多尖端旋转电极辉光放电甲烷偶联研究

石油资源的日趋短缺使人们对世界大储量能源天然气的开发利用越来越重视。甲烷（CH4）是天然气的主要成份,由于CH4分子具有很高的稳定性,用CH4直接偶联制C2炔（乙烷,;乙烯,乙炔）在热力学上十分不利,采用常规催化手段一直未取得突破性进展^[1],而辉光放电等冷等离子体对于CH4偶联是一种非常有效的方法,近年来已成为物理化学跨学科前沿研究热点。在本研究领域中,利用脉冲电晕等离子体结合催化剂进行甲烷转化^[2],其等离子体在空间分布上是非连续的,活性较低,反应区较小,甲烷的转化率及C2烃收率必须是有限的;利用微波诱导甲烷在催化剂上转化制C2烃^[3],由于温度很高,能量密度太大,很容易使甲烷完全裂解,生成大量积碳,C2烃的收率也较低;利用介质阻挡放电使CH4偶联^[4],能耗太大,能量利用率很低。因此,冷等离子体CH4偶联实现工业化的课题就是要在提高CH4转化率及C2烃收率的同时降低能耗,以提高能量利用率。     

交流非平衡等离子体裂解甲烷制C2烃

用介质势垒放电研究了甲烷在无氮条件下的直接转化。天然气（甲烷含量94%）在常温常压下通过介质势垒放电反应器形成非平衡态等离子本。反应器两电极间施圆满的交流电压为15-30kV，甲烷分子在此环境中裂解为CH3、CH2、CH和H，并偶联生成C2烃和氢气。实验表明，甲烷转化率和C2烃收率随放电电压和停留时间增加而增加，虽然C2烃总的选择性变化不大，但乙炔、乙烯各自的选择性随电压升高而增加。     

光谱诊断冷等离子体作用下甲烷转化机理的初步研究(英文)

冷等离子体是甲烷无氧活化制C2烃较为有效的技术手段之一,由于等离子体反应体系的复杂性,甲烷无氧活化制C2烃反应机理及过程尚不十分清楚。本文采用发射光谱原位诊断技术对冷等离子体作用下甲烷无氧活化制C2烃反应中若干激发态物种进行诊断研究,在250nm～670nm波长范围内检测到下列激发态物种:CH、C和C2。依据激发态物种检测结果、气相色谱反应产物分析结果及等离子体特性,推断了等离子体作用下甲烷无氧活化制C2烃的自由基反应历程。     

离子液体在甲烷等离子体转化中作用机理的光谱研究

在直流等离子体甲烷转化反应体系中分别引入C₆MIMBF₄,C₆MIMCF₃COO,C₆MIMHSO₄三种离子液体,采用光谱在线技术检测反应中活性物种的种类和光谱谱峰相对强度的变化,研究了离子液体在气液等离子体甲烷转化反应中的作用机理。结果表明：向甲烷等离子体体系中引入离子液体可得到稳定的气液界面,并提高了甲烷转化率和C₂烃产物收率,C₆MIMCF₃COO和C₆MIMBF₄有助于提高C₂烃选择性,而C₆MIMHSO₄则导致C₂烃选择性下降。在气液等离子体甲烷放电体系中检测到了C,C₂,C₃,CH,H等活性物种的发射光谱,与未引入离子液体时相比大多数活性物种的谱线强度均有增加。核磁共振研究表明反应后离子液体C₆MIMBF₄结构稳定,可认为离子液体作为液体导电介质提高了等离子体放电强度,促进等离子体区气相反应过程,同时离子液体在气液表面反应过程起催化作用。     

常压等离子体作用下CO2氧化CH4转化反应的光谱分析

采用光谱原位诊断技术在200～900nm范围内采集并标识了不同CO2添加量时CH4等离子体光谱。确定了常压下不同CO2添加量时CH4等离子体的活性物种。CO2添加量不同活性物种谱峰相对强度变化趋势不同,O活性物种谱峰相对强度随CO2添加量增加迅速增加。C2活性物种谱峰相对强度随CO2添加量增加逐渐降低。反应体系产生的活性O对CH4转化反应产物具有明显影响,CO2添加量不同,CH4转化反应机理不同。当CO2添加量小于30%时,CH4转化以偶联反应为主。CO2添加量大于30%时,CH4转化以重整反应为主。     

甲烷电离特性的等离子体发射光谱法研究

应用等离子体发射光谱法,用CCD(charge coupled device)光栅光谱仪记录并标识了脉冲电晕甲烷等离子体370～1 100 nm的发射光谱,确定了常温常压下高纯甲烷(99.99%)经100 kV, 100 Hz脉冲高压电离后的产物为H,C+,CH,C,C₂,C₃, C₄,C₅和烃等。通过分析实验检测到的甲烷等离子体发射光谱,给出了甲烷经脉冲高压电离形成电晕等离子体的机理和自由基CH_n(n=3,2,1)、碳、烃等产物的电离途径。结果显示甲烷分子经高能电子非弹性碰撞后脱氢程度很高,大量氢原子及其离子和甲烷自由基在进一步被高能电子作用下合成了烯烃、炔烃、烷烃和高聚碳化物。实验所获得的脉冲甲烷等离子体发射光谱及其机理分析可为甲烷及其转化研究提供相关依据。     

