Sorption equilibria of CO2/CH4 mixture on activated carbon in presence of water

The sorption isotherms of CO2 + CH4 mixtures on an activated carbon were collected in the presence of water at a temperature suitable for hydrate formation. The equilibrium composition of both phases was determined. The initial concentration of CO2 in mixtures was set at 33, 38 and 42%, and the total pressure was up to 10 MPa. CO2 hydrates were firstly formed following the increase of total pressure, and CO2 dominates the sorbed phase composition. CO2 concentration in the sorbed phase begins to decrease when the partial pressure of methane allows for the formation of methane hydrates. Competition for hydrate cavities was observed between CO2 and CH4 as reflected in the isotherm shape and phase composition at equilibrium. The formation pressure of hydrates is lower for mixtures than for pure gases, and the highest sorption capacity of each gas decreased in the mixture sorption either.     

Phase equilibrium measurements and crystallographic analyses on structure-H type gas hydrate formed from the CH4-CO2-neohexane-water system

Phase equilibrium conditions and the crystallographic properties of structure-H type gas hydrates containing various amounts of methane (CH4), carbon dioxide (CO2), neohexane (2,2-dimethylbutane; NH), and liquid water were investigated. When the CH4 concentration was as high as approximately 70%, the phase equilibrium pressure of the structure-H hydrate, which included NH, was about 1 MPa lower at a given temperature than that of the structure-I hydrate with the same composition (except for a lack of NH). However, as the CO2 concentration increased, the pressure difference between the structures became smaller and, at CO2 concentrations below 50%, the phase equilibrium line for the structure-H hydrate crossed that for the structure I. This cross point occurred at a lower temperature at higher CO2 concentration. Extrapolating this relation between the cross point and the CO2 concentration to 100% CO2 suggests that the cross-point temperature would be far below 273.2 K. It is then difficult to form structure-H hydrates in the CO2-NH-liquid water system. To examine the structure, guest composition, and formation process of structure-H hydrates at various CH4-CO2 compositions, we used the methods of Raman spectroscopy, X-ray diffraction, and gas chromatography. Raman spectroscopic analyses indicated that the CH4 molecules were found to occupy both 5(12) and 4(3)5(6)6(3) cages, but they preferably occupied only the 5(12) cages. On the other hand, the CO2 molecules appeared to be trapped only in the 4(3)5(6)6(3) cages. Thus, the CO2 molecules aided the formation of structure-H hydrates even though they reduced the stability of that structure. This encaged condition of guest molecules was also compared with the theoretical calculations. In the batch-type reactor, this process may cause the fractionation of the remaining vapor composition in the opposite sense as that for CH4-CO2 hydrate (structure-I), and thus may result in an alternating formation of structure-H hydrates and structure-I in the same batch-type reactor.     

Co-Generation of C2 Hydrocarbons and Synthesis Gases from Methane and Carbon Dioxide： a Thermodynamic Analysis

This paper deals with thermodynamic chemical equilibrium analysis using the method of direct minimization of Gibbs free energy for all possible CH4 and CO2 reactions. The effects of CO2/CH4 feed ratio, reaction temperature, and system pressure on equilibrium composition, conversion, selectivity and yield were studied. In addition, carbon and no carbon formation regions were also considered at various reaction temperatures and CO2/CH4 feed ratios in the reaction system at equilibrium. It was found that the reaction temperature above 1100 K and CO2/CH4 ratio=1 were favourable for synthesis gas production with H2/CO ratio unity, while carbon dioxide oxidative coupling of methane （CO2 OCM） reaction to produce ethane and ethylene is less favourable thermodynamically. Numerical results indicated that the no carbon formation region was at temperatures above 1000 K and CO2/CH4 ratio larger than 1.     

