Model‐based optimization of hydrogen generation by methane steam reforming in autothermal packed‐bed membrane reformer

An autothermal membrane reformer comprising two separated compartments, a methane oxidation catalytic bed and a methane steam reforming bed, which hosts hydrogen separation membranes, is optimized for hydrogen production by steam reforming of methane to power a polymer electrolyte membrane fuel cell (PEMFC) stack. Capitalizing on recent experimental demonstrations of hydrogen production in such a reactor, we develop here an appropriate model, validate it with experimental data and then use it for the hydrogen generation optimization in terms of the reformer efficiency and power output. The optimized reformer, with adequate hydrogen separation area, optimized exothermic‐to‐endothermic feed ratio and reduced heat losses, is shown to be capable to fuel kW‐range PEMFC stacks, with a methane‐to‐hydrogen conversion efficiency of up to 0.8. This is expected to provide an overall methane‐to‐electric power efficiency of a combined reformer‐fuel cell unit of ～0.5. Recycling of steam reforming effluent to the oxidation bed for combustion of unreacted and unseparated compounds is expected to provide an additional efficiency gain. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Low-level CO in hydrogen-rich gas supplied by a methanol processor for PEMFCs

The present study developed a low-CO methanol processor for the online supply of hydrogen to a proton exchange membrane fuel cell (PEMFC) composed of a steam reformer, a catalytic combustor and a reactor for the removal of CO. Commercial Cu/ZnO/Al₂O₃- and Pt/Al₂O₃-based catalysts were used in the methanol steam reforming and the preferential oxidation (PROX) reactor, respectively. The steam reformer was successfully heated with a catalytic combustor at room temperature without any additional electrical power supply. Hydrogen gas was obtained at a flow rate of 43.0 L h⁻¹ using a feed flow rate of 39.5 ml h⁻¹ (S/C=1.1) and an operation temperature of 250 °C, corresponding to a power output of 59 W_e. The CO concentration could be maintained at 4–5 ppm for stable operation.     

Steam Reforming of Bio‐Oil for Hydrogen Production: Effect of Ni‐Co Bimetallic Catalysts

Various Ni‐Co bimetallic catalysts were prepared by incorporating sol‐gel and wet impregnation methods. A laboratory‐scale fixed‐bed reactor was employed to investigate their effects on hydrogen production from steam reforming of bio‐oil. The catalyst causes the condensation reaction of bio‐oil, which generates coke and inhibits the formation of gas at temperatures of 250 °C and 350 °C. At 450 °C and above the transformation of bio‐oil is initiated and gaseous products are generated. The catalyst also can promote the generation of H₂ as well as the transformation of CO and CH₄ and plays an active role in steam reforming of bio‐oil or gaseous products from bio‐oil pyrolysis. The developed 3Ni9Co/Ce‐Zr‐O catalyst achieved maximum hydrogen yield and lowest coke formation rate and provided a better stability than a commercial Ni‐based catalyst.     

Hydrogen Production from Partial Oxidation and Steam Reforming of N‐octane Over Alumina‐supported Ni and Ni‐Pd Catalysts

Hydrogen production by partial oxidation and steam reforming (POSR) of n‐octane was investigated over alumina‐supported Ni and Ni‐Pd catalysts. It showed that Ni‐Pd/Al₂O₃ had higher activity and hydrogen selectivity than the nickel catalyst under the experimental conditions, which indicated Ni‐Pd/Al₂O₃ could be an effective catalyst for the production of hydrogen from hydrocarbons.     

Steam Reforming of Methanol in a Compact Copper Microchannel Foam Reactor

Hydrogen production via steam reforming of methanol over a rare earth‐promoted Cu‐based catalyst washcoated on a microchannel foam reactor (MFR) was investigated. A low reforming temperature of 242 °C at a weight hourly space velocity for the methanol/catalyst of 10 h^–1 was observed in the MFR, which is lower than the 270 °C reforming temperature observed in a traditional packed‐bed reactor (PBR). According to a measurement of the reforming temperature distribution, the MFR made of Cu foam in this study exhibits extraordinary heat conductivity. The heat rate supplied from the external heating source can be transferred instantly to the reaction sites of the washcoated catalyst layer through a three‐dimensional framework of Cu microchannels. As a result, the cold spots normally encountered in a PBR are minimized effectively so that a high conversion of steam reforming of methanol is obtained. Moreover, the use of a high performance compact MFR with a volume of 4 mL as a portable hydrogen source is suggested. A hydrogen production rate of 280 mL min^–1 with a CO fraction of 1.5% was obtained, which can yield a practical power output of 25 W using a commercial proton exchange membrane fuel cell with an operational efficiency of 50%.     

