水分子对初始碳烟颗粒形成过程影响的分子动力学模拟

采用LAMMPS软件,基于ReaxFF,以十氢化萘、萘、2-甲基蒽、1-乙基芘为催化油浆的模型化合物研究了600～2500 K温度下催化油浆形成初始碳烟颗粒的过程,考察了2500 K时水分子对初始碳烟颗粒形成过程的影响。研究表明温度在600 K时模型化合物分子主要是物理聚集成核。温度在900～1700 K时模型化合物分子处于聚集和分离的动态过程,无法从单体向碳烟颗粒转变。温度高于2100 K时主要是化学成核,模型化合物分子碳氢键先断裂,然后碳碳键断裂产生大量短碳链,碳链经成键和环化形成初始碳烟颗粒。温度在2500 K时水分子抑制模型化合物分子化学成核,随着体系氢碳比的增加,抑制初始碳烟颗粒形成的作用增强。水分子产生氢自由基和氢氧自由基,这些基团会直接导致模型化合物分子的侧链断裂和碳碳键断裂形成大量短碳链。碳链继续与氢自由基和氢氧自由基作用形成一氧化碳、二氧化碳、氢气、甲烷等而被消耗,水分子的作用为促进短碳链形成和抑制短碳链向形成初始碳烟颗粒的方向进行。     

高压下H2/CO稀释剂对乙烷/空气层流扩散火焰中碳烟形成的影响

采用CoFlame程序模拟研究了高压下H₂/CO稀释剂对乙烷/空气层流扩散火焰中碳烟形成的影响。结果表明:H₂和CO添加之后,火焰温度均略有增加,且碳烟体积分数随着H₂/CO稀释比的增加而降低。H₂的添加使得碳烟表面生长区域的H自由基浓度增加,减少了初始碳烟颗粒成核及表面生长的活性位点数,导致脱氢加乙炔(HACA)反应中氢提取速率减缓以及碳烟颗粒表面生长速率减缓。CO的添加使得苯(A1)和芘(A4)摩尔分数减少,减缓了碳烟成核速率,导致碳烟的生成受到抑制。     

聚异戊二烯橡胶硫化胶交联网络的自修复

橡胶拉伸时,分子链发生断裂会生成碳自由基;经硫黄硫化形成的交联网络中交联键发生断裂则生成硫自由基。自由基的化学性质十分活泼,其发生的反应是影响硫化胶性能变化的因素之一。     

煤中含硫模型物萘基苄基硫醚的热解热力学

采用密度泛函理论计算方法研究了煤中含硫醚键的模型化合物萘基苄基硫醚的热稳定性.计算得到的微观结构参数和热力学函数表明,萘基苄基硫醚中各化学键的稳定性顺序为:苄基亚甲基上C与S之间的键在热解时最容易发生断裂而形成更加稳定的具有p-π共轭体系的苄基自由基;其次是萘基上的C与S之间的键断裂;再次是苄基亚甲基C上的H脱除;接着是苯基脱除;最后才是六元环上的H脱除.萘基苄基硫醚的热解是吸热反应,升高温度有利于热裂解反应的进行.     

煤液化油中低级酚生成的影响因素研究

为了探究反应温度、反应压力、催化剂添加量以及供氢溶剂对褐煤直接液化油中低级酚生成的影响以及低级酚生成的机理,利用模型化合物邻苄基苯酚在煤直接液化条件下进行加氢反应。实验结果表明:邻苄基苯酚在液化条件下主要发生桥键断裂反应生成低级酚,苯环不易被加氢饱和。温度升高对促进邻苄基苯酚桥键断裂有利;压力升高则不利于其桥键断裂;铁系催化剂添加量的增加会促进桥键断裂;供氢溶剂四氢萘相比十氢萘会抑制低级酚的生成。邻苄基苯酚加氢液化的产物以苯酚与甲苯为主,邻甲酚与苯相对较少。     

