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Cθp,m及熵Sθ298 K,并通过设计等键反应获得了各物种的标准生成焓△f Hθ298 K。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。
The geometry optimizations and vibrational frequencies of reactions,products and transition states involved in pyrolysis of n-decane w ere performed using the hybrid method B3LYP w ith 6-311G（d,p） basis set based on density functional theory.The potential energy surfaces of n-decane w ere built by the B3LYP / aug-ccpVTZ methods.The rate constants of all reactions w ith Eckart correction w ere calculated by the TheRate program package.The heat capacity and entropy（Cθ p,m and Sθ 298 K） at different temperatures were obtained by statistic thermodynamics.In order to calculate the standard formation enthalpy（△ f Hθ 298 K） for all species,isodesmic reactions w ere designed.The Chemkin II program w as used to model the product distribution and heat sink.The effects of the temperature and pressure on the heat sink and product distribution w ere 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 1,3butadiene and the product distributions vary w ith temperatures.The total heat sink of n-decane is 2.334 MJ / kg at 600 ℃ and 2.5 MPa,w ith the conversions of 25.9%,w hich could meet the cooling requirement of aircrafts at 5 ~ 6 Mach number.
出处
《燃料化学学报》
EI
CAS
CSCD
北大核心
2013年第9期1136-1145,共10页
Journal of Fuel Chemistry and Technology
基金
国家自然科学基金(21173139)
关键词
正癸烷
热裂解机理
速率常数
动力学模拟
热沉
产物分布
n-decane
mechanism of thermal decomposition
rate constant
kinetic modeling
heat sink
product distribution
