【作者】 程占军；

【导师】 齐飞； 李玉阳；

【作者基本信息】 中国科学技术大学 ， 同步辐射及应用， 2014， 博士

【摘要】 本论文利用同步辐射真空紫外光电离质谱技术研究了呋喃及其衍生物的热解,利用不同温度下的光电离质谱和光电离效率谱对热解产物进行了全面的鉴定,尤其是自由基和同分异构体,并测量了热解产物的摩尔分数曲线。结合前人和本文的理论计算,发展了呋喃类燃料宽压力、宽温度范围的热解模型,并利用本文的实验和前人的热解实验对模型进行了深入验证。第一章主要论述了开展呋喃及其衍生物变压力热解研究的依据和意义。简单介绍了在当前国际能源环境的大背景下,开发生物燃料的必要性,以及呋喃类新型生物燃料的优势和燃烧研究现状。第二章主要介绍了本文中使用的实验、理论和模型方法。对光束线、热解实验装置和实验方法等进行了简要描述,并通过详细的实验和理论推导证明了α-刚玉管的催化效应很弱,可以忽略。简要介绍了呋喃及其衍生物关键反应的量子化学和速率常数计算方法,以及利用CHEMKIN-PRO软件的模拟方法。第三章主要对呋喃低压热解中燃料分解和芳烃生成过程进行了详细的讨论。实验中,观察到了呋喃的主要单分子解离产物：丙炔+CO和乙炔+乙烯酮。基于本章计算的呋喃单分子解离反应的速率常数和本章实验数据发展了一个包含174个物种和950步反应的呋喃低压热解模型。基于实验结果和理论计算,炔丙基的生成主要来自于丙炔的后续分解反应,而非前人认为的呋喃单分子解离反应。另外,本文中的流动反应器出口位置的中低温区对高浓度自由基的复合反应较为灵敏,可用于验证此类反应的中低温区速率常数。实验和模型分析表明,炔丙基自复合生成苯的反应在中低温区的速率常数偏快。第四章是对2-甲基呋喃(MF)变压力热解的实验和动力学模型进行研究。利用量子化学方法(CBS-QB3)计算了MF的单分子解离反应、2-呋喃基甲基和H原子进攻MF反应的势能面。基于本章与前人的实验和计算结果,对前人发展的模型进行了更新,并且利用本章和前人工作中的热解实验数据对模型进行了验证。生成速率和灵敏性分析表明,MF的初始分解路径是通过单分子解离反应生成1-丁炔+CO和乙酰基+炔丙基、H提取反应生成2-呋喃基甲基并进一步分解生成大量的乙烯基乙炔、H原子加成取代反应生成呋喃+甲基以及H进攻反应生成CH2CHCHCO+甲基和C4H7+CO。另外,在MF热解过程中还探测到了大量的大质量芳烃产物包括苯、苄基、甲苯、苯乙炔、苯乙烯、茚基、茚和萘等。生成速率分析表明MF热解过程中高浓度的苯、甲苯和其它芳烃的生成是源于炔丙基和1,3-丁二烯的大量生成。第五章详细介绍了2,5-二甲基呋喃(DMF)的变压力热解实验和动力学模型研究。在DMF热解过程中观察到了大量苯酚、1,3-环戊二烯、2-甲基呋喃、乙烯基乙炔和1,3-丁二烯的生成。基于对DMF主要单分子解离反应的压力相关速率常数的计算,发展了一个包含285个物种和1173个反应的DMF热解反应动力学模型,并利用本章和前人的实验数据对模型进行了验证。生成速率分析和灵敏性分析表明DMF的主要分解路径为单分子解离反应生成CH3CHCCH+乙酰基、H提取反应生成5-甲基-2-呋喃基甲基、H原子本位取代反应生成2-甲基呋喃和H进攻反应生成1,3-丁二烯+乙酰基。5-甲基-2-呋喃基甲基的后续分解生成大量的苯酚和1,3-环戊二烯,而它们很容易分解生成大质量芳烃的前驱体环戊二烯基、苯基和苯。最终导致相比其它类似结构的环烷烃来说,DMF有较强的芳烃生成趋势。就三种呋喃类燃料比较而言,MF由于能够生成大量的炔丙基、苯和甲苯,因此其热解过程中产生的芳烃总浓度最高。这表明对于MF和DMF两种重要的新型生物燃料而言,需要在实际应用中关注其碳烟排放特性,而本论文对其热解过程中碳烟形成前驱物的实验和模型分析结果将有助于针对这两种燃料的碳烟抑制方案的设计。因此,本论文的工作一方面有助于三种呋喃类燃料燃烧反应动力学模型的发展,另一方面也为这些燃料实际应用中污染物排放问题的解决提供了理论支撑。更多还原

