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Two fluidized bed membrane reactor concepts for hydrogen production via autothermal reforming of methane with integrated CO2 capture are proposed. Ultra-pure hydrogen is obtained via hydrogen perm-selective Pd-based membranes, while the required reaction energy is supplied by oxidizing part of the CH4 in situ in the methane combustion configuration or by combusting part of the permeated H2 in the hydrogen combustion configuration (oxidative sweeping). In this first part, the technical feasibility of the two concepts has been studied experimentally, investigating the reactor performance (CH4 conversion, CO selectivity, H2 production and H2 yield) at different operating conditions. A more detailed comparison of the performance of the two proposed reactor concepts is carried out with a simulation study and is presented in the second part of this work. [ABSTRACT FROM AUTHOR]

The reactor performance of two novel fluidized bed membrane reactor configurations for hydrogen production with integrated CO2 capture by autothermal reforming of methane (experimentally investigated in Part 1) have been compared using a phenomenological reactor model over a wide range of operating conditions (temperature, pressure, H2O/CH4 ratio and membrane area). It was found that the methane combustion configuration (where part of the CH4 is combusted in situ with pure O2) largely outperforms the hydrogen combustion concept (oxidative sweeping combusting part of the permeated H2) at low H2O/CH4 ratios (<2) due to in situ steam production, but gives a slightly lower hydrogen production rate at higher H2O/CH4 ratios due to dilution with combustion products. The CO selectivity was always much lower with the methane combustion configuration. Whether the methane combustion or hydrogen combustion configuration is preferred depends strongly on the economics associated with the H2O/CH4 ratio. [ABSTRACT FROM AUTHOR]

Abstract: The ethanol steam-reforming reaction to produce pure hydrogen has been studied theoretically. A mathematical model has been formulated for a traditional system and a palladium membrane reactor packed with a Co-based catalyst and the simulation results related to the membrane reactor for both co-current and counter-current modes are presented in terms of ethanol conversion and molar fraction versus temperature, pressure, the molar feed flow rate ratio and axial co-ordinate. Although the counter-current mode does not always give an ethanol conversion higher than the one obtained in membrane reactor operated in co-current mode, in the first case it is always possible to extract more hydrogen from the reaction zone. With this theoretical analysis, different values of the operating parameters that allow to have a CO-free hydrogen stream and a complete recovery of the hydrogen from the lumen side of the reactor are investigated. [Copyright &y& Elsevier]

Abstract: This paper focuses on methane reaction with carbon dioxide to perform the dry reforming reaction in the temperature range 350–450°C. It is well known that CO2 in the atmosphere is the main cause of the greenhouse effect world-wide: several strategies are proposed for its consumption, for example pumping into subsoil (exhaust oil reservoirs) or into sea background. In this work, we propose CO2 consumption via chemical reaction with methane. In particular, the reaction of dry reforming of methane to produce syngas was carried out firstly in a traditional reactor, and subsequently in two different membrane reactors. A porous and a dense Pd–Ag tubular membranes have been used for this purpose. The reactors have been compared in terms of: experimental results regarding methane, carbon dioxide conversions, reaction products selectivities and hydrogen recovery. The experimental results achieved have also been compared with what we found in the specialised literature. [Copyright &y& Elsevier]

Abstract: In this experimental work, the acetic acid steam reforming reaction for producing pure hydrogen was studied in a Pd–Ag dense membrane reactor (MR). Two kinds of catalytic bed patterns have been considered: in the first pattern a Ni-based commercial catalyst has been packed inside the membrane lumen while, in the second one both a Ru-based and a Ni-based commercial catalysts have been packed together in the membrane lumen. The experimental tests have been performed in the temperature range 400–450°C and in the pressure range 1.5–2.5bar. The results are reported in terms of acetic acid conversion, hydrogen recovery and products selectivities. It has been found that the MR is able to give a rather high acetic acid conversion with a 30–35% hydrogen recovery. Moreover, the second catalytic bed pattern is able to increase the hydrogen production and to decrease the methane production with respect to the first pattern. [Copyright &y& Elsevier]

