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.     

Impact of Ni-based catalyst patterning on hydrogen production from MSR: External steam reformer modelling

Wall-coated Methane Steam Reformers (MSR) are commonly used as fuel processing in the hydrogen production chain. In such devices, the catalyst which is generally nickel-based is coated on the walls, and the heat supply influences directly the fuel processing efficiency. In this work, two-dimensional CFD study is carried out to explore an enhancement on MSR thermal behavior. Two configurations in terms of catalyst coating are investigated. The first MSR configuration is equipped with continuous catalytic layer, while in the second, discrete catalyst layers separated by an inert gap are imposed. The effect of the catalyst patterning on the thermal and mass behavior of MSR is discussed. The results show that the MSR efficiency can be improved by extending the catalytic zone and discretizing the catalyst coating. Comparing to conventional MSR with continuous catalytic layers, enhancement of 28.71% in CH₄ conversion and 88.574% in H₂ production is realized by using discretized catalytic layers.     

Novel structured catalysts configuration for intensification of steam reforming of methane

Structured catalysts, using highly conductive carriers, can improve the heat transfer along the catalytic bed, affording high performance with a flattened radial temperature gradient. The effect of thermal conductivity of structured carriers on highly endothermic Steam Reforming reaction is investigated. The performance of the structured catalysts, obtained on Cordierite and Silicon Carbide (SiC) monoliths, demonstrates the direct correlation between the thermal conductivity of the carrier, the methane conversion and the hydrogen productivity. The evaluation of the monolith configuration shows that the SiC “wall flow” guarantees a better axial and radial thermal distribution, with respect to the SiC “flow through”, resulting in better catalytic activity up to a temperature reaction of 750 °C. The comparison among the performance of the structured catalysts and the commercial 57-4MQ, provided by Katalco-JM, highlights the choice of structured catalysts, which require a lower temperature outside of the reactor, increasing the process efficiency.     

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.     

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.     

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.     

Catalytic performance of a high-cell-density Ni honeycomb catalyst for methane steam reforming

The catalysis of methane steam reforming (MSR) by pure Ni honeycombs with high cell density of 2300 cells per square inch (cpsi) was investigated to develop efficient and inexpensive catalysts for hydrogen production. The Ni honeycomb catalyst was assembled using 30-μm-thick Ni foils, and showed much higher activity than that of a Ni honeycomb catalyst with cell density of 700 cpsi at a steam-to-carbon ratio of 1.36 and a gas hourly space velocity of 6400 h^?1 in a temperature range of 873–1173 K. Notably, the activity increased approximately proportional to the increasing geometric specific surface area of the honeycombs. The turnover rate of the Ni honeycomb catalyst was higher than that of supported Ni catalysts. The changes in chemical state of the Ni catalyst during hydrogen reduction and MSR reaction were analyzed by in situ X-ray absorption fine structure spectroscopy, which revealed that deactivation was mainly due to oxidation of the surface Ni atoms. These results demonstrated that the high-cell-density Ni honeycomb catalyst exhibits good performance for MSR reaction, and easy regeneration of the deactivated Ni honeycomb catalyst is possible only via hydrogen reduction.     

Direct electrification of Rh/Al2O3 washcoated SiSiC foams for methane steam reforming: An experimental and modelling study

Electrified methane steam reforming (eMSR) is a promising concept for low-carbon hydrogen production. We investigate an innovative eMSR reactor where SiSiC foams, coated with Rh/Al₂O₃ catalyst, act as electrical resistances to generate the reaction heat via the Joule effect. The novel system was studied at different temperatures, space velocities, operating pressures and catalyst loadings. Thanks to efficient heating, active catalyst and optimal substrate geometry, complete methane conversions were observed even at a high space velocity of 200000 Nl/h/kg_cat. A specific energy demand as low as 1.24 kWh/Nm³_H2, with an unprecedented energy efficiency of 81%, was achieved on a washcoated foam with catalyst density of 86.3 g/L (GHSV = 150000 Nl/h/kg_cat, S/C = 4.1, ambient pressure). A mathematical model was validated against measured performance indicators and used to design an intensified eMSR unit for small scale H₂ production.     

Demonstration of a scaled-down autothermal membrane methane reformer for hydrogen generation

A novel concept for hydrogen generation by methane steam reforming in a thermally coupled catalytic fixed bed membrane reformer is experimentally demonstrated. The reactor, built from three concentric compartments, indirectly couples the endothermic methane steam reforming with the exothermic methane oxidation, while hydrogen is separated by a permselective Pd membrane. The study focuses on the determination of the key operation parameters and understanding their influence on the reactor performance. It has been shown that the reactor performance is mainly defined by the dimensionless ratio of the methane steam reforming feed flow rate to the hydrogen maximal membrane flow rate and by the ratio of the oxidation and steam reforming methane feed flow rates.     