High Temperature Seedless Synthesis of Au NRs Using BDAC/CTAB Co-surfactant

采用等离子体活化技术制备了一种新型Ni/γ-Al2O3催化剂用于CO2重整CH4反应. 等离子体强化制备的催化剂表现出较高的反应活性和较好的抗积碳能力. 为了达到相同CH4转化率,常规焙烧的催化剂需要比等离子体处理的催化剂高出50 °C 的反应温度. 反应结束后,等离子体处理催化剂的失活率仅为1.7%,而常规催化剂上的失活率为15.2%。通过对催化剂进行BET、H2-TPR、XRD、CO2-TPD和TG等表征分析,结果表明等离子体增强制备方法使催化剂的平均孔直径减小,比表面积增加;催化剂的还原性,镍物种的分散度和催化剂对CO2的吸附量都有显著的提高.     

低温等离子体活化转化煤层甲烷机理的光谱诊断

为了探究低温等离子体活化转化煤层甲烷的机理,采用自制的介质阻挡放电实验系统对体积组成为CH440%、O212%、N248%的模拟煤层甲烷进行等离子体活化转化。采用色谱分析方法对煤层甲烷介质阻挡放电稳定产物进行分析,结果表明低温等离子体活化煤层甲烷的主要产物为CH3OH、CO和CO_2。采用发射光谱原位诊断技术在200~700 nm波长范围内研究了放电气体的发射光谱,检测到O·、CH·、C·、Hα、N2(A3Σ+U)等激发态物种。基于发射光谱原位诊断和气相色谱分析结果,对煤层甲烷活化转化的自由基反应过程进行了推断。同时,明晰了反应气中N2对煤层甲烷活化和主要产物的生成具有促进作用,即N2产生了存活时间更长的亚稳态离子,该亚稳态离子将能量传递给反应气中的O2和CH4,进而加速了煤层甲烷的活化和稳定产物的生成。     

螺旋波激发甲烷等离子体光谱诊断

利用螺旋波激发等离子体化学气相沉积（LPP-CVD）技术,以甲烷和氦气为反应气体产生等离子体。通过采集到甲烷的可见光到紫外发射光谱,对甲烷等离子体进行原位诊断,发现存在CH、Hα及Hβ等碎片粒子的光辐射,同时,分析了不同入射功率、气压下CH粒子以及Hβ、Hγ的相对强度变化情况。结果表明：CH粒子的相对强度随着射频功率是先增大而后减小,随工作气压的增大而逐渐减小;随气压及功率的增加,Hβ、Hγ相对强度变化的总体趋势都是先增加而后减小的。     

螺旋波激发甲烷等离子体光谱诊断

利用螺旋波激发等离子体化学气相沉积(LPP-CVD)技术,以甲烷和氦气为反应气体产生等离子体.通过采集到甲烷的可见光到紫外发射光谱,对甲烷等离子体进行原位诊断,发现存在CH、Ha及Hβ等碎片粒子的光辐射,同时,分析了不同入射功率、气压下CH粒子以及Hβ、Hγ的相对强度变化情况.结果表明:CH粒子的相对强度随着射频功率是先增大而后减小,随工作气压的增大而逐渐减小;随气压及功率的增加,Hβ、Hγ相对强度变化的总体趋势都是先增加而后减小的.     

大气压非平衡等离子体甲烷干法重整零维数值模拟

大气压非平衡等离子体由于其独特的非平衡特性,可为甲烷和二氧化碳稳定温室气体分子活化和重整提供非热平衡和活化环境.本文采用了零维等离子体化学反应动力学模型,考虑了详细的CH₄/CO₂等离子体化学反应集,重点研究了反应气体CH₄/CO₂摩尔分数(5%—95%)对大气压非平衡等离子体甲烷干法重整制合成气和重要含氧化合物的影响.首先,给出了进料气体不同体积比时电子密度和温度随时间的演化规律,结果表明初始甲烷摩尔分数的提高有利于获得较高的电子密度和电子温度.随后,讨论了主要自由基和离子数密度在不同的甲烷摩尔分数下随着时间的变化规律,并给出了反应气体的转化率、合成气体和重要含氧化合物的选择性.此外,还明确了合成气和含氧化合物主要生成和损耗的化学反应路径,发现甲基和羟基是合成含氧化合物的关键中间体.最后,归纳总结给出了主要等离子体粒子之间的总体等离子体化学反应流程图.     

