Experimental studies on hydrogen generation by methane autothermal reforming over nickel-based catalyst

This paper presents the experimental studies on the hydrogen generation by methane autothermal reforming method. An experimental system was built in-house for this study. The temperature profile along the axis of the reformer was measured and discussed. The peak temperature of the reformer appeared in the part of 1/4 to 2/4 of the reformer length from inlet to outlet. The maximum hydrogen yield, hydrogen mole numbers generated per mole of methane consumed of 2.71, was achieved at molar oxygen-to-carbon ratio of 1.68 and molar steam-to-carbon ratio of 2.5. Under this condition, the energy conversion efficiency of the reforming process reached 81.4% based on the lower heating values.     

Membrane reformer module with Ni-foam catalyst for pure hydrogen production from methane: Experimental demonstration and modeling

Results of experiments and modeling of a compact (800 cm³) membrane reformer module for the production of 0.25–0.30 Nm³/h hydrogen by methane steam reforming are reported. The module consists of a two-sided composite membrane disc with a 50 μm PdAg layer and two adjacent 4 mm thick Ni foam discs (60 ppi). A nickel catalyst and a porous support were deposited on the foam discs to give the final composition of 10%Ni/10%MgO/Ni-foam. Membrane permeability by pure hydrogen was investigated, and coefficients of transverse hydrogen transport across the Ni foam to the membrane in the case of inlet binary N₂H₂ mixture were refined in order to account for concentration polarization effect into the model. Activity of the catalytic discs was measured in a differential laboratory scale reactor at a pressure of 1 bar and temperature of 400–600 °C. Modules were tested at a 8–13 bar pressure of the mixture in the reforming zone and at 1 bar of pure hydrogen under the membrane, H₂O/C = 2.5–3 and a module temperature of 550–680 °C (with and without hydrogen removal). Two modifications of the module were tested: consecutive (I-type) and parallel (II-type) flow of the reaction mixture around two sides of the membrane disc. In order to optimize construction of the module, calculations were made for revealing the effect of thickness of the PdAg membrane layer (5–50 μm), thickness of the Ni foam discs (0.5–8 mm) and temperature (600–700 °C) on the hydrogen output of the module. A comparison of the values obtained in our experiments (>1 MW/m³ and >0.7 kg(H₂)/h/m²) with the literature data reported by other authors showed that the developed modules are promising for practical application as components of a fuel processor section for mobile applications.     

Pure hydrogen production via autothermal reforming of ethanol in a fluidized bed membrane reactor: A simulation study

In this paper the production of ultra-pure hydrogen via autothermal reforming of ethanol in a fluidized bed membrane reactor has been studied. The heat needed for the steam reforming of ethanol is obtained by burning part of the hydrogen recovered via the hydrogen perm-selective membrane thereby integrating CO₂ capture. Simulation results based on a phenomenological model show that it is possible to obtain overall autothermal reforming of ethanol while 100% of hydrogen can in principle be recovered at relatively high temperatures and at high reaction pressures. At the same operating conditions, ethanol is completely converted, while the methane produced by the reaction is completely reformed to CO, CO₂ and H₂.     

Novel micro-channel methane reformer assisted combustion reaction for hydrogen production

A metal catalyst-containing, 80 ml, micro-channel reactor (MCR) with a section dedicated to combustion reaction was investigated for the potential application of on-board methane steam reforming (MSR) to hydrogen production. The metal catalyst was introduced into the MCR as a shape of a thin plate that was diffusion-bonded with the other micro-channel plates. The combustion reaction was performed on the other side of the MCR for direct provision of the necessary heat for the endothermic MSR and for miniaturizing the system volume. In the MCR, both the methane conversion and the hydrogen production rate are extremely high compared with those of the equilibrium under atmospheric pressure. The required heat of reaction is successfully provided by the combustion of either hydrogen or the methane mixture on the other side of the MCR without the need for any heating cartridges. This novel micro-channel reformer is suitable for application as a compact fuel processor due to its production of hydrogen-rich syn-gas, small volume, simple catalyst loading and use of an active and easily stackable catalyst.     