阿拉伯糖醇自由基β-消除反应的理论研究

自由基机理是纤维素老化降解和生物质能热解的重要反应途径,本文采用密度泛函理论方法,在B3LYP/6-311++G**//B3LYP/6-31G**水平,对纤维素降解或裂解初级可能生成的阿拉伯糖醇自由基的分子内氢迁移重排及其氧位自由基的β-消除反应、β-脱水反应以及形成呋喃环分子内取代消除反应的机理进行了理论研究。计算结果表明,糖醇自由基中不同碳位自由基的相对能量接近(<4.5 k J/mol),比氧位自由基相对能量低约38~65 kJ/mol。氧位自由基的β-消除反应有两种方式:α(C-H)键的断裂和α(C-C)键的断裂,前者生成五碳醛糖/酮糖,后者生成低碳醛糖和另一分子低碳糖醇自由基(或羟甲基自由基),但后者所需的活化能(约12~40 kJ/mol)比前者(约100~130 kJ/mol)小的多。而β-脱水反应和形成呋喃环反应所需活化能相当,比β-氢原子消除反应的活化能还大些。因此,在低温下糖醇烷氧自由基α(C-C)键断裂的β-消除反应是纤维素老化自由基降解机理的主要方式,该降解方式可产生羟甲基自由基,其夺取一个氢原子而生成绝缘纸老化的重要信号分子―甲醇。而在高温下则β-氢原子消除、β-脱水和形成呋喃环化合物等反应形成复杂竞争,但脱水反应是这些反应中明显的放热反应。     

二苄基硫醚和二苄基二硫醚中硫的热迁移机理

以二苄基硫醚(DBS)和二苄基二硫醚(DBDS)为有机含硫模型化合物,以二苯甲烷(DPM)亚甲基作为活性氢源,研究了反应温度对DBS中C烷—S键及DBDS中C烷—S和S—S键断裂以及硫的热迁移的影响.结果表明:200℃以下,DBS中C烷—S键未断裂;225℃以上,DBS中C烷—S键能够发生有效热断裂.而模型化合物DBDS在200℃时C烷—S和S—S键可发生有效热断裂.两种化合物热断裂反应遵循自由基型反应机理,两种模型化合物中硫的热迁移历程基本相同,主要产物是甲苯(PhMe)、二苯乙烯(DPE)、二苯乙烷(DPEA)和三苯乙烯(TPE),有机含硫化合物很少,说明温和条件下化合物DBS中C烷—S键及DBDS中的C烷—S和S—S键能有效热断裂,热断裂硫能有效以气体H2S形式迁出,少量转化为其他形态有机硫.     

含K成分形成初始沉积层的数学模型及烟气条件影响分析

针对积灰初始沉积层形成的两种主要机理即凝结和热泳机理,建立了含K成分形成初始沉积层的数学模型,采用文献中的实验结果检验了模型,表明考虑沉积层厚度、表面温度随位置和时间的变化对模型预测有合理的改善。应用该模型研究含K气体成分和气溶胶颗粒在受热面上的沉积过程,并考察烟气中含K成分组成、烟温和烟速等因素的影响。研究表明,由于烟气中含K气体成分和气溶胶颗粒相对浓度的差异,凝结和热泳在沉积过程开始时都可能对初始沉积层的形成起主要作用,而在沉积过程后期热泳沉积则占据主导地位;烟温和烟速对含K成分沉积过程的影响相似,即较高的烟气温度和速度,其初期沉积速率高,而后期沉积速率相对低,形成的沉积层厚度较低。     

含K成分形成初始沉积层的数学模型及烟气条件影响分析

针对积灰初始沉积层形成的两种主要机理即凝结和热泳机理,建立了含K成分形成初始沉积层的数学模型,采用文献中的实验结果检验了模型,表明考虑沉积层厚度、表面温度随位置和时间的变化对模型预测有合理的改善。应用该模型研究含K气体成分和气溶胶颗粒在受热面上的沉积过程,并考察烟气中含K成分组成、烟温和烟速等因素的影响。研究表明,由于烟气中含K气体成分和气溶胶颗粒相对浓度的差异,凝结和热泳在沉积过程开始时都可能对初始沉积层的形成起主要作用,而在沉积过程后期热泳沉积则占据主导地位;烟温和烟速对含K成分沉积过程的影响相似,即较高的烟气温度和速度,其初期沉积速率高,而后期沉积速率相对低,形成的沉积层厚度较低。     

聚烯烃抗老化助剂的选择及应用

聚烯烃在自然界巾会遇到氧和阳光的作用，使树脂的分子链和助剂产生自由基，它会和氧进一步反应形成氧化自由基及过氧化自由基，所产生自由基活性强，能夺取其他树脂分子链及助剂中的氢，生成氢过氧化物。不稳定的氢过氧化物又会裂解成新的自由基，这两个活泼的自由基进一步与氧反应，还能形成新的氢过氧化物。     