PEM – Fuel Cell System for Residential Applications

Viessmann is developing a PEM fuel cell system for residential applications. The uncharged PEM fuel cell system has a 2 kW electrical and 3 kW thermal power output. The Viessmann Fuel Processor is characterized by a steam‐reformer/burner combination in which the burner supplies the required heat to the steam reformer unit and the burner exhaust gas is used to heat water. Natural gas is used as fuel, which is fed into the reforming reactor after passing an integrated desulphurisation unit. The low temperature (600 °C) fuel processor is designed on the basis of steam reforming technology. For carbon monoxide removal, a single shift reactor and selective methanisation is used with noble metal catalysts on monoliths. In the shift reactor, carbon monoxide is converted into hydrogen by the water gas shift reaction. The low level of carbon monoxide at the outlet of the shift reactor is further reduced, to approximately 20 ppm, downstream in the methanisation reactor, to meet PEM fuel cell requirements. Since both catalysts work at the same temperature (240 °C), there is no requirement for an additional heat exchanger in the fuel processor. Start up time is less than 30 min. In addition, Viessmann has developed a 2 kW class PEFC stack, without humidification. Reformate and dry air are fed straight to the stack. Due to the dry operation, water produced by the cell reaction rapidly diffuses through the electrolyte membrane. This was achieved by optimising the MEA, the gas flow pattern and the operating conditions. The cathode is operated by an air blower.     

Optimum operating conditions for a two-stage gasification process fueled by polypropylene by means of continuous reactor over ruthenium catalyst

We studied fuel gas production by means of pyrolysis and steam reforming of waste plastics for applications in solid oxide fuel cells. More specifically, we evaluated the effects of pyrolytic gasification temperature, catalyst content, steam reforming temperature, and weight hourly space velocity for a Ru catalyst used in a 60 g h^− 1-scale continuous experimental apparatus, which consisted of a tank reactor for pyrolysis and a packed-bed catalytic reactor for steam reforming. Polypropylene (PP) pellets were used as a model waste plastic. Ru/γ-Al₂O₃ catalysts with two different Ru contents were investigated. To suppress residue formation, the optimum operating temperature of the pyrolyzer was 673 K. To ensure suppressed coke formation, sufficient carbon conversion to gaseous products, and minimized heat loss from the reactor, the optimum operating conditions for the reformer were determined to be 903 K and 0.11 g-sample g-catalyst^− 1 h^− 1 with a 5 wt.% Ru/γ-Al₂O₃ catalyst. The composition of the gas produced with the 5 wt.% catalyst was almost the same as that predicted by chemical equilibrium laws, and it was applicable for a direct hydrocarbon fuel cell.     

Unlocking dynamics of compact methanol reformers during on-line catalyst activation using transient computational fluid dynamics simulation

On-board methanol reforming is a practical solution to supply hydrogen for fuel cell vehicles (FCVs). For commonly employed Cu-based reforming catalysts, activation has a profound influence on subsequent reaction performance. However, tailoring of this process at the reformer level has received little research attention. Herein, we present the dynamics of compact methanol reformers with Cu/ZnO/Al₂O₃ catalysts during in situ H₂/N₂ pre-activation as a preliminary step of online catalyst activation by computational fluid dynamics simulations. Raising inlet temperatures or hydrogen fractions is demonstrated to accelerate activation while generating a high-temperature band within the catalyst bed, which hampers effective activation. Increasing the reductant flow rates improves the homogeneity of activation thanks to enhanced convective heat and mass transfer. Notably, we revealed that inlet reductants exceeding 453 K trigger temperature runaway that may severely damage the reformer. These new insights will enlighten optimization of operation and control of on-board methanol reforming for FCVs.     