Abstract: The simulation of a dense Pd-based membrane reactor for carrying out the methane, the methanol and the ethanol steam reforming (SR) reactions for pure hydrogen production is performed. The same simulation is also performed in a traditional reactor. This modelling work shows that the use of membrane reactor is effective for carrying out the methane SR reaction, giving in the best conditions a conversion increase of 800% with respect to a traditional system, and can be really useful for carrying out the methanol SR reaction (25% conversion increase). Vice versa, the use of the membrane reactor in the ethanol SR reaction is still affected by the low catalytic activity. However, also for the ethanol SR reaction system, the use of the membrane reactor gives an increase of the ethanol conversion (30%) and a relatively high increase of the hydrogen yield. [Copyright &y& Elsevier]

Abstract: The ethanol steam-reforming reaction for the production of synthesis gas has been studied theoretically. A mathematical model has been formulated for a traditional reactor packed with a Co-based catalyst and then applied to a membrane reactor (MR) in which the hydrogen production is increased by removing the hydrogen produced from the reaction mixture through a highly selective (100%) palladium-based membrane. Our simulation results show that with MR it is possible to obtain both higher conversions of ethanol and higher hydrogen selectivities compared to those obtained in a traditional reactor operating at the same experimental conditions. The theoretical analysis provides a set of parameters allowing to maximize the (pure) hydrogen production and/or ethanol conversion if adopted in an experimental device. [Copyright &y& Elsevier]

Abstract: In this theoretical work the effects of the parameters governing the hydrogen permeation through the dense palladium membranes on the membrane reactor performances are studied. The model for the methane steam reforming was used as test reaction system and the effects of the parameters of the Richardson equation (, and ), on the reactor performances were studied. The effect of the hydrogen flux pressure and temperature dependence factors on the methane conversion and on the hydrogen recovery for both the co-current and counter-current modes are reported and discussed. [Copyright &y& Elsevier]

In this work a comparison between methanol steam reforming (MSR) reaction and ethanol steam reforming (ESR) reaction to produce hydrogen in membrane reactors (MRs) is discussed from an experimental point of view. Both reaction systems have been investigated by considering the influence of the membrane characteristics as well as the influence of the operating temperature. In the case of a dense membrane, the sweep gas flow rate and the different flux configurations have also been analysed. Experimental results, in terms of reactant conversions as well as hydrogen production and gases selectivity in MRs and in a traditional reactor (TR), are presented. Catalyst stability in both reaction systems has also been tested. [Copyright &y& Elsevier]

A Rh-based catalyst for low temperature hydrogen generation in membrane microreactor applications has been developed and characterized. A RhZrO2 catalyst with 1.4 wt% Rh was prepared by incipient wetness impregnation and was tested for both methane reforming and autothermal reforming at temperatures interesting for membrane reactor applications (i.e. temperatures below 700 °C and steam-to-carbon ratio of 2). The kinetic parameters to describe the reaction rate of both methane steam reforming (SMR) and auto-thermal reforming (ATR) over the RhZrO2 catalyst have been determined using a 1D heterogeneous packed bed reactor model to properly account for mass and heat transfer resistances. [ABSTRACT FROM AUTHOR]

Abstract: A dual-function catalyst particle which integrates the exothermic oxidative coupling and endothermic steam reforming of methane for the simultaneous autothermal production of ethylene and synthesis gas has been designed and studied by detailed numerical simulations. Compared to conventional oxidative coupling of methane, the introduction of a catalytic reforming activity significantly increases the methane conversion without deteriorating the productivity towards the desired ethylene and ethane. Moreover, the presence of an intra-particle heat sink enables local autothermal operation, opening the possibility to couple these reactions in a packed bed membrane reactor with improved product yield. It is proposed to use a catalyst particle in which the two processes are physically separated by an inert, porous layer, such that additional diffusional resistances are intentionally created. The reforming activity is located in the particle center, while the oxidative coupling catalyst is present only in the outer shell of the particle. It has been demonstrated by means of numerical simulations that at low oxygen concentration (representing conditions in a packed bed membrane reactor), the internal mass transfer limitations can be effectively utilized to regulate the total reforming reaction rates and to prevent oxygen from reaching the reforming catalyst. Additionally, the size of the reforming catalytic core can, together with the effective diffusion properties inside the particle (viz. particle porosity and tortuosity) and the bulk gas phase concentrations, be used to tune the process to local autothermal operation. [Copyright &y& Elsevier]

