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Nitrogen release during high temperature pyrolysis of coals and catalytic role of calcium in N2formation

Publication Date
DOI: 10.1016/s0016-2361(02)00173-4
  • Coal Pyrolysis
  • N2Formation
  • Carbon Crystallization
  • Solid Phase Reaction


Abstract Pyrolysis of 10 coals with carbon contents of less than 80 wt%(daf) has been studied with a fixed bed quartz reactor to examine mainly nitrogen release from char-N without volatile matters. When temperature is raised from 1000 to 1350 °C, N 2 yield increases but char-N decreases for all the coals used. There is a strong reverse correlation between N 2 and char-N, which points out that most of N 2 arises from char-N via solid phase reactions. NH 3 is also formed from char-N at high temperatures of ≥1000 °C. In the pyrolysis of low rank coals, demineralization by HCl washing increases yields of tar-N, HCN and char-N, but decreases NH 3 and N 2. The addition of 3 wt% Ca to the demineralized coals shows almost the reverse effect. The XRD measurements after pyrolysis at 1000–1350 °C reveal that the Ca exists predominantly as CaO with the average crystallite size of 25–65 nm and promotes carbon crystallization. As the extent of crystallized carbon increases, N 2 yield increases remarkably. It is likely that the highly dispersed CaO catalyzes efficiently conversion reactions of char-N to N 2 in the process of carbon crystallization. The reaction mechanism is discussed in term of interactions between CaO particles and char-N.

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