摘要
选取丙氨酸为含氮模型化合物,用密度泛函理论(DFT)B3LYP/6-31+G(d,p)基组对丙氨酸高温热解过程进行量子化学模拟计算,设计了三条初反应路径与一条次反应路径,对每条反应路径中的反应物、过渡态、中间体及产物进行几何结构优化和频率计算,分析热解机理。用热重和红外光谱对热解实验释放的含氮气体进行分析,验证模拟结果的正确性。结果表明,初反应是两个丙氨酸分子通过缩合反应脱去水分子生成丙-丙二肽,丙-丙二肽通过缩合反应生成2,5-二酮哌嗪类化合物(DKPs),此路径焓变值小且反应所需活化能最少,为主反应。约290℃时,NH3产率最大,400~450℃时HCN生成量增加,丙氨酸裂解主要的含氮气体产物是HCN,NH3和HNCO,实验所得含氮气体产物与计算结果一致。
Alanine was selected as a nitrogen-containing model to research the conversion mechanism of nitrogen-containing gas, the quantum chemical simulationcalculation was carried out by using density functional theory(DFT) methods at B3 LYP/6-31+G(d, p) level. Three initial reaction paths and one secondary reaction path were designed. Geometric optimization and frequency calculation were used in reactants, transition states, intermediates, and products in each reaction path.The standard kinetic parameters in each reaction pathway were calculated and the formation and evolution mechanism of main pyrolysis products were analyzed. The thermogravimetric and Fourier transformer technology(TG-FT-IR) technique was used to identify the released gas during the nitrogen-containing gas pyrolysis process, to verify the simulation results. The experimental and simulation results showed that the initial reaction was that two alanine molecules dehydrated by a condensation reaction to form a propylene-propylene dipeptide, and then the propylene-propylene dipeptide formed diketopiperazine(DKP) by condensation reaction. This path had the smallest enthalpy change value and the minimum activation energy required for its reaction as the main reaction, and the secondary reaction path of path 1 was the cleavage of DKP. During the pyrolysis of alanine,there were mainly three kinds of nitrogen-containing products HCN, NH3 and HNCO. The nitrogen-containing gas products detected in the experiment were consistent with the products obtained by the simulated route.The alanine pyrolysis interval range was 250~330 ℃. At 290 ℃, the yield of NH3 was higher than that of HCN, and the yield of HNCO was the lowest. At 400~450℃, the amount of HCN was increased. Nitrogen-containing products were mainly NH3 and HCN.The above analysis was consistent with previous experimental results and analysis.
作者
刘亮
蔡宜捷
田红
夏辉
曹亚
Liang LIU;Yijie CAI;Hong TIAN;Hui XIA;Ya CAO(Energy and Power Engineering Institute, Changsha University of Science and Technology, Changsha, Hunan 410114, China)
出处
《过程工程学报》
CAS
CSCD
北大核心
2019年第4期792-800,共9页
The Chinese Journal of Process Engineering
基金
国家自然科学基金资助项目(编号:51706022)
湖南省自然科学基金资助项目(编号:2018JJ3545)
关键词
丙氨酸
密度泛函理论
高温热解
NOx前驱体
alanine
density functional theory
high temperature pyrolysis
NO_xprecursor