In this work, a novel Pd–Ag double-skinned (DS-) membrane is used for the first time in conditions typical of propane dehydrogenation (PDH). This membrane presents a protective layer on top of the H 2 -selective one, which acts as shield against chemical deactivation and mechanical erosion under reaction conditions. While the protective layer is already been proven as an efficient barrier against membrane erosion in fluidized beds, there is no validation yet under PDH reaction. The DS- membrane performance is compared with a conventional (C-) Pd–Ag membrane under alkane/alkene exposure, at 400–500 °C and 3 bar, to investigate whether the incorporation of the protective layer would be suited for H 2 separation in PDH systems, and if coking rate would be affected. The novel membrane shows a H 2 permeance of 2.28 × 10−6 mol∙m−2 s−1∙Pa−1 at 500 ᵒC and 4 bar of pressure difference, overcoming the performance of the conventional PdAg one (1.56x∙10−6 mol m−2 s−1∙Pa−1). Both membranes present a stable H 2 flux under alkane exposure, while deactivation occurs under exposure to alkenes. A model able to describe the H 2 flux through Pd-based membranes is presented to fit the experimental data and predict membrane performance. The model includes mass transfer limitations in the retentate and a corrective inhibition factor to account for the competitive adsorption of hydrocarbon species in the H 2 selective layer. The experimental results obtained under alkene exposure deviates from model predictions; this can be attributed to carbon deposition on the surface of the selective layer, as further detected on the DS-membrane by Scanning Electron Microscopy (SEM)/Energy Dispersive X-Ray Analysis (EDX), which is the main factor for membrane deactivation. • First investigation of a novel double-skinned PdAg membrane for propane dehydrogenation. • Transient deactivation trend observed under alkene exposure. • Development of a 1D model describing concentration polarization and co-adsorption. • Carbon deposition detected on the selective Pd–Ag layer by preliminary SEM-EDX analysis. [ABSTRACT FROM AUTHOR]

Pd-based membranes prepared by pore-plating technique have been investigated for the first time under fluidization conditions. A palladium thickness around 20 μm was achieved onto an oxidized porous stainless steel support. The stability of the membranes has been assessed for more than 1300 h in gas separation mode (no catalyst) and other additional 200 h to continuous fluidization conditions. Permeances in the order of 5·10−7 mol s−1 m−2 Pa−1 have been obtained for temperatures in a range between 375 and 500 °C. During fluidization, a small decrease in permeance is observed, as consequence of the increased external (bed-to-wall) mass transfer resistances. Moreover, water gas shift (WGS) reaction cases have been carried out in a fluidized bed membrane reactor. It has been confirmed that the selective H 2 separation through the membranes resulted in CO conversions beyond the thermodynamic equilibrium (of conventional systems), showing the benefits of membrane reactors in chemical conversions. Image 1 • Novel Pd membranes prepared by pore-plate techniques are presented. • These membranes are tested under fluidizitation conditions for the first time. • Stability of these membranes is assessed for 1500 h in empty reactors. • CO conversion in the FBMR is above the one obtained in conventional reactors. [ABSTRACT FROM AUTHOR]

In this work a novel reactor concept referred to as Membrane-Assisted Chemical Looping Reforming (MA-CLR) has been demonstrated at lab scale under different operating conditions for a total working time of about 100 h. This reactor combines the advantages of Chemical Looping, such as CO 2 capture and good thermal integration, with membrane technology for a better process integration and direct product separation in a single unit, which in its turn leads to increased efficiencies and important benefits compared to conventional technologies for H 2 production. The effect of different operating conditions (i.e. temperature, steam-to-carbon ratio or oxygen feed in the reactor) has been evaluated in a continuous chemical looping reactor, and methane conversions above 90% have been measured with (ultra-pure) hydrogen recovery from the membranes. For all the cases a maximum recovery factor of around 30% has been measured, which could be increased by operating the concept at higher pressures and with more membranes. The optimum conditions have been found at temperatures around 600 °C for a steam-to-carbon ratio of 3 and diluted air in the air reactor (5% O 2 ). The complete demonstration has been carried out feeding up to 1 L/min of CH 4 (corresponding to 0.6 kW of thermal input) while up to 1.15 L/min of H 2 was recovered. Simultaneously, a phenomenological model has been developed and validated with the experimental results. In general, good agreement is observed, with overall deviations below 10% in terms of methane conversion, H 2 recovery and separation factor. The model allows better understanding of the behavior of the MA-CLR concept and the optimization and design of scaled-up versions of the concept. [ABSTRACT FROM AUTHOR]

