Study Of Nitrogen And Sulfur Transfer Mechanism In The CO₂ Gasification Of Lignite

The CO₂ gasification of lignite is an important method to improve the utilization of lignite.In this work,the molecular dynamics method based on reactive force field?ReaxFF?was used to simulate reaction process in the CO₂ gasification of lignite.Then we could obtain the intermediate radicals and related elementary reactions in this process.Finally,we could get the formation mechanism of H₂S,COS,SO₂ and HCN,NH₃.The Wolfrum's model as the basic structural unit is selected.Two models of the pyrolysis and CO₂ gasification of the lignite were constructed.Using ReaxFF MD in Packmol software,the two systems were simulated for 1 ns at 3000 K.And the simulated trajectory was analyzed by C++program and the related elementary reactions were counted.The results shown that the sulfur-containing elemental reaction started from the decomposition of thiophenol,thioether and thiophene in both the pyrolysis and the CO₂gasification lignite.R-S,SCO₂,R-S-O and S-O radicals are important intermediates for the formation mechanism of H₂S,COS and SO₂.In addition,CO₂ also participated in and promoted the formation of SCO₂ and COS.And a large amount of CHO and R-O radicals were produced during CO₂ gasification.On the one hand,CHO radicals contributed to the formation of H₂S and R-O radicals;on the other hand,CHO radicals could also promote the production of R-S-O radicals and SO₂.The production of HCN and NH₃ was closely related to the concentration of H radicals.In both systems,the elemental reaction of N atoms started from the decomposition of hydroxylamines,amides,heterocycles and amines.CN and NH/NH₂radicals were important intermediates for the formation of HCN and NH₃.They were obtained by the R-N-R?H?releasing a hydrogen atom.COH and COOH were generated during CO₂ gasification to increase the concentration of H atoms.Much active H reacts with CN and NH/NH₂.Then the production of HCN and NH₃ were promoted.These mechanisms explained the formation process of sulfur-containing and nitrogen-containing gas during the CO₂ gasification of lignite at the molecular level.It could provides a reliable theoretical basis for the transfer mechanism of nitrogen and sulfur in the gasification.Figure 27;Table 4;Reference 75...