Hydrogen production by the catalytic steam reforming of methanol: Part 3: Kinetics of methanol decomposition using C18HC catalyst

The rate of catalytic decomposition of methanol in the presence of steam has been studied using a commercial CuO-ZnO-Al₂O₃. low temperature shift catalyst from 150-270°C at one atmosphere pressure in a fixed bed reactor. Mole ratios of steam to methanol of 0.66. 1.0 and 1.5 and catalyst mass to molar feed rate ratios of 25 to 1025 kg. s. mol ^?1 were utilized. The data were correlated and equations developed to successfully predict methanol conversions and carbon monoxide concentrations in the product gas stream over the temperature range studied. No evidence of mass transfer limitations was observed.     

甲醇水蒸汽重整制氢催化剂制备的研究

针对燃料电池用氢制备用于甲醇水蒸汽重整制氢的Cu/Zn/Al系列催化剂,研究催化剂组成、制备方法对催化剂性能的影响。利用热分析和X射线衍射等分析手段对催化剂前驱体和焙烧后催化剂样品进行分析和表征。结果表明,铜基催化剂对甲醇水蒸汽重整制氢反应有较好的活性和选择性,合适的组成是Cu、Zn和Al的原子质量百分比为45∶45∶10和47.5∶47.5∶5,210 ℃反应转化率达到100%;并流共沉淀法和热分解法制备的催化剂都具有较好的催化性能。     

甲醇氨氧化催化剂的制备及催化性能

铁钼催化剂用于甲醇氨氧化制氰化氢具有能耗低、活性高、工艺简单及副产物少等特点。研究催化剂制备工艺,并对甲醇氨氧化制氰化氢用铁钼催化剂进行活性评价。结果表明,甲醇氨氧化制氰化氢用铁钼催化剂的制备条件为:铁钼原子比为1.5,p H=2,750℃焙烧5 h,在此最佳条件下制备的催化剂上氰化氢收率最高。采用合适的催化剂成型方法可以有效提高甲醇氨氧化制氰化氢用铁钼催化剂利用率和催化剂活性。     

Deactivation of Cu/ZnO catalyst during dehydrogenation of methanol

The deactivation of Cu/ZnO catalyst during methanol dehydrogenation to form methyl formate has been studied. The Cu/ZnO catalyst was seriously deactivated under the reaction conditions: various temperatures of 493, 523 and 553 K, atmospheric pressure and methanol GHSV of 3000 ml (STP)/g-cat h. The weight loss due to reduction of ZnO in the Cu/ ZnO catalyst was monitored by a microbalance. X-ray induced Auger spectroscopy of Zn(L₃M_4,5M_4,5) showed the increase in the concentration of metallic Zn on the catalyst surface after the reaction. Temperature-programmed reduction (TPR) of the Cu/ZnO catalyst with methanol demonstrated that the reduction of ZnO in Cu/ ZnO was suppressed by introduction of CO₂ into the stream of helium-methanol. As the concentration of CO₂ in the feed gas increased, the weight loss of the Cu/ZnO catalyst due to the reduction of ZnO decreased. The deactivation of the Cu/ZnO catalyst in the methanol dehydrogenation was also retarded by the addition of CO₂. In particular, oxygen injection into the reactant feed regenerated the Cu/ ZnO catalyst deactivated during the reaction. Based on these observations, the cause of deactivation of the Cu/ZnO catalyst has been discussed.     

Numerical methodology for proton exchange membrane fuel cell simulation using computational fluid dynamics technique

To analyze the physical phenomena occurring in the Proton Exchange Membrane Fuel Cell (PEMFC) using Computational Fluid Dynamics (CFD) technique under an isothermal operating condition, four major governing equations such as continuity equation, momentum conservation equation, species transport equation and charge conservation equation should be solved. Among these governing equations, using the interfacial boundary condition is necessary for solving the water transport equation properly since the concept of water concentration in membrane/electrode assembly (MEA) and other regions is totally different. It was first attempted to solve the water transport equation directly in the MEA region by using interfacial boundary condition; and physically-meaningful data such as water content, proton conductivity, etc. were successfully obtained. A detailed problem-solving methodology for PEMFC is presented and result comparison with experimental data is also implemented in this paper.     

