乙醇/空气扩散火焰制备碳纳米管的影响因素

采用乙醇为燃料和碳源,改变取样时间、催化剂种类和基板材料,在扩散火焰中进行了合成碳纳米管的试验研究．对于制备出的碳纳米材料的微观形貌采用高分辨扫描电镜(HRSEM)、透射电镜(TEM)进行了表征．研究结果表明,取样时间较短(小于5,min)或过长(大于20,min)时,基板表面都无法生成碳纳米材料;催化剂的种类和浓度对合成碳纳米材料具有重要影响;含有多种催化活性金属元素的基板不利于合成均一碳纳米管;试验条件下合成碳纳米管的最优工艺条件是温度在650～750,℃,取样高度为20,mm,取样时间为10,min,基板材料和催化剂分别为铜和1.0,mol/L硝酸镍．     

甲烷受控扩散火焰合成碳纳米管的实验研究

燃烧火焰法是合成碳纳米管的新方法，具有设备简单、容易实现等优点。以硝酸镍为催化剂，在甲烷-空气受控扩散火焰中合成了多壁碳纳米管，燃烧产物中还发现了碳纳米颗粒、碳纳米纤维和碳黑。实验结果表明，随着采样高度的增加，所合成的无定形多壁碳纳米管和富勒烯状碳纳米颗粒逐渐转变为石墨化程度较高的竹节形多壁碳纳米管和洋葱状碳纳米颗粒。分析表明，火焰温度、甲烷裂解产物以及催化剂种类等因素影响碳纳米管的形态和结构。     

碳纳米粒子促进水合物生成的研究进展

综述了碳纳米管、石墨烯、纳米石墨以及各自的功能化产物等碳纳米材料对水合物生成诱导时间、耗气量、生成速率、储气量等动力学参数的影响。碳纳米材料因其粒径小、比表面积大、导热性强等特点，可大大促进水合物的生成。碳纳米材料与部分传统促进剂复配可得到更好的促进效果，也是近年来国内外水合物领域的研究热点。未来可尝试其他类型的碳纳米材料，研究出更好的材料处理方法和复配体系，以期得到更好的促进效果。还可利用分子动力学手段，从微观方面研究碳纳米材料的促进机理。     

稀土固体超强酸SO42-/SnO2-CeO2催化合成生物柴油

以工业棕榈酸和甲醇为原料,采用溶胶-凝胶法制备稀土固体超强酸催化剂SO42-/SnO2-CeO2,催化合成生物柴油。考察了稀土氧化铈添加量、焙烧温度、焙烧时间、硫酸浓度、醇酸质量比、催化剂用量和反应时间对酯化反应的影响。结果表明,当氧化铈添加量为5%时,在2.0 mol/L硫酸浸渍后,于550℃下焙烧3 h制备的催化剂性能最好。正交试验结果表明,合成生物柴油的优化条件为醇酸质量比为15∶25,催化剂用量为棕榈酸质量的4%,反应时间为4 h,在此条件下,酯化率为95.4%。经GC-MS分析,酯产物主要为直链十六烷酸甲酯和10-十八碳烯酸甲酯。     

铜钼基硫氧化物催化剂及其光催化产氢性能

以[NH_4]_2MoS_4和CuCl为原料,合成了一系列铜钼基硫氧化物催化剂,并利用x射线衍射(XRD),UV-Vis漫反射光谱、X射线荧光(XRF)等化学物理手段对其进行了表征,制备的催化剂对光表现出较强的吸收特性,同时研究了该系列催化剂在可见光条件下的光催化制氢性能,并考察了反应温度和反应时间对催化剂产氢活性的影响.结果表明,在140℃条件下水热24h合成的催化剂制氢性能最好,平均产氢速率为10.7μmol/h·g.     

