单环苯并噁嗪树脂热解的ReaxFF反应动力学模拟

采用ReaxFF动力学方法模拟了非交联固化单环苯并噁嗪树脂在不同温度下的热解特性。模拟结果表明,N桥键的断裂是热解的主要引发反应,H_2,H_2O和大分子碳团簇是热解的主要产物。随着反应温度升高,H_2的数量急剧增加,而H_2O的数量反而降低,高温有利于促进相对分子质量较大的碳团簇的形成,还观察到了CO,NH_3,N_2和HCN等小分子产物。用ReaxFF动力学方法模拟所得的气体产物以及含类似石墨烯结构的碳团簇与实际实验结果一致,ReaxFF动力学模拟方法可以作为一种研究苯并噁嗪树脂高温热解反应的有效途径。     

ReaxFF molecular dynamics simulations of n-eicosane reaction mechanisms during pyrolysis and combustion

The pyrolysis and combustion mechanism of the hydrocarbon fuel has important scientific and practical significance. However, it is difficult to detect the whole intermediates and products using traditional methods, which brings trouble to the analysis of the reaction process. In this paper, the microscopic reaction mechanism and the main products of n-eicosane (C₂₀H₄₂) were simulated based on the reactive force field molecular dynamics (ReaxFF-MD). The effects of temperature (2000–3500 K) and oxygen on the initial decomposition, the distribution of main products, and the reactive pathways of C₂₀H₄₂ fuel were studied to determine its reaction mechanism. The initial decomposition of C₂₀H₄₂ was mainly initiated by small alkyl radicals in pyrolysis, and by the oxygen-containing radicals in combustion. The participation of oxygen had a greater effect on accelerating the decomposition reaction. The reactions involving oxygen of C₂₀H₄₂ initial decomposition accounted for 87.5% of the total reactions at 2000 K. Moreover, the detailed distribution and formation pathways of the main products of H₂, C₂H₄, CH₄, H₂O, CO, and CO₂ were depicted to construct the overall reaction mechanism of C₂₀H₄₂. •H radical formed from the composition of C₂H₄ was exactly consistent with the •H radical consumed by the generation of CH₄ and H₂ in the pyrolysis stage. The feasibility of the simulation method was verified by the result of thermal analysis. The results are helpful for further research on the reaction mechanism of hydrocarbon fuels.     

Chemical reactions of oily sludge catalyzed by iron oxide under supercritical water gasification condition

Supercritical water gasification is a promising technology in dealing with the degradation of hazardous waste, such as oily sludge, accompanied by the production of fuel gases. To evaluate the mechanism of Fe₂O₃ catalyst and the migration pathways of heteroatoms and to investigate the systems during the process, reactive force field molecular dynamics simulations are adopted. In terms of the catalytic mechanisms of Fe₂O₃, the surface lattice oxygen is consumed by small carbon fragments to produce CO and CO₂, improving the catalytic performance of the cluster due to more unsaturated coordination Fe sites exposed. Lattice oxygen combines with •H radicals to form water molecules, improving the catalytic performance. Furthermore, the pathway of asphaltene degradation was revealed at an atomic level, as well as products. Moreover, the adsorption of hydroxyl radical on the S atom caused breakage of the two C–S bonds in turn, forming •HSO intermediate, so that the organic S element was fixed into the inorganic liquid phase. The heteroatom O was removed under the effects of supercritical water. Heavy metal particles presented in the oily sludge, such as iron in association with Fe₂O₃ catalyst, helped accelerate the degradation of asphaltenes.     

基于改进ReaxFF 力场的全氟己酮热分解机理研究

采用基于密度泛函的紧束缚模型（DFTB）和改进的反作用力场（ReaxFF）对全氟己酮的热分解机理进行反应分子动力学仿真研究,分析了热分解的初始反应路径、微观反应过程以及体系内气体的生成机理,探讨了温度对全氟己酮热分解的影响,建立了以仿真数据为基础的一级动力学方程并对热分解过程进行一级动力学评估。结果表明,全氟己酮热分解的起始反应为：全氟己酮→全氟异戊烷+一氧化碳,全氟己酮热分解的主要产物为一氧化碳、四氟甲烷、六氟丙烯、全氟异丁烯、十氟丁烷、全氟异戊烷及大量活性基团。经一级动力学评估得到指前因子和表观活化能分别为5.021 7×1014 s-1和1 771.96 kJ/mol。     

萘热解生焦过程的反应分子动力学模拟

采用分子模拟的方法深入研究萘在热解生成针状焦过程的反应分子动力学。运用反应力场ReaxFF模拟该反应过程,并进行量子化学分析,推断得到萘分子在热解生焦过程中的主要反应历程。萘分子在自由基夺氢的情况下生成自由基•C₁₀H₇, •C₁₀H₇两两结合生成1,1′-联萘,1,1′-联萘再脱氢缩合生成苝,苝再进行脱氢缩合反应,芳核也随之增大。反应分子动力学模拟结果表明,在萘生焦过程中,反应生成的小分子和自由基会促进萘热解反应。在针状焦生成前期,应当控制热解反应的温度和压力,适当抑制气体挥发速率,以保证小分子和自由基能够参与芳核的生长反应。     