Performance Research on a Methane Compact Reformer Integrated with Catalytic Combustion

A multichannel reformer integrated with catalytic combustion was investigated for methane steam reforming to produce hydrogen. In this system, the main portion of the required heat was supplied by methane oxidation in the catalytic combustor located on two sides of the reformer. In the compact multichannel reactor, the methane conversion rate is high enough compared to the equilibrium values at different temperatures. The performance of the multichannel reformer was investigated under various operating conditions, such as the reformer temperature and the feed stream ratios in both the reformer and the catalytic combustor. The best feed flow rate ratio of reforming to combustion ranged from 1.3 to 1.5, with > 95 % methane conversion. It is anticipated that this multichannel reformer can generate enough hydrogen for a 30‐W fuel cell system, due to its small volume.     

Analysis of hydrogen production from methane autothermal reformer with a dual catalyst-bed configuration

This paper presents a performance analysis of a dual-bed autothermal reformer for hydrogen production from methane using a non-isothermal, one dimensional reactor model. The first section of Pt/Al₂O₃ catalyst is designed for oxidation reaction, whereas the second one based on Ni/MgAl₂O₄ catalyst involves steam reforming reaction. The simulation results show that the dual-bed autothermal reactor provides higher reactor temperature and methane conversion compared with a conventional fixed-bed reformer. The H₂O/CH₄ and O₂/CH₄ feed ratios affect the methane conversion and the H₂/CO product ratio. The addition of steam at lower temperatures to the steam reforming section of the dual-bed reactor can produce the synthesis gas with a higher H₂/CO product ratio.     

Exhaust-gas reforming using precious metal catalysts

Rh-only and Rh bimetallic catalysts have been screened for exhaust-gas reforming, under conditions that mimic the output of an autoignition gasoline engine. Propane has been used as a model fuel, with simulated exhaust-gas providing the co-reactants (O₂ and H₂O) needed to generate hydrogen. Based on oxygen-conversion as a measure of light-off, Pt–Rh on ceria–zirconia shows the highest activity. In the presence of SO₂, adsorbed sulphur species do not inhibit the oxidation reactions that induce light-off, but suppress the major pathway to hydrogen (steam reforming). By excluding platinum and using silica-enriched alumina as the underlying support, light-off is delayed, but the steam reforming reaction becomes much more insensitive to the presence of sulphur. The Pt–Rh catalyst is most suited to exhaust-gas reforming systems in which the engine runs on a sulphur-free fuel, whereas the Rh-only catalyst is the better choice when the fuel is conventional gasoline.     

Investigation of alumina-supported Ni and Ni-Pd catalysts by partial oxidation and steam reforming of n-octane

Aseries of nickel and nickel-palladium supported upon alumina catalysts were prepared in order to obtain a suitable catalyst that could be used in the process of producing hydrogen by partial oxidation and steam reforming of n-octane. Hydrogen production by partial oxidation and steam reforming (POSR) of n-octane was investigated over alumina-supported Ni and Ni-Pd catalysts. The process occurred by a combination of exothermic partial oxidation and endothermic steam reforming of n-octane. It was found that Ni/Al₂O₃ catalyst activity was high at high temperatures and increased with the Ni loadings. Its activity, however, was not obviously increased when Ni loadings were over 5.0 wt%. Compared with nickel catalyst, the bimetallic catalyst of Ni-Pd/A1₂O₃ showed markedly increased activity and hydrogen selectivity at experimental conditions. The catalytic performance also became more stable when the palladium was added, which indicated that palladium plays an essential role in the catalytic action. The used catalysts of Ni-Pd/A1₂O₃ were regenerated three times by using air at space velocity of 2,000 h⁻¹ to obtain a long duration catalyst. Also, the typical catalyst was characterized by using SEM, BET, TG and ICP methods in detail.     

