Study On Mechanism Of NOx Precursors Formation During Coal Pyrolysis

With the development of our society and the improvement of living level, the issue of environment attractes more and more people'attention. Air pollution is the most serious environment problem. SO2 and NOX are the main composition in the air pollution, and how to remove them has become a focus in recent years. Because the limite of analysis method, at present there still has some unknown about the mechanism of nitrogen release, especially the form mechanism of HCN and NH3. It is significant to build the relationship of NOX procursors and organic nitrogen in coal.Based on Quantum Chemistry theory and Organic Chemistry theory, formation mechanism of NOX procursors during coal combustion was studied in this paper by Quantum Chemistry Calculation.The model of pyridinic nitrogen and pyrrolic nitrogen was predigested rationally based on former researches at first. Pyrrolic nitrogen may release two types of pyrrolic free radicals and pyridinic nitrogen may release three types of pyridinic free radicals. The pyrolysis mechanisms of two types of pyrrolic free radicals and three types of pyridinic free radicals have been investigated using Density Functional Theory (DFT) UB3LYP/6-31G(d) by Gaussian 98 in this paper. Comparing the Bond Mulliken Population, we found C-N bond was the initial bond for pyrolysis. Pyridinic nitrogen was released in the form of HCN. BGA Pyrrolic free radical release C2H2 and NH3, but BGB Pyrrolic free radical release propene and HCN.Then the release modeles of pyridinic nitrogen and pyrrolic nitrogen were built. Activation energy of two types of two types of pyrrolic free radicals and three types of pyridinic free radicals was calculated. The active energy of pyrrolic free radicals is smaller than the pyridinic free radicals's , so pyridinic free radicals is more stable than pyrrolic free radicals. Pyrrolic free radicals can convert to pyridinic free radicals during pyrolysis.Pyrolysis experiences were carried out using Datong,Fushun and Neimeng coal. When heating temperature growing, nitrogen groupes in coal decompose deeply and the quantity of HCN and NH3 grows. At certain temperature the quantity reach peak. After that, when temperature growing, HCN will begin to convert to NH3 and the quantity of HCN reduce, but the quantity of NH3 is stable.