Modeling and analysis of microchannel autothermal methane steam reformer focusing on thermal characteristic and thermo-mechanically induced stress behavior

The application of fuel cells boosts the hydrogen demand particularly for distributed hydrogen production facility. As a potential candidate of hydrogen supply, microchannel autothermal methane steam reactor operates at high temperature and results in high thermal impact, which would decrease its stability and lifespan. A three-dimension numerical model based on finite element method was developed to evaluate the thermal characteristic and thermo-mechanically induced stress behavior of the reactor. Three different potential manufacturing materials, Fe–Cr–Al alloy, ceramic and quartz, were chosen. The results indicate that the cold-spot temperature appears near reactor inlet while the hotspot temperature appears near reactor outlet for reactor manufactured by different materials. Corresponding to the hot spot temperature, the maximum Von Mises stress appears near reactor outlet. The difference is the maximum Von Mises stress appears in catalyst layer for quartz reactor while it appears in interconnect rib for both Fe–Cr–Al alloy reactor and ceramic reactor. Meanwhile the maximum Von Mises stress reaches 1830 MPa for ceramic reactor. While the maximum Von Mises stress is 1197 MPa for quartz reactor and 1760 MPa for Fe–Cr–Al alloy reactor respectively. It implies the outlet catalyst layer region is vulnerable for quartz reactor. While the outlet interconnect rib is most vulnerable for both Fe–Cr–Al alloy reactor and ceramic reactor.     

Modelling and simulation of a catalytic autothermal methane reformer with Rh catalyst

A model of a ATR fixed bed reactor with Rh catalyst has been developed and validated on the basis of experimental results.Experiments have been conducted in a small scale reactor and solid temperature profiles have been measured with IR camera. Temperature profiles present high peak temperature at reactor entrance as consequence of the partial separation in space of the reforming and oxidation reactions. Thus, the kinetic model for Rh catalyst refers to an indirect scheme including a shift factor which is crucial for good predictive capabilities of the reactor model. The model validation has been conducted by comparing solid temperature profiles with those obtained experimentally at different feed compositions, total flow rate and preheating temperatures. The model well describes the experimental results in all the investigated operating conditions. The validated model has been then used to analyze the effect of thermal conductivity and of the flow rate on overall reactor performances.     

The evaluation of methane mixed reforming reaction in an industrial membrane reformer for hydrogen production

In this work, the performance of an industrial dense PdAg membrane reformer for hydrogen production with methane mixed reforming reaction was evaluated. The rate parameters of mixed reforming reaction on a Ni based catalyst optimized by using the experimental results. One-dimensional models have been considered to model the steam reforming industrial membrane reformer (SRIMR) and mixed reforming industrial membrane reformer (MRIMR). The models are validated by experimental data.The proficiency of MRIMR and SRIMR at similar conditions used as a basis of comparison in terms of temperature, methane conversion, hydrogen yield, syngas production rate and CO₂ flow rate. Results revealed that the methane conversion, hydrogen yield and syngas production rate in MRIMR is considerably higher than SRIMR. Furthermore, the operation temperature of MRIMR could be 195 °C lower than that for SRIMR. This would contribute to a major decrease in process costs as well as a reduction in catalyst sintering. On the other hand, although MRIMR consumes CO₂, the exited CO₂ flow rate at the SRIMR is three times more than that of at the MRIMR, which is a main advantage of MRIMR from the environmental issues point of view.     

Chemical and transport behaviors in a microfluidic reformer with catalytic-support membrane for efficient hydrogen production and purification

Microchannel reformer integrated with H₂ selective membrane offers an efficient, compact and portable way to produce hydrogen. The performance of a membrane-based microfluidic reformer is restricted by species diffusion limitation within the porous support of the membrane. Recent development in novel catalytic-supported membranes has the potential to enhance H₂ production by decimating the diffusion limitation. Loading a Pd-Ag layer on to a Ni-catalytic porous support, the membrane achieves both H₂ separation and production functions. In this study, a two-dimensional CFD model combined with chemical kinetics has been developed to simulate a microchannel autothermal reformer fed by methane. The species conversion and transport behaviors have been studied. The results show that the permeation process enhances the mass transport within the catalytic layer, and as a result, the reactions are intensified. Most notably, the effectiveness factor of the water-gas shift reaction as high as 6 is obtained. In addition, the effects of gaseous hourly space velocity (GHSV) on methane conversion and H₂ flux through the membrane are also discussed, and an optimal value of GHSV is suggested.     

