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 simulation calculation was carried out by using density functional theory (DFT) methods at B3LYP/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.
[1] 黄鑫, 曹景沛, 王敬贤,等. 污水污泥快速热解过程中氮迁移规律研究[J]. 中国矿业大学学报, 2016, 45(1):176-181.
[2] 谭涛, 崔燕妮, 周岩枫,等. 微波热解污泥过程中NOx前驱物产生影响因素[J]. 哈尔滨商业大学学报(自然科学版), 2011, 27(5):667-670.
[3] 王宗华, 张军营, 赵永椿,等. 污泥热解和气化过程中NO_x前驱物的释放特性[J]. 华中科技大学学报(自然科学版), 2011(1):98-101.
[4] 郝菊芳, 王洪波, 曹得坡,等. 升温速率对氨基酸裂解生成含氮气体的影响研究[J]. 化学研究与应用, 2013(7):981-986.
[5] Zhou P, Xiong S, Zhang Y, et al. Study on the nitrogen transformation during the primary pyrolysis of sewage sludge by Py-GC/MS and Py-FTIR[J]. International Journal of Hydrogen Energy, 2017.
[6] Lin Y, Liao Y, Yu Z, et al. A study on co-pyrolysis of bagasse and sewage sludge using TG-FTIR and Py-GC/MS[J]. Energy Conversion & Management, 2017, 151:190-198.
[7] 张军. 微波热解污水污泥过程中氮转化途径及调控策略[D].哈尔滨工业大学,2013.
[8] Ratcliff M A, Johnson D K, Posey F L, et al. Hydrodeoxygenation of lignins and model compounds[J]. Applied Biochemistry & Biotechnology, 1988, 17(1-3):151-160.
[9] Karl-Martin Hansson, et al. Pyrolysis of poly--leucine under combustion-like conditions ☆[J]. Fuel, 2003, 82(6):653-660..
[10] 黄金保, 刘朝, 曾桂生,等. 左旋葡聚糖热解机理的密度泛函理论研究[J]. 燃料化学学报, 2012, 40(7):807-815.
[11] 黄金保. 纤维素快速热解机理的分子模拟研究[D]. 重庆大学, 2010.
[12] Liang J. Application of Gaussian09 in Structural Chemistry Teaching: Optimizing the Structure of Molecule[J]. Guangdong Chemical Industry, 2017.
[13] Becke A D. Density‐functional thermochemistry. III. The role of exact exchange[J]. Journal of Chemical Physics, 1993, 98(7):5648-5652.
[14] Lee C, Yang W, Parr R G. Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density[J]. Physical Review B Condensed Matter, 1988, 37(2):785.
[15] 黄晓露. 木质素模型化合物热解的微观机理研究[D]. 重庆大学, 2012..
[16] Jr R M, Medley E E, Simmonds P G. Pyrolysis of amino acids. Mechanistic considerations.[J]. Chemischer Informationsdienst, 1974, 5(40):1481.
[17] 黎新.α-丙氨酸热分解机理的从头算研究[J].渝西学院学报(自然科学版),2002(03):32-35.
[18] 徐晓赫, 陈小耘, 黎新. α-丙氨酸热分解机理的AM1研究[J]. 重庆文理学院学报, 2000(1):67-68.
[19] 罗海银. 基于量子化学理论的木质素热裂解中环类化合物形成机理的研究[D]. 长沙理工大学, 2015.
[20] 黄金保, 刘朝, 魏顺安,等. 丙三醇脱水反应机理的密度泛函理论研究[J]. 化学学报, 2010, 68(11):1043-1049.
[21] 翁诗甫. 傅里叶变换红外光谱分析[M]. 化学工业出版社, 2010.
[22] Jr M A R, Medley E E, Simmonds P G. Pyrolysis of amino acids. Mechanistic considerations[J]. Chemischer Informationsdienst, 1974, 39(11):1481.
[23] Johnson W R, Kan J C. Mechanisms of hydrogen cyanide formation from the pyrolysis of amino acids and related compounds[J]. Journal of Organic Chemistry, 1971, 36(1):189-192.
[24] Hansson K M, Samuelsson J, Tullin C, et al. Formation of HNCO, HCN, and NH3, from the pyrolysis of bark and nitrogen-containing model compounds[J]. Combustion & Flame, 2004, 137(3):265-277.
