Hydrogen production from propane in Rh-impregnated metallic microchannel reactors and alumina foams

Rh-impregnated alumina foams and metallic microchannel reactors have been studied for production of hydrogen-rich syngas through short contact time catalytic partial oxidation (POX) and oxidative steam reforming (OSR) of propane. Effects of temperature and residence time have been compared for the two catalytic systems. Temperature profiles obtained along the central axis were valuable in understanding the different behaviour of the reactor systems. Gas phase ignition occurs in front of the metallic monolith at furnace temperatures above 700 °C, leading to lower hydrogen selectivity. Lowering the residence time below 10 ms for the microchannel monolith increases the syngas selectivity. This probably due to quenching of the gas phase reactions at high linear gas velocity, and suggests that microchannel reactors have potential for isolating kinetic effects and minimising gas phase contributions. The Rh/Al₂O₃ foam systems show higher initial syngas selectivity than the Rh-impregnated microchannel reactors, but deactivate rapidly upon temperature cycling, especially when steam is added as a reactant.     

Novel circulating fast fluidized-bed membrane reformer for efficient production of hydrogen from steam reforming of methane

The coupling of steam reforming and oxidative reforming of methane for the efficient production of hydrogen is investigated over Ni/Al₂O₃ catalyst in a novel circulating fast fluidized-bed membrane reformer (CFFBMR) using a rigorous mathematical model. The removal of product hydrogen using palladium hydrogen membranes “breaks” the thermodynamic equilibrium barrier exists among the reversible reactions. Oxygen can be introduced into the adiabatic CFFBMR for oxidative reforming by direct oxygen (or air) feed and through dense perovskite oxygen membranes. The simulations show that high productivity of hydrogen can be obtained in the CFFBMR. The combination of these two different processes does not only enhance the hydrogen productivity but also save the energy due to the exothermicity of the oxidative reforming. Based on the preliminary investigations, four parameters (number of hydrogen membranes, number of oxygen membranes, direct oxygen feed rate and steam-to-carbon feed ratio) are carefully chosen as main variables for the process optimization. The optimized result shows that the hydrogen productivity (moles of hydrogen produced per hour per m³ of reactor) in the novel CFFBMR is about 8.2 times higher than that in typical industrial fixed-bed steam reformers.     

Reactivity of steam in exhaust gas catalysis III. Steam and oxygen/steam conversions of propane on a Pd/Al2O3 catalyst

A 1% Pd catalyst (38% dispersion) was prepared by impregnating a γ-alumina with palladium acetylacetonate dissolved in acetone. The behaviour of this catalyst in oxidation and steam reforming (SR) of propane was investigated. Temperature-programmed reactions of C₃H₈ with O₂ or with O₂ + H₂O were carried out with different stoichiometric ratios S(S =[O₂]/5[C₃H₈]). The conversion profiles of C₃H₈ for the reaction carried out in substoichiometry of O₂ (S < 1) showed two discrete domains of conversion: oxidation at temperatures below 350°C and SR at temperatures above 350°C. The presence of steam in the inlet gases is not necessary for SR to occur: there is sufficient water produced in the oxidation to form H₂ and carbon oxides by this reaction. Contrary to what was observed with Pt, an apparent deactivation between 310 and 385°C could be observed with Pd in oxidation. This is due to a reduction of PdO_x into Pd⁰, which is much less active than the oxide in propane oxidation. Steam added to the reactants inhibits oxidation while it prevents the reduction of PdO_x into Pd⁰. Compared to Pt and to Rh, Pd has a higher thermal resistance: no deactivation occurred after treatment up to 700°C and limited deactivation after treatment up to 900°C, provided that the catalyst is maintained in an oxygen-rich atmosphere during the cooling.     

热解油模型化合物甲醇的蒸汽转化制氢研究

研究了Ce促进的Ni基镁橄榄石催化剂上热解油模型化合物甲醇的水蒸汽转化制氢反应过程，得到活性和稳定性较好的催化剂。浸渍法制备了添加Ce的Ni基镁橄榄石催化剂，Ce的添加改善了催化剂的活性和稳定性。催化剂活性受镍铈原子比的影响，选择合适的镍铈原子比可以得到性能较好的催化剂。在750 ℃、水与甲醇物质的量比为1.5和气体体积空速11 200 h^－1条件下，6%Ni－3%Ce/Olivine催化剂有最好的催化效果，此条件下，甲醇转化率达到85.72%，氢气收率为55.31％。     

负载型金属催化剂在乙醇水蒸气重整制氢中的应用

系统地阐述了近年来对乙醇水蒸气重整制氢催化剂的研究进展;对影响催化剂性能的因素及对策进行了分析与讨论;展望了乙醇水蒸气制氢催化剂的研究方向.     

