and the transformations of N-6 to pyridine-N and nitrile-N. While higher NaCl addition promotes the transformations of char-N to volatile-N. Sodium decreases the yield of tar, especially amine-N and nitrile-N through promoting the transformation of nitrile-N and pyridine-N in tar to HCN and the transformation of amine-N and pyrrole-N in tar to NH3. Both of promotion of NaCl on HCN release and inhibition on tar-N yield are stronger than CH3COONa. The HCN release of NaCl-added samples is higher 2.69%–4.29% than CH3COONa-added samples, while the content of char-N in NaCl-added samples is lower 2.6%–18.6% than CH3COONa-added samples.