甲烷三重整制合成气

甲烷三重整是利用CO₂-H₂O-O₂ 同时重整甲烷的过程。该工艺既可以生产H₂/CO 为1.5 —2.0的合成气,又可以缓解甚至消除催化剂的积炭,适合于更廉价地生产用于合成甲醇、二甲醚以及清洁燃料等下游产品的合成气。本文重点评述了近年来国内外甲烷三重整制合成气在热力学、催化剂、反应器、动力学等方面的研究进展,指出甲烷三重整反应在电厂烟气、煤层气、天然气综合利用方面具备良好前景,但要通过该过程实现廉价合成气的生产,仍需研制高活性、抗积炭性能强的催化剂,并对反应器进行改进,以及进行反应机理和反应动力学的深入研究。     

Ni/TiO2 Catalyst for Partial Oxidation of Methane to Syngas

Ni/TiO₂ catalyst was firstly used for the partial oxidation of methane to produce synthesis gas. The reaction was carried out in a fixed-bed continuous flow quartz reactor at atmospheric pressure. The flow rate was regulated by a mass controller with a space velocity of 1.5×10⁵ h^-1 and a CH₄/O₂ molar ratio of 2/1. Prior to the introduction of feed gas, the Ni/TiO₂ catalyst was activated in flowing H₂ at 700℃ for 30 min. TiO₂ is known to be a poor support for partial oxidation because which can easily result in complete oxidation. But at 700℃, Ni/TiO₂ catalyst exhibited a better performance than Ni/SiO₂ and Ni/ZrO₂. The conversion of methane was 81.5, and the selectivity of hydrogen and carbon monoxide were 93.4 and 89.4 respectively. After 6h of continuous reaction, the conversion of methane descended a little and then remained a steady yield on the whole,but the selectivity of H₂ and CO gradually declined, as far as to a constant. The selectivity of H₂ was always higher than that of CO and the ratio of H₂/CO wouldn't change with the increasing of reaction time.     

Energy-efficient dehydrogenation of methanol in a membrane reactor: a mathematical modeling

A two-dimensional non-isothermal stationary mathematical model of the catalytic membrane reactor for the process of methanol dehydrogenation is described. Copper supported on the carbonaceous support was considered as a catalyst. The reaction of methanol dehydrogenation was thermodynamically conjugated with a reaction of hydrogen oxidation taking place in a shell side of the membrane reactor. The effects of various parameters on the methanol conversion and the methyl formate yield have been calculated with the developed model and discussed. Two different types of heating the gas flow were considered and compared. In the case of conjugated dehydrogenation process, the methyl formate yield reaches 77%, when the reactor outer wall was heated up to 150 °C. When the inlet gas flows in the tube and shell sides were heated up to 100 and 83 °C, correspondingly, the yield was 72%.     

STUDIES OF METHANE REFORMING WITH CARBON DIOXIDE TO PRODUCE SYNTHESIS GAS ?¤?¤CATALYST RESISTANCE TO CARBON DEPOSITION

Catalyst resistance to carbon deposition in methane reforming with carbon dioxide to produce synthesis gas was studied using fixed-bed pulse reactor chromatography, XRD, TPR and XPS. R was found that the addition of CeO2 and MgO to Ni/Al2O3 catalyst would increase the ability of catalyst resistance to carbon deposition, which might result from the increase in Ni dispersion and in the interaction between Ni active site and support.     

High-temperature pyrolysis of ethanol

A small, heated alumina tube was used as a pyrolysis reactor to study the thermal decomposition of ethanol at residence times of about 5 ms and temperatures from 1050 to 1275 K. The gas mixture leaving the reactor was analysed by molecular beam sampling mass spectroscopy. The products observed were ethene, water, hydrogen, methane and carbon monoxide and acetaldehyde as an intermediate. The ratio of the amounts of ethene and water formed to the other products was ca. 2:1. The experimental results are discussed in terms of a reaction mechanism and compared with other literature data. The disappearance of ethanol can be modelled by a first-order overall reaction.     

Hydrogen production by catalytic decomposition of methane using a Fe-based catalyst in a fluidized bed reactor

Catalytic decomposition of methane using a Fe-based catalyst for hydrogen production has been studied in this work. A Fe/Al2O3 catalyst previously developed by our research group has been tested in a fluidized bed reactor (FBR). A parametric study of the effects of some process variables,including reaction temperature and space velocity,is undertaken. The operating conditions strongly affect the catalyst performance. Methane conversion was increased by increasing the temperature and lowering the space velocity. Using temperatures between 700 and 900℃ and space velocities between 3 and 6LN/(gcat·h),a methane conversion in the range of 25%-40% for the gas exiting the reactor could be obtained during a 6 hrun. In addition,carbon was deposited in the form of nanofilaments (chain like nanofibers and multiwall nanotubes) with similar properties to those obtained in a fixed bed reactor.     