MXene基纳米材料在氧还原电催化中的应用

氧气还原反应(ORR)是燃料电池和金属-空气电池中的一个关键过程,反应动力学缓慢是制约其发展的瓶颈.MXene基纳米材料(包括MXenes复合材料)作为一种新型的二维层状材料,具有丰富的组成、高比表面积和化学稳定性、可调电子状态、大量暴露的活性位点等独特的结构特点,被认为是当前最有前途的一类ORR电催化剂或载体.开发高性能MXene基ORR催化剂为加速燃料电池和金属-空气电池阴极的缓慢ORR提供了新的途径.本文通过对近期相关文献进行分类总结,综述了MXene基ORR催化剂的设计原则,着重介绍了MXenes和MXenes复合材料在合成策略,组分、形态、结构与其电催化性能之间的构效关系,以及材料电催化反应机理等方面的最新研究进展.综合分析表明,通过构建MXene/过渡金属氧化物、MXene/过渡金属硫族化物、MXene/过渡金属氮化物、MXene/碳基材料、MXene/金属等MXenes复合材料,有望获得高活性、高稳定性的MXene基ORR催化剂.最后,本文提出该类催化剂目前在实际应用中面临的挑战,并指出MXene基纳米材料在电催化ORR方面的未来发展趋势.     

铋取代对LaMnO_3催化剂的结构和催化碳烟燃烧性能的影响

采用柠檬酸溶胶法合成了一系列LaMn1-xBixO3(x为0,0.1,0.2,0.3,0.4)钙钛矿型催化剂,通过X射线衍射(XRD)、比表面积测定(BET)、傅里叶红外光谱(FT-IR)、程序升温还原(H2-TPR)和程序升温脱附(O2-TPD)手段对催化剂的物理化学特性进行了表征.采用热重分析法(TG/DTA)研究了铋(Bi)金属的取代对催化剂催化去除碳烟活性的影响.研究结果表明,Bi取代导致催化剂样品中Bi0.775,La0.225,O1.5氧化物的形成,并随着Bi取代量的提高该氧化物的量逐渐增多.相对于LaMnO3,金属Bi取代提高了催化剂的比表面积、表面吸附氧含量(α-O2)以及低温氧化还原能力,因此催化剂使碳烟燃烧的催化活性得到了显著的提高.该系列样品中,LaMn0.7,Bi0.3,O3样品表现出最高的催化活性,碳烟燃烧速率峰值温度(Tm)仅为394,℃.     

秸秆合成气催化合成甲醇催化剂优化试验研究

生物质能是一种可再生能源,为了研究秸秆类生物质转化为燃料甲醇以有效地利用生物质能,采用热化学方法在下吸式固定床气化炉中生产低热值燃气,对该燃气进行脱硫、脱氧、焦油催化分解、纯化、配氢等优化试验,制备出秸秆合成气。在直流流动等温积分反应器中进行了催化合成甲醇的试验,在235℃和5MPa条件下进行了催化剂种类及粒度对合成甲醇的影响试验。试验结果表明:合成甲醇的适宜催化剂型号为C301,最优化颗粒粒度为0.833mm×0.351mm,该研究为生物质(秸秆)气催化合成甲醇的深入研究提供了基础数据。     

固定化光合细菌利用低分子有机酸的产氢特性

通过固定化光合细菌对低分子有机酸进行了光合产氢的批式试验研究.利用修正的Gompertz方程进行产氢动力学分析,并且对产氢过程中pH变化、有机酸的氢转化率以及有机酸初始浓度对产氢的影响等进行了分析.结果表明固定化能提高产氢率,以海藻酸钠为固定化载体的产氢效果最佳.同时发现有机酸产氢存在最佳初始浓度,其中乳酸产氢的最佳初始浓度为0.049mol/L,对于乙酸、丙酸和丁酸这3种小分子羧酸,其最佳初始浓度的大小随着有机酸碳原子数的增加而减小,即乙酸(0.043mol/L)丙酸(0.029mol/L)丁酸(0.022mol/L).乙酸的最大氢转化率最高,达到65.3%.浓度对氢气含量没有影响,而对于乙酸、丙酸和丁酸,氢气含量随着有机酸碳原子数的增加而增大.     