Methane steam reforming using a membrane reactor equipped with a Pd-based composite membrane for effective hydrogen production

Herein, a methane steam reforming (MSR) reaction was carried out using a Pd composite membrane reactor packed with a commercial Ru/Al₂O₃ catalyst under mild operating conditions, to produce hydrogen with CO₂ capture. The Pd composite membrane was fabricated on a tubular stainless steel support by the electroless plating (ELP) method. The membrane exhibited a hydrogen permeance of 2.26 × 10^?3 mol m² s^?1 Pa^?0.5, H₂/N₂ selectivity of 145 at 773 K, and pressure difference of 20.3 kPa. The MSR reaction, which was carried out at steam to carbon ratio (S/C) = 3.0, gas hourly space velocity (GHSV) = 1700 h^?1, and 773 K, showed that methane conversion increased with the pressure difference and reached 79.5% at ΔP = 506 kPa. This value was ～1.9 time higher than the equilibrium value at 773 K and 101 kPa. Comparing with the previous studies which introduced sweeping gas for low hydrogen partial pressure in the permeate stream, very high pressure difference (2500–2900 kPa) for increase of hydrogen recovery and very low GHSV (<150) for increase hydraulic retention time (HRT), our result was worthy of notice. The gas composition monitored during the long-term stability test showed that the permeate side was composed of 97.8 vol% H₂, and the retentate side contained 67.8 vol% CO₂ with 22.2 vol% CH₄. When energy was recovered by CH₄ combustion in the retentate streams, pre-combustion carbon capture was accomplished using the Pd-based composite membrane reactor.     

Biogas steam reformer for hydrogen production: Evaluation of the reformer prototype and catalysts

This work aims to investigate a biogas steam reforming prototype performance for hydrogen production by mass spectrometry and gas chromatography analyses of catalysts and products of the reform. It was found that 7.4% Ni/NiAl₂O₄/γ-Al₂O₃ with aluminate layer and 3.1% Ru/γ-Al₂O₃ were effective as catalysts, given that they showed high CH₄ conversion, CO and H₂ selectivity, resistance to carbon deposition, and low activity loss. The effect of CH₄:CO₂ ratio revealed that both catalysts have the same behavior. An increase in CO₂ concentration resulted in a decrease in H₂/CO ratio from 2.9 to 2.4 for the Ni catalyst at 850 °C, and from 3 to 2.4 for the Ru catalyst at 700 °C. In conclusion, optimal performance has been achieved in a CH₄:CO₂ ratio of 1.5:1. H₂ yield was 60% for both catalysts at their respective operating temperature. Prototype dimensions and catalysts preparation and characterization are also presented.     

Methane steam reforming in a Pd-Ag membrane reformer: An experimental study on reaction pressure influence at middle temperature

In this experimental work, methane steam reforming (MSR) reaction is performed in a dense Pd-Ag membrane reactor and the influence of pressure on methane conversion, CO_x-free hydrogen recovery and CO_x-free hydrogen production is investigated. The reaction is conducted at 450 °C by supplying nitrogen as a sweep gas in co-current flow configuration with respect to the reactants. Three experimental campaigns are realized in the MR packed with Ni-ZrO catalyst, which showed better performances than Ni-Al₂O₃ used in a previous paper dealing with the same MR system. The first one is directed to keep constant the total pressure in both retentate and permeate sides of the membrane reactor. In the second case study, the total retentate pressure is kept constant at 9.0 bar, while the total permeate pressure is varied between 5.0 and 9.0 bar. As the best result of this work, at 450 °C and 4.0 bar of total pressure difference between retentate and permeate sides, around 65% methane conversion and 1.2 l/h of CO_x-free hydrogen are reached, further recovering 80% CO_x-free hydrogen over the total hydrogen produced during the reaction. Moreover, a study on the influence of hydrogen-rich gas mixtures on the hydrogen permeation through the Pd-Ag membrane is also performed and discussed.     

Steam reforming of methane in a tapered membrane - Assisted fluidized - Bed reactor: Modeling and simulation

A compartment model was developed to describe the flow pattern of gas within the dense zone of a tapered membrane-assisted fluidized-bed reactor (TMAFBR), in the bubbling mode of operation for steam reforming of methane under wall heat flux. The parameters of the developed model (i.e., number of compartments for the bubble and emulsion phases) were determined using the experimental data reported elsewhere [Adris AM, Lim CJ, Grace JR. The fluidized bed membrane reactor system: a pilot scale experimental study. Chem Eng Sci 1994; 49:5833-43.] and good agreements were obtained between model predictions and corresponding experimental data. The developed model was then utilized to predict the behavior of TMAFBR under various operating and design conditions. Moreover, the influences of tapered angle, bed operating temperature and pressure, and feed temperature on the methane conversion and the total yield of hydrogen were carefully investigated. Furthermore, the performance capability of the TMAFBR was compared with that of a columnar one under identical operating conditions.     

