Abstract
The effect of CaCl2 on the precipitation characteristics of NH3, HCN, CH3CN, and HNCO during Zhundong Coal pyrolysis are investigated by thermogravimetry-mass spectrometry (TG-MS). Density functional theory is used to study the formation mechanism of NH3 and HCN in the presence of Ca. Seven-membered ring containing pyridine is selected as carbonaceous surface, and the stucture of Ca adsorption on coal surface is used as coal model containing Ca. The experimental results show that the addition of CaCl2 shifts the NOx precursors formation, including NH3, HCN, CH3CN and HNCO, toward a lower temperature. CaCl2 promotes the formation of NH3 and CH3CN while it inhibits the formation of HCN and HNCO, and the release laws of HCN and HNCO are basically consistent. The theoretical calculation results reveal that Ca can increase coal surface activity, so that the energy barrier value of the rate-determining step during NH3 formation in the presence of Ca is 274.74 kJ/mol lower than that in the absence of Ca, and obviously promotes NH3 formation. The presence of Ca significantly increases the interatomic bonding force between N5 and C6 in the pyridine ring, so that the N atom stripping from benzene ring in the rate-determining step of HCN formation requires a higher activation energy, and inhibits HCN formation. Ca obviously increases NH3 formation rate and is more conducive to NH3 formation.
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