Study on the structural characteristics of nitrogen-containing compounds in co-pyrolysis tar of low rank coal using 1H-15N HMBC analysis

Clarifying the structure, category, and content of nitrogen-containing compounds in coal tar is not only the key to directional regulation of pyrolysis processes, but also one of the needs for refined utilization of coal resources. developing simple, direct, and efficient structural analysis methods for nitrogen-containing compounds is very important for further investigation of nitrogen-rich tar. In this study, nitrogen-rich tar was obtained by co-pyrolysis through low rank coal and NH ₄ Cl; meanwhile, ¹⁵ NH ₄ Cl were selected as the NMR signal enhancement for the structural characteristics research. The results indicated that the nitrogen-rich tar primarily consisted of substituted aromatic amines, aliphatic amines, piperidine, pyrrole, pyridine, quinoline, and other nitrogen-containing compounds. Various nitrogen-containing compounds exhibit distinct functional properties. Compared with GCMS analysis method, ¹ H- ¹⁵ N HMBC NMR provides more structural information about nitrogen-containing compounds, especially the substitution characteristics of aromatic amines; at the same time, ¹ H- ¹⁵ N HMBC provides very “clean” 2D spectrum compared to ¹ H- ¹³ C HSQC simultaneously.