Development of membrane reformer system for highly efficient hydrogen production from natural gas

A membrane reformer is composed of a steam reformer equipped with palladium-based alloy membrane modules and can perform steam reforming reaction of natural gas and hydrogen separation processes simultaneously, without shift converters and purification systems. We have developed a membrane reformer system with nominal hydrogen production capacity of 40 Nm³/h. The system has demonstrated the potential advantages of the membrane reformer: simple system configuration as benefited by single-step production of high-purity hydrogen (99.999% level), compactness, and high-energy efficiency of 70–76%. We are promoting development towards commercialization of the membrane reformer technology, focusing on further improvement of energy efficiency, proof of long-term durability and reliability, and establishment of system engineering technologies. The target of our current project is to develop a membrane reformer system that can produce 99.99% or higher-purity hydrogen from natural gas at a rate of 40 Nm³/h with hydrogen production energy efficiency of over 80%.     

Hydrogen production from methane autothermal reforming over CaTiO3, BaTiO3 and SrTiO3 supported nickel catalysts

Nickel supported on perovskite supports were investigated in the autothermal reforming of methane. The catalysts were prepared by incipient wetness impregnation and characterized by energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), N₂ physisorption, H₂ temperature programmed reduction (H₂-TPR), H₂ chemisorption, dehydrogenation of cyclohexane model reaction and Raman spectroscopy. The alumina supported catalyst exhibited highest initial conversion and selectivity to H₂, however it deactivated. All catalysts with perovskite support were very stable, with Ni/CaTiO₃ and Ni/BaTiO₃ converting over 70% of the methane. Due to carbon formation, Ni/SrTiO₃ conversion was only 50%. Turnover frequency was higher on perovskite supported catalysts. Deactivated Ni/Al₂O₃ favored total oxidation of methane instead of methane reforming, however the selectivity of catalysts supported on perovskites remained stable.     

Analysis of heptane autothermal reformer to generate hydrogen for fuel cell applications

In this paper, reaction engineering principles are utilized to analyze process conditions for producing sufficient hydrogen in a heptane autothermal reformer for generating 1 kW of power in a fuel cell. It is shown that operating the reformer adiabatically results in a sharp decrease in temperature due to endothermic reactions, which results in low conversion of heptane. For this reason, a heating jacket is added to the reformer where heptane is combusted to provide heat for the endothermic reactions. It is observed that when the reactor is operated non-isothermally, it is possible to get complete conversion of heptane and produce sufficient hydrogen to generate 1 kW of power via a fuel cell.     

Design and operational considerations of packed-bed membrane reactor for distributed hydrogen production by methane steam reforming

Methane steam reforming will still account for most of hydrogen production in the coming decades. Membrane reactor can play a key role in both energy saving and process/equipment compactness, particularly for its decentralized applications. Here we design a particles-based packed-bed membrane reactor and explore the operational window and design challenges by conducting systematic study experimentally and computationally, particularly emphasizing geometrical scale of membrane reactor and catalyst activity. The results show that membrane reactor presents maximum hydrogen flux by consuming unit methane under the optimized operation conditions of GHSV (i.e., 1134 hr^?1) and steam-to-carbon ratio (i.e., 2), and computational study shows that optimal operation window is around 30 atm and 773.15 K. Moreover, the design criteria of “Catalyst activity – Membrane performance – Radial depth” is revealed quantitatively and catalyst activity is identified as the key limiting factor for further process intensification. Briefly, these results shed some lights on operation, optimal design, and further improvement of membrane reactor in methane steam reforming.     

Design of a methane processing system producing high-purity hydrogen

Design of a catalytic methane-to-proton exchange membrane fuel cell (PEMFC) grade hydrogen conversion system consisting of indirect partial oxidation (IPOX), water–gas shift (WGS) and preferential carbon monoxide oxidation (PROX) reactors is investigated using modeling and simulation techniques. Steady-state simulation, design and sizing of reactors, which are considered to be packed-bed tubular type, are carried out for twelve different feed composition and PEMFC power output configurations, namely (CH₄/O₂, H₂O/CH₄) = (2.24, 1.17), (1.89, 1.56) and (10, 50, 100, 500, 1000, 1500 W). For every configuration, material balance calculations are executed to obtain the flow rates of each species at each stream. These results are then used as boundary conditions to estimate the catalyst weights in each reactor via simulations conducted using a one-dimensional pseudo-homogeneous reactor model. Finally, reactor and catalyst particle dimensions are estimated by considering pressure drop and a set of criteria to quantify interfacial heat and intraparticle mass transfer resistances and fluid flow characteristics in packed beds. The total catalyst quantity is found to increase almost linearly with the PEMFC power output at both feed compositions. Total system volume, excluding piping, pumping, heat exchange and other peripheral units, is estimated to be 6.3, 40.3, 83.4, 488, 985 and 1527 cm³ for 10, 50, 100, 500, 1000 and 1500 W operations, respectively. WGS unit requires the highest space corresponding to ca. 50% of the total reactor volume, followed by IPOX (ca. 39%) and PROX (ca. 11%) reactors. Power densities, based on the weight and volume of the reactors are estimated as 1.1 kW/kg and 1.2 kW/l, respectively.     