二甲醚水蒸气重整制氢催化剂的研究进展

高品质氢气的在线稳定供给是质子交换膜燃料电池（PEMFC）商业化的瓶颈和亟待解决的关键问题,以二甲醚为原料经水蒸气重整制取氢气是近中期最为现实和有效的氢源供给方案之一。本文总结和评述了近期二甲醚水蒸气重整制氢催化剂的研究进展,主要集中在固体酸催化剂中氧化铝和HZSM-5分子筛酸强度、酸类型以及结构的调变对性能的影响,同时对金属催化剂特别是Pd基贵金属催化剂和Zn基催化剂的研究现状、整体式催化剂以及催化剂的失活与再生的相关研究进行了重点介绍。根据对相关研究结果的总结,提出今后该领域的重要研究方向为：开发新型In₂O₃催化剂;构建具有多级孔、纳米结构的催化剂体系;创制具有特殊结构的催化剂（以多级孔分子筛/氧化铝为核,连续无缺陷的金属催化剂为壳）。     

Stable equilibrium shift of methane steam reforming in membrane reactors with hydrogen‐selective silica membranes

Equilibrium shifts of methane steam reforming in membrane reactors consisting of either tetramethoxysilane‐derived amorphous hydrogen‐selective silica membrane and rhodium catalysts, or hexamethyldisiloxane‐derived membrane and nickel catalysts is experimentally demonstrated. The hexamethyldisiloxane‐derived silica membrane showed stable permeance as high as 8 × 10^?8 mol m^?2 s^?1 Pa^?1 of H₂ after exposure to 76 kPa of vapor pressure at 773 K for 60 h, which was a much better performance than that from the tetramethoxysilane‐derived silica membrane. Furthermore, the better silica membrane also maintained selectivity of H₂/N₂ as high as 10³ under the above hydrothermal conditions. The degree of the equilibrium shifts under various feedrate and pressure conditions coincided with the order of H₂ permeance. In addition, the equilibrium shift of methane steam reforming was stable for 30 h with an S/C ratio of 2.5 at 773 K using a membrane reactor integrated with hexamethyldisiloxane‐derived membrane and nickel catalyst. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Kinetic simulation of a compact reactor system for hydrogen production by steam reforming of higher hydrocarbons

A bubbling fluidized bed membrane reactor for steam reforming of higher hydrocarbons is modelled, using n‐heptane as a model component to represent steam reforming of naphtha. The reformer is modelled as a bubbling fluidized bed reactor, consisting of two pseudo phases, a dense phase and a bubble phase, both in plug flow. In situ H₂ permselective membranes remove H₂ continuously as a pure product, greatly enhancing the H₂ yield per mole of heptane fed. A fluidized bed membrane reformer for higher hydrocarbons could give a very compact reactor system combining all the units from the pre‐reformer to the hydrogen purification system in a traditional steam reforming plant into a single unit.     

Co/ZrO2催化乙醇水蒸汽重整制氢反应的研究

采用浸渍-热分解-氢还原法制备Co/ZrO2催化剂,并用XRD、BET比表面、TPR、差热-热重等测试分析手段对该催化剂进行表征。采用固定床反应器考察了催化剂对乙醇水蒸汽重整制氢反应的催化性能。结果表明:700℃焙烧的ZrO2以单斜和四方相形式共存,负载Co后观察不到有四方相。3%Co/ZrO2催化剂对乙醇水蒸汽重整制氢反应表现出较高的活性。在500℃、水醇比为3∶1时,乙醇的转化率达到76.6%,H2的产率和选择性为0.57mol/mol和81.8%。反应温度升高,提高了乙醇的转化率和H2产率,同时也促进了催化剂表面的积炭。     

Effective parameters for DME steam reforming catalysts for the formation of H2 and CO

Recently, DME has received attention as a clean fuel and is now considered an alternative fuel for diesel engines. DME diesels need de-NOx catalysts such as LNT (Lean NOx Trap) and SCR (Selective Catalytic Reduction) systems. DME is an attractive source of hydrogen because it can be stored easily and is a good transportation fuel. Hydrogen and CO enriched gas as a reductant was used with the LNT catalyst in order to reduce NOx emissions. The steam reforming catalyst of DME was used to formation of hydrogen. It has been reported that Cu-based catalysts have high selectivity and activity in the steam reforming of DME. This research used 600 cPsi cordierite as a catalyst, which was coated with copper. The catalysts were made via a sol–gel and impregnation methods. The formation of H₂ and CO under the prepared catalysts was tested by a model gas. Experimental parameters were considered; the space velocity (SV) and concentrations of H₂O, O₂, and CO₂ were evaluated. The Cu 30%/γ-Al₂O₃ catalyst from the sol–gel method exhibited high and stable activity in the production of hydrogen from the steam reforming of DME. Both DME conversion and the selectivity of hydrogen were affected by SV and the concentrations of H₂O, O₂, and CO₂.     