Modeling of microreactor for syngas production by catalytic partial oxidation of methane

Fixed-bed reactors for the catalytic partial oxidation of methane (CPOM) to produce synthesis gas still pose hot spots problems. Microreactor is a good alternative reactor proposed to resolve these problems. In this paper, synthesis gas (hydrogen and carbon monoxide) production was investigated by a two-dimensional numerical model of single microchannel. CFD modeling with detailed chemistry was conducted to understand the CPOM on platinum (Pt) catalyst. Gas inlet velocity, microchannel pressure, and fuel to air ratio (F/A) are selected as the effective parameters on microchannel performance. Study results show that Reynolds number has considerable effect on methane conversion, hydrogen to carbon monoxide ratio (H2/CO), and product distribution. Increasing gas inlet velocity causes all the above parameters to decrease. It is noted that increasing microchannel pressure and decreasing the ratio of fuel to air cause the decrease of the H2/CO ratio.     

STUDIES ON THE CERAMIC MEMBRANE REACTOR FOR OXIDATIVE COUPLING OF METHANE

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生物质焦油模拟物重整制取富氢气体实验研究

以流化床作为反应器,进行生物质焦油模拟物(苯)催化重整制取富氢气体的实验研究,主要探究实验温度(780℃~900℃)、水蒸气/焦油模拟物质量比S/T (3.0~6.0)、床高(5.0cm~20.0cm)和床料(催化剂)对焦油模拟物重整制取富氢气体过程的影响。实验结果表明,焦油模拟物重整制取富氢气体的理想操作工况分别是温度为860℃~900℃,S/T 值为5.0,床层高度为15.0cm~20.0cm;通过比较,在上述理想操作条件下,合成的碱土金属催化剂(20CaAl)具有较好的催化活性,而其改性后的SCaFeNiAl催化剂具有更好的活性。在SCaFeNiAl作用下,焦油模拟物重整过程的活化能为58.87kJ/mol,指前因子为1.36×10⁷h^-1,且获得较好的实验效果,H₂体积分数为67.28%,H₂产率为303.50g/kg-tar,焦油模拟物转化率为95.93%,总气体产率为5.05m³/kg-tar。     

漫反射付立叶红外光谱法研究二氧化碳的催化甲烷化

用漫反射付立叶红外光谱法（ＤＲＩＦＴ）研究了二氧化碳甲烷化催化剂Ｎｉ／Ａｌ２Ｏ３体系的表面物种及催化反应过程．结果表明：二氧化碳难以直接在催化剂表面发生吸附，而是通过与其它反应物的作用，生成含氧酸根类表面吸附物种，并以此为主要中间物进行下一步反应．含氧酸根类物种主要吸附于载体表面．一氧化碳不是反应的主要中间物，而仅作为一种副产物出现     

Synthesis and characterization of niobium-promoted cobalt/iron catalysts supported on carbon nanotubes for the hydrogenation of carbon monoxide

Bimetallic Co /Fe catalysts supported on carbon nanotubes( CNTs) were prepared,and niobium( Nb) was added as promoter to the 70 Co ∶30Fe /CNT catalyst. The physicochemical properties of the catalysts were characterized,and the catalytic performances were analyzed at the same operation conditions( H_2 ∶CO( volume ratio) = 2 ∶1,p = 1 MPa,and t = 260 ℃) in a tubular fixed-bed microreactor system. The addition of Nb to the bimetallic catalyst decreases the average size of the oxide nanoparticles and improves the reducibility of the bimetallic catalyst. Evaluation of the catalyst performance in a Fischer-Tropsch reaction shows that the catalyst results in high selectivity to methane,and the selectivity to C_(5+) increased slightly in the bimetallic catalyst unlike that in the monometallic catalysts. The addition of 1% Nb to the bimetallic catalyst increases CO conversion and selectivity to C_(5+). Meanwhile,a decrease in methane selectivity is observed.     