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。     

Pure hydrogen production by methane steam reforming with hydrogen-permeable membrane reactor

Low temperature steam reforming of methane mainly to hydrogen and carbon dioxide (CH₄ + 2H₂O → 4H₂ + CO₂) has been performed at 773 and 823 K over a commercial nickel catalyst in an equilibrium-shift reactor with an 11-μm thick palladium membrane (Mem-L) on a stainless steel porous metal filter. The methane conversion with the reactor is significantly higher than its equilibrium value without membrane due to the equilibrium-shift combined with separation of pure hydrogen through the membrane. The methane conversion in a reactor with an 8-μm membrane (Mem-H) is similar to that with Mem-L, although the hydrogen permeance through Mem-H is almost double of that through Mem-L. The amount of hydrogen separated in the reaction with Mem-H is significantly large, showing that the hydrogen separation overwhelms the hydrogen production because of the insufficient catalytic activity.     

烃类水蒸汽重整制氢研究进展

烃类水蒸汽重整是工业上大规模制氢的主要方法.综述了近十年来国内外烃类水蒸汽重整制氢技术的研究进展,重点从催化剂以及反应工艺方面进行介绍及评述,并指出烃类水蒸汽重整制氢的重点发展方向.     

国内外蒸汽转化制氢催化剂及工艺进展

本文分别对烃类蒸汽转化制氢技术中涉及的原料、工艺、设备及催化剂等方面的国内外进展进行了讨论，评述了烃类蒸汽转化制氢技术的发展趋势并提出有关建议。     

Production of hydrogen over bimetallic Pt–Ni/δ-Al2O3: I. Indirect partial oxidation of propane

Indirect partial oxidation (IPOX) of propane was studied over bimetallic 0.2 wt.% Pt–15 wt.% Ni/δ-Al₂O₃ catalyst in the 623–743 K temperature range. The unreduced and reduced forms of the catalyst were characterized by ESEM–EDAX and X-ray diffraction (XRD). In the IPOX tests, the effects of steam to carbon ratio (S/C), carbon to oxygen ratio (C/O₂) and residence time (W/F (g_cat h/mol HC)) on the hydrogen production activity, selectivity and product distribution were studied in detail. The effect of temperature program applied (increasing from 623 to 743 K, ITP; decreasing from 743 to 623 K, DTP) during reaction was also tested. The results showed that the Pt–Ni bimetallic system has superior performance characteristics compared to the monometallic catalysts reported in literature. The reason is thought to be the utilization of the catalyst particles as micro heat exchangers during IPOX; the heat generated by Pt sites during exothermic total oxidation (TOX) being readily transferred through the catalyst particles acting as micro heat exchangers to the Ni sites, which promote endothermic steam reforming (SR). The optimal conditions were found as S/C = 3, C/O₂ = 2.70 and W/F = 0.51 g_cat h/mol HC for IPOX of propane on the basis of high hydrogen productivity and selectivity between 623 and 748 K for the experimental conditions tested. The thermo-neutral points obtained showed the sustainability of reaction in terms of energy.     

The effects of cobalt and cerium promoters on hydrogen production performance of alumina-supported nickel catalysts in propane steam reforming

BACKGROUND: The effects of Co and Ce promoters on the performance of Ni (10 wt%)–Co (0.0, 2.75, 5.5 wt%)/Ce (0.0, 5.0, 10.0 wt%)–Al₂O₃ catalysts have been studied for steam reforming of C₃H₈ (SRP). In this work, Ni (NO₃)₂ and Co (NO₃)₂ are co-impregnated on the co-precipitated Al₂O₃–CeO₂ supports. X-ray diffraction, N₂ adsorption–desorption, H₂-temperature-programmed reduction, high-resolution transmission electron microscopy, scanning electron microscopy and thermogravimetric/differential thermal analysis were accomplished to explain the SRP activity of the catalysts. The performance of the resulting catalysts was evaluated under the gas hourly space velocity (GHSV) = 45 000 mL h^-1 g_cat⁻¹, T = 600 °C, steam/C₃H₈ ratio (S/C) = 3 and P = 1 atm. RESULTS: The experimental findings revealed that Ce and Co promoters markedly improved the catalyst activity, stability and H₂ yield of Ni/Al₂O₃ catalyst. The sample with 2.75 wt% Co and 10.0 wt% Ce showed highest C₃H₈ conversion, while maximum yield of H₂ was obtained for catalyst containing 5.5 wt% Co and 5.0 wt% Ce. CONCLUSION: Higher loadings of Co decreased C₃H₈ conversion and catalyst stability due to more coke formation on the catalyst surface, whereas Ce significantly improved catalyst resistance to coke deposition due to the enhanced Ni metal particles distribution over the support. © 2020 Society of Chemical Industry     