煤炭解耦燃烧过程N迁移与转化Ⅱ:单组分气相化学反应实验

在理想平推流反应器中进行了模拟热解气对模拟烟气中NO、N₂O的还原实验研究,考察了反应温度、过剩空气系数λ、热解气中CH₄、CO、H₂、NH₃浓度、烟气中NO、N₂O浓度变化对NO、N₂O出口浓度的影响。实验结果表明,当模拟热解气仅含其中一种气体时,在反应温度973~1 223 K时热解气中CH₄、CO、H₂基本不与NO发生反应,当λ小于或等于1.0时可降低N₂O浓度0%~30%;热解气中NH₃可降低NO 10%~60%,但NH₃不与N₂O发生反应。     

甲烷选择催化还原NO研究进展

 近十年来,甲烷选择催化还原NOx已引起各国环境研究工作者的关注．综述了近年来甲烷选择催化还原NOx方面的研究进展,着重分析了用于该反应的催化剂的研究状况,探讨了目前比较公认的甲烷选择催化还原NOx的反应机理（NO2机理）,详细介绍了目前催化剂用于提高甲烷DeNOx反应活性的方法;并展望了甲烷选择催化还原NOx今后的研究方向．     

High-precision, automated stable isotope analysis of atmospheric methane and carbon dioxide using continuous-flow isotope-ratio mass spectrometry

Small-scale developments have been made to an off-the-shelf continuous-flow gas chromatography/isotope-ratio mass spectrometry (CF-GC/IRMS) system to allow high-precision isotopic analysis of methane (CH(4)) and carbon dioxide (CO(2)) at ambient concentrations. The repeatability (1sigma) obtainable with this system is 0.05 per thousand for delta(13)C of CH(4), 0.03 per thousand for delta(13)C of CO(2), and 0.05 per thousand for delta(18)O of CO(2) for ten consecutive analyses of a standard tank. An automated inlet system, which allows diurnal studies of CO(2) and CH(4) isotopes, is also described. The improved precision for CH(4) analysis was achieved with the use of a palladium powder on quartz wool catalyst in the combustion furnace, which increased the efficiency of oxidation of CH(4) to CO(2). The automated inlet further improved the precision for both CH(4) and CO(2) analysis by keeping the routine constant. The method described provides a fast turn-around in samples, with accurate, reproducible results, and would allow a long-term continuous record of CH(4) or CO(2) isotopes at a site to be made, providing information about changing sources of the gases both seasonally and interannually.     

Study on methane selective catalytic reduction of NO on Pt/Ce0.67Zr0.33O2 and its application

Monolithic catalysts of Pt/La-Al2O3 and Pt/Ce0.67Zr0.33O2 were prepared to investigate methane selective catalytic reduction (SCR) of NO.The results indicate that Pt/Ce0.67Zr0.33O2 shows high activity and both NO and CH4 can be converted completely at 450 ℃.Meanwhile,NO and CH4 can be converted completely when there exists excess oxygen.The Pt/Ce0.67Zr0.33O2 catalyst were further investigated by using methane as reducing agent to SCR NO in a novel equipment which combined the CH4 selective catalytic reduction of NO with methane combustion.The result shows that the catalyst is high active and the novel equipment is very effective.The conversion of NO is above 92% under the conditions used in this work.The prepared burner and catalysts have great potential for application.     

Ni／Al2O3催化剂上CH4／CO2重整的脉冲反应研究

报道了用脉冲反应研究Ｎｉ／Ａｌ２Ｏ３催化剂上ＣＨ４／ＣＯ２重整反应的结果。脉冲反应显示，在还原的Ｎｉ／Ａｌ２Ｏ３催化剂上，ＣＨ４在６７３Ｋ就开始发生分解，并有Ｃ２Ｈ６、Ｃ２Ｈ４生成，１０２３Ｋ下，ＣＨ４几乎完全分解，单纯的ＣＯ２则很难在还原的催化剂上发生反应，在９７３Ｋ以上的高温下才会有少量Ｃ胜成ＣＯ．ＣＨＣＯ２的脉冲反应表明，当ＣＨ４在较低温度下开始分解时，ＣＯ２也会发生分解，并生成ＣＯ。脉冲反     

Thermal lens spectroscopy in liquid argon solutions: (Deltav = 6) C-H vibrational overtone absorption of methane

A dual-beam thermal lens technique has been used to obtain the absorption spectrum of the (Deltav = 6) C-H stretch of liquid methane and methane in liquid argon solutions. The lowest concentration detected was 1 x 10(-3) (mole fraction) of CH(4) in liquid Ar with a continuous wave laser power of 20 mW. The thermal lens signal is linear with the mole fraction of methane up to 1 x 10(-2) but not for higher concentrations. Considering the system CH(4)-Ar as an ideal solution, the factors that contribute to the thermal lens signal were calculated as a function of the concentration of methane. A mechanism of energy transfer based on the gas-phase results could explain qualitatively the dependence of the magnitude of the signal on the mole fraction of methane.     