共沉淀法制备Cu-Mn-Al尖晶石催化剂用于甲醇水蒸气重整制氢

以硝酸铜、硝酸铝和硝酸锰为原料,用共沉淀法制备了Cu-Mn-Al尖晶石固溶体催化剂,用于甲醇水蒸气重整制氢反应.采用BET、H2-TPR、XRD、SEM、XPS等方法对催化剂进行了表征,考察了Mn的添加比例(CuMnxAl4–x,x=0～0.5)对催化剂物理化学性质、形貌及催化性能的影响.结果表明,Mn添加比例不同,催化剂的比表面积、还原性能以及表面化学性质发生改变,随着Mn比例从0增大到0.5(以Cu的物质的量为基准,下同),CuAl尖晶石粒径增大、比表面积下降,并且更难被还原.催化剂的催化性能在x=0.25时最佳,在260℃、0.3 MPa、n(H2O):n(CH3OH)=1:1、质量空速(WHSV)为3.0 g-feed/(g-cat·h)的反应条件下,最高甲醇转化率为91.7％,连续运行150 h后甲醇转化率降至78.8％,均明显高于未含Mn的CuAl尖晶石催化剂.     

甲醇水蒸气重整制氢研究进展

氢气需求的持续增长,带动制氢技术的不断进步。煤制氢技术投资较高,天然气制氢原料来源受到限制,电解水制氢成本较高。甲醇制氢投资适中,适合各种规模的制氢装置,铜基催化剂反应温度低,低温活性和氢气选择性好,价格低廉,因而甲醇制氢技术得到广泛应用。催化剂载体和助剂的改进研究,对工业催化剂的改进具有重要的指导意义。综述甲醇水蒸气重整制氢工艺、反应机理和催化剂,介绍了催化剂载体和助剂等方面的研究进展情况。     

甲醇水蒸气催化重整制氢技术研究进展

针对甲醇水蒸气催化重整制氢的应用背景,综述了甲醇水蒸气重整制氢的反应机理和动力学,对用于该反应的催化剂进行了总结分类,阐述了催化剂制备和反应阶段相关因素对催化剂特性的影响。在此基础上,指出甲醇水蒸气重整制氢技术研究与应用存在的问题与瓶颈,并对两种创新的研究--太阳能驱动的甲醇水蒸气重整制氢技术和甲醇重整制氢微通道反应器的开发技术进行了总结展望。     

Deactivation of ICI low temperature methanol catalyst in an industrial reactor

The deactivation behavior of one of the ICI low temperature methanol catalysts (ICI-51-Z) in a typical ICI multibed quench reactor has been studied in relation to methanol production with respect to time of operation, using some representative sets of plant data collected over two years time span. A pseudo-homogeneous first order model of the methanol synthesis reactor was formulated for this purpose. The best set of catalyst deactivation parameters for different beds was found using a nonlinear parametric estimation technique. Catalyst in the entering bed was found to deactivate most with the time of operation, while subsequent beds deactivate progressively less quickly.     

Production of H2 for fuel cell applications: methanol steam reforming with sufficiently thorough cleaning of H2 from CO impurity

Methanol steam reforming (MSR) and preferential CO oxidation (PROX) were studied with the view of improving the generation of H₂-rich gases. In MSR, conventional catalysts of methanol synthesis were tested, various Cu-based catalysts were prepared and studied. A theoretic kinetic model (based on the reaction mechanism established using independent methods [1]) is developed and checked out. PROX was studied over various Ru/Al₂O₃ catalysts using a flow “quasi-adiabatic” reactor. On-line recording of gas temperature in the catalyst bed and CO residual concentration at varied reaction conditions allowed to observe ignition and extinction of the catalyst surface and the transition states of the process. It is shown that in the ignition mode a sharp decrease in CO residual concentration can be achieved. The combination of proposed catalyst and the control of the macrokinetic regime of PROX allows high degree of CO removal from gaseous mixtures produced by MSR. Residual CO content in a H₂-rich gaseous mixture can be lowered to < 15 ppm at GHSV∼100 m³/(kg cat)/h and O₂/CO ratio of 1. Obtained data show the possibility of designing a high-throughput set-up for generation of H₂-rich gases from methanol with one-step cleaning from the CO impurity.     