处理方法对活性炭在流化床反应器内甲烷催化裂解制氢活性的影响

在流化床反应器内,初步研究了处理方法对活性炭在甲烷裂解制氢过程中催化活性的影响。结果表明,浓硝酸处理后,活性炭表面会生成大量的含氧基团,未处理的活性炭上,850℃和900℃时甲烷的初始转化率在8%和11%左右,浓硝酸处理后,850℃和900℃时初始转化率分别上升到12%和16%,稳定性也明显改善。离子交换法负载微量金属的活性炭比采用浸渍法负载的有更好的活性和稳定性。     

CeO2 as the Oxygen Carrier for Partial Oxidation of Methane to Synthesis Gas in Molten Salts： Thermodynamic Analysis and Experimental Investigation

A new technique -- the direct partial oxidation of methane to synthesis gas using lattice oxygen in molten salts medium has been introduced. Using CeO2 as the oxygen carrier, thermodynamic data were calculated in the reaction process, and the results indicated that direct partial oxidation of methane to synthesis gas using lattice oxygen of cerium oxide is feasible in theory. In a stainless steel reactor, the effects of temperature and varying amounts of γ-Al2O3 supported CeO2 on cn4 conversion, H2 and CO selectivity, were investigated, respectively. The results show that 10% CeO2/γ-Al2O3 has the maximal reaction activity at a temperature of 865 ℃ and above, the H2/CO ratio in the gas that has been produced reaches 2 and the CH4 conversion, H2 and CO selectivity reached the following percentages： i.e. 61%, 89%, and 91% at 870 ℃, respectively. In addition, increase of reaction temperature is favorable for the partial oxidation of methane.     

KOH对超临界水中褐煤连续制氢的影响

采用连续式超临界水反应装置,以20%的水煤浆为反应原料,考察了不同KOH/煤质量比、温度、压力对褐煤制氢过程的影响。实验结果表明,在水煤浆中添加KOH可以提高碳气化率及H2的体积分数和产率,在600℃、25 MPa、KOH/煤质量比为4.1%时,与未加KOH相比,气相产物收率由29.6%提高到49.5%,碳气化率由23.0%增大到31.5%;H2的产率由135.4 mL/(g daf coal)提高到239.1 mL/(g daf coal)。随着温度的升高,H2产率逐渐增大,650℃时达到287.8 mL/(g daf coal),是500℃时的5.4倍;高温、高压下,KOH对煤气化过程的催化作用更为明显。     

COx-Free Hydrogen and Carbon Nanofibers Produced from Direct Decomposition of Methane on Nickel-Based Catalysts

Direct decomposition of methane was carried out using a fixed-bed reactor at 700℃for the production of COx-free hydrogen and carbon nanofibers. The catalytic performance of NiO-M/SiO2 catalysts (where M=AgO, CoO, CuO, FeO, MnOx and MoO) in methane decomposition was investigated. The experimental results indicate that among the tested catalysts, NiO/SiO2 promoted with CuO give the highest hydrogen yield. In addition, the examination of the most suitable catalyst support, including Al2O3, CeO2, La2O3, SiO2, and TiO2, shows that the decomposition of methane over NiO-CuO favors SiO2 support. Furthermore, the optimum ratio of NiO to CuO on SiO2 support for methane decomposition was determined. The experimental results show that the optimum weight ratio of NiO to CuO fell at 8:2 (w/w) since the highest yield of hydrogen was obtained over this catalyst.     

Influence of Gas Components on the Formation of Carbonyl Sulfide over Water-Gas Shift Catalyst B303Q

Water-gas shift reaction catalyst at lower temperature (200—400℃) may improve the conversion of carbon monoxide. But carbonyl sulfide was found to be present over the sulfided cobalt-molybdenum/alumina catalyst for water-gas shift reaction. The influences of temperature, space velocity, and gas components on the formation of carbonyl sulfide over sulfided cobalt-molybdenum/alumina catalyst B303Q at 200—400℃were studied in a tubular fixed-bed quartz-glass reactor under simulated water-gas shift conditions. The experimental results showed that the yield of carbonyl sulfide over B303Q catalyst reached a maximum at 220℃with the increase in temperature, sharply decreased with the increase in space velocity and the content of water vapor, increased with the increase in the content of carbon monoxide and carbon dioxide, and its yield increased and then reached a stable value with the increase in the content of hydrogen and hydrogen sulfide. The formation mechanism of carbonyl sulfide over B303Q catalyst at 200—400℃was discussed on the basis of how these factors influence the formation of COS. The yield of carbonyl sulfide over B303Q catalyst at 200-400℃was the combined result of two reactions, that is, COS was first produced by the reaction of carbon monoxide with hydrogen sulfide, and then the as-produced COS was converted to hydrogen sulfide and carbon dioxide by hydrolysis. The mechanism of COS formation is assumed as follows: sulfur atoms in the Co9S8-MOS2/Al2O3 crystal lattice were easily removed and formed carbonyl sulfide with CO, and then hydrogen sulfide in the water-gas shift gas reacted with the crystal lattice oxygen atoms in CoO-MoO3/Al2O3 to form Co9S8-MoS2/Al2O3. This mechanism for the formation of COS over water-gas shift catalyst B303Q is in accordance with the Mars-Van Krevelen's redox mechanism over metal sulfide.     