Methane oxidation mechanism on Pt(111): a cluster model DFT study

The electronic energy barriers of surface reactions pertaining to the mechanism of the electrooxidation of methane on Pt (111) were estimated with density functional theory calculations on a 10-atom Pt cluster, using both the B3LYP and PW91 functionals. Optimizations of initial and transition states were performed for elementary steps that involve the conversion of CH(4) to adsorbed CO at the Pt/vacuum interface. As a first approximation we do not include electrolyte effects in our model. The reactions include the dissociative chemisorption of CH(4) on Pt, dehydrogenation reactions of adsorbed intermediates (*CH(x) --> *CH(x-1) + *H and *CH(x)O --> *CH(x-1)O + *H), and oxygenation reactions of adsorbed CH(x) species (*CH(x) + *OH --> *CH(x)OH). Many pathways were investigated and it was found that the main reaction pathway is CH(4) --> *CH(3) --> *CH(2) --> *CH --> *CHOH --> *CHO --> *CO. Frequency analysis and transition-state theory were employed to show that the methane chemisorption elementary step is rate-limiting in the above mechanism. This conclusion is in agreement with published experimental electrochemical studies of methane oxidation on platinum catalysts that have shown the absence of an organic adlayer at electrode potentials that allow the oxidation of adsorbed CO. The mechanism of the electrooxidation of methane on Pt is discussed.     

分解炉内CO2浓度对煤焦燃烧NO释放的影响

利用高温气固悬浮实验台对水泥行业中两种典型煤焦在不同CO₂浓度下燃烧时NO的释放特性进行了实验研究,考察了不同CO₂浓度气氛下,温度变化和添加生料对煤焦炭氮向NO转化的影响。研究结果表明,随着气氛中CO₂浓度的升高,煤焦燃烧时NO的释放速率减小,体积浓度的峰值降低,焦炭氮转化为NO的转化率下降。水泥生料对焦炭氮向NO的转化具有正催化作用;温度升高也会促进焦炭氮向NO的转化。但随着气氛中CO₂浓度的升高,升高温度和添加生料对焦炭氮向NO转化的促进作用相对减弱。     

空气污染组分H2O和CO2对乙烯燃烧性能的影响

超燃冲压发动机在高空工作时, 以高温高速纯净空气作氧化剂使燃料燃烧. 但在地面实验中, 高温空气往往通过燃烧加热方式获得, 从而使空气包含了H2O和CO2污染组分. 本文用电阻加热来流空气并添加污染组分的方法, 研究了燃烧室模型中乙烯的燃烧状态和壁面压力受污染组分的影响. 用化学反应动力学模拟的方法, 在绝热刚性反应器模型中用H2O和CO2取代空气中的N2, 研究了污染组分对点火延迟和燃烧温度的影响, 并从链反应机理的角度讨论了实验和动力学模拟结果.     

煤与甲烷共转化过程中煤焦二氧化碳气化动力学研究

以煤与甲烷共转化为背景,运用热重方法进行了由煤焦、甲烷和二氧化碳组成的共转化反应体系中碳的反应动力学研究。在1173K~1273K考察了温度对碳转化的影响。结果表明,该反应体系中碳的表观反应速率比煤焦的纯二氧化碳气化速率慢一倍左右,且表观上碳不能完全被气化。通过改变甲烷和二氧化碳的比例考察了气相组成变化对共转化反应中碳转化速率的影响,发现甲烷浓度的增加和二氧化碳浓度的减少都会降低碳的转化速率,且随着甲烷浓度的增加,表观上碳最终所能达到的转化率也会降低。通过数据分析发现,该反应适合采用均相反应模型进行描述,关联得到其表观活化能为312.4kJ/mol,甲烷的反应级数为-0.13,二氧化碳的反应级数为0.3。     