Analysis of energy transfer and ternary non-covalent filler/matrix/UV stabilizer interactions in carbon nanofiber and oxidized carbon nanofiber filled poly(methyl methacrylate) composites

Ternary non-covalent interactions between carbon nanofibers (CNFs), oxidized carbon nanofibers (ox-CNFs), poly(methyl methacrylate) (PMMA) chains, and benzotriazole-containing UV stabilizers were analyzed using Fourier-transform infra red spectroscopy (FTIR), time-resolved fluorescence emission spectroscopy, and fluorescence lifetime imaging microscopy. The results indicated that PMMA chains form hydrogen bonds both with ox-CNF fibers and the UV stabilizer molecules. It was also determined that UV stabilizers strongly interact with CNF particles via π-π interactions. The extent of π-π and hydrogen bonding interactions was determined to be lower between ox-CNF particles and UV stabilizers due to less perfect graphitic structure of the former. The morphology of the composites indicated that the hydrogen bonds between PMMA chains and ox-CNF particles resulted in highly improved state of filler dispersion in ox-CNF/PMMA composites.     

Soot in Diesel Combustion Systems

Diesel soot, one of the major environmental pollutants, is the finer particle produced during the high temperature pyrolysis or combustion of diesel fuel. Advances in the understanding of soot formation in diesel combustion systems during the recent decades are surveyed in this paper. It is universally accepted that soot formation steps can be summarized as (1) formation of molecular precursors of soot, (2) nucleation or inception of particles from heavy polycyclic aromatic hydrocarbon molecules, (3) mass growth of particles by addition of gas phase molecules, (4) coagulation via reactive particle‐particle collisions, (5) carbonization of particulate material, and, finally, (6) oxidation of polycyclic aromatic hydrocarbons and soot particles. Several mathematical models of diesel soot formation available in the related literature are offered in this review, which are Hiroyasu's model, Moss' model, Tesner's model, Lindstedt's model, and detailed soot formation models. Experimental and numerical studies currently play an important role in exploring the diesel soot formation mechanism. The success of such studies relies on the development of both diagnostic techniques to increase the quality of experiments and mathematical models for numerical simulations.     

Soot formation in isothermal pyrolysis of carbon tetrachloride and its mixture with methane

The formation of soot during pyrolysis of tetrachloride carbon in the temperature interval 1423–1623 K and its mixtures with methane at 1573 K is studied under conditions close to the isothermal ones. The induction periods of soot formation from CCl₄ are measured. The equations to calculate the induction period of soot formation, the concentration of soot particles, and its specific surface as a function of the temperature and concentration of CCl₄ are derived. The inhibition of soot formation is observed in the isothermal pyrolysis of a CCl₄−CH₄ mixture. It is shown that the particle nuclei are formed only from Cl₄, and the CH₄ molecules are spent only for the heterogeneous growth of the formed particles. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 4, pp. 41–47, July–August 1999.     

Conditional moment closure modelling of soot formation in turbulent, non-premixed methane and propane flames

Presented are results obtained from the incorporation of a semi-empirical soot model into a first-order conditional moment closure (CMC) approach to modelling turbulent, non-premixed methane-air and propane-air flames. Soot formation is determined via the solution of two transport equations for soot mass fraction and particle number density, with acetylene and benzene employed as the incipient species responsible for soot nucleation, and the concentrations of these calculated using a detailed gas-phase kinetic scheme involving 70 species. The study focuses on the influence of differential diffusion of soot particles on soot volume fraction predictions. The results of calculations are compared with experimental data for atmospheric and 3 atm methane flames, and propane flames with air preheated to 323 K and 773 K. Overall, the study demonstrates that the model, when used in conjunction with a representation of differential diffusion effects, is capable of accurately predicting soot formation in the turbulent non-premixed flames considered.     

Early soot formation stages in low-pressure diffusional counterflow hydrocarbon flames

Early soot formation stages were investigated in low-pressure counterflow hydrocarbon flames. A mechanism is proposed for the formation of aggregates and discrete spherical soot particles. It is proposed that the formation of the physical surface is preceded by the emergence of a skeleton structure consisting of carbon molecule chains as a result of their polarizing and dipole interaction with the charged soot nuclei.Kiev. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 3, pp. 97–100, May–June, 1993.     