Anti-carbon deposition mechanism of H2O on nickel-based anode of SOFC: A ReaxFF molecular modelling

Carbon deposition occurs when Dimethyl ether (DME) fuel is used for SOFC, leading to battery degradation. In order to study the effect of water addition on carbon deposition, this work used reactive force field molecular dynamics (Reaxff MD) to simulate the process of carbon deposition with or without water addition, and analyze its anti-carbon deposition mechanism on nickel-based anode.It is found that the number of carbon atoms on nickel can be effectively reduced by mixing water with fuel. As the H₂O/DME ratio increases, there are fewer carbon atoms on the nickel anode. And there are two main ways for water molecules to resist carbon deposition. First is that the OH group generated by decomposition of water molecules at high temperature reacts with CH component to form aldehyde group, which reduces the formation of carbon deposition precursor. The other is that the increase of water molecules introduces more oxygen atoms into the system, and the carbon atoms formed by DME molecules combine with oxygen atoms to form CO, thus reducing carbon deposition. This study is helpful to promote the industrialization of DME as SOFC fuel.     

局部高温诱发CL-20/TNT共晶炸药内反应流传播的ReaxFF分子动力学模拟

为了更好地理解含能材料热点火以及热点成长现象和机理,采用基于第一性原理的Reax FF反应力场分子动力学方法模拟了CL-20/TNT共晶炸药内反应流传播的时空行为和初始化学反应过程。通过NVT系统和Berendsen温度耦合方法对含能材料两端连续快速加热并维持在高温条件激发反应流的产生和传播,并采用两种不同的热载荷(3000,4000 K)比较温度差异对初始热分解速率的影响。两端热载荷为4000 K时,热冲击传播过程中粒子瞬时平动速率可达0.5 km·s~(-1),高于3000 K时的情况。于此同时,两端高温将引发含能材料逐渐发生分解反应,同温度条件下,共晶中CL-20的分解速率高于TNT。另外,热载荷温度越高,共晶完全分解所需的时间越少。产物识别分析显示,CL-20/TNT共晶热分解的主要产物为NO_2,NO,H_2O,N_2,CO,CO_2,HONO,H_2O_2,CHON,H_2N,CH_2O,其中,NO_2是初始热分解产物,而最终产物为N_2,CO_2和H_2O。     

H2 and CO production through coking wastewater in supercritical water condition: ReaxFF reactive molecular dynamics simulation

The degradation mechanism of benzo[a]pyrene (BaP), a representative component of coking wastewater, and the pathway for the production of H₂ and CO in supercritical water have been investigated via ReaxFF reactive molecular dynamics simulations. The BaP molecules in the SCWG, SCWPO and SCWO systems show different degradation pathways. The maximum H₂ yield is obtained at the oxygen ratio of 0.2. There are three routes for the generation of H₂ molecules and production from H radical-rich water is the main route. CO molecules are formed by the CC bond breakage and CO bond breakage in the reforming fragments. There is a time delay between the fuel gas generation reaction and the side reactions due to the change of the instantaneous concentrations of H₂ and CO, providing a possible pathway to increase the amount of the produced fuel gases by designing a suitable reactor and recovering the gas fuel in time. Finally, kinetic behaviors of coking wastewater have been analyzed.     

梯恩梯/萘共晶初始热分解的反应分子动力学模拟

ReaxFF反应力场在冲击起爆、爆轰等问题中的应用多围绕常规含能材料。利用增加了长程修正项E_lg的ReaxFF/lg反应力场对梯恩梯/萘（TNT/C₁₀H₈）共晶初始高温热分解进行模拟,并通过TNT单晶比较了C₁₀H₈对共晶整体反应特征的影响,利用指数函数及反应速率方程拟合得到共晶初级吸热反应和次级放热反应的活化能分别为35.7 kcal/mol和56.1 kcal/mol. 初级吸热反应的活化能与TNT单晶基本相同,而次级放热反应的活化能则远远高于TNT单晶,并且同温度条件下共晶次级反应放热量小于TNT单晶。拟合得到的反应物的衰减速率表明,C₁₀H₈的加入将抑制共晶内TNT的分解。产物识别分析显示初始产物为NO₂、NO和HONO,并且通过NO₂和TNT_—NO2,NO和TNT_—NO,HONO和TNT_—HONO分布数量的比较论证了固相共晶和TNT单晶的初始反应路径为双分子反应机制。共晶热分解最终主要产物为N₂,H₂O,CO₂和CO. 并且由于共晶内C₁₀H₈分子C—C键断裂所需的能量高于C—H键断裂所需的能量,C₁₀H₈分子的初始热分解路径为C—H键断裂,并且形成的H原子将促进共晶内H₂O的产率高于TNT单晶内H₂O的产率。