银在甲烷选择性催化还原NOx反应中不同催化行为的研究

 采用XRD,TEM和UV－Vis方法研究了Ag－HZSM－5催化剂中活性组分银的价态和结构变化,并将这种变化与其在CH4选择性催化还原NOx反应中的活性和选择性相关联．结果表明,惰性气氛下高温处理使交换到分子筛阳离子位上的Ag＋自还原为Ag0,并在热的作用下聚集成纳米尺度的银颗粒Agn．纳米银颗粒Agn的形成提高了银催化剂在CH4选择性催化还原NOx反应中的活性,但它的长大又促进了CH4和O2的直接燃烧,使CH4选择性催化还原NOx反应的选择性降低．氧气气氛下高温预处理抑制了银颗粒的长大,并且氧气的氧化作用使银颗粒带有一定电荷,形成小的荷电纳米银粒子Agy＋x．荷电纳米银粒子的形成使催化剂的活性降低,但提高了CH4选择性催化还原NOx反应的选择性．     

A gas chromatography/combustion/isotope ratio mass spectrometry system for high-precision delta13C measurements of atmospheric methane extracted from ice core samples

Past atmospheric composition can be reconstructed by the analysis of air enclosures in polar ice cores which archive ancient air in decadal to centennial resolution. Due to the different carbon isotopic signatures of different methane sources high-precision measurements of delta13CH4 in ice cores provide clues about the global methane cycle in the past. We developed a highly automated (continuous-flow) gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) technique for ice core samples of approximately 200 g. The methane is melt-extracted using a purge-and-trap method, then separated from the main air constituents, combusted and measured as CO2 by a conventional isotope ratio mass spectrometer. One CO2 working standard, one CH4 and two air reference gases are used to identify potential sources of isotope fractionation within the entire sample preparation process and to enhance the stability, reproducibility and accuracy of the measurement. After correction for gravitational fractionation, pre-industrial air samples from Greenland ice (1831 +/- 40 years) show a delta13C(VPDB) of -49.54 +/- 0.13 per thousand and Antarctic samples (1530 +/- 25 years) show a delta13C(VPDB) of -48.00 +/- 0.12 per thousand in good agreement with published data.     

Partial Oxidation of Methane to Syngas Using Lattice Oxygen of La1-xSrxFeO3

Catalytic partial oxidation of methane to syngas using the lattice oxygen of La1-xSrxFeO3 perovskite oxide catalysts in place of molecular oxygen was studied. La1-xSrxFeO3 (x＝0, 0.1, 0.2,0.5) perovskite oxides were prepared by the "auto-combustion method". XRD analysis showed that all La1-xSrxFeO3 samples have a single-phase perovskite-type oxide. The redox properties of the catalysts were investigated by temperature programmed reduction with hydrogen (H2-TPR). Reducibility of the catalysts increase with the increasing of the Sr2+ content. The oxygen species of the catalysts and their reaction with CH4 were studied by the temperature programmed surface reaction (CH4-TPSR). In the absence of gas phase oxygen, there exist two kinds of oxygen species on the catalysts. One kind of the oxygen species with strong oxidative ability is produced first, which can oxidize CH4 completely to CO2 and H2O.Then, the second oxygen species with weak oxidative ability is formed, which can oxidize CH4 partially to CO and H2 with high selectivity. The number of the oxygen species with strong oxidative ability in the CH4-TPSR tends to become zero at low x values (x≤0.1). Under suitable reaction conditions, switching alternatively the reactions of 11% O2-Ar and 11% CH4-He over a La0.sSr0.2FeO3 catalyst at 900 ℃ allows methane to be selectively converted to synthesis gas (CH4 conversion ～90%, CO selectivity ＞93%) using the lattice oxygen of the perovskite oxide catalyst in a redox mode.     