【Abstract】 Pyrolysis of furan and its derivatives in flow reactor at various pressures were investigated. The pyrolysis intermediates, especially the free radicals and isomers were identified and quantified by using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) technique. Based on the previous and present theoretical studies, the detailed kinetic pyrolysis models were developed and validated against the present work and previous pyrolysis experimental data.In Chapter1, the purpose and significance of the research on the pyrolysis of furan and its derivatives at various pressures were presented. Large production and exploitation of biofuels were essential under the background of international energy and environmental crisis. Besides, as new kinds biofuels, the advantages and recent research progress of furan and its derivatives were summarized.In Chapter2, the experimental methods, theoretical calculations and kinetic model were introduced. A brief description of beamlines and pyrolysis appratus were also displayed in this chapter. And a brief discussion of the catalytic effects of α-alumina flow reactor was presented, and the experimental observation reveals the negligible surface catalytic effects of our α-alumina flow tube. Besides, the theoretical methods on quantum chemistry and calculating rate constants of key reactions in furan and its derivatives are briefly introduced, as well as the simulation methods using CHEMKIN-PRO software.In Chapter3, fuel decomposition and aromatic ring formation in furan pyrolysis at low pressure were discussed in detail. Specific products, which are directly related to the unimolecular decomposition reactions of furan, were observed, such as propyne+CO and acetylene+ketene. Using the calculated rate constants of unimolecular decomposition reactions of furan, a low pressure pyrolysis model, which consists of174species and950reactions was developed and validated against the mole fraction profiles of pyrolysis species measured in this work. The decomposition of furan is mainly controlled by the unimolecular decomposition reactions under the investigated conditions. Based on the experimental results and theoretical calculation, propargyl radical is suggested to be mainly formed from the unimolecular decomposition of propyne rather than furan. Furthermore, the temperature drop region close to the flow reactor outlet provides a sensitive circumstance at low to intermediate temperature region to validation high concentration radical combination reactions for aromatics formation, and the propargyl self-combination may be over-estimated at low to intermediate temperature regions according to the modeling analysis and experimental validation.In Chapter4, experimental and kinetic modeling study of2-methylfuran pyrolysis at various pressures were introduced in detail. The potienal energy surface of unimolecular decomposition of MF and2-furanylmethyl and reactions of H atom attack MF were calculated using CBS-QB3. The kinetic model were optimized according to the previous model and the validation against the present and previous pyrolysis data of MF. Based on the rate of production (ROP) and sensitivity analyses, main pathways in the decomposition of MF and the growth of aromatics were determined. The unimolecular decomposition to produce1-butyne+CO and acetyl+propargyl, H-atom abstraction to produce2-furanylmethyl radical, ipso-substitution by H to produce furan and H-atom attack to produce CH2CHCHCO+CH3and C4H7+CO were concluded to dominate the primary decomposition of MF. Further decomposition of2-furanylmethyl radical leads to great production of vinylacetylene. Many large aromatic hydrocarbons, including benzene, benzyl radical, toluene, phenylacetylene, styrene, indenyl radical, indene, and naphthalene, were also detected. Based on the ROP analysis, it is concluded that the higher concentrations of benzene, toluene and other aromatics in the MF pyrolysis result from the greater formation of propargyl radical and1,3-butadiene.In Chapter5, experimental and kinetic modeling study of2,5-dimethylfuran pyrolysis at various pressures were introduced in detail. Dozens of pyrolysis products, especially a series of radicals and aromatics, were identified from the measurement of photoionization efficiency spectra; and their mole fraction profiles were measured at790-1470K. Phenol,1,3-cyclopentadiene,2-methylfuran, vinylacetylene and1,3-butadiene were observed with high concentrations in the decomposition of DMF. The pressure-dependent rate constants of the major unimolecular decomposition reactions of DMF were theoretically calculated, and were adopted in the pyrolysis model of DMF with285species and1173reactions developed in the present work. The model was validated against the species profiles measured in both the present work and the previous pyrolysis studies of DMF. Based on the rate of production and sensitivity analyses, main pathways in the decomposition of DMF and the growth of aromatics were determined. The unimolecular decomposition to produce CH3CHCCH and acetyl radicals, H-atom abstraction to produce5-methyl-2-furanylmethyl radical, ipso substitution by H-atom to produce2-methylfuran and H-atom attack to produce1,3-butadiene and acetyl radical were concluded to dominate the primary decomposition of DMF. Further decomposition of5-methyl-2-furanylmethyl radical leads to great production of phenol and1,3-cyclopentadiene which can be readily converted to precursors of large aromatics such as cyclopentadienyl radical, phenyl radical and benzene. As a result, the formation of aromatics in the pyrolysis of DMF is promoted compared with the pyrolysis of cyclohexane and methylcyclohexane under very close conditions. Among furan and its derivatives, MF produces the highest concentration of aromatic species due to the large amounts formaiton of propargyl radical, benzene and toluene. Therefore, this observation emphasizes the necessity to investigate the sooting behavior and soot formation mechanism in MF and DMF combustion for the potential application as new biofuels. The experimental and modeling analyses on the formation of soot precursors in the pyrolysis of MF and DMF provide significant benefits to the design for the inhibition of their soot emissions. As a consequence, the investigations in the present work can help not only develop a detailed combustion model for furan and its derivatives, but also provide theoretical guidance for the reduction of the emissions in their practical applications.更多还原