Theoretical study on the mechanism, heat sink and product distribution for thermal decomposition of endothermic hydrocarbon fuel n-decane
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摘要: 采用密度泛函理论(DFT)的B3LYP方法在6-311G(d,p)基组水平上对正癸烷裂解过程中涉及的反应物、产物及过渡态进行了几何构型优化和振动频率计算,运用B3LYP/aug-cc-pVTZ方法计算单点能并构建势能剖面图。利用TheRate程序包及Eckart校正模型计算了各反应速率常数k。采用统计热力学原理求得不同温度下的热容Cp,mθ及熵S298 Kθ,并通过设计等键反应获得了各物种的标准生成焓△fH298 Kθ。用Chemkin II程序模拟预测了产物分布,理论计算了热沉值,并讨论了温度、压力对产物分布和热沉的影响。结果表明,C-C键断裂过程是反应的初始步骤,且抽氢反应较β键断裂反应更易进行。裂解起始温度为500 ℃,反应主要发生在600~700 ℃,其主要产物为氢气、甲烷、乙烯、乙烷、丙烯和1,3-丁二烯,且产物分布随温度不同而变化。模拟计算获得正癸烷在温度600 ℃、压力2.5 MPa条件下的总热沉值为2.334 MJ/kg,对应的热裂解转化率为25.9%,该热沉值可以满足速率为5~6马赫数的飞行器的冷却要求。Abstract: The geometry optimizations and vibrational frequencies of reactions, products and transition states involved in pyrolysis of n-decane were performed using the hybrid method B3LYP with 6-311G (d,p) basis set based on density functional theory. The potential energy surfaces of n-decane were built by the B3LYP/aug-cc-pVTZ methods. The rate constants of all reactions with Eckart correction were calculated by the TheRate program package. The heat capacity and entropy (Cp,mθ and S298 Kθ) at different temperatures were obtained by statistic thermodynamics. In order to calculate the standard formation enthalpy (△fH298 Kθ) for all species, isodesmic reactions were designed. The Chemkin II program was used to model the product distribution and heat sink. The effects of the temperature and pressure on the heat sink and product distribution were discussed. The results show that the C-C bond breaking process is the initial step of all reactions and H-abstraction reaction is easier to proceed than the β-scission reaction. The cracking initial temperature is 500 ℃ and the reactions mainly occur in the range of 600~700 ℃. The major products are hydrogen, methane, ethylene, ethane, propylene and 1,3-butadiene and the product distributions vary with temperatures. The total heat sink of n-decane is 2.334 MJ/kg at 600 ℃ and 2.5 MPa, with the conversions of 25.9%, which could meet the cooling requirement of aircrafts at 5~6 Mach number.
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Key words:
- n-decane /
- mechanism of thermal decomposition /
- rate constant /
- kinetic modeling /
- heat sink /
- product distribution
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李春迎, 李凤仙, 杜咏梅, 吕剑. 吸热型碳氢燃料五环[6.3.1.02,7.03,5.09,11]十二烷的催化合成[J]. 燃料化学学报, 2007, 35(5): 637-640. (LI Chun-ying, LI Feng-xian, Du Yong-mei, LU Jian. Synthesis of endothermic hydrocarbon fuel pentacyclo[6.3.1.02,7.03,5.09,11] dodecane[J]. Journal of Fuel Chemistry and Technology, 2007, 35(5): 637-640.) 孙青梅, 米镇涛, 张香文. 吸热型碳氢燃料RP-3仿JP-7临界性质(tc、pc)的测定[J]. 燃料化学学报, 2006, 34(4): 466-470. (SUN Qing-mei, MI Zhen-tao, ZHANG Xiang-wen. Determination of critical properties (tc, pc) of endothermic hydrocarbon fuels RP-3 and simulated JP-7[J]. Journal of Fuel Chemistry and Technology, 2006, 34(4): 466-470.) HERBINET O, MARQUAIRE P M, FREDERIQUE B L, FOURNET R. Thermal decomposition of n-dodecane: Experiments and kinetic modeling[J]. J Anal App Pyrolysis, 2007, 78(2): 419-429. ZAMOSTNY P, BELOHLAV Z, STARKBAUMOVA L, PATERA J. Experimental study of hydrocarbon structure effects on the composition of its pyrolysis products[J]. J Anal Appl Pyrolysis, 2010, 87(2): 207-216. YU J, ESER S. Thermal decomposition of C10-C14 normal alkanes in near-critical and supercritical regions: Product distributions and reaction mechanisms[J]. Ind Eng Chem Res,1997, 36(3): 574-584. 