MK-121型甲醇合成催化剂的工业应用

陕西咸阳化学工业有限公司的甲醇合成工艺,采用丹麦托普索公司的MK-121型甲醇合成催化剂。介绍了MK-121的工业应用情况,结果显示,MK-121型甲醇合成催化剂初期活性、选择性、稳定性良好,中期活性衰减较快,末期活性和选择性明显变差,末期产品中蜡及杂醇显著增加。生产实践表明,MK-121型甲醇合成催化剂具有良好的活性、选择性及较高的碳效率,但活性衰减较快。     

Z型甲烷蒸汽转化催化剂用于补碳制合成甲醇合成气的研究

选择工业应用效果较好的CNYQ、Z-2和Z-3型催化剂，并补加CO₂,对在其上的甲烷水蒸汽转化制合成气催化反应过程进行了测试研究。结果表明，在适当补加CO₂、反应温度600～850 ℃下，制得的合成气适合于甲醇合成。Z型催化剂用于CH₄-H₂O-CO₂转化制合成甲醇合成气，在当前情况下可满足某些合成甲醇厂的需要。     

甲醇蒸汽重整制氢反应动力学研究进展

甲醇蒸汽重整制氢技术对于解决汽车、船舶等交通工具上燃料电池的氢源问题具有重要意义,近年来已成为碳氢燃料重整制氢的研究热点。本文首先综述了甲醇蒸汽重整制氢的5种反应机理,该方面的研究仍处于定性和推理阶段,尚未达成统一的结论。然后分析了甲醇蒸汽重整反应动力学的研究进展,发现大多研究是基于Cu系催化剂提出,反应温度集中在160～350℃,反应压力多为1atm,研究表明反应物水醇比最优值为1.3～1.4。最后,整理了研究中所提出的动力学模型,指出相较于单速率和三速率模型,双速率模型可反映产物中CO的含量及其对反应速率的影响,且模型相对简单,动力学方程的求解过程也相对容易,但其适用性还有待进一步验证。本文可为甲醇蒸汽重整制氢系统的设计与优化提供理论依据。     

Comparison of various radiation-cooled dew condensers using computational fluid dynamics

Radiation-cooled dew water condensers can serve as a complementary potable water source. In order to enhance passive dew collection water yield, a Computational Fluid Dynamics (CFD) software, PHOENICS, was used to simulate several innovative condenser structures. The sky radiation is calculated for each of the geometries. Several types of condensers under typical meteorological conditions were investigated using their average radiating surface temperature. The simulations were compared with dew yield measurements from a 1 m² 30°-inclined planar condenser used as a reference. A robust correlation between the condenser cooling ability and the corresponding dew yield was found. The following four shapes were studied: (1) a 7.3 m² funnel shape, whose best performance is for a cone half-angle of 60°. Compared to the reference condenser, the cooling efficiency improved by 40%, (2) 0.16 m² flat planar condenser (another dew standard), giving a 35% lower efficiency than the 30° 1 m² inclined reference condenser, (3) a 30 m² 30°-inclined planar condenser (representing one side of a dew condensing roof), whose yield is the same as the reference collector, and (4) a 255 m² multi-ridge condenser at the ground surface provided results similar to the reference collector at wind speeds below 1.5 m s^− 1 but about 40% higher yields at wind speeds above 1.5 m s^− 1.     

Simulation of fine particle formation by precipitation using computational fluid dynamics

The 4‐environment generalized micromixing (4‐EGM) model is applied to describe turbulent mixing and precipitation of barium sulfate in a tubular reactor. The model is implemented in the commercial computational fluid dynamics (CFD) software Fluent. The CFD code is first used to solve for the hydrodynamic fields (velocity, turbulence kinetic energy, turbulent energy dissipation). The species concentrations and moments of the crystal size distribution (CSD) are then computed using user‐defined transport equations. CFD simulations are performed for the tubular reactor used in an earlier experimental study of barium sulfate precipitation. The 4‐EGM CFD results are shown to compare favourably to CFD results found using the presumed beta PDF model. The latter has previously been shown to yield good agreement with experimental data for the mean crystal size at the outlet of the tubular reactor.     

Ag/CeO2-ZnO催化剂上甲醇部分氧化制氢气研究

研究了用于甲醇部分氧化制氢气反应的Ag/CeO2-ZnO催化剂的制备条件以及反应条件对催化剂性能的影响.Ag/CeO2-ZnO催化剂中银含量、焙烧温度、反应温度以及反应气的比例等对催化剂性能具有很大的影响.Ag/CeO2-ZnO催化剂的制备条件以及反应条件控制在一定范围内时,Ag/CeO2-ZnO催化剂对甲醇部分氧化制氢气具有很高的催化活性与选择性.     