不锈钢表面碳纳米管阵列制备及防霜性能研究

为了探究碳纳米管阵列在防结霜领域的应用前景,采用化学气相沉积法在不锈钢基底上制备了碳纳米管阵列疏水涂层,研究了制备参数(生长温度、生长时间和催化剂浓度)对碳纳米管阵列疏水性能和防结霜性能的影响。结果表明:生长温度和时间对碳纳米管阵列的疏水性能影响较小,催化剂浓度对疏水性能的影响较大。经碳纳米管阵列疏水改性后的不锈钢表面的结露时间、结霜时间均较原始不锈钢表面延长,结霜量也大幅度减少。本研究表明碳纳米管阵列可大程度上延缓结霜现象,证明了碳纳米管阵列在防霜方面的优异效果。     

Investigating the role of methane on the growth of aromatic hydrocarbons and soot in fundamental combustion processes

Experimental results are presented on the effect of methane content in a non-aromatic fuel mixture on the formation of aromatic hydrocarbons and soot in various fundamental combustion configurations. The systems considered consist of a laminar flow reactor, a laminar co-flow diffusion flame burner, and a laminar, premixed flame burner, all of which operate at atmospheric pressure. In the flow reactor, the experiments are performed at 1430 K, constant C-atom flow rates, 98% nitrogen dilution, C/O ratio = 2, and with fuel mixtures consisting of ethylene and methane. The diffusion flames are performed with fuel mixtures of methane and ethylene diluted in nitrogen to maintain a constant adiabatic flame temperature. The premixed flame experiments are performed with n-heptane and methane mixtures at a C/O ratio = 0.67 with nitrogen-impoverished air. The results show the existence of synergistic chemical effects between methane and other alkanes in the production of aromatics, despite reduced acetylene concentrations. This effect is attributable to the ability of methane to enhance the production of methyl radicals that will then promote production channels of aromatics that rely on odd-carbon-numbered species. Benzene, naphthalene, and pyrene show the strongest sensitivity to the presence of added methane. This synergy on aromatics trickles down to soot via enhanced inception and surface growth rates by polycyclic aromatic hydrocarbon condensation, but the overall effects on soot volume-fraction are smaller due to a compensating reduction in surface growth from acetylene. These results are observed under the very fuel-rich environments existing in the flow reactor and diffusion flames. In the premixed flames, however, instabilities did not permit investigation of conditions with sufficiently high equivalence ratios to perturb the aromatic and soot-growth regions.     

Effect of nitrogen on deflagration characteristics of hydrogen / methane mixture

In order to study the influence of nitrogen on the deflagration characteristics of premixed hydrogen/methane, the explosion parameters of premixed hydrogen/methane within various volume ratios and different dilution ratios were studied by using a spherical flame method at room temperature and pressure. The results are as follows: The addition of nitrogen makes the upper limit of explosion of hydrogen/methane premixed gas drop, and the lower limit rises. For explosion hazard (F-number), hydrogen/methane premixed fuel with a hydrogen addition ratio of 10% has the lowest risk, and nitrogen has a greater impact on the dangerous degree of hydrogen and methane premixed gas whose hydrogen addition ratio does not exceed 30%. In terms of flame structure, the spherical flame was affected by buoyancy instability as the percentage of nitrogen dilution increased, but the buoyancy instability gradually decreased as the percentage of hydrogen addition increased. The addition of diluent gas reduces the spreading speed of the stretching flame and reduces the stretching rate in the initial stage of flame development. The laminar flame propagation velocity calculated by the experiment in this paper is consistent with the laminar flow velocity of the hydrogen/methane premixed gas calculated by GRI Mech 3.0. Considering the explosion parameters such as flammability limit, laminar combustion rate and deflagration index, when hydrogen is added to 70%, it is the turning point of hydrogen/methane premixed fuel.     