焦毅, 李军, 王静波, 王健礼, 朱权, 陈耀强, 李象远. 正癸烷热裂解实验和动力学模拟[J]. 物理化学学报, 2011, 27(5): 1061-1067. (JIAO Yi, LI Jun, WANG Jing-bo, WANG Jian-li, ZHU Quan, CHEN Yao-qiang, LI Xiang-yuan. Experiment and kinetics simulation on the pyrolysis of n-decane[J]. Acta Phys Chim Sin, 2011, 27(5): 1061-1067.) ZEPPIERI S P, KLOTZ S D, DRYER F L. Modeling concepts for larger carbon mumber alkanes: A partially reduced skeletal mechanism for n-decane oxidation and pyrolysis[J]. Proc Combust Inst, 2000, 28(2): 1587-1595. FRISCH M J, TRUCKS G W. Gaussiah 03[CP]. Gaussion, Inc., Wallingford CT, 2004. DUNCAN W T, BELL R L, TRUONG T N. The rate: Program for ab initio direct dynamics calculations of thermal and vibrational-state-selected rate constants[J]. J Comput Chem, 1998, 19(9): 1039-1052. MANION J A, HUIE R E, LEVIN R D, BURGESS Jr, ORKIN V L, TSANG W, MCGIVERN W S, HUDEGENS J W, KNYAZEV V D, ATKINSON D B, CHAI E, TREREZA A M, LIN C-Y, ALLISON T C, MALLARD W G, WESTLEY F, HERRON J T, HAMPSON R F, FRIZZELL D H. Chemical Kinetics Database, NIST Standard Reference Database 17 (Web Version), Release 1. 4. 2, data version 08. 09 . National Institute of Standards and Technology, Gaithersburg, Maryland, 20899-8380. COHEN N. Revised group additivity values for enthalpies of formation(at 298 K) of carbon-hydrogen and carbon-hydrogen-oxygen compounds[J]. J Phys Chem Ref Data, 1996, 25(6): 1411-1481. 袁涛. 正庚烷、异辛烷热解和预混火焰的实验及动力学模型研究[D]. 合肥:中国科学技术大学, 2010. (YUAN Tao. Experimental and kinetic modeling studies on pyrolysis and premixed flames of n-hptane and iso-octane[D]. Hefei: University of Science and Technology of China, 2010.) CURRAN H J. Rate constant estimation for C1 to C4 alkyl and alkoxyl radical decomposition[J]. Int J Chem Kinet, 2006, 38(4): 250-275. FENG Y, NIIRANEN J T, BENCSURA A, KNYAZEV V D, GUTMAN D, TSANG W. Weak collision effects in the reaction C2H5→C2H4+H[J]. J Phys Chem, 1993, 97(4): 871-880. BENCSURA A, KNYAZEV V D, XING S B, SLAGLE I R, GUTMAN D. Kinetics of the thermal decomposition of the n-propyl radical[J]. Symp Int Combust Proc,1992, 24: 629-635. KNYAZEV V D, SLAGLE I R. Unimolecular decomposition of n-C4H9 and iso-C4H9 radicals[J]. J Phys Chem, 1996, 100(13): 5318-5328. KEE R J, RUPLEY F M, MILLER J A, COLTRIN M E, GRCAR J F, MEEKS E, MOFFAT H K, LUTZ A E, DIXON-LEWIS G, SMOOKE M D, WARNATZ J, EVANS G H, LARSON R S, MITCHELL R E, PETZOLD L R, REYNOLDS W C, CARACOTSIOS M, STEWART W E, GLARBORG P, WANG C, ADIGUN O, HOUF W G, CHOU C P, MILLER S F. 2002 PaSR Application user manual: Modeling the mixing and kinetics in partially stirred reactors[Z]. Chemkin Collection Release 3.7, Reaction Design, Inc., San Diego, CA, 2002. 贾贞健. 吸热型碳氢燃料正癸烷高温裂解机理研究[D]. 哈尔滨: 哈尔滨工业大学, 2011. (JIA Zhen-jian. Pyrolysis mechanism study of endothermic hydrocarbon fuel n-decane at high temperature[D]. Harbin: Harbin Institute of Techonlogy, 2011.) 刑燕, 方文军, 谢文杰, 郭永胜, 林瑞森. 吸热型碳氢燃料模型化合物在超临界条件下的裂解及热沉测定[J]. 化学学报, 2008, 66(20): 2243-2247. (XING Yan, FANG Wen-jun, XIE Wen-jie, GUO Yong-sheng, LIN Rui-sen. Thermal cracking and heat sink measurement of model compounds of endothermic hydrocarbon fuels under supercritical conditions[J]. Acta Chimica Sinica, 2008, 66(20): 2243-2247.) 朱丹阳. 吸热型碳氢燃料热沉的测定及影响因素[D]. 天津: 天津大学, 2004. (ZHU Dan-yang. Measuring of heat sink of endothermic hydrocarbon fuels and some factors[D]. Tianjin: Tianjin University, 2004.)
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