Hydrogen production from methanol by oxidative steam reforming carried out in a membrane reactor

The aim of this work is to study from an experimental point of view the oxidative steam reforming of methanol by investigating the behaviour of a dense Pd/Ag membrane reactor (MR) in terms of methanol conversion as well as hydrogen production. The main parameters considered are the operating temperature and the O₂/CH₃OH feed ratio. This is a pioneer work in the application of MR to this kind of reaction, whose goal should be to produce a CO-free hydrogen stream suitable for hydrogen fuel cell applications. The experimental results show that the MR gives methanol conversions higher than traditional reactors (TRs) at each temperature investigated, confirming the good potential of the membrane reactor device for this interesting reaction system.     

Fuel constituent effects on fuel reforming properties for fuel cell applications

The effect of different types of compounds commonly found in diesel fuel (e.g., paraffins, naphthenes, and aromatics), as well as their chemical structure (e.g., branched versus linear paraffins) on fuel reforming has been investigated. Diesel reforming is very complicated because diesel is a complex mixture of hundreds of compounds with greatly different reactivities. The syngas production rates at the same conditions were observed in this order: paraffins > naphthenes ? aromatics. Additionally, the type of reforming performed (OSR, CPOX, or SR) as well as the process parameters (space velocity and reaction temperature) significantly affected the syngas production rates as well as carbon formation. The reactivity of one fuel component can affect the conversion pattern of others, e.g., overall yields from the reforming of a fuel mixture are not additive of yields from individual fuel components, rather the more reactive component is consumed first. Furthermore, the type of substituent in aromatics and naphthenes, the carbon chain length in n-paraffins, branching in paraffins, and degree of aromatic saturation affect the overall hydrocarbon conversion, syngas selectivity, and carbon formation. The presence of sulfur compounds in the fuel caused significant drops in H₂ yields compared to CO yields.     

生物油水蒸气催化重整制氢研究进展

氢气作为重要的清洁能源和化工原料,目前主要来源于化石燃料,而生物质经快速热解制得生物油用于水蒸气催化重整制氢被认为是一种高效、环保、经济的可再生能源制氢途径。本文首先综述了近年来生物油水蒸气催化重整制氢相关反应原料;然后重点讨论了生物油水蒸气催化重整反应催化剂研究近况;总结了生物油水蒸气重整反应机理与动力学分析;最后列举了重整反应器等方面的研究进展。相比于生物油,生物油模型化合物因结构简单、转化率与氢气收率高,得到广泛研究;以Ni为代表的活性金属组分催化活性高,金属间协同作用强;不同类型的载体可增强催化剂的稳定性,碱性载体还可吸收CO₂、提高催化剂抗积炭、防烧结等方面的性能;不同结构的反应器在性能方面表现各异,主要以固定床反应器为主。研制高活性、稳定性强的催化剂,提高重整反应的循环稳定性,并总结最符合动力学规律的反应机理,以及研发高效的反应器是今后生物油水蒸气催化重整制氢研究的重点。     

Spectroscopic evidences of the double hydrogen hydrates stabilized with ethane and propane

Hydrogen molecules are known to occupy the small cages of structure I (sI) and II (sII) hydrates with the aid of coguests, leading to the highly stable state of their crystalline framework. For the first time, we synthesized the double hydrogen hydrates incorporated with ethane and propane that play a special role as the hydrate promoters or stabilizers. The resulting hydrate structures cage occupancy was identified by the spectroscopic methods of the PXRD and solid-state NMR. In addition, direct GC analysis confirmed that the encaged hydrogen amounts are 0.127 for sI ethane and 0.370 for sII propane at 120 bar and 270 K. The proper hydrate thermodynamics particularly focusing on the cage occupancy estimated that 0.17 and 0.33 wt% of hydrogen are observed in small cages of sI and sII hydrates. The overall spectroscopic and physicochemical analysis strongly imply that the sII cages act as much more favorable sites than sI cages in storing hydrogen.     