The effect of oxygen and carbon dioxide concentration on soot formation in non-premixed flames

The influence of oxygen concentration and carbon dioxide as diluents in the oxidizer side on soot formation was studied by Time Resolved Laser Induced Incandescence (TIRE-LII) and TEM photography in non-premixed co-flowing flames. TIRE-LII method was used to measure the distribution of two-dimensional soot volume fraction and primary particle size. The soot was directly sampled by the thermophoretic method, and its diameter was examined by TEM photography. Two suitable delay times of the TIRE-LII method affecting measurable range and sensitivity were determined by comparing TEM photographs with the TIRE-LII signal. The effects of oxygen concentration and carbon dioxide as diluents in the oxidizer side on soot formation were investigated with these calibrated techniques. An O₂+(CO₂, N₂, and [Ar+CO₂]) mixtures in co-flow were used to isolate carbon dioxide effects systematically. The primary particle number concentration and soot volume fraction were abruptly decreased by the addition of carbon dioxide to co-flow. This suppression was resulted from the short residence time in inception region because of the late nucleation and the decrease of surface growth distance by the low flame temperature due to the higher thermal capacity and the chemical change of carbon dioxide. The increase of oxygen concentration in the co-flow caused an enhancement of soot nucleation and thus the residence time increase, but the specific growth rate showed almost the same value regardless of the co-flow mixture in the growth region. This result suggests that the specific growth rate has a weak dependence on the relative change of co-flow conditions in non-premixed co-flowing flames.     

生物质碳烟颗粒物生成机理研究进展

介绍了生物质燃烧过程中碳烟颗粒物的生成机理,主要包括生物质碳烟的各种生成路径,生物质碳烟生成的中间产物多环芳烃,以及中间产物多环芳烃生成碳烟,多环芳烃、反应气氛、反应压力及反应温度等对碳烟颗粒物生成的影响,生物质金属离子对碳烟生成及碳烟的成长过程等影响。总结了现有生物质碳烟生成机理研究的不足,并对碳烟中间产物,碳烟一次、二次生成机理以及影响碳烟生成量的各种因素等进行系统研究;采用量子化学理论、矩方法以及激光检测试验等方法来研究生物质碳烟的生成机理,并可借鉴燃煤碳烟生成机理及柴油碳烟生成机理的研究方法及试验等;从生物质碳烟生成的热力学及动力学机制、成核演变理论、影响机制及试验方面等,并从化学反应和工程热物理的角度,深入研究生物质燃烧过程中碳烟颗粒物的生成机理与碳烟核成长演变行为,得到合理的生物质碳烟生成机理,为控制并减少雾霾环境影响的实际工程应用提供理论与实践指导。     

Hydrogen production by the catalytic steam reforming of methanol part 1: The thermodynamics

The thermodynamic equilibria involved in the catalytic steam reformation of methanol to produce hydrogen have been examined over the ranges of pressure 101–3040 kPa, temperature 400–700K and water to methanol feed ratio 1.5–0.67. Four models have been considered based upon possible reaction products and the equilibrium composition of each model calculated. The presence of methane and carbon reduce the quantity and quality of hydrogen produced. The best condition for hydrogen production occurs at 500K in the model in which carbon (soot) and methane gas are excluded and where pressures are low, and water is in excess in the feed. To achieve these conditions in practice the reactions for methane formation, which is thermodynamically favoured, and the appearance of carbon (soot) must be inhibited.     

Effect of an alternating electric field on soot formation in diffusional low-pressure counterflow hydrocarbon flames

Effects are investigated of constant and alternating electric and of magnetic fields on the soot formation in plane diffusional acetylene—and benzene—oxygen low-pressure counterflow flames. When electric fields are applied to the flame, reduction in the soot outflow and formation in the flame of dense aggregates shaped like laminae and droplets were observed. It was shown that the soot aggregates possess a skeleton. Alternating electric fields imposed on the flame inhibit skeleton formation and move the aggregate formation process to the later stages of soot aerosol formation, which leads to the production of dense aggregates and reduces the soot outflow. It is concluded that the observed smallest carbon particles (below 1 nm) are the basic structural soot units. In flames permeated by a magnetic field, the structural soot units form chains, from which domains are formed.Dnepropetrovsk. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 3, pp. 100–105, May–June, 1993.