This work reports the integration of thin (∼3–4 μm thick) Pd-based membranes for H 2 separation in a fluidized bed catalytic reactor for ethanol auto-thermal reforming. The performance of a fluidized bed membrane reactor has been investigated from an experimental and numerical point of view. The demonstration of the technology has been carried out over 50 h under reactive conditions using 5 thin Pd-based alumina-supported membranes and a 3 wt%Pt-10 wt%Ni catalyst deposited on a mixed CeO 2 /SiO 2 support. The results have confirmed the feasibility of the concept, in particular the capacity to reach a hydrogen recovery factor up to 70%, while the operation at different fluidization regimes, oxygen-to-ethanol and steam-to-ethanol ratios, feed pressures and reactor temperatures have been studied. The most critical part of the system is the sealing of the membranes, where most of the gas leakage was detected. A fluidized bed membrane reactor model for ethanol reforming has been developed and validated with the obtained experimental results. The model has been subsequently used to design a small reactor unit for domestic use, showing that 0.45 m 2 membrane area is needed to produce the amount of H 2 required for a 5 kW e PEM fuel-cell based micro-CHP system. [ABSTRACT FROM AUTHOR]

In this paper, the main achievements of several European research projects on Pd based membranes and Pd membrane reactors for hydrogen production are reported. Pd-based membranes have received an increasing interest for separation and purification of hydrogen. In addition, the integration of such membranes in membrane reactors has been widely studied for enhancing the efficiency of several dehydrogenation reactions. The integration of reaction and separation in one multifunctional reactor allows obtaining higher conversion degrees, smaller reactor volumes and higher efficiencies compared with conventional systems. In the last decade, much thinner dense Pd-based membranes have been produced that can be used in membrane reactors. However, the thinner the membranes the higher the flux and the higher the effect of concentration polarization in packed bed membrane reactors. A reactor concept that can circumvent (or at least strongly reduce) concentration polarization is the fluidized bed membrane reactor configuration, which improves the heat transfer as well. Tecnalia and TU/e are involved in several European projects that are related to development of fluidized bed membrane reactors for hydrogen production using thin Pd-based (<5 μm) supported membranes for different application: In DEMCAMER project a water gas shift (WGS) membrane reactor was developed for high purity hydrogen production. ReforCELL aims at developing a high efficient heat and power micro-cogeneration system (m-CHP) using a methane reforming fluidized membrane reactor. The main objective of FERRET is the development of a flexible natural gas membrane reformer directly linked to the fuel processor of the micro-CHP system. FluidCELL aims the Proof-of-Concept of a m-CHP system for decentralized off-grid using a bioethanol reforming membrane reactor. BIONICO aims at applying membrane reactors for biogas conversion to hydrogen. The fluidized bed system allows operating at a virtually uniform temperature which is beneficial in terms of both membrane stability and durability and for the reaction selectivity and yield. [ABSTRACT FROM AUTHOR]

The catalytic performance of RePt/CeO 2 –TiO 2 catalysts for the WGS reaction under conditions compatible with membrane reactor was investigated. The WGS activity and stability of the Pt/CeO 2 –TiO 2 catalyst was significantly influenced by the addition of rhenium. The intrinsic WGS activity per atom of platinum improves with the addition of Re to Pt/CeO 2 –TiO 2 catalyst. The addition of rhenium also has a beneficial effect on its stability under WGS conditions compatible with membrane reactor use. The improvement in WGS activity and stability is proposed to be associated with the improvement in the reduction behavior of the highly dispersed CeO 2 and ReO x species present in the bimetallic RePt catalyst respect to the monometallic Pt/CeTi counterpart and to the presence of rhenium species in close contact with Pt that could introduce an additional redox activity sites stable under WGS conditions and/or prevent the sintering of Pt crystallites under WGS conditions. [ABSTRACT FROM AUTHOR]