Methanol steam reforming kinetics using a commercial CuO/ZnO/Al2O3 catalyst: Simulation of a reformer integrated with HT-PEMFC system

This study provides a kinetic examination of methanol steam reforming (MSR) over a Cu-based commercial catalyst (CuO/ZnO/Al₂O₃, Alfa Aesar) as a function of CH₃OH and H₂O partial pressures at 246 °C and 1 atm in a once-through flow reactor. A power rate law was used to best describe the experimental rate data by linear and non-linear regressions at the operating conditions where transport bottlenecks were eliminated. Comparison of the rate parameters indicated that a strong correlation was suggested by non-linear regression giving reaction orders of 0.29 for methanol and 0.09 for water along with a frequency factor of 53.48 (mol_CH3OH s⁻¹ g_catalyst⁻¹ kPa^−0.38) and an activation energy of 65.59 kJ mol⁻¹. A simulation study of the rate equation to analyze an integrated system of a reformer and an HT-PEMFC was also conducted. The results demonstrate that the system has the potential to produce 15 W power output.     

CFD study of heat and mass transfer in ethanol steam reforming in a catalytic membrane reactor

This work shows the analysis of ethanol steam reforming process within a catalytic membrane reactor. A 2-D non-isothermal CFD model was developed using Comsol Multiphysics, based on previous experimentally validated isothermal model. A comprehensive heat and mass transfer study was carried out utilizing the model. Operating conditions such as liquid hourly space velocity (LHSV) (3.77–37.7 h^?1), temperature (673–823 K), reaction side pressure (4–10 bar) and permeate side sweep gas flow pattern were discussed. A temperature gradient along the reactor was observed from the model and a “cold spot” was seen at the reactor entrance area, which is unfavorable for the highly endothermic ethanol steam reforming process. By changing the sweep gas pattern to counter-current, the “cold spot” appears to be smaller with a reduced temperature drop. By studying the individual reaction rates, reverse methane steam reforming (methanation) was observed, caused by the low temperature in the “cold spot”. Optimal operating conditions were found to be under LHSV = 37.7 h^?1 and counter-current sweep gas conditions.     

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.     

Millisecond methane steam reforming for hydrogen production: A computational fluid dynamics study

The potential of methane steam reforming to produce hydrogen in thermally integrated micro-chemical systems at short contact times was theoretically explored. Methane steam reforming coupled with methane catalytic combustion in microchannel reactors for hydrogen production was studied numerically. A two-dimensional computational fluid dynamics model with detailed chemistry and transport was developed. To provide guidelines for optimal design, reactor behavior was studied, and the effect of design parameters such as catalyst loading, channel height, and flow arrangement was evaluated. To understand how steam reforming can happen at millisecond contact times, the relevant process time scales were analyzed, and a heat and mass transfer analysis was performed. The importance of energy management was also discussed in order to obtain a better understanding of the mechanism responsible for efficient heat exchange between highly exothermic and endothermic reactions. The results demonstrated the feasibility of the design of millisecond reforming systems, but only under certain conditions. To achieve this goal, process intensification through miniaturization and the improvement in catalyst performance is very important, but not sufficient; very careful design and implementation of the system is also necessary to enable high thermal integration. The channel height plays an important role in determining the efficiency of heat exchange. A proper balance of the flow rates of the combustible and reforming streams is an important design criterion. Reactor performance is significantly affected by flow arrangement, and co-current operation is recommended to achieve a good energy balance within the system. The catalyst loading must be carefully designed to avoid insufficient reactant conversion or hot spots. Finally, operating windows were identified, and engineering maps for designing devices with desired power were constructed.     

Investigation of a methanol processing system comprising of a steam reformer and two preferential oxidation reactors for fuel cells

Methanol steam reforming is able to produce hydrogen-rich syngas onsite for fuel cells and avoids the problems of hydrogen storage. Nevertheless, CO in the reformate needs to be further removed to ppm level before it can be fed into proton exchange membrane fuel cells. In this study, a methanol processing system consisting of a methanol reformer and two-stage preferential oxidation reactors is developed. The hydrogen production performance and scalability of the reformer are experimentally investigated under various operating conditions. The methanol reformer system shows stable methanol conversion rate and linearly increased H₂ flow rate as the number of repeating unit increases. Methanol conversion rate of 96.8% with CO concentration of 1.78% are achieved in the scaled-up system. CO cleanup ability of the two-stage preferential oxidation reactors is experimentally investigated based on the reformate compositions by varying the operating temperature and O₂ to CO ratios. The results demonstrate that the developed CO cleanup train can decrease the CO concentration from 1.6% to below 10 ppm, which meets the requirement of the fuel cell. Finally, stability of the integrated methanol processing system is tested for 180 h operation.     

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).     

