Coal/NH3 interactions during co-pyrolysis and their effects on the char reactivity for NO-reduction: A ReaxFF MD study
Coal/NH3 interactions during co-pyrolysis and their effects on the char reactivity for NO-reduction: A ReaxFF MD study
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DOI：
10.1016/j.fuel.2023.128415
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发表时间：
2023-04-14
期刊：
影响因子：
7.4
通讯作者：
Wei, Riguang
中科院分区：
文献类型：
--
作者：
Hong, Dikun;Guo, Yajing;Wei, Riguang
在这项工作中，NH3和煤之间的相互作用，在共热解及其对焦炭结构和焦炭还原NO的反应性的影响进行了研究，采用反应分子动力学（ReaxFF MD）模拟，揭示了煤促进NH3的热分解，因为它提供了H自由基攻击NH3中的N-H键。NH3中心点抑制了煤的一次热解反应（弱共价键的热断裂），NH3还通过两个方面影响煤热解的二次反应：（1）促进焦油裂解生成气体;（2）抑制焦油聚合生成焦炭。与煤热解相比，煤/NH3共热解过程中半焦的H/C比以及半焦中O和N原子数的下降速度较慢。而NH3对H2S的释放影响不大。分析了NH3对煤焦理化性质的影响。在煤热解炭和煤/NH3共热解炭中，氧原子主要以羟基、醚和羰基形式存在，氮原子主要以氰化物和氨基形式存在。与煤热解半焦相比，煤/NH3共热解半焦具有较低的氦密度、较低的石墨化度和较大的孔隙。最后，考察了煤热解半焦和煤/NH3共热解半焦还原NO的反应性能。煤/NH3共热解半焦更有利于NO的化学吸附和N2-的生成。采用一级动力学模型，确定了煤热解半焦和煤/NH3共热解半焦还原NO反应的活化能分别为180和123 kJ/mol。
In this work, the interactions between NH3 and coal during co-pyrolysis and their influences on char structure and char reactivity for NO reduction are investigated using reactive molecular dynamic (ReaxFF MD) simulations, revealing that coal promotes the thermal decomposition of NH3 because it provides H radicals to attack the N-H bonds in NH3. The primary pyrolysis reactions (thermal breaking of weak covalent bonds) of coal are inhibited by NH3 center dot NH3 also influences the secondary reactions in coal pyrolysis through two aspects: (1) promotes tar cracking to generate gas, and (2) inhibits the polymerization of tar to form char. Compared with coal pyrolysis, the H/C ratio of char and number of O and N atoms in char decrease more slowly during coal/NH3 copyrolysis. However, NH3 has little influence on the release of H2S. The effect of NH3 on the physicochemical properties of the char is then analyzed. The oxygen atoms are present mainly as hydroxyl, ether, and carbonyl forms, and the nitrogen atoms are present mainly as cyanide and amino forms in both coal pyrolysis char and coal/NH3 co-pyrolysis char. The coal/NH3 co-pyrolysis char has lower helium density, lower graphitization degree, and larger pores compared with coal pyrolysis char. Finally, the reactivity of coal pyrolysis char and coal/NH3 co-pyrolysis char for NO reduction are examined. The coal/NH3 co-pyrolysis char is more conducive to NO chemisorption and N-2 generation. Using a first-order kinetics model, the activation energy of NO reduction reactions on coal pyrolysis char and coal/NH3 co-pyrolysis char are determined as 180 and 123 kJ/mol, respectively.