A Kinetic Model for the Reactions of Co and H2 to CH4 and C2H2 in a Flow Microwave Discharge Reactor

A kinetic model was developed to describe the reactions of CO and H2 to CH4 and C2H2in a microwave plasma. The experimental system consisted of a 24 mm I.D. tubular quartz reactor which passed through a microwave cavity. A variable-incident power waveguide system could supply up to 800 watts of incident microwave power to the cavity. The reactant gas mixture of H2 and CO flowed through the reactor, where a plasma was maintained under pressures of 20 - 100 mm Hg. The reactor effluent was analyzed by IR spectroscopy for CH4 and C2H2. Conversions of up to 5.3% CO to C2H2 and 7.2% CO to CH4 were observed. A 26-reaction kinetic model was developed and fitted to the experimental data. The plasma reactor was modeled in two zones: a discharge zone where electron-impact dissociations produce H, C, and O, and a downstream recombination zone where the atomic species from the discharge recombine. The discharge zone was modeled as a well-mixed reactor, and the recombination zone was modeled as a plug-flow reactor. The model was able to explain the asymptotic shape of the observed conversion versus residence time data; the effect is due to a kinetic limitation. This also explains why the conversions obtained in the plasma cannot be predicted by thermodynamic equilibrium.     

RRKM理论研究N(4S)+CH2X(X=F,Cl)的反应通道

采用RRKM理论和疏松过渡态模型计算了N(4S) +CH2 X(X =F ,Cl)反应的微正则速率常数和通道分支比 .计算结果表明 ,在较低的内能下 (E =2 80 .2 9kJ/mol) ,N(4S) +CH2 F的主要产物为NCHF +H ,占总产物的5 9.2 % ,次要产物为H2 CN +F ,占 37.4 % .而N(4S) +CH2 Cl反应在E =2 6 7.78kJ/mol时 ,主要产物是H2 CN +Cl,占 90 .3% ,NCHCl+H只占 9.0 % .在内能较高的时候 (取E =5 0 0 .0 0kJ/mol) ,N(4S) +CH2 F的主要通道并未变化 ,而N(4S) +CH2 Cl的主要通道变为NCHCl+H ,比例为 5 1.5 % ,H2 CN +Cl的比例降到 4 0 .4 % .     

Oxidation of 13C-labeled methane in surface crusts of pig- and cattle slurry

Storage tanks for slurry from animal production constitute important point sources for emission of CH4 into the atmosphere. Recent investigations have demonstrated that surface crust formed on top of animal slurry provides a habitat for CH4 oxidation activity, a finding which may open for new opportunities to reduce greenhouse gas emissions during storage of animal wastes. In this work, 13C-labeled CH4 was used as a tracer to examine the absolute rates of CH4 oxidation and production in intact crust materials, collected from six different pig- and cattle slurry tanks in late autumn. Methane concentrations were generally reduced in the presence of surface crust samples, with the exception of a LECA-based (light expanded clay aggregates) crust from a pig slurry tank. In four samples, CH4 consumption was induced following a 2-4 days lag phase, whereas one cattle slurry crust consumed CH4 immediately and showed a 92% decline in CH4 concentration within the first week. Consumption of 13C-labeled CH4 was paralleled by the production of 13C-labeled CO2, thus providing direct evidence that microbial oxidation of CH4 to CO2 was taking place. Between 23% and 36% of the CH4-13C consumed in the active samples was accounted for in the gas phase CO2 indicating incomplete conversion of CH4 to CO2; however, comparable amounts of 13C was immobilized in the crust samples. Overall, the results showed that significant CH4 oxidation to CO2 in slurry crust samples occurs immediately or is inducible upon exposure to CH4.     

Spectral distribution of X-Ray yield of the M-shell emission fromlaser produced gold plasma

Experimental measurements of the spectral distribution of keV X-ray energy conversion of the M-shell emission from gold plasma produced by a 4 GW, 5 nS Nd:glass laser are presented. At a laser intensity of 2×10¹³ W/cm², the overall X-ray yield for 2.0 ⩽hv⩽3.6 keV is determined to be 0.1% of the laser energy. The effect of the keV X-ray spectral distribution on radiation preheat is discussed     

Study on CH4 dry reforming process by high power inductively coupled plasma torch at atmospheric pressure

CO₂ dissociation and CH₄ dry reforming, by high power inductively coupled plasma (ICP) torch at atmospheric pressure, have been studied. At a frequency of 400 kHz and power of 30 kW, the ICP torch source dissociates CO₂ gas directly, causing CH₄ dry reforming. The resulting products are composed of syngas, C₂H₆, C₂H₄, and C₂H₂. The results show conversion efficiencies (CE) for both CO₂ and CH₄ of 95%. At an input power of 22 kW, a CO₂ flow rate of 30 SLM, and a CH₄ flow rate of 36 SLM, the energy conversion efficiency (ECE) is 57%. As input CH₄ flow rate increases, the selectivity of CO and H₂ decreases and that of C₂ hydrocarbons increases. In this condition, ECE increases. As a result, the high CE of CO₂ and CH₄, the large amount of products, and the high selectivity of C₂ hydrocarbons can be seen as important factors for achieving higher energy conversion efficiency in the CH₄ dry reforming process. The associated chemical reactions are simulated using CHEMKIN-PRO tool, and the results illustrate the tendency of CE to vary with variations in selected parameters, and syngas and C₂ hydrocarbons production trends achieved in the simulation agree with experimental results.