Abstract
Coal is a major contributor to the global emission of nitrogen oxides (NOx). The NOx formation during coal utilization typically derives from the thermal decomposition of N-containing compounds (e.g., pyrrolic groups). NH3 and HCN are common precursors of NOx from the decomposition of N-containing compounds. The existence of H2O has significant influences on the pyrrole decomposition and NOx formation. In this study, the effects of H2O on pyrrole pyrolysis to form NOx precursors HCN and NH3 are investigated using the density functional theory (DFT) method. The calculation results indicate that the presence of H2O can lead to the formation of both NH3 and HCN during pyrrole pyrolysis, while only HCN is formed in the absence of H2O. The initial interaction between pyrrole and H2O determines the N products. NH3 will be formed when H2O attacks the C2 position of pyrrole with its hydroxyl group. On the contrary, HCN will be generated instead of NH3 when H2O attacks the C3 position of pyrrole with its hydroxyl group. In addition, the DFT calculations clearly indicate that the formation of NH3 will be promoted by H2O, whereas the formation of HCN is inhibited.
Highlights
Coal is the major energy source in the modern industrial production process
The formation mechanisms of HCN and NH3 during pyrrole pyrolysis in the presence of H2 O are investigated by density functional theory (DFT) calculation
The results show that H2 O and pyrrole can interact in four ways, followed by 13 possible pyrolysis pathways
Summary
Coal is the major energy source in the modern industrial production process. Coal-mining, coal-burning factories, and other coal-related usage are the dominant sources of NOx emission [1,2].The harmful atmospheric pollutants of NOx (i.e., NO, NO2 , N2 O, etc.) can form acid rain and photochemical smog and endanger human health [3,4,5]. Coal-mining, coal-burning factories, and other coal-related usage are the dominant sources of NOx emission [1,2]. Nitrogen compounds in coal are primarily pyrrole and pyridine, which have already been widely used in different coal structural models, such as the Given, Wiser, and Shinn models [7,8,9]. The well-known Given model, mainly containing carbon, hydrogen, oxygen, and small amounts of sulfur and nitrogen, was intended to show the types of hydrogen structures in the bituminous coal, and has been widely adopted as a structural representation. The Shinn model was created at a larger scale (10,000 amu), in which three relatively small unconnected molecular entities were held within a larger molecule [8]
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