The implementation of CO 2 capture systems in conventional processes has been proposed by the IPCC as an effective way to reduce anthropogenic CO 2 emissions. However, these capture systems may represent an important decrease in the global efficiency for conventional processes. Chemical Looping has already been demonstrated as a promising technology for more efficient CO 2 capture. Novel reactor concepts have been proposed in the literature, in which the reactions take place at lower temperatures with increased overall energy efficiency. However, few investigations have been carried out regarding the behaviour of oxygen carriers at relatively low operating temperatures. In this work, an active Ni-based oxygen carrier supported on CaAl 2 O 4 inert material has been tested and characterized. The oxygen carrier has shown a promising behaviour for low temperature applications. However, it has been demonstrated that the oxygen carrier has to be pre-treated because of an interesting activation process which takes place only at high reduction temperatures. Oxygen carrier activation is caused by a reorganization of superficial nickel. Fresh oxygen carrier is covered by a layer of nickel with a strong interaction with the support. However, once the sample is reduced at high temperatures Ni is reorganized into small grains with reduced interaction with the support. This results in an enhancement in the reactivity and a higher oxygen transport capacity. After about 200 redox cycles, a small decrease in the solid conversion is observed due to agglomeration of the NiO grains. Nevertheless, the redox kinetics is still sufficiently fast for low temperature applications, provided that the oxygen carrier is pre-activated. The kinetics rates for the gas–solid reactions and gas-phase catalytic reactions have been determined, which can be used to predict the performance of the activated NiO/CaAl 2 O 4 oxygen carrier for low temperature chemical looping applications. [ABSTRACT FROM AUTHOR]

In hydrogen production, the syngas streams produced by reformers and/or coal gasification plants contain a large amount of H 2 and CO in need of upgrading. To this purpose, reactors using Pd-based membranes have been widely studied as they allow separation and recovery of a pure hydrogen stream. However, the high cost of Pd-membranes is one of the main limitations for scaling up technology. Therefore, many researchers are now pursuing the possibility of using supported membranes with as thin as possible Pd-alloy layers. In this work, the upgrading of a syngas stream is experimentally investigated in a water gas shift membrane reactor operated in a high temperature range with an ultra-thin supported membrane (3.6 micron-thick). The membrane permeance was measured before and after catalyst packing and also after reaction for 2100 h of operation in total. Membrane reactor performance was evaluated as a function of operating conditions such as temperature, pressure, gas hourly space velocity, feed molar ratio, and sweep gas. A CO conversion significantly higher than the thermodynamics upper limit of a traditional reactor was achieved, even at high gas hourly space velocities and a 25% less reaction volume than that of a traditional reactor was enough to achieve a 90% equilibrium conversion. [ABSTRACT FROM AUTHOR]

Abstract: There is great consensus that hydrogen will become an important energy carrier in the future. Currently, hydrogen is mainly produced by steam reforming of natural gas/methane on large industrial scale or by electrolysis of water when high-purity hydrogen is needed for small-scale hydrogen plants. Although the conventional steam reforming process is currently the most economical process for hydrogen production, the global energy and carbon efficiency of this process is still relatively low and an improvement of the process is key for further implementation of hydrogen as a fuel source. Different approaches for more efficient hydrogen production with integrated CO2 capture have been discussed in literature: Chemical Looping Combustion (CLC) or Chemical Looping Reforming (CLR) and membrane reactors have been proposed as more efficient alternative reactor concepts relative to the conventional steam reforming process. However, these systems still present some drawbacks. In the present work a novel hybrid reactor concept that combines the CLR technology with a membrane reactor system is presented, discussed and compared with several other novel technologies. Thermodynamic studies for the new reactor concept, referred to as Membrane-Assisted Chemical Looping Reforming (MA-CLR), have been carried out to determine the hydrogen recovery, methane conversion as well as global efficiency under different operating conditions, which is shown to compare quite favorably to other novel technologies for H2 production with CO2 capture. [Copyright &y& Elsevier]