Hydrogen production from bioethanol reforming in supercritical water

Hydrogen production by reforming and oxidative reforming of ethanol in supercritical water (SCW) at the intermediate temperature range of 500-600 °C and pressure of 25 MPa were investigated at different ethanol concentrations or water to ethanol ratios (3, 20 and 30), with the absence and the presence of oxygen (oxygen to ethanol ratio between 0 and 0.156). Hydrogen was the main product accompanied with relatively low amounts of carbon dioxide, methane and carbon monoxide. Some liquid products, such as acetaldehyde and, occasionally, methanol were present. The ethanol conversion and hydrogen yield and selectivity increased substantially as the water to ethanol ratio and the reaction temperature increased. Ethanol was almost completely reformed and mainly converted to hydrogen giving a H₂/CO ratio of 2.6 at 550 °C and water to ethanol ratio of 30 without carbon formation. Coke deposition was favored at low water to ethanol ratio, especially at high temperatures (≥550 °C). The hydrogen yield improved as the ethanol was partially oxidized by the oxygen added into the feed at oxygen to ethanol ratios <0.071. It was evidenced that the metal components in Inconel 625 reactor wall reduced by a hydrogen stream acted as a catalyst promoting hydrocarbon reforming as well as water-gas-shift reactions while dehydrogenation of ethanol forming acetaldehyde can proceed homogeneously under the SCW condition. However, at high oxygen to ethanol ratio, the reactor wall was gradually deactivated after being exposed to the oxidant in the feed. The loss of the catalytic activity of the reactor surface was mainly due to the metal oxide formation resulting in reduction of catalytic activity of the reactor wall and reforming of carbon species was no longer promoted.     

Hydrogen production from raw bioethanol over Rh/MgAl2O4 catalyst: Impact of impurities: Heavy alcohol, aldehyde, ester, acid and amine

The effect of various impurities added in a pure ethanol + water mixture was studied. The impurities chosen were acetic acid, diethylamine, butanol, butanal, ethyl acetate and diethylether. It was shown that the addition of diethylamine or butanal increases the ethanol conversion, compared to that obtained with a pure ethanol + water mixture, without changing the product selectivity. In the presence of the other impurities, butanol, ethylether and ethyl acetate, a strong deactivation of the catalyst with a decreased ethanol conversion was observed. Moreover, the selectivity in hydrogen was also strongly decreased, whereas an increase in intermediate products especially ethylene was observed. The deactivation was explained in terms of coke deposition at the catalyst surface. The poisoning effect induced by the presence of impurities can be classified in the following increasing order: diethylamine  butanal < no impurity < acetic acid < butanol < diethylether  ethyl acetate.     

Solid state chemistry of bulk mixed metal oxide catalysts for the selective oxidation of propane to acrylic acid

Syntheses of Mo–V–Sb–Nb–O bulk materials, which are candidate catalyst systems for the selective oxidation of propane to acrolein and acrylic acid, were made using soluble precursor materials. The products were characterized by X-ray powder diffraction and Raman spectroscopic studies. The objectives of this work were to explore the utility of liquid phase automated synthesis for the preparation of bulk mixed metal oxides, and the identification of the oxide phases present in the system. This is the first published study of the phase composition for these materials. After calcination of these bulk oxides under flowing nitrogen at 600°C, and using stoichiometric ratios of Mo–V–Sb–Nb (1:1:0.4:0.4) and Mo–V–Sb–Nb (3.3:1:0.4:0.4) it was demonstrated that a mixture of phases were obtained for the syntheses. X-ray powder diffraction studies distinguished SbVO₄, Mo₆V₉O₄₀, MoO₃, and a niobium-stabilized defect phase of a vanadium-rich molybdate, Mo_0.61–0.77V_0.31–0.19Nb_0.08–0.04O_x, as the major phases present. Complementary data were provided by the Raman spectroscopic studies, which illustrated the heterogeneity of the phases present in the mixture. Raman also indicated bands attributable to the presence of phases containing terminal M=O bonds as well as M–O–M polycrystalline phases. Previous studies on this system have identified SbVO₄ and niobium-stabilized vanadium molybdate species as the active phases necessary for the selective oxidation of alkanes.     

Thermodynamic analysis of glycerol partial oxidation for hydrogen production

Thermodynamics of glycerol partial oxidation for hydrogen production has been studied by Gibbs free energy minimization method. The optimum conditions for hydrogen production are identified: reaction temperatures between 1000 and 1100 K and oxygen-to-glycerol molar ratios of 0.4-0.6 at 1 atm. Under the optimal conditions, complete conversion of glycerol, 78.93%-87.31% yield of hydrogen and 75.12%-87.97% yield of carbon monoxide could be achieved in the absence of carbon formation. The glycerol partial oxidation with O₂ is suitable for providing hydrogen-rich fuels for Molten Carbonate Fuel Cell and Solid Oxide Fuel Cell. The carbon-formed and carbon-free regions are found, which are useful in guiding the search for suitable catalysts for the reaction. Inert gases have a positive effect on the hydrogen and carbon monoxide yields.