海底充油电缆的安全稳定运行至关重要,但内部的十二烷基苯(DDB)绝缘油在热故障导致的局部高温下会快速热解和产气.基于反应分子动力学模拟(ReaxFF-MD)和热重-红外光谱(TG-IR)实验,对十二烷基苯绝缘油的热解和产气过程进行探究.热解模拟结果表明:十二烷基苯分子初始裂解反应主要为C—C键的断裂产生长链大分子,后逐渐热解产生小烷基自由基和烯烃分子,DDB 最终会热解为侧链为·C2H5、·CH3 和·C3H7 基团的短链烷基苯分子.热解过程中主要特征气体为C2H4、H2、CH4,与 IR 实验结果相同,特征气体生成的主要反应机理分别为:β位C—C键的断裂、加氢反应和脱氢反应;·H自由基攻击其他自由基上的H原子;甲基自由基(·CH3)与游离的氢(·H)自由基反应.动力学结果表明TG实验与ReaxFF-MD的活化能分别为86.606 kJ/mol以及 99.867 kJ/mol,相近的活化能进一步验证了仿真结果的合理性.研究结论为深入了解十二烷基苯绝缘油的裂解和产气机理提供了理论支持.
Probing the pyrolysis mechanism of alkylbenzene insulating oil in oil-filled cables based on ReaxFF-MD and TG-IR
The safe and stable operation of submarine oil-filled cables is critical,but the internal dodecylbenzene(DDB)insulating oil is subject to rapid pyrolysis and gas production at localized high temperatures due to thermal faults.Against this issue,the pyrolysis and gas production processes of dodecylbenzene insulating oil are investigated based on reactive molecular dynamics simulations(ReaxFF-MD)and thermogravimetric-infrared spectroscopy(TG-IR)experiments.The pyrolysis simulation results show that,the initial cracking reaction of the dodecylbenzene molecule is mainly the breaking of C—C bond to produce long-chain macromolecules,and then the gradual pyrolysis produces small alkyl radicals and olefinic molecules,and the DDB will eventually be pyrolyzed to the short-chain alkylbenzene molecules with the side chains of·C2H5,·CH3 and·C3H7 groups.The main characteristic gases during pyrolysis are C2H4,H2,and CH4,which are the same as the results of IR experiments,and the main reaction mechanisms for the generation of the characteristic gases are:(i)the breaking of the C—C bond at the β-position,the hydrogenation reaction,and the dehydrogenation reaction;(ii)the attack of-H radicals to the H atoms on other radicals;and(iii)the reaction of the methyl radicals(·CH3)with the free hydrogen(·H)radicals,respectively.The kinetic results show that the activation energies of the TG experiment and ReaxFF-MD are 86.606 kJ/mol as well as 99.867 kJ/mol,respectively,and the similar activation energies further validate the reasonableness of the simulation results.The study conclusion provides theoretical support for deep understanding of the cracking and gas production mechanism of dodecylbenzene insulating oil.
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