五彩湾煤热解的反应分子动力学研究  

Molecular dynamics simulation of Wucaiwan coal pyrolysis via ReaxFF

作　　者：洪迪昆 刘亮[1] 操政 杨昌敏 郭欣[1] HONG Dikun;LIU Liang;CAO Zheng;YANG Changmin;GUO Xin(State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology,Wuhan 430074,China)

机构地区：[1]华中科技大学煤燃烧国家重点实验室,湖北武汉430074

出　　处：《煤炭学报》2019年第S01期271-277,共7页Journal of China Coal Society

基　　金：国家自然科学基金资助项目(51876073)。

摘　　要：采用基于反应力场的分子动力学方法研究准东五彩湾煤的热解过程。首先,对五彩湾煤样进行元素分析、13 C核磁分析以及X射线光电子能谱分析,发现五彩湾煤中芳香化合物主要以萘的形式存在,羟基或醚氧基、羰基和羧基为主要的含氧官能团,分别占56.90%,23.94%和19.16%;其次,基于实验表征结果对经典的Hatcher低阶煤分子模型进行修正,构建了五彩湾煤有机组分的分子结构模型;最后,对构建的煤分子模型进行热解反应分子动力学模拟,探索了温度和升温速率对五彩湾煤热解特性的影响。结果表明,在较低温度下煤热解以初次热解反应为主,部分弱共价键受热解离产生焦油自由基碎片和气体产物,体系势能随着热解时间的增加先急剧增加后保持不变;在较高温度下焦油自由基碎片的二次反应显著,体系势能先急剧增加后缓慢增加;与初次热解过程相比,焦油自由基碎片的二次反应过程需要更长的反应时间,CO 2主要来源于煤的初次热解,而焦油自由基碎片二次反应会导致大量的CO,H 2以及C 2 H 2的生成;C 5 H 5和C 2 H 2 O是主要的热解中间产物,通过分析热解产物的动态演变规律,揭示了焦油聚合反应和裂解反应机制;快速升温条件下焦油的二次反应不明显,但在慢速升温条件下焦油的二次反应显著,降低了焦油产率,提高了焦炭和气体产物的产量。The pyrolysis of Zhundong Wucaiwan coal was studied using the reactive molecular dynamics simulation method.First,the molecular model of Wucaiwan coal was built based on the ultimate analysis,solid-state 13 C NMR spectroscopy and X-ray photoelectron spectroscopy of coal sample.It was found that the aromatic ring in Zhundong coal mainly exists in the form of naphthalene.The hydroxyl or etheroxy,carbonyl and carboxyl are the main oxygen-containing functional groups in Zhundong coal,accounting for 56.90%,23.94%and 19.16%,respectively.Then,the classical Hatcher low-rank coal model was modified to construct the molecular structure of Wucaiwan coal based on the experimental characterization results.Finally,the reactive molecular dynamics simulation of coal pyrolysis was carried out to study the effect of temperature and heating rate on the pyrolysis characteristics of Wucaiwan coal.The results show that the pyrolysis process was dominated by the primary pyrolysis reaction,leading to the formation of char,tar radical fragments and gas,the potential energy of the system increased rapidly first and then kept unchanged with pyrolysis time.However,the secondary reaction of tar radical fragments was significant at high temperatures,the potential energy of the system increased continuously with pyrolysis time.Compared with the primary pyrolysis process,the secondary reaction of tar free radical fragments required longer reaction time.CO 2 was mainly derived from the primary pyrolysis of coal,while the secondary reaction of tar free radical fragments led to a large amount of CO,H 2 and C 2H 2 generation.C 5H 5 and C 2H 2O were observed as the main intermediates.By analyzing the dynamic evolution of pyrolysis products,the secondary reaction mechanism of tar radical fragments was revealed.The secondary reaction of tar was not significant at rapid heating conditions,but was significant at slow heating conditions,leading to the decrease of tar yield and the increase of gas and char yields.

关 键 词：五彩湾煤 热解 二次反应 反应力场 分子动力学 

分 类 号：TQ530.2[化学工程—煤化学工程]