Migration and transformation characteristics of zigzag char-N in lean oxygen environment
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摘要: 采用量子化学方法探究了还原区高浓度NO存在下zigzag结构焦炭氮中N的迁移转化规律，并通过构建含羟基焦炭N模型，从分子层面对氧存在下焦炭N的转化特性进行了系统的理论计算。结果表明，还原区NO的存在会与焦炭中的N结合为N2释放；并且氧的存在增强了焦炭表面化学活性，进一步促进了焦炭中N的析出。还原区氧和NO的共存使得焦炭中N的释放与C的燃烧同时发生，表现为NO与焦炭中N结合为N2的同时，伴随有氧将焦炭中C氧化成CO2或CO。动力学计算C燃烧产物的限速步速率常数发现，低温低氧条件下C更容易氧化生成CO；随着温度的升高，CO2生成速率明显增大，高温更利于CO2的生成。Abstract: The migration and transformation of N in zigzag char-N with the presence of high concentration NO in the reduction zone is investigated by quantum chemistry method. Transformation characteristics of N in lean oxygen environment are systematically calculated from the molecular level by constructing a char-N model containing a hydroxyl group. The results show that NO in the reduction zone can combine with N in the char to form N2; and the presence of oxygen enhances the char chemical activity and further promotes the release of N in the char. The co-existence of oxygen and NO in the reduction zone makes the release of N and the combustion of C occur simultaneously, which is manifested by NO and N in the char combining to form N2, and at the same time oxygen and C in the char formation CO2 or CO. The kinetic calculations of the rate-limiting step rate constants of the C combustion products show that C is easily oxidized to CO under low temperature and lean oxygen conditions, and with the temperature rise the CO2 generation rate increases significantly and the high temperature is conducive to CO2 formation.
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Key words:
- char-N /
- NO /
- hydroxyl group /
- CO /
- CO2
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图 2 带有相应的原子序数的R1及IM1的稳定结构示意图
Figure 2 Optimized configuration of R1 and IM1 with corresponding atomic numbers
图 3 NO参与下R1转化过程的中间体和过渡结构(键长单位 nm)
Figure 3 Intermediate and transition state structures during R1 conversion with the presence of NO (bond unit: nm)
图 4 NO参与下R1转化过程的能量变化示意图
Figure 4 Schematic diagram of energy change in the process of R1 conversion with the presence of NO
图 6 带有相应原子序数的R2及IM1的优化构型示意图
Figure 6 Optimized configuration of R2 and IM1 with corresponding atomic numbers
图 7 氧和NO参与下R2转化过程中稳定构型的结构参数(键长单位 nm)
Figure 7 Structural parameters of stable configuration during R2 conversion with the participation of oxygen and NO (bond unit: nm)
图 8 氧和NO参与下R2转化过程的能量示意图
Figure 8 Schematic diagram of energy change in the process of R2 conversion with the participation of oxygen and NO
图 11 限速步CO2脱附和CO脱附的在不同温度下的k-T关系图
Figure 11 k-T diagram of the rate-limiting rate constant of CO2 and CO desorption at different temperatures
表 1 NBO计算的一些重要原子的自然密度
Table 1 Natural population of some important atoms calculated by NBO
Atom Species Charge Valence N3 IM4 -0.11611 2.60384 IM5 -0.06121 2.54506 C7 IM4 0.08531 1.90433 IM5 0.17767 1.81130 N8 IM4 0.12140 2.35500 IM5 0.08398 2.4017] O9 IM4 -0.19029 3.18171 IM5 -0.20992 3.20406 
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