High-throughput parallel reactor system for propylene oxidation catalyst investigation

A high-throughput reactor system was designed for catalyst testing, which includes two important sections: the gas flow splitters and the parallel reactor. Each gas flow splitter could split one gas stream to 64 streams (8 x 8). The current system has two gas splitters that could feed two kinds of gases (from mass flow controllers) to a 64-channel (8 x 8) parallel fixed-bed reactor. The reactor is composed of tube connectors, a reactor tube array, a heating block, a product collector, and a temperature controller. The reactor system could test 64 catalysts simultaneously and give results, which are comparable with a regular single-channel microreactor. For the purpose of verifying the validity of the reactor system, propylene oxidation to prepare acrolein was used as the probing reaction. In order to analyze the reaction products, a high-throughput colorimetric diffusion-reflection imaging method was developed for the analysis of acrolein. By comparing the results from colorimetric diffusion-reflection imaging analysis with that from the traditional gas chromatography spectrometer with thermal conductivity detectors, a colorimetric diffusion-reflection imaging method was confirmed to be reliable and accurate in acrolein analysis.     

Partial oxidation of simulated hot coke oven gas to syngas over Ru-Ni/Mg（Al）O catalyst in a ceramic membrane reactor

Hydrogen amplification from simulated hot coke oven gas (HCOG) was investigated in a BaCo0.7Fe0.2Nb0.1O3−δ (BCFNO) membrane reactor combined with a Ru-Ni/Mg(Al)O catalyst by the partial oxidation of hydrocarbon compounds under atmospheric pressure. Under optimized reaction conditions, the dense oxygen permeable membrane had an oxygen permeation flux around 13.3 ml/(cm2·min). By reforming of the toluene and methane, the amount of H2 in the reaction effluent gas was about 2 times more than that of original H2 in simulated HCOG. The Ru-Ni/Mg(Al)O catalyst used in the membrane reactor possessed good catalytic activity and resistance to coking. After the activity test, a small amount of whisker carbon was observed on the used catalyst, and most of them could be removed in the hydrogen-rich atmosphere, implying that the carbon deposition formed on the catalyst might be a reversible process.     

甲烷自热重整制氢的热力学和动力学分析

对甲烷自热重整进行了系统的热力学分析,并采用预混合层流模型结合甲烷氧化、蒸汽重整、干重整机理对反应过程进行了动力学分析。结果表明,甲烷自热重整的平衡产物及其浓度主要受温度、O₂/CH₄、H₂O/CH₄的影响;压力影响不是十分明显,主要影响达到平衡的速度。在715℃~730℃、压力0.7MPa~1.0MPa,控制O₂/CH₄在0.60~0.70、H₂O/CH₄在3.15~3.25,可以得到H₂>68%、CO<10%的产物气,积炭率接近于0。动力学分析表明,自热重整过程分为两个主要阶段进行,在起始阶段主要发生甲烷氧化反应,产物主要为H₂O和CO₂;第二阶段以甲烷蒸汽重整反应为主,伴随水气变换反应（WGS）和微弱的干重整,H_2、CO和CO₂为主要产物。调节初始水浓度可以控制快速氧化阶段反应速率,避免“热点”出现,抑制CO的生成。     

Efficiency of Zn/TiO<Subscript>2</Subscript> catalyst operation in a microchannel reactor in methanol steam reforming

The activity of a Zn/TiO₂ catalyst deposited on metal microchannel plates in methanol steam reforming was studied. The catalyst exhibited maximum activity upon deposition on microchannel plates made of copper foam. In this case, the specific hydrogen production of a microreactor at 450°C was 78.6 l (g Cat)^?1 h^?1. The catalysts deposited on a microchannel plate of nickel foam and on corrugated brass foil exhibited lower activity because of the lower efficiency of heat transfer to the reaction zone. A correlation between the thermal conductivity of the microchannel plate material and the activity of the catalyst was observed in the following order: copper, brass, and nickel. The kinetic parameters of the process of methanol steam reforming in a microreactor were calculated with the use of a plug-flow reactor model. In this case, the calculated formal activation energy of 132 kJ/mol was independent of the microchannel plate material. A comparison of the equilibrium concentrations of reaction products at the reactor outlet, which were calculated from thermodynamic data, with the experimental data demonstrated that methanol steam reforming at a temperature higher than 400°C occurred in the nonequilibrium region. The concentration of carbon monoxide at the microreactor outlet was lower than 1 mol %, which is lower than the equilibrium concentration by one order of magnitude. This effect was attributed to the suppression of the reversed water gas shift reaction on the catalyst.