Abstract: The methanol steam reforming (MSR) reaction was studied by using both a dense Pd-Ag membrane reactor (MR) and a fixed bed reactor (FBR). Both the FBR and the MR were packed with a new catalyst based on CuOAl2O3ZnOMgO, having an upper temperature limit of around 350°C. A constant sweep gas flow rate in counter-current mode was used in MR and the experiments were carried out by varying the water/methanol feed molar ratio in the range 3/1–9/1 and the reaction temperature in the range 250–300°C. The catalyst shows high activity and selectivity towards the CO2 and the H2 formation in the temperature range investigated. Under the same operative conditions, the MR shows higher conversions than FBR and, in particular, at 300°C and H2O/CH3OH molar ratio higher than 5/1 the MR shows complete methanol conversion. [Copyright &y& Elsevier]

Abstract: The performance of an original membrane methane reformer is analyzed by a two-dimensional mathematical model. The reactor is a bundle of four coaxial double tubes inserted in a shell in which a heating fluid flows. The annular region of each tube is the reaction zone, whereas the inner tube is the selective membrane for hydrogen removal. Many simulations have been carried out in order to find a suitable set of values of geometric and operating design variables. The effect of pressure and sweeping gas flow rate at permeation side, of membrane diameter and of axial profile of heat flux supplied to the reactor is analyzed in 81 virtual experiments. Suitable operating conditions are found: over 58% methane conversion can be reached, within a proper membrane temperature range and extra methane consumption for thermal duty. [Copyright &y& Elsevier]

Abstract: The ethanol steam reforming has been carried out in a membrane reactor consisting of a Ru-based catalyst bed packed into a thin wall Pd-Ag permeator tube produced via cold-rolling and diffusion welding of metal foils. The experimental tests have been performed in the temperature range 400–450°C with the aim of studying the performances of the membrane reactor in terms of hydrogen yields. The main investigated operating parameters have concerned the water/ethanol feed molar ratio (8.4–13.0), the pressure inside the membrane (150–200kPa), the sweep gas mode (co-current and counter-current) and the spatial velocity. In all the tests, ultra pure hydrogen has been separated through the Pd-Ag membrane: especially, operating at 450°C and 200kPa, a hydrogen yield higher than 80% has been produced thus demonstrating the membrane ability of promoting the reaction conversion (shift effect). [Copyright &y& Elsevier]

Abstract: The method of preparation of thin foil Ti–Ni–Pd alloy membranes with 2, 5 and 9wt% of Pd was developed and the phase content and hydrogen permeability of membranes were studied. It was found that Pd adding into Ti–Ni alloy increases the hydrogen permeability of the foils. Thus, the permeability of the foil with 9% of Pd was about one order of magnitude higher than that of the Ti–Ni foil. Cyclohexane dehydrogenation on commercial catalyst carried out in a flow reactor with a Ti–Ni–Pd membrane shows the higher conversions than those of a reactor without membrane due to the hydrogen permeability through the membrane. [Copyright &y& Elsevier]

Abstract: The methanol steam reforming (MSR) reaction to produce hydrogen was studied from an experimental point of view in membrane reactors (MRs). In order to investigate the behaviour of methanol conversion, the influence of the membrane characteristics, the sweep gas flow rate, as well as the influence of the operating temperature and the different flux configurations were analysed. Experimental results, in terms of methanol conversion as well as hydrogen production and gases selectivity in MRs and a traditional reactor (TR), are proposed. A set of values of key parameters to obtain the maximum hydrogen production is given. [Copyright &y& Elsevier]

Abstract: Methanol steam reforming (MSR) reaction to produce pure hydrogen has been studied, from an experimental point of view, in a flat Pd–Ag membrane reactor (MR). The membrane consisted of a pinhole free palladium–silver alloy, thick. In order to investigate the behaviour of methanol conversion in the MSR reaction carried out in MR, the influence of methanol feed flow rate, as well as the influence of the operating temperature have been analysed. The dependence of the increasing feed ratio on the methanol conversion has been also studied. Experimental results in terms of methanol conversion as well as hydrogen permeation and CO selectivity for MR are proposed. Some experimental data concerning methanol conversion have been compared with the literature data. [Copyright &y& Elsevier]