NH_(3)对煤物理吸氧影响规律的量子化学研究

Quantum Chemistry Study on Effects of NH_(3) on Physical Oxygen Adsorption of Coal

为探究矿井中NH_(3)对煤吸附氧气的影响,通过建立吸附性能显著的含氮活性基团煤分子片段模型,运用量子化学包含色散矫正的密度泛函理论方法(DFT-D3)研究了煤分子分别与NH_(3)和O_(2)之间单独吸附的微观机理以及NH_(3)和O_(2)在煤表面共存条件下的相互依存关系。结果表明:煤对O_(2)的物理吸附性小于NH_(3),煤与O_(2)分子的吸附位置主要集中在—NH2侧链,煤的自燃氧化过程主要发生在—NH2侧链;煤与NH_(3)和O_(2)发生混合吸附时,NH_(3)和O_(2)分子在煤表面的吸附存在相互促进的作用,且NH_(3)对煤分子吸附O_(2)的促进作用要强于O_(2)对煤分子吸附NH_(3)的促进作用;当煤表面吸附NH_(3)与O_(2)的分子数之比为1~3时,NH_(3)对煤吸附O_(2)的促进作用随着O_(2)分子数目的增加而不断增强;矿井中NH_(3)的存在会促进煤对O_(2)的吸附,加速煤的自燃氧化进程,进而影响电厂烟气抑制煤自燃的效果,因此,对于通入采空区的电厂烟气需有效控制烟气中氨气的含量。

In order to explore the influences of the NH_(3) on the adsorption of the oxygen on coal,the microscopic mechanism of the adsorption between a coal molecule and NH_(3)/O_(2)(taken separately or a mixture)was studied by using the dispersion-corrected density functional theory of the quantum chemistry(DFT-D3).The results show that O_(2) is less physically adsorbed on the surface of coal molecules than NH_(3),and the adsorption of coal and O_(2) molecules is mainly concentrated in the—NH2 side chain,indicating that the spontaneous combustion oxidation process of coal mainly occurs in the—NH2 side chain.When coal is mixed with NH_(3) and O_(2),the adsorption of NH_(3) and O_(2) molecules has mutually reinforcing effects on the adsorption of the coal surface,and the promotion effect of NH_(3) on the adsorption of O_(2) by coal molecules is stronger than that of O_(2) on the adsorption of NH_(3) by coal molecules.When the ratio of NH_(3) to O_(2) molecules adsorbed on coal surface is 1-3,the promoting effect of NH_(3) on the O_(2) adsorption by coal increases with the increase in the number of the O_(2) molecules.In conclusion,the presence of NH_(3) in the mine will significantly promotes the adsorption of O_(2) on coal,accelerates the oxidation process of the coal spontaneous combustion,and then affects the suppressing effects on the coal spontaneous combustion by the flue gas from power plants.Therefore,the content of the ammonia in the flue gas should be effectively controlled when the flue gas of the power plant flows into the goaf.