Autothermal reforming of methane for producing high-purity hydrogen in a Pd/Ag membrane reactor

Autothermal reforming of methane includes steam reforming and partial oxidizing methane. Theoretically, the required endothermic heat of steam reforming of methane could be provided by adding oxygen to partially oxidize the methane. Therefore, combining the steam reforming of methane with partial oxidation may help in achieving a heat balance that can obtain better heat efficacy. Membrane reactors offer the possibility of overcoming the equilibrium conversion through selectively removing one of the products from the reaction zone. For instance, only can hydrogen products permeate through a palladium membrane, which shifts the equilibrium toward conversions that are higher than the thermodynamic equilibrium. In this study, autothermal reforming of methane was carried out in a traditional reactor and a Pd/Ag membrane reactor, which were packed with an appropriate amount of commercial Ni/MgO/Al₂O₃ catalyst. A power analyzer was employed to measure the power consumption and to check the autothermicity. The average dense Pd/Ag membrane thickness is 24.3 μm, which was coated on a porous stainless steel tube via the electroless palladium/silver plating procedure. The experimental operating conditions had temperatures that were between 350 °C and 470 °C, pressures that were between 3 atm and 7 atm, and O₂/CH₄ = 0–0.5. The effects of the operating conditions on methane conversion, permeance of hydrogen, H₂/CO, selectivities of CO_x, amount of power supply, and the carbon deposition of the catalyst after the reaction is thoroughly discussed in this paper. The experimental results indicate that an optimum methane conversion of 95%, with a hydrogen production rate of 0.093 mol/m². S, can be obtained from the autothermal reforming of methane at H₂O/CH₄ = 1.3 and O₂/CH₄ near 0.4, at which the reaction does not consume power, and the catalysts are not subject to any carbon deposition.     

Comparison of steam and autothermal reforming of methanol using a packed-bed low-cost copper catalyst

Small-scale reformers for hydrogen production via steam and autothermal reforming of hydrocarbon feedstocks can be a solution to the lack of hydrogen distribution infrastructure. A packed-bed reactor is one possible design for such purpose. However, the two reforming processes of steam and autothermal methods have different characteristics, thus they have different and often opposite design requirements. In implementing control strategy for small-scale reformers, understanding the overall chemical reactions and the reactor physical properties becomes essential. This paper presents some inherent features of a packed-bed reactor that can both improve and/or degrade the performance of a packed-bed reactor with both reforming modes.The high thermal resistance of the packed bed is disadvantageous to steam reforming (SR), but it is beneficial to the autothermal reforming (ATR) mode with appropriate reactor geometry. The low catalyst utilization in steam reforming can help to prevent the unconverted fuel leaving the reactor during transient by allowing briefly for higher reactant fuel flow rates. In this study, experiments were performed using three reactor geometries to illustrate these properties and a discussion is presented on how to take advantages of these properties in reactor design.     

Ultra-compact microstructured methane steam reformer with integrated Palladium membrane for on-site production of pure hydrogen: Experimental demonstration

A novel metal-based modular microstructured reactor with integrated Pd membrane for hydrogen production by methane steam reforming is presented. Thin Pd foils with a thickness of 12.5 μm were leak-tight integrated with laser welding between microstructured plates. The laser-welded membrane modules showed ideal H₂/N₂ permselectivities between 16,000 and 1000 at 773 K and 6 bar retentate pressure. An additional metal microsieve support coated with an YSZ diffusion barrier layer (DBL) facilitated the operation at temperatures up to 873 K and pressures up to 20 bar pressure difference. The membrane permeability in this configuration is expressed with Q = 1.58E-07*exp(−1460.2/T) mol/(msPa^0.5).