Asymptotic analysis of transport properties and burning velocities for premixed hydrocarbon flames

IntroductionThe fundamental meChedsm Of a p~xed flamewith the flow near the front stagnation point of a platewall has receiVed considerable attention in the field ofcombushon, which helps us to realize the behavior offlame Propagation. The CO~thew teChnique,inboduced by Law and coworkers["n, has produced theIndnar flame speed data that are ~ntiy usedextensively fof validation Of chemical ldnetics and themodeling of turbulent combustion. The laminar flamespeed is an important Property of a …     

Interactions for flames in a coaxial flow with a stagnation point

The possible burning structures existing in two co-flowing combustible mixtures with different compositions, and their implications to the field of turbulent combustion are examined in this study. A coaxial burner with a quartz plate was used to experimentally investigate the flames of methane/air and propane/air mixtures propagating in a coaxial flow impinging onto a stagnation surface. The possible burning structures were observed to be: (1) a single-flame (a lean or rich premixed flame); (2) a double-flame (two lean or rich premixed flames, or a rich premixed flame and a diffusion flame); and (3) a triple-flame (a rich premixed flame, a diffusion flame and a lean premixed flame). An inner (or outer) mixture, far beyond the flammability limit, can still burn if a stronger outer (or inner) flame supports it. The extinction limit of the top part of the inner hat-shaped premixed flame is nearly independent of the burning intensity of the outer flame. It was found that the inner flame has a wider flammable region than the outer flame, and that the latter has a narrower flashback region than the former. Both propane and methane flames may exhibit flame-front instability, although the former displays much more clearly than the latter. Cellular and polyhedral instabilities can exist individually or appear simultaneously in the inner flame. However, only polyhedral (stripped-pattern) instability was observed in the outer flame. Finally, the experiments were analyzed theoretically using a simple geometrical model incorporated with the numerical simulations. The predicted shapes and locations of the flames are in good agreement with the experimental observations qualitatively.     

Enhanced hydrogen production in a UASB reactor by retaining microbial consortium onto carbon nanotubes (CNTs)

Biohydrogen and subsequent biomethane generation from biomass is a promising strategy for renewable energy supply, because this combination can lead to higher energy recovery efficiency and faster fermentation than single methane fermentation. Microbial consortium control by retaining hydrogen-producers through the addition of microbial carriers is an alternative to constructing hydrogen-producing reactors. Here we report the use of carbon nanotubes (CNTs) as microbial carriers to enhance microbial retention and the production of biohydrogen. Laboratory-scale upflow anaerobic sludge blanket (UASB) reactors with CNTs at 100 mg/L achieved a maximal hydrogen production rate of 5.55 L/L/d and a maximal hydrogen yield of 2.45 mol/mol glucose. Compared to frequently used activated carbon (AC) particles, CNTs resulted in quicker startup and better performance of hydrogen fermentation in UASB reactors. Scanning electron microscopy (SEM) and pyrosequencing results revealed that the reactor with CNTs led to a high proportion of hydrogen-producing bacteria among the microbial consortium, which endowed the microbes with strong flocculation capacity and hydrogen productivity.     

甲烷预混多喷嘴阵列燃烧器热声振荡模态实验研究

为研究燃气轮机模型燃烧室的非预混燃烧流场,采用大涡模拟方法分别结合火焰面生成流形模型（FGM）和部分预混稳态火焰面模型（PSFM）对甲烷/空气同轴射流非预混燃烧室开展了数值模拟研究,并与试验结果进行对比。结果表明：FGM所预测的速度分布、混合分数分布、燃烧产物及CO分布与试验结果更符合;两种模型均能捕捉到燃烧室中的火焰抬举现象;燃烧过程中的火焰结构较为复杂,同时存在预混燃烧区域和扩散燃烧区域,扩散燃烧主要分布在化学恰当比等值线附近,预混燃烧区域主要分布在贫油区。     

Approximating the chemical structure of partially premixed and diffusion counterflow flames using FPI flamelet tabulation