Steady-state modeling and bifurcation behavior of circulating fluidized bed membrane reformer-regenerator for the production of hydrogen for fuel cells from heptane

The production of hydrogen for fuel cells by steam reforming of heptane is investigated in a Circulating Fluidized Bed Membrane Reformer-Regenerator (CFBMRR) system (A.I.Ch.E. Journal 49(5) (2003) 1250). Palladium based hydrogen permselective membranes are used for hydrogen removal and dense perovskite oxygen permselective membranes are used for oxygen introduction. A series of pseudo-steady-state simulations show that when the catalyst is not regenerated, the circulating nickel reforming catalyst deactivates quickly and the “half catalyst activity life” for efficient production of hydrogen is quite short, especially at high temperatures. Efficient continuous catalyst regeneration can keep the catalyst activity high (∼1.0). With continuous catalyst regeneration, autothermal operation for the entire adiabatic reformer-regenerator system is achievable when the exothermic heat generated from the catalyst regenerator is sufficient to compensate for the endothermic heat consumed in the riser reformer. This type of autothermal operation becomes less likely at high steam to carbon feed ratios. This is due to the fact that carbon deposition rate decreases leading to the decrease of autothermal circulating feed temperature and energy-based hydrogen yield (adiabatic hydrogen yield in autothermal reformer-regenerator system). Multiplicity of the steady states for the reformer is possible for this configuration. With the steam to carbon feed ratio as the bifurcation parameter, multiplicity occurs between the two bifurcation points 1.444 and 2.251 mol/mol. In this multiplicity region, the energy-based hydrogen yield at the upper steady state with high regenerator output temperature is surprisingly the lowest one. While it is the highest one at the lower steady state with low regenerator output temperature. The maximum energy-based hydrogen yield is about 15.58 moles of hydrogen per mole of heptane fed at the lower steady-state when steam to carbon feed ratio is very close to the bifurcation value of 1.444 mol/mol. After removing the sweep gas steam by downstream cooling and de-humidification, the product hydrogen from steam reforming of hydrocarbons can be used for fuel cells with high purity (∼100%).     

Simulation of autothermal reforming in a staged‐separation membrane reactor for pure hydrogen production

Steam methane reforming with oxygen input is simulated in staged‐separation membrane reactors. The configuration retains the advantage of regular membrane reactors for achieving super‐equilibrium conversion, but reaction and membrane separation are carried out in two separate units. Equilibrium is assumed in the models given the excess of catalyst. The optimal pure hydrogen yield is obtained with 55% of the total membrane area allocated to the first of two modules. The performance of the process with pure oxygen input is only marginally better than with air. Oxygen must be added in split mode to reach autothermal operation for both reformer modules, and the oxygen input to each module depends on the process conditions. The effects of temperature, steam‐to‐carbon ratio and pressure of the reformer and the area of the membrane modules are investigated for various conditions. Compared with a traditional reformer with an ex situ membrane purifier downstream, the staged reactor is capable of much better pure hydrogen yield for the same autothermal reforming operating conditions.     

Low temperature exhaust gas fuel reforming of diesel fuel

The application of exhaust gas assisted fuel reforming in diesel engines has been investigated. The process involves hydrogen generation by direct catalytic interaction of diesel fuel with engine exhaust gas. Using a laboratory reforming mini reactor incorporated in the exhaust system of a diesel engine, up to 16% hydrogen in the reactor product gas was achieved at a reactor inlet temperature of 290 °C. The results showed that such levels of hydrogen can be produced with appropriate control of the reaction parameters at temperatures typical of exhaust gas temperatures of diesel engines operating at part load without any requirement for external heat source or air and steam supply. The use of simulated reformed fuel was shown to be beneficial in terms of engine exhaust emissions and resulted in reduction of NO_X and smoke emissions.