Evidence for the migration of ZnOx in a Cu/ZnO methanol synthesis catalyst

The behavior and role of ZnO in Cu/ZnO catalysts for the hydrogenations of CO and CO₂ were studied using XRD, TEM coupled with EDX, TPD and FT-IR. As the reduction temperature increased, the specific activity for the hydrogenation of CO₂ increased, whereas the activity for the hydrogenation of CO decreased. The EDX and XRD results definitely showed that ZnO _x (x = 0–1) moieties migrate onto the Cu surface and dissolve into the Cu particle forming a Cu-Zn alloy when the Cu/ZnO catalysts were reduced at high temperatures above 600 K. The content of Zn dissolved in the Cu particles increased with reduction temperature and reached 18% at a reduction temperature of 723 K. The CO-TPD and FT-IR results suggested the presence of Cu⁺ sites formed in the vicinity of ZnO _x on the Cu surface, where the Cu⁺ species were regarded as an active catalytic component for methanol synthesis.     

发泡镍负载CuO/ZnO/Al2O3对甲醇水蒸汽重整的催化作用

以三维网状多孔发泡镍为载体，制备了负载CuO/ZnO/Al₂O₃的催化剂，研究了催化剂对甲醇水蒸汽重整制氢气的催化作用，考察了催化剂的制备方法、重整反应温度、催化反应器液体空速对催化反应以及催化剂稳定性的影响。结果表明，通过预先在发泡镍上包覆一层Al₂O₃，能够提高催化剂负载的均匀性，所制备的催化剂具有很好的低温初活性和选择性。在反应温度为220 ℃，液体空速为7.2 h^-1的条件下，甲醇初始转化率为98.36%，CO₂选择性为98.4%，产品气中CO摩尔分数为0.41%。通过40 h的连续实验，甲醇转化率始终维持在80%以上，产品气中CO摩尔分数保持在0.5%，CO2的选择性维持在98%。     

Manufacturing of high quality hydrotalcite by computational fluid dynamics simulation of an impinging jet crystallizer

Hydrotalcite was produced by solid-state reaction with magnesium hydroxide particles as the precursor using the impinging stream method. Traditional impinging stream reactors are complex or prone to blockage during the reaction process. To solve this problem, computational fluid dynamics (CFD) simulation was used to optimize the operating conditions in 1 L and 10 L impinging jet crystallizers to produce hydrotalcite. The produced hydrotalcite had a uniform morphology, large particle size, narrow particle size distribution and high purity (>99%), which enabled the controlled reactive crystallization of high-quality hydrotalcite and provided theoretical support for industrial scale-up. Moreover, the solid-state reaction kinetics were analyzed and showed that the reactive crystallization of hydrotalcite could be explained by nucleation and nuclei growth mechanism.     

Analysis of energy dissipation in stirred suspension polymerisation reactors using computational fluid dynamics

This work evaluates the spatial distribution of normalised rates of droplet breakage and droplet coalescence in liquid–liquid dispersions maintained in agitated tanks at operation conditions normally used to perform suspension polymerisation reactions. Particularly, simulations are performed with multiphase computational fluid dynamics (CFD) models to represent the flow field in liquid–liquid styrene suspension polymerisation reactors for the first time. CFD tools are used first to compute the spatial distribution of the turbulent energy dissipation rates (ε) inside the reaction vessel; afterwards, normalised rates of droplet breakage and particle coalescence are computed as functions of ε. Surprisingly, multiphase simulations showed that the rates of energy dissipation can be very high near the free vortex surfaces, which has been completely neglected in previous works. The obtained results indicate the existence of extremely large energy dissipation gradients inside the vessel, so that particle breakage occurs primarily in very small regions that surround the impeller and the free vortex surface, while particle coalescence takes place in the liquid bulk. As a consequence, particle breakage should be regarded as an independent source term or a boundary phenomenon. Based on the obtained results, it can be very difficult to justify the use of isotropic assumptions to formulate particle population balances in similar systems, even when multiple compartment models are used to describe the fluid dynamic behaviour of the agitated vessel. © 2011 Canadian Society for Chemical Engineering