Various strategies have been proposed to tabulate complex chemistry for subsequent introduction into fluid mechanics computations. Some of them are grounded on laminar flame calculations, which are useful to seek out key relations linking a few control parameters with relevant species responses. The objective of this paper is to estimate whether approaches based on premixed flamelets (FPI or FGM) can be extended to partially premixed and diffusion flames. Prototypes of nonpremixed laminar and strained counterflow flames are simulated using fully detailed chemistry. The configuration studied is a jet of methane/air mixture opposed to an air stream. A set of reference flames is then obtained, to which FPI results are compared. By varying the equivalence ratio of the free stream of methane/air mixture, from stoichiometry up to pure methane, premixed, partially premixed, and diffusion flames are analyzed. When the fresh fuel/oxidizer mixture equivalence ratio takes values within the flammability limits, excellent results are obtained with FPI. When this equivalence ratio is outside the flammability limits, diffusive fluxes across isomixture fraction surfaces lead to a departure between the FPI tabulation and the reference detailed chemistry flames. This is associated mainly with the appearance of a double-flame structure, progressively evolving into a single diffusion flame when the fuel side equivalence ratio is further increased. Using an improved flame index to distinguish between premixed and diffusion flame burning, hybrid partially premixed combustion is reproduced from a combination of FPI and diffusion flamelets.     

Hydrogen and carbon allotrope production through methane cracking over Ni/bimodal porous silica catalyst: Effect of nickel precursor

Nickel-based catalyst is highly active for hydrogen production through methane cracking reaction at moderate reaction temperature. However, Ni catalyst is easily deactivated by carbon encapsulation. In order to solve this problem, this research studies the effect of nickel precursors—nickel acetate (NA), nickel carbonate (NC) and nickel nitrate (NN)—on the activity and stability of nickel/bimodal porous silica (Ni/BPS) catalyst in methane cracking reaction. It was found that these nickel precursor solutions had different pH values, resulting in different interactions between surface silanol groups of BPS supports and Ni. Among these catalysts, Ni(NC)/BPS catalyst exhibited high nickel dispersion and weak interaction between Ni and BPS support; it then gave the highest CH₄ conversion and better stability compared to the other catalysts. In addition, H₂ yield of Ni(NC)/BPS catalyst was 2.90 and 1.40 times higher than those of Ni(NA)/BPS and Ni(NN)/BPS catalysts, respectively. Moreover, carbon nanofibers were grown in Ni(NC)/BPS and Ni(NN)/BPS catalysts, whereas carbon nanotubes were formed on Ni(NA)/BPS catalyst, due to the different nickel particle sizes, dispersions, and Ni—BPS support interactions.     

Characterization of the effects of hydrogen addition in premixed methane/air flames

The use of hydrogenated fuels shows considerable promise for applications in gas turbines and internal combustion engines. In the present work, the effects of hydrogen addition in methane/air flames are investigated using both a laminar flame propagation facility and a high-pressure turbulent flame facility. The aim of this research is to contribute to the characterization of lean methane/hydrogen/air premixed turbulent flames at high pressures, by studying the flame front geometry, the flame surface density and the instantaneous flame front thermal thickness distributions. The experiments and analyses show that a small amount of hydrogen addition in turbulent premixed methane–air flames introduces changes in both instantaneous and average flame characteristics.     

Aromatic formation pathways in non-premixed methane flames

A kinetic mechanism, previously developed and successfully applied to the prediction of the formation of benzene and aromatics in different flame conditions, was applied to assess the importance of the various benzene and aromatic formation pathways in non-premixed flames. Four sets of data were tested: the methane flame and the same flame doped with toluene, ethylbenzene, and tert-butylbenzene, as studied by Anderson and co-workers. The model predicts, with good accuracy, the growth of hydrocarbons and the formation of benzene and aromatic species. The modeling shows that in the undoped methane flame, benzene formation is controlled by propargyl radical combination. Acetylene addition to C4 radicals contributes a moderate amount, whereas toluene decomposition is insignificant. The predictions are almost unaffected by the fulvene pathway. Benzene is strongly perturbed by dopant addition to methane. Predictions agree quite well with benzene concentrations in the undoped flame and agree with the increase in benzene concentration when alkylbenzenes are added. Key reactions leading to the formation of naphthalene are the propargyl addition to benzyl radicals, and, to a lesser extent, the hydrogen-abstraction acetylene-addition mechanism. Cyclopentadienyl radical combination, which is the dominant route in premixed and partially premixed flames, is insignificant in these flame conditions.