空气污染组分H2O和CO2对乙烯燃烧性能的影响(II)——反应机理和动力学模拟

超燃冲压发动机在高空工作时, 以高温高速纯净空气作氧化剂使燃料燃烧. 但在地面实验中, 高温空气往往通过燃烧加热方式获得, 会使空气中含有H2O和CO2等污染组分. 本文用活塞流反应器进行动力学模拟, 研究在不同初温、压强和燃气比的条件下, H2O和CO2污染组分对乙烯燃烧的温度、压强和点火延迟时间等特性的影响. 模拟结果表明: 乙烯在含有H2O/CO2污染物的空气中燃烧, 相比纯净的空气而言, H2O对乙烯的点火有一定的促进作用, 而CO2有一定的抑制作用; 空气中含H2O和CO2污染物使乙烯燃烧的平衡温度和压强降低, 在污染物浓度相同时, CO2引起的下降幅度比H2O的大. 模拟结果能较好地解释现有的实验现象.     

气体燃料化学链燃烧技术中的溶胶凝胶Ni基氧载体研究

高性能氧载体是实现具有CO2富集特性的化学链燃烧技术的关键。选用Ni(NO3)2和Al(OC3H7)3为主要原料,匹配合适的实验操作参数,通过溶胶 凝胶法制备了NiO/NiAl2O4氧载体,其中60%NiO含量、1300℃烧结6h的该种氧载体物化指标较好。在热重分析上研究了NiO/NiAl2O4氧载体与甲烷/空气的还原 氧化反应性,利用XRD、SEM和BET对反应前后的氧载体进行表征。结果表明,制备的氧载体具有良好的还原 氧化反应循环能力。随着循环次数的增多,每次还原阶段被还原的程度缓慢加深,每次氧化阶段被氧化的程度逐渐下降,且还原加深幅度和氧化下降的幅度均逐渐减小,整体上其循环反应性呈缓慢增加的趋势。循环反应过程中,氧载体颗粒间无任何烧结,仍然保持为多孔结构。这些结果初步证明采用溶胶凝胶法制备的NiO/NiAl2O4氧载体具有实现气体燃料化学链燃烧技术的可行性。     

Oxidative reforming of methane for hydrogen and synthesis gas production:Thermodynamic equilibrium analysis

A thermodynamic analysis of methane oxidative reforming was carried out by Gibbs energy minimization (at constant pressure and temperature) and entropy maximization (at constant pressure and enthalpy) methods,to determine the equilibrium compositions and equilibrium temperatures,respectively.Both cases were treated as optimization problems (non-linear programming formulation).The GAMS 23.1 software and the CONOPT2 solver were used in the resolution of the proposed problems.The hydrogen and syngas production were favored at high temperatures and low pressures,and thus the oxygen to methane molar ratio (O 2 /CH 4) was the dominant factor to control the composition of the product formed.For O 2 /CH 4 molar ratios higher than 0.5,the oxidative reforming of methane presented autothermal behavior in the case of either utilizing O 2 or air as oxidant agent,but oxidation reaction with air possessed the advantage of avoiding peak temperatures in the system,due to change in the heat capacity of the system caused by the addition of nitrogen.The calculated results were compared with previously published experimental and simulated data with a good agreement between them.     

High pressure effects on the mutual sensitization of the oxidation of NO and CH4-C2H6 blends

The mutual sensitization of the oxidation of NO and a CH(4)-C(2)H(6) (10 : 1) simulated natural gas (NG) blend was studied under fuel lean conditions (Phi = 0.5) at 50 atm and 1000-1500 K in the UIC high pressure shock tube (HPST). New experimental results were also obtained for the mutual sensitization of methane and the NG blend in the CNRS jet stirred reactor (JSR) at 10 atm. A detailed chemical kinetic model was assembled to describe the observed changes in reactivity in the CH(4) and NG blends, with and without NO, in the HPST and the JSR. The data and the validated model (tested against a variety of targets) show a reduced difference of reactivity between methane and NG blends in the presence of NO at characteristic reaction times for the JSR (250-1000 micros). However the HPST data and subsequent simulations using the validated model have revealed that at higher pressures and in the millisecond time scale regime representative of the HPST experiments (and practical combustion devices) there still persists a significant difference in reactivity between methane and NG blends in the presence of NO. The experimental data, the model development and validations and its predictions and utility as a tool to probe the NO-hydrocarbon sensitization effects under practical combustion conditions is discussed.