Oxidative steam reforming of ethanol over a Pt/Al2O3 catalyst in a Pd-based membrane reactor

In this study, the ability of a Pd-Ag membrane reactor of producing ultrapure hydrogen via oxidative steam reforming of ethanol has been evaluated. A self supported Pd-Ag tube of wall thickness 60 μm has been filled with a commercial Pt-based catalyst and assembled into a membrane module in a finger-like configuration. In order to evaluate the hydrogen yield behavior under different operating conditions, experimental tests have been performed at temperatures of 400 and 450 °C and pressures of 150 and 200 kPa. The oxidative steam reforming of ethanol has been carried out by feeding the membrane reactor with a gas stream containing a dilute water-ethanol mixture and air. Different water/ethanol feed flow rates (5, 10, 15 g h⁻¹), several water/ethanol (4, 10, 13) and oxygen/ethanol (0.3, 0.5, 0.7) feed molar ratios have been tested. The results pointed out that the highest hydrogen yield (moles of permeated hydrogen per mole of ethanol fed) corresponding to almost 4.1 has been attained at 450 °C and 200 kPa of lumen pressure by using a water/ethanol/oxygen feed molar ratio of 10/1/0.5.The results of these tests have been compared with those reported for the ethanol steam reforming in a Pd-Ag membrane reactor filled with the same Pt-based catalyst. This comparison has shown a positive effect on the hydrogen yield of small oxygen addition in the feed stream.     

The performance evaluation of an industrial membrane reformer with catalyst-deactivation for a domestic methanol production plant

Methane reforming is the most important and economical process for hydrogen and syngas generation. In this work, the dynamic simulation of methane steam reforming in an industrial membrane reformer for synthesis gas production is developed. A novel deactivation model for commercial Ni-based catalysts is proposed and the monthly collected data from an existing reformer in a domestic methanol plant is used to optimize the model parameters. The plant data is also employed to check the model accuracy. It was observed that the membrane reformer could compensate for the catalyst deactivating effect.In order to assure the long membrane lifetime and decrease the unit price, the membrane reformer with 5 μm thick Pd on stainless steel supports is modeled at the temperature below the maximum operating temperature of Pd based membranes (around 600 °C). The dynamic modeling showed that the methane conversion of 76% could be achieved at a moderate temperature of 600 °C for an industrial membrane reformer. The cost-effective generation of syngas with an appropriate H₂/CO ratio of 2.6 could be obtained by membrane reformer. This is while the conventional reformer exhibits a maximum conversation of 64 at 1200 °C challenging due to its high syngas ratio (3.7). On the other hand, the pure hydrogen from membrane reformer can supply part of the ammonia reactor feed in an adjacent ammonia plant.     

Parameter study of a porous solar-based propane steam reformer using computational fluid dynamics and response surface methodology

Solar-driven steam reforming of fossil fuels is a promising renewable method for hydrogen production that reduces emissions compared with traditional approaches such as combustion-based technologies. In the present study, a steady-state computational fluid dynamic (CFD) model is developed to investigate a porous solar propane steam reformer (PSR). P1 approximation for radiation heat transfer is coupled with the CFD model, employing User-Defined Functions (UDFs). Innovative propane steam reformers have received less attention in terms of optimization and sensitivity analysis to improve their performance and efficiency. Hence, the effects of porosity, pore diameter, inlet velocity, solar irradiation flux, inlet temperature, and foam thermal conductivity on the propane conversion, hydrogen production rate, and pressure drop are studied using response surface methodology (RSM). The inlet velocity, solar irradiation flux, and pore diameter are found to be the most influential parameters, among those mentioned, on propane conversion, hydrogen productivity, and pressure drop, respectively. Furthermore, optimization is carried out in order to minimize pressure drop and maximize hydrogen production. The reformer with the 70% propane conversion provides the lowest pressure drop maintaining the same hydrogen productivity compared with 80% and 90% propane conversions.     

Pd-Ag dense membrane application to improve the energetic efficiency of a hydrogen production industrial plant

This paper investigates the possibility of increasing the energetic efficiency of a hydrogen production industrial plant through the introduction of dense membranes in the steam reforming process. A simulation tool, developed in the Aspen Plus^® framework has been used to model a 1500 N m³/h hydrogen production plant. Besides the original plant layout with a PSA purification unit, three different membrane installation configurations have been considered: before the shift reactor, at the exit of the shift reactor and before the PSA unit. For all the three configurations the plant capacity was set at 75%, changing the permeated hydrogen flow. The membrane surface and cost were also estimated for each solution. Membranes installation just after the shift reactor gives the best solution in terms of both plant energetic efficiency and cost reduction.     

Thermal design of methane steam reformer with low-temperature non-reactive heat source for high efficiency engine-hybrid stationary fuel cell system

In hybrid fuel cell systems, the fuel-lean anode-off gas is very useful to improve the system efficiency via additional power generation or utilization of thermal energy for heating up of auxiliary devices. In this study, the thermal energy of the hybrid systems is firstly utilized in homogeneous charge combustion engine for additional power and is then supplied to heat up the external reformer. Different from other hybrid fuel cell systems, it is very difficult to utilize heat energy of exhausted gas from engine due to its low temperature characteristics. This study is concentrated on the computation analysis of external methane steam reformers with engine out exhausted gases. Computational model is validated with experiment and parametric study is conducted. Results show that the temperature uniformity of the longitudinal and radial directions is crucial for the methane conversion efficiency. Additionally, the methane conversion rate also depends on the performance of tube-side heat transfer. When the total methane flow is fixed, the methane conversion rate shows trade-off with increasing steam-to-carbon ratio (SCR). Finally, the sensitivity study shows that heat transfer area and reactor length are dominant parameters for steam reforming with engine out exhausted gases.